Earth Sciences - Revision history

Claudia.Prajanu at 15:33, 7 September 2018

2018-09-07T15:33:13Z

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	\|YearOfPublication=2013		\|YearOfPublication=2013
	\|Logo=GMV		\|Logo=GMV
	~~\|Title={{PAGENAME}}~~
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	Earth Science covers sciences related to understanding the planet Earth, being the use of GNSS signals most relevant on the aspects of Earth physics (as opposed to chemistry or biology). The main fields of this science that are studied using GNSS as tools are:		Earth Science covers sciences related to understanding the planet Earth, being the use of GNSS signals most relevant on the aspects of Earth physics (as opposed to chemistry or biology). The main fields of this science that are studied using GNSS as tools are:
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	=Geodesy and Geodynamics=		=Geodesy and Geodynamics=
	The International Association of Geodesy (IAG) organized the Global Geodetic Observing System (GGOS) composed by several IAG technique-services that aims mainly the support of the Earth Science research. The service that provides the means to use GNSS data is the ~~[http://igscb.jpl.nasa.gov~~ International GNSS Service (IGS)] that nowadays has a fundamental contribution to the overall GNSS community since provides the highest quality data and products as the standard for Global Navigation Satellite Systems (GNSS). In addition there are also services combining the products of the technique specific services, such as the [http://www.iers.org International Earth Rotation and Reference Systems Service (IERS)]. The GGOS enables research in three fundamental areas of geodesy:		The International Association of Geodesy (IAG) organized the Global Geodetic Observing System (GGOS) composed by several IAG technique-services that aims mainly the support of the Earth Science research. The service that provides the means to use GNSS data is the International GNSS Service (IGS) that nowadays has a fundamental contribution to the overall GNSS community since provides the highest quality data and products as the standard for Global Navigation Satellite Systems (GNSS). In addition there are also services combining the products of the technique specific services, such as the [http://www.iers.org International Earth Rotation and Reference Systems Service (IERS)]. The GGOS enables research in three fundamental areas of geodesy:
	* The geometric shape of the Earth (land, ice and ocean surface) as well as its variation in time;		* The geometric shape of the Earth (land, ice and ocean surface) as well as its variation in time;
	* The orientation of the Earth in inertial space as a function of time;		* The orientation of the Earth in inertial space as a function of time;
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	GNSS have brought greater precision in position determination and above all enabled sustained monitoring at an acceptable cost and in a very efficient and timely way, which enables monitoring variations of geodetic station positioning induced by various geophysical processes. The global network of IGS stations can provide continuous information about motions of the continents or smaller tectonic plates. In addition at a local or regional scale, the ease with which a GNSS can be used and combined with positioning precision using [[Differential GNSS]] (DGNSS) techniques or [[Precise Point Positioning]] (PPP) technique means that the number of measurement points in areas of seismic or volcanic activity can be increased to monitor changes that might warn of coming disasters.		GNSS have brought greater precision in position determination and above all enabled sustained monitoring at an acceptable cost and in a very efficient and timely way, which enables monitoring variations of geodetic station positioning induced by various geophysical processes. The global network of IGS stations can provide continuous information about motions of the continents or smaller tectonic plates. In addition at a local or regional scale, the ease with which a GNSS can be used and combined with positioning precision using [[Differential GNSS]] (DGNSS) techniques or [[Precise Point Positioning]] (PPP) technique means that the number of measurement points in areas of seismic or volcanic activity can be increased to monitor changes that might warn of coming disasters.
	After an earthquake or volcanic eruption, the extent of deformation can be measured too. The [http://itrf.ensg.ign.fr/ International Terrestrial Reference Frame (ITRF)] networks (using GNSS data as well other geodetic data) also provides a means of aligning local deformation aiding the attempt to understand the forces behind it on a worldwide scale. In regions of significant seismic activity (e.g. California, Japan), local GNSS networks are used for permanent monitoring of the ground deformations that provides data used to develop or to validate models of crustal movements and earthquakes prediction. In the research of Tectonic Motions and Local Deformations the GNSS contribution is the most substantial and the most productive in combination with other space geodesy techniques<ref>Springer, T., Gendt, G., Dow J.M., (Editors), “The International GNSS Services (IGS): Perspectives and Visions for 2010 and Beyond” Workshop 2006 Proceedings		After an earthquake or volcanic eruption, the extent of deformation can be measured too. The [http://itrf.ensg.ign.fr/ International Terrestrial Reference Frame (ITRF)] networks (using GNSS data as well other geodetic data) also provides a means of aligning local deformation aiding the attempt to understand the forces behind it on a worldwide scale. In regions of significant seismic activity (e.g. California, Japan), local GNSS networks are used for permanent monitoring of the ground deformations that provides data used to develop or to validate models of crustal movements and earthquakes prediction. In the research of Tectonic Motions and Local Deformations the GNSS contribution is the most substantial and the most productive in combination with other space geodesy techniques<ref>Springer, T., Gendt, G., Dow J.M., (Editors), “The International GNSS Services (IGS): Perspectives and Visions for 2010 and Beyond” Workshop 2006 Proceedings
	~~http://igscb.jpl.nasa.gov/overview/pubs/06_darmstadt.html~~ - Darmstadt, 2006</ref>.		- Darmstadt, 2006</ref>.

