Abstract
This paper compares evapotranspiration estimates from two complementary satellite sensors - NASA's Moderate Resolution Imaging Spectroradiometer (MODIS) and ESA's ENVISAT Advanced Along-Track Scanning Radiometer (AATSR) over the savannah area of the Volta basin in West Africa. This was achieved through solving for evapotranspiration on the basis of the regional energy balance equation, which was computationally-driven by the Surface Energy Balance Algorithm for Land algorithm (SEBAL). The results showed that both sensors are potentially good sources of evapotranspiration estimates over large heterogeneous landscapes. The MODIS sensor measured daily evapotranspiration reasonably well with a strong spatial correlation (R²=0.71) with Landsat ETM+ but underperformed with deviations up to ~2.0 mm day-1, when compared with local eddy correlation observations and the Penman-Monteith method mainly because of scale mismatch. The AATSR sensor produced much poorer correlations (R²=0.13) with Landsat ETM+ and conventional ET methods also because of differences in atmospheric correction and sensor calibration over land.
Highlights
Understanding the spatial dynamics of evapotranspiration (ET) is critically important for food security and water resources management in Africa
This paper evaluated the potential of both Moderate Resolution Imaging Spectroradiometer (MODIS) and Advanced Along-Track Scanning Radiometer (AATSR) sensors for measuring regional-scale evapotranspiration (ET), based on the regional energy balance equation and driven by the Surface Energy Balance Algorithm for Land algorithm (SEBAL) algorithm
The results show that both MODIS and AATSR can derive reasonable estimates of key variables such as NDVI, surface temperature (Ts) and ET over large vegetated savannah landscapes
Summary
Understanding the spatial dynamics of evapotranspiration (ET) is critically important for food security and water resources management in Africa. The quality of satellite data, the ease of application and availability of algorithms for retrieving key ET model parameters remains very important In this context, it is necessary to evaluate the utility of different sensor data to ascertain their quality and value in terms of information sharing among scientific users, policy managers and data providers. MODIS has a higher radiometric resolution than AVHRR using 16 bits of quantization in all bands as opposed to AVHRR’s 10 bits [8] This is the first study to compare MODIS with AATSR. The paper seeks to examine the relative potential of MODIS and AATSR for measuring key components of the energy balance equation such as surface temperature (Ts) and ET over the Volta basin, which might potentially be used to predict regional water availability
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