Cross and Col-Pol Phase Difference Related to Crop Structures in the Quad-Pol SAR Data and its Potential for Crop Monitoring

The amplitude and phase of synthetic aperture radar (SAR) backscatter coefficients are sensitive to surface dielectric constant, canopy structure, and surface roughness. Particularly, quad-pol SAR observations which provide HH, VV, and HV/VV polarimetry information are more beneficial for crop monitoring compared with single and dual-pol data. Considering the difference of penetrability of horizontal and vertical signals over oriented canopy structure, we explores the potential of co-pol and cross-pol phase difference, like ∆ϕ
HH−VV
and ∆ϕ
HH−HV
and ∆ϕ
VV−VH
, for crop phenology and structure monitoring. Besides, time-series variation of phase difference is supposed to be able to track crop growth. This paper introduces the form of the co-pol and cross-pol phase difference derived from Sinclare scattering matrix (S
2×2
) and the covariance matrix (C
3×3
). Subsequently, the mechanism of phase difference relating with the scattering phase center, the oriented crop structure, and the penetration depths of different polarization are provided. Time-series L-band quad-pol UAVSAR data which are collected from June 22 to July 17, 2012 in Winnipeg, Canada are used for the analysis of temporal and spacial phase difference characteristics over canola, soybean, and wheat fields. Results indicate significant potential of co-pol and cross-pol phase differences in crop structure and phenology monitoring. Especially, the evolution of time-series ∆ϕ
HH−VV
is more consistent with taht of LAI measurements compared with the cross-pol phase difference.