ABSTRACT

The measurements of surface soil moisture, net radiation, sensible heat flux, and latent heat flux have many applications in different disciplines such as hydrology, agriculture, meteorology, and forestry. These important biophysical variables are either measured or estimated using the different methods available. For example, surface fluxes can be measured using lysimeters, Bowen ratio and, eddy correlation systems, water balance methods, gas exchange chambers, and micrometeorological methods (Dugas et al. 1991). The soil moisture can be measured using gravimetric methods, neutron probes, tensiometers, and hygrometric methods (Schmugge et al. 1980). However, point measurements produce reliable results only for the site at which the measurements were taken and are not spatially representative at larger regional scales. Furthermore, the use of point measurements as a typical value for a larger area is likely to introduce significant errors because of the heterogeneity of most land surfaces. Striking differences in these variables occur over short distances even within the same field. For example, Davenport and Hudson (1967) measured evaporation rates from open-water, using evaporimeter dishes, and found a decrease of about 30% in latent heat flux with in a 60 m distance of the upwind edge of a cotton field. Other researchers (Burman et al. 1975; Holmes 1970) report similar results.