Calculation Of Gravity Anomalies Over The South China Sea Derived From ICESat-2 Sea Surface Height Data

Since the 1970s,the use of satellite altimetry data to invert ocean gravity anomalies has attracted increasing attention from scholars at home and abroad.Using the vertical deviation as the input data is the mainstream method to invert the ocean gravity anomaly,and the traditional altimetric satellite data include pulse radar,Interferometric Radar Altimeter(InRA)mode and Synthetic Aperture Radar(SAR)mode.However,their flight period is short and they need to adjust their orbits between different periods to accomplish global coverage.The orbital inclination of the satellite tends to be approximately north-south direction,and the deflection of vertical(DOV)between the two span orbits is less accurate in the east-west direction due to the time-varying sea surface effect and other effects.This paper is based on the new Lidar altimetry satellite ICESat-2(The Ice,Cloud and Land Elevation Satellite-2)sea surface height(SSH)data,we calculate the DOV in the cross-orbit direction for its multi-beam simultaneous observation characteristics.At the same time,the accuracy of the sea surface height is verified with the Jason-2 satellite data in the same time series.The inverse Vening-Meinesz formula is used to invert the 2’×2’ ocean gravity anomalies in the South China Sea(103°-120°E,0°-23°N),and it is compared with the newly released XGM2019 gravity field model and the National Centers for Environmental Information(NCEI)shipboard gravity field model.The main research contents and conclusions are as follows.(1)The principle of acquiring SSH by the new lidar altimetry satellite ICESat-2 is explained,and the photonic technology system of the Advanced Topographic Laser Altimeter System(ATLAS)on board ICESat-2 to acquire se a surface height is given.(2)ICESat-2 high accuracy assessment of the sea surface.The SSH data of ICESat-2 and Jason-2 were evaluated by inter-mission as well as intra-mission methods,and the results showed that the quality of ICESat-2 data was similar to that of Pulsed Radar altimetry satellite,and the discrepancy value of SSH self-crossing point was 14.08 cm,and the discrepancy value of Jason-2 SSH was 13.74 cm.The discrepancy value of intra-mission methods is between 12.60 cm and 22.67 cm.(3)The advantage of ICESat-2 in solving the directional components of the DOV in the cross-track direction is analyzed.The ICESat-2 DOV directional components are calculated at the crossover point,along-track point and grid point respectively,and the accuracy of the DOV prime components is greatly improved at the along-track point.In addition,the accuracy of the DOV direction component at the along-track point of the six beams is higher than that of the direct gridding of the DOV direction component at the grid point after gridding.(4)The ICESat-2 single-mission inversion gravity anomalies in the South China Sea are obtained by using the inverse Vening-Meinesz formula(one-dimensional Fourier translate method).The accuracy is 1.35 mGal and 2.47 mGal after verified with shipboard and model gravity anomaly data,respectively.ICESat-2 deserves the attention of altimetry community,and its advantages are expected to make it an alternative data source for multi-mission fusion inversion of ocean gravity field in the future.