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  • Testing the Hapke photometr...
    Helfenstein, Paul; Shepard, Michael K.

    Icarus (New York, N.Y. 1962), 09/2011, Letnik: 215, Številka: 1
    Journal Article

    ► We present a new analysis method for investigating light scattered by regoliths. ► We connect the effect of porosity on albedo to the shadow-hiding opposition effect. ► Soil physical property detection is improved for low to moderate albedo regoliths. ► No improvement is found for high-albedo regoliths. In conjunction with a companion paper (Shepard, M.K., Helfenstein, P. 2011. Icarus, submitted for publication), we derive, test, and apply a detailed approach for visualizing the phase angle dependence of light scattering in particulate soils from both whole-disk and disk-resolved observations. To reduce the number of model parameters and provide stronger constraints on model fits, we combine Hapke’s (Hapke, B. 2008. Icarus 195, 918–926) recent correction for effects of porosity with his (Hapke, B. 1986. Icarus 67, 264–280) model of the shadow hiding opposition effect. We further develop our method as a tool for least-squares fitting of Hapke’s model to photometric data. Finally, we present an improved method for estimating uncertainties in retrieved values of Hapke model parameters. We perform a preliminary test of the model on spectrogoniometric measurements from three selected laboratory samples from Shepard and Helfenstein (Shepard, M.K., Helfenstein, P. 2007. J. Geophys. Res. 112 (E03001), 17). Our preliminary suite of test samples is too small and selective to permit the drawing of general conclusions. However, our results suggest that Hapke’s porosity correction improves the fidelity of fits to samples composed of low- and moderate-albedo particles and may allow for more reliable retrieval of porosity estimates in these materials. However, we find preliminary evidence that in high-albedo surfaces, the effects of porosity may be difficult to detect.