Retrieval of soil moisture using SIR-C polarimetric data
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Photonirvachak
J. Indian Soc. Remote Sens. (June 2008) 36:109–122
RESEARCH ARTICLE
Retrieval of Soil Moisture using SIR-C Polarimetric Data K. S. Rao . Y. S. Rao . H. K. Al Jassar
Received: 25 May 2006 / Accepted: 28 January 2007
Keywords
Soil moisture retrieval . SIR-C
Abstract Spaceborne Imaging Radar (SIR-C) polarimetric data acquired over Gujarat test site, India, during April and October 1994 were processed to retrieve soil moisture and surface roughness using multi-polarization techniques. Synchronous field data were collected and compared with the results obtained using SIR-C data. Indian Remote Sensing Satellite (IRS) images in visible region were used for locating groundtruth points. Multi-polarization inversion techniques are found to be sensitive to retrieval of soil moisture and surface roughness parameters. However, the accuracy is not adequate. There K. S. Rao1 . Y. S. Rao2 () . H. K. Al Jassar1 Department of Physics, Kuwait University, Kuwait e-mail: [email protected], [email protected] 2 CSRE, Indian Institute of Technology Bombay, India
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e-mail: [email protected]
is a need to improve the existing inversion models to suit to the Indian agricultural fields.
Introduction The early field investigations by Schmugge et al. (1974), Wang et al. (1983) and Ulaby et al. (1986) demonstrated the feasibility of retrieval of soil moisture from microwave sensors. A great deal of research was conducted all over to demonstrate the capability of spaceborne synthetic aperture radar (SAR) systems (SEASAT, ERS-1 and 2, JERS, Radarsat-1) for the retrieval of soil moisture and vegetation (MDA Document (1982), Wang et al. (1990), Sylvie et al. (2002)). The results were well correlated with the field measurements. However, it was often experienced difficulty in putting these models into operation as the available systems are of single frequency and single polarization. The backscattering coefficient measured through SAR systems is an integrated result of several target parameters such as surface roughness, soil moisture and vegetation cover (Rao et al., 1995a) Therefore, it is not possible to resolve
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J. Indian Soc. Remote Sens. (June 2008) 36:109–122
these multi-parameters from a single measurement of backscattering coefficient. Therefore, there is a need to adopt multi-frequency and multi-polarization approaches as envisaged by several researchers (Wang and Mo, 1990). Multi-frequency Polarimetric SAR systems seems to be a viable solution to resolve the target parameters. Cumming et al. (1991) summarized all the parameters that can be derived from polarimetric SAR data. Some of the important parameters are σhh, σvv, σhv, polarization phase difference (PPD), decomposition of the backscattered signal into even and odd reflection components and volume scattering, polarization signatures and polarization index (PI). These multi-dimensional parameters enhanced the accuracy of retrieval of soil moisture (Oh et al., 1992, Shi et al., 1997). Polarimetric SIR-C/X-SAR (Spaceborne Imaging Radar C
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