This paper presents an improved polar format algorithm (PFA) for geosynchronous synthetic aperture radar which undergoes a near-circular track (GeoCSAR). GeoCSAR imaging geometry and signal formulation considering orbit perturbations were derived to ensure accurate slant range between antenna and targets. The illuminated area is more than one million square kilometers due to the long slant distance, resulting in large amount of data to be processed and that the scene is a spherical crown rather than a plane. By assuming spherical wavefronts instead of planar wavefronts, improved polar format algorithm (PFA) was proposed to focus GeoCSAR raw data on a spherical reference surface (ground surface), so that the size of focused scene is no longer limited by the range curvature phase error. Thus, this method could deal with large area imaging for GeoCSAR precisely and efficiently. The implementation procedure, computational complexity, phase error and achievable resolution were presented to show the focusing capabilities of this imaging algorithm. Numerical simulation was further performed to validate the feasibility of this imaging algorithm and the correctness of analysis.
2. Bruno, D. and S. E. Hobbs, "Radar imaging from geosynchronous orbit: Temporal decorrelation aspects," IEEE Trans. Geosci. Remote Sens., Vol. 48, No. 7, 2924-2929, 2010.
3. Sun, J., S. Mao, G.Wang, and W. Hong, "Extended exact transfer function algorithm for bistatic SAR of translational invariant case ," Progress In Electromagnetics Research, Vol. 99, 89-108, 2009.
4. Soop, E. M., Handbook of Geostationary Orbits, Springer, 1994.
5. Tan, W. X., W. Hong, Y.-P. Wang, and Y.-R. Wu, "A novel spherical-wave three-dimensional imaging algorithm for microwave cylindrical scanning geometries," Progress In Electromagnetics Research, Vol. 111, 43-70, 2011.
6. Soumekh, M., "Reconnaissance with slant plane circular SAR imaging," IEEE Trans. Image Processing, Vol. 5, No. 8, 1252-1265, 1996.
7. Lin, Y., W. Hong, W. X. Tan, and Y. R. Wu, "Extension of range migration algorithm to squint circular SAR imaging," IEEE Geosci. Remote Sens. Lett., Vol. 8, No. 4, 651-655, 2011.
8. Carrara, W. G., R. S. Goodman, and R. M. Majewski, Spotlight Synthetic Aperture Radar: Signal Processing Algorithms, Artech House, Norwood, MA, 1995.
9. Mao, X. H., D.-Y. Zhu, L. Ding, and Z. D. Zhu, "Comparative study of RMA and PFA on their responses to moving target," Progress In Electromagnetics Research, Vol. 110, 103-124, 2010.
10. Sun, J. P., S. Y. Mao, G. H. Wang, and W. Hong, "Polar format algorithm for spotlight bistatic SAR with arbitrary geometry configuration," Progress In Electromagnetics Research, Vol. 103, 323-338, 2010.
11. Mao, X. H., D. Y. Zhu, and Z. D. Zhu, "Signatures of moving target in polar format spotlight SAR image," Progress In Electromagnetics Research, Vol. 92, 47-64, 2009.
12. Nie, X., D.-Y. Zhu, and Z. D. Zhu, "Application of synthetic bandwidth approach in SAR polar format algorithm using the deramp technique ," Progress In Electromagnetics Research, Vol. 80, 447-460, 2008.
13. Wang, X., D.-Y. Zhu, and Z.-D. Zhu, "An implementation of bistatic PFA using chirp scaling," Journal of Electromagnetic Waves and Applications, Vol. 24, No. 5-6, 745-753, 2010.
14. Chen, C. W., Modified polar format algorithm for processing spaceborne SAR data, Proc. IEEE Radar Conference, 44-49, 2004.