This document discusses satellite geodesy and navigation. It provides an overview of the historical development of satellite geodesy beginning in 1957 with Sputnik 1. It describes the basic concepts and methods of satellite geodesy including Earth to space, space to Earth, and space to space observation techniques. Applications of satellite geodesy include global geodesy, geodetic control, geodynamics, navigation, and related fields. The document also discusses satellite orbital motion, perturbation forces, and orbit determination methods.
•Lunar laser telemetry consists in determining the round-trip travel time of the light between a transmitter on the Earth and a reflector on the Moon, which is an equivalent measurement of the distance between these two points
This notes helps one to acquire noteable knowledege in the field of satellite geodesy. It also includes the moevement of satellites in orbit, how they communicate with people on earth. This satellites communicate using GPS receivers which are placed on earth. Waves are sent and these waces contain data.
GPS helps us identify exact location of a place/feature in the globe. Now-a-days we can carry out survey, enter data and process data. GPS is very helpful in soil survey
1) The document examines the performance of the EGM2008 global geoid model against GPS and leveling data from Scandinavia, adjacent Baltic areas, and Greenland.
2) Testing in Scandinavia and Baltic areas found that EGM2008 performs at the same level as the best regional geoid model NKG2004, with a standard deviation from leveling-derived geoid heights of 0.24 meters.
3) In Greenland, EGM2008 could not be directly evaluated due to a lack of leveling data, but comparisons to GPS-altimetry data showed performance on par with the regional model GOCINA04.
Refined parameters of the HD 22946 planetary system and the true orbital peri...Sérgio Sacani
Multi-planet systems are important sources of information regarding the evolution of planets. However, the long-period
planets in these systems often escape detection. These objects in particular may retain more of their primordial characteristics compared
to close-in counterparts because of their increased distance from the host star. HD 22946 is a bright (G = 8.13 mag) late F-type star
around which three transiting planets were identified via Transiting Exoplanet Survey Satellite (TESS) photometry, but the true orbital
period of the outermost planet d was unknown until now.
Aims. We aim to use the Characterising Exoplanet Satellite (CHEOPS) space telescope to uncover the true orbital period of HD 22946d
and to refine the orbital and planetary properties of the system, especially the radii of the planets.
Methods. We used the available TESS photometry of HD 22946 and observed several transits of the planets b, c, and d using CHEOPS.
We identified two transits of planet d in the TESS photometry, calculated the most probable period aliases based on these data, and
then scheduled CHEOPS observations. The photometric data were supplemented with ESPRESSO (Echelle SPectrograph for Rocky
Exoplanets and Stable Spectroscopic Observations) radial velocity data. Finally, a combined model was fitted to the entire dataset in
order to obtain final planetary and system parameters.
Results. Based on the combined TESS and CHEOPS observations, we successfully determined the true orbital period of the planet d
to be 47.42489 ± 0.00011 days, and derived precise radii of the planets in the system, namely 1.362 ± 0.040 R⊕, 2.328 ± 0.039 R⊕, and
2.607 ± 0.060 R⊕ for planets b, c, and d, respectively. Due to the low number of radial velocities, we were only able to determine 3σ
upper limits for these respective planet masses, which are 13.71 M⊕, 9.72 M⊕, and 26.57 M⊕. We estimated that another 48 ESPRESSO
radial velocities are needed to measure the predicted masses of all planets in HD 22946. We also derived stellar parameters for the host
star.
Conclusions. Planet c around HD 22946 appears to be a promising target for future atmospheric characterisation via transmission
spectroscopy. We can also conclude that planet d, as a warm sub-Neptune, is very interesting because there are only a few similar
confirmed exoplanets to date. Such objects are worth investigating in the near future, for example in terms of their composition and
internal structure.
GPS uses a network of satellites to determine location through trilateration. Satellites continuously transmit timing signals, while receivers calculate distance based on signal travel time to intersect with other satellite spheres and determine position at their cross-section. At least 4 satellites are needed - 3 for 2D location and 4 for 3D including altitude. Precise timing is crucial, and receivers correct for clock errors between satellites and receivers. GPS provides navigation, mapping and a wide range of applications based on positioning calculations.
•Lunar laser telemetry consists in determining the round-trip travel time of the light between a transmitter on the Earth and a reflector on the Moon, which is an equivalent measurement of the distance between these two points
This notes helps one to acquire noteable knowledege in the field of satellite geodesy. It also includes the moevement of satellites in orbit, how they communicate with people on earth. This satellites communicate using GPS receivers which are placed on earth. Waves are sent and these waces contain data.
GPS helps us identify exact location of a place/feature in the globe. Now-a-days we can carry out survey, enter data and process data. GPS is very helpful in soil survey
1) The document examines the performance of the EGM2008 global geoid model against GPS and leveling data from Scandinavia, adjacent Baltic areas, and Greenland.
2) Testing in Scandinavia and Baltic areas found that EGM2008 performs at the same level as the best regional geoid model NKG2004, with a standard deviation from leveling-derived geoid heights of 0.24 meters.
3) In Greenland, EGM2008 could not be directly evaluated due to a lack of leveling data, but comparisons to GPS-altimetry data showed performance on par with the regional model GOCINA04.
Refined parameters of the HD 22946 planetary system and the true orbital peri...Sérgio Sacani
Multi-planet systems are important sources of information regarding the evolution of planets. However, the long-period
planets in these systems often escape detection. These objects in particular may retain more of their primordial characteristics compared
to close-in counterparts because of their increased distance from the host star. HD 22946 is a bright (G = 8.13 mag) late F-type star
around which three transiting planets were identified via Transiting Exoplanet Survey Satellite (TESS) photometry, but the true orbital
period of the outermost planet d was unknown until now.
Aims. We aim to use the Characterising Exoplanet Satellite (CHEOPS) space telescope to uncover the true orbital period of HD 22946d
and to refine the orbital and planetary properties of the system, especially the radii of the planets.
Methods. We used the available TESS photometry of HD 22946 and observed several transits of the planets b, c, and d using CHEOPS.
We identified two transits of planet d in the TESS photometry, calculated the most probable period aliases based on these data, and
then scheduled CHEOPS observations. The photometric data were supplemented with ESPRESSO (Echelle SPectrograph for Rocky
Exoplanets and Stable Spectroscopic Observations) radial velocity data. Finally, a combined model was fitted to the entire dataset in
order to obtain final planetary and system parameters.
Results. Based on the combined TESS and CHEOPS observations, we successfully determined the true orbital period of the planet d
to be 47.42489 ± 0.00011 days, and derived precise radii of the planets in the system, namely 1.362 ± 0.040 R⊕, 2.328 ± 0.039 R⊕, and
2.607 ± 0.060 R⊕ for planets b, c, and d, respectively. Due to the low number of radial velocities, we were only able to determine 3σ
upper limits for these respective planet masses, which are 13.71 M⊕, 9.72 M⊕, and 26.57 M⊕. We estimated that another 48 ESPRESSO
radial velocities are needed to measure the predicted masses of all planets in HD 22946. We also derived stellar parameters for the host
star.
Conclusions. Planet c around HD 22946 appears to be a promising target for future atmospheric characterisation via transmission
spectroscopy. We can also conclude that planet d, as a warm sub-Neptune, is very interesting because there are only a few similar
confirmed exoplanets to date. Such objects are worth investigating in the near future, for example in terms of their composition and
internal structure.
