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.
The document discusses the use of full-range spectroradiometers for measuring solar spectral energy. ASD spectroradiometers are portable instruments that measure wavelengths from 350-2500 nm, allowing for calculation of parameters like aerosol optical depth. They are optimally designed for faster field measurements and calibrated for radiometric collection. ASD instruments offer a solution for analyzing and measuring solar spectral energy with accessories like diffuse fore optics for measuring full sky irradiance.
Instrument to measure the bidirectional reflectanceajsatienza
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.
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
This document summarizes an experiment that uses four laser beams to trap thousands of sub-micron polystyrene particles in water, forming an optically induced crystal. Bragg scattering patterns from the crystal agree with the calculated lattice structure and polarization dependence. By observing the decay and rise of Bragg scattering intensity when turning the lattice on and off, the researchers study the Brownian motion dynamics of particles in the periodic potential, finding agreement with simulations based on the Langevin equation.
11.the optical constants of highly absorbing films using the spectral reflect...Alexander Decker
This document summarizes a study that determined the optical constants of thin films of rhodium metal using spectral reflectance measurements. The researchers measured the reflectance of rhodium films of varying thicknesses using a double beam spectrophotometer. They then used Kramers-Kronig relations to calculate the phase angle from the reflectance data and determine the real refractive index and extinction coefficient. Their method provides accurate optical constants without needing transmission measurements. They found the refractive index and extinction coefficient were nearly equal for thin films and that their method compared well to values from other interference-based techniques.
Hottel's Clear Day Model for a typical arid city - Jeddahinventionjournals
International Journal of Engineering and Science Invention (IJESI) is an international journal intended for professionals and researchers in all fields of computer science and electronics. IJESI publishes research articles and reviews within the whole field Engineering Science and Technology, new teaching methods, assessment, validation and the impact of new technologies and it will continue to provide information on the latest trends and developments in this ever-expanding subject. The publications of papers are selected through double peer reviewed to ensure originality, relevance, and readability. The articles published in our journal can be accessed online.
Greg Smestad, Leonardo Micheli, Thomas Germer, and Eduardo Fernández presented research on characterizing the optical effects of soiling on PV glass and modules. They measured the transmission of glass coupons exposed outdoors at multiple locations over 8 weeks and found soiling reduced transmission more at shorter wavelengths. Particle area coverage on the coupons correlated linearly with reduced hemispherical transmittance. Angular measurements showed soiling impacts transmission more for direct light than hemispherical. The research aims to better understand how soiling impacts PV performance globally.
The document discusses the use of full-range spectroradiometers for measuring solar spectral energy. ASD spectroradiometers are portable instruments that measure wavelengths from 350-2500 nm, allowing for calculation of parameters like aerosol optical depth. They are optimally designed for faster field measurements and calibrated for radiometric collection. ASD instruments offer a solution for analyzing and measuring solar spectral energy with accessories like diffuse fore optics for measuring full sky irradiance.
Instrument to measure the bidirectional reflectanceajsatienza
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.
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
This document summarizes an experiment that uses four laser beams to trap thousands of sub-micron polystyrene particles in water, forming an optically induced crystal. Bragg scattering patterns from the crystal agree with the calculated lattice structure and polarization dependence. By observing the decay and rise of Bragg scattering intensity when turning the lattice on and off, the researchers study the Brownian motion dynamics of particles in the periodic potential, finding agreement with simulations based on the Langevin equation.
11.the optical constants of highly absorbing films using the spectral reflect...Alexander Decker
This document summarizes a study that determined the optical constants of thin films of rhodium metal using spectral reflectance measurements. The researchers measured the reflectance of rhodium films of varying thicknesses using a double beam spectrophotometer. They then used Kramers-Kronig relations to calculate the phase angle from the reflectance data and determine the real refractive index and extinction coefficient. Their method provides accurate optical constants without needing transmission measurements. They found the refractive index and extinction coefficient were nearly equal for thin films and that their method compared well to values from other interference-based techniques.
Hottel's Clear Day Model for a typical arid city - Jeddahinventionjournals
International Journal of Engineering and Science Invention (IJESI) is an international journal intended for professionals and researchers in all fields of computer science and electronics. IJESI publishes research articles and reviews within the whole field Engineering Science and Technology, new teaching methods, assessment, validation and the impact of new technologies and it will continue to provide information on the latest trends and developments in this ever-expanding subject. The publications of papers are selected through double peer reviewed to ensure originality, relevance, and readability. The articles published in our journal can be accessed online.
Greg Smestad, Leonardo Micheli, Thomas Germer, and Eduardo Fernández presented research on characterizing the optical effects of soiling on PV glass and modules. They measured the transmission of glass coupons exposed outdoors at multiple locations over 8 weeks and found soiling reduced transmission more at shorter wavelengths. Particle area coverage on the coupons correlated linearly with reduced hemispherical transmittance. Angular measurements showed soiling impacts transmission more for direct light than hemispherical. The research aims to better understand how soiling impacts PV performance globally.
Optical Characterization of PV Glass Coupons and PV Modules Related to Soilin...Greg Smestad
Optical Characterization of PV Glass Coupons and PV Modules Related to Soiling Losses,
Greg P. Smestad, Ph.D., Sol Ideas Technology Development
December 6th, 2017, 11:35 AM - 12:00 PM
Session 5: Characterization (Chair: Xiaohong Gu, NIST)
Atlas/NIST Workshop on PV Materials Durability
December 5-6, 2017, Gaithersburg, Maryland
National Institute of Standards and Technology, Gaithersburg, Maryland
https://www.nist.gov/el/mssd/agenda
Thermal Tuning of Omni-Directional Reflection Band in Si-Based 1d Photonic Cr...ijrap
The temperature dependence of the omni-directional reflection (ODR) band in a one-dimensional photonicbcrystal is proposed simultaneously considering thermal expansion effect and thermo-optic effect. The structure proposed in this study consists of a periodic arrangement of alternate layers of SiO2 as the material of low refractive index and Si as the material of high refractive index. As the refractive index and thickness of both materials used in this study are modulated by temperature, the ODR band can be tuned as a function of temperature. With the increase of temperature, it is noted that the ODR band shifts towards the longer wavelength region. Also, the ODR band broadens slightly. The ODR band can be tuned by variation in the operating temperature of the structure.
DESIGN, OPTIMIZATION AND DEVELOPMENT OF SOLAR THERMAL HEAT RECEIVER SYSTEM WI...Journal For Research
Against a backdrop of our world’s changing climate solar thermal power generation shows great potential to move global energy production away from fossil fuels to non-polluting sources. A parameter study was conducted based on the previous analysis to improve specific aspects of the initial design using a value of benefit analysis to evaluate the different design. This project focused on the design, analysis and verification of a high temperature solar receiver. Computational Fluid Dynamic (CFD) analysis of Radiation model is carried out with new geometry design of receiver. Discrete Transfer Radiation Model (DTRM) model is used for numerical simulation.
