SHAtrop: Empirical ZTD Model Based on CMONOC GNSS Network

Modelling errors of tropospheric delay have much impact on the application of the Global Navigation Satellite System (GNSS). Temporal and spatial characteristics of the zenith tropospheric delay (ZTD) over mainland China are analyzed using the Crustal Movement Observation Network of China (CMONOC) GNSS network over 6 years. Annual ZTD of each site exhibits an exponential function of sites' altitude in spatial frame, and the temporal variation exhibits both annual and semi-annual periods. Therefore, we establish a new empirical ZTD model:SHAtrop. It combines the exponential and periodical functions and is provided as grids covering mainland China with a resolution of 2.5°×2.0°. Using the SHAtrop model, the ZTD over the ellipsoid is firstly calculated using the gridded parameters, and then the site's true ZTD is derived using the exponential function. The validation using 220 GNSS sites over 6 years shows that the precision of SHAtrop is of 3.4 cm in root mean square (RMS) quantity. The SHAtrop is easy to implement, where the input parameters are the station's location and time. Thanks to the use of the long ZTD time series of the densified GNSS network in mainland China, the SHAtrop has better performance and finer regional resolution.