Seismoacoustic Sensor System for Low Frequency Seabed Characterization
Abstract
This proposal is to provide the University of Rhode Island with a seismoacoustic sensor system for the measurement of seabed compre"ssional and shear speeds and attenuation. The proposed system consists of four Geospace OBX ocean bottom seismometer packages with one three-axis geophone and a collocated hydrophone. The new system will augment URI~s existing capabilities by providing the capability to measure seabed particle motion in 3-D. The availability of the three component data will increase our ability to understand the complicated arrival pattern observed by the ocean bottom sensors. The richness of the arrival structure, if fully understood and identified, will enhance our ability to estimate the bottom properties. The accurate timing provided by the CSAC clocks in the sensor packages will enable us to calculate the exact travel times when the source (such as the existing iWaSP source) is synchronized with GPS time. The existing system consists of eight vertical axis (gimbaled) geophones, two three axis geophones, two four channel data acquisition systems, and a bender beam vibrator source to generate interface waves. The proposed sensor packages are self-contained and integrating them to the existing system is not complicated. All the sensors will be periodically calibrated using the laser vibrometer requested in this proposal. The proposed equipment will enhance the capability to measure shear wave speed and attenuation in shallow water. This unique capability will provide the geoacoustic research community a valuable tool to understand the seabed physics. The proposed amplifier will extend the capability of the source to very low frequencies (~ 5 Hz). When operated in contact with the seabed this source can be used as an interface wave generator, and the low frequency capability will provide greater depth penetration for the inversions. In addition, this can also be operated in the water column as low frequency acoustic source. The Principal Investigators have been working for a number of years on acoustic sensing of compressional and shear speeds and attenuation in the seafloor of shallow water regions including the New Jersey Shelf, New England Bight, New England Mud Patch area, East China Sea and Barents Sea. The scientific goal of the research using the proposed system is to understand the effects of these sediments properties on low frequency acoustic propagation and thereby improve the understanding of Navy sonar system performance in littoral waters. The frequency dependence of attenuation in the sediment is a subject of intensive investigations from a number of researchers and institutions. One of the key components of the effective attenuation is the conversion of acoustic energy into shear waves at interfaces including the seafloor. This system will allow the estimation of shear speed and ttenuation and hence provide valuable information for modeling intrinsic ttenuation. The combination of existing and proposed three axis sensor ackages can be combined to form a seabed (or on ice) array which provides opportunities for source localization. The system also has the potential to investig"ate the Arctic ice characteristics.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jun 13, 2019
- Source ID
- N000141912395
Entities
People
- James M. L. Miller
Organizations
- Office of Naval Research
- United States Navy
- University of Rhode Island