[1] Dual frequency GPS observables only allow the elimination of the 1st -order ionospheric term. Although higher -order ionospheric terms may cause a range bias of several centimeters, accounting for such effects is not yet a common strategy for GPS data analysis. In comparison to previous investigations a rigorous application of 2nd and 3rd -order ionospheric corrections is examined for the estimation not only of receiver positions but of all included parameters. The results reveal a linear dependence of the frame's origin on the integrated electron density. Furthermore, satellite positions are affected at the centimeter level when applying the above -mentioned corrections. Since the ionospheric correction terms show a significant impact on various GPS estimates, their consideration becomes necessary for scientific applications. Hence, the modeling of 2nd and 3rd -order ionospheric correction terms is part of the optimized strategy in an ongoing reprocessing project dealing with a global GPS network and spanning the time period from 1994 up to present time. Citation: Fritsche, M., R.
Land glacier extent and volume at the northern and southern margins of the Drake Passage have been in a state of dramatic demise since the early 1990s. Here time‐varying space gravity observations from the Gravity Recovery and Climate Experiment (GRACE) are combined with Global Positioning System (GPS) bedrock uplift data to simultaneously solve for ice loss and for solid Earth glacial isostatic adjustment (GIA) to Little Ice Age (LIA) cryospheric loading. The present‐day ice loss rates are determined to be −26 ± 6 Gt/yr and −41.5 ± 9 Gt/yr in the Southern and Northern Patagonia Ice Fields (NPI+SPI) and Antarctic Peninsula (AP), respectively. These are consistent with estimates based upon thickness and flux changes. Bounds are recovered for elastic lithosphere thicknesses of 35 ≤ h ≤ 70 km and 20 ≤ h ≤ 45 km and for upper mantle viscosities of 4–8 × 1018 Pa s and 3–10 × 1019 Pa s (using a half‐space approximation) for NPI+SPI and AP, respectively, using an iterative forward model strategy. Antarctic Peninsula ice models with a prolonged LIA, extending to A.D. 1930, are favored in all χ2 fits to the GPS uplift data. This result is largely decoupled from Earth structure assumptions. The GIA corrections account for roughly 20–60% of the space‐determined secular gravity change. Collectively, the on‐land ice losses correspond to volume increases of the oceans equivalent to 0.19 ± 0.045 mm/yr of sea level rise for the last 15 years.
[1] During the 10 years since the official start of the International GNSS Service (IGS) in 1994 considerable improvements in the processing strategies and modeling of global GPS solutions were achieved. Owing to changes at the individual IGS Analysis Centers during these years the resulting time series of global geodetic parameters are very inhomogeneous and inconsistent. A geophysical interpretation of these long series and the realization of a high-accuracy global reference frame are therefore difficult and questionable. In view of these deficiencies, the Technical Universities of Munich and Dresden decided to perform a reprocessing of a global GPS network over the last decade in a joint effort. First results of the reprocessing of 11 years of data show significant improvements in the quality and homogeneity of the estimated parameters and will allow for new geodynamic and geophysical interpretations. In the early years an improvement of the coordinate repeatability by a factor of more than 2 could be achieved. The formal errors of subdaily Earth rotation parameters could be reduced by 30%. Advanced modeling approaches like a mapping function based on numerical weather models, consideration of second-and third-order ionospheric corrections and absolute antenna phase center corrections for receivers and satellites were tested to achieve further improvements.
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