## GPS Reprocessing

### Motivation

A global network of nowadays 370 stations is operated by the International GNSS Service (IGS) since its official start in 1994. Nine analysis centers process subsets of this network in near-realtime, and their results are combined to the official IGS products. During the first ten years of IGS, considerable improvements in the processing strategies and modeling of global GPS solutions were achieved. Thus, the resulting operational time series of global geodetic parameters are very inhomogeneous and inconsistent. In view of these deficiencies TU München and TU Dresden decided to reprocess more than a decade of GPS data with a consistent strategy. This GPS reprocessing project GPS-PDR (Potsdam Dresden Reprocessing) was later continued by GFZ Potsdam and TU Dresden. The Bernese GPS Software and a processing scheme similar to the one used at the CODE IGS analysis center in Bern were used.

### Orbit Quality

The figure above shows the internal consistency of the operational CODE orbits and the reprocessed orbits. 3-day orbit arcs were ﬁtted through three consecutive 1-day orbits, the mean RMS of the 3-day arc w.r.t. the three 1-day arcs serves as quality indicator. A significant improvement can be seen in the first years. The quality of the CODE orbits clearly gets better in June 2000 when the orbit modeling was changed. After switching to an improved ambiguity resolution strategy at the beginning of 2002 the internal consistency of the CODE and the reprocessed orbits is on almost the same level.

#### Station Coordinate Repeatability

The repeatabilities of seven single coordinate solutions, used for the weekly solutions, compared to the weekly solutions are shown in the figure above for the reprocessed time series and the operational CODE series. Two changes are striking in the CODE series: at the beginning of 1998 the reference frame used for datum definition was changed and the number of datum stations grew from 13 to 47. Starting with the same date, station displacement due to ocean loading is corrected for. Both changes cause an improvement of the repeatability by a factor of about two. At the beginning of 2002 an improved ambiguity resolution strategy was implemented at the CODE analysis center. It is the same strategy that is also used for reprocessing. The effects on the coordinate repeatability are clearly visible: in particular the east-west component benefits from the improved ambiguity resolution. After this change the repeatabilities of the CODE and the reprocessed solution are on almost the same level.

### Data Download

GPS satellite orbits and Earth rotation parameters from the GPS reprocessing are available at the following data centers:

### Publications

Steigenberger, P.; Rothacher, M.; Dietrich, R.; Fritsche, M.; Rülke, A.; Vey, S.: **Reprocessing of a global GPS network**; Journal of Geophysical Research, Vol. 111, DOI: 10.1029/2005JB003747, 05/2006

Fritsche, M.; Dietrich, R.; Knöfel, C.; Rülke, A.; Vey, S.; Rothacher, M.; Steigenberger, P.: **Impact of higher-order ionospheric terms on GPS estimates**; Geophysical Research Letters, Vol. 32, No. 23, DOI: 10.1029/2005GL024342, 12/2005

Fritsche, M.; Dietrich, R.; Rülke, A.; Rothacher, M.; Steigenberger, P.: **Low-degree Earth deformation from reprocessed GPS observations**; GPS Solutions, Vol. 14, Nr. 2, pp 165-175, Springer, ISSN 1521-1886, DOI: 10.1007/s10291-009-0130-7, 2010

Rülke, A.; Dietrich, R.; Fritsche, M.; Rothacher, M.; Steigenberger, P.: **Realization of the Terrestrial Reference System by a reprocessed global GPS network**; Journal of Geophysical Research, Vol. 113, DOI: 10.1029/2007JB005231, 08/2008

Steigenberger, P.; Tesmer, V.; Krügel, M.; Thaller, D.; Schmid, R.; Vey, S.; Rothacher, M.: **Comparisons of homogeneously reprocessed GPS and VLBI long time-series of troposphere zenith delays and gradients**; Journal of Geodesy, Vol. 81, No. 6-8, pp 503-514, DOI: 10.1007/s00190-006-0124-y, 06/2007, Externer Link

Steigenberger, P.; Rothacher, M.; Fritsche, M.; Rülke, A.; Dietrich, R.: **Quality of reprocessed GPS satellite orbits**; Journal of Geodesy, Vol. 83, Nr. 3-4, pp 241-248, Springer, ISSN 0949-7714, DOI: 10.1007/s00190-008-0228-7, 2/2009.

Vey, S.; Dietrich, R.; Fritsche, M.; Rülke, A.; Rothacher, M.; Steigenberger, P.: **Influence of mapping function parameters on global GPS network analyses: Comparisons between NMF and IMF**; Geophysical Research Letters, Vol. 33, DOI: 10.1029/2005GL024361, 01/2006

Vey, S.; Dietrich, R.; Rülke, A.; Fritsche, M.; Steigenberger, P.; Rothacher, M.: **Validation of precipitable water vapor within the NCEP-DOE reanalysis using global GPS observations from one decade**; Journal of Climate, Vol. 23, Nr. 7, pp 1675-1695, DOI: 10.1175/2009JCLI2787.1 , 2010

### Links

- GGOS-D project