This document discusses the design, optimization, and development of a solar thermal heat receiver system with a parabolic concentric collector. A computational fluid dynamics (CFD) analysis was conducted using a discrete transfer radiation model (DTRM) to simulate heat transfer and optimize the receiver design. The CFD analysis found that the receiver design achieved an average temperature of 453K on the receiver wall and outlet temperature of air at 392K with an air mass flow rate of 0.08kg/s. Higher temperatures can be achieved by using materials with higher reflectivity for the reflector and selecting optimal working fluids.
This document discusses using Mueller matrices to characterize textured films and periodic grating structures. It begins by explaining how Mueller matrices can measure depolarization, which provides new insights into surface roughness characterization compared to conventional ellipsometry. It then discusses using Mueller matrices to characterize the angular distribution of slopes on rough surfaces and relates this to a depolarization index. The document provides examples of using Mueller matrix polarimeters to characterize materials like aluminum films, plastic films, and silicon nanowires. It also discusses using Mueller matrix scatterometry to characterize periodic grating structures for applications like lithography.
Measure the refractive index of air using a Michelson interferometer.UCP
The document describes using a Michelson interferometer to measure the refractive index of air. It begins with introductions on refractive index and how a Michelson interferometer works by splitting and recombining light beams to produce interference patterns. It then details the experimental procedure, which involves counting interference fringe shifts as air pressure is decreased in one beam path. Calculations show this allows determining the refractive index of air as about 0.000192 based on the fringe shifts measured.
2004-10-14 AIR-257: Satellite Detection of Aerosols Concepts and TheoryRudolf Husar
The document summarizes a course on detecting aerosols using satellites. The course covers:
1) Introduction to satellite aerosol detection, different satellite types and their usage.
2) How satellites detect aerosol events like fires, dust storms and haze.
3) Using satellite data to study aerosols for projects like analyzing their fast response to changing environmental conditions.
4) Applications of satellite data in air quality management and issues around its use.
Application of remote sensing in agriculturevajinder kalra
The document discusses the concepts and applications of remote sensing, GIS, and GPS in agriculture. It defines remote sensing as sensing things from a distance using electromagnetic radiation and describes the different platforms (ground, air, satellite) used. It explains key remote sensing concepts including spectral signatures, spectral reflectance curves, spatial/spectral/radiometric/temporal resolutions, and indices like NDVI. Interpretation of remote sensing imagery involves analyzing tone, shape, size, pattern, texture, shadow, and association. Spectral signatures can provide information about vegetation, soil moisture, organic matter, iron content, and other properties. Remote sensing allows monitoring and analyzing agriculture from a distance.
Estimation of diffuse solar radiation in the south of cameroonAlexander Decker
This document presents a study that developed models to estimate monthly mean daily diffuse solar radiation for locations in southern Cameroon between 2°N and 5°N latitude. It analyzed monthly mean daily data on global and diffuse solar radiation from 1985-2005 for five cities. Linear and quadratic regression models were developed relating diffuse fraction to clearness index. The proposed models were compared to existing models from Liu and Jordan, Page, Iqbal, and Erbs, finding the proposed models had better statistical performance and agreement with observed values. The study concludes the developed models can reliably estimate diffuse solar radiation for locations in southern Cameroon.
This presentation covers the principles of remote sensing and reflectance profiling and explains how the concept of spectral signature is utilized in entomology research
This document provides an overview of remote sensing and describes its key principles and applications. It defines remote sensing as acquiring information about planetary surfaces from a distance without direct contact. The main components of a remote sensing system are described as the energy source, atmosphere, target interaction, sensor recording, transmission and processing, interpretation and analysis, and applications. Common data types like raster and vector data are also explained. Remote sensing techniques like digital image processing, classification, and analysis are outlined. Examples of satellite imagery and classifications are provided.
Hyperspectral remote sensing for oil explorationJayanth Joshua
Hyperspectral remote sensing uses sensors that collect data across a wide range of electromagnetic wavelengths, with more than 100 contiguous bands that provide detailed spectral signatures. This allows identification of subtle mineral and material differences that can indicate oil and gas deposits. Seeps at the surface cause alterations detectable by hyperspectral analysis, like calcite, pyrite and clay changes. A Hydrocarbon Index highlights absorption peaks related to hydrocarbons. Classification algorithms like Spectral Angle Mapper can map hydrocarbon-bearing zones by comparing spectra to known samples. Soil tonal anomalies from bleaching or iron/clay changes also indicate subsurface structures and seepage areas for exploration.
This document summarizes the IrSOLaV methodology for estimating solar radiation from satellite images. The methodology uses geostationary satellite images and atmospheric data as inputs. Satellite images provide information on cloud cover characteristics, while atmospheric data includes parameters like Linke turbidity factor. A cloud index is computed from the satellite images and related to clear sky index to estimate solar radiation. Validation shows the methodology achieves a 12% RMSE for hourly solar radiation estimates compared to ground measurements.
This document provides an overview of digital image processing. It discusses what image processing entails, including enhancing images, extracting information, and pattern recognition. It also describes various image processing techniques such as radiometric and geometric correction, image enhancement, classification, and accuracy assessment. Radiometric correction aims to reduce noise from sources like the atmosphere, sensors, and terrain. Geometric correction geometrically registers images. Image enhancement improves interpretability. Classification categorizes pixels. The document outlines both supervised and unsupervised classification methods.
Typical Meteorological Year Report for CSP, CPV and PV solar plantsIrSOLaV Pomares
This technical report analyzes the solar resource available at a site in Northern Cape, South Africa selected to host a solar thermal power plant. It presents a typical meteorological year (TMY) developed using 12 years of hourly solar radiation data for the site. The TMY is generated using a methodology that selects the most representative month from each year for key meteorological variables. It is comprised of months from 2007 to 2010 that best match the long-term averages for global horizontal and direct normal solar radiation at the site. The TMY and long-term averages are presented and show a close match in monthly and daily solar radiation patterns for use in modeling solar power production at the site.
