Measuring Tropospheric Delay from a Floating GPS Receiver

摘要

Obtaining accurate measurements of atmospheric water vapour content and its variability is important for both meteorological applications and climate research. During the last decade considerable research has been carried out to develop a technique of estimating tropospheric delay using static GPS. The tropospheric delay estimates can then be converted into estimates of atmospheric water vapour, which can be used in weather prediction models. It has been shown that it is possible to obtain estimates of atmospheric water vapour using static GPS to within 1-2 kg/m{sup}2 of WVR and radiosonde measurements (Rocken et al, 1997, Dodson and Baker, 1998a). It would be beneficial to extend this technique so that tropospheric delay can be estimated using moving GPS receivers. Estimates of tropospheric delay, and hence atmospheric water vapour, could then be obtained from offshore locations, which would provide a valuable calibration tool for Space Based WVRs, and allow much higher temporal resolution of atmospheric water vapour. Removing the tropospheric delay from the GPS observations may also improve the accuracy of the position estimates that can be obtained from kinematic processing over baselines where the atmospheric conditions are different at each end. This could be useful for wide area networks (e.g. WAAS, EGNOS) where inaccuracies in the tropospheric model used might otherwise cause significant range and positioning errors (Dodson et al, 1999a). A technique known as the Horizontal Constraint Method was developed in Dodson et al (1999b), and this was shown to give tropospheric delay estimates at a moving receiver that were of a comparable accuracy to those obtained from the static GPS technique. This paper describes new work that has been performed to verify if the findings of Dodson et al (1999b) could be reproduced in a more dynamic environment and for longer baseline lengths. The results show that the accuracy of tropospheric delay estimates using static GPS can also be obtained using GPS data from a moving receiver, even if the baseline length is such that atmospheric conditions at the rover are different to those at the base.