Application Briefs

Avalanches pose a significant threat to human life and settlements, so studying them is key to formulating risk zones. Previously, validating models in order to predict avalanche behavior was limited by a lack of high-quality field data. Radar sensors can be used to gather field data, but in their current form, they only provide single-dimension range measurements. The transmitter power also limits them to a range resolution in the order of 50 m, which is too coarse to provide a true representation of the avalanche dynamics.

Radar antenna arrays at the VDLS bunker.
This project studied the underlying dynamics of avalanche flows with the aid of a newly developed frequency modulated continuous wave (FMCW) phased array radar. With this unique radar, highresolution 2D velocity measurements and a fully animated 2D reconstruction of avalanche events could be produced. The project involved several institutions: University of Sheffield, University of Cambridge, and University College London (UCL). At UCL, radar system development and the associated radar signal processing were the focus.

The radar operates in a reinforced concrete bunker at a well-equipped avalanche test site in Switzerland, Vallée de la Sionne (VDLS). The bunker is positioned at the foot of a slope opposing the avalanche track, and provides protection for the radar equipment. The test site is used to study avalanche processes using an array of sensors such as radar, pressure sensors, and acoustic sensors. Avalanches can be artificially triggered for experimental measurements by setting off explosives at the peak of the mountain after heavy snowfall. The site is also prone to natural avalanches that can be measured with instruments that are automatically triggered by acoustic sensors.

Data Acquisition and Radar Control

Several specialized data acquisition systems appeared to meet the design requirements, but a National Instru - ments solution offered tight enough integration between existing hardware and software. An NI PXIe-1082 chassis, NI PXIe-8130 controller, and an 8-channel, 16-bit NI PXIe-6366 X Series DAQ device were chosen with specifications that met the data throughput and dynamic range requirements. Com - bined with a fast, solid-state drive from a third party, the system can measure entire avalanche events (expected to last at least two minutes) without data loss or buffer overflows.

System cooperation with NI LabVIEW was vital for system software design. The radar had to operate throughout the winter without fail, so software reliability was critical. The radar also interfaces with a triggering system at the avalanche test site bunker. LabVIEW was configured to detect a trigger and begin data acquisition, and also to control relays to turn on the radar transmitter. The software based on LabVIEW was extensively tested before deployment.