The accuracy of GPS data analysis for the vertical component has reached a level where the vertical crustal deformation due to the ocean tidal loading should be taken into consideration. Ocean loading affects in particular the results of the GPS analysis for those observation sets covering less than 24 hours. Especially in these cases, a correction for this phenomenon should be performed during the data analysis. On the other hand, it is possible to estimate the ocean loading effect from GPS data sets. In this way it is possible to validate models for the loading deformation derived from global ocean tide models. Keywords ocean tide models, ocean loading effect, GPS heightsIn the Bernese GPS Software, Version 4.0 (Beutler et al. 1996) solid earth tides are taken into account in the data analysis as the only periodic crustal deformation. The vertical deformation due to ocean tidal loading is not modeled. The frequencies of the main ocean tides are in the diurnal and semidiurnal band. Consequently, if one has solutions from exactly 24 hours of GPS observations-which is usually the case for the IGS data analysis-the in uence of ocean loading on the station heights can be assumed to be very small.On the other hand, the ocean loading effect can rise up to values of several centimeters for coastal stations, see e.g., Baker, Curtis, and Dodson (1995). The Bernese GPS Software applies an algorithm for the parameter estimation using double differences of the observations. Therefore, the difference of the ocean loading effect between the two stations of a baseline is essential for GPS data analysis. For a baseline with a length of about 100 km directed inland from the coast, this effect may have a magnitude of 1 cm. If one takes into account the actual accuracy of the GPS solutions, also for the vertical component, the ocean loading effect should be taken into detailed consideration.To investigate the in uence of the ocean loading effect on the results of GPS analysis, several modi cations in the source code of the Bernese GPS Software, Version 4.0, were performed for the investigations presented here:
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