Monitoring Evapotranspiration for Terrestrial Groundwater Dependant Ecosystems Using Satellite-based Energy Balance Model

Understanding and mitigating against the impact of land use change and groundwater extraction on groundwater dependant ecosystems (GDE) requires information on the distribution and environmental water needs of these ecosystems. Conventional field based techniques for determining plant water use and plant stress are very labour intensive and time consuming. In this study, we proposed an alternative method using multi-temporal satellite images and the application of the Surface Energy Balance Algorithm for Land (SEBAL). Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper (ETM+) images were used to derive land surface temperatures and evapotranspiration (ET) for the targeting ecosystems and species. The radiative transfer model (MODTRAN 4.1) was used with atmospheric profile data to atmospherically correct the Landsat data. Vegetation indices and surface temperature were derived from the satellite images and used to estimate fractional vegetation cover, leaf area index (LAI), emissivity and net radiation. These data, along with meteorological data, provided inputs for the SEBAL model which was in turn used to determine the actual ET, pixel by pixel, for selected groundwater management areas in the central west of New South Wales, Australia. The remote sensing estimated ET was imported into geographic information systems (GIS) for further spatial analysis and mapping, in combination with land use and other ancillary data. The estimated ET results were evaluated using a Vegetation Index/Temperature Trapezoid (VITT) model and field measurements. Ancillary GIS data were also used in the quality control process to ensure accepted accuracy. It is expected that this technique and the resulting ET maps will assist us to monitor the effects of groundwater management on the water uses and the indicative health of these terrestrial groundwater ecosystems. * Corresponding author.