Cross-scale intercomparison of different approaches for measuring and modeling heat energy fluxes in West-Africa
Ulrike Falk1, Christopher Conrad2, Jan Hendrickx3
1 Center for Development Research (ZEF), University Bonn
2 Department of Remote Sensing, University of Wuerzburg
3 Dept of Earth & Environmental Science, New Mexico Tech
2 Department of Remote Sensing, University of Wuerzburg
3 Dept of Earth & Environmental Science, New Mexico Tech
O 6.6 in SVAT-Modeling and scale interactions
08.10.2009, 12:05-12:30, Kutschenhaus
Evapotranspiration (ET) mapping from remotely sensed satellite images is critical for water management since the estimation of spatial and temporal ET distributions over large areas is impossible using only ground measurements. A major difficulty for the calibration and validation of operational ET remote sensing algorithms is the ground measurement of ET at a scale similar to the spatial resolution of the remote sensing image. While the spatial length scale of remote sensing images covers a range from 30 m (LandSat) to 1000 m (MODIS), direct methods to measure the latent heat flux (W/m2) –i.e. the evapotranspiration rate (mm/day) multiplied by the latent heat for vaporization– such as eddy covariance (EC) only provide measurements at a scale that may be considerably smaller than the estimate obtained from a remote sensing method. The Large Aperture Scintillometer (LAS) flux footprint area is larger (here about 1 km²) and its spatial extent better constraint than that of EC systems. Nevertheless, it is only an indirect method for estimation of ET. Two years of continuous data from LAS as well as EC systems are analyzed and compared to modeled estimates of ET using remote sensing. Major difficulties here are the different areas probed by either ground measurements or remote sensing, but also the heterogeneity of small-scale agricultural landscape found in Burkina Faso. A method to estimate the LAS footprint is presented as well as application of existing footprint methods for the EC measurements. The objective of this contribution is to present our experiences with time series of ET mapping using ground observations and the Surface Energy Balance Algorithms for Land (SEBAL). This research is part of the BIOTA West and GLOWA Volta projects, funded by the BMBF.
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