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Evaluation of rosette infrasonic noise-reducing spatial filters
Michael A H Hedlin1, Benoit Alcoverro, Gerald D'Spain
1Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093-0225, USA. hedlin@ucsd.edu
The Journal of the Acoustical Society of America
|November 1, 2003
Summary
Rosette infrasonic filters effectively reduce wind noise, with an 18-m filter showing 15-20 dB reduction above 0.2 Hz. However, resonance in the 70-m filter impacts acoustic signal reception above 0.7 Hz.
Area of Science:
- Geophysics
- Acoustics
- Signal Processing
Background:
- Atmospheric infrasound monitoring relies on spatial filters to mitigate wind-generated noise.
- Rosette spatial filters are designed to improve signal-to-noise ratios for infrasonic acoustic arrivals.
Purpose of the Study:
- To evaluate the noise-reducing capabilities of 18-m and 70-m aperture rosette infrasonic filters.
- To investigate the impact of these filters on spatially coherent acoustic signals.
- To analyze the phenomenon of standing wave resonance within the filters.
Main Methods:
- Testing rosette filters (18-m and 70-m aperture) and a reference port at Pinon Flat Observatory.
- Collecting data across a frequency band of 0.02 to 10 Hz.
- Utilizing analytical simulations to model filter performance and resonance.
- Performing cross-spectral analysis of signals, including those from a large bolide explosion.
Main Results:
- The 18-m filter reduced wind noise by 15-20 dB above 0.2 Hz at wind speeds up to 5.5 m/s.
- The 70-m filter achieved 15-20 dB noise reduction between 0.02 and 0.7 Hz.
- Standing wave resonance in the 70-m filter degraded acoustic signal reception above 0.7 Hz, with notable resonance modes at 2.65 Hz and 7.95 Hz.
- Analytical simulations accurately predicted observed noise reduction and resonance phenomena.
- Filter response showed frequency and angle dependence, with signal cancellation at specific grazing angles and frequencies.
Conclusions:
- Rosette filters offer significant wind noise reduction in specific frequency bands.
- Internal resonance within larger filters can degrade the reception of desired acoustic signals.
- Understanding and mitigating resonance is crucial for optimizing rosette filter performance.
- Theoretical models align well with experimental observations, aiding in filter design and interpretation.