The extraction of soil dielectric properties from AIRSAR data

Complex dielectric constants determined by inversion of the polarized returns of radar images acquired in wet conditions clearly delineate the distribution of saline soils in the Tragowel Plains Irrigation Area of Victoria, Australia. There is good agreement between the areas delineated as having anomalous dielectric constants by the radar backscatter inversion techniques with saline areas as defined by geophysics and as inferred from dielectric constants determined in the field. The radar-determined complex dielectric constants are significantly smaller than might be expected from the known moisture contents of the soils at the time of image acquisition. The magnitudes of P-band radar-delermined dielectric constants most closely approach those expected from field determinations although the distribution of L-band-determined dielectric constants give the best discrimination between saline and non-saline areas as seen at the surface. Modification of the inversion algorithm to allow for the effects of vegetation produces complex dielectric constant magnitudes in the saline regions that are closer to expected values but still underestimate the complex dielectric constant in non-saline regions. The more general regional distribution of high dielectric areas seen at P-band may be a more accurate indication of the salinity at depth.