The 2004 catastrophic Indian-Ocean tsunami has strongly emphasized the need for reliable tsunami ... more The 2004 catastrophic Indian-Ocean tsunami has strongly emphasized the need for reliable tsunami early- warning systems. Another giant tsunamigenic earthquake may occur west of Sumatra, close to the large city of Padang. We demonstrate that the presence of islands between the trench and the Sumatran coast makes earthquake-induced tsunamis especially sensitive to slip distribution on the rupture plane: wave heights at Padang may differ by more than a factor of 5 for earthquakes having the same seismic moment (magnitude) and rupture zone geometry but different slip distribution. Hence, reliable prediction of tsunami wave heights for Padang can not be provided using traditional, earthquake-magnitude-based methods. We show, however, that such prediction can be issued within less than 10 minutes of an earthquake by incorporating special types of near-field GPS arrays ('GPS Shield'). These arrays measure both vertical and horizontal displacements and can resolve higher order features of the slip distribution on the fault than seismic moment if placed above the rupture zone or less than some 100 km away of the rupture zone. Stations in the arrays are closely spaced (10-20 km) and aligned perpendicular to the trench, i.e., parallel to the expected gradient of surface coseismic displacement. In the case of Sumatra and Java, the GPS-Shield arrays should be placed at Mentawaii Islandes, located between the trench and Sumatra and directly at the Sumatra and Java western coasts where no islands are present. We demonstrate that the 'GPS Shield' can also be applied to northern Chile, where giant earthquake may also occur in the near future. Moreover, this concept may be applied globally, to many other tsunamigenic active margins where the land is located above or close to seismogenic zones.
International Association of Geodesy Symposia, 1993
ABSTRACT The GeoForschungsZentrum (GFZ) Potsdam has been selected as one of the analysing centres... more ABSTRACT The GeoForschungsZentrum (GFZ) Potsdam has been selected as one of the analysing centres for the International Geodynamics CPS Service (IGS). This paper discusses the GPS tracking data management procedures at GFZ during the IGS campaign from June 21 to October 31, 1992.
The German satellite CHAMP (Challenging mini-satellite Payload), launched in mid- 2000, exploits ... more The German satellite CHAMP (Challenging mini-satellite Payload), launched in mid- 2000, exploits radio signals from the GPS (Global Positioning System) satellite con- stellation for the remote sensing of upper tropospheric and stratospheric temperatures. Due to the limb sounding geometry of the measurements, CHAMP's radio occultation measurements provide a high vertical vertical resolution in the tropopause region. The accuracy of the temperature soundings is also highest in the vicinity of the tropopause. Since the first measurements taken in early 2001, CHAMP has collected more than 40000 vertical profiles of the temperature distribution around the tropopause, and sev- eral multi-week periods of continuous measurements are available during all seasons. We intercompare tropopause temperatures, heights, pressures, and water vapor sat- uration mixing ratios obtained from CHAMP soundings with data from the global network of radiosonde data as well as with tropopause characteristic...
The Carte du Ciel (CdC) project consisted of two parts: the sky chart itself, and the Astrographi... more The Carte du Ciel (CdC) project consisted of two parts: the sky chart itself, and the Astrographic Catalogue. The plates of both series are of high value for proper motion studies due to their early epochs. We describe here technical details of modelling digitized triple images on a plate taken for the chart part of the Paris zone. The three images of each star are very close, so that they are not separable for bright stars. As a mathematical model we used the sum of three overlapping elliptical Gaussians including a saturation parameter. We found a strong photographic adjacency effect which increases the distances between the three images for each star from about 140 micrometers for faint stars to more than 300 micrometers for the brightest stars. However, thanks to the arrangement of the three images in an equilateral triangle their centre of gravity allows to derive a usable astrometric position.
The standard method for the processing of CHAMPSs (CHAllenging Minisatellite Payload) GPS occulta... more The standard method for the processing of CHAMPSs (CHAllenging Minisatellite Payload) GPS occultation data at the GeoForschungsZentrum (GFZ) Potsdam is the double difference technique to correct for satellite clock errors. In order to apply this technique the implementation of a global fiducial GPS ground network is necessary. This network (High Rate and Low Latency network) was installed jointly by GFZ and Jet Propulsion Laboratory (JPL) in preparation of the CHAMP occultation experiment and is operated jointly by both institutes. In the current configuration (January 2002) it consists of 28 stations. Various aspects of utilizing the ground station data for occultation processing are dis- cussed. E.g. a correlation between the network topology and the global distribution of ground data redundancy for occultation processing is given. Furthermore the influence of an acquisition rate reduction (compared to the standard 1 Hz rate) to the quality of the atmospheric profiles is discussed...
