Compared to low Earth orbit (LEO) synthetic aperture radar (SAR), geosynchronous (GEO) SAR has a larger coverage and shorter revisit period. However, due to its longer integration timeit will be affected byionospheric time-variant total electron content (TEC), which introduces a phase error into the SAR azimuth signal.Using U.S. total electron content (USTEC) data, TEC variation with timeon GEO SAR trackis analyzed. It is shown thatquadratic phase error caused by time-variant TEC is main effect on image focusing compared to higher order errors. Therefore, contrast optimization autofocus (COA) algorithm can beusedfor compensation. The key steps of COA are given. Simulations based on scenes derived from PALSAR2 data demonstrate the effectiveness of COA.
2. Bruno, D., S. E. Hobbs, and G. Ottavianelli, "Geosynchronous synthetic aperture radar: Concept design, properties and possible applications," Acta Astronaut, Vol. 59, 149-156, 2006.
3. Zhao, B., X. Qi, H. Song, W. Gao, X. Han, and R. P. Chen, "The accurate fourth-order doppler parameter calculation and analysis for geosynchronous SAR," Progress In Electromagnetics Research, Vol. 140, 91-104, 2013.
4. Zeng, T., W. Yang, Z. Ding, D. Liu, and T. Long, "A refined two-dimensional nonlinear chirp scaling algorithm for geosynchronous earth orbit SAR," Progress In Electromagnetics Research, Vol. 143, 19-46, 2013.
5. Yu, Z., et al., "Correcting spatial variance of RCM for GEO SAR imaging based on time-frequency scaling," Sensors, Vol. 16, No. 7, 1091, 2016.
6. Guarnieri, A. M., et al., "Geosynchronous SAR for earth monitoring by interferometry and imaging," IEEE International Geoscience and Remote Sensing Symposium (IGARSS), 210-213, 2012.
7. Hu, C., et al., "Background ionosphere effects on geosynchronous SAR focusing: Theoretical analysis and verification based on the BeiDou navigation satellite system (BDS)," IEEE Journal of Selected Topics in Applied Earth Observation and Remote Sensing, Vol. 9, No. 3, 1143-1162, 2016.
8. Tian, Y., et al., "Theoretical analysis and verification of time variation of background ionosphere on geosynchronous SAR imaging," IEEE Geoscience and Remote Sensing Letters, Vol. 12, No. 4, 721-725, 2015.
9. Chen, J. and Z. Li, "Simultaneous measurement of time-variant TEC for compensating ionospheric effect on geosynchronous SAR using HF-radar," IEEE 13th International Conference on Signal Processing (ICSP), 87-90, 2016.
10. Zhang, Q. B., Z. Yu, and P. Xiao, "Impacts of ionospheric temporal variability on L-band GEO SAR Imaging," IEEE International Geoscience and Remote Sensing Symposium (IGARSS), 1194-1197, 2016.
11. Belcher, D. P. and N. C. Rogers, "Theory and simulation of ionospheric effects on synthetic aperture radar," IET Radar Sonar Navig., Vol. 3, No. 5, 541-551, 2009.
12. Jehle, M., et al., "Measurement of ionospheric TEC in spaceborne SAR data," IEEE Transactions on Geoscience and Remote Sensing, Vol. 48, No. 6, 2460-2468, 2010.
13. Carrara, W. G., R. S. Goodman, and R. M. Majewski, Spotlight Synthetic Aperture Radar: Signal Processing Algorithms, Artech House, Boston and London, 1995.