Cruise Report AASGH -1

Gas Hydrate Research Cruise (Deep Tow digital Side scan sonar imaging & Chirp sonar Investigations)

Goa Offshore, West coast

Marmugoa - Goa Offshore – Marmugoa

(22 October to 5 November 2002)

ACKNOWLEDGEMENTS

Dr. Ehrlich Desa, Director and his colleagues of Gas Hydrate Research Group

at NIO express their sincere thanks to Dr. Avinash Chandra, Director General,

Directorate General of Hydrocarbons, New Delhi for his keen interest and constant

encouragement in undertaking these geoscientific investigations in the Goa offshore

to infer the proxies related to gas hydrates.

Director and his colleagues would like to extend their sincere thanks to Ms

Vandana Singhal, Secretary, Oil India Development Board (Ministry of Petroleum &

Natural Gas), Government of India, New Delhi for granting the funds to execute the

project under National Gas Hydrate Programme (NGHP).

The chief Scientist and entire scientific team express their sincere thanks to the

Director, Dr. E. Desa for his kind support and constant encouragement. They are also

grateful to the Master and Russian Chief of Expedition Mr. Anatolyi Sapiridi, Mr. Sitnik

Pavlov and their colleagues for completion of installation of all heavy-duty winches

(Deep tow side scan sonar, CTD, High resolution sparker equipment, installation of

DGPS systems antenna etc), connecting hosepipes, providing high tension/ high

voltage power supply to the equipments and onboard excellent cooperation.

This cruise was undertaken as a part of Grant-in-Aid project (GAP 1336)

funded by Gas Authority of India Ltd, (GAIL) to infer the proxies related to the

presence of Gas Hydrates.

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Contents

1.0 Cruise summary 4

2.0 Introduction 6

3.0 Itinerary 7

4.0 Cruise tracks 7

5.0 Participants 8

6.0 Objective 9

7.0 Equipment 10

7.1 Geo acoustic Deep Tow Elementary System 10

7.2 High Resolution sparker system, Geo Spark- 800 16

7.2.1 Deck equipment 16

7.2.2 Sub sea equipment 17

7.3 LEICA Differential Global Positioning System 17

8.0 Results 20

9.0 Weather during the cruise 20

10.0 Ships general performance 20

Figure Captions 21

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1.0. CRUISE SUMMARY

The cruise AASGH-1 of ocean research vessel AA Sidorenko has been under

taken in Goa offshore, West Coast under the National Gas Hydrate Program (NGHP)

with the primary objective of i) collection of deep tow digital side scan sonar, chirp

sonar, echosounder and high resolution sparker data, and ii) to infer the gas escape

features based on the geophysical data. The deep tow digital side scan sonar and

high-resolution digital sparker systems were procured by the National Institute of

Oceanography during 2002 exclusively to be deployed for exploration of gas hydrates.

It was planned to install these two new equipments on board AA Sidorenko, and

carryout sea trails before proceeding to acquire the planned data in Goa offshore,

West Coast. Accordingly, the vessel AA Sidorenko was under charter from 11th

October 2002. All the scientific equipments for gas hydrate exploration programme

were loaded on board AA Sidorenko. The deep tow digital side scan sonar system

(Deep Tow Telemetry) was installed with the help of Installation Engineers from UK

between 14 and 17 October 2002. Meanwhile, some of the components of the high-

resolution sparker system were brought by the Engineers from The Netherlands on 18

October were also loaded the vessel for installation of High Resolution sparker

system.

The vessel AA Sidorenko sailed for testing of the digital side scan sonar

system. It was found that this system is working satisfactorily. The vessel returned

back to Marmugoa Port on 20 October. The sparker system installation has been

completed during this period. The vessel sailed from Marmugoa on 22 October 2002

and reached the Goa offshore on 23 October for carrying out geophysical surveys.

Several initial problems were faced during the cruise and three times the vessel came

back to Marmugoa for repairs of the Deep tow digital side scan sonar system

acquisition of data. The main problem faced was related to the crashing of hard disc.

Similarly, the high-resolution sparker system has given several problems during the

sea trails and the Engineers from the Geo resources finally confirmed that the system

performance is not satisfactory.

