GPS and Sentinel-3 Satellite Observations Combination Using Least Squares Collocation Interpolation Method for Tropospheric Delay Model Generation

The main goal of global navigation satellite systems is to determine the precise coordinate of points in all weather conditions. On the other hand, the waves transmitted from the satellites of these systems pass through different layers of the atmosphere such as the troposphere, and this leads to refraction in the path of the wave and ultimately delays in receiving the waves. Therefore, the study of the troposphere and its effects on the signals of the global positioning system is particularly important. The tropospheric delay is divided into two parts, dry and wet, which due to the dependence of the wet part on water vapor changes is the most challenging part of the tropospheric delay.  The aim of this paper is modeling of tropospheric zenith wet delay in Los Angeles in the United States, utilizing a combination of OLCI sensor data of Sentinel-3 satellite with high spatial resolution and data from 97 high temporal resolution GPS stations in this area. The least-squares collocation method is applied for spatio-temporal modeling of the tropospheric zenith wet delay. In order to estimate the trend in the least-squares collocation method, a combination of data from the above two sources was used and a four-dimensional (temporal-spatial) surface was fitted to the tropospheric zenith wet delay data obtained from the OLCI sensor and GPS stations. In the estimation of the observation signal part, instead of considering a spatial-temporal covariance function, the modeling time interval is divided into smaller sub-intervals and the spatial covariance functions are estimated in each sub-interval. The results of the article method and Sastamoinen model which uses the analyzed GFS data were compared with control points values. The RMS of estimated zenith wet delay in control points by least squares collocation was 1.86 centimeter, while the RMS of the Sastamoinen method is 15.97 centimeters.