Ns. Chauhan, SOIL-MOISTURE ESTIMATION UNDER A VEGETATION COVER - COMBINED ACTIVE-PASSIVE MICROWAVE REMOTE-SENSING APPROACH, International journal of remote sensing, 18(5), 1997, pp. 1079-1097
Data gathered during the NASA sponsored Multisensor Aircraft Campaign
Hydrology (MACHYDRO) experiment in central Pennsylvania (U.S.A.) in Ju
ly, 1990 have been analysed to study the combined use of active and pa
ssive microwave sensors for estimating soil moisture from vegetated ar
eas. These data sets were obtained during an eleven-day period with NA
SA's Airborne Synthetic Aperture Radar (AIRSAR), and Push-Broom Microw
ave Radiometer (PBMR) over an instrumented watershed, which included a
gricultural fields with a number of different crop covers. Simultaneou
s ground truth measurements were also made in order to characterize th
e state of vegetation and soil moisture under a variety of meteorologi
cal conditions. Various multi-sensor techniques are currently under in
vestigation to improve the accuracy of remote sensing estimates of the
soil moisture in the presence of vegetation and surface roughness con
ditions using these data sets. One such algorithm involving combinatio
n of active and passive microwave sensors is presented here, and is ap
plied to representative corn fields in the Mahantango watershed that w
as the focus of study during the MACHYDRO experiment. In this algorith
m, a simple emission model is inverted to obtain Fresnel reflectivity
in terms of ground and vegetation parameters. Since Fresnel reflectivi
ty depends on soil dielectric constant, soil moisture is determined fr
om reflectivity using dielectric-soil moisture relations. The algorith
m requires brightness temperature, vegetation and ground parameters as
the input parameters. The former is measured by a passive microwave t
echnique and the later two are estimated by using active microwave tec
hniques. The soil moisture estimates obtained by this combined use of
active and passive microwave remote sensing techniques, show an excell
ent agreement with the in situ soil moisture measurements made during
the MACHYDRO experiment.