Land cover characterization for hydrological modelling using thermal infrared emissivities

Remote sensing with multispectral thermal infrared can improve regional estimation of evapotranspiration (ET) by providing new constraints on land surface energy balance. Current models use visible and near infrared bands to obtain vegetative cover, and sometimes use thermal infrared data for land surface temperature. Together these can yield good ET estimates. However, it may be possible to do even better by using remotely sensed thermal infrared emissivity, a surface property related to fractional vegetative cover but independent of plant greenness. Emissivities derived from clear-sky Moderate Resolution Imaging Spectroradiometer (MODIS) observations obtained in 2007 over the Southern Great Plains (Oklahoma and Kansas), USA, were compared with changes in Normalized Difference Vegetation Index (NDVI) for winter wheat and grazing land. Emissivity changes were independent of NDVI and sensitive to standing canopies, regardless of growth stage or senescence. Thus emissivities were seasonally dynamic, able to detect wheat harvest timing, and helpful for modelling ET.