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P J Clarke - One of the best experts on this subject based on the ideXlab platform.
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ocean tide loading displacements in western europe 1 validation of kinematic gps estimates
Journal of Geophysical Research, 2015Co-Authors: Nigel T. Penna, P J Clarke, M S Bos, T F BakerAbstract:GPS has been extensively used to estimate tidal ground displacements, but the accuracy of this has not been systematically verified. Using more than 20 sites distributed across western Europe, we show that postprocessed kinematic precise point positioning GPS with appropriately tuned process noise constraints is capable of recovering synthetic tidal displacements inserted into real data, with a typical accuracy of 0.2 mm depending on the time series noise. The kinematic method does not result in erroneous propagation of signals from one Coordinate Component to another or to the simultaneously estimated tropospheric delay parameters. It is robust to the likely effects of day-to-day equipment and reference frame changes, and to outages in the data. A minimum data span of 4 years with at least 70% availability is recommended. Finally, we show that the method of reducing apparent Coordinate time series noise by constraining the tropospheric delay to values previously estimated in static batch GPS analysis, in fact, results in the suppression of true tidal signals. Using our kinematic GPS analysis approach, periodic displacements can be reliably observed at the 0.2 mm level, which is suitable for the testing and refinement of ocean tide and solid Earth response models.
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validation of ocean tide models around antarctica using onshore gps and gravity data
Journal of Geophysical Research, 2005Co-Authors: Matt A King, N T Penna, P J Clarke, Edward C KingAbstract:Ocean tide models around Antarctica are presently only sparsely tested against independent data. Ocean tide modeling errors, along with subsequent ocean tide loading (OTL) displacement modeling errors, alias into altimetry and time variable gravity (e.g., Gravity Recovery and Climate Experiment (GRACE)) time series, for example. To validate various ocean tide models around Antarctica, GPS data from 15 sites have been used to derive three-dimensional displacement estimates at eight diurnal and semidiurnal tidal frequencies. Using hundreds of days of GPS data, harmonic parameters were estimated on a daily basis then combined. These were then compared with OTL displacement estimates derived from global and regional ocean tide models. In East Antarctica, where the tides are well defined, submillimeter differences are demonstrated in each Coordinate Component with the lunar N2 and Q1 constituents in closest agreement. As found in other studies, K1 and, especially, K2 agree less well. The spatial variation in the misfits for these two constituents indicates a site dependency, with the K2 errors also suggesting an interaction with satellite-dependent effects. In West Antarctica, where sites are nearer the largest ice shelves, agreement with the older models (CSR3 and TPXO.2) and NAO.99b is poor for all constituents. Modeled tidal gravity variations were also compared with gravity measurements at the South Pole. Overall the GPS and gravity data agree best with newer tide models, namely, TPXO.6, CADA00.10, FES99, and CATS02.01. However, validation data are lacking at the southern extents of the large ice shelves, and hence some uncertainty still exists in all ocean tide models in these regions.
Nigel T. Penna - One of the best experts on this subject based on the ideXlab platform.
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ocean tide loading displacements in western europe 1 validation of kinematic gps estimates
Journal of Geophysical Research, 2015Co-Authors: Nigel T. Penna, P J Clarke, M S Bos, T F BakerAbstract:GPS has been extensively used to estimate tidal ground displacements, but the accuracy of this has not been systematically verified. Using more than 20 sites distributed across western Europe, we show that postprocessed kinematic precise point positioning GPS with appropriately tuned process noise constraints is capable of recovering synthetic tidal displacements inserted into real data, with a typical accuracy of 0.2 mm depending on the time series noise. The kinematic method does not result in erroneous propagation of signals from one Coordinate Component to another or to the simultaneously estimated tropospheric delay parameters. It is robust to the likely effects of day-to-day equipment and reference frame changes, and to outages in the data. A minimum data span of 4 years with at least 70% availability is recommended. Finally, we show that the method of reducing apparent Coordinate time series noise by constraining the tropospheric delay to values previously estimated in static batch GPS analysis, in fact, results in the suppression of true tidal signals. Using our kinematic GPS analysis approach, periodic displacements can be reliably observed at the 0.2 mm level, which is suitable for the testing and refinement of ocean tide and solid Earth response models.
