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1. APPENDIX A: SEISMIC EQUIPMENT

EQUIPMENT:

To achieve a good trade-off between penetration and resolution, a seismic source consisting of a 420 in3 (7 litres) linear array of two GI-gun was adopted. The data were logged by a complete acquisition system composed by a 300 m long digital streamer interfaced to a Geometrics CNT-2 Recorder. The complete block diagram is illustrated in Figure A-1.

Figure A-1. Equipment block diagram.

SEISMIC SOURCE

The GI GUN is made up of two independent chambers within the same casing, used to control and reduce bubble oscillations. The first chamber is called the Generator, as it generates the primary pulse and creates the bubbles. The second one is called the Injector, as it injects air inside the bubble. Each gun has its own reservoir, its own shuttle, its own set of exhaust ports, and its own solenoid valve. A common hydrophone provides both the time break and the shape of the near field signal. This gun phone is located inside the bubble and responds to the actual air blast.

Basic principle Phase 1: The Generator (G) is fired. The blast of compressed air produces the primary pulse and the bubble starts to expand.

Phase 2: When the bubble approaches its maximum size, it encompasses the Injector ports, and its internal pressure is far below the outside hydrostatic pressure. At this time, the Injector (I) is fired, injecting air directly inside the bubble. Due to the quasi-static state of the bubble, the timing of the Injector is not critical.

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Phase 3: The volume of air released by the Injector increases the internal pressure of the bubble, and prevents its violent collapse. The oscillations of the bubble and the resulting secondary pressure pulses are reduced and re-shaped.

The bubble represents a secondary blast of energy that eventually appears in the seismic trace as a fake signal following the primary reflection with a delay equal to the bubble period. In Figure A-2, the sensor response is illustrated (green line) when only the Generator is activated (top) and when both chambers (Generator Injector) are activated (bottom). The reduction of the bubble effect (between 130 ms and 160 ms in the top) is evident.

Figure A-2. Gun controller display, basic principle and GI gun underwater bubble.

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Table A-1. Source characteristics.

SOURCE ARRAY

Manufacturer SERCEL

Model 2 GI Gun (CSIRO)

Volume 210 cu.in. (3.44l)

Mode Harmonic 105 G / 105 I

Weight 1. 74 Kg

Firing cycle 1. 7 sec

Air pressure 2000 psi (140 bar)

ARRAY GEOMETRY

Figure A-3. Gun array deployment.

Air Compressor and high pressure manifold

Manufacturer Hamworthy (Wärtsilä)

Model 4TH565EW100

Number of compressors 2

Air delivery 678 m3/h

Speed 1200 RPM

Power 205 kV

Pressure max 207 bar

Number of stage 4

Total weight 2680 kg

Receiver tanks 8 x 50 litres

Regulation Fisher valve

4

Gun

synchronization

GUN CONTROLLER FEATURES AND TECHNICAL SPECIFICATIONS

Manufacturer Real Time systems

Model Big Shot

Installation Fixed

Number of modules 2

Number of guns 16

Gun types Bolt, Sleeve, G and G.I.

Timing resolution 0.1 msec

Record out 100 msec closure (programmable time)

Predicted fire out 5 ms TTL high going

Field Time Break Out Summed sensor or hydrophone signal

Sensors and hydrophone signature 16 bit D / A

Aim Point 25 – 75 msec after trigger

Fire pulse width 1 -80 msec

Delta error Q / C limits 0.1 – 5.0 msec

Auto-fire detect level 0 – 10 Volts

Sensor signal gain x 0.1 – x 5

Sensor detection look window 2 – 40 msec

Sensor peak threshold 0 – 10 Volt

Sensor peak type Threshold, Peak or Zero Cross

Figure A-4. Starboard side air compressor High-pressure manifold

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Figure A-5. The Big Shot gun controller main window. It is possible to see the first four bursts of energy perfectly centred on the 50 ms aim point (red vertical solid line), that is the delay between the navigation trigger arrival and the actual shot time.

