Precise determination of ocean tide loading gravity effect for absolute gravity stations in coastal area of China: Effects of land–sea boundary and station coordinate

• A high-resolution land–sea boundary is indispensable for coastal stations where the shoreline is more complex.
• SRTM DEM is effective for land–sea boundary definition for OTL gravity computation.
• OTL gravity effect is very sensitive, in different extents, to the accuracies of the horizontal and vertical coordinates.

Gravity effect due to ocean tide loading (OTL) is an important signal and correction in various gravimetric applications. In this paper, we assessed the OTL gravity effects at four absolute gravity (AG) stations in coastal China from several perspectives. The integrated Green's function of the Newtonian part was derived analytically and that of the elastic part was computed based on the PREM earth model. Ocean tide (OT) records near the four AG stations were used to enhance the accuracy of the global ocean tide model of NAO99b and the regional model of NAO99jb for the innermost field (<0.02°). The high-resolution digital elevation model (DEM) from the Shuttle Radar Topography Mission (SRTM) was used to define the land–sea boundary in the optimized near field (<1.0°). Results show that the high-resolution land–sea boundary is indispensible for OTL gravity modeling when the shoreline near a coastal station is complex. The SRTM-based OTL model outperforms the GMT-based model shoreline in terms of the agreement between modeled and observed gravity residuals at the four stations. The final gravity residuals, corrected for OTL, at the four stations are significantly smaller than those without OTL corrections. We give examples of accuracy requirements in coordinates at Qingdao for different station heights. At a station height of 80 m and to ensure a 0.1 μgal accuracy in OTL modeling, the required accuracies in the horizontal and vertical coordinate are 2.5 and 1. 3 m, respectively. For a new coastal station and an expected OTL accuracy, one should inspect the variation of OTL due to coordinate variation to find a best strategy to determine the required accuracy of coordinate.