GPS uses a network of satellites to determine location through trilateration. Satellites continuously transmit timing signals, while receivers calculate distance based on signal travel time to intersect with other satellite spheres and determine position at their cross-section. At least 4 satellites are needed - 3 for 2D location and 4 for 3D including altitude. Precise timing is crucial, and receivers correct for clock errors between satellites and receivers. GPS provides navigation, mapping and a wide range of applications based on positioning calculations.
This document provides an overview of geodetic methods, including both traditional and modern space-based techniques. It discusses the history of geodesy and how the field has split into physical and positional geodesy. Modern methods like GPS, VLBI, and satellite laser ranging now allow simultaneous determination of positions and the gravity field by using orbiting satellites. The document reviews various space-based techniques and how they have revolutionized geodetic accuracy by removing limitations of line-of-sight measurements.
GPS relies on principles of special and general relativity to account for relativistic effects that would otherwise cause errors. The Sagnac effect, which results from light traveling in opposite directions around a rotating object, must be considered and can cause time differences of hundreds of nanoseconds depending on satellite and receiver positions. An experiment in 1984 precisely measured the Sagnac effect using GPS satellites and atomic clocks at three locations, finding results that matched relativity predictions to within 5 nanoseconds.
GPS uses trilateration to determine a receiver's location based on distance measurements to multiple satellites. The receiver uses signal transit times to calculate distances to at least four satellites. Each distance defines a sphere around the satellite, and the intersection of these spheres pinpoints the receiver's location. GPS consists of three segments - space, control, and user. The space segment consists of 32+ satellites. The control segment monitors and controls the satellites. Users can access GPS for civilian and military navigation, tracking, and timing applications.
The document discusses the Global Positioning System (GPS). It provides an overview of GPS including that it is a satellite-based navigation system consisting of 24 satellites maintained by the US Department of Defense. GPS is used to determine location, time, and speed. The document describes the key components and principles of how GPS works including its space, control, and user segments. It involves calculating distance via signal travel time from 4 or more satellites to determine a position.
GPS uses a constellation of 24 satellites orbiting Earth to enable GPS receivers to determine their precise location. The system works by using triangulation based on distance measurements from at least three satellites. The GPS segments include the space segment (satellites), control segment (ground stations that monitor satellites), and user segment (GPS receivers). GPS has both military and civilian applications including navigation, mapping, vehicle tracking, and monitoring fishing fleets.
This document discusses how satellite observations over the past 50 years have revolutionized the field of earth sciences. It describes how early satellite missions taught scientists not only about the earth but how to improve satellite technology. Precise measurements from satellites have enabled major advances in understanding plate tectonics, topography, seismology and more. The ubiquity of GPS has provided vital data on phenomena like sea level change, earthquakes and volcanoes. Open data policies have maximized the benefits of earth observations.
Transit photometry has been the most successful exoplanet discovery method to date. It works by detecting the dimming of a star's light as a planet passes in front of it. From the transit light curve, properties of the planet like its radius and orbital parameters can be derived. However, transits have a low probability of being aligned with our line of sight. False positives from eclipsing binaries can also mimic transits, so follow-up observations are needed to confirm planetary discoveries. Past and current transit surveys have found over a hundred planets, and future surveys aim to detect smaller planets orbiting brighter stars.
Now-a-days the field of Remote Sensing and GIS has become exciting and glamorous with rapidly expanding opportunities. Many organizations spend large amounts of money on these fields. Here the question arises why these fields are so important in recent years. Two main reasons are there behind this. 1) Now-a-days scientists, researchers, students, and even common people are showing great interest for better understanding of our environment. By environment we mean the geographic space of their study area and the events that take place there. In other words, we have come to realize that geographic space along with the data describing it, is part of our everyday world; almost every decision we take is influenced or dictated by some fact of geography. 2) Advancement in sophisticated space technology (which can provide large volume of spatial data), along with declining costs of computer hardware and software (which can handle these data) has made Remote Sensing and G.I.S. affordable to not only complex environmental / spatial situation but also affordable to an increasingly wider audience.
The Global Positioning System (GPS) is a satellite-based navigation system that provides location and time information to GPS receivers anywhere on Earth. It was developed by the United States Department of Defense in the 1970s to overcome limitations of previous navigation systems. GPS uses a constellation of satellites that continuously transmit precise timing signals, allowing GPS receivers to determine their location by calculating the time difference of signals from multiple satellites. The system consists of three segments - space, control, and user - with the space segment comprising the satellites, the control segment managing the satellites, and the user segment being anyone using a GPS receiver.
High-resolution UV/Optical/IR Imaging of Jupiter in 2016–2019Sérgio Sacani
Imaging observations of Jupiter with high spatial resolution were acquired beginning in 2016, with a cadence of 53
days to coincide with atmospheric observations of the Juno spacecraft during each perijove pass. The Wide Field
Camera 3 (WFC3) aboard the Hubble Space Telescope (HST) collected Jupiter images from 236 to 925 nm in 14
filters. The Near-Infrared Imager (NIRI) at Gemini North imaged Jovian thermal emission using a lucky-imaging
approach (co-adding the sharpest frames taken from a sequence of short exposures), using the M′ filter at 4.7 μm.
We discuss the data acquisition and processing and an archive collection that contains the processed WFC3 and
NIRI data (doi:10.17909/T94T1H). Zonal winds remain steady over time at most latitudes, but significant
evolution of the wind profile near 24°N in 2016 and near 15°S in 2017 was linked with convective superstorm
eruptions. Persistent mesoscale waves were seen throughout the 2016–2019 period. We link groups of lightning
flashes observed by the Juno team with water clouds in a large convective plume near 15°S and in cyclones near
35°N–55°N. Thermal infrared maps at the 10.8 micron wavelength obtained at the Very Large Telescope show
consistent high brightness temperature anomalies, despite a diversity of aerosol properties seen in the HST data.
Both WFC3 and NIRI imaging reveal depleted aerosols consistent with downwelling around the periphery of the
15°S storm, which was also observed by the Atacama Large Millimeter/submillimeter Array. NIRI imaging of
the Great Red Spot shows that locally reduced cloud opacity is responsible for dark features within the vortex. The
HST data maps multiple concentric polar hoods of high-latitude hazes.
Satellite applications can be categorized into four main types: communication satellites, navigation satellites, observation satellites, and weather satellites. Communication satellites allow for radio, television, and telephone transmissions globally. Navigation satellites like GPS use timing signals from satellites to precisely determine location. Observation satellites are used for non-military purposes like environmental monitoring and map making. Weather satellites scan Earth with instruments to form images of cloud cover, temperatures, and weather systems.
The document discusses the history and development of GPS (Global Positioning System). It describes how:
1) The US Department of Defense developed GPS, originally called NAVSTAR, launching the first experimental satellite in 1978.
2) GPS uses a constellation of 24 satellites that orbit 12,000 miles above Earth, transmitting signals used to calculate positions on Earth.
3) GPS determines location using triangulation based on the time difference between when a signal was transmitted by a satellite and received. This allows calculation of distance and therefore position.
This document summarizes an 8-year survey using the HARPS spectrograph to detect super-Earth and Neptune-mass planets around solar-type stars. Over 50% of solar-type stars were found to harbor at least one planet within 100 days. The mass distribution of super-Earths and Neptune-mass planets increases sharply from 30-15 Earth masses. Most of these planets belong to multi-planetary systems and have orbital eccentricities under 0.45. In contrast, giant planets are more common around metal-rich stars and can have eccentricities over 0.9. The precision of HARPS enables detection of planets in the habitable zones of solar-type stars.
