Partitioning Energy Balance in the Murrumbidgee Catchment, Australia: Examples from Airborne and Satellite Data

Spatial knowledge of land surface evapotranspiration and root zone soil moisture is of prime interest for environmental applications, such as optimizing irrigation water use, irrigation system performance, crop water deficit, drought mitigation strategies and accurate initialisation of climate prediction models especially in arid and semiarid catchments where water shortage is a critical problem. The recent drought in Australia and concerns about climate change has highlighted the need to manage water resources more sustainably especially in the Murrumbidgee catchment which utilizes bulk water for food production. This study examines the components of the surface energy balance as part of the National Airborne Field Experimentation (NAFE) project carried out over Yanco and Kyeamba creek in a Murrumbidgee catchment over a month in November 2006. Instruments like a thermal imager and a tri-spectral scanner was flown onboard a small environmental research aircraft at different altitudes to map at 20 m resolution 11 times (every 1-3 days) over a 40 by 55 km area in the Yanco region and 3 times over a 40 by 50 km area that includes Kyeamba Creek catchment. The near-surface soil moisture using Hydra Probe data Acquisition System (HYDAS) and surface temperature using handheld thermal imager was measured extensively on the ground in eight sampling farms concurrently with the aircraft flights. In addition, surface roughness, LAI, crop reflectance, skin and soil temperature, and vegetation water content was measured on the ground in eight sampling farms. High resolution optical-thermal satellite images (like Terra/ASTER, and Landsat 5 TM) were acquired on November 14-15, 2006 to estimate actual evapotrasnpiration and soil moisture by solving an energy balance using SEBAL and SEBS algorithm over Yancoo and Kyeamba catchment. Similarly, high resolution airborne data for the same days was used to solve energy balance for an estimation of actual evapotranspiration and soil moisture over the same area. Results of actual ET estimated from airborne and satellite data were compared with Eddy Covariance Flux tower to figure out possible deviations in actual ET measurements. Similarly, soil moisture estimated from satellite data was compared with the soil moisture profile monitored at 41 sites. Results show a good correlation of values of actual ET measured from airborne and satellite data. Finally an error matrix and possible reasons of small deviations in measurement of actual crop water consumption at different spatial scales (from pixel to catchment) are discussed.