Community Research and Development Information Service - CORDIS

Realisation of an improvement high resolution system

The result relates to the use of a chirp source vibrator. Such a source lead to a full control of the transmitted signal and to its spectral content. It was mainly used for P wave generation. The chirp generation was associated with real-time pulse compression in order to validate the concept during the trials. The task improved the receiving side of the seismics first by increasing the number of the receivers in the array for both P and S waves and then by investigating beam forming and array processing in order to increase the system penetration and accuracy.Two different set-ups for high resolution seismic on the seabottom have been tested and operated during the first and second sea trials respetively.

The elements of the seismic system operated during the sea trials is given here below:

1)Underwater elements:
-1 x streamer.
-Dragged on the sea bottom, 8 x 3 receivers (see description above).
-1 x airgun, Bolt airgun, volume range 10-80 cubic inches.
-1 x sled, weight in water approx. 1 ton.

-Seismic source, winch to winch in and winch out the streamer.
-Hydraulic power pack to power the winch.
-Electronics to handle the hydraulic power pack, the seabed-to-surface connections.
-Electronics to handle the winch in / winch out / shot / record sequence.
-Pressure sensor checking the compression of the air in the airgun.

3) Seabed-to-surface connections:
-1 x 500m long umbilical comprising 1x air hose, data lines (upward and downward flows), power lines to the hydraulic power pack (600V, 3-10 Amps).

-1 winch fed with umbilical.
-1 traction cable to the sled (fed on 1 of the Belgicas winch)

4) Surface equipment:

-1 x seismic recorder with QC software.
-1 x firing box.
-1 x power pack and power handling system.
-1 x Shark software to handle the acquisition sequence and visualise all sensors other than seismic sensors.
-1 x compressor and 24 x compressed air bottles to continuously feed the airgun. The acquisition sequence was defined as follows:
-Step 1: Winch streamer out during x seconds until stabilisation of gimbal mounted geophones.
-Step 2: Shot and record before end of winch out phase.
-Step 3: End of record and winch in phase.
-Step 4: End of winch in phase, Sailing, all instruments quiet, back to winch streamer out phase.

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