DETERMINATION OF SOIL-MOISTURE DISTRIBUTION FROM IMPEDANCE AND GRAVIMETRIC MEASUREMENTS

Daily measurements of the soil dielectric properties at 5 and 10 cm were obtained at five locations throughout the First ISLSCP Field Experiment (FIFE) test site during the 1987 intensive field campaigns (IFCs). An automated vector voltmeter was used to monitor the complex electrical impedance, at 10 MHz, of cylindrical volumes of soil delineated by specially designed soil moisture probes buried at these locations. The objective of this exercise was to test the hypothesis that the soil impedance is sensitive to the moisture content of the soil and that the imaginary part (that is, capacitive reactance) can be used to calculate the volumetric water content of the soil. These measurements were compared with gravimetric samples collected at these locations by the FIFE staff science team. In addition to the five fixed locations, measurements were made throughout each of the IFCs along three transects underlying airborne push broom microwave radiometer (PBMR) flights and compared with the results of gravimetric sampling done in support of these flights. Examination of the data reveals that the impedance probe is a more consistent source of time series information than traditional measurements and is potentially more closely linked to the physical parameters which are both remotely sensible and required for surface energy/mass exchange determination.