	==Earth’s Gravity Field and Ocean Surface Determination==		==Earth’s Gravity Field and Ocean Surface Determination==
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	=Credits=		=Credits=
	The information provided in this article has been compiled by GMV. In some cases, figures, tables and paragraphs have been extracted from the indicated references, in particular from the ''Galileo Science Opportunity Document.''<ref>Galileo Science Opportunity Document, ~~http://egep.esa.int/egep_public/file/GSOD_v2_0.pdf~~</ref>		The information provided in this article has been compiled by GMV. In some cases, figures, tables and paragraphs have been extracted from the indicated references, in particular from the ''Galileo Science Opportunity Document.''<ref>Galileo Science Opportunity Document, </ref>

	=References=		=References=

Teresa.Ferreira: /* Retrieval of Total Water Vapour Content */

2015-01-29T11:46:56Z

Retrieval of Total Water Vapour Content

← Older revision		Revision as of 11:46, 29 January 2015
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	Water vapour is an important constituent of the atmosphere, contributing strongly to the weather and playing a critical role in the global climate system. It absorbs and re-radiates energy from the sun and it influences the formation of clouds. Despite its importance to atmospheric processes over a wide range of spatial and temporal scales, it is one of the least understood and poorly described components of the Earth’s atmosphere. Furthermore, it is the most abundant of the greenhouse gases and a better understanding of its role in climate change is needed. Total tropospheric water vapour content can be measured directly by means of a radiosonde (a small meteorological sensor attached to a balloon) or by ground-based microwave radiometry. The radiosonde approach is typically restricted to about one thousand locations worldwide with 1 – 2 measurements per day. Water vapour radiometers are rather expensive instruments which require frequent calibration.		Water vapour is an important constituent of the atmosphere, contributing strongly to the weather and playing a critical role in the global climate system. It absorbs and re-radiates energy from the sun and it influences the formation of clouds. Despite its importance to atmospheric processes over a wide range of spatial and temporal scales, it is one of the least understood and poorly described components of the Earth’s atmosphere. Furthermore, it is the most abundant of the greenhouse gases and a better understanding of its role in climate change is needed. Total tropospheric water vapour content can be measured directly by means of a radiosonde (a small meteorological sensor attached to a balloon) or by ground-based microwave radiometry. The radiosonde approach is typically restricted to about one thousand locations worldwide with 1 – 2 measurements per day. Water vapour radiometers are rather expensive instruments which require frequent calibration.
	GNSS receivers can measure the slant delay in the direction of a satellite, remove the contribution of the ionosphere and with some considerable post-processing estimate the system related errors (such as clock, orbit, phase centre) and obtain the total tropospheric delay. In order to arrive at vertical total delay (also called zenith total delay ZTD), the slant values are mapped to the vertical. To extract the water vapour content, the zenith hydrostatic delay (which can be obtained by measuring the pressure at the surface) is subtracted from the ZTD, giving the zenith wet delay (ZWD). The water vapour can be estimated from ZWD and the atmospheric temperature.		GNSS receivers can measure the slant delay in the direction of a satellite, remove the contribution of the ionosphere and with some considerable post-processing estimate the system related errors (such as clock, orbit, phase centre) and obtain the total tropospheric delay. In order to arrive at vertical total delay (also called zenith total delay ZTD), the slant values are mapped to the vertical. To extract the water vapour content, the zenith hydrostatic delay (which can be obtained by measuring the pressure at the surface) is subtracted from the ZTD, giving the zenith wet delay (ZWD). The water vapour can be estimated from ZWD and the atmospheric temperature.

	~~An example of an application is to use [[Monitoring_Climate_Using_Ground-based_GNSS_Measurements\|integrated water vapour to monitor climate]].~~

	=Credits=		=Credits=

Teresa.Ferreira: /* Retrieval of Total Water Vapour Content */

2015-01-29T11:46:18Z

Retrieval of Total Water Vapour Content

← Older revision		Revision as of 11:46, 29 January 2015
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	Water vapour is an important constituent of the atmosphere, contributing strongly to the weather and playing a critical role in the global climate system. It absorbs and re-radiates energy from the sun and it influences the formation of clouds. Despite its importance to atmospheric processes over a wide range of spatial and temporal scales, it is one of the least understood and poorly described components of the Earth’s atmosphere. Furthermore, it is the most abundant of the greenhouse gases and a better understanding of its role in climate change is needed. Total tropospheric water vapour content can be measured directly by means of a radiosonde (a small meteorological sensor attached to a balloon) or by ground-based microwave radiometry. The radiosonde approach is typically restricted to about one thousand locations worldwide with 1 – 2 measurements per day. Water vapour radiometers are rather expensive instruments which require frequent calibration.		Water vapour is an important constituent of the atmosphere, contributing strongly to the weather and playing a critical role in the global climate system. It absorbs and re-radiates energy from the sun and it influences the formation of clouds. Despite its importance to atmospheric processes over a wide range of spatial and temporal scales, it is one of the least understood and poorly described components of the Earth’s atmosphere. Furthermore, it is the most abundant of the greenhouse gases and a better understanding of its role in climate change is needed. Total tropospheric water vapour content can be measured directly by means of a radiosonde (a small meteorological sensor attached to a balloon) or by ground-based microwave radiometry. The radiosonde approach is typically restricted to about one thousand locations worldwide with 1 – 2 measurements per day. Water vapour radiometers are rather expensive instruments which require frequent calibration.
	GNSS receivers can measure the slant delay in the direction of a satellite, remove the contribution of the ionosphere and with some considerable post-processing estimate the system related errors (such as clock, orbit, phase centre) and obtain the total tropospheric delay. In order to arrive at vertical total delay (also called zenith total delay ZTD), the slant values are mapped to the vertical. To extract the water vapour content, the zenith hydrostatic delay (which can be obtained by measuring the pressure at the surface) is subtracted from the ZTD, giving the zenith wet delay (ZWD). The water vapour can be estimated from ZWD and the atmospheric temperature.		GNSS receivers can measure the slant delay in the direction of a satellite, remove the contribution of the ionosphere and with some considerable post-processing estimate the system related errors (such as clock, orbit, phase centre) and obtain the total tropospheric delay. In order to arrive at vertical total delay (also called zenith total delay ZTD), the slant values are mapped to the vertical. To extract the water vapour content, the zenith hydrostatic delay (which can be obtained by measuring the pressure at the surface) is subtracted from the ZTD, giving the zenith wet delay (ZWD). The water vapour can be estimated from ZWD and the atmospheric temperature.

