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Innovative Approaches to Subsea Orientation of Seismic Instrumentation

Description: 

The quality of ocean bottom seismic data is presently limited by uncertainty in the azimuth of the horizontal channels. While various methods exist to determine azimuth orientation, all of them have practical limitations. The obvious method of a magnetic compass is inaccurate because of the presence of magnets in seismic sensors and motors, and ferrous metals such as in anchors for station systems. The most common method is to calculate azimuth based on polarization of seismic signals propagating from a known source direction, however this method is affected by heterogeneity of material properties along the source-receiver path and at the station, so that neither the direction of propagation nor the resulting polarization may be determined with reliable accuracy. When the station is installed with an ROV (Remotely Operated Vehicle), it is possible to use the gyrocompass in the ROV navigation system to orient the seismic package, although a means to accurately orient the seismic instrument with respect to the ROV during installation has often been lacking. Regardless of the method used to determine the initial azimuth, it is possible for the system to move later on during operation, introducing additional error.

The ideal way to determine azimuth would be to have a gyrocompass included as one of the instruments at each seismic station, and periodically measure true azimuth throughout operation. However the size, cost, and power consumption of a gyrocompass has historically been similar to that of a broadband seismometer, so it was generally not practical to add a gyrocompass at each OBS station, although some proof-of-concept experiments have been done (e.g. D’Alessandro and D’Anna, 2014). Recent developments in gyrocompass technology have made it possible to reduce size, cost, and power to the point where commercialization may become practical for OBS. This presentation details the results of recent research to develop this concept.

Session: ESC-SSA Joint Session:Seismology in the Global Oceans: Advances in Methods and Observations - I

Type: Oral

Date: 4/15/2025

Presentation Time: 05:30 PM (local time)

Presenting Author: Geoffrey

Student Presenter: No

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