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Sensitivity of C-band SAR polarimetric variables to unvegetated agricultural fields

Adams, J.R., Berg, A.A., McNairn, H., Merzouki, A. (2013). Sensitivity of C-band SAR polarimetric variables to unvegetated agricultural fields, 39(1), 1-16.


The interaction of linear polarized microwaves with agricultural features is well understood. Much less is understood about polarimetric data and the potential use of these data to improve surface parameter retrieval models. This paper explores the soil surface information provided by quad-polarimetric SAR through a review of previous work and an empirical sensitivity study of RADARSAT-2 data at four incidence angles. Soil moisture, surface roughness, and crop residue data are quantitatively sampled in unvegetated fields. RADARSAT-2 variables include: linear backscatter and polarization ratios; copolarized phase difference and magnitude of the copolarized complex correlation; pedestal height; extrema of the scattered intensity, completely polarized, and completely unpolarized components; and parameters of the Cloude–Pottier scattering decomposition. Results demonstrated that sensitivities of field averaged linear backscatter were reproduced from previous reports, lending confidence to the experiment. Field averaged pedestal height and copolarized complex correlation coefficient showed significant relationships to crop residue and surface roughness, suggesting an ability to characterize volume and multiple scattering. Similarly, dynamic range of the degree of polarization showed significant relationships with crop residue cover at higher incidence angles. Target averaged or variance of copolarized phase difference did not produce a consistent relationship with the surface parameters, in contrast to qualitative based suggestions of previous experiments. Extremas of the scattered intensity and completely polarized components indicated comparable relationships to surface features as the like polarized linear intensity channels, suggesting sensitivities of these variables to surface scattering. The extrema of the completely unpolarized component showed comparable relationships to surface features as the pedestal height. Results of this paper contribute to identification of optimal SAR variables for use in agricultural monitoring and evaluate potential contributions of polarimetric data for improving surface parameter retrieval models. © 2013, Taylor & Francis Group, LLC. All rights reserved.

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