			An example of an application is to use [[Monitoring_Climate_Using_Ground-based_GNSS_Measurements\|integrated water vapour to monitor climate]].

	=Credits=		=Credits=

Teresa.Ferreira: /* Troposphere Monitoring */

2015-01-29T11:45:27Z

Troposphere Monitoring

← Older revision		Revision as of 11:45, 29 January 2015
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	The optimal signal linear combination in terms of wavelength and noise level depends on the baseline length. Typical baseline lengths within [[Real Time Kinematics]] (RTK) GNSS-networks which are frequently used for ground-based tropospheric monitoring are between 50 km and 120 km. The set of new signals provided by Galileo as well as GPS/GLONASS ongoing modernization programs will allow for improved ambiguity resolution techniques over such long baselines. Furthermore, GNSS signals at three frequencies will allow modelling of the higher order terms of the ionospheric refraction (on the order of 1 cm), which in turn reduces the error of the tropospheric wet delay estimates.		The optimal signal linear combination in terms of wavelength and noise level depends on the baseline length. Typical baseline lengths within [[Real Time Kinematics]] (RTK) GNSS-networks which are frequently used for ground-based tropospheric monitoring are between 50 km and 120 km. The set of new signals provided by Galileo as well as GPS/GLONASS ongoing modernization programs will allow for improved ambiguity resolution techniques over such long baselines. Furthermore, GNSS signals at three frequencies will allow modelling of the higher order terms of the ionospheric refraction (on the order of 1 cm), which in turn reduces the error of the tropospheric wet delay estimates.

	An example of an application is ~~using~~ [[Monitoring_Climate_Using_Ground-based_GNSS_Measurements\|integrated water vapour to monitor climate]].		An example of an application is to use [[Monitoring_Climate_Using_Ground-based_GNSS_Measurements\|integrated water vapour to monitor climate]].

	==Retrieval of Total Water Vapour Content==		==Retrieval of Total Water Vapour Content==

Teresa.Ferreira: /* Troposphere Monitoring */

2015-01-29T11:44:03Z

Troposphere Monitoring

← Older revision		Revision as of 11:44, 29 January 2015
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	Microwave signals of the GNSS satellites are time delayed when passing through the atmosphere. Based on this, signal delay parameters, such as the humidity distribution within the troposphere, can be determined. It has already been shown by several international and national projects that the delivery of Zenith Wet Delays (ZWD) derived from a GNSS-network solution with hourly resolution and an accuracy of 1mm in Precipitable Water Vapour (PWV) is achievable. These ZWD-estimates have been successfully assimilated into meteorological models<ref>Karabatic A., Weber R., Haiden, Th. and Leroch, S., “Near real-time estimation of tropospheric water vapour content from ground based GNSS data and its potential contribution to weather now-casting in Austria”, accepted for publication in Advances in Space Research.</ref>. Preconditions to derive accurate ZWD estimates are accurate satellite orbit and clock information and an almost complete and successful fixing of ambiguities of the chosen phase linear combination.		Microwave signals of the GNSS satellites are time delayed when passing through the atmosphere. Based on this, signal delay parameters, such as the humidity distribution within the troposphere, can be determined. It has already been shown by several international and national projects that the delivery of Zenith Wet Delays (ZWD) derived from a GNSS-network solution with hourly resolution and an accuracy of 1mm in Precipitable Water Vapour (PWV) is achievable. These ZWD-estimates have been successfully assimilated into meteorological models<ref>Karabatic A., Weber R., Haiden, Th. and Leroch, S., “Near real-time estimation of tropospheric water vapour content from ground based GNSS data and its potential contribution to weather now-casting in Austria”, accepted for publication in Advances in Space Research.</ref>. Preconditions to derive accurate ZWD estimates are accurate satellite orbit and clock information and an almost complete and successful fixing of ambiguities of the chosen phase linear combination.
	The optimal signal linear combination in terms of wavelength and noise level depends on the baseline length. Typical baseline lengths within [[Real Time Kinematics]] (RTK) GNSS-networks which are frequently used for ground-based tropospheric monitoring are between 50 km and 120 km. The set of new signals provided by Galileo as well as GPS/GLONASS ongoing modernization programs will allow for improved ambiguity resolution techniques over such long baselines. Furthermore, GNSS signals at three frequencies will allow modelling of the higher order terms of the ionospheric refraction (on the order of 1 cm), which in turn reduces the error of the tropospheric wet delay estimates.		The optimal signal linear combination in terms of wavelength and noise level depends on the baseline length. Typical baseline lengths within [[Real Time Kinematics]] (RTK) GNSS-networks which are frequently used for ground-based tropospheric monitoring are between 50 km and 120 km. The set of new signals provided by Galileo as well as GPS/GLONASS ongoing modernization programs will allow for improved ambiguity resolution techniques over such long baselines. Furthermore, GNSS signals at three frequencies will allow modelling of the higher order terms of the ionospheric refraction (on the order of 1 cm), which in turn reduces the error of the tropospheric wet delay estimates.

