Toward the Autonomous Recording and Transmission of Seismic Data from the Oceans: Testing the Son-O-Mermaid Float in the Sargasso Sea

Abstract:

We report on the deployment of two new Son-O-Mermaid floats into the
Sargasso Sea during a cruise aboard the R/V Atlantic Explorer, which
departed from Bermuda in May of 2015. Son-O-Mermaid is a freely
floating and autonomous oceangoing system composed of a surface buoy
connected to a length of cable from which a three-hydrophone array is
suspended. The main objective of the Son-O-Mermaid project is to
record signals suitable for global tomography in the deep ocean and
provide the seismic community with an abundance of novel raypaths from
previously unsampled regions of the Earth. The Son-O-Mermaid float,
with its ability to continually record, analyze, and transmit seismic
data from the oceans in near-real time has the potential to
revolutionize the field of seismology. We analyze new data returned
from this deployment, a previous Son-O-Mermaid test, as well as the
ongoing MERMAID mission in the time, spectral, and wavelet domains. A
full description of the float and deployment report will be presented.
A short-term goal of the project is determining realistic magnitude,
distance, and pressure relationships for teleseismic earthquakes that
are recorded in the water column. Our analysis of this question is
aided by synthetics created using SPECFEM2D and guided by the data,
especially noise records recorded by Son-O-Mermaid and MERMAID from
oceans throughout the world. Synthetics provide an idealized waveform
useful for understanding the often very messy and noisy arrivals
common in midcolumn acoustic recordings. Notably, synthetics allow
the confirmation or rejection of unlikely phases which are matched to
earthquake databases after arrivals are detected by automatic picking
algorithms. Additionally, marine-acoustic processing techniques will
be improved once the underwater acoustic field is better modeled using
realistic signal-to-noise ratios and noise spectra returned from
Son-O-Mermaid and MERMAID missions. This analysis, particularly when
implemented in the wavelet domain, is proving fruitful both for
current applications such as automating the picking and recognition of
arriving wave trains, and has broad impacts for terrestrial seismology
and the seismic community as a whole.