With the launch of JASON-1 the successful mission TOPEX/Poseidon (T/P) is extended to a second de... more With the launch of JASON-1 the successful mission TOPEX/Poseidon (T/P) is extended to a second decade. Various analyses have shown that any altimetry mission is subject to performance degradation resulting in an apparent sea level rise. Comparisons of RA with in situ measurements of the instantaneous sea level at Harvest Oil Platform have been used to monitor the absolute sea level measurements of T/P, but not for other missions. However, only a combination of e.g. ENVISAT and JASON-1 gives a sufficient coverage in time and space. For the past and current missions different strategies are used for the calibration and the drift monitoring, e.g. using crossovers or tide gauges as a height reference. The disadvantage of all calibration methods is, that no direct measurement beneath the sub-satellite tracks are available for all missions and, therefore, models have to be used to account for e.g. the sea surface slope or time varying signals. As shown for ERS and Topex/Poseidon, a GPS-eq...
Since aging and other effects on the electronics of satellite radar altimeters (RA) are leading t... more Since aging and other effects on the electronics of satellite radar altimeters (RA) are leading to apparent sea level variations, absolute calibration sites become more and more important. The absolute bias and drift of RA can be determined best by simultaneous in-situ observations of the instantaneous sea level in the sub-satellite track. In the context of the Helmholtz Association's strategic project Sea Level Change (SEAL) the GFZ Potsdam has developed a ruggedized offshore GPS-buoy which is able to measure the instantaneous sea level with high accuracy. In May 2002 the buoy has been deployed at a triple crossover where the actual RA missions Topex/Jason-1, ERS-2/Envisat and GFO-1 intersect. The position is the only triple crossover in the German Bight that allows data transmission to a land station (List/Sylt) via an HF radio link. The first deployment spans more than three months, until end of August 2002, with 26 RA overflights altogether. Each data set comprises one hour ...
The paper describes some selected GNSS-based precise technologies developed and used for various ... more The paper describes some selected GNSS-based precise technologies developed and used for various maritime applications. Firstly two PVT projects are presented. GNSS-based buoys developed at GFZ Potsdam have been used for calibration of satellite altimeters and for monitoring of sea- and river water levels. Performance and accuracy of PVT can be dramatically degraded by ionospheric threads. Thus, ionospheric mitigation approaches in the PVT solutions are discussed here as well. Finally GNSS remote-sensing technology for monitoring of sea surface roughness and sea level, using reflections of GNSS signals is described. A long-term coastal experiment has been conducted in winter season 2008/09 at Disko Bay with partners (IEEC Barcelona, GFZ Potsdam and ESTEC Nordwijk) as part of the GPS-SIDS project (GPS for Sea Ice and Dry Snow remote sensing). Altimetric and scatterometric applications of ocean reflected signals have been studied to estimate instantaneous sea surface height (SSH) and ...
In this paper, we assess the performance of a sequential Monte Carlo based filter called Cost-Ref... more In this paper, we assess the performance of a sequential Monte Carlo based filter called Cost-Reference Particle Filter (CRPF) in comparison to Extended Kalman Filter (EKF) and Hyperbolic Positioning (HP) based on the time difference of arrival approach for dynamic target tracking. Our results show that CRPF performs better than EKF which in turn performs better than HP. The paper highlights the robustness of CRPF to model inaccuracies which are common in most practical filter implementation problems. The findings of the paper suggest that usage of the CRPF is a promising technique to tackle the problems of random dynamic systems with unknown statistics in ultra-wideband based localization techniques in challenging indoor environments.
Ionospheric disturbances are fast and random variabilities in the ionosphere and they are difficu... more Ionospheric disturbances are fast and random variabilities in the ionosphere and they are difficult to detect and model. Some strong disturbances can cause, among others, interruption of GNSS signal or even lead to loss of signal lock. These phenomena are especially harmful for kinematic real-time applications, where the system availability is one of the most important parameters influencing positioning reliability. Our investigations were conducted using long time series of GNSS observations gathered at high latitude, where ionospheric disturbances more frequently occur. Selected processing strategy was used to monitor ionospheric signatures in time series of the coordinates. Quality of the data of input and of the processing results were examined and described by a set of proposed parameters. Variations in the coordinates were compared with available information about the state of ionosphere derived from Neustrelitz TEC Model (NTCM) and with the time series of raw observations. So...