PPT Obstructs: Outline about Meteorological satellites and their types. principle of Satellite remote sensing - Electro Magnetic Spectrum, Data from weather satellites.
The document provides an overview of GPS (Global Positioning System) including:
- GPS uses 24 satellites and their ground stations as reference points to calculate positions accurate to within meters.
- It works globally in all weather and allows users to determine their location, velocity, and time.
- GPS was originally developed by the US Department of Defense but is now widely used by civilians as well as the military.
The document provides an overview of the Global Positioning System (GPS). It describes how GPS works using a constellation of 24 satellites that orbit the Earth and transmit radio signals. GPS receivers triangulate their position by timing the signals from at least 3 satellites. The system has space, control, and user segments. It is maintained by the US Air Force and provides location services to users worldwide for applications like navigation, mapping, and tracking. Key sources of error include clock errors and atmospheric effects.
The harps n-rocky_planet_search_hd219134b_transiting_rocky_planetSérgio Sacani
Usando o espectrógrafo HARPS-N acoplado ao Telescopio Nazionale Galileo no Observatório de Roque de Los Muchachos, nas Ilhas Canárias, os astrônomos descobriram três exoplanetas, classificados como Super-Terras e um gigante gasoso orbitando uma estrela próxima, chamada de HD 219134.
A HD 219134, também conhecida como HR 8832 é uma estrela do tipo anã-K de quinta magnitude, localizada a aproximadamente 21 anos-luz de distância da Terra, na constelação de Cassiopeia.
A estrela é levemente mais fria e menos massiva que o nosso sol. Ela é tão brilhante que pode ser observada a olho nu.
O sistema planetário HD 219134, abriga um planeta gigante gasoso externo e três planetas internos classificados como super-Terras, um dos quais transita em frente à estrela.
Two temperate Earth-mass planets orbiting the nearby star GJ 1002Sérgio Sacani
We report the discovery and characterisation of two Earth-mass planets orbiting in the habitable zone of the nearby M-dwarf GJ 1002 based on
the analysis of the radial-velocity (RV) time series from the ESPRESSO and CARMENES spectrographs. The host star is the quiet M5.5 V star
GJ 1002 (relatively faint in the optical, V ∼ 13.8 mag, but brighter in the infrared, J ∼ 8.3 mag), located at 4.84 pc from the Sun.
We analyse 139 spectroscopic observations taken between 2017 and 2021. We performed a joint analysis of the time series of the RV and full-width
half maximum (FWHM) of the cross-correlation function (CCF) to model the planetary and stellar signals present in the data, applying Gaussian
process regression to deal with the stellar activity.
We detect the signal of two planets orbiting GJ 1002. GJ 1002 b is a planet with a minimum mass mp sin i of 1.08 ± 0.13 M⊕ with an orbital period
of 10.3465 ± 0.0027 days at a distance of 0.0457 ± 0.0013 au from its parent star, receiving an estimated stellar flux of 0.67 F⊕. GJ 1002 c is a
planet with a minimum mass mp sin i of 1.36 ± 0.17 M⊕ with an orbital period of 20.202 ± 0.013 days at a distance of 0.0738 ± 0.0021 au from
its parent star, receiving an estimated stellar flux of 0.257 F⊕. We also detect the rotation signature of the star, with a period of 126 ± 15 days. We
find that there is a correlation between the temperature of certain optical elements in the spectrographs and changes in the instrumental profile that
can affect the scientific data, showing a seasonal behaviour that creates spurious signals at periods longer than ∼ 200 days.
GJ 1002 is one of the few known nearby systems with planets that could potentially host habitable environments. The closeness of the host star
to the Sun makes the angular sizes of the orbits of both planets (∼ 9.7 mas and ∼ 15.7 mas, respectively) large enough for their atmosphere to be
studied via high-contrast high-resolution spectroscopy with instruments such as the future spectrograph ANDES for the ELT or the LIFE mission.
Scanners, image resolution, orbit in remote sensing, pk maniP.K. Mani
This document provides information about different types of satellite orbits and sensors. It discusses polar orbits, geostationary orbits, and examples of weather satellites like METEOSAT, NOAA, and GOES that use these orbit types. It also describes imaging sensors on these satellites and their specifications. Sensors on other platforms like Landsat, SPOT, ERS, and Radarsat are outlined along with their characteristics and applications. Scanning techniques for collecting multispectral data like across-track and along-track scanning are defined.
This document presents an analysis of transit spectroscopy observations of three exoplanets - WASP-12 b, WASP-17 b, and WASP-19 b - using the Wide Field Camera 3 instrument on the Hubble Space Telescope. The observations achieved almost photon-limited precision but uncertainties in the transit depths were increased by the uneven sampling of the light curves. The final transit spectra for all three planets are consistent with the presence of a water absorption feature at 1.4 microns, though the amplitude is smaller than expected from previous Spitzer observations possibly due to hazes. Due to degeneracies between models, the data cannot unambiguously constrain the atmospheric compositions without additional observations.
This document provides an overview of geodetic methods, including both traditional and modern space-based techniques. It discusses the history of geodesy and how the field has split into physical and positional geodesy. Modern methods like GPS, VLBI, and satellite laser ranging now allow simultaneous determination of positions and the gravity field by using orbiting satellites. The document reviews various space-based techniques and how they have revolutionized geodetic accuracy by removing limitations of line-of-sight measurements.
GPS relies on principles of special and general relativity to account for relativistic effects that would otherwise cause errors. The Sagnac effect, which results from light traveling in opposite directions around a rotating object, must be considered and can cause time differences of hundreds of nanoseconds depending on satellite and receiver positions. An experiment in 1984 precisely measured the Sagnac effect using GPS satellites and atomic clocks at three locations, finding results that matched relativity predictions to within 5 nanoseconds.
GPS uses trilateration to determine a receiver's location based on distance measurements to multiple satellites. The receiver uses signal transit times to calculate distances to at least four satellites. Each distance defines a sphere around the satellite, and the intersection of these spheres pinpoints the receiver's location. GPS consists of three segments - space, control, and user. The space segment consists of 32+ satellites. The control segment monitors and controls the satellites. Users can access GPS for civilian and military navigation, tracking, and timing applications.
The document discusses the Global Positioning System (GPS). It provides an overview of GPS including that it is a satellite-based navigation system consisting of 24 satellites maintained by the US Department of Defense. GPS is used to determine location, time, and speed. The document describes the key components and principles of how GPS works including its space, control, and user segments. It involves calculating distance via signal travel time from 4 or more satellites to determine a position.
GPS uses a constellation of 24 satellites orbiting Earth to enable GPS receivers to determine their precise location. The system works by using triangulation based on distance measurements from at least three satellites. The GPS segments include the space segment (satellites), control segment (ground stations that monitor satellites), and user segment (GPS receivers). GPS has both military and civilian applications including navigation, mapping, vehicle tracking, and monitoring fishing fleets.
This document discusses how satellite observations over the past 50 years have revolutionized the field of earth sciences. It describes how early satellite missions taught scientists not only about the earth but how to improve satellite technology. Precise measurements from satellites have enabled major advances in understanding plate tectonics, topography, seismology and more. The ubiquity of GPS has provided vital data on phenomena like sea level change, earthquakes and volcanoes. Open data policies have maximized the benefits of earth observations.
