Albert D G
US Army Cold Regions Research and Engineering Laboratory, Hanover, New Hampshire 03755-1290, USA.
J Acoust Soc Am. 2001 Jan;109(1):91-101. doi: 10.1121/1.1328793.
The amplitude and waveform shape of atmospheric acoustic pulses propagating horizontally over a seasonal snow cover are profoundly changed by the air forced into the snow pores as the pulses move over the surface. This interaction greatly reduces the pulse amplitude and elongates the waveform compared to propagation above other ground surfaces. To investigate variations in snow-cover effects, acoustic pulses were recorded while propagating horizontally over 11 different naturally occurring snow covers during two winters. Two inversion procedures were developed to automatically match the observed waveforms by varying the snow-cover parameters in theoretical calculations. A simple frequency-domain technique to match the dominant frequency of the measured waveform suffered from multiple solutions and poor waveform matching, while a time-domain minimization method gave unique solutions and excellent waveform agreement. Results show that the effective flow resistivity and depth of the snow are the parameters controlling waveform shape, with the pore shape factor ratio of secondary importance. Inversion estimates gave flow resistivities ranging from 11 to 29 kN s m(-4), except for two late-season cases where values of 60 and 140 were determined (compared to 345 for the vegetation-covered site in the summer). Acoustically determined snow depths agreed with the measured values in all but one case, when the depth to a snow layer interface instead of the total snow depth was determined. Except for newly fallen snow, the pore shape factor ratio values clustered near two values that appear to correspond to wet (1.0) or dry (0.8) snow.
当大气声脉冲在季节性积雪表面水平传播时，随着脉冲在雪面上移动，被压入雪孔隙中的空气会使脉冲的幅度和波形形状发生显著变化。与在其他地面上传播相比，这种相互作用极大地降低了脉冲幅度并拉长了波形。为了研究积雪效应的变化，在两个冬季期间，记录了声脉冲在11种不同自然积雪上水平传播时的情况。开发了两种反演程序，通过在理论计算中改变积雪参数来自动匹配观测到的波形。一种简单的频域技术用于匹配测量波形的主导频率，但存在多种解且波形匹配不佳的问题，而时域最小化方法给出了唯一解且波形一致性良好。结果表明，积雪的有效流动阻力率和深度是控制波形形状的参数，孔隙形状因子比的重要性次之。反演估计得出的流动阻力率范围为11至29 kN s m(-4)，但有两个季节后期的情况除外，其值分别为60和140（相比之下，夏季植被覆盖地的该值为345）。除了一个情况外，声学确定的积雪深度与测量值一致，在该情况下确定的是到雪层界面的深度而非总积雪深度。除了新降雪外，孔隙形状因子比值集中在两个值附近，这两个值似乎分别对应湿雪（1.0）或干雪（0.8）。