Application of Seismic Reflection Surveys to Detect Massive Sulphide Deposits...iosrjce
Seismic reflection techniques, the most widely used geophysical method for hydrocarbon exploration
has the capability to delineate and provide better images of regional structure for exploration of mineral
deposits in any geological settings. Previous tests on detection and imaging of massive sulphide ores using
seismic reflection techniques have been done mostly in crystalline environments. Application of seismic
reflection techniques for imaging sedimentary hosted massive sulphide is relatively new and the few experiments
carried out are at local scale (<500m). In this study, we analyze the feasibility of such regional exploration by
modelling three massive sulphide ore and norite lenses scenario using 2D seismic survey with relatively sparse
source-receiver geometry to image these deposits within 1.5km depth range. Results from the modelling
experiment demonstrate that 2-Dimensional seismic reflections survey can be used to detect massive sulphides
at any scale. The test further indicates that geologic setting and acquisition parameters are very important for
the detection of these ore bodies. Overall, the outcomes of the results support our started objective which is to
demonstrate that seismic reflection surveys can be used to detect the presence of sediment hosted massive
sulphides at regional scale
When Practicing Writing Chinese, Is It RecommendeJim Webb
Catherine de Medici of France and Isabella I of Spain both pursued strict Catholic policies, eliminating other religions through massacres. Catherine approved the St. Bartholomew's Day massacre in France that killed 3000 Huguenots. Isabella wanted to remove Muslims and Jews from Spain. Both rulers sought to establish Catholicism as the sole religion and remove perceived religious threats.
016 King Essay Example Stephen Why We Crave HJim Webb
The document provides instructions for using the HelpWriting.net service to request that writers complete assignments. It outlines a 5-step process: 1) Create an account; 2) Submit a request with instructions and deadline; 3) Review bids and choose a writer; 4) Review the completed paper and authorize payment; 5) Request revisions to ensure satisfaction. The service aims to provide original, high-quality content and offers refunds for plagiarized work.
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Optical Characterization of PV Glass Coupons and PV Modules Related to Soilin...Greg Smestad
Optical Characterization of PV Glass Coupons and PV Modules Related to Soiling Losses,
Greg P. Smestad, Ph.D., Sol Ideas Technology Development
December 6th, 2017, 11:35 AM - 12:00 PM
Session 5: Characterization (Chair: Xiaohong Gu, NIST)
Atlas/NIST Workshop on PV Materials Durability
December 5-6, 2017, Gaithersburg, Maryland
National Institute of Standards and Technology, Gaithersburg, Maryland
https://www.nist.gov/el/mssd/agenda
Thermal Tuning of Omni-Directional Reflection Band in Si-Based 1d Photonic Cr...ijrap
The temperature dependence of the omni-directional reflection (ODR) band in a one-dimensional photonicbcrystal is proposed simultaneously considering thermal expansion effect and thermo-optic effect. The structure proposed in this study consists of a periodic arrangement of alternate layers of SiO2 as the material of low refractive index and Si as the material of high refractive index. As the refractive index and thickness of both materials used in this study are modulated by temperature, the ODR band can be tuned as a function of temperature. With the increase of temperature, it is noted that the ODR band shifts towards the longer wavelength region. Also, the ODR band broadens slightly. The ODR band can be tuned by variation in the operating temperature of the structure.
DESIGN, OPTIMIZATION AND DEVELOPMENT OF SOLAR THERMAL HEAT RECEIVER SYSTEM WI...Journal For Research
Against a backdrop of our world’s changing climate solar thermal power generation shows great potential to move global energy production away from fossil fuels to non-polluting sources. A parameter study was conducted based on the previous analysis to improve specific aspects of the initial design using a value of benefit analysis to evaluate the different design. This project focused on the design, analysis and verification of a high temperature solar receiver. Computational Fluid Dynamic (CFD) analysis of Radiation model is carried out with new geometry design of receiver. Discrete Transfer Radiation Model (DTRM) model is used for numerical simulation.
This document discusses the design, optimization, and development of a solar thermal heat receiver system with a parabolic concentric collector. A computational fluid dynamics (CFD) analysis was conducted using a discrete transfer radiation model (DTRM) to simulate heat transfer and optimize the receiver design. The CFD analysis found that the receiver design achieved an average temperature of 453K on the receiver wall and outlet temperature of air at 392K with an air mass flow rate of 0.08kg/s. Higher temperatures can be achieved by using materials with higher reflectivity for the reflector and selecting optimal working fluids.
This document discusses using Mueller matrices to characterize textured films and periodic grating structures. It begins by explaining how Mueller matrices can measure depolarization, which provides new insights into surface roughness characterization compared to conventional ellipsometry. It then discusses using Mueller matrices to characterize the angular distribution of slopes on rough surfaces and relates this to a depolarization index. The document provides examples of using Mueller matrix polarimeters to characterize materials like aluminum films, plastic films, and silicon nanowires. It also discusses using Mueller matrix scatterometry to characterize periodic grating structures for applications like lithography.
Measure the refractive index of air using a Michelson interferometer.UCP
The document describes using a Michelson interferometer to measure the refractive index of air. It begins with introductions on refractive index and how a Michelson interferometer works by splitting and recombining light beams to produce interference patterns. It then details the experimental procedure, which involves counting interference fringe shifts as air pressure is decreased in one beam path. Calculations show this allows determining the refractive index of air as about 0.000192 based on the fringe shifts measured.
2004-10-14 AIR-257: Satellite Detection of Aerosols Concepts and TheoryRudolf Husar
The document summarizes a course on detecting aerosols using satellites. The course covers:
1) Introduction to satellite aerosol detection, different satellite types and their usage.
2) How satellites detect aerosol events like fires, dust storms and haze.
3) Using satellite data to study aerosols for projects like analyzing their fast response to changing environmental conditions.
4) Applications of satellite data in air quality management and issues around its use.
Application of remote sensing in agriculturevajinder kalra
The document discusses the concepts and applications of remote sensing, GIS, and GPS in agriculture. It defines remote sensing as sensing things from a distance using electromagnetic radiation and describes the different platforms (ground, air, satellite) used. It explains key remote sensing concepts including spectral signatures, spectral reflectance curves, spatial/spectral/radiometric/temporal resolutions, and indices like NDVI. Interpretation of remote sensing imagery involves analyzing tone, shape, size, pattern, texture, shadow, and association. Spectral signatures can provide information about vegetation, soil moisture, organic matter, iron content, and other properties. Remote sensing allows monitoring and analyzing agriculture from a distance.
Estimation of diffuse solar radiation in the south of cameroonAlexander Decker
This document presents a study that developed models to estimate monthly mean daily diffuse solar radiation for locations in southern Cameroon between 2°N and 5°N latitude. It analyzed monthly mean daily data on global and diffuse solar radiation from 1985-2005 for five cities. Linear and quadratic regression models were developed relating diffuse fraction to clearness index. The proposed models were compared to existing models from Liu and Jordan, Page, Iqbal, and Erbs, finding the proposed models had better statistical performance and agreement with observed values. The study concludes the developed models can reliably estimate diffuse solar radiation for locations in southern Cameroon.
This presentation covers the principles of remote sensing and reflectance profiling and explains how the concept of spectral signature is utilized in entomology research
This document provides an overview of remote sensing and describes its key principles and applications. It defines remote sensing as acquiring information about planetary surfaces from a distance without direct contact. The main components of a remote sensing system are described as the energy source, atmosphere, target interaction, sensor recording, transmission and processing, interpretation and analysis, and applications. Common data types like raster and vector data are also explained. Remote sensing techniques like digital image processing, classification, and analysis are outlined. Examples of satellite imagery and classifications are provided.
