Contribution Analysis of the SGG Observation from Different GOCE Orbital Altitudes to Static Gravity Field Solution

The Satellite Gravity Gradiometry (SGG) data from the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellite demonstrated unprecedented accuracy in estimating the gravity field model across medium and long wavelengths. However, the GOCE satellite re-entered Earth’s atmosphere in Nov. 2013. Leveraging SGG data for gravity field estimation will be a prominent research focus within the Next-Generation Gravity Mission (NGGM) to enhance further the spatial resolution and accuracy of solved gravity field models. During the final 15 months of the GOCE mission, there was a notable reduction in orbital altitude from 259.5 to 229 km. This decline provides essential data for assessing how different orbital altitudes affect static gravity field estimation. Based on Tongji-GMMG2021S (Gravity field Model from Multi-Gravity observation [Satellites]), this paper conducts a quantitative analysis, leading to the following conclusions: (1) The Tongji-GMMG2021S model derived from reprocessed Level-1b SGG data and the normal equation of Tongji-Grace02s, exhibits spatial and accuracy levels comparable to those of the GOCO06s model. (2) The contribution analysis at the normal matrix level shows that SGG data primarily contributes between 95 and 260 degrees to the Tongji-GMMG2021S normal matrix. (3) In terms of the geoid grid height difference to the Tongji-GMMG2021S model in the spatial domain, the period of Low Orbital Altitude from Aug. 2012 to Oct. 2013 significantly contributes to reducing residuals compared to the period of Higher Orbital Altitude from Nov. 2009 to Jul. 2012. These findings also provide a valuable reference for balancing the orbital altitude of NGGMs, the lifespan of NGGMs operational and the accuracy of the gravity field models.