Forecasting snow avalanche danger in mountainous regions is of major importance for the protection of infrastructure in avalanche run-out zones. Inexpensive measurement devices capable of measuring snow height and layer properties in avalanche starting zones may help to improve the quality of risk assessment. We present a low-cost L-band frequency modulated continuous wave radar system (FMCW) in upward-looking configuration. To monitor the snowpack evolution, the radar system was deployed in fall and subsequently was covered by snowfalls. During two winter seasons we recorded reflections from the overlying snowpack. The influence of reflection magnitude and phase to the measured frequency spectra, as well as the influence of signal processing were investigated. We present a method to extract the phase of the reflection coefficients from the phase response of the frequency spectra and their integration into the presentation of the measurement data. The phase information significantly improved the detectability of the temporal evolution of the snow surface reflection. We developed an automated and a semi-automated snow surface tracking algorithm. Results were compared with independently measured snow height from a laser snow-depth sensor and results derived from an upward-looking impulse radar system (upGPR). The semi-automated tracking used the phase information and had an accuracy of about 6 to 8 cm for dry-snow conditions, similar to the accuracy of the upGPR, compared to measurements from the laser snow-depth sensor. The percolation of water was observable in the radargrams. Results suggest that the upward-looking FMCW system may be a valuable alternative to conventional snow-depth sensors for locations, where fixed installations above ground are not feasible.

中文翻译：

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用于积雪监测的仰视 L 波段 FMCW 雷达

预测山区雪崩危险对于保护雪崩流出区的基础设施具有重要意义。能够测量雪崩起始区的雪高和雪层特性的廉价测量设备可能有助于提高风险评估的质量。我们提出了一种上视配置的低成本 L 波段调频连续波雷达系统 (FMCW)。为了监测积雪的演变，雷达系统在秋季部署，随后被降雪覆盖。在两个冬季，我们记录了上覆积雪的反射。研究了反射幅度和相位对测量频谱的影响，以及信号处理的影响。我们提出了一种从频谱的相位响应中提取反射系数相位的方法，并将它们整合到测量数据的表示中。相位信息显着提高了雪面反射时间演变的可探测性。我们开发了一种自动和半自动雪面跟踪算法。结果与来自激光雪深传感器的独立测量雪高和来自向上看脉冲雷达系统 (upGPR) 的结果进行了比较。半自动跟踪使用相位信息，与激光雪深传感器的测量值相比，干雪条件下的精度约为 6 至 8 厘米，与 upGPR 的精度相似。在雷达图中可以观察到水的渗透。