Hyperspectral remote sensing for oil explorationJayanth Joshua
Hyperspectral remote sensing uses sensors that collect data across a wide range of electromagnetic wavelengths, with more than 100 contiguous bands that provide detailed spectral signatures. This allows identification of subtle mineral and material differences that can indicate oil and gas deposits. Seeps at the surface cause alterations detectable by hyperspectral analysis, like calcite, pyrite and clay changes. A Hydrocarbon Index highlights absorption peaks related to hydrocarbons. Classification algorithms like Spectral Angle Mapper can map hydrocarbon-bearing zones by comparing spectra to known samples. Soil tonal anomalies from bleaching or iron/clay changes also indicate subsurface structures and seepage areas for exploration.
This document summarizes the IrSOLaV methodology for estimating solar radiation from satellite images. The methodology uses geostationary satellite images and atmospheric data as inputs. Satellite images provide information on cloud cover characteristics, while atmospheric data includes parameters like Linke turbidity factor. A cloud index is computed from the satellite images and related to clear sky index to estimate solar radiation. Validation shows the methodology achieves a 12% RMSE for hourly solar radiation estimates compared to ground measurements.
This document provides an overview of digital image processing. It discusses what image processing entails, including enhancing images, extracting information, and pattern recognition. It also describes various image processing techniques such as radiometric and geometric correction, image enhancement, classification, and accuracy assessment. Radiometric correction aims to reduce noise from sources like the atmosphere, sensors, and terrain. Geometric correction geometrically registers images. Image enhancement improves interpretability. Classification categorizes pixels. The document outlines both supervised and unsupervised classification methods.
Typical Meteorological Year Report for CSP, CPV and PV solar plantsIrSOLaV Pomares
This technical report analyzes the solar resource available at a site in Northern Cape, South Africa selected to host a solar thermal power plant. It presents a typical meteorological year (TMY) developed using 12 years of hourly solar radiation data for the site. The TMY is generated using a methodology that selects the most representative month from each year for key meteorological variables. It is comprised of months from 2007 to 2010 that best match the long-term averages for global horizontal and direct normal solar radiation at the site. The TMY and long-term averages are presented and show a close match in monthly and daily solar radiation patterns for use in modeling solar power production at the site.
Application of Seismic Reflection Surveys to Detect Massive Sulphide Deposits...iosrjce
Seismic reflection techniques, the most widely used geophysical method for hydrocarbon exploration
has the capability to delineate and provide better images of regional structure for exploration of mineral
deposits in any geological settings. Previous tests on detection and imaging of massive sulphide ores using
seismic reflection techniques have been done mostly in crystalline environments. Application of seismic
reflection techniques for imaging sedimentary hosted massive sulphide is relatively new and the few experiments
carried out are at local scale (<500m). In this study, we analyze the feasibility of such regional exploration by
modelling three massive sulphide ore and norite lenses scenario using 2D seismic survey with relatively sparse
source-receiver geometry to image these deposits within 1.5km depth range. Results from the modelling
experiment demonstrate that 2-Dimensional seismic reflections survey can be used to detect massive sulphides
at any scale. The test further indicates that geologic setting and acquisition parameters are very important for
the detection of these ore bodies. Overall, the outcomes of the results support our started objective which is to
demonstrate that seismic reflection surveys can be used to detect the presence of sediment hosted massive
sulphides at regional scale
When Practicing Writing Chinese, Is It RecommendeJim Webb
Catherine de Medici of France and Isabella I of Spain both pursued strict Catholic policies, eliminating other religions through massacres. Catherine approved the St. Bartholomew's Day massacre in France that killed 3000 Huguenots. Isabella wanted to remove Muslims and Jews from Spain. Both rulers sought to establish Catholicism as the sole religion and remove perceived religious threats.
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LAND USE LAND COVER AND NDVI OF MIRZAPUR DISTRICT, UPRAHUL
This Dissertation explores the particular circumstances of Mirzapur, a region located in the
core of India. Mirzapur, with its varied terrains and abundant biodiversity, offers an optimal
environment for investigating the changes in vegetation cover dynamics. Our study utilizes
advanced technologies such as GIS (Geographic Information Systems) and Remote sensing to
analyze the transformations that have taken place over the course of a decade.
The complex relationship between human activities and the environment has been the focus
of extensive research and worry. As the global community grapples with swift urbanization,
population expansion, and economic progress, the effects on natural ecosystems are becoming
more evident. A crucial element of this impact is the alteration of vegetation cover, which plays a
significant role in maintaining the ecological equilibrium of our planet.Land serves as the foundation for all human activities and provides the necessary materials for
these activities. As the most crucial natural resource, its utilization by humans results in different
'Land uses,' which are determined by both human activities and the physical characteristics of the
land.
The utilization of land is impacted by human needs and environmental factors. In countries
like India, rapid population growth and the emphasis on extensive resource exploitation can lead
to significant land degradation, adversely affecting the region's land cover.
Therefore, human intervention has significantly influenced land use patterns over many
centuries, evolving its structure over time and space. In the present era, these changes have
accelerated due to factors such as agriculture and urbanization. Information regarding land use and
cover is essential for various planning and management tasks related to the Earth's surface,
providing crucial environmental data for scientific, resource management, policy purposes, and
diverse human activities.
Accurate understanding of land use and cover is imperative for the development planning
of any area. Consequently, a wide range of professionals, including earth system scientists, land
and water managers, and urban planners, are interested in obtaining data on land use and cover
changes, conversion trends, and other related patterns. The spatial dimensions of land use and
cover support policymakers and scientists in making well-informed decisions, as alterations in
these patterns indicate shifts in economic and social conditions. Monitoring such changes with the
help of Advanced technologies like Remote Sensing and Geographic Information Systems is
crucial for coordinated efforts across different administrative levels. Advanced technologies like
Remote Sensing and Geographic Information Systems
9
Changes in vegetation cover refer to variations in the distribution, composition, and overall
structure of plant communities across different temporal and spatial scales. These changes can
occur natural.
Communicating effectively and consistently with students can help them feel at ease during their learning experience and provide the instructor with a communication trail to track the course's progress. This workshop will take you through constructing an engaging course container to facilitate effective communication.
it describes the bony anatomy including the femoral head , acetabulum, labrum . also discusses the capsule , ligaments . muscle that act on the hip joint and the range of motion are outlined. factors affecting hip joint stability and weight transmission through the joint are summarized.
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.
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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 ...
