This instrument measures the bidirectional reflectance distribution function (BRDF) of surfaces with the following properties:
1. It measures the BRDF for eight illumination angles from 0 to 65 degrees, three colors (475, 570, 658 nm), and over 100 selected viewing angles.
2. The viewing zenith angles range from 5 to 65 degrees, and the azimuth angles range from 0 to ±180 degrees relative to the illumination direction.
3. Tests show it can measure the BRDF of flat surfaces with a precision of 1-5% and an accuracy of 10% of the measured reflectance.
The document describes a new algorithm for correcting the bidirectional reflectance distribution function (BRDF) of remote sensing reflectance measurements in coastal waters. Through radiative transfer simulations for a wide range of conditions, the authors developed a model relating remote sensing reflectance to the inherent optical properties of coastal waters. The new BRDF correction algorithm was shown to reduce uncertainty to below 1% when applied to both in situ and satellite ocean color data, improving on an existing open ocean algorithm. Its application significantly improved the match between in situ and MODIS satellite measurements of coastal waters.
Bright and dark_polar_deposits_on _mercury_evidence_for_surface _volatilesSérgio Sacani
1) Laser albedometer measurements from Mercury's north pole reveal unusually dark and bright surface deposits near permanently shadowed regions.
2) The dark deposits coincide with areas exhibiting low radar backscatter, suggesting a thin, dark material overlies buried ice.
3) Bright deposits are found in the largest craters above 84.9° latitude and match areas predicted to be cold enough for surface ice. This provides evidence that water ice is exposed directly at the surface in these locations.
The document describes the development of an anti-reflection coating for the extended hemispherical silicon lenses used in the Polarbear-2 experiment. A two-layer coating of Stycast epoxies was applied using a precise molding process to achieve less than 1% absorption loss. Thermal cycling and beam mapping tests showed the coating survived multiple temperature cycles and performed as expected based on simulations. The coating allows Polarbear-2 to achieve its detector performance requirements for measuring the cosmic microwave background.
Correction of ionospheric distortions in low frequency interferometric SAR da...grssieee
This document discusses methods for correcting distortions caused by the ionosphere in low frequency synthetic aperture radar (SAR) interferometric data. The ionosphere can cause displacement and defocusing in SAR images. The authors propose estimating the total electron content (TEC) and its spatial variation to model ionospheric distortions. They develop approaches using full-band and sub-band interferograms to estimate azimuth shifts and correct for ionospheric phase screens. Simulation results demonstrate the effectiveness of their correction methods, especially when using multiple sub-bands and increasing the number of looks, though this reduces spatial resolution. The authors conclude sub-band methods provide finer structure of the ionosphere compared to full-band approaches.
Numerical studies of the radiation patterns of resistively loaded dipolesLeonid Krinitsky
This document describes a numerical study of the radiation patterns of resistively loaded dipole antennas. It computes the far field radiation patterns as a superposition of transient solutions for infinitesimal dipole elements. The current excitation for each dipole element is modeled as a half cycle of a sine squared waveform that propagates along the antenna at an adjustable speed. The radiation patterns are presented for different dielectric media to model antennas used in ground penetrating radar applications in various materials like water, ice, and soil. Comparisons are made to field observations.
The document summarizes findings from images and data collected by the Lunar Reconnaissance Orbiter regarding the Compton-Belkovich thorium anomaly on the lunar farside. Key findings include:
1) A central feature covering 25 by 35 km is identified, characterized by elevated topography and relatively high reflectance, including several volcanic domes from less than 1 km to over 6 km across.
2) Arcuate to irregular circular depressions observed are interpreted as collapse features associated with volcanism.
3) Spectral data finds the volcanic feature enriched in silica or alkali-feldspar, indicative of compositionally evolved, rhyolitic volcanic materials.
4)
Aerosol retrieval using modis data & rt codeAhmad Mubin
This document summarizes information about aerosols including their sources, sizes, health effects, measurement techniques, and a methodology for satellite aerosol retrieval. It discusses using MODIS data at 500m resolution to estimate aerosol optical thickness over Hong Kong and compares the results to AERONET ground measurements. Key steps in the methodology include calculating top-of-atmosphere reflectance, accounting for Rayleigh scattering, surface reflectance, gas transmissions, and atmospheric effects to derive aerosol reflectance and optical thickness.
The document discusses improvements to satellite imaging technology, focusing on the new Advanced Baseline Imager (ABI) onboard GOES-R satellites. ABI will provide higher resolution images, new spectral channels, and improved temporal resolution compared to current GOES imagers. Specifically:
1) ABI will capture visible, infrared, and near-infrared channels at finer resolutions of 0.5-2km compared to 1-4km for current imagers.
2) It adds new spectral channels that improve monitoring of vegetation, fires, snow/ice, and hurricane intensities.
3) ABI allows for more frequent full Earth scans every 15 minutes compared to every 26 minutes currently, improving weather monitoring capabilities.
The document describes a new algorithm for correcting the bidirectional reflectance distribution function (BRDF) of remote sensing reflectance measurements in coastal waters. Through radiative transfer simulations for a wide range of conditions, the authors developed a model relating remote sensing reflectance to the inherent optical properties of coastal waters. The new BRDF correction algorithm was shown to reduce uncertainty to below 1% when applied to both in situ and satellite ocean color data, improving on an existing open ocean algorithm. Its application significantly improved the match between in situ and MODIS satellite measurements of coastal waters.
Bright and dark_polar_deposits_on _mercury_evidence_for_surface _volatilesSérgio Sacani
1) Laser albedometer measurements from Mercury's north pole reveal unusually dark and bright surface deposits near permanently shadowed regions.
2) The dark deposits coincide with areas exhibiting low radar backscatter, suggesting a thin, dark material overlies buried ice.
3) Bright deposits are found in the largest craters above 84.9° latitude and match areas predicted to be cold enough for surface ice. This provides evidence that water ice is exposed directly at the surface in these locations.
The document describes the development of an anti-reflection coating for the extended hemispherical silicon lenses used in the Polarbear-2 experiment. A two-layer coating of Stycast epoxies was applied using a precise molding process to achieve less than 1% absorption loss. Thermal cycling and beam mapping tests showed the coating survived multiple temperature cycles and performed as expected based on simulations. The coating allows Polarbear-2 to achieve its detector performance requirements for measuring the cosmic microwave background.
Correction of ionospheric distortions in low frequency interferometric SAR da...grssieee
This document discusses methods for correcting distortions caused by the ionosphere in low frequency synthetic aperture radar (SAR) interferometric data. The ionosphere can cause displacement and defocusing in SAR images. The authors propose estimating the total electron content (TEC) and its spatial variation to model ionospheric distortions. They develop approaches using full-band and sub-band interferograms to estimate azimuth shifts and correct for ionospheric phase screens. Simulation results demonstrate the effectiveness of their correction methods, especially when using multiple sub-bands and increasing the number of looks, though this reduces spatial resolution. The authors conclude sub-band methods provide finer structure of the ionosphere compared to full-band approaches.
Numerical studies of the radiation patterns of resistively loaded dipolesLeonid Krinitsky
This document describes a numerical study of the radiation patterns of resistively loaded dipole antennas. It computes the far field radiation patterns as a superposition of transient solutions for infinitesimal dipole elements. The current excitation for each dipole element is modeled as a half cycle of a sine squared waveform that propagates along the antenna at an adjustable speed. The radiation patterns are presented for different dielectric media to model antennas used in ground penetrating radar applications in various materials like water, ice, and soil. Comparisons are made to field observations.
The document summarizes findings from images and data collected by the Lunar Reconnaissance Orbiter regarding the Compton-Belkovich thorium anomaly on the lunar farside. Key findings include:
1) A central feature covering 25 by 35 km is identified, characterized by elevated topography and relatively high reflectance, including several volcanic domes from less than 1 km to over 6 km across.
2) Arcuate to irregular circular depressions observed are interpreted as collapse features associated with volcanism.
3) Spectral data finds the volcanic feature enriched in silica or alkali-feldspar, indicative of compositionally evolved, rhyolitic volcanic materials.
4)
Aerosol retrieval using modis data & rt codeAhmad Mubin
This document summarizes information about aerosols including their sources, sizes, health effects, measurement techniques, and a methodology for satellite aerosol retrieval. It discusses using MODIS data at 500m resolution to estimate aerosol optical thickness over Hong Kong and compares the results to AERONET ground measurements. Key steps in the methodology include calculating top-of-atmosphere reflectance, accounting for Rayleigh scattering, surface reflectance, gas transmissions, and atmospheric effects to derive aerosol reflectance and optical thickness.
The document discusses improvements to satellite imaging technology, focusing on the new Advanced Baseline Imager (ABI) onboard GOES-R satellites. ABI will provide higher resolution images, new spectral channels, and improved temporal resolution compared to current GOES imagers. Specifically:
1) ABI will capture visible, infrared, and near-infrared channels at finer resolutions of 0.5-2km compared to 1-4km for current imagers.
2) It adds new spectral channels that improve monitoring of vegetation, fires, snow/ice, and hurricane intensities.
3) ABI allows for more frequent full Earth scans every 15 minutes compared to every 26 minutes currently, improving weather monitoring capabilities.
Optical power output of an unidentified high altitude light source by bruc...PublicLeaker
- A Royal Canadian Air Force pilot photographed an unidentified bright disc-shaped object from his plane at an altitude of 11 km.
- Analysis of the photograph suggests the object was radiating over 1 gigawatt of power within the visible light spectrum captured by the film.
- Calculations estimate the object's radiance was around 2 watts per steradian per square centimeter, and if it was a Lambertian radiator, its total power output within the film's spectrum would have been over 1 billion watts.
MSHOT microscope imaging analysis software V1.3 is a full functional laboratory microscope image analysis system, it is outstanding of fluorescence processing functions.