			An example of an application is using [[Monitoring_Climate_Using_Ground-based_GNSS_Measurements\|integrated water vapour to monitor climate]].

	==Retrieval of Total Water Vapour Content==		==Retrieval of Total Water Vapour Content==

Filipe.Pelica: Included some ilustrations.

2013-12-11T15:25:45Z

Included some ilustrations.

← Older revision		Revision as of 15:25, 11 December 2013
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	==Earth’s Gravity Field and Ocean Surface Determination==		==Earth’s Gravity Field and Ocean Surface Determination==

			::::[[File:615px-Atlantic Ocean surface.jpg\|right\|thumb\|200px\|'''''Figure 1:''''' Atlantic Ocean Surface represented by NASA’s globe software World Wind.]]

	One of the main inputs for the ocean surface determination is the altimetry of sufficiently low earth orbit (LEO) satellites accurately measuring the distance between the satellite and the ocean surface. However the orbits are heavily perturbed by the gravity field, by drag, and by radiation pressure and therefore it is of high importance to achieve centimeter precision in the radial direction of the orbits. Precision of this kind can only be achieved by using various space techniques. One of the fundamental contributions to those techniques is the use of onboard GNSS receivers which in combination with GNSS orbits and clock corrections issued by the [http://igscb.jpl.nasa.gov\|IGS], can provide the position of the LEO satellites as a function of time with centimeter accuracy.		One of the main inputs for the ocean surface determination is the altimetry of sufficiently low earth orbit (LEO) satellites accurately measuring the distance between the satellite and the ocean surface. However the orbits are heavily perturbed by the gravity field, by drag, and by radiation pressure and therefore it is of high importance to achieve centimeter precision in the radial direction of the orbits. Precision of this kind can only be achieved by using various space techniques. One of the fundamental contributions to those techniques is the use of onboard GNSS receivers which in combination with GNSS orbits and clock corrections issued by the [http://igscb.jpl.nasa.gov\|IGS], can provide the position of the LEO satellites as a function of time with centimeter accuracy.
	Furthermore the use of GNSS for tracking LEOs is a significant improvement in orbit determination of the LEO satellites due continuity and homogeneity. Using GNSS means enables a permanent tracking, 24 hours per day without interruptions. Such coverage could never be achieved with ground tracking systems, where weather conditions (for laser) or visibility limitations (due to the sparseness of the observatories) produce long data gaps.		Furthermore the use of GNSS for tracking LEOs is a significant improvement in orbit determination of the LEO satellites due continuity and homogeneity. Using GNSS means enables a permanent tracking, 24 hours per day without interruptions. Such coverage could never be achieved with ground tracking systems, where weather conditions (for laser) or visibility limitations (due to the sparseness of the observatories) produce long data gaps.
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	=Remote Sensing Using GNSS-R=		=Remote Sensing Using GNSS-R=
	The concept of GNSS-R (GNSS-Reflectometry) or PARIS (Passive Reflectometry and Interferometry System) is that of a bi-static radar, where the transmitter is a GNSS satellite and where the receiver can receive both the signal coming directly from the source and the signal reflected from the Earth’s surface. In spite of the fact that the properties of GNSS signals have been optimized for navigation applications, the reflected signal contains information about the state of the reflecting surface. An illustration of such concept is presented in the ~~following~~ figure.
			::::[[File:Gnss-r.png\|right\|thumb\|500px\|'''''Figure 2:''''' Ilustration of the GNSS-R concept.]]

			The concept of GNSS-R (GNSS-Reflectometry) or PARIS (Passive Reflectometry and Interferometry System) is that of a bi-static radar, where the transmitter is a GNSS satellite and where the receiver can receive both the signal coming directly from the source and the signal reflected from the Earth’s surface. In spite of the fact that the properties of GNSS signals have been optimized for navigation applications, the reflected signal contains information about the state of the reflecting surface. An illustration of such concept is presented in the figure on the right.

