Relating Radar Backscatter to Biophysical Properties of Temperate Perennial Grassland

The response of polarimetric airborne synthetic aperture radar (SAR) to grassland is investigated. Synthetic aperture radar from the National Aeronautical and Space Administration/ Jet Propulsion Laboratory (NASA/JPL) airborne imaging system was acquired over a diverse grassland site in northern NSW, Australia in September 1993. Grassland and high backscatter targets are classified using images from C, L, and P band for hh, hv, and vv polarizations. The grassland classes cover a wide dynamic range of backscatter from −7 dB to −14 dB in C band and −9 dB to −23 dB in L band. Significant regression relationships are formulated between measurements of grassland height and radar backscatter using site data aggregated by 25 mm height class. The relationship between species composition and grassland classes is explored. Polarization effects include an enhanced range of backscatter across grassland classes for 45° cross polarization at L band and differences in the pedestal height of the C band polarization signature for species classes. The results of drainage modeling suggest that soil moisture is a significant confounding factor influencing radar backscatter from the grassland. Simple models using logistic probability of association between height class and radar backscatter in a Bayesian inference engine, and a simple threshold based on logistic probability of association between wet areas and P vv are examined. Our results suggest that combined imagery from C and L band satellite-borne SAR sensors have potential for current application in grassland monitoring.