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STREAMER

Table A-2 Streamer characteristics.

STREAMER

Manufacturer Geometrics

Model GeoEel Digital

Active streamer length 300 m

Number of groups 96

Active group length 3.125 m

Hydrophones per group 16

Streamer towing depth 2 m 1 m

Source to 1st channel offset 25 m

Figure A-6. Geometrics GeoEel streamer detail

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Table A-3 Streamer characteristics.

FEATURES AND TECHNICAL SPECIFICATIONS 1

Manufacturer Geometrics

Model GeoEel Digital

Number of channels 96

Length 300 m

Number of active sections 12

A/D Modules

Channels per module 8

Sample Rates 1/16 msec, 1/8 msec, ¼ msec, ½ msec, 1 msec, 2 msec

Programmable gains 0 dB, 8 dB, 18 dB, 30 dB, 42 dB

Record Length Up to 30,000 samples/trace

I/O Communications 100Base TX Fast Ethernet, IEEE 802.3 compliant

Dead Time Between Shots 100 msec

Bandwidth DC to 8 kHz

Resolution 24 bits including sign

Maximum Input Range +2.25V

Dynamic Range 120 dB typical @ 1 msec, 70 dB typical @ 1/16 msec

Common-mode Rejection 90 dB @ ¼ msec, 190 Hz

Gain Accuracy +6.25% @ ¼ msec, 30 dB, 100 Hz; +6.0% @ 2 msec, 30 dB, 25 Hz

THD 0.007% @ ¼ msec, 30 dB, 100 Hz; 0.003% @ 2 msec, 30 dB, 25 Hz

Crosstalk -105 dB @ 30 dB, ¼ msec, 190 Hz

Noise Floor 1.4 μV rms @ 30 dB, ¼ ms; 0.2 μV rms @ 30 dB, 2 msec

Power Consumption Approximately 100 mA at 48VDC (12.5 mA/channel)

Dimensions 44 mm diameter x 330 mm long (1.75” by 11”)

Weight in air 900 grams (2.0 lbs)

Weight in water 520 grams (1.1 lbs)

Packaging Titanium body

Connectors Waterproof, high-density stainless, 41-pin

Data Format SEG2, SEGD, SEGY

Deck Unit

Power Requirements 115/230 VAC, 3.0/1.5 A max, 50/60 Hz

Voltage to Streamer 36-72 VDC

I/O Communications 100Base TX Fast Ethernet, IEEE 802.3 compliant

Ethernet Connection RJ-45

Trigger Connection BNC

Trigger Requirements Contact closure, positive or negative TTL

Auxiliary Inputs 4 analog channels with 24-bit resolution

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Table A-4. Streamer characteristics.

FEATURES AND TECHNICAL SPECIFICATIONS 2

Deck Cable

Electrical Conductors 7 twisted 24GA pairs and 10 16GA conductors

Strain Member Vectran

Length 50 m

Diameter 18.6 mm

Weight 21 kg for 50 meters

Termination Water tight connector

Bend Diameter 12 inches Tow Cable

Electrical Conductors 7 twisted 24GA pairs and 10 16GA conductors

Strain Member Vectran

Break Strength Over 2200 kg (5000 lbs)

Length 70 m

Diameter 18.6 mm

Weight 21 kg for 50 meters

Active Section

Number of channels 8 per section

Group Interval 3.125 m

Section Length 25 m

Hydrophones per Group 4

Hydrophones per Section 32

Hydrophone Type Benthos RDA Geopoint

Group Sensitivity 9 V /bar

Jacket Material Clear polyurethane, 70 duro, 3.18 mm (1/8 in) wall thickness

Diameter 41 mm (1.6 in)

Ballast fluid Inert, high flashpoint, non-polluting silicone oil, 100 cSt to 3 cSt

Weight 1.35 kg (3 lbs) /m

Strain Member Vectran

Break Strength 2200 kg (5000 lbs)

Typical Towing Noise <7 μbars at 4.5 knots, 8 Hz low-cut filter, Beaufort 5-6 seas

Minimum Bend Radius 750 mm (30 in)

Compass / Bird Coil I/O Model 587

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Table 2 Streamer winch characteristics.