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The main problems suspected with the new HRS system were I) the Front-End-

Module (data acquisition and processing unit f high-resolution sparker) is not working

satisfactorily, and 2) interference of with the ships propulsion noise with the acoustic

signals. However, at a later stage, it was suspected by NIO participants that the 24

channel mini seismic streamer also appears to be not properly configured and

fabricated. After a thorough check up of all procedures and performance of the

different units of HRS system, the Engineers from Geo Resources (Netherlands), who

boarded the vessel for installation and seas trails informed that the Front-End-Module

requires to be shifted to NIO for repair work. Accordingly, the equipment after

suspending the surveys was shifted to NIO. On 25 October, the repaired equipment

was reloaded onboard and preceded to survey area again. Despite of several

attempts, the recording unit’s performance was not satisfactory and no high-resolution

data could be recorded. On 28 October, the engineers from Geo Resources were

dropped on their request at Marmugoa and proceeded to the survey area to acquire

the deep tow digital side scan sonar, chirp sonar and sub-bottom profiler data.

We also encounter another serious problem with the Geopro acquisition and

processing unit of digital side scan sonar system, which was frequently hanging. The

service engineers from shore were contacted, and tried to solve the problem by

changing the hard disc with higher memory capacity. Part of the survey has been

completed.

Differential Global positioning system was used throughout the cruise and

obtained the accurate position of the ship along the pre-planned survey tracks. The

Leica SR 520 differential GPS receiver was used to achieve this. Using the Tsunami-

Electronic chart/navigation software, the vessel movement along the predetermined

survey track was monitored. About 200 line km each of deep tow digital side scan

sonar and chirp sonar data were acquired besides about 225 line km of sub-bottom

profiler data in the GAIL block. Since sampling cruise will be immediately following,

the vessel returned back to Marmugoa on 5 November 2002.

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2.0. INTRODUCTION

The world is looking for newer and alternate energy resources due to the

increase in consumption of fossil fuels. Gas hydrates appear to be the future alternate

energy resources world over in the pure form. Hence, tremendous interest has been

generated in the field of research on these deposits world over.

Gas hydrates, or hydrates also referred in the literature as gas clathrates, are

naturally occurring solids comprised of water molecules forming rigid lattice of cages,

each containing a molecule of natural gas. These hydrates usually occur in the

continental slope regions under certain pressure temperature conditions and

availability of gas with in the marine sediments. Theoretically 1 m3 of methane hydrate

contains about 164 m3 of pure methane gas and 0.8 m3 of water at normal standard

temperature and pressure conditions. This enormous gas concentration factor in the

methane hydrates explains the global interest in their exploration. The gas hydrates

resource potential has been estimated based on the existing geoscientific data and

theoretical models. The gas hydrates contain over 1019 grams of methane-carbon,

which exceeds the half way mark of the total global carbon content. Favorable

thermobaric conditions for stability of these hydrates in the tropical regions prevail

either at shallow sub-surface regions of deep-waters or deep sub-surface regions of

shallow waters.

The Gas Hydrate Resource Map of India (NIO, 1997), and multichannel seismic

reflection records depict probable occurrence of Gas hydrates within the EEZ in the

water depths beyond 800m at moderate sub-surface depths. The presence of shallow

gas escape features such as pockmarks, vents, gas plumes and mud diapers all along

the continental margins of India paved a way for a detailed exploration of these

precious deposits.

Realising the significance of these new energy resources, the Directorate

General of Hydrocarbons (DGH) has drawn up an ambitious plan and prepare a road

map to tap these gas hydrate resources from the continental margins. National

Institute of Oceanography, Goa in collaboration with Gas Authority of India Limited

(GAIL) and Oil and Natural Gas Corporation Limited (ONGC) has submitted two

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proposals for carrying out geoscientific investigations of shallow sediments in the Goa

offshore, West Coast and KG offshore Basin, East Coast. On the recommendations of

the 2 Steering Committee, Chaired by the Secretary, Ministry of Petroleum & Natural

Gas, the OIDB (Oil Industries Development Board), a funding agency of Ministry of

Petroleum and Natural Gas, Govt. of India has sanctioned an amount of Rs 9.27

Crores for the two major projects for a detail geoscientific investigations in the

selected corridors of western and eastern offshore.

