Remote sensing estimates of actual evapotranspiration in an irrigation district

Abstract

Accurate estimates of the spatial distribution of actual evapotranspiration (AET) are useful in hydrology but can be difficult to obtain. Remote sensing provides a potential capability for routinely monitoring AET by combining remotely sensed surface temperature and vegetation cover observations with near surface meteorological data in a surface energy balance model. Results from two different energy balance models are compared to airborne and ground measurements of surface energy fluxes over an irrigation district in northern Victoria during January 2003. Ground data collected include eddy correlation measurements of latent and sensible heat fluxes and associated meteorological measurements. The airborne data include eddy correlation measurements of latent and sensible heat fluxes (35 m above ground level), surface temperature transects and normalised difference vegetation index (NDVI) imagery (1 m resolution). Surface temperature and NDVI maps were derived from Landsat ETM+ data and combined with the ground meteorological observations in both a one- and two-source energy balance model. The two models produced similar results over irrigated sites, but large discrepancies were present over sparsely vegetated and bare soil areas. Although both models overestimated the latent and sensible heat fluxes in comparison to the ground and airborne measured fluxes, it was found that the modelled and observed Bowen ratios compared well.