Infrasound observations can be used to measure the energy radiated by an avalanche into the atmosphere and detect avalanches over large areas. Accompanying significant improvements in avalanche dynamics research, the use of infrasound for avalanche monitoring has increased over the last few decades. Our research team conducted infrasound observations in Tokamachi, Niigata Prefecture, Japan, over the past few winter seasons. In the 2014-2015 winter season, we deployed three sensors spaced by 1-2km in a triangular array and attempted to automatically extract signals associated with avalanches from the observed raw data using time-domain processing. The locations of avalanches were estimated from the extracted signals using the cross-correlation method. Twelve events were detected and located. The estimated locations were in an area with multiple steep slopes. An infrasound array monitoring system with real-time processing would be capable of providing significant amounts of information concerning avalanche activity in snow-covered regions.
We performed airborne synthetic aperture radar (SAR) observations at two glaciers (San’nomado and Komado glaciers) on the eastern slope of Mt. Tsurugi, Japan, in August and October 2013, and August 2014. The Pi-SAR2 system used in this study consists of two X-band SAR antennas. Taking advantage of single-pass interferometry, we have generated digital elevation models (DEM) at each epoch. Differencing the DEMs at August and October 2013, the elevations at the glaciers were reduced by ~20m or more with errors on the order of ~20m or more. As we could visually identify the reduction in the snow-covered areas in the SAR images of August and October 2013, those changes are attributable to seasonal melting of the snow but are apparently overestimated. Full polarimetric observations were also performed, indicating significant changes over the glaciers from August to October that were largely due to the reduction in snow cover. We could further identify localized spots that indicated strong intensity in the cross-polarized HV channel (transmission of vertically polarized wave and reception in horizontally polarized channel) over the glaciers. Bright HV signals are unexpected, because HV signals are often interpreted as volume scattering and appear to originate from the inside of the glaciers that are unlikely in the X-band SAR system; no penetration deeper than 1m is expected in the X-band over the snow/ice areas. We interpret the apparent HV signals as due to double bouncing from both sides of the valley, which were apparently imaged over the glaciers.
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