volume | PIER Journals

Abstract

To understand the mechanisms of decorrelation in interferometric SAR (InSAR) images of bare soil, a model has been developed. Under the Kirchhoff and stationary phase approximations, coherence can be related to the statistical variations of dielectric constant and roughness parameters of surfaces. With the help of an empirical model for the dependence of dielectric constant on soil moisture, coherence due to the inhomogeneity of soil moisture is numerically demonstrated. It has been shown that the decorrelation of the radar signal from rough soil is mainly due to the moisture variability within the resolution cell. The effect of roughness on decorrelation is complex. The effect is negligible compared to that of the dielectric variability for homogeneous resolution cells (no dielectric variability within a resolution cell). However, the coherence depends strongly on the roughness parameters for resolution cells with large moisture variability. It is concluded that the loss of coherence induced by variability of dielectric constant can be related to the relative variation of moisture expressed by the ratio of standard deviation and mean value, and that large relative variations of moisture could lead to much decorrelation. If the moisture variability is small the coherence will be very high even if the values of mean moisture of the two SAR observations are different, which means that coherence can be high in spite of much backscatter differences.

1. Dammert, P. B. G., "Spaceborne SAR interferometry: Theory and applications,", Technical Report No. 382, ISBN 91-7197-851-8, School of Electrical and Computer Engineering, Chalmers University of Technology, Gothenburg, Sweden, 1999.
doi:10.1109/36.377933 Google Scholar

2. Gens, R. and J. L. Van Genderen, , Review article: ``SAR interferometry-issues, techniques, applications,'' International Journal of Remote Sensing, Vol. 17, 1803–1835, 1996. International Journal of Remote Sensing, Vol. 17, 1803–1835, 1996' target='_blank'> Google Scholar

3. Hagberg, J. O., L. M. H. Ulander, and J. Askne, "Repeat pass SAR interferometry over forested terrain," IEEE Trans. Geosci. Remote Sensing, Vol. 33, 331-340, 1995. Google Scholar

4. Askne, J., P. B. G. Dammert, and G. Smith, "Understanding ERS InSAR coherence of boreal forests," IGARSS’99, 2111-2114, 1999. Google Scholar

5. Floury, N., T. L. Toan, J. C. Souyris, and J. Bruniquel, "A study of SAR interferometry over forests: theory and experiment," IGARSS’97, 1868-1870, 1997. Google Scholar

6. Rodriguez, E. and J. M. Martin, "Theory and design of interferometric synthetic aperture radars," IEE Proc-F, Vol. 139, No. 2, April 1992.
doi:10.1029/96RS01763 Google Scholar

7. Smith, G., P. B. G. Dammert, and J. I. H. Askne, "Decorrelation mechanisms in C-band SAR interferometry over boreal forest," Microwave Sensing and Synthetic Aperture Radar, G. Franceschetti, C. J. Oliver, F. S. Rubertone, and S. Tajbakhsh, Editors, Proceedings of SPIE, Vol. 2958, 300–310, 1996. Google Scholar

8. Treuhaft, R. N., S. N. Madsen, M. Moghaddam, and J. J. van Zyl, "Vegetation characteristics and surface topography from interferometric radar," Radio Science, Vol. 31, 1449-1485, 1996. Google Scholar

9. Zebker, H. A. and J. Villasenso, "Decorrelation in interferometric radar echoes," IEEE Trans. Geosci. Remote Sensing, Vol. 30, No. 5, Sept. 1992.
doi:10.1163/156939397X00279 Google Scholar

10. Franceschetti, G., A. Lodice, M. Migliaccio, and D. Riccio, "On the baseline decorrelation," IGARSS’96, 680-682, 1996. Google Scholar

11. Franceschetti, G., A. Lodice, M. Migliaccio, and D. Riccio, "The effect of surface scattering on IFSAR baseline decorrelation," J. Electromagnetic Waves & Applications, Vol. 11, 353-370, 1997. Google Scholar

12. Nesti, G., D. Tarchi, and J. P. Rudant, "Decorrelation of backscattered signal due to soil moisture changes," IGARSS’95, 2026-2028, 1995. Google Scholar

13. Nesti, G., D. Tarchi, D. Despan, J. P. Rudant, A. Bedidi, P. Borderies, and E. Bachelier, "Phase shift and decorrelation of radar signal related to soil moisture changes," Proc. of the 2nd International Workshop on Retrieval of Bio- & Geo-Physical Parameter from SAR Data for Land Applications, ESTEC, Noordwijk, The Netherlands, October 21–23, 1998. (ESA SP-441, 423–430, December 1998).
doi:10.1364/JOSAA.13.001057 Google Scholar

14. Ulaby, F. T., R. K. Moore, and A. K. Fung, Microwave Remote Sensing, Active and Passive, Vol. 2, 931, Addison-Wesley Publishing Company, 1982.

15. Le, C., Y. Kuga, and A. Ishimaru, "Angular correlation function based on the second-order Kirchhoff approximation and comparison with experiments," J. Opt. Soc. Am. A, Vol. 13, No. 5, 1996. Google Scholar

16. Ulander, L. M. H. and J. O. Hagberg, "Radiometric and interferometric calibration of ENVISAT-1 ASAR,", Research Report No. 172, Department of Radio and Space Science with Onsala Space Observatory, Chalmers University of Technology, Gothenburg, Sweden, 1995. Google Scholar

17. Hallikainen, M., F. T. Ulaby, M. C. Dobson, M. El-Rayes, and L. K. Wu, "Microwave dielectric behavior of wet soil - Part I: Empirical models and experimental observations," IEEE Trans. Geosci. Remote Sensing, Vol. 23, 25-34. Google Scholar

Dr. X. Luo

Dr. J. Askne

Dr. G. Smith

Dr. P. Dammert