Transit photometry has been the most successful exoplanet discovery method to date. It works by detecting the dimming of a star's light as a planet passes in front of it. From the transit light curve, properties of the planet like its radius and orbital parameters can be derived. However, transits have a low probability of being aligned with our line of sight. False positives from eclipsing binaries can also mimic transits, so follow-up observations are needed to confirm planetary discoveries. Past and current transit surveys have found over a hundred planets, and future surveys aim to detect smaller planets orbiting brighter stars.
Now-a-days the field of Remote Sensing and GIS has become exciting and glamorous with rapidly expanding opportunities. Many organizations spend large amounts of money on these fields. Here the question arises why these fields are so important in recent years. Two main reasons are there behind this. 1) Now-a-days scientists, researchers, students, and even common people are showing great interest for better understanding of our environment. By environment we mean the geographic space of their study area and the events that take place there. In other words, we have come to realize that geographic space along with the data describing it, is part of our everyday world; almost every decision we take is influenced or dictated by some fact of geography. 2) Advancement in sophisticated space technology (which can provide large volume of spatial data), along with declining costs of computer hardware and software (which can handle these data) has made Remote Sensing and G.I.S. affordable to not only complex environmental / spatial situation but also affordable to an increasingly wider audience.
The Global Positioning System (GPS) is a satellite-based navigation system that provides location and time information to GPS receivers anywhere on Earth. It was developed by the United States Department of Defense in the 1970s to overcome limitations of previous navigation systems. GPS uses a constellation of satellites that continuously transmit precise timing signals, allowing GPS receivers to determine their location by calculating the time difference of signals from multiple satellites. The system consists of three segments - space, control, and user - with the space segment comprising the satellites, the control segment managing the satellites, and the user segment being anyone using a GPS receiver.
High-resolution UV/Optical/IR Imaging of Jupiter in 2016–2019Sérgio Sacani
Imaging observations of Jupiter with high spatial resolution were acquired beginning in 2016, with a cadence of 53
days to coincide with atmospheric observations of the Juno spacecraft during each perijove pass. The Wide Field
Camera 3 (WFC3) aboard the Hubble Space Telescope (HST) collected Jupiter images from 236 to 925 nm in 14
filters. The Near-Infrared Imager (NIRI) at Gemini North imaged Jovian thermal emission using a lucky-imaging
approach (co-adding the sharpest frames taken from a sequence of short exposures), using the M′ filter at 4.7 μm.
We discuss the data acquisition and processing and an archive collection that contains the processed WFC3 and
NIRI data (doi:10.17909/T94T1H). Zonal winds remain steady over time at most latitudes, but significant
evolution of the wind profile near 24°N in 2016 and near 15°S in 2017 was linked with convective superstorm
eruptions. Persistent mesoscale waves were seen throughout the 2016–2019 period. We link groups of lightning
flashes observed by the Juno team with water clouds in a large convective plume near 15°S and in cyclones near
35°N–55°N. Thermal infrared maps at the 10.8 micron wavelength obtained at the Very Large Telescope show
consistent high brightness temperature anomalies, despite a diversity of aerosol properties seen in the HST data.
Both WFC3 and NIRI imaging reveal depleted aerosols consistent with downwelling around the periphery of the
15°S storm, which was also observed by the Atacama Large Millimeter/submillimeter Array. NIRI imaging of
the Great Red Spot shows that locally reduced cloud opacity is responsible for dark features within the vortex. The
HST data maps multiple concentric polar hoods of high-latitude hazes.
Satellite applications can be categorized into four main types: communication satellites, navigation satellites, observation satellites, and weather satellites. Communication satellites allow for radio, television, and telephone transmissions globally. Navigation satellites like GPS use timing signals from satellites to precisely determine location. Observation satellites are used for non-military purposes like environmental monitoring and map making. Weather satellites scan Earth with instruments to form images of cloud cover, temperatures, and weather systems.
The document discusses the history and development of GPS (Global Positioning System). It describes how:
1) The US Department of Defense developed GPS, originally called NAVSTAR, launching the first experimental satellite in 1978.
2) GPS uses a constellation of 24 satellites that orbit 12,000 miles above Earth, transmitting signals used to calculate positions on Earth.
3) GPS determines location using triangulation based on the time difference between when a signal was transmitted by a satellite and received. This allows calculation of distance and therefore position.
This document summarizes an 8-year survey using the HARPS spectrograph to detect super-Earth and Neptune-mass planets around solar-type stars. Over 50% of solar-type stars were found to harbor at least one planet within 100 days. The mass distribution of super-Earths and Neptune-mass planets increases sharply from 30-15 Earth masses. Most of these planets belong to multi-planetary systems and have orbital eccentricities under 0.45. In contrast, giant planets are more common around metal-rich stars and can have eccentricities over 0.9. The precision of HARPS enables detection of planets in the habitable zones of solar-type stars.
PPT Obstructs: Outline about Meteorological satellites and their types. principle of Satellite remote sensing - Electro Magnetic Spectrum, Data from weather satellites.
The document provides an overview of GPS (Global Positioning System) including:
- GPS uses 24 satellites and their ground stations as reference points to calculate positions accurate to within meters.
- It works globally in all weather and allows users to determine their location, velocity, and time.
- GPS was originally developed by the US Department of Defense but is now widely used by civilians as well as the military.
The document provides an overview of the Global Positioning System (GPS). It describes how GPS works using a constellation of 24 satellites that orbit the Earth and transmit radio signals. GPS receivers triangulate their position by timing the signals from at least 3 satellites. The system has space, control, and user segments. It is maintained by the US Air Force and provides location services to users worldwide for applications like navigation, mapping, and tracking. Key sources of error include clock errors and atmospheric effects.
The harps n-rocky_planet_search_hd219134b_transiting_rocky_planetSérgio Sacani
Usando o espectrógrafo HARPS-N acoplado ao Telescopio Nazionale Galileo no Observatório de Roque de Los Muchachos, nas Ilhas Canárias, os astrônomos descobriram três exoplanetas, classificados como Super-Terras e um gigante gasoso orbitando uma estrela próxima, chamada de HD 219134.
A HD 219134, também conhecida como HR 8832 é uma estrela do tipo anã-K de quinta magnitude, localizada a aproximadamente 21 anos-luz de distância da Terra, na constelação de Cassiopeia.
A estrela é levemente mais fria e menos massiva que o nosso sol. Ela é tão brilhante que pode ser observada a olho nu.
O sistema planetário HD 219134, abriga um planeta gigante gasoso externo e três planetas internos classificados como super-Terras, um dos quais transita em frente à estrela.
Two temperate Earth-mass planets orbiting the nearby star GJ 1002Sérgio Sacani
We report the discovery and characterisation of two Earth-mass planets orbiting in the habitable zone of the nearby M-dwarf GJ 1002 based on
the analysis of the radial-velocity (RV) time series from the ESPRESSO and CARMENES spectrographs. The host star is the quiet M5.5 V star
GJ 1002 (relatively faint in the optical, V ∼ 13.8 mag, but brighter in the infrared, J ∼ 8.3 mag), located at 4.84 pc from the Sun.
