# Impact of Satellite Attitude on Altimetry Calibration with Microwave Transponders
## 5 Conclusions
Most importantly, it solely depends on publicly available data (i.e., attitude quaternions and GDR products) that do not require any type of pre-processing from the distribution agencies. A reanalysis of transponder results using the proposed procedure can be performed for present and past altimetry missions, resulting in an updated estimation of range and datation biases, including relative biases between missions. The evaluation of attitude effects on calibration with a transponder can also be tested on satellite altimetry missions equipped with an interferometric radar altimeter, such as the operating CryoSat-2 [49], and the upcoming missions of Surface Water and Ocean Topography (SWOT) [50], the Copernicus polaR Ice and Snow Topography ALtimeter (CRISTAL) [51] and Guanlan [52]. For these missions, the accurate knowledge of the interferometric baseline orientation and length in three-dimensional space is an absolute prerequisite for their nominal operation. Apart from attitude effects, a possible impact of the phase center variation of the altimeter antenna on transponder results can also be evaluated. Modelling and accounting for all these effects can lead to even more rigorous calibration procedures. Conceptualization, C.K. and D.P. ; methodology, C.K. ; software, D.P. ; validation, C.K., D.P., S.P.M. ; formal analysis, C.K., D.P., S.P.M. ; investigation, C.K. and D.P. ; resources, S.P.M. ; data curation, C.K., D.P., S.P.M. ; writing--original draft preparation, C.K. and D.P. ; writing--review and editing, S.P.M. ; visualization, C.K., D.P., S.P.M. ; supervision, S.P.M. ; project administration, S.P.M. ; funding acquisition, S.P.M. All authors have read and agreed to the published version of the manuscript. This work has been produced with the financial assistance of the European Union and the European Space Agency under the project FRM456 (Fiducial Reference Systems for Sentinel-6A MF, No. 4000129892/20/NL/FF/ab). The views expressed herein can in no way be taken to reflect the official opinion of the European Union and/or European Space Agency. Jason-3 body quaternion files are available through NASA's Crustal Dynamics Data Information System (CDDIS) server at [[ftp://cddis.gsfc.nasa.gov/doris/ancillary/](ftp://cddis.gsfc.nasa.gov/doris/ancillary/)]([ftp://cddis.gsfc.nasa.gov/doris/ancillary/](ftp://cddis.gsfc.nasa.gov/doris/ancillary/)) quaternions/, accessed on 1 September 2022. The Jason-3 mass and CoG history file is available through International DORIS Service (IDS) server at [[ftp://ftp.ids-doris.org/pub/ids/satellites/ja3](ftp://ftp.ids-doris.org/pub/ids/satellites/ja3)]([ftp://ftp.ids-doris.org/pub/ids/satellites/ja3](ftp://ftp.ids-doris.org/pub/ids/satellites/ja3)) mass.txt, accessed on 1 September 2022 and the history of satellite maneuvers at [[ftp://ftp.ids-doris.org/pub/ids/satellites/ja3](ftp://ftp.ids-doris.org/pub/ids/satellites/ja3) att.txt]([ftp://ftp.ids-doris.org/pub/ids/satellites/ja3](ftp://ftp.ids-doris.org/pub/ids/satellites/ja3) att.txt), accessed on 1 September 2022. The quaternion files for Sentinel-6A MF analysis was downloaded from Eumetsat Observation Portal at [[https://eoportal.eumetsat.int](https://eoportal.eumetsat.int)]([https://eoportal.eumetsat.int](https://eoportal.eumetsat.int)), accessed on 1 September 2022. The help and support of Achilles Tripolitsiotis from Space Geomatica and Xenofon Frantzis from the Technical University of Crete was invaluable and improved this work immensely. In addition, we thank very much Milen Tahtadjiev and the altimetry team at Eumetsat for making available to us the Sentinel-6A MF quaternions. The authors declare no conflict of interest. The following abbreviations are used in this manuscript: