Estimating the surface water and radiation balance in an upland area from space

The Synthetic Aperture Radar ( SAR) carried aboard ERS-1 and -2 has been us ed to estimate soil moisture in a naturally vegetated area of upland moor i n Lancashire, north-west England. This holds promise for the determination of catchment-scale evapotranspiration rates using direct measurements of ch anges in soil moisture content. Combining such measurements as these with o bservations of net radiation from the NOAA AVHRR passive radiometer has led to the development of a method, based upon the techniques of Price (IEEE T ransactions on Geoscience and Remote Sensing, 28, 940-948, 1990) combined w ith some new methodologies, whereby the sensible heat flux can be found by the closure of the energy balance equation. A review of the methodology developed is presented together with the potent ial for refining the system using further instruments. There are limitation s of the procedure due to the restricted temporal coverage of the sensors c oncerned, and their inability to penetrate the surface to investigate soil- water-vegetation processes within the root zone. It is believed, however, t hat models can be constructed to account for these deficiencies to enable r etrieval of an entire surface energy and water budget. These would have a p lethora of applications, both direct and as inputs to atmospheric and hydro logical models.