Directional radiative temperature observations for improvement of land-atmosphere interactions
Along with a brief account of the characteristics of the Advanced Along Track Scanning Radiometer (AATSR) data onboard of the ENVISAT satellite, field observations of directional radiometric temperatures are analysed to examine the possibilities of using AATSR data to improve the estimates of the energy and water balances on land surfaces, especially for the purpose of numerical weather forecasts and climate research. In the summer of 1998, the authors have participated in the Inner Mongolia Grassland-Atmosphere Surface Study (IMGRASS) campaign. Apart from many other measurements (tower, eddy correlation, tethered-balloon, total and spectral radiation, soil temperature gradients, etc.), intensive measurements were carried out for directional radiative temperatures. Preliminary analysis of the data indicates that the difference in radiative temperature between different view angles is primarily caused by the vegetation fraction viewed. The difference between nadir and 23 degree is around 0.5 K, and that between nadir and 52 degree reaches 1.5 to 2 K dependent on the time of the measurements. This finding is similar for two independent measurement set-ups at two separate locations, both having similar sparse grass covers of around 10 cm high, and a leaf area index of 0.5.