The influence of ambient light intensity on in situ laser diffractometers
The influence of ambient light intensity on in situ laser diffractometers
复制标题
环境光强度对原位激光衍射仪的影响
DOI：
10.1029/2010wr009841
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发表时间：
2011
影响因子：
5.4
通讯作者：
S. Schladow
中科院分区：
文献类型：
--
作者：
S. Andrews;D. M. Nover;K. Reardon;J. Reuter;S. Schladow
原位激光衍射仪通过测量小颗粒在小前向角范围内散射的激光产生的光来表征悬浮颗粒的粒度分布（PSD）。在具有低颗粒浓度或高环境光条件的环境中，由光电探测器感测的自然下降的阳光与散射的激光的比率高，并且测量受到影响。在这里，我们评估的影响，环境光场强度的测量与激光原位散射和透射（LISST）100 X型B仪器。在高浊度和低浊度水的水下光强度范围内记录成对的光暗散射分布。光测量显示最小尺寸箱（1.25-1.48 μm）中存在大量错误的颗粒浓度，并显示对PSD整个范围的影响。环境光被发现表现出相同的恒定分布在两个水样的仪器光电探测器，虽然响应的幅度，每单位环境光强度的激光计数，是PSD依赖。本文介绍了一种用于后处理数据以消除光照影响的技术，用于在美国加州-内华达州太浩湖采集的系泊部署和垂直剖面数据。虽然成功地重建了去除光效应的测量结果，但该技术可能不适用于PSD或LISST相对于太阳方向的取向迅速变化的数据，或者当光强度足够高以熄灭仪器光电探测器时。环境光对太浩湖PSD测量的影响可以忽略不计，其强度低于30 W m−2。
In situ laser diffractometers characterize the suspended particle size distribution (PSD) by measuring laser‐generated light scattered off small particles over a range of small forward angles. In environments with low particulate concentrations or high ambient light conditions the ratio of natural downwelling sunlight to scattered laser light sensed by the photodetectors is high and measurements are influenced. Here, we evaluate the effect of the ambient light field intensity on measurements made with a Laser In Situ Scattering and Transmissometry (LISST) 100X type B instrument. Paired light‐dark scattering distributions are recorded over a range of underwater light intensities in high‐turbidity and low‐turbidity water. Light measurements displayed large erroneous concentrations of particles in the smallest size bin (1.25–1.48 μm) and showed effects over the full range of the PSD. Ambient light was found to exhibit the same constant distribution over the instrument photodetectors in both water samples, although the magnitude of the response, in laser counts per unit ambient light intensity, was PSD dependent. A technique for postprocessing data to remove the influence of light is presented for moored deployment and vertical profile data collected at Lake Tahoe, California‐Nevada, United States. While measurements removed of the light effect were successfully reconstructed, the technique may not be applicable to data where the PSD or the LISST orientation relative to the sun direction change rapidly or when light intensities are high enough to quench the instrument photodetectors. Ambient light was found to have negligible effects on PSD measurements in Lake Tahoe was below intensities of ∼30 W m−2.