বাংলাদেশ অর্থনৈতিক সমীক্ষা (Economic Review) ২০২৪ UJS App.pdf
About The Importance Of The Definition Of Reflectance Quantities-Results Of Case Studies
1. ABOUT THE IMPORTANCE OF THE DEFINITION OF REFLECTANCE QUANTITIES -
RESULTS OF CASE STUDIES
G. Schaepman-Strub a, b
, T. Painter c
, S. Huber a
, S. Dangel a
, M. E. Schaepman d
, J. Martonchik e
, F. Berendse b
a
RSL, Dept. of Geography, Univ. of Zurich, 8057 Zurich, Switzerland - gschaep@geo.unizh.ch
b
Nature Conservation and Plant Ecology Group, WUR, 6708 PD Wageningen, The Netherlands
c
National Snow and Ice Data Center, University of Colorado Boulder, Boulder, CO, USA
d
Centre for Geo-Information, WUR, 6700 AA Wageningen, The Netherlands
e
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
KEY WORDS: Terminology, Comparison, Simulation, Accuracy, Vegetation, Snow, MISR
ABSTRACT:
In the remote sensing user community there is a lack of consistency in definitions and properties of reflectance quantities. On
one hand, more recent satellite programs such as NASA's MODIS and MISR sensors take into account the directional
dimension of the different reflectance products. On the other hand, many published studies still remain unspecific on the
reflectance quantities they are based on, or do not follow common definitions. One example is the term 'albedo' assigned to
significantly differing products. This fact makes it difficult and confusing to evaluate and compare published results.
Our contribution briefly summarizes basic reflectance nomenclature articles. The main aim is to quantify differences of
reflectance products to stress the importance of adequate usage of reflectance definitions and quantities. Results from the
comparison of directional-hemispherical reflectance versus bihemispherical reflectance and bidirectional reflectance factors
versus hemispherical-directional reflectance factors are shown. We exemplify differences of these quantities using modelling
results of a black spruce forest canopy and snow cover, as well as selected biome-specific MISR reflectance products of the
year 2001.
The presented case studies can only give an insight into the dimension of the problem. The actual differences in the
reflectance products of a remotely sensed surface depend on the atmospheric conditions, the surroundings, topography, and
the scattering properties of the surface itself. Never the less the presented results are urging the user community to be more
specific on the application and definition of reflectance quantities.
1. INTRODUCTION
The Earth-looking remote sensing community increasingly
understands the effects of solar illumination geometry and
sensor viewing geometry on airborne and satellite data due
to the anisotropic reflectance of the Earth’s surface and the
atmosphere. Not only the direction of illumination and
observation influence the measured reflectance, but also
their opening angle. Different reflectance quantities have
been defined to describe the corresponding conditions of
the measurements (Nicodemus, 1977; Martonchik, 2000).
Nevertheless, these conditions are often partly or fully
neglected by the user community, and different reflectance
quantities are equated, which is especially true for the so-
called surface reflectance and albedo (e.g., Breuer, 2003).
The reflectance anisotropy of observed surfaces contains
unique information about its structure and the optical
properties of the scattering elements. The underlying
concept for the characterization of the anisotropy is the
bidirectional reflectance distribution function (BRDF). It
describes the radiance reflected by a surface as a function of
a parallel beam of incident light from a single direction into
another direction of the hemisphere. Under natural
conditions, i.e. for all field, airborne and spaceborne sensor
measurements, the assumption of a single direction of the
incident beam does not hold true. Natural light is composed
of a direct part, thus uncollided radiation, as well as a diffuse
component scattered by the atmosphere, and/ or the
surroundings of the observed target. The amount and
spectral character of the diffuse light irradiating the
observed surface is thus depending on the atmospheric
conditions, as well as on the topography and the scattering
properties of the surroundings. Previous studies have shown
the effects of different atmospheric conditions in simulated
and measured data. The aim of this study is to highlight the
differences in reflectance caused by different geometries of
the opening angle of the illumination, i.e., directional and
hemispherical extent. To get a better impression of the
influence of the diffuse component included in the
hemispherical extent, different direct to diffuse irradiance
scenarios are considered. This modelling approach is
performed for a black spruce forest canopy, and a snow
cover. Secondly, first results of a comparison between
directional and hemispherical reflectance products from the
Multi-angle Imaging SpectroRadiometer (MISR) are
presented for selected test sites.
This study gives an easy access to the basic concept of
reflectance quantities for the user community, by
summarizing the nomenclature articles of Nicodemus (1977)
and Martonchik (2000). It highlights the importance of a
proper usage of definitions through quantitative
comparison of different reflectance products.
2. DEFINITIONS
2.1 Radiance, reflectance, reflectance factors
Spectral radiance is the most important quantity to be
measured in spectroradiometry. In particular it is the
quantity required for quantitatively analyzing directional
effects. The surface leaving radiance is assumed to be
dependent on the incident radiation onto the surface, thus
the reflectance is defined as the ratio of reflected to incident
flux. Following the concept of energy conservation, its
values are in the inclusive interval 0 to 1. The reflectance
factor is the ratio of the radiant flux reflected by a surface to
that reflected into the same reflected-beam geometry by an
ideal (lossless) and diffuse (Lambertian) standard surface,
2. irradiated under the same conditions. For measurement
purposes, a Spectralon panel commonly approximates the
ideal diffuse standard surface. Reflectance factors may reach
values beyond 1, especially for highly specular reflecting
surfaces.
2 . 2 Geometrical considerations of the incident and
reflected fluxes
The basic concept describing the reflectance anisotropy of a
surface is the BRDF. Conceptual quantities of reflectance
include the assumption that the size/ distance ratio of the
illuminating source (usually the sun or lamp) and the
observing sensor is assumed to be zero and are usually
labelled directional in the general terminology. Since
infinitesimal elements of solid angle do not include
measurable amounts of radiant flux, and unlimited small
light sources and sensor field of views do not exist, all
measurable quantities of reflectance are performed in the
c o n i c a l or hemispherical domain of geometrical
considerations. Thus, actual measurements always involve
non-zero intervals of direction and the underlying basic
quantity for all radiance and reflectance measurements is the
conical case, including the special case of a cone of
hemispherical extent. In the case of hemispherical
illumination under field conditions, the irradiance can be
divided into a direct sunlight component and a second
irradiance component scattered by the atmosphere and
terrain, which leads to an anisotropic, diffuse sky
illumination. Being a function of wavelength, the ratio of
diffuse/direct incident irradiance highly influences the
spectral dependence of directional effects as shown in the
snow case study below.
According to Nicodemus (1977), the angular characteristics
of the incoming radiance are named first in the term and are
followed by the angular characteristics of the reflected
radiance. This leads to the following nomenclature of
reflectance quantities (Table 1):
Reflected
Incoming
Directional Conical Hemispherical
Directional Bidirectional
Case 1
Directional-
conical
Case 2
Directional-
hemispherical
Case 3
Conical Conical-
directional
Case 4
Biconical
Case 5
Conical-
hemispherical
Case 6
Hemispheri
cal
Hemispherica
l-directional
Case 7
Hemispherica
l-conical
Case 8
Bihemispherica
l
Case 9
Table1: Relation of incoming and reflected radiance
terminology used to describe reflectance
quantities. The labelling with ‘Case’ corresponds
to Nicodemus (1977). Grey fields correspond to
measurable quantities, whereas the others denote
conceptual quantities.
