DREA OCEAN BOTTOM SEISMOMETER IMPROVEMENTS

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Authors
  1. Dodds, D.J.
Corporate Authors
Defence Research Establishment Atlantic, Dartmouth NS (CAN);GeoAcoustics Inc, Aurora ONT (CAN)
Abstract
The acoustic sensor module (ASM) of the ocean bottom seismometer (OBS) assembled by Defence Research Establishment Atlantic was modified by adding a phase reference to the internal vibrator of the ASM. This allows the amplitude and phase of the ASM velocity response to the vibrator when on the seafloor to be compared to the response when suspended in water. Experimental results suggest that the amplitude and phase measurement is repeatable within about 1 dB and a few degrees. The transfer function between sea floor motion and the ASM response can be estimated from the ratio of the vibrator response on the sea floor to the response suspended in water. The effect of vertical vanes on the coupling to the sea floor was studied by this technique. At two sites, the coupling to horizontal motion is improved significantly by the vanes. The coupling at high frequencies (20-50 Hz) is not good, even with the vanes, but observed signal amplitudes can be corrected by using the estimated transfer function to reduce the effect of the poor coupling. This does not overcome the effect of coupling between the ASM and horizontal motion of the water.
Keywords
Sea floor vibrations;Geophones;Acoustic coupling
Report Number
DREA-CR-95-498 — Contractor Report
Date of publication
15 Nov 1995
Number of Pages
28
DSTKIM No
96-02923
CANDIS No
499451
Format(s):
Hardcopy;Document Image stored on Optical Disk

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