We analyse 139 spectroscopic observations taken between 2017 and 2021. We performed a joint analysis of the time series of the RV and full-width
half maximum (FWHM) of the cross-correlation function (CCF) to model the planetary and stellar signals present in the data, applying Gaussian
process regression to deal with the stellar activity.
We detect the signal of two planets orbiting GJ 1002. GJ 1002 b is a planet with a minimum mass mp sin i of 1.08 ± 0.13 M⊕ with an orbital period
of 10.3465 ± 0.0027 days at a distance of 0.0457 ± 0.0013 au from its parent star, receiving an estimated stellar flux of 0.67 F⊕. GJ 1002 c is a
planet with a minimum mass mp sin i of 1.36 ± 0.17 M⊕ with an orbital period of 20.202 ± 0.013 days at a distance of 0.0738 ± 0.0021 au from
its parent star, receiving an estimated stellar flux of 0.257 F⊕. We also detect the rotation signature of the star, with a period of 126 ± 15 days. We
find that there is a correlation between the temperature of certain optical elements in the spectrographs and changes in the instrumental profile that
can affect the scientific data, showing a seasonal behaviour that creates spurious signals at periods longer than ∼ 200 days.
GJ 1002 is one of the few known nearby systems with planets that could potentially host habitable environments. The closeness of the host star
to the Sun makes the angular sizes of the orbits of both planets (∼ 9.7 mas and ∼ 15.7 mas, respectively) large enough for their atmosphere to be
studied via high-contrast high-resolution spectroscopy with instruments such as the future spectrograph ANDES for the ELT or the LIFE mission.
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CHINA’S GEO-ECONOMIC OUTREACH IN CENTRAL ASIAN COUNTRIES AND FUTURE PROSPECTjpsjournal1
The rivalry between prominent international actors for dominance over Central Asia's hydrocarbon
reserves and the ancient silk trade route, along with China's diplomatic endeavours in the area, has been
referred to as the "New Great Game." This research centres on the power struggle, considering
geopolitical, geostrategic, and geoeconomic variables. Topics including trade, political hegemony, oil
politics, and conventional and nontraditional security are all explored and explained by the researcher.
Using Mackinder's Heartland, Spykman Rimland, and Hegemonic Stability theories, examines China's role
in Central Asia. This study adheres to the empirical epistemological method and has taken care of
objectivity. This study analyze primary and secondary research documents critically to elaborate role of
china’s geo economic outreach in central Asian countries and its future prospect. China is thriving in trade,
pipeline politics, and winning states, according to this study, thanks to important instruments like the
Shanghai Cooperation Organisation and the Belt and Road Economic Initiative. According to this study,
China is seeing significant success in commerce, pipeline politics, and gaining influence on other
governments. This success may be attributed to the effective utilisation of key tools such as the Shanghai
Cooperation Organisation and the Belt and Road Economic Initiative.
A SYSTEMATIC RISK ASSESSMENT APPROACH FOR SECURING THE SMART IRRIGATION SYSTEMSIJNSA Journal
The smart irrigation system represents an innovative approach to optimize water usage in agricultural and landscaping practices. The integration of cutting-edge technologies, including sensors, actuators, and data analysis, empowers this system to provide accurate monitoring and control of irrigation processes by leveraging real-time environmental conditions. The main objective of a smart irrigation system is to optimize water efficiency, minimize expenses, and foster the adoption of sustainable water management methods. This paper conducts a systematic risk assessment by exploring the key components/assets and their functionalities in the smart irrigation system. The crucial role of sensors in gathering data on soil moisture, weather patterns, and plant well-being is emphasized in this system. These sensors enable intelligent decision-making in irrigation scheduling and water distribution, leading to enhanced water efficiency and sustainable water management practices. Actuators enable automated control of irrigation devices, ensuring precise and targeted water delivery to plants. Additionally, the paper addresses the potential threat and vulnerabilities associated with smart irrigation systems. It discusses limitations of the system, such as power constraints and computational capabilities, and calculates the potential security risks. The paper suggests possible risk treatment methods for effective secure system operation. In conclusion, the paper emphasizes the significant benefits of implementing smart irrigation systems, including improved water conservation, increased crop yield, and reduced environmental impact. Additionally, based on the security analysis conducted, the paper recommends the implementation of countermeasures and security approaches to address vulnerabilities and ensure the integrity and reliability of the system. By incorporating these measures, smart irrigation technology can revolutionize water management practices in agriculture, promoting sustainability, resource efficiency, and safeguarding against potential security threats.
2. UNIT I FUNDAMENTALS OF TOTAL STATION AND GPS 9+6
Methods of Measuring Distance, Basic Principles of Total Station,
Historical Development, Classifications, applications and comparison
with conventional surveying. Global Navigation System, Regional
Navigation System and SBAS - Basic concepts of GNSS, GLONASS,
IRNSS - Historical perspective and development - applications - Geoid
and Ellipsoid- satellite orbital motion - Keplerian motion – Kepler’s
Law - Perturbing forces - Geodetic satellite - Doppler effect- Different
Coordinate and Time System.
3. Satellite Geodesy comprises the observational and computational
techniques which allow the solution of geodetic problems by the use of
precise measurements to, from, or between artificial, mostly near-Earth,
satellites.
Further to Helmert’s definition, which is basically still valid, the objectives
of satellite geodesy are today mainly considered in a functional way. They
also include, because of the increasing observational accuracy, time-
dependent variations.
The basic problems are
1. determination of precise global, regional and local three-dimensional
positions (e.g. the establishment of geodetic control)
2. determination of Earth’s gravity field and linear functions of this field
(e.g. a precise geoid)
3. measurement and modeling of geodynamical phenomena (e.g. polar
motion, Earth rotation, crustal deformation).
4. Basic Concepts of Satellite Geodesy
The importance of artificial satellites in
geodesy becomes evident from the following
basic considerations.
(1) Satellites can be used as high orbiting
targets, which are visible over large
distances. Following the classical concepts of
Earth-bound trigonometric networks, the
satellites may be regarded as “fixed” control
points within large-scale or global three-
dimensional networks. If the satellites are
observed simultaneously from different
ground stations, it is of no importance that
the orbits of artificial satellites are governed
by gravitational forces. Only the property
that they are targets at high altitudes is used.
This purely geometric consideration leads to
the geometrical method of satellite geodesy
5. (2) Satellites can be considered to be a probe or
a sensor in the gravity field of Earth. Of
particular interest is the relation between the
features of the terrestrial gravity field and the
resulting deviations of the true satellite orbit
from an undisturbed Keplerian motion. The
essential value of the satellite is that it is a
moving body within Earth’s gravity field. This
view leads to the dynamical method of satellite
geodesy.
In dynamical satellite geodesy orbital arcs of
different lengths are considered. The orbits are
described in suitable geocentric reference
frames. The satellite can thus be considered to
be the “bearer of its own coordinates”. The
geocentric coordinates of the observing ground
stations can be derived from the known satellite
orbits. This so-called orbital method of
coordinate determination
6. Classification of the observation techniques refers to the relation between
the observation platform and the target platform.
(1) Earth to Space methods
− directions from camera observations,
− satellite laser ranging (SLR),
− Doppler positioning (TRANSIT, DORIS),
− geodetic use of the Global Positioning System (GPS, GLONASS, GNSS).
(2) Space to Earth methods
− radar altimetry,
− spaceborne laser,
− satellite gradiometry.
(3) Space to Space methods
− satellite-to-satellite tracking (SST).
