BIOGRAPHY

significantly to the theory of geoide determination, and has published numerous papers on physical geodesy and GPS. He is also the general secretary of the Inter-national Association of Geodesy. Frede Madsen is a senior geodetic consultant in the Department of Geodesy at KMS. He is a past head of the department, and was in this position responsible for the introduction of GPS for geodesy in Denmark. He has worked within the area for more than 30 years, the last years with consulting tasks related to high accuracy applications of GPS. When the GPS satellite signals are transmitted through the atmosphere they are affected by the media. In the neutral atmosphere the refraction is a function of the meteorological conditions such as pressure, temperature, and humidity along the signal path, and this effect is in GPS terminology referred to as the tropospheric delay. In the GPS positioning process this effect is normally handled by utilising global tropospheric delay models. For high accuracy differential positioning based on the carrier phase observables modelling of the error is however not giving sufficiently accurate results, and other techniques must be implemented. This paper describes a solution where numerical weather predictions (NWP) are introduced in high accuracy GPS data processing. NWPs are predictions of the three dimensional meteorological conditions for a given area and point in time. A NWP can thus be used for predicting the tropospheric delay for a satellite signal by integration along the signal path through th