Acoustic waveform inversion with application to seasonal snow covers

Area of Science:

• Acoustics
• Geophysics
• Environmental Science

Background:

• Atmospheric acoustic pulses undergo significant amplitude and waveform changes when propagating over seasonal snow cover.
• This interaction is caused by air forced into snow pores, reducing pulse amplitude and elongating waveforms compared to other ground surfaces.

Purpose of the Study:

• To investigate variations in snow-cover effects on acoustic pulse propagation.
• To develop and compare inversion procedures for determining snow-cover parameters from acoustic data.

Main Methods:

• Recorded acoustic pulses propagating horizontally over 11 different natural snow covers over two winters.
• Developed two inversion procedures: a frequency-domain technique and a time-domain minimization method.
• Utilized the time-domain method for its unique solutions and excellent waveform agreement.

Main Results:

• The effective flow resistivity and snow depth were identified as primary parameters controlling waveform shape.
• Pore shape factor ratio was found to be of secondary importance.
• Inversion estimates yielded flow resistivities from 11 to 29 kN s m(-4), with higher values in late-season snow.
• Acoustically determined snow depths generally agreed with measured values.

Conclusions:

• The time-domain inversion method provides accurate and unique solutions for snow-cover parameters.
• Flow resistivity and snow depth are key factors influencing acoustic pulse propagation over snow.
• Pore shape factor ratio can distinguish between wet and dry snow conditions.