Determination of the shortwave anisotropic function for clear-sky desert scenes from meteosat data

Journal Article · Thu Jun 01 04:00:00 EDT 1995 · Journal of Applied Meteorology

DOI:https://doi.org/10.1175/1520-0450(1995)034<1349:DOTSAF>2.0.CO;2· OSTI ID:160138

Capderou, R; Kandel, R ^[1]

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1. Laboratoire de Meteorologie Dynamique du CNRS, Palaiseau (France)

Determination of planetary albedo on the basis of satellite observations of reflected shortwave (SW) radiances requires taking into account the anisotropic (non-Lambertian) reflectance properties of the earth-atmosphere system, depending both on the cloud cover and the nature of the underlying surface. One approach frequently used has been to represent these properties by a limited set of normalized bidirectional reflectance functions (BDRF) for different scene types. The construction of the normalized BDRFs used to process the Earth Radiation Budget Experiment (ERBE) measurements was based mostly on data from the sun-synchronous Nibus-7 mission, observing close to local noon. Consequently, because desert zones are fairly restricted in latitude, only a small range of solar zenith angles was sampled. Here the authors consider, for clear-sky desert areas, the improvements that can be made using data from the geostationary satellite Meteostat, which samples all solar zenith angles that occur. The authors define BDRF ratios (between two instants on the same day for the same area) that depend on viewing geometry (five angles for a geostationary satellite) and that together with infrared window radiance measurements allow to distinguish clear and cloudy desert scenes. Using three to five Meteostat images per day over the year 1985, and considering 42 areas in desert zones, the authors compute roughly 12500 clear-sky BDRF ratios (representing 4.5 million B2 pixels), and sort these into bins in five-dimensional angular space. Values of the BDRF ratio are well defined and stable in each of these bins. Application of the Helmholtz reciprocity principle yields data for angular bins not directly observed. After spectral corrections and normalizations, the authors obtain a completely defined SW angular model (i.e., normalized anisortropic function and directional albedo) for clear-sky desert scenes. The authors discuss the improvements obtained. 18 refs., 14 figs., 9 tabs.

• OSTI ID: 160138
• Journal Information: Journal of Applied Meteorology, Journal Name: Journal of Applied Meteorology Journal Issue: 6 Vol. 34; ISSN JOAMEZ; ISSN 0894-8763
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
99 GENERAL AND MISCELLANEOUS
ALBEDO
ANISOTROPY
CLOUD COVER
CORRECTIONS
DESERTS
EARTH ATMOSPHERE
EARTH PLANET
GOES SATELLITES
INCIDENCE ANGLE
MATHEMATICAL MODELS
SOLAR RADIATION