7. Historical Development of Satellite Geodesy
The proper development of satellite geodesy started with the launch of the first
artificial satellite, SPUTNIK-1, on October 4, 1957. In 1802, Laplace used lunar nodal
motion to determine the flattening of Earth to be f = 1/303. Other solutions came, for
example, from Hansen (1864) with f = 1/296, Helmert (1884) with f = 1/297.8, and Hill
(1884) with f = 1/297.2.
The geometrical approach in satellite geodesy also has some forerunners in the
lunar methods. The Moon is regarded as a geometric target, where the geocentric
coordinates are known from orbital theory. The directions between the observer and the
Moon are determined from relative measurements of nearby stars, or from occultation
of stars by the Moon. Geocentric coordinates are thereby received. Within the
framework of the International Geophysical Year 1957/58 a first outcome from a global
program was obtained with the Dual Rate Moon Camera, developed by Markovitz
(1954). The methods of this so-called Cosmic Geodesy were treated comprehensively in
1960 by Berroth, Hofmann. They also form a considerable part of the classical book of
Mueller (1964) “Introduction to Satellite Geodesy”.
One of the first outstanding results was the determination of Earth’s flattening as
f = 1/298.3 from observations of EXPLORER-1 and SPUTNIK-2 by O’Keefe (1958) , King-
Hele, Merson (1958).
8. Historical Development of Satellite Geodesy
The significantevents during the years following 1957 are
1957 Launch of SPUTNIK-1,
1958 Earth’s Flattening from Satellite Data (f = 1/298.3),
1958 Launch of EXPLORER-1,
1959 Third Zonal Harmonic (Pear Shape of Earth),
1959 Theory of the Motion of Artificial Satellites (Brouwer),
1960 Launch of TRANSIT-1B,
1960 Launch of ECHO-1,
1960 Theory of Satellite Orbits (Kaula),
1962 Launch of ANNA-1B,
1962 Geodetic Connection between France and Algeria (IGN).
1964 Basic geodetic problems had been successfully tackled, namely the
− determination of a precise numerical value of Earth’s flattening
− determination of the general shape of the global geoid
− determination of connections between the most important geodetic datums (to ±50m).
9. Historical Development of Satellite Geodesy
1958 to around 1970. Determination of the leading harmonic coefficients of the
geopotential, and the publication of the first Earth models, for instance the
Standard Earth models of the Smithsonian Astrophysical Observatory (SAO SE I
to SAO SE III), and the Goddard Earth Models (GEM) of the NASA Goddard Space
Flight Center. The only purely geometrical and worldwide satellite network was
established by observations with BC4 cameras of the satellite PAGEOS.
1970 to around 1980. Phase of the scientific projects. The TRANSIT system was
used for geodetic Doppler positioning. Refined global geoid and coordinate
determinations were carried out, and led to improved Earth models (e.g. GEM
10, GRIM). Doppler surveying was used worldwide for the installation and
maintenance of geodetic control networks (e.g. EDOC, DÖDOC, ADOS).
1980 to around 1990. Satellite methods were increasingly used by the surveying
community, replacing conventional methods. This process started with the first
results obtained with the NAVSTAR Global Positioning System (GPS) and resulted
in completely new perspectives in surveying and mapping. The second aspect
concerned the increased observation accuracy. One outcome was the nearly
complete replacement of the classical astrometric techniques for monitoring
polar motion and Earth rotation by satellite methods. Projects for the
measurement of crustal deformation gave remarkable results worldwide
10. Historical Development of Satellite Geodesy
1990 to around 2000. The International Earth Rotation Service IERS, initiated in
1987 and exclusively based on space techniques, provides highly accurate Earth
orientation parameters with high temporal resolution, maintains and constantly
refines two basic reference frames. These are the International Celestial
Reference Frame ICRF, based on interferometric radio observations, and the
International Terrestrial Reference Frame ITRF, based on different space
techniques. The International GPS Service IGS, started in 1994 and evolved to be
the main source for precise GPS orbits as well as for coordinates and
observations from a global set of more than 300 permanently observing
reference stations. At the national level permanent services for GPS reference
data have been established and are still growing, e.g. CORS in the USA, CACS in
Canada and SAPOS in Germany
11. Historical Development of Satellite Geodesy
2000 onwards. After more than 40 years of satellite geodesy the development of
geodetic space techniques is continuing. We have significant improvements in
accuracy as well as in temporal and spatial resolution. New fields of application
evolve in science and practice. For the first decade of the new millennium
development will focus on several aspects:
− launch of dedicated gravity field probes like CHAMP, GRACE, and GOCE for the
determination of a high resolution terrestrial gravity field,
− establishment of a next generation Global Navigation Satellite System GNSS
with GPS Block IIR and Block IIF satellites, Block III and new components like the
GLONASS, European Galileo, Chinese COMPASS
− refinement in Earth observation, e.g. with high resolution radar sensors like
interferometric SAR on various platforms,
− further establishment of permanent arrays for disaster prevention and
environmental monitoring,
− unification of different geodetic space techniques in mobile integrated
geodetic geodynamic monitoring systems.
12. Applications of Satellite Geodesy
Global Geodesy
− general shape of Earth’s figure and gravity field,
− dimensions of a mean Earth ellipsoid,
− establishment of a global terrestrial reference frame,
− detailed geoid as a reference surface on land and at sea,
− connection between different existing geodetic datums,
− connection of national datums with a global geodetic datum.
Geodetic Control
− establishment of geodetic control for national networks,
− installation of three-dimensional homogeneous networks,
− analysis and improvement of existing terrestrial networks,
− establishment of geodetic connections between islands or with the mainland,
− densification of existing networks up to short interstation distances.
Geodynamics
− control points for crustal motion,
− permanent arrays for 3D-control in active areas,
− polar motion, Earth rotation,
− solid Earth tides.
13. Applications of Satellite Geodesy
Applied and Plane Geodesy
− detailed plane surveying (land register, urban and rural surveying, geographic
information systems (GIS), town planning, boundary demarcation etc.),
− installation of special networks and control for engineering tasks,
− terrestrial control points in photogrammetry and remote sensing,
− position and orientation of airborne sensors like photogrammetric cameras,
− control and position information at different accuracy levels in forestry,
agriculture, archaeology, expedition cartography etc.
Navigation and Marine Geodesy
− precise navigation of land, sea, and air-vehicles,
− precise positioning for marine mapping, exploration, hydrography, oceanography,
marine geology, and geophysics,
− connection and control of tide gauges (unification of height systems).
Related Fields
− position and velocity determination for geophysical observations (gravimetric,
magnetic, seismic surveys), also at sea and in the air,
− determination of ice motion in glaciology, Antarctic research, oceanography, −
determination of satellite orbits,
− tomography of the atmosphere (ionosphere, troposphere).
14.
15.
16.
17.
18.
19. Satellite Navigation
A satellite navigation is a system that uses satellites to provide
autonomous geo-spatial positioning. It allows small electronic receivers to
determine their location (longitude, latitude, and altitude/elevation) to high
precision (within a few centimeters to metres) using time signals transmitted
along a line of sight by microwave from satellites.
The system can be used for providing position, navigation or for tracking
the position of something fitted with a receiver (satellite tracking). The signals
also allow the electronic receiver to calculate the current local time to high
precision, which allows time synchronization. These uses are collectively known
as Positioning, Navigation and Timing (PNT).
