A study of spatial water vapor distributions by using one-way residuals ofGPS phase measurements

We investigated water vapor distribution in the troposphere, concentrating especially on meso-scale phenomena, such as a cumulus cloud, with dimension less than about 10 km in the horizontal direction by using GPS phase signa ls along their propagation paths. Slant path water vapor can be estimated f rom the GPS phase residuals obtained by subtracting the theoretical phase v alue from the observed one. We obtained the residuals as by-products of pha se data analysis with the GIPSY-OASIS II software. We analyzed a 11-day cam paign data set obtained at Yamagawa (31.2 degreesN, 130.6 degreesE), Japan in June, 1996. During the observation, four sudden weather condition change s were seen, the passage of a cold front and Baiu fronts. The fluctuation o f the residuals is dominated by their dependence on elevation angles of the GPS Satellites rather than the fine variation of water vapor. Thus, we cor rected the residuals by subtracting the elevation-angle-dependence, which w as obtained by means of the residuals, for each elevation angle over the en tire observation period. The water vapor distribution calculated from the c orrected residuals showed more realistic features that correspond to fronta l structures. However, this correlation occurred only in several cases of c hanges of weather condition with the passage of fronts. We further obtained good consistency with the corrected residuals even among the different typ es of antennas which were located within a few meters by using the another data-sets of past campaigns which were carried out on the campus of Nagoya Univ. (35.2 degreesN, 137.0 degreesE), Japan in October.