FEATURES AND TECHNICAL SPECIFICATIONS

Engine Lombardini DIESEL 15LD350

Drum diameter 1.5 m

Winch Weight 650 kg

Overall Weight (winch + 300 m long streamer + tow cable) 960 kg

Dimensions 200 cm X 125 cm X 200 (H) cm

Figure A-7. The GeoEel streamer wrapped around the winch drum

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Table A-6. DigiSCAN system characteristics.

DigiSCAN STREAMER DEPTH CONTROL Manufacturer

DigiCourse

Model DigiBIRD5010

Operating Range 0 to 122 m

Resolution 0.15 m

Number of birds 4

Power Supply 4 D cell Lithium batteries

Figure A-8. Shipboard control: Real time birds depth monitoring In water device: DigiBIRD

Figure A-9. Seismic acquisition workstation on board the RV Investigator: DigiSCAN shipboard control (A), navigation PC with PDS200 software (B), seismic acquisition PC with CNT 2 Marine controller software (C), CNT 1 topside (D) and QINSy / deck camera screen monitor (E).

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SEISMIC LINES

Table A-7. Seismic line acquisition. Li

ne

Nam

e

Star

t /

End

Dat

e

[dd

/mm

/yyy

y]

Tim

e

[UTC

hh

:mm

]

Du

rati

on

[m

m]

Sho

t P

oin

t

Sho

ts /

lin

e

An

ten

na

Lat

E [d

d°m

m.m

mm

'S]

An

ten

na

Lon

S

[dd

°mm

.mm

m'E

]

An

ten

na

X

[m U

TM50

S w

gs84

]

An

ten

na

Y

[m U

TM50

S w

gs84

]

Be

arin

g

Surv

eye

d D

ista

nce

[m

]

Ave

rage

SP

dis

tan

ce [

m]