20.
21. Satellite Navigation
Positioning, the ability to accurately and precisely determine one's location
and orientation two-dimensionally (or three-dimensionally when required)
referenced to a standard geodetic system (such as World Geodetic System
1984, or WGS84);
Navigation, the ability to determine current and desired position (relative or
absolute) and apply corrections to course, orientation, and speed to attain a
desired position anywhere around the world, from sub-surface to surface and
from surface to space; and
Timing, the ability to acquire and maintain accurate and precise time from a
standard (Coordinated Universal Time, or UTC), anywhere in the world and
within user-defined timeliness parameters. Timing also includes time transfer.
36. The basic principle of operation on which GNSS
systems is based is often referred to as resection
(also called triangulation), and it involves estimating
the distances from at least three satellites orbiting
the Earth along different and sufficiently separated
trajectories to determine the position of an object in
2-D along with the uncertainty in measurement. If
four or more satellites are in view, the receiver can
determine three-dimensional (3D) position (latitude,
longitude, and altitude) of the user. GPS is one-way
ranging or pseudo ranging.
51. Satellite Orbital Motion
Precise time-dependent satellite positions in a suitable reference frame
are required for nearly all tasks in satellite geodesy. The computation and
prediction of precise satellite orbits, together with appropriate observations and
adjustment techniques is, essential for the determination of
− geocentric coordinates of observation stations,
− field parameters for the description of the terrestrial gravity field as well as for
the determination of a precise and high resolution geoid
− trajectories of land, sea, air, and space-vehicles in real-time navigation
− Earth’s orientation parameters in space
52.
53.
54.
55.
56.
57.
58.
59.
60.
61. Equation of Motion
Newton introduced his three laws of motion:
1. Every body continues in its state of rest or of uniform motion in a straight line
unless it is compelled to change that state by an external impressed force.
2. The rate of change of momentum of the body is proportional to the force
impressed and is in the same direction in which the force acts.
3. To every action there is an equal and opposite reaction.
The second law expressed in mathematical form is K = mϔ
where K is the vector sum of all forces acting on the mass m and ϔ is the vectorial
acceleration of the mass, measured in an inertial reference frame.
62. Every particle of matter in the Universe attracts every other particle of
matter with a force directly proportional to the product of their masses
and inversely proportional to the square of the distance between them
Keplerian orbital parameters
63. Perturbed Satellite Motion
The motion of a satellite with negligible mass under the central
gravitative force of a single point mass M. This Keplerian motion
was described by the basic equation:
64.
65. Orbit Determination
The basic task in orbit determination is to derive elements for the description of
orbits from observations or from a priori known information. The fundamental
equations and procedures for the solution of this problem were developed.
In classical celestial mechanics, the task of orbit determination, divided into
− initial orbit determination without over-determination,
− orbit improvement using all available observations.
With the initial orbit determination a preliminary orbit is usually derived from three
sets of directional observations at different epochs, neglecting all perturbations. On
the other hand, analytical considerations are required to study the time dependent
behavior of orbits, and to select appropriate orbital characteristics. When satellite
observations are analyzed, or when predicted orbits are used, it is often necessary
to represent short orbital arcs with suitable smoothing algorithms. A new tool for
precise orbit determination (POD) stems from the fact that satellite trajectories can
now be determined directly with onboard packages like GPS, PRARE or DORIS.
66. Satellites Used in Geodesy
Examples of satellites which were exclusively, or primarily, launched for geodetic
and/or geodynamic purposes are:
PAGEOS (PAssive GEOdetic Satellite) USA 1966,
STARLETTE, STELLA France 1975, 1993,
GEOS-1 to 3 (GEOdetic Satellite 1 to 3) USA 1965, 1968, 1975,
LAGEOS-1, 2(LAser GEOdynamic Satellite) USA 1976, 1992,
AJISAI (EGS, Experimental Geodetic Satellite) Japan 1986,
GFZ-1 (GeoForschungs Zentrum) Germany 1986,
CHAMP (CHAllenging Mini Satellite Payload) Germany 2000
This group of dedicated satellites includes some which were used during the first
years of the satellite era for the establishment of geodetic datum connections
(e.g. SECOR, ANNA-1B (1962))
67. A frequently used distinction for the purposes of subdivision is passive and
active satellites.
Passive Satellites Active Satellites
ECHO-1, ETALON-1 ANNA-1B, ERS-2
ECHO-2, ETALON-2 GEOS-3, TOPEX/POSEIDON
PAGEOS, GFZ-1 SEASAT-1, GFO (Geosat Follow On)
STARLETTE NNSS satellites, CHAMP
STELLA NAVSTAR satellites, JASON
LAGEOS-1 GLONASS satellites, ENVISAT
LAGEOS-2 GEOSAT, GRACE, Galileo satellites,
EGS (AJISAI) ERS-1, COMPASS (Beidou)
IRNSS, QZSS
68. Another possible subdivision is into:
− Geodetic Satellites are mainly high targets like LAGEOS, STARLETTE, STELLA,
ETALON, ASIJAI, and GFZ which carry laser retro-reflectors. They are massive
spheres designed solely to reflect laser light back to the ranging system. The
orbits can be computed very accurately, because the non-gravitational forces
are minimized.
− Earth Sensing Satellites like ERS, GFO, TOPEX, JASON, ENVISAT carry
instruments designed to sense Earth, in particular to monitor environmental
changes. Many of these satellites carry altimeters. Most are equipped with an
orbit determination payload, e.g. PRARE, GPS, and/or DORIS. In addition most
satellites carry laser reflectors to facilitate precise orbit determination.
− Positioning Satellites are equipped with navigation payload. To this class
belong the former TRANSIT, GPS, GLONASS, GALILEO, COMPASS, IRNSS and
QZSS satellites. Some of the spacecraft carry laser reflectors (e.g. GPS-35, -36,
and all GLONASS satellites). The satellites are arranged in constellations to
provide global or regional coverage.
69. − Experimental Satellites support missions with experimental character. They
are used in the development of various other kinds of satellites, to test their
performance in real space operations. A large number of experimental satellites
have been launched for communication technology. Experimental satellites of
interest to geodesy are mostly irregularly shaped and fly in low orbits. Precise
orbit determination (POD) is supported by laser cube corner reflectors and/or a
navigation payload like GPS. Examples include TiPs (Tether Physics and
Survivability), and Gravity Probe B.
70.
71.
72.
73.
74. The frequency shift caused by the Doppler effect can be described as a function
of time and yields a characteristic curve. The Doppler curve of an artificial
satellite lies in between curves (2) and (3), depending on the satellite’s range and
altitude. If the observer were directly in the path of the satellite the Doppler shift
Δf would stay constant at all times, the only change being a sudden jump (curve
(4)) from f + Δf to f − Δf as the satellite passed the observer.
With increasing distance of the observer from
the orbit, the frequency change becomes
smoother and is described an S-shaped curve. In
case (1) the observer is so far away that no
significant change of range occurs; the curve
deforms into a straight line. The turning point of
the curvature corresponds to the time of closest
approach (TCA) of the satellite with respect to
the observer
75. The method of orbit determination based on Doppler
measurements from a known tracking station on the ground was
reversible, i.e. that unknown observer positions could be derived from the
measured Doppler shift when the satellite positions are known This idea
led to the development of a global satellite-based navigation system, the
Navy Navigation Satellite System (NNSS), also known as the NAVSAT or
TRANSIT system. Because of its continuously increasing accuracy, the
TRANSIT system became of interest for geodetic applications.
