HR: 1330h
AN: H32B-0561    [PDF]
TI: New Angular Distribution Models for Shortwave and Longwave Top-of-Atmosphere Radiative Flux Estimation From the Clouds and the Earth's Radiant Energy System Instrument
AU: * Loeb, N G
EM: n.g.loeb@larc.nasa.gov
AF: Hampton University, 23 Tyler Street, Hampton, VA 23681-2199 United States
AU: Kato, S
EM:
AF: Hampton University, 23 Tyler Street, Hampton, VA 23681-2199 United States
AU: Loukachine, K
EM:
AF: Science Applications International Corporation, One Enterprise Way, Hampton, VA 23666 United States
AU: Manalo-Smith, N
EM:
AF: Analytical Services and Materials, Inc., One Enterprise Way, Hampton, VA 23666 United States
AB: The Clouds and the Earth's Radiant Energy System (CERES) provides highly accurate top-of-atmosphere (TOA) shortwave (SW), longwave (LW) and window (WN) radiance measurements and radiative flux estimates together with coincident cloud and aerosol properties inferred from the Moderate Resolution Imaging Spectrometer (MODIS). These data are needed to investigate the critical role that clouds and aerosols play in modulating the radiative energy flow within the Earth-atmosphere system. To estimate TOA fluxes from measured CERES radiances, one must account for the angular dependence in the radiance field, which is a strong function of the physical and optical characteristics of the scene (e.g. surface type, cloud fraction, cloud/aerosol optical depth, cloud phase), as well as the illumination angle. Because the CERES instrument can rotate in azimuth as it scans in elevation, it is acquires data over a wide range of angles. Consequently, one can construct angular distribution models (ADMs) for radiance-to-flux conversion from the CERES measurements. Furthermore, since CERES and MODIS are on the same spacecraft, the ADMs can be derived as a function of MODIS-based scene type parameters that have a strong influence on radiance anisotropy. This presentation provides a brief overview of the methodology and validation results for a new set of global CERES ADMs developed from two years of CERES measurements on the Terra spacecraft. The uncertainty in regional monthly mean SW and LW TOA fluxes from the new ADMs is less than 0.5 W m-2 based on comparisons with TOA fluxes evaluated by direct integration of the measured radiances. From multiangle CERES radiance measurements, instantaneous TOA flux errors are estimated to be $< 10$ W m-2 in the SW and $< 3.5$ W m-2 in the LW. Uncertainties in TOA fluxes from the new CERES ADMs are a factor of 2-5 smaller than those based on ADMs developed during the Earth Radiation Budget Experiment (ERBE). The improved accuracy in the Terra radiative fluxes is essential in studies that examine radiative forcing by cloud type and studies that combine TOA fluxes with surface measurements from specific locations.
DE: 3309 Climatology (1620)
DE: 3359 Radiative processes
DE: 3360 Remote sensing
SC: Hydrology [H]
MN: 2003 Fall Meeting