The western offshore area has been selected after careful and intensive study

of the existing multichannel seismic reflection data, which depicted unmistakable

presence of the acoustic indicators, known as the Bottom Simulating Reflections

(BSRs) and the gas hydrates stability zone thickness map (prepared by NIO in

collaboration with GAIL). NIO has undertaken detailed geoscientific investigations to

infer the proxies related to gas hydrate on a Mission Mode with time bound

deliverables.

The scientific cruises onboard AA Sidorenko (Fig.1) were planned to acquire

deep tow digital side scan sonar, sub bottom profiler, chirp sonar and high resolution

sparker data to infer the gas escaping features in Goa offshore.

3.0 ITINERARY

Departure : Marmugoa, 22 October 2002

Arrival : Marmugoa, 05 November 2002

4.0 Cruise tracks

The BSRs inferred from the studies carried out by NIO& NGRI based on the

existing multichannel seismic reflection data of NIO & ONGC have been projected on

to a map of 1:100000, and cruise tracks (Fig.2) were plotted parallel to these BSR

lines with a line spacing of ~2 Km. The deep tow digital side scan sonar, chirp sonar

and 3.5 KHZ sub bottom profiler data were acquired along the predetermined cruise

track map. The deep tow digital side scan sonar system was rated to 3000m water

depth, hence the survey activity was mostly focused to this 3000 m water depth only.

About 200 line km of deep tow side scan sonar and chirp sonar data were acquired in

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the Goa offshore area. The echosounder, which is having a facility to operate at

different selectable frequencies, has facilitated us to record the sub-bottom

information using a 3.5 KHZ frequency. A maximum penetration of more than 40

meters has been recorded in some areas.

5.0 PARTICIPANTS

5.1 Scientific Party

1. Dr. M. V. Ramana Chief Scientist 2. Dr. V. N. Kodagali Scientist EII 3. Sh. T. Ramprasad Scientist EII 4. Sh. G. H. Ranade Scientist EII 5. Sh. F. Almeida Scientist EII 6. Sh. N. Prabhaharan Technical Officer 7. Sh. P. Marathe Technical Officer 8. Sh. G. M. Padte Technical Officer 9. Sh. V. D. Khedekar Technical Officer 10. Sh. D. Gracias Technical Officer 11. Sh. K. Srinivas Technical Officer 12. Sh. P. N.V.N. Kishore Project Trainee III 13. Sh. P. Sree Kumar Project Trainee III 14. Sh. Narendra Kumar Manager (GAIL) 15. Sh. T. Mandal Electronics Engineer, Elcome Marine 16. Sh. Hasib Khot Electronics Engineer, Elcome Marine

5.2 Ship’s Complement

1. Capt. Ionov Vladimir Master 2. Mr. Drobyazga Ilya Ch. Officer 3. Mr. Onishko Vladimir 2nd Mate 4. Mr. Syvorotchenko Alexander 3rd Mate 5. Mr. Sysoev Sergey Radio Officer 6. Dr. Kuzneтsov Boris Physician 7. Mr. Simonov Sergey Ch. Engineer 8. Mr. Moskaev Boris 2nd Engineer 9. Mr. Chevychalov Valeriy 3rd Engineer 10. Mr. Sherstyuchenko Pavel 4th Engineer 11. Mr. Saltykov Anatoliy Ch. El. Engineer 12. Mr. Ermolenko Mikhail 2nd El. Engineer 13. Mr. Gladkov Andrey Ref. Engineer 14. Mr. Salokhin Petr Ref. Engineer 15. Mr. Grigorenko Evgeniy Welder 16. Mr. Verkhososov Mikhail Motorman 17. Mr. Khorshev Vladimir Motorman 18. Mr. Rezunenko Andrey Motorman 19. Mr. Pavlov Aleksandr Motorman