This slide is all about proximal sensing of soil properties including lab techniques and proximal remote sensing. Hope it will help soil science scholars and acade
An optical prism is a transparent optical element with flat, polished surfaces that refract light. At least one surface must be angled—elements with two parallel surfaces are not prisms. The traditional geometrical shape of an optical prism is that of a triangular prism with a triangular base and rectangular sides, and in colloquial use "prism" usually refers to this type. Some types of optical prism are not in fact in the shape of geometric prisms. Prisms can be made from any material that is transparent to the wavelengths for which they are designed. Typical materials include glass, plastic, and fluorite.
1. Prisms deviate light towards their apex. The angle of deviation depends on the prism's refracting angle, the light's angle of incidence, and the prism material's refractive index.
2. Prisms form an erect, virtual image that is laterally displaced towards the apex.
3. Ophthalmic prisms are calibrated according to Prentice's position, where the incidence angle is zero, deviating light entirely at the second surface.
Calculate refractory index of light using snells lawNitin Jain
This document describes an experiment to determine the refractive index of a prism material using Snell's law and by measuring the angle of deviation for different angles of incidence. The experiment involves measuring the angle of deviation for light passing through a prism at varying angles of incidence, plotting a graph of angle of deviation versus angle of incidence, and using the minimum angle of deviation to calculate the refractive index. The motivation was to quantify how much light is deviated when passing through a prism using measurable quantities like the angles of incidence, refraction, and the prism angle.
Determination of 2D shallow S wave velocity profile using waveform inversion ...Tokugawa Moumouh
The document discusses determining 2D shallow S-wave velocity profiles using full waveform inversion of P-SV refraction data. It proposes inverting surface Rayleigh wave time series from refraction surveys to estimate 2D soil profiles. Numerical modeling is done using a 2.5D finite difference staggered grid. Waveform deconvolution removes source signatures. Numerical experiments show the algorithm can reconstruct complex 2D soil structures, though noise effects are more pronounced in low impedance soils. An empirical test inverts field data showing acceptable agreement with borehole measurements. The method inverts all Rayleigh wave energy in signals without relying on dispersion curves.
Application Of Resistivity For Groundwater, Hydrogeology and Pollution ResearchOmokpariolaElshalom
It was a group seminar geophysics course presentation in my year 3 of which I was asked to represent the group in giving an oral presentation of how we can apply resistivity in the geophysical investigation of groundwater, pollution ansd hydrogeology.
1) A field study was conducted in Adventdalen valley, Svalbard to measure active layer thaw depth across ice-wedge polygon networks of varying sizes.
2) Over 120 measurements of active layer depth were taken and GPS coordinates were recorded. A digital elevation model was also constructed.
3) Kriging geostatistical analysis showed active layer was on average 0.41m deep and depth varied somewhat with polygon size, being slightly shallower under larger polygons.
Vegetation cover influences thaw depth but water infiltration into ice wedges may also impact the process.
Non mare silicic volcanism on the lunar farside at compton–belkovichSérgio Sacani
1. Images from the Lunar Reconnaissance Orbiter reveal a central feature within the Compton–Belkovich thorium anomaly on the lunar farside characterized by elevated topography and relatively high reflectance.
2. The central feature contains several volcanic domes ranging from less than 1 km to over 6 km across, as well as arcuate and irregular depressions interpreted as collapse features associated with volcanism.
3. Spectral data indicates the volcanic feature is enriched in silica and alkali-feldspar, suggesting a composition of rhyolitic volcanic materials. This provides evidence for rare non-basaltic volcanism on the lunar farside far from the Procellarum
What do you means by seismic resolutionHaseeb Ahmed
Seismic resolution refers to the ability to differentiate between two seismic features. Vertical resolution is the ability to resolve two vertically stacked seismic horizons, and depends on factors like frequency and wavelength. Higher frequencies and shorter wavelengths improve vertical resolution but are attenuated at greater depths. Lateral resolution is the ability to resolve two horizontally separated features, and depends on factors like frequency, velocity, aperture, and whether pre-stack or post-stack migration is used. Both vertical and lateral resolution decrease with depth due to attenuation of higher frequencies. Increasing bandwidth, using phase rotation techniques, and migration can help enhance seismic resolution.
The document discusses the methods and equipment used for near-surface seismic refraction surveying. It describes how a typical refraction survey is conducted using a seismograph, geophones in a spread, and a hammer source. The key steps covered are survey geometry, data acquisition parameters, first break picking, analysis using travel time curves, and layered velocity modeling to determine subsurface layer velocities.
2004-10-03 Co-retrieval of Aerosol and Surface Reflectance: Analysis of Daily...Rudolf Husar
The document discusses a method for co-retrieving aerosol and surface reflectance from daily SeaWiFS satellite data from 2000-2002. It describes preprocessing the raw satellite data, identifying preliminary clear days using a time series analysis approach, and further refining the surface reflectance estimates and removing residual haze through spectral analysis. Results show seasonal surface reflectance maps for the eastern and western US and an 8-month animation of the retrieved data.
This document provides information on fireplace inserts. It discusses how fireplace inserts can increase the efficiency of existing wood burning fireplaces from 5-10% to over 65% by creating an insulated, closed system. It also notes that fireplace inserts come in different fuel types, including natural gas, propane, wood, pellet and coal fuels. The document provides a checklist for consumers to consider when selecting a fireplace insert, such as size, location, venting, features, style, installation and maintenance requirements.
This document summarizes a report on the Conservation Stewardship Program (CSP) from the perspectives of both NRCS field staff and organic farmers in California. There were several common themes identified: 1) The CSP application process is too complex and time-consuming for both farmers and staff; 2) The program lacks flexibility with contract lengths and rules; 3) CSP is better suited to large farms and provides little incentive for small farms; 4) The program is not well-aligned with California's diverse crop rotations or organic farming practices. Suggested improvements included simplifying the application, offering shorter contract options, increasing payment rates for small farms, and developing applications tailored more toward California's cropping systems.
Kevin was appointed as the new general manager of a German company in Istanbul. After 6 months, he finds managing the Turkish culture more difficult than expected. He struggles with employees coming to his office in groups of 3, saying "yes, but" instead of making decisions, and not informing him of problems. The document discusses cultural dimensions to understand Turkey based on Hofstede's model and provides advice for expatriate managers in Turkey, emphasizing building trust and respect, encouraging growth, and adapting one's leadership style to the local culture.
Sharesy: Creating a launch strategy for a new social game Kenty Empire
Sharesy is launching a new slots-based game for the bingo market that allows users to play in teams and share winnings. To launch successfully in the crowded gaming market, the strategy is to 1) attract influential Facebook users by gifting them free coins and gifts to unlock on the app, 2) facilitate player connections through an in-app friend finder and team selector, and 3) reward participation by recognizing high-scoring players and teams on the app and Facebook each week. This will build an engaged Facebook fanbase through character-led engagement and incentivizing users to invite friends and create winning teams.
Este documento agradece aos colegas de curso de Direito que participaram diretamente ou indiretamente na luta pelo retorno das aulas na Unitins. Faz um agradecimento especial a Kleiton Barbosa e Neila Guedes, que tiveram papel fundamental na conquista dessa vitória. Expressa gratidão a todos que merecem respeito e admiração pelo que fizeram.
Optical power output of an unidentified high altitude light source by bruc...PublicLeaker
- A Royal Canadian Air Force pilot photographed an unidentified bright disc-shaped object from his plane at an altitude of 11 km.
- Analysis of the photograph suggests the object was radiating over 1 gigawatt of power within the visible light spectrum captured by the film.
- Calculations estimate the object's radiance was around 2 watts per steradian per square centimeter, and if it was a Lambertian radiator, its total power output within the film's spectrum would have been over 1 billion watts.
MSHOT microscope imaging analysis software V1.3 is a full functional laboratory microscope image analysis system, it is outstanding of fluorescence processing functions.
This slide is all about proximal sensing of soil properties including lab techniques and proximal remote sensing. Hope it will help soil science scholars and acade
An optical prism is a transparent optical element with flat, polished surfaces that refract light. At least one surface must be angled—elements with two parallel surfaces are not prisms. The traditional geometrical shape of an optical prism is that of a triangular prism with a triangular base and rectangular sides, and in colloquial use "prism" usually refers to this type. Some types of optical prism are not in fact in the shape of geometric prisms. Prisms can be made from any material that is transparent to the wavelengths for which they are designed. Typical materials include glass, plastic, and fluorite.
1. Prisms deviate light towards their apex. The angle of deviation depends on the prism's refracting angle, the light's angle of incidence, and the prism material's refractive index.
2. Prisms form an erect, virtual image that is laterally displaced towards the apex.
3. Ophthalmic prisms are calibrated according to Prentice's position, where the incidence angle is zero, deviating light entirely at the second surface.
Calculate refractory index of light using snells lawNitin Jain
This document describes an experiment to determine the refractive index of a prism material using Snell's law and by measuring the angle of deviation for different angles of incidence. The experiment involves measuring the angle of deviation for light passing through a prism at varying angles of incidence, plotting a graph of angle of deviation versus angle of incidence, and using the minimum angle of deviation to calculate the refractive index. The motivation was to quantify how much light is deviated when passing through a prism using measurable quantities like the angles of incidence, refraction, and the prism angle.
Determination of 2D shallow S wave velocity profile using waveform inversion ...Tokugawa Moumouh
The document discusses determining 2D shallow S-wave velocity profiles using full waveform inversion of P-SV refraction data. It proposes inverting surface Rayleigh wave time series from refraction surveys to estimate 2D soil profiles. Numerical modeling is done using a 2.5D finite difference staggered grid. Waveform deconvolution removes source signatures. Numerical experiments show the algorithm can reconstruct complex 2D soil structures, though noise effects are more pronounced in low impedance soils. An empirical test inverts field data showing acceptable agreement with borehole measurements. The method inverts all Rayleigh wave energy in signals without relying on dispersion curves.
Application Of Resistivity For Groundwater, Hydrogeology and Pollution ResearchOmokpariolaElshalom
It was a group seminar geophysics course presentation in my year 3 of which I was asked to represent the group in giving an oral presentation of how we can apply resistivity in the geophysical investigation of groundwater, pollution ansd hydrogeology.