	The concept GNSS-R was proposed in 1993 by ESA<ref> Martin-Neira, M., “A Passive Reflectometry and Interferometry System (PARIS): Application to Ocean Altimetry”, ESA Journal 1993, Vol. 17, pp. 331-355.</ref> to provide additional measurements of the sea surface to increase the spatial and temporal resolution provided by radar altimeters. In 1998, the application to remote sensing of the sea roughness and winds was demonstrated<ref> Garrison, J.L., Katzberg, S.J. and Hill, M.I., “Effect of sea roughness on bistatically scattered range coded signals from the Global Positioning System,” Geophys. Res. Lett., 25(13), pp. 2257–2260.</ref>. Most of the applications are based on a bi-static radar model adapted to the GNSS-R, as described in<ref> Zavorotny, V.U., Voronovich, A.G., “Scattering of GPS signals from the ocean with wind remote sensing application”, IEEE Transactions on Geoscience and Remote Sensing, 38(2), pp. 951-964, doi:10.1109/36.841977.</ref>.		The concept GNSS-R was proposed in 1993 by ESA<ref> Martin-Neira, M., “A Passive Reflectometry and Interferometry System (PARIS): Application to Ocean Altimetry”, ESA Journal 1993, Vol. 17, pp. 331-355.</ref> to provide additional measurements of the sea surface to increase the spatial and temporal resolution provided by radar altimeters. In 1998, the application to remote sensing of the sea roughness and winds was demonstrated<ref> Garrison, J.L., Katzberg, S.J. and Hill, M.I., “Effect of sea roughness on bistatically scattered range coded signals from the Global Positioning System,” Geophys. Res. Lett., 25(13), pp. 2257–2260.</ref>. Most of the applications are based on a bi-static radar model adapted to the GNSS-R, as described in<ref> Zavorotny, V.U., Voronovich, A.G., “Scattering of GPS signals from the ocean with wind remote sensing application”, IEEE Transactions on Geoscience and Remote Sensing, 38(2), pp. 951-964, doi:10.1109/36.841977.</ref>.
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	==Ionospheric Monitoring==		==Ionospheric Monitoring==

	::::[[File:radio_occultation.png\|right\|thumb\|500px\|'''''Figure 1:''''' Ionospheric radio occultation measurements in the limb sounding mode (dotted line) and topside measurements (solid line).]]		::::[[File:radio_occultation.png\|right\|thumb\|500px\|'''''Figure 3:''''' Ionospheric radio occultation measurements in the limb sounding mode (dotted line) and topside measurements (solid line).]]

	Ionospheric tomography based on GPS data has been successfully used in regional and wide area [[Differential GNSS]] (DGNSS) to improve the location precision and to allow greater distances between the rover and the reference stations. In those cases, ionospheric tomography contributes to the improvement in the resolution of carrier-phase ambiguity. Ionospheric tomography can provide fast and accurate estimates of TEC under conditions of high electron density variability, such as those observed close to the geomagnetic equator, during solar maximum<ref>Colombo O., Hernández-Pajares, M., Juan J.M., and Sanz, J. , “Wide-Area, Carrier-Phase ambiguity resolution using a tomography model of the ionosphere”, Journal of the Institute of Navigation, vol. 49, No.1, 2002.</ref>. Tomography modelling is based on a set of three-dimensional cells that covers spatially the sampled ionosphere. In these cells, the electron density is considered constant at a given time. Despite other possibilities to choose the cell distribution, a regular distribution is adequate for describing a region with samples from a more or less homogeneously distributed network of reference stations. The estimate of ionospheric electron density in each cell is based on the ionospheric data obtained from the satellite receiver ray paths crossing that particular cell.		Ionospheric tomography based on GPS data has been successfully used in regional and wide area [[Differential GNSS]] (DGNSS) to improve the location precision and to allow greater distances between the rover and the reference stations. In those cases, ionospheric tomography contributes to the improvement in the resolution of carrier-phase ambiguity. Ionospheric tomography can provide fast and accurate estimates of TEC under conditions of high electron density variability, such as those observed close to the geomagnetic equator, during solar maximum<ref>Colombo O., Hernández-Pajares, M., Juan J.M., and Sanz, J. , “Wide-Area, Carrier-Phase ambiguity resolution using a tomography model of the ionosphere”, Journal of the Institute of Navigation, vol. 49, No.1, 2002.</ref>. Tomography modelling is based on a set of three-dimensional cells that covers spatially the sampled ionosphere. In these cells, the electron density is considered constant at a given time. Despite other possibilities to choose the cell distribution, a regular distribution is adequate for describing a region with samples from a more or less homogeneously distributed network of reference stations. The estimate of ionospheric electron density in each cell is based on the ionospheric data obtained from the satellite receiver ray paths crossing that particular cell.
	Another technique commonly used in the ionospheric monitoring uses the [[Earth Sciences#Remote Sensing Using GNSS-R\|GNSS-R]] concept above described. Since the space-based receiver on board a LEO satellite is mainly used for accurate positioning and precise timing, the dual frequency navigation measurements can be used to get information on the topside ionosphere above the LEO satellite orbit too. The data enable reconstructing the 3D electron density distribution of the topside ionosphere/plasmasphere in the vicinity of the LEO orbit plane<ref>Heise, S., Jakowski, N., Wehrenpfennig, A., Reigber Ch. and Lühr, H., “Sounding of the Topside Ionosphere/Plasmasphere Based on GPS Measurements from CHAMP: Initial Results”, Geophysical Research Letters, 29, No. 14, 10.1029/2002GL014738, 2002.</ref>. The more data links from GNSS satellites that are available, the more accurate and higher resolved is the tomographic or assimilative reconstruction of the electron density distribution.		Another technique commonly used in the ionospheric monitoring uses the [[Earth Sciences#Remote Sensing Using GNSS-R\|GNSS-R]] concept above described. Since the space-based receiver on board a LEO satellite is mainly used for accurate positioning and precise timing, the dual frequency navigation measurements can be used to get information on the topside ionosphere above the LEO satellite orbit too. The data enable reconstructing the 3D electron density distribution of the topside ionosphere/plasmasphere in the vicinity of the LEO orbit plane<ref>Heise, S., Jakowski, N., Wehrenpfennig, A., Reigber Ch. and Lühr, H., “Sounding of the Topside Ionosphere/Plasmasphere Based on GPS Measurements from CHAMP: Initial Results”, Geophysical Research Letters, 29, No. 14, 10.1029/2002GL014738, 2002.</ref>. The more data links from GNSS satellites that are available, the more accurate and higher resolved is the tomographic or assimilative reconstruction of the electron density distribution.

