# Impact of Satellite Attitude on Altimetry Calibration with Microwave Transponders
## 4 Results
### Jason-3 and Sentinel-6A MF Crossover Analysis  
The GVD1 Cal/Val site is located at a crossover point, which is defined by A109 and D018 passes of Jason-3 nominal orbit (Figure 1). The time difference between two consecutive satellite passes over GVD1 is about five days. Altimeter calibrations conducted using the GVD1 transponder offer the possibility of a crossover analysis. In this section, we calculate the range bias of Jason-3 for both A109 and D018 passes using the conventional and new calibration procedure. We then evaluate the range bias difference per cycle between A109 and D018 for each calibration procedure. This difference defines the crossover bias. It can be used to assess the altimeter performance and help identify systematic effects. The evaluation and comparison of crossover bias for the two calibration procedures can also yield valuable information regarding attitude effects on transponder results. This experiment is especially interesting for the case of Jason-3 since the spacecraft passes over GVD1 with opposite pitch angles (positive pitch angle for D18 and negative pitch angle for A109), as presented in Figure 7. The same crossover analysis is also performed for Sentinel-6A MF mission, as its orbital characteristics are identical to Jason-3.  
Figure 10: Jason-3 attitude effects \(\delta B\)**(top)** and \(\delta T\)**(bottom)** as a function of yaw plotted with respect to roll, pitch and yaw for the CDN1 transponder Cal/Val site and the descending pass D018.  
According to the results, the proposed calibration procedure improves the Jason-3 crossover bias. Specifically, the mean difference between D018 and A109 using the new calibration is reduced to 7 mm and shows an improvement of 12% compared to conventional calibration (Figure 12). The absence of results for cycles 216 and 225 is because the GVD1 transponder was not operational during that time. The level of improvement presented here is comparable with the results of Jason-3 sea surface height (SSH) crossover analysis reported in Blossfeld et al. [18]. In their study, the calculation of SSH is based on orbits estimated using model-based and observation-based attitude realization.  
The results of Sentinel-6A MF crossover analysis are presented in Figure 13. Implementing the proposed calibration procedure on Sentinel-6A MF also results in better agreement between the range bias of the ascending and descending pass. In this case, the averaged crossover bias is reduced from 28 mm to 24 mm, which corresponds to an improvement of 14%. It should be emphasized that the results with the new calibration procedure are preliminary, as the quaternions used (obtained by the Eumetsat Observation Portal) may not provide accurate satellite orientation. According to the documentation [48], these quaternions indeed contain information regarding the satellite orientation but were produced primarily for radio occultation analysis. The use of this dataset is motivated by the fact that it was the only readily available attitude information for Sentinel-6A MF during the time that the present analysis was conducted. Therefore, the Sentinel-6A crossover  
Figure 11: Amplitude spectrum of Jason-3 attitude effects on range and datation bias on CDN1 D018. The framed area on the bottom left is zoomed and presented on the upper right part of the figures.  
Figure 12: Jason-3 crossover bias determined by the GVD1 transponder using the conventional (red) and new (blue) calibration procedure.  
analysis results may change when attitude quaternions for altimetry processing become publicly available [48].