Please join us for the following AOS Seminar Thursday, June 9 at 4:00pm in Spiess Hall 330:
Speaker: Zhao Chen, Scripps Institution of Oceanography
Title: Microseism cross-correlation.
Inhomogeneous noise sources surrounding stations produce asymmetric amplitudes in cross-correlation functions that yield preferential source directions. Here we show that preprocessing biases the dominant source direction estimate towards the source produce long-duration signal by down-weighting high-amplitude signals. Tests with both synthetic data and observations show that conventional preprocessing, where only earthquakes and local transients (e.g. trawling, fish impacts) are removed, is more sensitive to coherent energy, while one-bit preprocessing and running-absolute-mean (RAM) preprocessing are more influence by signal duration. Comparisons between different preprocessing methods are made on data from the Cascadia Initiative (CI) ocean bottom seismometer (OBS) array, where we find that the total energy arriving from pelagic and coastal areas is similar. Moreover, pelagic-generated signals tend to be weaker but have longer duration, in contrast to coastal-generated signals that tend to be stronger but have shorter duration.
Speaker: Edward Richards, Scripps Institution of Oceanography
Title: Acoustic surface scatter
Recent work at the Marine Physical Laboratory on acoustic communication has led to interest in variations of channel impulse responses occurring on short time scale (of order 10 seconds). Initial work determined surface waves as the cause of these fluctuations using geometric ray reflection models. This led to more complete surface scattering models based on the Helmholtz-Kirchoff approximation. This talk will review basic methodology of surface scatter modeling, some initial findings, and thoughts on future research directions.