	Figure 1 shows the geometry of combined limb-sounding and topside-sounding geometries for reconstruction of the topside ionosphere as it is shown in the background figure based on CHAMP data<ref>Jakowski, N., Wilken, V., Tsybulya K. and Heise, S., “Search of earthquake signatures by ground and space based GPS measurements”, in Flury, J., Rummel, R., Reigber, C., Rothacher, M., Boedecker, G., Schreiber, U. (Eds.) Observation of the Earth System from Space, Springer Berlin Heidelberg New York,ISBN: 3-540-29520-8, 2006.</ref>.		Figure 3 shows the geometry of combined limb-sounding and topside-sounding geometries for reconstruction of the topside ionosphere as it is shown in the background figure based on CHAMP data<ref>Jakowski, N., Wilken, V., Tsybulya K. and Heise, S., “Search of earthquake signatures by ground and space based GPS measurements”, in Flury, J., Rummel, R., Reigber, C., Rothacher, M., Boedecker, G., Schreiber, U. (Eds.) Observation of the Earth System from Space, Springer Berlin Heidelberg New York,ISBN: 3-540-29520-8, 2006.</ref>.

	Whereas the ground-based measurements are especially suited for imaging the horizontal distribution of plasma, the space-borne measurements are suited to map the vertical distribution of the ionospheric plasma.		Whereas the ground-based measurements are especially suited for imaging the horizontal distribution of plasma, the space-borne measurements are suited to map the vertical distribution of the ionospheric plasma.

	==Troposphere Monitoring==		==Troposphere Monitoring==

			::::[[File:Moon Limb & Troposphere.JPG\|right\|thumb\|500px\|'''''Figure 4:''''' Moon at centre, with the limb of Earth near the bottom transitioning into the orange-coloured troposphere, the lowest and most dense portion of the Earth's atmosphere.]]

	Microwave signals of the GNSS satellites are time delayed when passing through the atmosphere. Based on this, signal delay parameters, such as the humidity distribution within the troposphere, can be determined. It has already been shown by several international and national projects that the delivery of Zenith Wet Delays (ZWD) derived from a GNSS-network solution with hourly resolution and an accuracy of 1mm in Precipitable Water Vapour (PWV) is achievable. These ZWD-estimates have been successfully assimilated into meteorological models<ref>Karabatic A., Weber R., Haiden, Th. and Leroch, S., “Near real-time estimation of tropospheric water vapour content from ground based GNSS data and its potential contribution to weather now-casting in Austria”, accepted for publication in Advances in Space Research.</ref>. Preconditions to derive accurate ZWD estimates are accurate satellite orbit and clock information and an almost complete and successful fixing of ambiguities of the chosen phase linear combination.		Microwave signals of the GNSS satellites are time delayed when passing through the atmosphere. Based on this, signal delay parameters, such as the humidity distribution within the troposphere, can be determined. It has already been shown by several international and national projects that the delivery of Zenith Wet Delays (ZWD) derived from a GNSS-network solution with hourly resolution and an accuracy of 1mm in Precipitable Water Vapour (PWV) is achievable. These ZWD-estimates have been successfully assimilated into meteorological models<ref>Karabatic A., Weber R., Haiden, Th. and Leroch, S., “Near real-time estimation of tropospheric water vapour content from ground based GNSS data and its potential contribution to weather now-casting in Austria”, accepted for publication in Advances in Space Research.</ref>. Preconditions to derive accurate ZWD estimates are accurate satellite orbit and clock information and an almost complete and successful fixing of ambiguities of the chosen phase linear combination.
	The optimal signal linear combination in terms of wavelength and noise level depends on the baseline length. Typical baseline lengths within [[Real Time Kinematics]] (RTK) GNSS-networks which are frequently used for ground-based tropospheric monitoring are between 50 km and 120 km. The set of new signals provided by Galileo as well as GPS/GLONASS ongoing modernization programs will allow for improved ambiguity resolution techniques over such long baselines. Furthermore, GNSS signals at three frequencies will allow modelling of the higher order terms of the ionospheric refraction (on the order of 1 cm), which in turn reduces the error of the tropospheric wet delay estimates.		The optimal signal linear combination in terms of wavelength and noise level depends on the baseline length. Typical baseline lengths within [[Real Time Kinematics]] (RTK) GNSS-networks which are frequently used for ground-based tropospheric monitoring are between 50 km and 120 km. The set of new signals provided by Galileo as well as GPS/GLONASS ongoing modernization programs will allow for improved ambiguity resolution techniques over such long baselines. Furthermore, GNSS signals at three frequencies will allow modelling of the higher order terms of the ionospheric refraction (on the order of 1 cm), which in turn reduces the error of the tropospheric wet delay estimates.