The 2004 catastrophic Indian-Ocean tsunami has strongly emphasized the need for reliable tsunami ... more The 2004 catastrophic Indian-Ocean tsunami has strongly emphasized the need for reliable tsunami early- warning systems. Another giant tsunamigenic earthquake may occur west of Sumatra, close to the large city of Padang. We demonstrate that the presence of islands between the trench and the Sumatran coast makes earthquake-induced tsunamis especially sensitive to slip distribution on the rupture plane: wave heights at Padang may differ by more than a factor of 5 for earthquakes having the same seismic moment (magnitude) and rupture zone geometry but different slip distribution. Hence, reliable prediction of tsunami wave heights for Padang can not be provided using traditional, earthquake-magnitude-based methods. We show, however, that such prediction can be issued within less than 10 minutes of an earthquake by incorporating special types of near-field GPS arrays ('GPS Shield'). These arrays measure both vertical and horizontal displacements and can resolve higher order features of the slip distribution on the fault than seismic moment if placed above the rupture zone or less than some 100 km away of the rupture zone. Stations in the arrays are closely spaced (10-20 km) and aligned perpendicular to the trench, i.e., parallel to the expected gradient of surface coseismic displacement. In the case of Sumatra and Java, the GPS-Shield arrays should be placed at Mentawaii Islandes, located between the trench and Sumatra and directly at the Sumatra and Java western coasts where no islands are present. We demonstrate that the 'GPS Shield' can also be applied to northern Chile, where giant earthquake may also occur in the near future. Moreover, this concept may be applied globally, to many other tsunamigenic active margins where the land is located above or close to seismogenic zones.
International Association of Geodesy Symposia, 1993
ABSTRACT The GeoForschungsZentrum (GFZ) Potsdam has been selected as one of the analysing centres... more ABSTRACT The GeoForschungsZentrum (GFZ) Potsdam has been selected as one of the analysing centres for the International Geodynamics CPS Service (IGS). This paper discusses the GPS tracking data management procedures at GFZ during the IGS campaign from June 21 to October 31, 1992.
The German satellite CHAMP (Challenging mini-satellite Payload), launched in mid- 2000, exploits ... more The German satellite CHAMP (Challenging mini-satellite Payload), launched in mid- 2000, exploits radio signals from the GPS (Global Positioning System) satellite con- stellation for the remote sensing of upper tropospheric and stratospheric temperatures. Due to the limb sounding geometry of the measurements, CHAMP's radio occultation measurements provide a high vertical vertical resolution in the tropopause region. The accuracy of the temperature soundings is also highest in the vicinity of the tropopause. Since the first measurements taken in early 2001, CHAMP has collected more than 40000 vertical profiles of the temperature distribution around the tropopause, and sev- eral multi-week periods of continuous measurements are available during all seasons. We intercompare tropopause temperatures, heights, pressures, and water vapor sat- uration mixing ratios obtained from CHAMP soundings with data from the global network of radiosonde data as well as with tropopause characteristic...
The Carte du Ciel (CdC) project consisted of two parts: the sky chart itself, and the Astrographi... more The Carte du Ciel (CdC) project consisted of two parts: the sky chart itself, and the Astrographic Catalogue. The plates of both series are of high value for proper motion studies due to their early epochs. We describe here technical details of modelling digitized triple images on a plate taken for the chart part of the Paris zone. The three images of each star are very close, so that they are not separable for bright stars. As a mathematical model we used the sum of three overlapping elliptical Gaussians including a saturation parameter. We found a strong photographic adjacency effect which increases the distances between the three images for each star from about 140 micrometers for faint stars to more than 300 micrometers for the brightest stars. However, thanks to the arrangement of the three images in an equilateral triangle their centre of gravity allows to derive a usable astrometric position.
The standard method for the processing of CHAMPSs (CHAllenging Minisatellite Payload) GPS occulta... more The standard method for the processing of CHAMPSs (CHAllenging Minisatellite Payload) GPS occultation data at the GeoForschungsZentrum (GFZ) Potsdam is the double difference technique to correct for satellite clock errors. In order to apply this technique the implementation of a global fiducial GPS ground network is necessary. This network (High Rate and Low Latency network) was installed jointly by GFZ and Jet Propulsion Laboratory (JPL) in preparation of the CHAMP occultation experiment and is operated jointly by both institutes. In the current configuration (January 2002) it consists of 28 stations. Various aspects of utilizing the ground station data for occultation processing are dis- cussed. E.g. a correlation between the network topology and the global distribution of ground data redundancy for occultation processing is given. Furthermore the influence of an acquisition rate reduction (compared to the standard 1 Hz rate) to the quality of the atmospheric profiles is discussed...
