## 2 Experimental Data  
To simulate spaceborne GNSS-R SSH interferometric altimetry data, the GNSS-R specular point trajectory data from the FY-3E and FY-3F satellites were utilized as input. The FY-3E and FY-3F satellites were launched in July 2021 and August 2023, respectively, and have formed a three-satellite constellation observation with the FY-3G satellite, which was launched in April 2023 [61]. All of these satellites carry the GNOS-II payload, which is capable of receiving GNSS reflection signals from the earth's surface through eight signal-receiving channels, including GPS, BDS, and GALILEO. However, compared to the FY-3G satellite with an orbital altitude of 407 km and an inclination angle of 50\({}^{\circ}\), the FY-3E and FY-3F satellites are more ideal for global SSH observations with an orbital altitude of 836 km and an inclination angle of 98.75\({}^{\circ}\), aligning with the orbit parameters of geodetic missions. Therefore, the Level 2 (L2) GNSS-R specular points trajectory of FY-3E/F satellites in October 2023 are utilized to evaluate the ability to detect global monthly marine gravity anomalies through spaceborne GNSS-R interferometry altimetry. Figure 2 displays the daily trajectory map of specular points for FY-3E and FY-3F. It can be observed that the specular points trajectories of these two satellites are adjacent, which allows them to complement each other and improve the coverage of spaceborne GNSS-R through constellation observation. In addition, due to strict data control and filtering of L2 data, the number of observation strips of each satellite does not always reach the maximum observable number. After calculation, in the selected L2 data for October 2023, FY-3E satellite utilized an average of 3.5 channels out of 8 channels, while FY-3F utilized an average of 3.8 channels. In recent years, spaceborne GNSS-R interferometric altimetry performance and methodologies have been extensively studied and optimized. However, the PARIS interferometric altimetry performance model proposed by [PERSON] (2011) remains the most classic and representative achievement in this field [50]. Therefore, this study adopts it as the theoretical foundation and a typical representation of GNSS-R interferometric altimetry performance. According to the error budget table analyzed by [PERSON], the antenna gain for PARIS in IOD and Operational scenarios are 23 dBi and 30 dBi, respectively, with orbital altitudes of 800 km and 1500 km. After incoherently integrating power waveforms from multiple samples and considering correction accuracies for instrument noise, ionosphere, troposphere, electromagnetic bias, skewness bias, and orbit, the altimetry accuracy can reach 17.5 cm and 7.5 cm at the edge of a swath with a 100 km along-track resolution. This altimetric performance can meet the detection requirements of its main target of ocean mesoscale studies. To meet the detection requirements for high-frequency information of gravity field, the minimum along-track resolution (10 km) achieved by spaceborne GNSS-R interferometric altimetry should be taken as the parameter. Based on the altimetry accuracy proposed by [PERSON] for a 100 km along-track resolution and its relationship with along-track resolution, the altimetry accuracy for the IOD and Operational scenarios at a 10 km along-track resolution can be extrapolated. Additionally, [PERSON]'s error budget table omits the impact of geophysical error corrections such as tide correction and inverted barometer correction, which are crucial for gravity field inversion. Referring to the geophysical correction error budgets of radar altimeters, this study sets the correction accuracy for geophysical errors at 3 cm [62]. Furthermore, the orbital altitude of FY-3E/F differs from that of PARIS IOD and Operational scenarios, and orbital altitude significantly affects the detection efficiency and altimetry accuracy of GNSS-R.