Submitted to: International Journal of Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2007
Publication Date: N/A
Interpretive Summary: Accurate evapotranspiration (ET) models and observational tools are needed for monitoring and managing crop productivity at field to watershed scales. Accuracy of one model, SEBAL, was evaluated for an agricultural region in southwestern France from 2000 to 2003. The region included wheat, maize, soybean, sunflower, and sorghum. The model used satellite remote sensing data from the ASTER sensor, local meteorological and agricultural cover data, and regional atmospheric data. Model outcomes were consistent with agricultural practices where ET estimates were dominated by irrigation practices. However, the spatial resolution (15-90 m) and temporal frequency (16 days or greater) of ASTER data were inadequate for monitoring crops over this diverse area. These results show that crop water use could be monitored from satellites in the future provided the availability of high spatial and temporal resolution data. Agricultural researchers investigating ways to predict crop water use will be interested in the findings from this study.
Technical Abstract: Soil - vegetation - atmosphere transfers significantly influence interactions and feedbacks between vegetation and boundary layer, in relation with plant phenology and water status. The current study focused on linking micrometeorological conditions to cultural practices at the local and regional scales (lower than 100km²), over an agricultural region in South Western France. This was achieved considering observation and modelling tools designed for characterizing spatial variabilities over land surfaces. These tools were the ASTER high spatial resolution optical remote sensing data, and the SEBAL spatialised surface energy balance model. Surface bidirectional reflectance and brightness temperature were first derived from ASTER data through solar and thermal atmospheric radiative transfer codes, and next used to infer surface radiative properties required for model simulations. Assessing model consistency in terms of air temperature simulations gave satisfactory results when intercomparing against weather station data, although basic model assumptions were not systematically verified in terms of spatial variability. Next, spatialised simulations of evapotranspiration and air temperature were analysed at the regional and local scales, in relation with pedology, land use, and agricultural practices. It was shown model estimates were consistent with the considered crops and the related cultural practices. Irrigation appeared as the main factor amongst others (soil, landuse, sowing date…) explaining the micrometeorological variability. Although interesting and promising in terms of linking micrometeorological conditions to cultural practices, the results reported here emphasized several difficulties, specially about capturing subfield scale variability and monitoring the considered processes at an appropriate temporal sampling.