1) A field study was conducted in Adventdalen valley, Svalbard to measure active layer thaw depth across ice-wedge polygon networks of varying sizes.
2) Over 120 measurements of active layer depth were taken and GPS coordinates were recorded. A digital elevation model was also constructed.
3) Kriging geostatistical analysis showed active layer was on average 0.41m deep and depth varied somewhat with polygon size, being slightly shallower under larger polygons.
Vegetation cover influences thaw depth but water infiltration into ice wedges may also impact the process.
Non mare silicic volcanism on the lunar farside at compton–belkovichSérgio Sacani
1. Images from the Lunar Reconnaissance Orbiter reveal a central feature within the Compton–Belkovich thorium anomaly on the lunar farside characterized by elevated topography and relatively high reflectance.
2. The central feature contains several volcanic domes ranging from less than 1 km to over 6 km across, as well as arcuate and irregular depressions interpreted as collapse features associated with volcanism.
3. Spectral data indicates the volcanic feature is enriched in silica and alkali-feldspar, suggesting a composition of rhyolitic volcanic materials. This provides evidence for rare non-basaltic volcanism on the lunar farside far from the Procellarum
What do you means by seismic resolutionHaseeb Ahmed
Seismic resolution refers to the ability to differentiate between two seismic features. Vertical resolution is the ability to resolve two vertically stacked seismic horizons, and depends on factors like frequency and wavelength. Higher frequencies and shorter wavelengths improve vertical resolution but are attenuated at greater depths. Lateral resolution is the ability to resolve two horizontally separated features, and depends on factors like frequency, velocity, aperture, and whether pre-stack or post-stack migration is used. Both vertical and lateral resolution decrease with depth due to attenuation of higher frequencies. Increasing bandwidth, using phase rotation techniques, and migration can help enhance seismic resolution.
The document discusses the methods and equipment used for near-surface seismic refraction surveying. It describes how a typical refraction survey is conducted using a seismograph, geophones in a spread, and a hammer source. The key steps covered are survey geometry, data acquisition parameters, first break picking, analysis using travel time curves, and layered velocity modeling to determine subsurface layer velocities.
2004-10-03 Co-retrieval of Aerosol and Surface Reflectance: Analysis of Daily...Rudolf Husar
The document discusses a method for co-retrieving aerosol and surface reflectance from daily SeaWiFS satellite data from 2000-2002. It describes preprocessing the raw satellite data, identifying preliminary clear days using a time series analysis approach, and further refining the surface reflectance estimates and removing residual haze through spectral analysis. Results show seasonal surface reflectance maps for the eastern and western US and an 8-month animation of the retrieved data.
This document provides information on fireplace inserts. It discusses how fireplace inserts can increase the efficiency of existing wood burning fireplaces from 5-10% to over 65% by creating an insulated, closed system. It also notes that fireplace inserts come in different fuel types, including natural gas, propane, wood, pellet and coal fuels. The document provides a checklist for consumers to consider when selecting a fireplace insert, such as size, location, venting, features, style, installation and maintenance requirements.
This document summarizes a report on the Conservation Stewardship Program (CSP) from the perspectives of both NRCS field staff and organic farmers in California. There were several common themes identified: 1) The CSP application process is too complex and time-consuming for both farmers and staff; 2) The program lacks flexibility with contract lengths and rules; 3) CSP is better suited to large farms and provides little incentive for small farms; 4) The program is not well-aligned with California's diverse crop rotations or organic farming practices. Suggested improvements included simplifying the application, offering shorter contract options, increasing payment rates for small farms, and developing applications tailored more toward California's cropping systems.
Kevin was appointed as the new general manager of a German company in Istanbul. After 6 months, he finds managing the Turkish culture more difficult than expected. He struggles with employees coming to his office in groups of 3, saying "yes, but" instead of making decisions, and not informing him of problems. The document discusses cultural dimensions to understand Turkey based on Hofstede's model and provides advice for expatriate managers in Turkey, emphasizing building trust and respect, encouraging growth, and adapting one's leadership style to the local culture.
Sharesy: Creating a launch strategy for a new social game Kenty Empire
Sharesy is launching a new slots-based game for the bingo market that allows users to play in teams and share winnings. To launch successfully in the crowded gaming market, the strategy is to 1) attract influential Facebook users by gifting them free coins and gifts to unlock on the app, 2) facilitate player connections through an in-app friend finder and team selector, and 3) reward participation by recognizing high-scoring players and teams on the app and Facebook each week. This will build an engaged Facebook fanbase through character-led engagement and incentivizing users to invite friends and create winning teams.
Este documento agradece aos colegas de curso de Direito que participaram diretamente ou indiretamente na luta pelo retorno das aulas na Unitins. Faz um agradecimento especial a Kleiton Barbosa e Neila Guedes, que tiveram papel fundamental na conquista dessa vitória. Expressa gratidão a todos que merecem respeito e admiração pelo que fizeram.
El documento resume los conceptos clave de la lectura como un proceso complejo que implica la interacción del lector con el texto para construir la comprensión de la información. Además, destaca el papel activo del lector y la importancia del contexto y los conceptos previos en la comprensión lectora.
El documento proporciona información sobre el bádminton, incluyendo que fue aceptado como deporte olímpico en los Juegos de Barcelona 1992, originalmente se llamaba battledore y se jugaba con paletas de madera y una pelota, los campos miden entre 13,40 y 6,10 metros, y las lesiones más comunes son esguinces de tobillo y problemas en hombros y muñecas. También señala que surgió en la India y se implantó en Estados Unidos en 1890.
The Capabilities and Innovations of Joint Communications Support Element (JCS...AFCEA International
The document provides an overview of the Joint Communications Support Element (JCSE) including its mission, organization, equipment, initiatives and training programs. JCSE's mission is to provide rapidly deployable command, control, communications and intelligence support to combatant commanders. It maintains various en route and early entry communications packages. Future focus areas include supporting the Joint Information Environment, developing next generation transport networks, and establishing an episodic Mission Partner Environment to enable information sharing at the tactical edge. The document outlines JCSE's capabilities, equipment, organization and initiatives to fulfill its mission of providing scalable C4ISR support globally.
This presentation outlines how those undertaking Return Home Interviews can support young people to develop their resilience and co-create safety plans.
Study, design and development of an integration component with sensory featur...José Fidalgo
This document describes a project to develop a smart irrigation platform leveraging an existing IoT middleware. The platform supports sensors and actuators and uses complementary information from weather services. It exposes functionality through a service to enable remote access. The goal is to integrate connected objects and expose them as internet services. An IoT middleware was selected to integrate objects and a literature review analyzed reference architectures and commercial irrigation products.
Mi ficha de resultados obtenidos en los test de condición físicaIES El Médano
Este documento resume los resultados de un alumno en varias pruebas de acondicionamiento físico realizadas en tres trimestres. Incluye datos personales como nombre, edad, estatura y peso, así como marcas y notas obtenidas en pruebas de capacidad física, lanzamiento de balón medicinal, salto horizontal, abdominales, flexibilidad, resistencia aeróbica, agilidad y una carrera de 10x5 metros. Al final, el alumno evalúa sus puntos fuertes y débiles en fuerza, resistencia,
A igreja dá as boas-vindas ao visitante, expressando que sua presença traz alegria e que tanto Deus quanto a igreja o amam. A mensagem convida o visitante a viver com base no amor de Deus.
About The Importance Of The Definition Of Reflectance Quantities-Results Of C...Jim Webb
1) The document discusses the importance of properly defining reflectance quantities used in remote sensing studies. It notes inconsistencies in how terms like "albedo" have been used in different studies.
2) It summarizes definitions of key reflectance terms like BRDF, BRF, DHR, HDRF, and provides examples of measurable versus conceptual quantities.
3) Case studies are presented comparing modeling results for directional versus hemispherical reflectance quantities for a black spruce forest canopy and snow cover, as well as MISR satellite data products, to demonstrate differences between these reflectance definitions.
This document discusses the bidirectional reflectance distribution function (BRDF) in coastal waters and its application to validating ocean color satellites. It presents a new BRDF correction algorithm optimized for coastal waters dominated by sediments or colored dissolved organic matter. The algorithm improves match-ups between in situ measurements and MODIS satellite data by reducing uncertainties from 10% to below 1%. It is validated using a one year time series of above-water radiometer measurements in coastal Long Island Sound.
The document discusses bidirectional reflectance distribution functions (BRDF) in coastal waters and their application to validating ocean color satellites. It presents a BRDF correction algorithm optimized for coastal waters dominated by sediments or colored dissolved organic matter. Validation using in situ radiometer data from the Long Island Sound Coastal Observatory shows the proposed algorithm reduces dispersion in water leaving radiances compared to standard open ocean algorithms, improving satellite matchup comparisons.
Definition significance measurement_modelling_BRDFLinyuan Li
This document defines BRDF and discusses its significance and measurement. It begins by defining key terms like reflectance, albedo, and BRDF. It then discusses how BRDF captures directional and spectral surface properties and reflects biophysical information. BRDF measurement involves sampling strategies, platforms like field goniometers and satellites, and considerations like solar angle, intensity, and positioning accuracy. BRDF modelling uses functions like Minnaert, Lommel-Seeliger and kernel functions to model measured BRDF data.
1. The document describes measuring and analyzing the radiation patterns of a dual-polarized meteorological radar antenna that was upgraded from single to dual polarization.
2. A Fresnel-zone holographic technique was used to measure the antenna's co-polarized and cross-polarized radiation patterns. The sidelobes were found to be higher than predicted.
3. Analysis of the aperture field data identified surface errors in the reflector dish and shadowing from the feed crook as contributing to the elevated sidelobes. Both theoretical modeling and manipulation of the measured data supported this finding.
This document describes a refractometer that measures the refractive index of liquids. It does this by determining the critical angle of total reflection at the interface between a measuring prism and the liquid sample. Light is passed through the prism and its intensity as a function of angle is measured and compared to a reference curve. The device uses a second prism and optical elements to generate a reference light that matches the expected intensity curve, allowing identification of the critical angle through a measurement of equal intensities between the sample and reference lights. This provides an accurate means of determining the critical angle and refractive index of liquids.
