GPS meteorology can be successfully used to model the tropospheric refraction effect on radiowave signals. We describe an approach to estimate and model the spatial distribution of the tropospheric water vapor. We refine the tomographic software package AWATOS which is based on the assimilation of GPS double difference observations. The observations are allocated to a voxel model, which is defined according to the distribution of the GPS stations. Performing a least‐squares adjustment, the refractivity of each voxel is determined. Tests of the software are performed, based on simulated and real data. The latter were obtained during a dedicated field campaign on the Big Island of Hawaii. The tomographic profiles are compared with radiosonde data. The results obtained for continuous atmospheric conditions fit well, whereas larger differences occur in discontinuous atmospheric weather conditions. Overall, an accuracy of 5–20 ppm (refractivity units) has been achieved.
S U M M A R YTropospheric water vapour is the main limiting factor in using GPS to determine crustal deformation at highest accuracy. On the other hand, it is an important variable to monitor meteorological and climatic processes. This paper discusses both aspects: the modelling of tropospheric water vapour using meteorological data as well as the determination of the integrated amount of water vapour and its spatiotemporal variation using GPS data. Switzerland has been chosen as experiment area. The Swiss continuous GPS (CGPS) network AGNES is used as a reference network, which represents a realistic scenario for GPS-based water vapour determination. Data of the Swiss numerical weather model aLMo are used for systematic comparison and validation.For the first aspect, integrated tropospheric wet refractivity values are determined from meteorological measurements and compared with GPS path delays. An overall agreement of 1 cm of zenith wet path delay was achieved. For the second aspect a tomographic approach has been developed. A total of 6720 GPS-determined profiles are compared with data of the numerical weather model and radio soundings. The results are statistically evaluated and systematically compared with each other. A correlation between the accuracy and the weather situation was found. Overall, an agreement of 5-7 ppm (refractivity unit) was obtained compared to aLMo.The use of GPS-determined path delays from a permanent GPS network is the recommended method to correct GPS measurements. In all other cases, the two methods presented (COITROPA, COMEDIE) are a feasible alternative to determine path delays accurately. Furthermore, GPS is a convenient application to determine the amount of water vapour in the troposphere. It is demonstrated that the vertical distribution of water vapour can be deduced by applying the tomographic approach.
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