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

A comprehensive forward radiative transfer model is used to construct a snow grain size retrieval algorithm that relies on the use of NIR radiances. Data collected by the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) at the wavelengths 0.86, 1.05, 1.24 and 1.73 μm are used to retrieve snow grain size. Based on a single-layer (homogeneous) snow model, the retrieved snow grain size appears to depend on wavelength. The photon penetration depth defined as the e-folding flux attenuation depth has be computed for different snow grain sizes and different wavelengths. It reveals that this apparent wavelength dependence occurs because (i) the snow grain size generally 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 dependence of the snow grain size.