Defining the sensitivity of multi-frequency and multi-polarized radar backscatter to post-harvest crop residue

Following harvest, agricultural fields are left with varying amounts of crop residue cover. The erodibility and health of the topsoil is determined, in part, by the amount and type of this residue cover Although radar sensors could be useful for mapping residue and/or tillage in order to monitor soil conservation practices, little is understood about the relationship between residue and radar backscatter. Two ground-based microwave scatterometer experiments were conducted on agricultural plots at the Central Experimental Farm of Agriculture and Agri-Food Canada, in Ottawa (Canada). The experiments were designed to address the influence of residue ope (corn and barley), residue moisture content and residue amount on radar backscatter and to examine the effect of look direction on radar response. Scatterometer measurements (C- and L-Band in four linear transmit-receive polarization combinations) were taken of corn and barley plots where treatments varied in residue amount and moisture level, The experiments demonstrated that crop residue can retain significant amounts of moisture and that residue is not transparent to incident microwaves. Residue cover will impede the use of radar sensors for mapping soil moisture. Both residue amount and residue moisture content were correlated with radar backscatter with the strongest correlations associated with corn residue treatments, C-Band cross-polarized backscatter and shallow incidence angles. Cross-polarized scattering was not sensitive to radar look direction effects. Results from these experiments indicate that cross-polarized backscatter could be used to provide information on conservation tillage practices.