Partitioning Signal and Noise Using Non Linear Thresholding
Abstract
A comprehensive approach to phased array processing is developed around the use of continuous wavelet transforms that includes denoising, partitioning waveforms into component phases, scale-time gating of partitioned phases across the elements of a phased array, and beam forming in the wavelet domain. These methods were tested using an extensive waveform dataset from the 2016 IRIS Wavefields Community Experiment in northern Oklahoma that recorded natural seismicity and 12 explosions commissioned by AFTAC. Array analysis of explosion seismograms was used to develop a velocity model for near-surface structure under the array from surface wave dispersion inversion. High frequency Rayleigh wave data show multipathing and lateral refraction caused by lateral variations in the upper half km. Partitioning and beamforming earthquake waveforms allows the identification of near source surface reflections that constrain source depth for local seismicity. A comparison of standard frequency-wavenumber beam forming and CWT beam forming is made for explosions of the AFTAC experiment to show how CWT noise thresholding improves wave attribute determinations. The September 2017 North Korean nuclear test is analyzed at KSRS array using CWT techniques to show systematic changes in back azimuth of P and S regional phases. Empirical template correlation for detecting small events is theoretically extended to the CWT domain using empirical mother wavelets and is successfully tested using the AFTAC explosion dataset.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 31, 2020
- Accession Number
- AD1125087
Entities
People
- Charles Langston