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23 February 1985 Infrared Measurement Of Grain Size And Melting Degree Of Snow
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Hemispherically integrated reflectance of snow has been studied both experimentally and theoretically. Spectral measurements in the range of 600 to 2000 nm have been done for several types of snow including meta-morphic states from nearly-fallen to melt-refreezed and density variations from 0.10 to 0.45 g/cm3. The effect of the melting degree up to 20 volume per cent of free water has also been studied. Snow reflection is a multiple scattering phenomenon and it is strongly dependent on the grain size and spectral variations in the ice absorption coefficient. Due to differences between the absorption coefficient of ice and water, the reflection spectrum of dry snow differs from that of wet snow. A reflectance model based on an approximate solution of the radiative transfer equation is used for theoretical analysis. Based on the theory and experiments, it is shown that by using three optimally selected wavelengths the relative free water content and average grain size can be determined. In the experiments of snow with an average grain size of 1 mm, a 0,8 per cent change in the reflectance ratio at wavelengths 1260 and 1370 nm corresponds to one volume per cent variation of the free water content. Reflectance measurement at a third wavelength 1160 nm can be used for computer elimination of grain size de-pendent scattering effects. Further, the reflectance ratio of 1160 and 1260 nm can be used as a measure of the average grain size. For dry snow a change of 1.5 to 2.1 in the reflectance ratio corresponds to an increase of the grain size from 0.25 to 1.5 mm, respectively. The third wavelength 1370 nm can be used here to elimin-ate variations in the free water content. It can be estimated based on the measurements made so far that an accuracy of ±1.5 volume per cent and ±0.2 mm in the measurement of the free water content and average grain size, respectively, can be achieved.
© (1985) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
T. Hyvarinen and J. Lammasniemi "Infrared Measurement Of Grain Size And Melting Degree Of Snow", Proc. SPIE 0572, Infrared Technology XI, (23 February 1985);


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