Polarimetric Analysis of Natural Terrain Observed With a Ku-Band Terrestrial Radar

Terrestrial radar interferometers (TRI) are complimentary to spaceborne synthetic aperture radar systems for deformation monitoring in natural terrain: they permit shorter revisit times and greater flexibility in acquisition mode and timing. The additional diversity offered by polarimetric data can also be beneficial for TRI observations because polarized waves are sensitive to the dielectric and geometrical properties of the scatterers. Polarimetric data helps to distinguish different scattering mechanisms in a resolution cell while at the same time estimating terrain displacements. However, the polarimetric scattering signatures of natural surfaces at Ku -Band are not as well characterized as the ones at longer wavelengths, owing to relative rarity of full polarimetric systems operating in Ku -band. This band is often employed in TRI to obtain a fine azimuth resolution with a limited aperture size. This article aims at assessing the potential of polarimetric measurements in Ku -band TRI through an experimental study of polarimetric scattering signatures of natural surfaces using two datasets acquired over a glacier and in an agricultural and urban scene. The main finding of this analysis is that the Cloude–Pottier entropy is high for all land cover types; it is only observed to be less than 0.5 for scatterers with a large radar cross section. Several plausible hypotheses for this observation are formulated and tested, the most likely assumes a combination of depolarizing scattering from natural surfaces and the effect of the large ratio of wavelength to resolution cell size.