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20. Mr. Vasilev Igor Boatswain 21. Mr. Chernyy Vadim Sailor 22. Mr. Yemchenko Yuriy Sailor 23. Mr. Karasev Aleksey Sailor 24. Mr. Filimonov Yury Sailor 25. Mr. Piven Boris Sailor 26. Mr. Prikhodko Maxim Mess boy 27. Ms. Ionova Liybov 1st Cook 28. Ms. Vishnevskaya Elena 2nd Cook 29. Mr. Drizhepolov Andrey 3rd Cook 30. Mr. Petunina Nelli Bar Attender 31. Ms. Stepanova Elena Bar Attender 32. Ms. Glukhovtseva Inna Laundry Attendant 33. Mr. Sapir 0idi Anatoliy Ch. Expedition 34. Mr. Sitnik Pavlo Group Master 35. Mr. Seleshchuk Leonid Hydrographer 36. Mr. Popov Sergey Engineer 37. Mr. Bogomyagkov Andrey Engineer 38. Mr. Anisimov Sergey Engineer 39. Mr. Dabizha Pavel Engineer 40. Mr. Lyapin Andrey Engineer 41. Mr. Slastenov Sergey Technician 42. Mr. Antony Ganagaraj Cook 43. Mr. Briston Kumar Deck Hand 44. Mr. Sundaram Amarnath Deck Hand

6.0 OBJECTIVES

I. Investigate the Goa offshore with hydrosweep, deep tow digital side scan

sonar, high-resolution digital sparker and sub-bottom profiler techniques to

detect bathymetric anomalies, gas escape features (pock marks, plumes, gas

seepages, diapiric like structures), and back-scatter characters of the seafloor

sediments

II. Collection of large number of long sediment cores to study hydrocarbon

gasses and geochemical, Sedimentological, microbial indicators.

III.Collection of water samples to study dissolved methane and oxygen

concentrations in water column.

IV.Determination of near bottom salinity and temperature anomalies of the water

column.

V. Map the potential gas hydrate zones from geological, geophysical,

geochemical, and microbial proxies.

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The gas hydrate cruise AASGH-1 on board AA Sidorenko was under taken to

collect deep tow digital side scan sonar, chirp sonar and sub-bottom profiler data

along the lines spaced ~2km parallel to the BSRs mapped from the multichannel

seismic reflection data. While the cruise AASGH2 would be totally dedicated to the

collection of sediment and water samples to meet the objectives. The report related to

sampling work has been given as Part B in this report.

6.1 Quantum of data acquired

I. Digital Side scan sonar data : 200 lkm

II. Digital Chirp sonar data : 200 lkm

III. Sub-bottom profiler data : 350 lkm

IV. Echo Sounder data : 1100 lkm*

7.0 THE EQUIPMENT:

7.1 Geo acoustics Deep Tow Telemetry System

The Geo Acoustics Deep Tow telemetry system (Fig.3) is designed to allow

simultaneous operation of a Geo Acoustics Chirp II Profiler, Geo Acoustics Side Scan

Sonar, Magnetometer, Responder and an Attitude sensor all via a single coaxial tow

cable. This is a high-resolution search and survey instrument designed for both object

location and the study of the sea floor geology. Block diagram depicting various

components of the system is shown in Figure.4.

7.1.1 The Deep Tow telemetry system has the following features:

• Auto ranging power supply system operated from standard line voltage (115V

or 230V ac) and frequency (50Hzor 60HZ).

• Efficient high voltage Tow fish power supply to minimize transmission losses.

• Continuous Tow Cable safety monitoring.

• Simultaneous profiler and side scan sonar data transmission from Tow fish to

deck unit

• Bi-directional RS32 communications with responder

• Tow fish attitude information including depth, heading, pitch, roll and

temperature.

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7.1.2 System Components:

The Tow fish is designed to house the sub sea unit and all associated

electronic bottles. It consists of heavy galvanized steel plate at the front, a tail pipe

section and cylindrical tail at the rear. The block diagram of Deep Tow Telemetry

System is as shown in the figure and specifications of both 1. Deck unit and 2. Sub

Sea unit are given in the tables.

7.1.3 Deck Unit: Specifications of Telemetry System Deck Unit

Weight : 35 Kilograms Dimensions : Height…..275 millimeters

Width……428 millimeters (free standing) …… 482 millimeters (rack mounted)

Depth…… : 488 millimeters Temperature : Operating +10 to +30 degrees Celsius

Storage -10 to +40 degrees Celsius Mains Supply : Voltage 115 or 230 Volts AC +/- Frequency : 50 to 60 Hertz Power : 750 Watts Fuse : 7Amps, Time Delay, eg 7A (T) This unit is used to control and condition the signals from the tow fish. It

consists of i) Power supply, ii) Analogue processing circuitry, iii) Computer interface,

iv) Thermal record plotter, v) Winch for controlling the standard armored single coaxial

cable, which works as tow cable.

i) Power supply:

The Telemetry deck Unit provides power to the Tow-fish, controlling system

and interfacing unit. It also provides power factor correction and soft start. Because of

high power demand and safety requirements, the power supply is very substantial and

includes large heavy transformers. The auto-ranging power supply can operate from

115/ 230VAC, 50/60Hz.

