Geodesy using the Swedish Permanent GPS Network∷ Effects of snow accumulation on estimates of site positions

Jaldehag, R. T. Kenneth; Johansson, Jan M.; Davis, J. L.; Elósegui, P.

doi:10.1029/96gl00970

Cited by 45 publications

(17 citation statements)

References 5 publications

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“…Importantly, we note that the signals we simulate here are not the only subdaily signals present in GPS time series [ King et al , 2008]. Signals of tidal period (both ocean and atmospheric origins) [e.g., Tregoning and Watson , 2009], those related to accumulated snow and thermal expansion [ Jaldehag et al , 1996; Meertens et al , 1997; Penna et al , 2007], plus other signal propagation effects (e.g., mapping function, higher‐order ionosphere) and orbit modeling errors, will also be propagated into coordinate time series in a time‐varying way by the evolving GPS constellation. The importance of the temporal variability within the propagation mechanism in each of these cases remains to be examined.…”

Section: Discussionmentioning

confidence: 99%

Long GPS coordinate time series: Multipath and geometry effects

2010

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[1] Within analyses of Global Positioning System (GPS) observations, unmodeled subdaily signals propagate into long-period signals via a number of different mechanisms. In this paper, we investigate the effects of time-variable satellite geometry and the propagation of a time-constant unmodeled multipath signal. Multipath reflectors at H = 0.1 m, 0.2 m, and 1.5 m below the antenna are modeled, and their effects on GPS coordinate time series are examined. Simulated time series at 20 global IGS sites for 2000.0-2008.0 were derived using the satellite geometry as defined by daily broadcast orbits. We observe the introduction of time-variable biases in the time series of up to several millimeters. The frequency and magnitude of the signal is dependent on site location and multipath source. When adopting realistic GPS observation geometries obtained from real data (e.g., including the influence of local obstructions and hardware specific tracking), we observe generally larger levels of coordinate variation. In these cases, we observe spurious signals across the frequency domain, including very high frequency abrupt changes (offsets) in addition to secular trends. Velocity biases of more than 0.5 mm/yr are evident at some sites. The propagated signal has noise characteristics that fall between flicker and random walk and shows spectral peaks at harmonics of the draconitic year for a GPS satellite (∼351 days). When a perfectly repeating synthetic constellation is used, the simulations show near-negligible time correlated noise highlighting that subtle variations in the GPS constellation can propagate multipath signals differently over time, producing significant temporal variations in time series.

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Section: Discussionmentioning

confidence: 99%

Long GPS coordinate time series: Multipath and geometry effects

2010

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“…The simulations described here show that while time‐constant multipath or mismodeled antenna phase center variations may explain much of the subdaily signals, they are unable to explain the annual signals. Multipath which varies annually (including the effects of seasonal snow cover [ Jaldehag et al , 1996]), rather than being time constant, is a possible source of these signals, together with local soil expansion [ Langbein et al , 1999; Meertens et al , 1997] and thermal expansion at some sites. An argument against a multipath origin is that there is little difference between the 7°and 20° solutions at annual periods and very little frequency dependence to the solutions.…”

Section: Discussionmentioning

confidence: 99%

Apparent stability of GPS monumentation from short‐baseline time series

King

Williams

2009

J. Geophys. Res.

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[1] Long-running, short ((1 km) GPS baselines offer an insight into the accuracy budget of geophysical estimates inferred from GPS coordinate time series. In this paper, we report on analysis of 10 short baselines using data spanning several years and examine deviations from a constant baseline length. Annual signals with amplitude >0.5 mm are evident in various coordinate components at 6 of the 10 sites, with amplitudes exceeding 2.5 mm on two baselines. These signals are largely invariant to elevation cutoff angle. Multipath and phase center model errors are shown to probably have negligible effects at most sites at annual periods. They are therefore likely real monument motions, although linear thermal expansion is negligible at most sites. Linear trends >0.25 mm yr À1are evident on four baselines in at least one coordinate component. Subdaily signals are present at all sites at $K1 and its higher harmonics. Time-correlated noise, possibly in the form of flicker noise, dominates despite many common signals being eliminated as a result of the small baseline lengths, although it is around 1 order of magnitude smaller than for single site PPP solutions. We constrain monument random walk motion to be no more than 0.5 mm yr À1/2 . If these baseline motion results were representative of the $300 currently active IGS sites, 180 would have annual signals >0.5 mm in at least one coordinate component, 120 would have linear rates >0.25 mm yr À1, and almost all sites would have subdaily (K1, K2) signals of >0.1 mm, each solely due to local site effects.

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“…The application of mapping functions based on NWP model data-such as the isobaric mapping function used in this study-reduces the elevation dependence of the estimated ZTD parameters by 20% compared to a solution based on the NMF ). Site-specific effects like multipath signal masking or snow accumulation on top of a GPS antenna or radome can significantly influence the parameter estimation and cause errors in the ZTD estimates of up to 2 mm (Jaldehag et al 1996;Park et al 2004). Mapping functions based on NWP data are closer to reality than the NMF.…”

Section: A Accuracymentioning

confidence: 99%

Validation of Precipitable Water Vapor within the NCEP/DOE Reanalysis Using Global GPS Observations from One Decade

et al. 2010

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In contrast to previous studies validating numerical weather prediction (NWP) models using observations from the global positioning system (GPS), this paper focuses on the validation of seasonal and interannual variations in the water vapor. The main advantage of the performed validation is the independence of the GPS water vapor estimates compared to studies using water vapor datasets from radiosondes or satellite microwave radiometers that are already assimilated into the NWP models. Tropospheric parameters from a GPS reanalysis carried out in a common project of the Technical Universities in Munich and Dresden were converted into precipitable water (PW) using surface pressure observations from the WMO and mean atmospheric temperature data from ECMWF. PW time series were generated for 141 globally distributed GPS sites covering the time period from the beginning of 1994 to the end of 2004. The GPS-derived PW time series were carefully examined for their homogeneity. The validation of the NWP model from NCEP shows that the differences between the modeled and observed PW values are time dependent. In addition to establishing a long-term mean, this study also validates the seasonal cycle and interannual variations in the PW. Over Europe and large parts of North America the seasonal cycle and the interannual variations in the PW from GPS and NCEP agree very well. The results reveal a submillimeter accuracy of the GPS-derived PW anomalies. In the regions mentioned above, NCEP provides a highly accurate database for studies of longterm changes in the atmospheric water vapor. However, in the Southern Hemisphere large differences in the seasonal signals and in the PW anomalies were found between GPS and NCEP. The seasonal signal of the PW is underestimated by NCEP in the tropics and in Antarctica by up to 40% and 25%, respectively. Climate change studies based on water vapor data from NCEP should consider the large uncertainties in the analysis when interpreting these data, especially in the tropics.

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Geodesy using the Swedish Permanent GPS Network∷ Effects of snow accumulation on estimates of site positions

Cited by 45 publications

References 5 publications

Long GPS coordinate time series: Multipath and geometry effects

Long GPS coordinate time series: Multipath and geometry effects

Apparent stability of GPS monumentation from short‐baseline time series

Validation of Precipitable Water Vapor within the NCEP/DOE Reanalysis Using Global GPS Observations from One Decade

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