Teresa.Ferreira at 12:43, 1 December 2013

2013-12-01T12:43:44Z

← Older revision		Revision as of 12:43, 1 December 2013
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	\|Authors=ESA		\|Authors=ESA
	\|Editors=GMV		\|Editors=GMV
	\|Level=~~Basic~~		\|Level=Intermediate
	\|YearOfPublication=2013		\|YearOfPublication=2013
	\|Logo=GMV		\|Logo=GMV

Teresa.Ferreira: /* Remote Observation of Soil Moisture */

2013-12-01T12:43:08Z

Remote Observation of Soil Moisture

← Older revision		Revision as of 12:43, 1 December 2013
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	==Remote Observation of Soil Moisture==		==Remote Observation of Soil Moisture==
	The power level of the reflected signal, appropriately normalized, contains information about the soil moisture of the reflecting surface. Thus, GNSS-R data collected from aircraft and/or spacecraft can detect different soil types; urban areas, dry-soil, wetlands<ref>Masters, D., Zavorotny, V., Katzberg, S. and Emery, W., “GPS signal scattering from land for moisture content determination”, in: Proceeding of the IEEE International Geosciences and Remote Sensing Symposium, Honolulu, Hawaii, 24–28 July, pp. 3090–3092.</ref>		The power level of the reflected signal, appropriately normalized, contains information about the soil moisture of the reflecting surface. Thus, GNSS-R data collected from aircraft and/or spacecraft can detect different soil types; urban areas, dry-soil, wetlands<ref>Masters, D., Zavorotny, V., Katzberg, S. and Emery, W., “GPS signal scattering from land for moisture content determination”, in: Proceeding of the IEEE International Geosciences and Remote Sensing Symposium, Honolulu, Hawaii, 24–28 July, pp. 3090–3092.</ref>.

	==Sea Ice and Dry Snow==		==Sea Ice and Dry Snow==

Teresa.Ferreira: /* Measurement of Tectonic Motions and Local Deformations */

2013-12-01T12:42:18Z

Measurement of Tectonic Motions and Local Deformations

← Older revision		Revision as of 12:42, 1 December 2013
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	==Measurement of Tectonic Motions and Local Deformations==		==Measurement of Tectonic Motions and Local Deformations==
	GNSS have brought greater precision in position determination and above all enabled sustained monitoring at an acceptable cost and in a very efficient and timely way, which enables monitoring variations of geodetic station positioning induced by various geophysical processes. The global network of IGS stations can provide continuous information about motions of the continents or smaller tectonic plates. In addition at a local or regional scale, the ease with which a GNSS can be used and combined with positioning precision using [[Differential GNSS]] (DGNSS) techniques or [[Precise Point Positioning]] (PPP) technique means that the number of measurement points in areas of seismic or volcanic activity can be increased to monitor changes that might warn of coming disasters.		GNSS have brought greater precision in position determination and above all enabled sustained monitoring at an acceptable cost and in a very efficient and timely way, which enables monitoring variations of geodetic station positioning induced by various geophysical processes. The global network of IGS stations can provide continuous information about motions of the continents or smaller tectonic plates. In addition at a local or regional scale, the ease with which a GNSS can be used and combined with positioning precision using [[Differential GNSS]] (DGNSS) techniques or [[Precise Point Positioning]] (PPP) technique means that the number of measurement points in areas of seismic or volcanic activity can be increased to monitor changes that might warn of coming disasters.
	After an earthquake or volcanic eruption, the extent of deformation can be measured too. The [http://itrf.ensg.ign.fr/ \| International Terrestrial Reference Frame (ITRF)] networks (using GNSS data as well other geodetic data) also provides a means of aligning local deformation aiding the attempt to understand the forces behind it on a worldwide scale. In regions of significant seismic activity (e.g. California, Japan), local GNSS networks are used for permanent monitoring of the ground deformations that provides data used to develop or to validate models of crustal movements and earthquakes prediction. In the research of Tectonic Motions and Local Deformations the GNSS contribution is the most substantial and the most productive in combination with other space geodesy techniques<ref>Springer, T., Gendt, G., Dow J.M., (Editors), “The International GNSS Services (IGS): Perspectives and Visions for 2010 and Beyond” Workshop 2006 Proceedings		After an earthquake or volcanic eruption, the extent of deformation can be measured too. The [http://itrf.ensg.ign.fr/ International Terrestrial Reference Frame (ITRF)] networks (using GNSS data as well other geodetic data) also provides a means of aligning local deformation aiding the attempt to understand the forces behind it on a worldwide scale. In regions of significant seismic activity (e.g. California, Japan), local GNSS networks are used for permanent monitoring of the ground deformations that provides data used to develop or to validate models of crustal movements and earthquakes prediction. In the research of Tectonic Motions and Local Deformations the GNSS contribution is the most substantial and the most productive in combination with other space geodesy techniques<ref>Springer, T., Gendt, G., Dow J.M., (Editors), “The International GNSS Services (IGS): Perspectives and Visions for 2010 and Beyond” Workshop 2006 Proceedings
	http://igscb.jpl.nasa.gov/overview/pubs/06_darmstadt.html - Darmstadt, 2006</ref>.		http://igscb.jpl.nasa.gov/overview/pubs/06_darmstadt.html - Darmstadt, 2006</ref>.

