Radiometric sensitivity to soil moisture at 1.4 GHz through a corn crop at maximum biomass

Abstract

Radiometric sensitivity to soil moisture at 1.4 GHz through a corn canopy at a maximum biomass of 8.0 kg m−2 (water column density of 6.3 kg m−2) was much higher than expected. The magnitude of the measured sensitivity of horizontally polarized brightness temperature to the 0–3 cm volumetric soil water content was at least 1.5 K per 0.01 m3 m−3 and could have been as high as 2.5 K per 0.01 m3 m−3. Vertically polarized brightness temperature was 0.5 K per 0.01 m3 m−3 less sensitive than horizontally polarized brightness temperature. A widely used radiative transfer model that assumes a uniform distribution of vegetation in the canopy underestimated this soil moisture sensitivity at horizontal polarization by over 1 K per 0.01 m3 m−3. Given an appropriate emission model that correctly accounts for the differences in transparency between heterogeneous canopies (as compared to the wavelength) such as corn and relatively homogeneous canopies such as grass, it appears that there will be practical sensitivity to soil moisture through corn (and most, if not all, row crops) throughout the growing season.