COST-G: Status and recent developments

Three years after its inauguration we draw a very positive résumé of the work of IAG’s Combination Service for Time-variable Gravity Fields (COST-G). The operational combination of GRACE-FO monthly gravity fields runs flawlessly. All seven associated and partner analysis centres timely provide high quality gravity fields, the COST-G quality control returns reliable noise and signal assessment based on meanwhile almost 4 years of GRACE-FO data, and the evaluation confirms the robustness and low noise level of the combined products.

COST-G is a highly dynamic service that is further developed in the frame of the Horizon2020 project Global Gravity-Based Groundwater Product (G3P) project, where an alternative accelerometer transplant product was developed, which in COST-G test combinations showed a very positive effect on the C30 gravity field coefficient and led to a general noise reduction in the medium to high degree range. Moreover, a deterministic signal model based on the monthly combinations has been released for the first time in September 2021 as a new COST-G product. It is updated quarterly with the most recent GRACE-FO data and aims to support operational precise orbit determination of low Earth orbiters. For the near future an extension of COST-G to also include analysis centres from China is envisaged and plans go to a revised combination of the reprocessed GRACE time-series.