Doppler-based techniques for ocean current measurement have been demonstrated in the past years. The Doppler shift of the ocean backscattering from space-borne microwave instruments not only includes the contributions from ocean current but also includes satellite movement and the wind-wave induced. Geometrical Doppler shift induced by satellite movement is highly dependent on the accuracies of satellite attitude determinations and speed. In this study, we derive the detailed formulas to investigate how satellite attitude determination and speed errors affect ocean current retrieval for a Doppler scatterometer through the spatial correlation coefficient phase and the transformation between orbital coordinate system and satellite-carried local level frame (LLF). Our results show that ocean current speed retrieval accuracy is sensitive to the accuracies of satellite attitude determination and speed, and compared with the satellite speed error, satellite attitude error has a larger impact on ocean current retrieval. By comparisons, with the same attitude accuracy for satellite roll, pitch, and yaw, ocean current speed error induced by the roll error is found to be the smallest. With an accuracy of 0.001° satellite attitude determination and 0.01 m/s for satellite speed accuracy, the total ocean current speed retrieval error induced by satellite attitude determinations (including roll, pitch, and yaw) and speed errors reaches a maximum value of 16.37 cm/s at side-looking direction and a minimum value of 11.05 cm/s at forward and backward-looking directions. Our results confirm the importance of satellite attitude determination accuracy for future ocean current mission and will also be useful to motivate the design of future Doppler measurement instruments.
2. Shi, Q. and M. A. Bourassa, "Coupling ocean currents and waves with wind stress over the gulf stream," Remote Sensing, Vol. 11, No. 12, 1476, 2019. [Online]. Available: https://www.mdpi.com/2072-4292/11/12/1476.
3. Bao, Q., X. Dong, D. Zhu, S. Lang, and X. Xu, "The feasibility of ocean surface current measurement using pencil-beam rotating scatterometer," IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, Vol. 8, No. 7, 3441-3451, 2015, doi: 10.1109/JSTARS.2015.2414451.
4. Rodriguez, E., et al., "Estimating ocean vector winds and currents using a Ka-band pencil-beam doppler scatterometer," Remote Sensing, Vol. 10, 576, 2018, doi: 10.3390/rs10040576.
5. Miao, Y., X. Dong, Q. Bao, and D. Zhu, "Perspective of a Ku-Ka dual-frequency scatterometer for simultaneous wide-swath ocean surface wind and current measurement," Remote Sensing, Vol. 10, 1042, 2018, doi: 10.3390/rs10071042.
6. Ardhuin, F., et al., "Measuring currents, ice drift, and waves from space: The Sea surface KInematics Multiscale monitoring (SKIM) concept," Ocean Sci., Vol. 14, No. 3, 337-354, 2018, doi: 10.5194/os-14-337-2018.
7. Rodríguez, E., M. Bourassa, D. Chelton, J. T. Farrar, D. Long, D. Perkovic-Martin, and R. Samelson, "The winds and currents mission concept," Frontiers in Marine Science, Vol. 6, 438, 2019.
8. Du, Y., X. Dong, X. Jiang, Y. Zhang, and S. Peng, "Ocean Surface Current Multiscale Observation Mission (OSCOM): Simultaneous measurement of ocean surface current, vector wind, and temperature," Progress In Oceanography, Vol. 193, No. 3, 102531, 2021.
9. Chapron, B., F. Collard, and F. Ardhuin, "Direct measurements of ocean surface velocity from space: Interpretation and validation," Journal of Geophysical Research: Oceans, Vol. 110, C7, 2005, doi: 10.1029/2004JC002809.
10. Mouche, A. A., F. Collard, B. Chapron, K. Dagestad, G. Guitton, J. A. Johannessen, V. Kerbaol, and M. W. Hansen, "On the use of doppler shift for sea surface wind retrieval from SAR," IEEE Transactions on Geoscience and Remote Sensing, Vol. 50, No. 7, 2901-2909, 2012, doi: 10.1109/TGRS.2011.2174998.
11. Yurovsky, Y., V. Kudryavtsev, S. A. Grodsky, and B. Chapron, "Sea surface Ka-band doppler measurements: Analysis and model development," Remote. Sens., Vol. 11, 839, 2019.
12. Miao, Y., X. Dong, M. A. Bourassa, and D. Zhu, "Effects of different wave spectra on wind-wave induced doppler shift estimates," IGARSS 2020 - 2020 IEEE International Geoscience and Remote Sensing Symposium, 5705-5708, IEEE, 2020.
13. Miao, Y., X. Dong, M. A. Bourassa, and D. Zhu, "Effects of ocean wave directional spectra on doppler retrievals of ocean surface current," IEEE Transactions on Geoscience and Remote Sensing, 2021.
14. Elyouncha, A., L. E. B. Eriksson, R. Romeiser, and L. M. H. Ulander, "Measurements of sea surface currents in the baltic sea region using spaceborne along-track InSAR," IEEE Transactions on Geoscience and Remote Sensing, Vol. 57, No. 11, 8584-8599, 2019, doi: 10.1109/TGRS.2019.2921705.
15. Hansen, M. W., F. Collard, K.-F. Dagestad, J. A. Johannessen, P. Fabry, and B. Chapron, "Retrieval of sea surface range velocities from Envisat ASAR Doppler centroid measurements," IEEE Transactions on Geoscience and Remote Sensing, Vol. 49, No. 10, 3582-3592, 2011.
16. Bolandi, H., M. Haghparast, F. Saberi, B. Vaghei, and S. Smailzadeh, "Satellite attitude determination and contol," Measurement and Control, Vol. 45, No. 5, 151-157, 2012.
17. Bao, Q., M. Lin, Y. Zhang, X. Dong, S. Lang, and P. Gong, "Ocean surface current inversion method for a doppler scatterometer," IEEE Transactions on Geoscience and Remote Sensing, Vol. 55, No. 11, 6505-6516, 2017.
18. Bamler, R. and P. Hartl, "Synthetic aperture radar interferometry," Inverse Problems, Vol. 14, No. 4, R1, 1998.
19. Grewal, M. S., A. P. Andrews, and C. G. Bartone, Global Navigation Satellite Systems, Inertial Navigation, and Integration, John Wiley & Sons, 2020.
20. Noureldin, A., T. B. Karamat, and J. Georgy, Fundamentals of Inertial Navigation, Satellite-based Positioning and Their Integration, 2013.
21. Howley, B., "AA236: Overview of spacecraft attitude determination and control,", Lockheed Martin Space Systems Company, 2005.