CV_Unit 1.Introduction Light in space Linear Filterssmithashetty24
This document discusses key concepts in radiometry and measuring light. It defines radiance as the amount of energy travelling at a point in a specified direction per unit time, area, and solid angle. Radiance is a function of position and direction. The document also explains that radiance is constant along a straight line between two points, and discusses how light interacts with surfaces, such as being absorbed, transmitted, or scattered.
Heckbert p s__adaptive_radiosity_textures_for_bidirectional_rXavier Davias
The document describes a new rendering method called bidirectional ray tracing using adaptive radiosity textures. It separates surface interaction into diffuse and specular components. It computes the specular component on the fly during ray tracing, and stores the diffuse component (radiosity) in adaptive radiosity textures on diffuse surfaces. These textures adaptively subdivide to resolve sharp shadows. It uses a three-pass algorithm: 1) a size pass records visibility, 2) a light pass traces light rays to deposit photons and construct textures, 3) an eye pass traces eye rays to render the image using the textures. This hybrid approach aims to provide accurate global illumination simulation for realistic image synthesis.
Seismic data processing 15, kirchhof migrationAmin khalil
Kirchhoff migration is a widely used seismic data processing method. It works by back projecting observed seismic event energy from traces to possible subsurface reflection points based on traveltime. This smears the event energy to all possible subsurface locations, generating artifacts. Stacking multiple migrated traces helps resolve the true dipping reflector. Ray tracing is used to build the traveltime field. Kirchhoff migration is computationally expensive, taking days to process post-stack or months for pre-stack data. Representing the earth in 3D rather than 2D is preferable but requires knowing the 3D velocity model which is challenging.
Multi-Resolution Analysis: MRA Based Bright Band Height Estimation with Preci...Waqas Tariq
A method for reconstruction of cross section of rainfall situations with precipitation radar data based on wavelet analysis of Multi-Resolution Analysis (MRA) which allows extract a peak of the radar reflectivity is proposed in order to detect bright band height. It is found that the bright band height can be estimated by using the MRA with the basis of Daubechies wavelet family. It is also found that the boundaries in rainfall structure can be clearly extracted with MRA.
Method for Estimation of Grow Index of Tealeaves Based on Bi-Directional Refl...Waqas Tariq
Estimation methods for grow index as well as total nitrogen and fiber contents in tealeaves based on spectral reflectance and Bi-directional Reflectance Distribution Function: BRDF measurements with ground based network cameras is proposed. Also tea estate monitoring system with network cameras is proposed. Due to a fact that Near Infrared: NIR camera data shows a good correlation to total nitrogen while that shows negative correlation to fiber contents, it is possible to estimate nitrogen and fiber contents in tealeaves with NIR camera data. Through a comparison between actual direct measured and the estimated total nitrogen and fiber contents shows a good correlation so that a validity of the proposed method is confirmed. Also it is found that monitoring of a grow index of tealeaves with BRDF measured with networks cameras is capable. Thus it is concluded that a monitoring of tea estates is capable with network cameras of visible and NIR.
This document provides an overview of radiation heat transfer including:
- Defining view factor and developing relations to calculate view factors between surfaces.
- Calculating radiation heat transfer between black and gray surfaces using concepts of radiosity.
- Obtaining relations for net radiation heat transfer between surfaces of two-zone enclosures like parallel plates and cylinders.
- Quantifying the effect of radiation shields in reducing heat transfer between surfaces and their importance in temperature measurements.
This document summarizes an experiment to determine the refractive index of an unknown prism material. Measurements were taken of the prism's apical angle and angles of minimum deviation for three laser wavelengths. These values were used to calculate the refractive index for each wavelength. Constants A, B, and C were then determined, allowing calculation of the refractive index and dispersion for additional wavelengths. The material was identified as glass using a glass map based on its dispersion and refractive index values. Sources of error and their effects on the results are also discussed.
1. A parabolic primary mirror with an aperture of 15 cm and focal length of 1.49 m was made from soda-lime glass using abrasives like silicon carbide and aluminum oxide.
2. The mirror was tested using the Focult test and Ronchi test, which evaluated the uniformity and shape of the parabolic curve. The results indicated the mirror met quality standards.
3. It was concluded that the mirror making technique used was effective at producing precise optics for astronomical telescopes within budget constraints.
This document provides an overview of radar (RADAR) remote sensing. It discusses key concepts such as radar nomenclature, advantages and limitations of radar, geometric distortions in radar imagery including foreshortening and layover, polarization, resolution both in range and azimuth dimensions, and speckle. The document is intended to serve as an educational reference on the fundamentals and logic of radar remote sensing.
The document discusses methods for characterizing the global environment using satellite data to help overcome challenges posed by weather effects on missile defense sensors. It describes adjusting infrared imagery thresholds to approximate radar observations, extracting weather event boundaries, projecting 3D shapes onto a model Earth, and using an existing satellite constellation to provide continuous coverage. The goal is to determine visibility and sensor performance to optimize sensor selection and placement for missile defense.
This document discusses radar cross section (RCS) measurements of simple and complex targets using microwave absorbers. It provides definitions of key terms like RCS, scattering matrix, frequency regions. It describes the basic instrumentation for RCS measurements including a transmitter, receiver, positioners and data acquisition system. It discusses methods for calibrating RCS measurement systems, including direct calibration using reference targets and indirect calibration using the radar range equation. The goal is to determine target RCS and how absorber materials can be used to reduce RCS and make targets stealthier to radars.
Instruments for solar radiation measurement
Empirical equation for prediction of availability of solar radiation
Radiation on tilted surface
Types of solar collectors
kushsshah.blogspot.com
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Seismic sensors and networks in Hawaii monitor earthquakes and volcanoes on the Big Island. The USGS operates several types of seismic stations, including short period and broadband sensors. Other groups also operate stations, and data is shared. The network helps track earthquake activity and volcanic processes. Hawaii experiences large earthquakes that can cause tsunamis, making seismic monitoring important for hazards assessment and early warning. Efforts aim to expand the network and coordination to improve earthquake reporting and monitoring statewide.
This document provides a short overview of the RAYFRACT seismic refraction data interpretation software. It lists the main functions of the software such as creating new profiles, importing seismic data, reviewing first breaks, smoothing inversions, automatic and manual refractor mapping, wavefront modeling, automatic picking, and ASCII data import. More detailed instructions are available in the software manual and PDF help files on the company's website.
This document provides an overview of wireless sensor networks. It discusses what sensor networks are and their applications in areas like military, industry, science and more. It describes the constraints of sensor networks like limited battery power, storage and processing. It outlines several research challenges in sensor networks including energy efficiency, scalability, heterogeneity and self-configuration. The document also discusses various layers in the sensor network protocol stack from the physical layer to the application layer and highlights issues at each layer.
This document discusses the potential applications of embedded networked sensing systems. It outlines several motivating applications including monitoring seismic structure response, tracking contaminant transport, and monitoring ecosystems and biocomplexity. For each application, it describes the relevant science goals and how embedded networked sensing could provide data to advance understanding. It also discusses some of the research challenges for these applications and outlines initial steps being taken. The document concludes by discussing enabling technologies for embedded networked sensing systems.
The document summarizes research on using MEMS (Micro-Electro-Mechanical Systems) technology for seismology applications. It provides an overview of MEMS, discusses MEMS accelerometers and their commercial availability. It also describes the noise and detection requirements for seismology and current R&D efforts funded by DOE to develop low-noise MEMS seismometers, including projects using inductive, optical, and fluidic sensing techniques with proof masses up to 2 grams.
The document discusses seismic data networks, instruments, and data centers. It describes the different types of seismic networks including global, regional, local, temporary, and seismic arrays. It also discusses several major seismic data centers such as NEIC, ORFEUS, IRIS, ISC, GEOFON, EMSC, and EarthScope. Finally, it covers various seismic observables including translations measured as displacement, velocity, and acceleration. It also discusses strain, rotations, and the ranges of measurements for different seismic phenomena.
This document discusses various seismic methods and concepts. It begins by defining the critical angle and Snell's law for refraction seismology. It then distinguishes between the reflection and refraction seismic methods. The refraction method involves keeping the source fixed while spacing receivers further from the source, resulting in an x-t plot. Various seismic arrivals are described like direct waves, reflections, and refractions. Factors that affect seismic waves like attenuation and energy partitioning are also summarized. The document concludes by covering seismic sources, instruments, and refraction seismic methods.
Seismic sensors and networks in Hawaii monitor earthquakes and volcanoes on the Big Island. The USGS operates several types of seismic stations, including short period and broadband sensors. Other groups also operate stations, and data is shared. The network helps track earthquake activity and volcanic processes like movement of magma. Hawaii experiences large, damaging quakes due to active faults and volcanism. Better seismic coverage could help provide faster warnings for events and tsunamis, and protect infrastructure like the Mauna Kea observatories. The USGS works to modernize statewide monitoring through the ANSS program.
This document provides a short overview of the RAYFRACT seismic refraction data interpretation software. It lists the main functions of the software such as creating new profiles, importing seismic data, reviewing first breaks, smoothing inversions, automatic and manual refractor mapping, wavefront modeling, automatic picking, and ASCII data import. More detailed instructions are available in the software manual and PDF help files on the company's website.
This document provides an overview of wireless sensor networks. It discusses what sensor networks are and their applications in areas like military, industry, science and more. It describes the constraints of sensor networks like limited battery power, storage and processing. It outlines several research challenges in areas like medium access control, routing, time synchronization and localization. The document discusses different aspects of designing sensor network protocols and architectures to address issues of energy efficiency, scalability, heterogeneity and self-configuration.
This document discusses the potential applications of embedded networked sensing systems. It outlines three main applications: 1) seismic structure monitoring to better understand building and soil responses, 2) contaminant transport monitoring to track contaminant movement, and 3) ecosystem monitoring to study wildlife populations over time. The document also discusses enabling technologies, challenges, and a taxonomy for classifying different embedded sensing systems.
