Satellite estimates of surface radiative fluxes for the extended San PedroBasin: sensitivity to aerosols

Surface downwelling and upwelling radiative fluxes are important inputs int o hydrologic models that evaluate water budgets, and into land surface data assimilation schemes which are driven with radiative fluxes. For large-sca le needs, only remote sensing methods can provide such information. The acc uracy of the derived fluxes depends on the inference schemes and on the qua lity of auxiliary input parameters. At present, information on surface shor t-wave (SW) radiative fluxes over the United States is produced in real tim e by the National Oceanic and Atmospheric Administration (NOAA)/National En vironmental Satellite Data and Information Service (NESDIS) at 0.5 degrees resolution, at hourly time intervals, using independently derived auxiliary inputs. Information on aerosol properties and their temporal variability i s not available, and at best, is only estimated. During 1997 information on aerosol optical properties was collected at the USDA-Agricultural Research Service Walnut Gulch Experimental Watershed, Arizona, in preparation for f uture validation efforts in support of new satellite observations (e.g., AD EOS-II). This data set was used to test the sensitivity of a radiation infe rence scheme to aerosols, in particular, on the determination of clear sky fluxes and the surface albedo. Data from the Arizona meteorological network (AZMET) have been utilized to evaluate the satellite estimates for 1997. I t was found that the current satellite estimates are within 70 W m(-2) of t he ground observations on an hourly time scale and within 24 W m(-2) on a d aily time scale. In the latter case this is less than 10% of the mean. Use of actual observations of aerosols, as compared to climatological values, r educes the bias substantially, while less significant changes in the r.m.s. were found. (C) 2000 Elsevier Science B.V. All rights reserved.