Snow grain size retrieved from near-infrared radiances at multiple wavelengths

A comprehensive forward radiative transfer model is used to construct a sno w grain size retrieval algorithm that relies on the use of NIR radiances. D ata collected by the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS ) at the wavelengths 0.86, 1.05, 1.24 and 1.73 mum are used to retrieve sno w grain size. Based on a single-layer (homogeneous) snow model, the retriev ed snow grain size appears to depend on wavelength. The photon penetration depth defined as the e-folding flux attenuation depth has be computed for d ifferent snow grain sizes and different wave-lengths. It reveals that this apparent wavelength dependence occurs because (i) the snow grain size gener ally increases with depth, and (ii) the photon penetration depth decreases with increasing wavelength. The results show that the wavelength dependence of the photon penetration depth can be used to retrieve the depth dependen ce of the snow grain size.