When the Doppler principle is to be used for the establishment of a
precise, global navigation system with real-time capability, the satellite
system must meet at least the following requirements:
− global distribution of satellite orbits,
− real-time transfer of information about satellite positions and time to
users.
76. Reference Coordinate Systems and Frames in Satellite Geodesy
In modern terminology it is distinguished between
− reference systems,
− reference frames, and
− conventional reference systems and frames.
A reference system is the complete conceptual definition of how a coordinate system is
formed. It defines the origin and the orientation of fundamental planes or axes of the system.
It also includes the underlying fundamental mathematical and physical models. A conventional
reference system is a reference system where all models, numerical constants and algorithms
are explicitly specified. A reference frame means the practical realization of a reference system
through observations. It consists of a set of identifiable fiducial points on the sky (e.g. stars,
quasars) or on Earth’s surface (e.g. fundamental stations). It is described by a catalogue of
precise positions and motions (if measurable) at a specific epoch. In satellite geodesy two
fundamental systems are required:
− a space-fixed, conventional inertial reference system (CIS) for the description of satellite
motion
− an Earth-fixed, conventional terrestrial reference system (CTS) for the positions of the
observation stations and for the description of results from satellite geodesy
77. Conventional Celestial Reference System (CRS) (also
named as Conventional Inertial System, CIS)
This is a quasi-inertial reference system. It has its origin
at the earth's centre of mass. X-axis points in the
direction of the mean equinox at J2000.0 epoch, Z-axis is
orthogonal to the plane defined by the mean equator at
J2000.0 epoch (fundamental plane) and Y-axis is
orthogonal to the former ones, so the system is directly
(right handed) oriented. The practical implementation is
called (conventional) Celestial Reference Frame (CRF)
and it is determined from a set of precise coordinates of
extragalactic radio sources (i.e., it is fixed with respect to
distant objects of the universe). The mean equator and
equinox J2000.0 were defined by International
Astronomical Union (IAU) agreements in 1976, with 1980
nutation series (Seildelmann, 1982 and Kaplan, 1981),
which are valid analytic expressions for long time
intervals (the former reference epoch was 1950.0).
78. Conventional Terrestrial Reference System (TRS) (also named
Coordinated Terrestrial System, CTS)
This is a reference system co-rotating with the earth in its diurnal rotation,
also called Earth-Centred, Earth-Fixed (ECEF). Its definition involves a
mathematical model for a physical earth in which point positions are
expressed and have small temporal variations due to geophysical effects
(plate motion, earth tides, etc.). The TRS has its origin in the earth's
centre of mass. Z-axis is identical to the direction of the earth's rotation
axis defined by the Conventional Terrestrial Pole (CTP), X-axis is defined
as the intersection of the orthogonal plane to Z-axis (fundamental plane)
and Greenwich mean meridian, and Y-axis is orthogonal to both of them,
making the system directly oriented. The realization of this system is
named (conventional) Terrestrial Reference Frame (TRF) and it is carried
out through the coordinates of a set of points on the earth serving as
reference points[. An example of TRF is the International Terrestrial
Reference Frame (ITRF) introduced by the International Earth Rotation
and Reference Systems Service (IERS), which is updated every year
(ITRF98, ITRF99, etc.). Other terrestrial reference frames are the World
Geodetic System 84 (WGS-84), which is applied for GPS, the Parametry
Zemli 1990 (Parameters of the Earth 1990) (PZ-90) for GLONASS, or the
Galileo Terrestrial Reference Frame (GTRF) for Galileo system.
79. International Terrestrial Reference System (ITRS)
The ITRS represents the most precise global terrestrial reference system which
is a source system for the realization of other world reference systems (e.g.
WGS84) and of continental or regional reference systems (e.g. ETRS89 etc.).
ITRS has its origin on the earth's centre of mass (including the Ocean and
atmosphere). Z axis pointing toward CTP known as IRP (IERS Reference Pole), X
axis on the Earth equator and IRM (IERS Reference Meridian passing
Greenwich) and Y-axis is orthogonal to X and Z axes.
80.
81. Time
Three basic groups of time scales are of importance in satellite geodesy:
(1) The time-dependent orientation of Earth with respect to the inertial space is
required in order to relate the Earth-based observations to a space-fixed
reference frame. The appropriate time scale is connected with the diurnal
rotation of Earth, and is called Sidereal Time and Universal Time.
(2) For the description of the satellite motion we need a strictly uniform time
measure which can be used as the independent variable in the equations of
motion. An appropriate time scale can be derived from the orbital motion of
celestial bodies around the Sun. It is called Ephemeris Time, Dynamical Time,
or Terrestrial Time.
(3) The precise measurement of signal travel times, e.g. in satellite laser ranging,
requires a uniform and easily accessible time scale with high resolution. The
appropriate measure is related to phenomena in nuclear physics and is called
Atomic Time
82. Effect of timing errors in satellite geodesy
1 cm motion of a point on the equator caused by
Earth’s rotation corresponds to about 2 × 10−5 s,
1 cm motion of a near-Earth satellite in the orbit
corresponds to about 1×10−6 s,
1 cm in the satellite range derived from signal
travel time (e.g. laser ranging) corresponds to
about 1 × 10−10 s.
The related requirements for the accuracy of
time determination dTi are as follows:
dT1[s] ≤ 2 × 10−5 for Earth rotation,
dT2[s] ≤ 1 × 10−6 for orbital motion,
dT3[s] ≤ 1 × 10−10 for signal travel time.
83.
84.
85.
86.
87.
88.
89.
90.
91.
92.
93.
94. GMAT - Greenwich Mean Apparent Time TAI - International Atomic Time
GMT - Greenwich Mean Time TT - Terrestrial Time
UT0, UT1, UT1R, UT2 - Universal Time UTC - Coordinated Universal Time
GAST - Greenwich Apparent Solar Time TDT - Terrestrial Dynamical Time
GMST - Greenwich Mean Solar Time TDB - Barycentric Dynamical Time
LAST - Local Apparent Solar Time TCB - Barycentric Coordinate Time
ET - Equation of Time TCG - Geocentric Coordinate Time
95.
96.
97.
98.
99.
100.
101. Local standard time is the date/time reported by your PC (as seen by your web browser). If your PC clock is accurate to a
second then the other time scales displayed above will also be accurate to within one second.
UTC, Coordinated Universal Time, popularly known as GMT (Greenwich Mean Time), or Zulu time. Local time differs from
UTC by the number of hours of your time zone.
GPS, Global Positioning System time, is the atomic time scale implemented by the atomic clocks in the GPS ground control
stations and the GPS satellites themselves. GPS time was zero at 0h 6-Jan-1980 and since it is not perturbed by leap seconds
GPS is now ahead of UTC by 18 seconds.
Loran-C, Long Range Navigation time, is an atomic time scale implemented by the atomic clocks in Loran-C chain
transmitter sites. Loran time was zero at 0h 1-Jan-1958 and sinc
e it is not perturbed by leap seconds it is now ahead of UTC by 27 seconds.
TAI, Temps Atomique International, is the international atomic time scale based on a continuous counting of the SI second.
TAI is currently ahead of UTC by 37 seconds. TAI is always ahead of GPS by 19 seconds.