IN2017-V01-MCS01 SOL 22/01/2017 00.24

174 100

1214 064°15.005'S 115°37.557'E 433398 2874398

91.0 20498 16.9 EOL 22/01/2017 03.19 1313 064°15.391'S 116°02.909'E 453887 2874056

IN2017-V01-MCS05 SOL 23/01/2017 22.21

214 100

1176 064°33.311'S 116°08.834'E 459120 2840842

90.0 23010 19.6 EOL 24/01/2017 01.55 1275 064°33.313'S 116°37.620'E 482119 2841062

IN2017-V01-MCS05B SOL 24/01/2017 03.12

149 100

817 064°33.219'S 116°36.765'E 481434 2841233

90.0 15891 19.5 EOL 24/01/2017 05.41 916 064°33.316'S 116°56.623'E 497302 2841107

IN2017-V01-MCS02 SOL 24/01/2017 22.03

155 100

861 064°36.674'S 115°11.112'E 413187 2833629

91.0 16878 19.6 EOL 25/01/2017 00.38 960 064°36.623'S 115°32.261'E 430044 2834161

IN2017-V01-MCS06 SOL 27/01/2017 04.12

358 99

1977 064°41.646'S 114°36.248'E 385750 2823477

60.0 38684 19.6 EOL 27/01/2017 10.10 2075 064°31.987'S 115°19.122'E 419342 2842508

IN2017-V01-MCS07 SOL 29/01/2017 04.11

46 100

260 064°15.801'S 115°59.927'E 451491 2873258

90.0 5088 19.6 EOL 29/01/2017 04.57 359 064°15.794'S 116°06.226'E 456578 2873346

IN2017-V01-MCS07B SOL 29/01/2017 05.59

17 100

91 064°15.747'S 116°13.030'E 462070 2873506

90.0 1811 19.7 EOL 29/01/2017 06.16 190 064°15.742'S 116°15.273'E 463881 2873537

IN2017-V01-MCS07C SOL 29/01/2017 06.55

119 100

656 064°15.792'S 116°20.052'E 467742 2873488

90.0 12824 19.8 EOL 29/01/2017 08.54 755 064°15.921'S 116°35.920'E 480557 2873355

IN2017-V01-MCS08 SOL 03/02/2017 21.14

587 100

3271 065°03.643'S 118°49.100'E 585543 2783548

38.6 64207 19.6 EOL 04/02/2017 07.01 3370 064°36.903'S 119°39.294'E 626966 2831788

IN2017-V01-MCS09 SOL 06/02/2017 04.02

77 100

414 064°44.685'S 118°14.513'E 559118 2819412

48.2 8101 19.6 EOL 06/02/2017 05.19 513 064°41.362'S 118°20.174'E 563739 2825491

IN2017-V01-MCS09B SOL 06/02/2017 05.56

39 100

221 064°40.202'S 118°23.122'E 566130 2827596

48.2 4229 19.2 EOL 06/02/2017 06.35 320 064°38.659'S 118°27.026'E 569301 2830393

IN2017-V01-MCS09C SOL 06/02/2017 06.55

131 100

725 064°37.989'S 118°28.641'E 570616 2831606

48.2 14114 19.5 EOL 06/02/2017 09.06 824 064°32.642'S 118°40.998'E 580722 2841291

IN2017-V01-MCS09D SOL 06/02/2017 09.41

73 103

398 064°31.284'S 118°44.360'E 583477 2843739

48.2 7844 19.8 EOL 06/02/2017 10.54 500 064°28.401'S 118°51.515'E 589357 2848929

IN2017-V01-MCS10 SOL 13/02/2017 23.48

153 100

838 064°30.373'S 118°59.893'E 595953 2845064

114.6 16191 19.3 EOL 14/02/2017 02.21 937 064°33.717'S 119°18.549'E 610653 2838350

IN2017-V01-MCS10B SOL 14/02/2017 02.39

347 100

2000 064°34.144'S 119°20.671'E 612317 2837496

116.5 37293 19.6 EOL 14/02/2017 08.26 1999 064°42.336'S 120°03.389'E 645674 2820842

IN2017-V01-MCS11 SOL 17/02/2017 21.37

139 100

762 064°58.716'S 119°25.873'E 614718 2791725

100.9 14863 19.5 EOL 17/02/2017 23.56 861 064°59.912'S 119°44.554'E 629305 2788903

IN2017-V01-MCS11B SOL 18/02/2017 00.04

15 100

85 064°59.971'S 119°45.621'E 630139 2788757

101.0 1635 19.5 EOL 18/02/2017 00.19 184 065°00.081'S 119°47.684'E 631750 2788482

IN2017-V01-MCS11C SOL 18/02/2017 00.51

76 100

416 065°00.353'S 119°52.052'E 635157 2787824

100.6 8069 19.4 EOL 18/02/2017 02.07 515 065°01.003'S 120°02.188'E 643057 2786246

IN2017-V01-MCS12 SOL 24/02/2017 04.30

5 100

26 064°44.460'S 118°59.099'E 594499 2818930

291.3 483 19.3 EOL 24/02/2017 04.35 125 064°44.367'S 118°58.531'E 594053 2819117

IN2017-V01-MCS12B SOL 24/02/2017 05.51

101 100

530 064°43.300'S 118°51.720'E 588708 2821260

291.3 10254 19.4 EOL 24/02/2017 07.32 629 064°41.661'S 118°39.455'E 579051 2824575

IN2017-V01-MCS12C SOL 24/02/2017 09.16

6 100

28 064°39.978'S 118°30.253'E 571812 2827882

291.3 531 19.7 EOL 24/02/2017 09.22 127 064°39.884'S 118°29.623'E 571315 2828069

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