Infrared Measurement Of Free-Water Content And Grain Size Of Snow
Infrared Measurement Of Free-Water Content And Grain Size Of Snow
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红外测量雪的自由水含量和粒度
DOI：
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发表时间：
1987
期刊：
影响因子：
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通讯作者：
J. Lammasniemi
中科院分区：
文献类型：
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作者：
T. Hyvarinen;J. Lammasniemi
本文提出了一种利用近红外技术测量雪中自由水含量和粒径的方法。它不需要直接的物理采样，并使用三个最佳选择波长的反射率。该方法基于两个基本现象：首先，雪反射作为一种多重散射现象，强烈依赖于晶粒尺寸和冰吸收系数的光谱变化；其次，由于冰和水的吸收系数不同，干雪的反射光谱与湿雪的反射光谱不同。在600至2000 nm范围内测量了几种雪的半半球积分光谱反射率，包括从新降雪到融化再冻结的变质状态和密度从0.10至0.45 g/cm3。研究了对高达20 vol %自由水的反射率的影响。利用辐射传递方程的近似解对雪的反射率进行了理论分析。实验和理论计算表明，在1030、1260和1370 nm处的反射率测量可以得到自由水含量和平均粒径。从测量到目前为止，估计在测量自由水含量时可以达到A， ±1.5 vol %的精度，在测量平均晶粒尺寸时可以达到±0.2 mm的精度。
A method has been developed to measure the free-water content and grain size of snow by use of near-infrared methods. It requires no direct physical sampling and uses reflectances at three optimally selected wavelengths. The method is based on two basic phenomena: first, snow reflection as a multiple-scattering phenomenon is strongly dependent on the grain size and the spectral variations in the ice absorption coefficient, and second, owing to differences between the absorption coefficients of ice and water, the reflection spectrum of dry snow differs from that of wet snow. Hemispherically integrated spectral reflectance has been measured in the range between 600 and 2000 nm for several types of snow including metamorphic states from newly fallen to melted-refrozen and densities from 0.10 to 0.45 g/cm3. The effect on reflectance of up to 20 vol % free water has been studied. The reflectance of snow has also been analyzed theoretically using an approximate solution of the radiative transfer equation. The experiments and theoretical calculations show that the free-water content and average grain diameter can be derived from reflectance measurements made at 1030, 1260, and 1370 nm. From measurements made so far it is estimated that an accuracy of A‚± 1.5 vol % can be achieved in the measurement of the free-water content and of ± 0.2 mm can be achieved in the measurement of the average grain size.