GPS Application to Troposphere Monitoring

        In GPS application, in the early stage, mainly the orbit error affects the positioning accuracy, and the early GPS baseline is relatively short and the height difference is not big, so the study of the troposphere has not been given great attention. Until after the GPS orbit accuracy is greatly improved due to GPS, tropospheric refraction has become an important obstacle to limit the improvement of GPS positioning accuracy. Assuming an elevation of basically zero area, the GPS signal received by the receiver from the direction of the zenith, then, its delay can reach 2.2—2.6m this order of magnitude, and within 2 hours of this delay can reach up to 10cm is not uncommon, but also due to the actual situation, the tropospheric refraction to take into account and its stochastic process changes to be modeled.

In the application of GPS to tropospheric studies, the fast orbit and forecast orbit information from IGS can play a significant role in weather forecasting. In addition, the series of tropospheric zenith delays every 2 hours provided by IGS through the “IGS Tropospheric Comparison and Coordination Center” at the GFZ, Germany, are like control points for the

regional or localized tropospheric studies, and can serve to calibrate the absolute value of tropospheric delays.

        Unlike ground-based GPS atmospheric monitoring, the satellite-based or space-based GPS occultation technique for meteorological measurements has the advantages of wide coverage, good vertical resolution, and fast data acquisition. The principle of this technology is to put the GPS receiver on the platform of a certain low-orbit satellite (LEO) or vehicle, the GPS receiver on the one hand plays a role in the satellite (or vehicle) to determine the orbit of the role of precision, while at the same time applying GPS occultation technology to play the role of atmospheric detector. The GPS/MET research project carried out in 1997 confirmed that this idea is feasible. The CHAMP satellite, scheduled to be launched in April 2000, is to utilize the GPS occultation method for the determination of global tropospheric refraction (including atmospheric precipitable moisture).