The deck unit applies a high voltage (HV) to the Tow Cable (between +HV and

–HV) to power the Tow Fish. The HV can be enabled only if the Telemetry Deck Unit

top cover is fitted properly, the Deck-Cable is plugged in, and the cable loop on the

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winch slip rings is wired correctly. The HV will be automatically disabled and

discharged if a current of +/- 2 milliamps leaks between Earth and –HV or +HV.

ii) Computer interface:

The computer interface helps the user to monitor tow fish height, navigation

data and real time data quality. By using this interface the acquired data is stored in

the hard disk of the system, latter which can be transferred on to the CD ROMs. Mac

(Macintosh) Operating system and Geopro software are used to digital data storage,

real time processing and post advanced image processing.

iii) Thermal Graphic plotter:

The 9315CTP-975 Continuous tone printer is a general purpose thermal

graphic printer utilizing a centronics parallel interface and a single-ended small

computer (SCI) system interface for communications. The printer can reproduce a

maximum 256 shade of gray on low cost thermal media. A text mode is provided for

image annotation. The standard ASCII character set can be printed in a Courier-style

font, with up to 128 characters per line. The Centronics parallel and SCSI interface

provide fast, reliable, and efficient transfer of data. The printer has been designed for

minimum operator attention. The thermal print head technology eliminates the need

for replacing ink cartridges, worn ribbons or refilling toner canisters. Printer

configuration is entered through the printer’s keypad and stored in non-volatile random

access memory (RAM). Printer settings and status are displayed on the liquid crystal

display (LCD).

iv) Winch:

Winch is used to monitor the tow fish height by controlling the tow cable. The

winch is a hydraulic type of model OCG 9000, with 1 hydraulic motor mounted with

load cell. The winch is build and designed by NTD Offshore A/S. the winch is

designed for 9000 meter wire. The level wind is a diamond lead screw; with wire

diameter of 11.5 mm. Winch can be accessed either locally or remotely. To fix the

mode of operation there is a switch on the local control panel to change between local

and remote. The winch speed can be controlled by using a joystick. . Winch can be

stopped at any stage by pressing the stop button after selecting either high or low

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modes. If need emerges, the winch can be stopped suddenly by selecting the

Emergency stop button.

7.1.4 Sub Sea Unit:

Specifications of Telemetry System Sub sea unit

Weight : 22.5 Kilograms Dimensions : Length…..725 millimeters

Diameter..130 millimeters Temperature : Operating 0 to +30 degrees Celsius (must be in water)

Storage -10 to +40 degrees Celsius Maximum Operating Depth 2500 to 4000 meters

The telemetry tow fish is the main component of the sub sea unit. It is a

compact electrical pressure vessel. The main components of this vessel are i) Side

scan sonar, ii) Chirp II Sub bottom profiler, iii) Responder and Attitude sensor

i) Side Scan Sonar:

The Geo Acoustics dual frequency multiplexed Side scan system has been

designed and manufactured to IS O9000 in the UK, and has been designed for

exceptional reliability, accuracy, and simplicity in operation. The Geo Acoustics Side

Scan System employs a surface based Model SS981 Transceiver and Model 159 Tow

Vehicle with two Transducers of Model 196D and subsurface electronics bottle of

Model SS982. Four profiler transducers are mounted in the steel plate with their

working face pointed downwards. An integral pat of each transducer is a short rubber

covered pigtail lead terminating in a watertight electrical connector, in normal

operations the four transducers are connected parallel. The electronic bottles are

mounted along side the tail pipe, and projected backwards into the gaps in the

cylindrical tail. The power supply inside the telemetry bottle provides individually

isolated supplies to all external systems.

