Rapid Quantitative Snow Stratigraphy for Avalanche Forecasting Using Near-Infrared Photography

为了研究积雪加强和减少雪崩危险的方式，我们观察了积雪的整个深度剖面的积雪地层和烧结。前些年，我们使用光学显微镜和扫描电子显微镜来测量雪粒的几何形状和化学成分。由于这些观察所需的时间，我们只对两个地点进行了抽样。我们计划使用一种新的方法--近红外数码摄影，扩大我们的采样范围，以了解地层和烧结在空间上是如何变化的。这将使快速定量地层学和评估雪的稳定性和雪变质速率成为可能。从历史上看，雪崩预报的重点是积雪中可识别的层，但我们在雪崩一天内对风暴中雪崩顶面(最远的上坡拉伸断口)的近红外图像显示，床面和板层之间的光学性质几乎没有明显差异。在北美西部的海洋环境中，90%以上的破坏发生在风暴层内，并发生在非持续性软弱层上。我们的假设是，雪崩不需要明显的弱层。相反，我们建议将新雪的稳定性视为一个连续体问题，在任何时候，薄弱部分都位于应力/强度比最低的位置。覆盖层产生下坡应力，而烧结和压实可提高强度。为了验证这一假设，我们将使用近红外摄影和机械强度测量相结合的方法在冠面进行广泛的测量，并将开发一个包括暴风雨层所有深度的下坡应力和连续烧结的积雪稳定性连续模型。评估暴风雪期间的稳定性是困难的，但在一些环境中，几乎所有的雪崩都发生在暴风雨期间或之后不久。近红外摄影技术在雪崩危险性评价中的新应用，使得雪地层学的快速研究成为可能，可能的结果是，这些数据与雪的力学性质及其在雪崩危险性评价中的应用有关。虽然利用遥感手段研究了雪表面雪粒大小的非均质性，但对雪埋层，尤其是坡度尺度上雪性质的非均质性的研究要少得多。我们的经验、广泛的仪器设备、现场可访问性以及大量的雪崩控制记录使我们的野外位置猛犸象山成为测试如何使用近红外摄影来检查积雪轮廓中积雪发生故障的地点和时间的理想地点。我们将开发并提供开源软件，以处理近红外雪坑图像并绘制剖面的地层图。我们的软件与近红外数字摄影的低成本和速度相结合，可以使研究社区以外的广泛用户群体获得高分辨率定量地层学，包括导游、滑雪巡逻员、雪崩预报员，可能还有娱乐用户。我们对风暴期间失败的分析将揭示这组重要的雪崩，与那些在较深、较弱的较老层上失败的雪崩截然不同。最终，我们的结果和技术可能会减少北美雪崩死亡人数的增加。

To examine the ways a snowpack strengthens and reduces the avalanche hazard, we observe snow stratigraphy and sintering throughout the depth profile of the snowpack. In previous years, we used optical microscopy and scanning electron microscopy to measure snow grain geometry and chemical composition. Because of the time required for those kinds of observations, we sampled only two locations. We plan to extend our sampling to learn how stratigraphy and sintering vary spatially using a new method, near-infrared digital photography. This will allow for rapid quantitative stratigraphy and evaluation of snow stability and rates of snow metamorphism. Historically, snow avalanche forecasting has focused on identifiable layers in the snowpack, but our near-infrared images across in-storm avalanche crown faces (the furthest uphill tensile fracture) within one day of avalanching show little discernible difference in the optical properties between the bed surface and the slab. In the maritime environment of western North America, more than 90% of failures occur within the storm layer and fail on non persistent weak layers. Our hypothesis is that no obvious weak layer is needed for avalanches. Instead, we propose that stability of new snow should be treated as a continuum problem where, at any time, the weakness is located where the ratio of stress/strength is lowest. The overburden causes downslope stress, while sintering and compaction increase strength. To test this hypothesis, we will make extensive measurements at crown faces using near-infrared photography combined with measurements of mechanical strength, and we will develop a continuum model of snow stability that includes downslope stress and continuous sintering at all depths in the storm layer. Evaluating snow stability during storms is difficult, yet in some environments almost all avalanches occur during or shortly after storms. The novel application of near-infrared photography to avalanche hazard evaluation enables the rapid study of snow stratigraphy, with the likely results that the data are correlated with mechanical properties of snow and their application to avalanche hazard evaluation. While the heterogeneity of grain sizes at the snow surface has been investigated with remote sensing, there are many fewer studies of the heterogeneity of snow properties in buried layers, especially at the slope scale. Our experience, extensive instrumentation, site accessibility, and large number of avalanche control records make our field location, Mammoth Mountain, an ideal site to test how near-infrared photography can be used to examine where and when in the snow profile the snowpack fails. We will develop and make available open source software to process near-infrared snowpit images and to map stratigraphy of the profile. Our software, combined with the low cost and speed of near-infrared digital photography, could make high resolution quantitative stratigraphy available to a broad user group beyond the research community, including guides, ski patrollers, avalanche forecasters, and possibly recreational users. Our analysis of failure during storms will shed light on this important set of avalanches, distinct from those that fail on deep, weak older layers. Ultimately, our results and techniques may reduce the increasing number of avalanche fatalities in North America.