Utilization of satellite data in land surface hydrology: sensitivity and assimilation

This paper investigates the sensitivity of potential evapotranspiration to input meteorological variables, i.e. surface air temperature and surface va por pressure. The sensitivity studies have been carried out for a wide rang e of land surface variables such as wind speed, leaf area index and surface temperatures, Errors in the surface air temperature and surface vapor pres sure result in errors of different signs in the computed potential evapotra nspiration. This result has implications for use of estimated values from s atellite data or analysis of surface air temperature and surface vapor pres sure in large-scale hydrological modeling. The comparison of cumulative pot ential evapotranspiration estimates using ground observations and satellite observations over Manhattan, Kansas for a period of several months shows a variable difference between the two estimates, The use of satellite estima tes of surface skin temperature in hydrological modeling to update the soil moisture using a physical adjustment concept is studied in detail, includi ng the extent of changes in soil moisture resulting from the assimilation o f surface skin temperature. The soil moisture of the 1 cm surface layer was adjusted by 0.09 mm over a 10-day period as a result of a 3 K difference b etween the predicted and the observed surface temperature. This is a consid erable amount given the fact that the top layer can hold only 5 mm of moist ure. Copyright (C) 2001 John Wiley & Sons, Ltd.