Abstract: The accuracy, availability and reliability of shore-based GPS-R retrieval of water surface height are closely related to the azimuth, incident angle, effective arc length and number of visible satellites falling into the specified water area at the station. In order to improve the observation efficiency of inversion points, this paper comprehensively considers various factors such as the first Fresnel zone, the relationship between the station and the orientation of the water system, and the selection of the range of incidence angles for different water system types, then proposes the concept of inversion event and establish the optimization strategy of shore-based GPS-R spatio-temporal layout. The designed simulation experiment and the measured data are verified, and the results show that the both have good consistency. However, due to the existing GPS constellation structure, the distribution of inversion events by users in the northern hemisphere presents the characteristics of “the most in the north, followed by east and west”. Therefore, the optimization strategy based on inversion events can effectively carry out the evaluation and selection of candidate sites in the survey area. At the same time, according to the inversion events, the optimal period of the station and its periodic change law can be further screened, so as to verify that the research on the optimization of the space-time layout of the station can effectively guarantee the high efficiency and quality of the shore-based GPS-R inversion of water surface, and promote the GPS-R technology promotion from theory to application. The full use of GNSS permanent observation stations deployed around large and medium-sized reservoir dams, reservoir bank slopes, and coasts in our country at this stage are important references for the application of GPS-R inversion of water surface height.

Key words: GPS-R, space-time layout optimization, fresnel reflection zone, reverse event, multipath