The document summarizes research on using MEMS (Micro-Electro-Mechanical Systems) technology for seismology applications. It provides an overview of MEMS, discusses MEMS accelerometers and their commercial availability. It also covers noise and detection theory, current R&D efforts funded by DOE to develop low-noise MEMS seismometers, and the outlook for using MEMS in seismology. Key challenges include achieving large proof masses, weak springs, and low noise at low frequencies needed for weak motion seismology.
The document discusses seismic data networks, instruments, and data centers. It describes the different types of seismic networks including global, regional, local, temporary, and seismic arrays. It also discusses several major seismic data centers such as NEIC, ORFEUS, IRIS, ISC, GEOFON, EMSC, and EarthScope. Finally, it covers various seismic observables including translations (displacement, velocity, acceleration), strain, and rotations that seismometers are capable of measuring.
The document describes a wireless GPS wristwatch tracking solution called TIDGET. TIDGET is a low power GPS tracking device developed by NAVSYS for the US Army. It uses a client/server approach to send raw GPS data through a ZigBee wireless link to a LocatorNet server for processing. The server uses software defined radio to compute positions from the GPS data. TIDGET can operate for over 30 days on a wristwatch battery by offloading GPS processing to the server. A web portal allows users to access location data from the tracking devices.
This document provides a tutorial about a seismic sensor network. It discusses:
1) The special demands of seismic and acoustic applications including large-scale deployment, challenged networks, and remote monitoring requirements.
2) An overview of the software and hardware used in the network including the CDCCs, Q330 data loggers, Duiker data collection software, and DTS remote management software.
3) How to assemble a seismic node in 30 minutes by connecting sensors, data loggers, and wireless nodes together and reprogramming the nodes.
The HP MEMS sensor demonstrates potential for use in seismic imaging applications by providing a flat frequency response down to DC and low noise floor of less than 10 ng/√Hz. Testing at the USGS confirmed noise levels matching the lowest levels on Earth and matching signals down to 25 mHz compared to a reference sensor. A custom ASIC integrated circuit is being developed to enable low power sensors for dense wireless arrays to further improve seismic image resolution.
This document provides an overview of seismic waves:
1) It describes the three main types of seismic waves - P waves, S waves, and surface waves - and how they propagate through the Earth.
2) Key concepts discussed include body waves that travel through the Earth's interior and surface waves that travel along the Earth's surface.
3) The document also discusses seismic wave properties like velocity, period, wavelength, and attenuation as they travel through different Earth layers and are affected by geological structures.
The document discusses various sensor technologies and considerations for sensing systems. It covers topics such as phase linearity, transducer terminology, sensor categorization based on physical phenomena and measuring mechanism, specifications of sensors including accuracy and resolution, strain gauges, acceleration sensing, force sensing, displacement sensing, velocity sensing, shock sensing, angular motion sensing, MEMS technology, and considerations for designing sensing systems. The key aspects covered are the operating principles, advantages, and limitations of different sensor types.
This document provides an overview of seismic waves:
1) It describes the three main types of seismic waves - P waves, S waves, and surface waves - and how they propagate through the Earth.
2) Key concepts discussed include body waves that travel through the Earth's interior and surface waves that travel along the Earth's surface.
3) The document also discusses seismic wave properties like velocity, period, wavelength, and attenuation as they travel through different Earth layers and are affected by subsurface structures.
An illumination is a decorative embellishment added to handwritten manuscripts before the invention of the printing press. It enhances pages with gold leaf, silver, or other colors. Illuminated letters were enlarged and colored at the start of paragraphs to draw attention. Images of animals, plants, or mythical creatures were sometimes incorporated into the letters. Monks and nuns created illuminated manuscripts in monasteries, adding illuminations to important documents by request of royalty or religious leaders to make them appear more significant. The tradition originated in ancient Egypt and continued for hundreds of years in medieval Europe. Creating illuminations required specialized roles of parchment maker, scribe, illuminator, and bookbinder working together. Illuminations highlighted a time when reading
Beyond Degrees - Empowering the Workforce in the Context of Skills-First.pptxEduSkills OECD
Iván Bornacelly, Policy Analyst at the OECD Centre for Skills, OECD, presents at the webinar 'Tackling job market gaps with a skills-first approach' on 12 June 2024
Gender and Mental Health - Counselling and Family Therapy Applications and In...PsychoTech Services
A proprietary approach developed by bringing together the best of learning theories from Psychology, design principles from the world of visualization, and pedagogical methods from over a decade of training experience, that enables you to: Learn better, faster!
Strategies for Effective Upskilling is a presentation by Chinwendu Peace in a Your Skill Boost Masterclass organisation by the Excellence Foundation for South Sudan on 08th and 09th June 2024 from 1 PM to 3 PM on each day.
Walmart Business+ and Spark Good for Nonprofits.pdfTechSoup
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You will hear from Liz Willett, the Head of Nonprofits, and hear about what Walmart is doing to help nonprofits, including Walmart Business and Spark Good. Walmart Business+ is a new offer for nonprofits that offers discounts and also streamlines nonprofits order and expense tracking, saving time and money.
The webinar may also give some examples on how nonprofits can best leverage Walmart Business+.
The event will cover the following::
Walmart Business + (https://business.walmart.com/plus) is a new shopping experience for nonprofits, schools, and local business customers that connects an exclusive online shopping experience to stores. Benefits include free delivery and shipping, a 'Spend Analytics” feature, special discounts, deals and tax-exempt shopping.
Special TechSoup offer for a free 180 days membership, and up to $150 in discounts on eligible orders.
Spark Good (walmart.com/sparkgood) is a charitable platform that enables nonprofits to receive donations directly from customers and associates.
Answers about how you can do more with Walmart!"
ISO/IEC 27001, ISO/IEC 42001, and GDPR: Best Practices for Implementation and...PECB
Denis is a dynamic and results-driven Chief Information Officer (CIO) with a distinguished career spanning information systems analysis and technical project management. With a proven track record of spearheading the design and delivery of cutting-edge Information Management solutions, he has consistently elevated business operations, streamlined reporting functions, and maximized process efficiency.
Certified as an ISO/IEC 27001: Information Security Management Systems (ISMS) Lead Implementer, Data Protection Officer, and Cyber Risks Analyst, Denis brings a heightened focus on data security, privacy, and cyber resilience to every endeavor.
His expertise extends across a diverse spectrum of reporting, database, and web development applications, underpinned by an exceptional grasp of data storage and virtualization technologies. His proficiency in application testing, database administration, and data cleansing ensures seamless execution of complex projects.
What sets Denis apart is his comprehensive understanding of Business and Systems Analysis technologies, honed through involvement in all phases of the Software Development Lifecycle (SDLC). From meticulous requirements gathering to precise analysis, innovative design, rigorous development, thorough testing, and successful implementation, he has consistently delivered exceptional results.
Throughout his career, he has taken on multifaceted roles, from leading technical project management teams to owning solutions that drive operational excellence. His conscientious and proactive approach is unwavering, whether he is working independently or collaboratively within a team. His ability to connect with colleagues on a personal level underscores his commitment to fostering a harmonious and productive workplace environment.
Date: May 29, 2024
Tags: Information Security, ISO/IEC 27001, ISO/IEC 42001, Artificial Intelligence, GDPR
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বাংলাদেশের অর্থনৈতিক সমীক্ষা ২০২৪ [Bangladesh Economic Review 2024 Bangla.pdf] কম্পিউটার , ট্যাব ও স্মার্ট ফোন ভার্সন সহ সম্পূর্ণ বাংলা ই-বুক বা pdf বই " সুচিপত্র ...বুকমার্ক মেনু 🔖 ও হাইপার লিংক মেনু 📝👆 যুক্ত ..
আমাদের সবার জন্য খুব খুব গুরুত্বপূর্ণ একটি বই ..বিসিএস, ব্যাংক, ইউনিভার্সিটি ভর্তি ও যে কোন প্রতিযোগিতা মূলক পরীক্ষার জন্য এর খুব ইম্পরট্যান্ট একটি বিষয় ...তাছাড়া বাংলাদেশের সাম্প্রতিক যে কোন ডাটা বা তথ্য এই বইতে পাবেন ...
তাই একজন নাগরিক হিসাবে এই তথ্য গুলো আপনার জানা প্রয়োজন ...।
বিসিএস ও ব্যাংক এর লিখিত পরীক্ষা ...+এছাড়া মাধ্যমিক ও উচ্চমাধ্যমিকের স্টুডেন্টদের জন্য অনেক কাজে আসবে ...
How to Setup Warehouse & Location in Odoo 17 InventoryCeline George
In this slide, we'll explore how to set up warehouses and locations in Odoo 17 Inventory. This will help us manage our stock effectively, track inventory levels, and streamline warehouse operations.
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This document provides an overview of wound healing, its functions, stages, mechanisms, factors affecting it, and complications.
A wound is a break in the integrity of the skin or tissues, which may be associated with disruption of the structure and function.
Healing is the body’s response to injury in an attempt to restore normal structure and functions.
Healing can occur in two ways: Regeneration and Repair
There are 4 phases of wound healing: hemostasis, inflammation, proliferation, and remodeling. This document also describes the mechanism of wound healing. Factors that affect healing include infection, uncontrolled diabetes, poor nutrition, age, anemia, the presence of foreign bodies, etc.
Complications of wound healing like infection, hyperpigmentation of scar, contractures, and keloid formation.
