Confirmation of Helmholtz Reciprocity Using ScaRaB Satellite Data

Capderou, Michel

doi:10.1016/s0034-4257(98)00004-2

Cited by 7 publications

(2 citation statements)

References 21 publications

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“…The orbit plane precessed relative to the Sun‐Earth vector with a period of approximately 213 days, resulting in full coverage of the diurnal cycle in about 106 days. The ScaRaB instrument is a cross‐track scanning radiometer with a swath of 97.82° (that is, the maximum satellite nadir angle is 48.91°, yielding a maximum viewing zenith angle of 63.57° considering the curvature of the Earth) [ Capderou , 1998]. The angular resolution of instantaneous field of view is 48 × 48 mrad 2 , corresponding to a pixel size of 60 × 60 km 2 at nadir.…”

Section: Scarab Project and Inversion Methodsmentioning

confidence: 99%

Determination of top‐of‐atmosphere longwave radiative fluxes: A comparison between two approaches using ScaRaB data

Chen

Rossow

2002

J.‐Geophys.‐Res.

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[1] Two conceptually different approaches (broadband-based ERBE (Earth Radiation Budget Experiment) and narrowband-based ISCCP (International Satellite Cloud Climatology Project) approaches), used to derive the TOA (top of atmosphere) longwave radiative fluxes, are compared using the ScaRaB simultaneous narrowband and broadband measurements. Except for very thin cirrus clouds, differences between the ERBE and the ISCCP approaches are in general <10 W m À2for the TOA LW radiative fluxes. For clear pixels the model-calculated (ISCCP approach) TOA LW radiances are systematically smaller than the observations. Compared with the radiative transfer model used in this study, the ERBE LW angular dependence models are too weakly limb darkened for optically thin clouds but too strongly limb darkened for optically thick clouds, suggesting that more accurate instantaneous TOA LW flux estimations from the ERBE approach would require additional cloud classes based on cloud height and optical thickness.INDEX TERMS: 3399

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Section: Scarab Project and Inversion Methodsmentioning

confidence: 99%

Determination of top‐of‐atmosphere longwave radiative fluxes: A comparison between two approaches using ScaRaB data

Chen

Rossow

2002

J.‐Geophys.‐Res.

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“…At the 10 m scale in land surface remote sensing studies, Kriebel [1996] found some deviation to directional reciprocity using airborne data. At the 50 km scale, clear scenes of Earth radiation budget satellite sensor data showed an insignificant deviation from reciprocity [Davies, 1994;Capderou, 1998], while significant deviations were seen with scenes containing clouds [Davies, 1994;Loeb and Davies, 1997]. Lunar photometry measurements over large areas of the moon gave satisfactory directional reciprocity results at the scale of hundreds of kilometers [Minnaert, 1941].…”

Section: Introductionmentioning

confidence: 99%

Deviation from reciprocity in bidirectional reflectance

Leroy¹

2001

J. Geophys. Res.

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Abstract. The subject of the paper is to discuss and quantify deviations from reciprocity of the bidirectional reflectance distribution function (BRDF), i.e., the difference of BRDF obtained when inverting illumination and viewing directions. Directional reciprocity is not valid in general, because when the illumination beam has a spatial extension larger than the viewed area (as is most often the case for BRDF measurements), some of the scatterers building up the observed radiance are located at different places in reciprocal measurements. The physical systems under consideration in the two experiments are different, hence the breakdown of reciprocity. The paper develops a theory aiming at a quantitative estimation of deviations from directional reciprocity due to this factor. The theory is based on integral forms of the radiative transfer equation in a horizontal slab of heterogeneous absorbing and scattering media. The observed scene radiance is expanded in a series of scattering orders. Integral expressions of the single-and multiple-scattering radiance are derived and put in a form suitable for the analysis of the reciprocity problem. IntroductionThe principle of reciprocity, also referred to as Helmoltz reciprocity, is widely accepted in various branches of physics. Its modern and most general form [Van der Hulst, 1980] states that "in any linear physical system, the channels which lead from a cause at one point to an effect at another point can be equally well traversed in the opposite direction. Let the cause be first placed at P and the effect measured at Q; and in a second experiment, carried out in the same physical system, let the cause be at Q and the effect at P. The reciprocity principle is then expressed by the proportionality: effect at Q/cause at P = effect at P/cause at Q.

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