In the distributed small satellites synthetic aperture radar (DSS-SAR), baseline is usually coupled, that is, along-track baseline and across-track baseline exist simultaneously. However, coupling baseline makes it difficult to distinguish phase differences caused by terrain height and Doppler frequency difference. In SAR interferometry (InSAR) geometric model, across-baseline is necessary to bring interferometric phase to estimate terrain height. Oppositely, along-track baseline will bring extra phase difference and dramatically decrease the accuracy of terrain height estimation. Considering the aforementioned problem, this paper focuses on the study of baseline decoupling of DSS-SAR. We firstly analyze the effect of coupling baseline on terrain height estimation, and then propose the method of baseline decoupling through space projection theory. In order to realize baseline decoupling, equivalent slave satellite, equivalent baseline, and equivalent slant range are defined through projecting slave satellite on range-height plane of master satellite. Furthermore, based on our baseline decoupling, an advanced approach of estimating terrain height is presented, which is more effective than traditional InSAR geometric model. Simulation results illuminate that the baseline decoupling can eliminate along-track baseline effect on terrain height estimation effectively and confirm the validity and efficiency of terrain height estimation approach proposed in this paper.
2. Guo, D. M., H. P. Xu, and J. W. Li, "Extended wavenumber domain algorithm for highly squinted sliding spotlight SAR data processing," Progress In Electromagnetics Research, Vol. 114, 17-32, 2011.
3. Lim, S.-H., J.-H. Han, S.-Y. Kim, and N.-H. Myung, "Azimuth beam pattern synthesis for airborne SAR system optimization," Progress In Electromagnetics Research, Vol. 106, 295-309, 2010.
4. 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.
5. Zebker, H. A. and J. Villasenor, "Decorrelation in interferometric radar echoes," IEEE Trans. Geosci. Remote Sens., Vol. 30, No. 5, 950-959, 1992.
6. Wang, T., M. Liao, and D. Perissin, "InSAR coherence-decomposition analysis," IEEE Geosci. Remote Sens. Lett., Vol. 7, No. 1, 156-160, 2010.
7. Liu, D. and Y. Du, "Analysis of InSAR sensitivity to forest structure based on radar scattering model," Progress In Electromagnetics Research, Vol. 84, 149-171, 2008.
8. Krieger, G., H. Fiedler, and J. Mittermayer, "Analysis of multistatic configuration for spaceborne SAR interferometry," IEE Process Radar Sonar Navig., Vol. 150, No. 3, 87-96, 2003.
9. Xu, H. P., Y. Q. Zhou, and C. S. Li, "Correlation of distributed small satellites SAR echoes," Acta Electronics Sinica, Vol. 33, No. 6, 965-969, 2005.
10. Zhu, S. Q., G. S. Liao, Z. G. Zhou, and Y. Qu, "Robust moving targets detection and velocity estimation using multi-channel and multi-look SAR images," Signal Processing, Vol. 90, 2009-2019, 2010.
11. Rosen, P. A., S. Hensley, and I. R. Joughin, "Synthetic aperture radar interferometry," IEEE Proceeding, Vol. 88, No. 3, 333-382, 2000.
12. Xu, H. and C. Kang, "Equivalence analysis of accuracy of geolocation models for spaceborne InSAR," IEEE Trans. Geosci. Remote Sens., Vol. 48, No. 1, 480-490, 2010.
13. Collino, F., F. Millot, and S. Pernet, "Boundary-integral methods for iterative solution of scattering problems with variable impedance surface condition," Progress In Electromagnetics Research, Vol. 80, 1-28, 2008.
14. Carpentieri, B., "Fast iterative solution methods in electromagnetic scattering," Progress In Electromagnetics Research, Vol. 79, 151-178, 2008.
15. Nico, G., "Exact closed-form geolocation for SAR interferometry," IEEE Trans. Geosci. Remote Sens., Vol. 40, No. 1, 220-228, 2002.
16. Sansosti, E., "A simple and exact solution for the interferometric and stereo SAR geolocation problem," IEEE Trans. Geosci. Remote Sens., Vol. 42, No. 8, 1625-1634, 2004.
17. Rodriguez, E. and J. Martin, "Theory and design of interferometric synthetic aperture radars," IEE Proceedings-F, Vol. 139, No. 2, 147-159, 1992.
18. Ma, L., Z.-F. Li, and G. S. Liao, "System error analysis and calibration methods for Multi-channel SAR ," Progress In Electromagnetics Research, Vol. 112, 309-327, 2011.
19. Just, D. and R. Bamler, "Phase statistics of interferograms with applications to synthetic aperture radar," Applied Optics, Vol. 33, No. 20, 4361-4368, 1994.
20. Yao, J. and D. Yi, "A concise derivation of flat earth effect and terrain height effect for across-track InSAR," ISAPE'06, 2007.
21. Knedlik, S. and O. Loffeld, "A new approach to improve the accuracy of baseline estimation for spaceborn radar interferometry," IGARSS'09, 162-165, 2009.
22. Gini, F., F. Lombardini, and M. Montanari, "Layover solution in multibaseline SAR interferometry," IEEE Transaction on Aerospace and Electronic System, Vol. 38, No. 4, 1344-1356, 2002.
23. Wu, B.-I., M. Yeung, Y. Hara, and J. A. Kong, "InSAR height inversion by using 3-D phase projection with multiple baselines," Progress In Electromagnetics Research, Vol. 91, 173-193, 2009.
24. Lanari, R. and D. Riccio, "Generation of digital elevation models by using SIR-C/X SAR mutifrequency two-pass interferometry: The etna case study," IEEE Trans. Geosci. Remote Sens., Vol. 34, No. 5, 1097-1114, 1996.
25. Xu, H., C. Kang, and Y. Q. Zhou, "The equivalent analysis of direct geocoding model and spaceborne InSAR altitude model in height uncertainty ," Journal of Electronics & Information Technology, Vol. 32, No. 1, 48-53, 2010.
26. Zebker, H. A., T. G. Farr, R. P. Salazar, and T. H. Dixon, Mapping the world's topography using radar interferometry: The TOPSAT mission, Proc. IEEE, Vol. 82, No. 12, 1774-1786, 1994.
27. Li, Z. F., Z. Bao, H. Li, and G. S. Liao, "Image autocoregistration and InSAR interferogram estimation using joint subspace projection," IEEE Trans. Geosci. Remote Sens., Vol. 44, No. 2, 288-297, 2006.
28. Ghiglia, D. C. and M. D. Pritt, Two-Dimensional Phase Unwrapping: Theory, Algorithms, and Software, Wiley, Hoboken, NJ, 1998.
29. Li, C. and D. Y. Zhu, "A residue-pairing alogrithm for InSAR phase unwrapping," Progress In Electromagnetics Research, Vol. 95, 341-354, 2009.
30. Ferraiuolo, G., F. Meglio, and V. Pascazio, "DEM reconstruction accuracy in multichannel SAR interferometry," IEEE Trans. Geosci. Remote Sens., Vol. 47, No. 1, 191-201, 2009.