Considering that long-arc techniques is more likely to suppress the influence of atmospheric and oceanic mixing noise and observation errors, and amplifying the effect of small signals on low orbit satellites, we further optimize the short arc method based on the modified short arc method. By introducing position parameters into the boundary orbit of the integral arc segment and separating the GRACE orbit from the inter-satellite distance observation equation, the direct inversion of large-scale matrices is avoided, effectively reducing the condition number of the normal equation matrix, and successfully extending the arc length to 6 hours. The optimized short arc method effectively reduces the high-frequency noise of the time-variable gravity field model. Based on the optimized short arc method, we process GRACE Level1b RL03 observation data from April 2002 to December 2016, and solve 90 degree and order Tongji Grace 2018 time-variable gravity field model.

Corresponing author：Professor Qiujie Chen (qiujiechen@tongji.edu.cn)

The Tongji-Grace2018 solutions can be directly downloaded from the website of https://workdrive.zohopublic.com.cn/external/ec51983596e71232983774fb217bdf08de13c02675688774d3fa870b35c4dda8.

When using this data, please cite the following publications which provide details about the approach and the models used.

Chen Q, Shen Y, Chen W, Francis O, Zhang X, Chen Q, Li W, Chen T.(2019). An optimized short-arc approach: Methodology and application to develop refined time series of Tongji-Grace2018 GRACE monthly solutions. Journal of Geophysical Research: Solid Earth, 124(6): 6010-6038.

Chen Q, Shen Y, Francis O, Chen W, Zhang X, Hsu H (2018). Tongji-Grace02s and Tongji-Grace02k: high-precision static GRACE-only global Earth's gravity field models derived by refined data processing strategies. Journal of Geophysical Research, 123(7), 6111-6137.