2. Fig. 1. Diagram of measurement geometry for BRDF. Colli-
mated irradiance E comes in at angle i . The reflected radiance is Fig. 2. Diagram of instrument design with major components
sampled at a polar angle v with azimuth . listed.
oped. Thus there was a requirement to determine flected light from the surface is collected by the view
accurately the BRDF for natural surfaces, such as fibers, which carry this reflected light to an array.
sand. Each view fiber comes into the array at a different
Although the BRDF is an important factor in de- spot, and this array is imaged on a charge-coupled
scribing the surface reflectance, it can be difficult to device ͑CCD͒ camera. The array is displayed in the
measure, even for simple surfaces. Because the camera image as an array of bright dots; the bright-
function varies with both illumination angle and ness of each dot represents the reflectance into the
viewing angle, many measurements are required to specific angle. The instrument housing also con-
properly characterize a surface. Typically these tains the control computer and a hard drive for data
measurements have been performed by an instru- storage. The whole system can be powered by a bat-
ment with which individual measurements of view- tery, allowing remote operation. The instrument
ing directions are performed for each illumination case is a 39-cm-high cylinder with a diameter of 42
condition.4,5 The viewing directions and illumina- cm. The specific instrument components are de-
tion conditions can be varied either manually or au- scribed below.
tomatically. In either case there is a large number
of individual measurements to be performed. This A. Light Source
is time-consuming, few measurements have been per- To measure reflectance accurately one must have sta-
formed, and these have been laboratory measure- ble, even illumination of the surface and view this
ments for small surfaces. To make these surface with a stable detector. There are two
measurements in situ for benthic surfaces requires a choices for the basic optical design of a reflectometer.
different design because the instrument would be op- In one of these, the surface must be illuminated over
erated by a scuba diver with limited air and measure- a large area, and the instrument must view a portion
ment time. of the illuminated surface. This choice allows the
We developed an instrument design that allows instrument to be relatively insensitive to the distance
many viewing angles to be measured simultaneously between the receiver and the surface rrs ͑ignoring
for a specific illumination condition. With multiple attenuation in the path͒. This is because the change
illumination wavelengths and angles, the spectral in the observed area of the surface that is due to a
BRDF can be determined in a time suitable for mea- change in rrs is compensated by a change in the re-
surement in situ. This design can also be extended ceived flux that is due to a 1͞rrs2. However, this
into the laboratory for quick, accurate characteriza- measurement geometry requires a well-defined re-
tion of both natural and man-made surfaces. ceiver aperture and wastes some of the illuminating
beam. The second choice is to have a well-defined
2. Instrument Description small illumination area and overview the surface.
A schematic of the instrument design is shown in Fig. In this case the constraints on the receiver optics can
2. The two most important features of the instru- be relaxed as it is required that only a large area,
ment are that multiple viewing angles are measured including all the illuminated area, be viewed. How-
simultaneously and there are no moving parts in the ever, this choice is sensitive to rrs because when rrs is
design. Illumination is provided by three colors of increased, the increased area viewed by the receiver
light-emitting diodes ͑LED’s͒ which illuminate indi- is not illuminated. Even with this consideration,
vidual fibers. These fibers guide the light to a ball our design uses this geometry because we have many
lens which collimates the light and directs it onto the receivers ͑of the order of 100͒, and it is more efficient
sample surface. We select the color and illumina- to control the illumination optics than the receiver
tion angle by turning on individual LED’s. Re- optics.
6198 APPLIED OPTICS ͞ Vol. 39, No. 33 ͞ 20 November 2000
3. Illumination is provided by blue, green, and red were drilled in the dome pointed at the center of the
LED’s ͓Panasonic LNG992CFBW, Lumex SSL- sample area. These holes were drilled at the polar
LX1001333XGC, and Panasonic LN261CAL͑UR͒, re- angles of 5°, 15°, 25°, 35°, 45°, 55°, and 65°. They
spectively͔. There are separate LED’s for each were also dispersed azimuthally, with a concentra-
illumination angle ͑i ͒ from 0° to 65° ͑0°, 5°, 15°, 25°, tion of measurement locations in the forward ͑spec-
35°, 45°, 55°, 65°͒. A 1-mm plastic fiber is used to ular͒ and backward ͑hot-spot͒ directions as this was
carry the light from the illumination block to a ball anticipated to be an important feature of many sur-
lens which produces the collimated light that illumi- faces. Hence azimuthal angles ͑͒ measured are
nates the sample surface. We wanted the illumi- Ϯ5°, Ϯ10°, Ϯ15°, Ϯ30°, Ϯ45°, Ϯ60°, Ϯ75°, Ϯ90°,
nated area to be the same for each LED color, so we Ϯ105°, Ϯ120°, Ϯ135°, Ϯ150°, Ϯ165°, Ϯ172°, and
could not have a separate fiber for each color at a Ϯ180°. At the smaller polar angles some of the az-
specific i because multiple fibers at the focal plane of imuthal angles are missing because they physically
the ball lens would be directed into different direc- interfere with the illumination optics. All the avail-
tions. To get the light from three LED colors into able spaces on this grid were drilled, and choices were
the illumination fiber, a cavity was made in the illu-
made about which 100 viewing directions would be
mination block to allow the three LED’s, for a specific
used. We concentrated on the forward and the back-
i , to point at the tip of the fiber. The cavity was
made from polished aluminum; and, although the ward directions and spreading the available fibers in
fiber was not illuminated as efficiently as it would be the plus and minus azimuthal directions so that the
for a single LED, it does allow a single fiber to be used sample symmetry could be determined. For many
for each illumination angle. natural, in situ samples this symmetry could not be
The light from the fiber is collimated with 10-mm assumed.
BK-7 ball lenses ͑Edmund Scientific͒. The fibers are Illumination and view fibers are limited to polar
arranged so that the center of the illuminated spot on angles Ͻ65° because of mechanical constraints. Be-
the sample surface remains constant, independent of cause we were concerned with natural surfaces that
illumination angle. There is a small change of the have randomly oriented facets, if any facets at all, we
illuminated surface that is due to the circular spot expected the largest peaks to be in the hot-spot or
becoming oval with increased illumination angle. specular direction. Thus we had view fibers at the
The light from the ball lens exits through a hemi- same polar angles as the illumination fibers, and we
spherical window over the sample area. We used a tried to concentrate the measurements in the forward
20-cm-diameter compass dome ͑Rule Industries͒ as and the backward directions. Because we have dis-
the system window. The size of this hemisphere in- crete sampling directions we may miss sharp reflec-
volves several competing factors. The larger the tion features. But two factors make this less
dome, the less likely that the measurement will be important. First, with the natural samples it is less
affected by multiple reflections. Also, large sizes are likely that we will have sharp reflection features
preferred as deviations of the sample height are less other than in the specular and hot-spot directions.
critical because these affect the measurement by the Second, the data from this instrument will be used
inverse square of the relative change in distance. predominantly in models with less angular resolution
Unfortunately the ultimate instrument size is criti- than our measurements. Thus we do not consider
cally dependent on the size of this dome, and for that our resolution limits the applicability of our data
diver-operated instruments, the smaller the better. significantly.
Also, large dome sizes require longer path lengths The fibers have a numerical aperture of 0.58. The
through the medium, hence the opportunity for angular collection efficiency is described in Section 5.
greater attenuation of the illumination and reflected These fibers were led from the collection dome into a
light in the medium because the dome is flooded.
fiber array block. We then imaged this block onto a
The 20-cm compass dome was a reasonable compro-
Peltier-cooled CCD camera ͑First Magnitude Corpo-
mise between these factors. As the illumination
ration͒ using a 16-mm lens system. Each fiber is
goes through the dome normal to the surface, and the
curvature of the dome is small, there is little change imaged onto a 16-pixel-diameter spot on the camera.
in illumination spots between air and water measure- The camera cooling allowed low-noise imaging of the
ments because of the refractive index of the measure- fiber block and also a large dynamic range ͑16-bit
ment medium ͑dome and air or dome and water͒. dynamic range for digitization͒ for the signal. A me-
chanical shutter, provided with the camera, was used
B. Viewing Optics to control acquisition time. Along with the viewing
The sampling area is in the center of the hemisphere. fibers, a fiber was led from each illumination cavity to
An anodized aluminum ring is located at this position the fiber array block. This could be used to verify
and helps maintain the sample location and height which illumination fiber was on during the measure-
for uneven surfaces. We used 465-m core acrylic ment and provide a convenient normalization of the
fibers to view the sample surface. On the instru- data because it was proportional to the light incident
ment side of the compass dome a 19-mm-thick dome on the sample. It was also used to check the stabil-
of aluminum was machined to hold the illumination ity of the camera, the LED’s, and the operation of the
collimation optics and the receiver fibers. Holes camera shutter.
20 November 2000 ͞ Vol. 39, No. 33 ͞ APPLIED OPTICS 6199
4. C. System Control average pixel value in this spot is used. Two unil-
Control of the system is provided by an embedded 486 luminated portions of the image are used to find an
computer. Two two-line displays provide feedback average dark pixel value for the image which is sub-
to the diver ͑operator͒ of several instrument param- tracted from the data image during the initial pro-
eters ͑instrument temperature, supplied voltage lev- cessing. Therefore the array transferred from the
els, maximum and minimum counts in images, file internal computer is the average pixel value for a
names, etc͒. A numeric keypad is placed on the given viewing direction with an estimate of the dark
front of the case to allow the diver to control impor- value subtracted. Because there are approximately
tant parameters during operation of the instrument. 200 pixels averaged to obtain this spot measurement,
A 2.5-in. ͑6.3-cm͒ notebook hard drive ͑2 Gbytes͒ random image noise is greatly reduced. When an
stores the images in the instrument. A multiple unilluminated sample is reduced, the typical dark-
channel analog-to-digital board on the computer al- spot average value is significantly less than one count
lows instrument parameters to be measured, and a after this process.
digital input-output board controls the line displays After the subsetted array is transferred to the
and switches the illumination LED’s on and off. A other computer, the final processing is performed on
custom program controls data acquisition, allowing
the notebook computer. The first step is to sub-
the diver to modify exposure times and illumination
tract an average of the six ambient images collected
sequences.