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gps height time series short period origins of spurious long period signals
Journal of Geophysical Research, 2007Co-Authors: Nigel T. Penna, Matt A King, Mike StewartAbstract:GPS height time series used in geophysical studies are often formed from discrete, continuous, nonoverlapping 24 hour processing sessions. With such a strategy, unmodeled periodic ground displacements with approximately semidiurnal and diurnal periods have often been assumed to average close to zero. By analyzing several years of continuous GPS data from globally distributed sites at which controlled errors were not modeled, this paper shows such an assumption to be erroneous. It is shown that each unmodeled (sub-) daily periodic displacement can propagate to several spurious long-wavelength features in a GPS height time series, ranging in period from about 2 weeks to 1 year. Admittances (ratio of amplitude of spurious long-wavelength output signal in the GPS height time series to amplitude of unmodeled periodic ground displacement) depend on the Coordinate Component and the tidal constituent considered. For example, it is shown that an unmodeled S2 north Component periodic ground displacement can propagate to a semiannual height signal with admittance of greater than 100%, whereas the height admittance is around 5-10%. Since model errors in ocean tide loading, atmospheric pressure loading, and solid earth tide displacement amplitudes can be several millimeters, long-wavelength spurious signals of up to these amplitudes may be expected to appear in GPS height time series. This paper provides an indication of how such errors will propagate, where such errors are greatest and hence how spurious fortnightly, semiannual, and, in some cases, annual effects may be present at some sites. Copyright 2007 by the American Geophysical Union.
Matt A King - One of the best experts on this subject based on the ideXlab platform.
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gps height time series short period origins of spurious long period signals
Journal of Geophysical Research, 2007Co-Authors: Nigel T. Penna, Matt A King, Mike StewartAbstract:GPS height time series used in geophysical studies are often formed from discrete, continuous, nonoverlapping 24 hour processing sessions. With such a strategy, unmodeled periodic ground displacements with approximately semidiurnal and diurnal periods have often been assumed to average close to zero. By analyzing several years of continuous GPS data from globally distributed sites at which controlled errors were not modeled, this paper shows such an assumption to be erroneous. It is shown that each unmodeled (sub-) daily periodic displacement can propagate to several spurious long-wavelength features in a GPS height time series, ranging in period from about 2 weeks to 1 year. Admittances (ratio of amplitude of spurious long-wavelength output signal in the GPS height time series to amplitude of unmodeled periodic ground displacement) depend on the Coordinate Component and the tidal constituent considered. For example, it is shown that an unmodeled S2 north Component periodic ground displacement can propagate to a semiannual height signal with admittance of greater than 100%, whereas the height admittance is around 5-10%. Since model errors in ocean tide loading, atmospheric pressure loading, and solid earth tide displacement amplitudes can be several millimeters, long-wavelength spurious signals of up to these amplitudes may be expected to appear in GPS height time series. This paper provides an indication of how such errors will propagate, where such errors are greatest and hence how spurious fortnightly, semiannual, and, in some cases, annual effects may be present at some sites. Copyright 2007 by the American Geophysical Union.