Teresa.Ferreira: /* Geodesy and Geodynamics */

2013-12-01T12:40:58Z

Geodesy and Geodynamics

← Older revision		Revision as of 12:40, 1 December 2013
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	=Geodesy and Geodynamics=		=Geodesy and Geodynamics=
	The International Association of Geodesy (IAG) organized the Global Geodetic Observing System (GGOS) composed by several IAG technique-services that aims mainly the support of the Earth Science research. The service that provides the means to use GNSS data is the [http://igscb.jpl.nasa.gov\| International GNSS Service (IGS)] that nowadays has a fundamental contribution to the overall GNSS community since provides the highest quality data and products as the standard for Global Navigation Satellite Systems (GNSS). In addition there are also services combining the products of the technique specific services, such as the [http://www.iers.org\|International Earth Rotation and Reference Systems Service (IERS)]. The GGOS enables research in three fundamental areas of geodesy:		The International Association of Geodesy (IAG) organized the Global Geodetic Observing System (GGOS) composed by several IAG technique-services that aims mainly the support of the Earth Science research. The service that provides the means to use GNSS data is the [http://igscb.jpl.nasa.gov International GNSS Service (IGS)] that nowadays has a fundamental contribution to the overall GNSS community since provides the highest quality data and products as the standard for Global Navigation Satellite Systems (GNSS). In addition there are also services combining the products of the technique specific services, such as the [http://www.iers.org International Earth Rotation and Reference Systems Service (IERS)]. The GGOS enables research in three fundamental areas of geodesy:
	* The geometric shape of the Earth (land, ice and ocean surface) as well as its variation in time;		* The geometric shape of the Earth (land, ice and ocean surface) as well as its variation in time;
	* The orientation of the Earth in inertial space as a function of time;		* The orientation of the Earth in inertial space as a function of time;
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	==Measurement of Tectonic Motions and Local Deformations==		==Measurement of Tectonic Motions and Local Deformations==
	GNSS have brought greater precision in position determination and above all enabled sustained monitoring at an acceptable cost and in a very efficient and timely way, which enables monitoring variations of geodetic station positioning induced by various geophysical processes. The global network of IGS stations can provide continuous information about motions of the continents or smaller tectonic plates. In addition at a local or regional scale, the ease with which a GNSS can be used and combined with positioning precision using [[Differential GNSS]] (DGNSS) techniques or [[Precise Point Positioning]] (PPP) technique means that the number of measurement points in areas of seismic or volcanic activity can be increased to monitor changes that might warn of coming disasters.		GNSS have brought greater precision in position determination and above all enabled sustained monitoring at an acceptable cost and in a very efficient and timely way, which enables monitoring variations of geodetic station positioning induced by various geophysical processes. The global network of IGS stations can provide continuous information about motions of the continents or smaller tectonic plates. In addition at a local or regional scale, the ease with which a GNSS can be used and combined with positioning precision using [[Differential GNSS]] (DGNSS) techniques or [[Precise Point Positioning]] (PPP) technique means that the number of measurement points in areas of seismic or volcanic activity can be increased to monitor changes that might warn of coming disasters.
	After an earthquake or volcanic eruption, the extent of deformation can be measured too. The [http://itrf.ensg.ign.fr/\|International Terrestrial Reference Frame (ITRF)] networks (using GNSS data as well other geodetic data) also provides a means of aligning local deformation aiding the attempt to understand the forces behind it on a worldwide scale. In regions of significant seismic activity (e.g. California, Japan), local GNSS networks are used for permanent monitoring of the ground deformations that provides data used to develop or to validate models of crustal movements and earthquakes prediction. In the research of Tectonic Motions and Local Deformations the GNSS contribution is the most substantial and the most productive in combination with other space geodesy techniques<ref>Springer, T., Gendt, G., Dow J.M., (Editors), “The International GNSS Services (IGS): Perspectives and Visions for 2010 and Beyond” Workshop 2006 Proceedings		After an earthquake or volcanic eruption, the extent of deformation can be measured too. The [http://itrf.ensg.ign.fr/ \| International Terrestrial Reference Frame (ITRF)] networks (using GNSS data as well other geodetic data) also provides a means of aligning local deformation aiding the attempt to understand the forces behind it on a worldwide scale. In regions of significant seismic activity (e.g. California, Japan), local GNSS networks are used for permanent monitoring of the ground deformations that provides data used to develop or to validate models of crustal movements and earthquakes prediction. In the research of Tectonic Motions and Local Deformations the GNSS contribution is the most substantial and the most productive in combination with other space geodesy techniques<ref>Springer, T., Gendt, G., Dow J.M., (Editors), “The International GNSS Services (IGS): Perspectives and Visions for 2010 and Beyond” Workshop 2006 Proceedings
	http://igscb.jpl.nasa.gov/overview/pubs/06_darmstadt.html - Darmstadt, 2006</ref>.		http://igscb.jpl.nasa.gov/overview/pubs/06_darmstadt.html - Darmstadt, 2006</ref>.