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Directional optical transmission through a sand layer: a preliminary laboratory experiment

机译：通过沙层的定向光传输：初步的实验室实验

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Given the importance of penetration of light in the soil for seed germination, soil warming, and the photolytic degradation of pesticides, directional transmission of thin sand samples are studied in this paper under both dry and saturated conditions. The detector views upward through a glass-bottom sample holder, filled to 3 or 4 mm with a coarse, translucent, quartz sand sample. Transmission through the samples was measured as the illumination zenith angle moved from 0 to 70° in 5° intervals. In the most cases, transmission decreased monotonically, but slowly with increasing illumination angle at all wavelengths. A peak in transmission only appeared at 0° illumination for the low bulk density, dry sample at 3 mm depth. The 0° peak disappeared when the sample was wetted, when the bulk density increased, or when the depth of the sample increased, which indicates that the radiation transmitting through a sand layer can be diffused thoroughly with a millimeters-thin sand layer. For the saturated samples, water influences light transmission in contrasting ways in shorter and longer wavelength. Transmission increased in the VNIR when saturated relative to dry, while transmission decreased sharply after 1300 nm, with spectral absorption features characteristic of water absorption. In VNIR region, water absorption is low and the low relative index of refraction enhanced transmission through sand sample. In contrast, water absorption became dominant at longer wavelengths region leading to the strongly reduced transmission.
机译：考虑到光在土壤中的渗透对于种子发芽，土壤变暖和农药的光解作用具有重要意义，因此本文研究了在干燥和饱和条件下薄砂样品的定向传输。检测器通过玻璃底样品架向上注视，该样品架填充有3毫米或4毫米粗，半透明的石英砂样品。当照明天顶角以5°的间隔从0°移至70°时，测量通过样品的透射率。在大多数情况下，透射率在所有波长下单调降低，但随着照明角度的增加而缓慢降低。对于3mm深度的低堆积密度干燥样品，仅在0°照明下出现透射峰。当样品被润湿，堆积密度增加或样品深度增加时，0°峰消失，这表明透过沙层的辐射可以用毫米薄的沙层完全扩散。对于饱和样品，水以相反的方式影响波长越来越短的光传输。当相对于干燥饱和时，透射率在VNIR中增加，而透射率在1300 nm之后急剧下降，具有吸水特性。在VNIR区域，吸水率低，相对折射率低，从而提高了砂样品的透射率。相反，在更长的波长区域吸水占主导地位，从而导致透射率大大降低。

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