With the launch of JASON-1 the successful mission TOPEX/Poseidon (T/P) is extended to a second de... more With the launch of JASON-1 the successful mission TOPEX/Poseidon (T/P) is extended to a second decade. Various analyses have shown that any altimetry mission is subject to performance degradation resulting in an apparent sea level rise. Comparisons of RA with in situ measurements of the instantaneous sea level at Harvest Oil Platform have been used to monitor the absolute sea level measurements of T/P, but not for other missions. However, only a combination of e.g. ENVISAT and JASON-1 gives a sufficient coverage in time and space. For the past and current missions different strategies are used for the calibration and the drift monitoring, e.g. using crossovers or tide gauges as a height reference. The disadvantage of all calibration methods is, that no direct measurement beneath the sub-satellite tracks are available for all missions and, therefore, models have to be used to account for e.g. the sea surface slope or time varying signals. As shown for ERS and Topex/Poseidon, a GPS-eq...
Since aging and other effects on the electronics of satellite radar altimeters (RA) are leading t... more Since aging and other effects on the electronics of satellite radar altimeters (RA) are leading to apparent sea level variations, absolute calibration sites become more and more important. The absolute bias and drift of RA can be determined best by simultaneous in-situ observations of the instantaneous sea level in the sub-satellite track. In the context of the Helmholtz Association's strategic project Sea Level Change (SEAL) the GFZ Potsdam has developed a ruggedized offshore GPS-buoy which is able to measure the instantaneous sea level with high accuracy. In May 2002 the buoy has been deployed at a triple crossover where the actual RA missions Topex/Jason-1, ERS-2/Envisat and GFO-1 intersect. The position is the only triple crossover in the German Bight that allows data transmission to a land station (List/Sylt) via an HF radio link. The first deployment spans more than three months, until end of August 2002, with 26 RA overflights altogether. Each data set comprises one hour ...
The paper describes some selected GNSS-based precise technologies developed and used for various ... more The paper describes some selected GNSS-based precise technologies developed and used for various maritime applications. Firstly two PVT projects are presented. GNSS-based buoys developed at GFZ Potsdam have been used for calibration of satellite altimeters and for monitoring of sea- and river water levels. Performance and accuracy of PVT can be dramatically degraded by ionospheric threads. Thus, ionospheric mitigation approaches in the PVT solutions are discussed here as well. Finally GNSS remote-sensing technology for monitoring of sea surface roughness and sea level, using reflections of GNSS signals is described. A long-term coastal experiment has been conducted in winter season 2008/09 at Disko Bay with partners (IEEC Barcelona, GFZ Potsdam and ESTEC Nordwijk) as part of the GPS-SIDS project (GPS for Sea Ice and Dry Snow remote sensing). Altimetric and scatterometric applications of ocean reflected signals have been studied to estimate instantaneous sea surface height (SSH) and ...
In this paper, we assess the performance of a sequential Monte Carlo based filter called Cost-Ref... more In this paper, we assess the performance of a sequential Monte Carlo based filter called Cost-Reference Particle Filter (CRPF) in comparison to Extended Kalman Filter (EKF) and Hyperbolic Positioning (HP) based on the time difference of arrival approach for dynamic target tracking. Our results show that CRPF performs better than EKF which in turn performs better than HP. The paper highlights the robustness of CRPF to model inaccuracies which are common in most practical filter implementation problems. The findings of the paper suggest that usage of the CRPF is a promising technique to tackle the problems of random dynamic systems with unknown statistics in ultra-wideband based localization techniques in challenging indoor environments.
Ionospheric disturbances are fast and random variabilities in the ionosphere and they are difficu... more Ionospheric disturbances are fast and random variabilities in the ionosphere and they are difficult to detect and model. Some strong disturbances can cause, among others, interruption of GNSS signal or even lead to loss of signal lock. These phenomena are especially harmful for kinematic real-time applications, where the system availability is one of the most important parameters influencing positioning reliability. Our investigations were conducted using long time series of GNSS observations gathered at high latitude, where ionospheric disturbances more frequently occur. Selected processing strategy was used to monitor ionospheric signatures in time series of the coordinates. Quality of the data of input and of the processing results were examined and described by a set of proposed parameters. Variations in the coordinates were compared with available information about the state of ionosphere derived from Neustrelitz TEC Model (NTCM) and with the time series of raw observations. So...
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