The whole system is powered from an external from each data set array. This process has two
source. We have several choices depending on the effects: It accounts for any light leaks of ambient
measurement situation. The instrument is powered illumination into the measurement chamber and it
from a 24-V source and requires between 25 and 50 also accounts for residual position-dependent differ-
W. Thus we can use a neutrally buoyant instrument ences in the dark values of the spots. The next
cable and a dc power supply ͑either a surface battery step is to multiply the data arrays by an array that
or wall power if 115 V are available͒. We also have corrects for the relative collection efficiencies of the
battery packs that can be attached to the instrument individual viewing channels. A description of the
allowing operation independent of the instrument ca- process to obtain these calibration arrays is given
ble. This is more convenient for in-water use; how- below. For a given illumination angle and color,
ever, it increases the in-air weight of the instrument the viewing channels are divided by the illumina-
for laboratory use. tion intensity obtained from the fiber which sam-
ples the illumination chamber. Finally the array
is multiplied by an absolute calibration number,
3. Data Acquisition
correcting for the relative collection and collimation
A full measurement sequence consists of three ambi- efficiency of the specific illumination angle and
ent images ͑measurements with no LED turned on to color. Thus in the end there are three arrays re-
measure the background light leakage͒, 24 data im- quired for data reduction. The first is the associ-
ages for the three colors and eight illumination an-
ated ambient image, the second is an effective flat
gles, and three more ambient images. The total
fielding of the viewing channels, and the third is a
data set for one sample then consists of 30 images,
750 kbytes͞image or approximately 22 Mbytes͞set. 24-element array with an absolute calibration fac-
After a day of measurement, we downloaded the data tor for each illumination angle and color.
by transferring the data from the internal computer The later two arrays needed for data reduction are
to a notebook computer by a twisted-pair Ethernet obtained during the calibration process. Calibration
link. Because the important data are really an ar- of the device is done through comparison with a sam-
ray of approximately 110 spots of illumination ͑rath- ple of known BRDF characteristics, in our case a 99%
er than a 768 ϫ 512 pixel image͒, data are reflectance Spectralon plaque. We measured the
subsampled prior to the transfer process, reducing BRDF of this plaque for normal-incidence light in
the data set from 22 Mbytes to 64 kbytes. One full both air and water using a spectral gonio reflectome-
image is transferred along with the position file used ter.6 The results of these measurements are shown
in the subsampling to allow validation of the data in Fig. 3. The BRDF air measurements were com-
reduction process before the raw data are deleted pared with other published measurements of Spec-
from the internal hard disk. tralon BRDF, and these measurements were found to
agree well.7,8 The in-air and in-water measure-
4. Data Reduction and Calibration ments varied slightly, and the appropriate measure-
ment is used during the calibration process. For
Data reduction takes place in two stages. The first v Ն 15 deg, the air reflectance values were fit to the
stage takes place on the internal computer in the polynomial
device, to reduce the size of the data set, before it is
transferred to the notebook computer. The image of
the fiber array block appears as an array of bright BRDF͑i ϭ 0, v͒ ϭ 0.9686 ϩ 0.001976v
spots approximately 16 pixels in diameter. To ab-
stract this value for a given viewing direction, the Ϫ 6.470 ϫ 10Ϫ5v2,
6200 APPLIED OPTICS ͞ Vol. 39, No. 33 ͞ 20 November 2000
5. 5. System Tests and Characterizations
In this section we discuss several tests and charac-
terization experiments that we performed with the
instrument. We performed many characterization
experiments, such as system linearity and spectral
calibrations that help define our measurements. In
addition we performed tests in which the sample lo-
cation varied, which determines the final accuracy of
the measurement and the limitations of the tech-
nique. These tests are described below.
A. Spectral Calibration
We measured the spectral output of the LED’s using
a spectroradiometer with 1-nm resolution ͑Optronics
Fig. 3. Measured Spectralon BRDF values used in the calibra- 740A͒. The red and green LED’s were consistent;
tion. Values are given for both air and water ͑submerged͒. The however, the blue LED’s seemed to fall into two
Spectralon plaques are the nominally 99% reflectance plaques. groups both in intensity and in spectral emission.
Curves are fits to the data described in the text. We selected the group of blue LED’s which gave the
greater intensity to be used in the instrument. The
central wavelength ͑and standard deviation͒ of the
whereas for water the reflectance was fit to the equa- blue, green, and red LED’s were found to be 474.8
tion ͑2.5͒, 569.8 ͑0.8͒, and 657.6 ͑1.8͒ nm, respectively.
BRDF͑i ϭ 0, v͒ ϭ 0.9792 ϩ 0.0012770v The FWHM ͑and standard deviation͒ of the output
light was found to be 31.7 ͑1.3͒, 28.8 ͑0.3͒, and 24.1
Ϫ 7.430 ϫ 10Ϫ5v2. ͑1.3͒ nm for the blue, green, and red LED’s. Addi-
tion of the spectral attenuation of pure water10 sig-
These equations each fit the data with a standard
nificantly changes only the red LED’s characteristics.
deviation of 0.3%. As the water quality changes, the
For this LED the central wavelength moves to 654
attenuation of the viewing and illumination beams in
nm, and the FWHM narrows to 20 nm.
the measurement cavity will change slightly. This
is checked by our performing measurements with the
calibration plaque in situ. B. Illumination Spot Size
For calibration of the device, ten full measurement
sets of the Spectralon plaque are made for both air The illumination spots were examined carefully.
and water because measurements are desired in both The illumination optics form circular spots on the
media. Between each measurement set the Spec- sample surface approximately 1.3 cm in diameter for
tralon plaque is rotated 90 deg to eliminate any ori- the normal-incidence spot. As i increases, the spot
entation biases of the Spectralon surface. The ten becomes elongated, maintaining the same width but
sets of measurements are reduced through the above increasing in length to 3.5 cm at 65 deg. Spot size
data reduction process but with the absolute and rel- and location are independent of color because all col-
ative calibration arrays set to 1. Because we know ors use the same fiber to transfer light to the colli-
the BRDF for normal illumination for this spectralon mation ball lens. The spots from each i also overlap
surface we can use the normal illumination measure- on the sample surface and are centered within 2 mm.
ments to derive the flat-field array. We assume ͑and
tested͒ that the Spectralon surface BRDF is indepen-
dent of wavelength over the wavelengths relevant to C. Viewing Fibers
our measurement, so we use a combination of the The acceptance efficiency of the viewing fibers was
three colors of normal illumination as the flat-field measured as a function of angle in air. These data
sample. Once this flat-field array is known the cal- can be fit by a Gaussian function of the form A
ibration data are rereduced with this information. exp͓Ϫ͑͞20.64͒2͔. Because of refraction at the
The absolute calibration array for the various i window–water interface, the width of this curve is
and colors can be determined at this point. We use narrower in water. For water the corresponding fit
reciprocity of the reflectance from the Spectralon sur- is A exp͓Ϫ͑͞15.22͒2͔. The size of the dome ͑approx-
face, i.e., if i and v are switched, the reflectance imately 20 cm in diameter͒ and the size of the illu-
should remain the same.9 We know how the Spec- minated spot ͑1.3–3.5 cm in diameter͒ result in the
tralon surface behaves for i ϭ 0°; thus for 0° Յ i Յ illumination subtending a full angle of 7–20 deg for
65° we average v Յ 20° to make the v–i ͑v ϭ 0°͒ the viewing fiber for a view of 0-deg zenith. For this
pair with which to compare with i ϭ 0° and 65° Ն geometry the edge of the illuminated spot has a col-
v Ն 0°. This can then be used to derive an absolute lection efficiency of 0.97 ͑0.95͒– 0.77 ͑0.64͒ for air ͑wa-
calibration number for each color and illumination ter͒. For v Ͼ 0° the viewed area gets bigger, and
angle image. the illuminated spot is viewed more efficiently.
20 November 2000 ͞ Vol. 39, No. 33 ͞ APPLIED OPTICS 6201
6. with increasing v. For a sample depth of 1.2 cm,
this factor ranges from 1.35 to 1.10 as v changes from
5° to 65°, as is shown in Fig. 4. Figures 5–7 illus-
trate the residual dependence of the reflectance mea-
surement on sample depth, illumination angle, and
view angle. Each measurement set at a specific
depth was first normalized to the measurement at
0-cm depth ͑the correct position͒. Figure 5 repre-
sents the average of all values with v ϭ 5° as a
function of i . If this was the only factor affecting
the reflectance measurements, Figs. 5–7 should be
flat. The additional roll-off of the reflectance with
Fig. 4. Correction factor for sample depth as a function of v. sample depth can be accounted for by the change in
This factor is predicted by the given sample depth and was applied the spot location and the coincidence of the viewing
to the data in Figs. 5–7. spot with the illumination spot. As can be seen in
Fig. 5, for i Ͻ 45° and v ϭ 5°, the error is quite small
regardless of sample depth. In this case the illumi-
D. Variation with Sample Depth nation spot and viewed spot retain their coincidence.
Because we chose a geometry in which the illumi- As one increases i to 65°, the spot effectively moves
nated area is overviewed, our measurement is depen- off of the center. If the sample surface is 1.2 cm
dent on sample height through a 1͞rrs2 dependence. deeper than the correct position, the center of the
To investigate this sensitivity to sample location we illumination spot moves over 2.6 cm. This is approx-
performed a test in which a Spectralon plaque was imately two diameters of the spot and moves the
lowered away from the correct position in steps, and illumination center to a view angle of 15 deg. This
a measurement set was collected in each position. drops the collection efficiency of the viewing fiber to
The data were corrected for the expected 1͞rrs2 de- 60% and explains the reduction observed in this test.
pendence. This factor is dependent on v as it has What this indicates is that the sample must be lo-
the greatest effect at v ϭ 0° ͑relative change in rrs cated correctly within 0.5 cm for a measurement er-
versus sample depth is greatest here͒ and decreases ror less than 10%. If the distance to the sample
Fig. 5. Normalized BRDF and percent error in the BRDF as a Fig. 6. Normalized BRDF and percent error in the BRDF as a
function of sample depth and i for v ϭ 5°. function of sample depth and i for v ϭ 35°.
