Our Single Channel Seismic (SCS) profiler

Written by S.HOSOYA

This survey is several cruise in JAMSTEC using SCS profiler since the first cruise in 1999 (including test cruise). During the SCS survey, we used one GI Gun, one Steamer cable, each controllers, data processors. A streamer/source lay out is described in fig 1,2.

The SCS profiler used to explore the deep sea floor bottom structure of the Hawaiian volcanoes. The seismic source GI (Seismic Systems, Inc. TX, U.S.A.) gun is used to “ GI. mode” whose volume is 350 cu in. (Generator: 245 cu in., Injector: 105 cu in. ). GI gun has two structures (Generator and Injector) to make an ideal firing pulse. The first, Generator produces the primary pulse, while the second, Injector is used to control the oscillation of the bubble produced by the Generator. In this cruise, the GI gun was towed at ca. 30m on the center of R/V YOKOSUKA and towing depth was about 5-10m. Shooting rate was 20 sec with a ship speed of ca.5-5.5 knots (ca.30m). Air pressure of GI-GUN was 1300-1740psi.“Firing Controller” (Clover Tech, Inc., JAPAN) controls power supply to GI gun and firing time delay control between Generator and Injector.

Seismic data is received by an analog streamer filled with mineral oil. The streamer (made by Services et Instruments de Geophysique, FRANCE) has a 65m active section with 48 hydrophones (S.I.G.) and 200m leading cable. In this cruise, the streamer was towed on the center and the towing depth was 5-10m. Streamer depth depends on ship speed because it doesn’t have a depth controller “bird”. But if the operator would like to set the streamer deeper to reduce noise level, operator can sink the streamer deeper by opening “air connector” and weights.

Received seismic data is monitored with an on-line processing system and recorded in SEG-Y format. Delph Seismic (TRITON ELICS International, Inc., U.S.A.) is software that controls processing seismic data or control seismic source. It can also plot out to gray scale printer GSP-1086 (EPC LABORATORIES, Inc., Danvers MA U.S.A.). After seismic data is received, it is transferred to off-line processing system to print out and process. We used software SPW (parallel GEOSCIENCES, Inc. U.S.A.) to process seismic data.

Single channel seismic profiler system components

Source

GI-gun (Seismic Systems, Inc. Houston U.S.A.)

Total volume: 350 cu in. (Two structures: Generator; 245 cu in. Injector; 105cu in.)

Air pressure: 9-12Mpa (1300-1740psi)

We use one GI-gun. It is towed by 12mm dimension wire (SUS), which is combined electric cables and a high-pressure air hose. Towing length is ca. 30m.

GI-gun firing controller (Clover Tech, Tokyo JAPAN)

It controls shooting delay time between Generator and Injector from 0.1-99.9msec. The delay time depends on the GI gun depth and air pressure. And it provides firing pulse to G & I.

Oscilloscope

Oscilloscope displays the Time Break from hydrophone attached to the GI gun. Operator can find and control an ideal firing pulse shape from it. The operator had better use digital oscilloscope than analog one. Because digital oscilloscope can get signal before trigger and it has ability to sampling high resolution. Therefore, operator can keep good firing pulse and record the waveforms to PC and so on.

Gun depth sensor (Dorack Japan INC.)

This sensor is composed by a display and 100m-cable and a sensor. It can display a depth of the GI gun from 0 to 11m.It is an important thing to set a delay time of the GI gun.

Air compressor (Sanwa Steel Industries, co. Ltd., Yaizu JAPAN)

Type: 3 steps compressing and cooling by air and liquid

Rpm: 1000

Process volume: 103.2 m³/h

Output volume: 60.0 m³/h

Output pressure: 14.7 Mpa(2000psi)

Electric output: 22.0 kW

Power source: 440V, 60Hz (3 faze interchange)

Data Acquisition

Streamer (Services et Instruments de Geophysique, FRANCE)

The active section of the SIG Streamer (200m Lead in section, 65m active section and 30m-tail rope) contains 48 hydrophones (SIG 16a65) spaced at 1m interval. This streamer receives reflected wave from sea bottom and converts to electric signal at these hydrophones. In the middle transferring on board, the signal is amplified at a preamplifier in the streamer. And ahead of the streamer, there is a depth transducer that search depth of streamer.

SIG depth monitor and power supply

Depth monitor: Power supply; 100 VAC

Output; 24V / 30mA to transducer

Consumption; 10VA

Streamer power supply: 1 battery 12V, 600mA

Seismic data on-line processing system

DELPH SEISMIC (TRITON ERICS International, Watsonville CA U.S.A.)

DELPH SEISMIC the software is used to record or playback the seismic data (single or multi-channel) or Sub-bottom profiler (SBP) data in a Window-NT or 95 PC environments. Recorded seismic data can be saved any media, as you like; we saved in hard disk and CD-R(650MB).

Plotter (EPC LABORATORIES, Inc., Danvers MA U.S.A.)

We use gray scale plotter GSP-1086 to plot acquired seismic data in real time.

Seismic data off-line processing system

SPW (parallel GEOSCIENCES, Inc. U.S.A.)

SPW (Seismic Processing Workshop) is software of processing seismic data. After recording, we saved raw data (SEG-Y formatted) in CD-R (650MB) and transferred to the off-line processing system. In the off-line processing system, these raw data is reformatted to SPW format.

	TOP VIEW

Fig.1

	Fig.2