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validation of ocean tide models around antarctica using onshore gps and gravity data
Journal of Geophysical Research, 2005Co-Authors: Matt A King, N T Penna, P J Clarke, Edward C KingAbstract:Ocean tide models around Antarctica are presently only sparsely tested against independent data. Ocean tide modeling errors, along with subsequent ocean tide loading (OTL) displacement modeling errors, alias into altimetry and time variable gravity (e.g., Gravity Recovery and Climate Experiment (GRACE)) time series, for example. To validate various ocean tide models around Antarctica, GPS data from 15 sites have been used to derive three-dimensional displacement estimates at eight diurnal and semidiurnal tidal frequencies. Using hundreds of days of GPS data, harmonic parameters were estimated on a daily basis then combined. These were then compared with OTL displacement estimates derived from global and regional ocean tide models. In East Antarctica, where the tides are well defined, submillimeter differences are demonstrated in each Coordinate Component with the lunar N2 and Q1 constituents in closest agreement. As found in other studies, K1 and, especially, K2 agree less well. The spatial variation in the misfits for these two constituents indicates a site dependency, with the K2 errors also suggesting an interaction with satellite-dependent effects. In West Antarctica, where sites are nearer the largest ice shelves, agreement with the older models (CSR3 and TPXO.2) and NAO.99b is poor for all constituents. Modeled tidal gravity variations were also compared with gravity measurements at the South Pole. Overall the GPS and gravity data agree best with newer tide models, namely, TPXO.6, CADA00.10, FES99, and CATS02.01. However, validation data are lacking at the southern extents of the large ice shelves, and hence some uncertainty still exists in all ocean tide models in these regions.
Edward C King - One of the best experts on this subject based on the ideXlab platform.
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validation of ocean tide models around antarctica using onshore gps and gravity data
Journal of Geophysical Research, 2005Co-Authors: Matt A King, N T Penna, P J Clarke, Edward C KingAbstract:Ocean tide models around Antarctica are presently only sparsely tested against independent data. Ocean tide modeling errors, along with subsequent ocean tide loading (OTL) displacement modeling errors, alias into altimetry and time variable gravity (e.g., Gravity Recovery and Climate Experiment (GRACE)) time series, for example. To validate various ocean tide models around Antarctica, GPS data from 15 sites have been used to derive three-dimensional displacement estimates at eight diurnal and semidiurnal tidal frequencies. Using hundreds of days of GPS data, harmonic parameters were estimated on a daily basis then combined. These were then compared with OTL displacement estimates derived from global and regional ocean tide models. In East Antarctica, where the tides are well defined, submillimeter differences are demonstrated in each Coordinate Component with the lunar N2 and Q1 constituents in closest agreement. As found in other studies, K1 and, especially, K2 agree less well. The spatial variation in the misfits for these two constituents indicates a site dependency, with the K2 errors also suggesting an interaction with satellite-dependent effects. In West Antarctica, where sites are nearer the largest ice shelves, agreement with the older models (CSR3 and TPXO.2) and NAO.99b is poor for all constituents. Modeled tidal gravity variations were also compared with gravity measurements at the South Pole. Overall the GPS and gravity data agree best with newer tide models, namely, TPXO.6, CADA00.10, FES99, and CATS02.01. However, validation data are lacking at the southern extents of the large ice shelves, and hence some uncertainty still exists in all ocean tide models in these regions.
T F Baker - One of the best experts on this subject based on the ideXlab platform.
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ocean tide loading displacements in western europe 1 validation of kinematic gps estimates
Journal of Geophysical Research, 2015Co-Authors: Nigel T. Penna, P J Clarke, M S Bos, T F BakerAbstract:GPS has been extensively used to estimate tidal ground displacements, but the accuracy of this has not been systematically verified. Using more than 20 sites distributed across western Europe, we show that postprocessed kinematic precise point positioning GPS with appropriately tuned process noise constraints is capable of recovering synthetic tidal displacements inserted into real data, with a typical accuracy of 0.2 mm depending on the time series noise. The kinematic method does not result in erroneous propagation of signals from one Coordinate Component to another or to the simultaneously estimated tropospheric delay parameters. It is robust to the likely effects of day-to-day equipment and reference frame changes, and to outages in the data. A minimum data span of 4 years with at least 70% availability is recommended. Finally, we show that the method of reducing apparent Coordinate time series noise by constraining the tropospheric delay to values previously estimated in static batch GPS analysis, in fact, results in the suppression of true tidal signals. Using our kinematic GPS analysis approach, periodic displacements can be reliably observed at the 0.2 mm level, which is suitable for the testing and refinement of ocean tide and solid Earth response models.