2 . 3 Examples for measurable quantities and derived
products
Referring to Table 1, typical measurement instrumentation
with resulting reflectance products can be listed for the
individual cases. The biconical reflectance (Case 5) is a
typical laboratory setup, where a collimated light source
illuminates a target that is measured using a non-imaging
spectroradiometer. A special case is the conical-
hemispherical reflectance (Case 6), where in the laboratory
the sensor is replaced using a cosine receptor for
hemispherical measurement. The hemispherical-conical
reflectance (Case 8) corresponds to the most common
measurement of satellites or airborne and field instruments
(e.g., MERIS, ASD FieldSpec). Finally, bihemispherical
reflectance (Case 9) is measured using albedometers.
Even though measurable quantities only reflect Cases 5, 6, 8
and 9 in Table 1 above, the non-zero interval of the sensor’s
field of view may be neglected and resulting quantities are
reported as being bidirectional or hemispherical-directional
measurements. Most satellite reflectance products delivered
after atmospheric correction procedures are labelled ‘surface
reflectance’ (e.g., MODIS (Vermote, 1999)). Nevertheless, in
many cases the underlying concept of the used reflectance
nomenclature is unclear or undocumented, resulting in
significant difficulties to assign the proper terminology to
the delivered data product. As long as data from satellite or
airborne sensors and field spectrometers are not corrected for
the hemispherical angular extent of the incoming radiance,
the reflected measured quantity always depends on the
actual direct and diffuse components of the irradiance over
the whole hemisphere. As a consequence, data without a
proper specification of the corresponding beam geometries
are subject to misinterpretation and subsequently lead to
larger uncertainties.
Table 2 shows typical reflectance products and their
derivation from the satellite measurement. The integration of
the HDRF (Case 7) over the viewing hemisphere results in
the BHR (Case 9). Using a modelling approach (e.g.,
Martonchik 1994; Lyapustin, 1999), the HDRF data (Case 7)
is further used to derive BRF (Case 1), and finally, DHR
(Case 3) can be derived from BRF (Case1) by hemispherical
integration over the viewing hemisphere. A special case is
the derivation of the BRDF from the BRF (again Case 1),
which is simply scaling the BRF by 1/ π .
Measurement Derived Products
BRDF
Bidirectional
Reflectance
Distribution
Function
Case 1
BRF
Bidirectional
Reflectance
Factor
Case 1
DHR
Directional-
Hemispherica
l Reflectance
Case 3
Hemispherical
-Conical
Reflectance
Case 8
HDRF
Hemispheric
al-
Directional
Reflectance
Factor
Case 7
BHR
Bihemispheri
cal
Reflectance
Case 9
Table 2: Conceptual data processing chain of airborne and
satellite measurements. The table is read from the
left to the right side.
The abovementioned derivations of conceptual reflectance
quantities from measured reflectance data include the
application of a BRDF model. Thus, derived conceptual
quantities depend not only on the sampling scheme,
availability and accuracy of measured data, but also on the
model itself.
3. 3. CASE STUDIES COMPARING DIFFERENT
REFLECTANCE QUANTITIES
The following case studies highlight differences of the
above described reflectance quantities using model
simulations for a vegetation canopy, and a snow surface, as
well as MISR data products for several scenes. The
differences of hemispherical versus directional reflectance
quantities (i.e., BHR (Case 9) versus DHR (Case 3) and HDRF
(Case 7) versus BRF (Case1)) are computed for different
wavelengths regions and various ratios of direct to diffuse
illumination.
We concentrate on reflectance and reflectance factor
quantities. Deriving the bidirectional reflectance
distribution function from HDRF measurements without
correcting for the diffuse illumination, leads to severe
distortions of the resulting function (Lyapustin, 1999).
3.1 Vegetation canopy reflectance simulations using the
RPV model
3.1.1 Methods and data: Using the PARABOLA
instrument, black spruce forest HDRF data were acquired at
eight solar zenith angles (35.1º, 40.2º, 45.2º, 50.2º, 55.0º,
59.5º, 65.0º, 70.0º) (Deering, 1995). After applying a simple
HDRF to BRF atmospheric correction scheme, data of the red
band (650 to 670nm) were fitted to the parametric Rahman-
Pinty-Verstraete (RPV) model (Engelsen, 1996). Resulting
fit parameters and the RPV are used to simulate different
reflectance quantities of a black spruce canopy under
various illumination conditions. The model was run for a
solar zenith angle of 30° and increments of direct (d) and
diffuse irradiance of d =1.0, d = 0.8, d = 0.6, d = 0.4, d = 0.2,
and d = 0.0. These irradiance scenarios corresponded to BRF
(d = 1.0) and HDRF for the rest, including the special case of
white-sky HDRF, i.e. purely diffuse irradiance (d = 0.0).
3.1.2 Results: Figure 1 (top) reports the HDRF of black
spruce for indicated direct-diffuse ratios in the solar
principal plane, assuming the incident diffuse radiation to
be isotropic. The wavelength range is 650 to 670 nm. As is
expected for a vegetation canopy, there is a large amount of
backscattering, and a hot spot at view zenith 30º due to the
lack of shadowing. For d approaching 0, the anisotropy is
smoothed and the hot spot becomes invisible.
Fig. 1 (centre) reports the DHR of black spruce as a function
of the illumination zenith angle. As previously described for
vegetation, the DHR increases with increasing illumination
zenith (Kimes, 1983). For comparison, the white-sky BHR
(although not a function of any angle) is plotted. The actual
albedo can be expressed as a combination of DHR and white-
sky BHR if the diffuse incident radiation is assumed to be
isotropic. The actual albedo for a given illumination zenith
angle then lies on a vertical line between the DHR and white-
sky BHR as shown in the graph for an example of 20º solar
zenith.
Finally, Figure 1 (bottom) reports the BRF at nadir view as a
function of the illumination zenith angle, along with the
white-sky HDRF at nadir view (although not a function of
any illumination angle).
Figure 1. Simulated BRF data for a black spruce canopy in
the solar principle plane, and corresponding
HDRF for varying direct to diffuse irradiance
conditions (top), DHR, and BHR for pure diffuse
illumination as a reference (centre), BRF at nadir,
and HDRF at nadir for pure diffuse illumination
(bottom).
3.2 Snow reflectance simulations
3.2.1 Methods and data: This case study presents model
results from a snow directional reflectance model. The model
is the coupling of single-scattering parameters and a
discrete-ordinates multiple scattering model. Single-
scattering parameters were determined with a ray-tracing
model for spheroidal particles (Macke, 1996) and the
multiple scattering calculations were performed with the
DISORT model (Stamnes, 1988).