6202 APPLIED OPTICS ͞ Vol. 39, No. 33 ͞ 20 November 2000
7. Fig. 8. ͑a͒ System linearity and ͑b͒ percent error from linearity.
System is linear over 3 orders of magnitude of response. Multiple
data points are the results from each of the fiber viewing spots.
Fig. 7. Normalized BRDF and percent error in the BRDF as a
function of sample depth and i for v ϭ 65°.
F. System Stability
As a total system test, a Spectralon calibration re-
cannot be estimated, the error is of the order of 20% flectance plaque ͑nominally 99% reflector͒ was mea-
from this effect for surface variations of 0.5 cm. sured nine times. Between each measurement the
sample was rotated to avoid orientation effects of the
E. System Linearity
The next portion of the system response to test is the
linearity of the system to flux from the sample plane.
A thin sheet of diffusing material ͑drafting vellum,
0.6 mm thick͒ was placed at the location of the sample
surface, and this diffuser was illuminated from the
back by a stable light source. The position of the
light source was varied to change the illumination on
the back of the diffuser and act as a light source for
the BRDF system. The data were extracted for each
spot ͑view fiber͒, and these data were normalized to
be able to look at the combined linearity for all the
view directions. Figure 8͑a͒ shows this combined
response versus incident flux. Figure 8͑b͒ is the per-
cent error difference between the system response
and linearity. The standard deviation of the error in
the response from linearity was 5%. Some of the
standard deviation is due to how the data were com-
bined to form the total data set. As can be seen
Fig. 9. Standard deviation of repetitive measurements of a Spec-
there is also greater error at the high end of the
tralon plaque. The plaque was measured nine times, with a ro-
incident flux, where some pixels were starting to sat- tation between each measurement. Data points are the average
urate, and at the low end, where dark-noise varia- standard deviation for a whole image, v ϭ 5° and v ϭ 65°. Each
tions may be an appreciable portion of the signal. In set of vertical points is for a different illumination angle and LED
general the system shows good system response for color. Illumination angle sets are shown on the graph; colors for
nearly 3 orders of magnitude of flux. each set vary from red ͑R͒ to green ͑G͒ to blue ͑B͒ from left to right.
20 November 2000 ͞ Vol. 39, No. 33 ͞ APPLIED OPTICS 6203
8. Fig. 10. REFF polar plots of a mirror surface. ͑a͒ Polar plot illustrating the location of the view fibers. Each ϩ corresponds to a view
direction. The plot is orientated such that the middle ͑0,0͒ is looking normal to the surface. Descending along the y axis corresponds
to the specular direction. Ascending along the y axis corresponds to the backscattering directions ͑toward the illumination beam͒. Note
the increase of samples in the specular and backward directions. ͑b͒ Normal-incidence, red LED sample shows a large increase in
reflectance directly upward. Peak value was 2600%. ͑c͒ i ϭ 25°, red LED shows a large peak in the specular direction ͑1700%͒ and a
small peak in the back direction ͑20%͒. ͑d͒ i ϭ 65°, red LED also shows a large peak in the specular direction ͑4300%͒ and a relatively
small peak in the back direction ͑100%͒.
Spectralon. When the data were reduced, the stan- ilar. If the green LED channels are excluded, the
dard deviation was found for each illumination angle standard deviation of the measurements is less than
and color. In Fig. 9 the average standard deviations 1%, showing that the instrument can make precise
for the total image, v ϭ 5° and v ϭ 65°, are shown. measurements of the BRDF of surfaces.
These points are displayed as i and the colors are
varied. The first point on the left is the normal il- G. Sensitivity to Spurious Reflections
lumination, red LED. The points move from red to As a final test we show Fig. 10, which is the REFF for
green to blue as one moves from left to right. Illu- several illumination angles and the red LED. The
mination angles are listed on the graph. Several sample measured is a normal front surface mirror.
features should be noted in this figure. First, the Figure 10͑a͒ is a polar plot, showing the positions of
standard deviations are less than 5% for all cases, the 107 viewing fibers that we have in the instru-
and the average for the whole images are less than ment. For orientation, the ͑0,0͒ position is looking
3%. Second, the standard deviation is largest for the straight down at the surface. The illumination
green LED. This is the weakest LED, thus the comes in along the vertical direction above the 0° on
signal-to-noise ratio is smallest for this wavelength, the y axis. The polar angle moves outward from the
increasing the standard deviation between measure- center radially and is proportional to the radial dis-
ments. The standard deviation is largest for v ϭ tance from the center. We observe the increasing
65°. This is once again because the signal tends to polar angle, in the specular direction, by moving ver-
be less at large v, causing a decrease in the signal- tically downward ͑negative angles along the y axis͒.
to-noise ratio. There is a slight increase in the stan- Contours for this sample are at every 0.02 for
dard deviation with increasing illumination angle, REFF Ͻ 0.1, 0.1 for 0.1 Ͻ REFF Ͻ 1, 1 for 1 Ͻ
but this trend is not clear. Finally the standard de- REFF Ͻ 20, and 5 for 5 Ͻ REFF. Figure 10͑b͒ il-
viations for the red and blue LED channels are sim- lustrates the REFF͑i ϭ 0°, v, ͒ for the red LED.
6204 APPLIED OPTICS ͞ Vol. 39, No. 33 ͞ 20 November 2000
9. Fig. 11. REFF polar plots of dry and wet sand surfaces. ͑a͒ REFF ͑i ϭ 0°, v, ͒ at 658 nm for a dry sand surface. ͑b͒ REFF͑i ϭ 65°,
v, ͒ at 658 nm for a dry sand surface. ͑c͒ REFF͑i ϭ 0°, v, ͒ at 658 nm for a wet sand surface. ͑d͒ REFF͑i ϭ 65°, v, ͒ at 658 nm
for a wet sand surface.
As one would expect with a mirror, there is an in- 6. Example Data
crease in the reflectance in the specular direction, As an example of the measurements that we can ob-
and the reflectance is fairly symmetric around this tain with the system, we show two examples. The
direction. The peak value of the reflectance in this first example is a sample of dry construction-grade
case was 26 ͑note that 1 is relative to a diffuse sur- sand. This sand appeared white when dry. Figure
face͒. Figure 10͑c͒ is the REFF͑i ϭ 25°, v, ͒, also 11͑a͒ shows the REFF͑i ϭ 0°, v, ͒ for 658 nm. The
for the red LED. In this example the data show two orientation of the graph is the same as in Fig. 10. The
peaks. The first is the specular peak ͑peak value contours in Fig. 11͑a͒ are at 0.02 for REFF Ͻ 1, 0.1 for
observed was 17͒. Outside this specular peak the 1 Ͻ REFF Ͻ 2, and 0.2 for 2 Ͻ REFF. As can be seen,
reflectance is low; however, there is a peak in the
for normal illumination, the sand sample is diffuse and
backward direction of 0.20. This peak is approxi-
Lambertian to within Ϯ0.02. The lack of contours
mately 1% of the specular peak and is due to back-
reflection from the window of the specular peak back over most of the image indicates the uniformity of the
down to the mirror and up to this view direction. sample. The nominal reflectance of the sample is
This is the worst type of sample for this effect, and 0.30 Ϯ 0.01. This REFF can be contrasted with Fig.
still the error that is due to this retroreflection is only 11͑b͒, which is the REFF͑i ϭ 65°, v, ͒ for 658 nm.
of the order of 1%. Figure 10͑d͒ is the REFF͑i ϭ This sample is also dry sand, but with a large illumi-
65°, v, ͒, also for the red LED. Once again the nation angle. This sample illustrates two effects of-
specular peak is very high ͑43͒, and the retroreflec- ten seen in natural samples. First there is a fairly
tion is of the order of 2–3% of the specular peak. large specular peak. Although the reflectance, nor-
This data set illustrates that the instrument error mal to the surface, is still approximately 0.32, the spec-
that is due to internal reflection is very low, but must ular peak is 0.90. This sample also has an
be considered for intensely specular surfaces. Note enhancement in the backscattering direction. In this
that in water this effect would decrease because of direction the peak is approximately 0.70. This is the
decreased reflectance at the water–window interface. effect of the hot-spot commonly seen in BRDF’s of var-
Also a diffuse reflecting surface would spread the ious surfaces.3 At these larger angles of illumination
retroreflection down to the noise level. the samples are clearly not Lambertian.
20 November 2000 ͞ Vol. 39, No. 33 ͞ APPLIED OPTICS 6205
10. The next sample shown is actually the same dry This instrument will be used to make field measure-
sample measured above, but water was added to the ments of the BRDF in various environments to help
sand to make the surface wet, filling the pores with characterize benthic surfaces and to improve model-
water. This is not a submerged sample, but we ing and remote sensing algorithms.
changed the surface by adding water to the sand.
Figure 11͑c͒ is the REFF͑i ϭ 0°, v, ͒ for 658 nm. The research presented in this paper has been sup-
First it is obvious that the overall reflectance of the ported by the Ocean Optics Program of the U.S. Office
surface has changed significantly. In this case the of Naval Research ͑N001499-10008͒. We thank
nominal reflectance of the surface is 0.16 Ϯ 0.01. Karl Moore who helped in the early development of
Once again the surface is Lambertian at normal in- the instrument.
cidence. This is again contrasted with Fig. 11͑d͒
that is the REFF͑i ϭ 65°, v, ͒ for 658 nm for the References
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As in Fig. 11͑b͒, there is a large specular peak. In York, 1993͒.
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has increased to 1.60, which is much larger than in bottom albedo determination from in-water natural-light mea-
the dry sand. This is probably caused by having surements,” Appl. Opt. 38, 3199 –3205 ͑1999͒.
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The precision of the measurement has been shown to 9. W. C. Snyder, “Reciprocity of the bidirectional reflectance dis-
be 1–5%. The accuracy of the measurement is de- tribution function ͑BRDF͒ in measurements and models of
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determined. If the surface is correctly placed within 685– 691 ͑1998͒.
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6206 APPLIED OPTICS ͞ Vol. 39, No. 33 ͞ 20 November 2000