A general two-stream algorithm for retrieving spectral surface albedo

Abstract

Spectral surface albedo (SSA) has numerous applications in climate and environmental studies. Given that ground-based observations of SSA are very limited, space-borne remote sensing has been the primary means of acquiring SSA on large or global scales. To date, many satellite sensors measure reflectances in different spectral regions from which values of SSA are inferred. The inversion algorithms range from simple linear relationships to complex, full-fledged radiative transfer models. Often, algorithms were designed for application to a particular sensor or spectral band. In this study, we propose a more versatile parameterized algorithm that can be used for estimating SSA from satellite-measured spectral albedos at the top of the atmosphere (TOA). The algorithm was developed based on a three-layer atmospheric model. Monochromatic and band transmittances due to various absorbing species are parameterized. The reflectance and transmittance for direct and diffuse radiation in the second layer are determined by the generalized two-stream solutions. Except for the parameterization coefficients that vary with the bandpass and spectral response function of the satellite sensor, the framework of the inversion model is applicable to any sensor or spectral region. The model is tested by applying it to the results of detailed radiative transfer simulations for a wide range of conditions for various satellite sensors and spectral bands. The complexity and accuracy of the proposed model are intermediate relative to those of models currently in use. Résumé. L'albédo spectral de surface (SSA) a plusieurs applications dans les études climatiques ou environnementales. Étant donné que les observations de SSA au sol sont très limitées, la télédétection satellitaire constitue le moyen privilégié d'acquisition de SSA à grande échelle ou à l'échelle du globe. Aujourd'hui, plusieurs capteurs satellitaires mesurent les réflectances dans différentes bandes spectrales à partir desquelles la valeur de SSA est déduite. Les algorithmes d'inversion varient des simples relations linéaires aux modèles plus complexes de transfert radiatif. Souvent, les algorithmes ont été développés pour application à un capteur particulier ou une bande spectrale spécifique. Dans cette étude, nous proposons un algorithme de paramétrage plus versatile qui peut être utilisé pour l'estimation de SSA à partir de mesures d'albédo spectral acquises par satellite au sommet de l'atmosphère (TOA). L'algorithme a été développé à partir d'un modèle atmosphérique à trois couches. Les transmittances monochromatiques et intégrées sur la bande dues aux différentes composantes absorbantes de l'atmosphère sont paramétrées. La réflectance et la transmittance du rayonnement direct et diffus dans la …

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