The single-scattering parameters used in the model were the
single-scattering albedo, extinction efficiency, and the
single-scattering phase function. Model results shown here
are for a spheroid of minimum and maximum radii of 208 µm
and 520 µm, respectively. This spheroid has the same surface
area to volume ratio as a sphere of radius 250 µm. We then
determined 20 Legendre moments of the single-scattering
phase function for input to the multiple scattering model.
The multiple scattering model was run for a solar zenith of
30°, illumination scenarios as mentioned for the black
spruce canopy, and the wavelength range from 0.4 to 2.5 µm.
4. 3.2.2 Results: In Figure 2, we show resulting BRF and
HDRF data in the solar principle plane.
Figure 2. Simulated snow HDRF data for the range of
indicated irradiance scenarios, and BRF data in
the solar principal plane at 0.55 µm (top) and
1.03 µm (bottom).
The models for d = 1.0 through d = 0.2 irradiance exhibit a
forward reflectance distribution that decreases in magnitude
with increasing diffuse component. For the totally diffuse
irradiance scenario, the distribution has a shallow bowl
shape. This minimum at nadir results from the angular
intersection of the strong forward scattering phase function
with the surface. Off-zenith irradiance has a greater chance
than zenith irradiance of surviving multiple scatterings due
to the orders of magnitude greater single scattering in the
forward direction. In other words, zenith irradiance requires
far more scattering events to produce reflected radiance than
off-zenith. Therefore, the distribution will have greater
reflectance at the larger view zenith angles.
The bowl-shaped distribution for diffuse irradiance becomes
relatively deeper at longer wavelengths (Figure 2 (bottom)).
We show the 1.03 µm model because this is the wavelength
range in which snow reflectance is most sensitive to grain
size (Nolin, 2000; Green, 2002). The enhancement of the
bowl shape at greater diffuse irradiance is explained as
above coupled with a decrease in the single-scattering
albedo at the longer wavelengths. This in turn is due to the
increase in the imaginary part k of the complex refractive
index at these wavelengths (Warren, 1982). Only for the BRF
and d = 0.8 irradiance cases is the distribution properly
forward reflecting.
Figure 3 shows DHR of snow relative to the illumination
zenith angle with the associated white-sky BHR included for
reference. For both wavelengths, the DHR increases with
increasing zenith angle but the increase is far greater in
absolute and relative reflectance for the 1.03 µm case. The
increase in both cases is due to the change in the angle of the
intersection of the single scattering phase function with the
surface. The single scattering phase function of ice particles
in the forward angles is several orders of magnitude greater
than in the rest of the scattering domain. Therefore, as the
illumination zenith angle increases, the forward scattered
photons have a higher probability of escaping the
snowpack. This in turn increases the albedo of snow.
Because the single scattering albedo of ice particles (in this
case a spheroid of radii 208 µm and 520 µm) is 0.9999817 at
0.55 µm versus 0.9930210 at 1.03 µm, multiply scattered
photons are more likely to be absorbed at 1.03 µm. The
greater increase in albedo at 1.03 µm results then from the
increase in the contribution of singly scattered photons to
albedo due to the increase in illumination zenith angle. At
both wavelengths, the effective illumination zenith angle for
white-sky BHR is 49-50°, as discussed above.
Figure 3. DHR versus illumination zenith angle for snow at
0.55 µm (top) and 1.03 µm (bottom). The BHR for
diffuse illumination (white-sky BHR) is included
for comparison.
3.3 Analysis of MISR surface reflectance data products
3.3.1 Methodsand selecteddatasets: Various land
surface reflectance products are available from the MISR
sensor, launched in 1999. MISR has nine cameras with centre
view directions of 26.1, 45.6, 60.0, and 70.5 degrees in
forward and afterward direction, as well as one looking in
nadir direction. All cameras cover four spectral bands with a
centre wavelength at 446, 558, 672, and 867 nm. The
crosstrack IFOV and sample spacing of each pixel is 275 m
for all of the off-nadir cameras, and 250 m for the nadir
camera. Downtrack IFOV’s depend on view angle, ranging
from 214 m in the nadir to 707 m at the most oblique angle.
However, sample spacing in the downtrack direction is
275 m in all cameras (Diner, 1999).
We briefly describe the retrieval of the land surface products
HDRF, BHR, BRF, and DHR. For the mathematical
formulation refer to Martonchik (1998). The top-of-
atmosphere MISR radiances are atmospherically corrected to
produce the HDRF and BHR, surface reflectance properties as
would be measured at ground level but at the MISR spatial
resolution. The MISR surface retrievals do not explicitly
incorporate tilt or slope effects (Diner, 1999). The HDRF and
BHR then are further atmospherically corrected to remove all
5. diffuse illumination effects, resulting in the BRF and DHR.
The determination of these surface products obviously
requires that the atmosphere be sufficiently characterized in
order for the correction process to occur. This
characterization is accomplished by means of an aerosol
retrieval. After a BRF is determined, it is fitted to a three
parameter empirical BRF model, which provides a
convenient representation of the surface scattering
characteristics.
We statistically analyzed the differences of directional and
hemispherical MISR reflectance data products, namely DHR
versus BHR and BRF versus HDRF. These data products are
compared to each other by their respective mean values,
mean absolute and relative difference. Additionally, their
correlation is derived. For further analysis of the products
and their differences, the mean value of the absolute HDRF
uncertainty and relative BHR uncertainty product was
calculated, as well as the mean aerosol optical depth (AOD)
value in the green spectral band of all analyzed pixels.
The ratio of diffuse to direct illumination increases with
increasing AOD. Therefore we expect the largest difference
between HDRFs and BRFs in shorter wavelength ranges, i.e.,
in the blue band, where the diffuse component of the
illumination is largest. This wavelength dependence is due
to the decreasing influences of Rayleigh scattering and
aerosols with increasing wavelength.
We selected ten datasets, acquired in 2001, that correspond
to MISR data product version 12. For all analyzed data, a
comparison of MISR optical depths with those from an
included ground based AERONET site showed good
correlation in all four MISR spectral bands. The reliability of
the land surface reflectance values depends upon the AOD
magnitude. Therefore, pixels with an AOD larger 0.5 at
558 nm (green spectral band) have been excluded from the
MISR scenes. In the following, all quantities called ‘scene-
averaged’ rely on this exclusion.
The sites were selected to represent different biome types,
following the MODIS IGBP land cover map. Three sites are
covered twice, under different atmospheric conditions and
sun zenith angles (Table 3).
Site Country Date
2001
Mean
sz [°]
Main biome
type (IGBP)
Mean
AOD
Howland Maine,
US
07/21 27.7 Mixed f.,
decid. broadl f.
0.10
Railroad
Valley
Nevada,
US
08/17 28.4 Barren or
sparsely veg.
0.99
Mongu Zambia 07/11 44.6 Savannas,
croplands
0.05
Banizou
mbou
Niger 10/04 24.1 0.31
12/23 41.4 0.11
Hombori Mali 07/05 19.6 0.36
Avignon France 07/12 25.2 0.07
08/29 36.9 0.19
Bordeau
x
France 05/30 24.5 Everg. needlel.
f., croplands,
mixed forest
0.24
07/01 24.0 0.12
Table 3. Overview of MISR scenes selected for the analysis
of the land surface products.
3.3.2 Results: Differences between BHR (Case 9) and
DHR (Case 3)
In general, BHR and DHR product values derived from the
MISR sensor are highly correlated, with r2
values between
0.98 and 1.0 throughout all spectral bands and analyzed
scenes (with the exception of the Hombori scene blue band,
where r2
reaches 0.84 only).
For all analyzed MISR images, the relative scene-averaged
difference between BHR and DHR reaches a maximum of
2.7 % of the BHR value (with the exception of the difference
in the blue band of the Hombori scene reaching 5.1%) for all
four spectral bands (Table 4). Numerically, this is a small
difference, compared to the data uncertainties. The lowest
scene-averaged relative BHR uncertainty is 5.6% for the NIR
spectral band of the Avignon (07/12) scene, whereas relative
BHR uncertainty can easily reach values around 20% and
much higher, with a maximum of 88% for the blue spectral
band of the Banizoumbou (10/04) scene.
As detailed above, we expect a trend of decreasing
differences between BHR and DHR with increasing
wavelength, thus the blue band reflectances should show the
largest relative differences. Results show that the relative
reflectance difference of five scenes is biggest in the blue
band, whereas for the other 5 cases, differences reach the
same or even higher values in at least one of the other bands.
Mean BHR
Mean ((BHR-DHR)/BHR) [%]
Site SZ
[°]
Mean
AOD
446nm 558nm 672nm 867nm
Howland 27.7 0.10 0.031
2.1
0.053
1.5
0.028
1.1
0.318
0.7
Railroad
Valley
28.4 0.99 0.095
1.7
0.137
1.3
0.170
0.9
0.238
0.7
Mongu 44.6 0.05 0.046
0.5
0.078
0.3
0.094
0.3
0.246
0.6
Banizou
mbou
24.1 0.31 0.060
1.2
0.126
1.5
0.176
1.4
0.357
1.3
41.4 0.11 0.084
0.5
0.160
0.5
0.261
0.6
0.376
0.6
Hombori 19.6 0.36 0.108
5.1
0.232
2.5
0.349
1.6
0.412
1.2
Avignon 25.2 0.07 0.045
2.0
0.075
1.4
0.069
0.9
0.307
0.8
36.9 0.19 0.050
0.9
0.081
0.9
0.079
0.7
0.286
0.8
Bordeaux 24.5 0.24 0.059
1.5
0.097
2.0
0.087
1.4
0.320
1.2
24.0 0.12 0.048
1.8
0.078
1.5
0.073
1.0
0.304
0.9
Table 4. Comparison of BHR and DHR values for the
selected MISR scenes.
Differences between the BHR and DHR product can be related
to the actual aerosol optical depth in the green spectral band.
This relation is weak for the BHR-DHR differences in the
blue band (r2
= 0.29) and gets much stronger with increasing
wavelengths, with a maximum for the NIR region (r2
= 0.79).
Differences between HDRF (Case 7) and BRF (Case 1)
As with the results for the hemispherical reflectances, the
relationship between HDRF and BRF values show a high
correlation, with r2
values above 0.98 throughout all spectral
bands, and view angles of all scenes (with the exception of
the Hombori scene blue band reflectance reaching an r2
of
0.67 only).
Compared to the quantities integrated over an extrapolation
of the view hemisphere, the relative differences of the
reflectances of the single view angles are larger and reach up
to 10% of the HDRF value (with the exception of the
Hombori scene blue band reflectance difference of 14.2%).
The trend of decreasing differences with increasing
wavelength is much stronger for the directional quantities
than for the hemispherically integrated quantities. Thus, the
6. largest relative differences were mostly found in the blue
spectral band, with very few exceptions.
Comparing the relative HDRF-BRF differences with regard to
the viewing direction, there is a clear trend of higher
differences for the forward looking camera. Further we
investigated the relative differences of the HDRF-BRF
values with regard to the nine cameras. For most scenes and
spectral bands, the Ba camera (view zenith of 45.6º) shows
the smallest differences. This indicates, that whenever the
hemispherical irradiance component is neglected and HDRF
data are equated with BRF data, the introduced uncertainties
can be reduced by applying off-nadir data in the backward
scattering direction, instead of nadir data.
4. CONCLUSION
All remote sensing data depend on the illumination and
view geometry of the sensor, as well as on their opening
angle. Different reflectance quantities have been defined to
describe the corresponding conditions of the measurements.
The basis for the proper use of these reflectance quantities is
a standardized nomenclature, well known throughout the
remote sensing community. This study summarized the
nomenclature articles of Nicodemus (1977) and Martonchik
(2000) to give an easy access to the concept.
Further the importance of using the adequate reflectance
product is shown. All reflectance measurements performed
under natural conditions include a diffuse fraction. Its
amount is a function of the atmospheric conditions, the
topography, the surroundings of the observed surface, and
the wavelength. It thus introduces spectral effects to
spectrometer data. The presented case studies are
concentrating on the opening angle of the illumination,
restricting it to directional irradiance only, or allowing for a
diffuse irradiance component. The effect of varying direct to
diffuse irradiance ratio is significant in modelled data, as
well as in analysed MISR reflectance products.
This study is addressing different remote sensing
communities. It shows that the use of any remote sensing
data has to include the analysis of the corresponding
illumination and view geometry, and the opening angle, as a
prerequisite for any further analysis. This will explain many
unexpected results and significantly reduce uncertainties.
Some satellite products of the MODIS and MISR sensor
account for these considerations. It is the responsibility of
the users to choose for the adequate product, guided by the
reflectance nomenclature. Further, state of the art models
allow users to account for the anisotropy of the target and
the illumination conditions.
The publication shall motivate the remote sensing
community to take reflectance nomenclature into account
and use the presented common basis for the sake of
clarification and comparability. Even though not all
applications of remote sensing data take the directionality
of the reflectance signal into account, the appropriate
selection and denomination of the used reflectance quantity
is a prerequisite for every scientific publication.
5. ACKNOWLEDGEMENT
This work was supported by the Swiss National Science
Foundation, under contract 200020-101517. MISR data were
obtained from the NASA Langley Research Center
Atmospheric Sciences Data Center.
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