Operating Principle:

The side scan sonar transmitter generates very short high voltage electrical

waveforms (key-burst) at either 60 kHz or 110 kHz. The tow fish contains two

transducers on both starboard side and port sides as arrays operating either at 60 kHz

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or 110 kHz. The key-burst from the transmitter is fed to the side scans sonar

transducers. Side Scan Sonar transducers convert this electrical energy to acoustic

signals of high intensity. These acoustic signals travel through the sea until they reach

the seabed, where some of the energy is reflected back to the transducers. This

acoustic return energy is converted by the same transducers to a much lower voltage

electrical signal. These low sonar return signals are accepted by the receiver

electronics and processed using the time varied gain (TVG) and then converted to

separate frequency, which are transmitted back through the cable to the surface. All

power Control signals and received sonar signals as well as optional data telemetry

are multiplexed on to a standard armoured single coaxial cable, which also acts as a

tow cable. The Deck unit accepts the signals from the cable, and filters out the

separate port and starboard raw side scan signals. These signals can be manually

adjusted for time varied gain (TVG) or automatic gain control (AGC) by analogue

controls on the side scan transceiver unit before hard copy output is provided as a raw

analogue signal for high speed digitization by the GeoPro Side Scan Processor.

Specifications of Side Scan Transducers:

Port channel 60 /100 kHz. Starboard channel 60 /100 kHz. Sensitivity -190 dB re 1 V/u Pa Depression angle 10° ±1° down. Source level 223±3dB re 1uPa @ 1m Beam width 50°by 1°on 114 kHz 40°by 0.5° on 410 kHz Bandwidth 20 kHz. Power requirements 150 VDC at 100 mA. TVG 80 dB dynamic range, corrected for spreading and frequency related losses (through water attenuation) ii) Geo Chirp Sub-bottom Profiler:

The Geo Acoustics Geo Chirp II is a new type of Sub-bottom profiler which can

for the first time combined high penetration through compacted sediments such as

sand and gravel, whilst achieving high resolutions of the order of 6cm.The system can

do this because it can transmit very high energies into the water per ping, 2Kw RMS

for 32ms equates to 64J. Each output waveform can sweep between 1kHz and

13.5kHz at high amplitude, giving high bandwidth and thus high resolution. The

waveforms contain significant amounts of energy at low frequencies, giving the

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system high penetration. Four profiler transducer units are fitted to the main body

plate of the Two-Fish, with the face pointing down. Fiberglass shells cove the

transducers and electronics to provide a streamlined shape and physical protection.

Operating principle:

The Geo Chirp system works on the sweep frequency or chirp principal. An

amplitude shaped pulse 0f 32ms, which sweeps from 1.5Hz to 11.5Hz in high-

resolution mode is transmitted through the water from a linear high-powered amplifier,

which is situated in the Tow-Fish. This acoustic energy will either be transmitted

through, or reflected by the seabed interface and every successive sediment interface

as it penetrates the seabed. The amount of energy reflected and the amount disperse

in the medium depend on the properties of the medium.The return acoustic energy is

received by a hydrophone. The hydrophone consists of separate receive elements

either in the form of a towed mini streamer or as mini arrays.

The specifications of Geo chirp sub bottom profiler

Power output 4kW peak at 50Ω load Maximum repetition rate for 32 ms chirp waveforms 4 pps Maximum repetition rate for 1ms Pinger waveforms 10 pps DC power supply 200VDC to 400VDC Trigger Isolated TTL Hydrophone output Analogue 50Ω impedance Hydrophone amplifier gain 20dB plus TVG Waveforms Up to 200 user selectable sweeps or pings Frequency range 0.5 kHz to 13.5 kHz Resolution 6cm using 0.5 kHz to 13.5 kHz chirp Cable interface Up to 6km of 11mm single armoured coaxial Cable Rochester A302799 or equivalent iii) Responder and attitude sensor:

The nose cone on the front of the Two-Fish contains two transducers, one

forward and upward facing responder operating at 23 kHz, and a downward facing

echo sounder operating at 250 kHz. The deck unit triggers the Responder and

Echosounder. After receiving the key form deck unit the responder provides the track

of two fish, whereas the echosounder provides the height of the two fish above the

sea bed. Attitude sensor contains individual sensors that detect depth, heading, pitch,

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roll, and internal temperature. The sensors can be interrogated on a ping by ping

basis to allow full geometric correction.

7.2 GeoSpark-800

This is a high-resolution multi channel seismic recording and processing

system (Fig.4). The overall system consists of A). Deck equipment, and B). Sub-sea

equipment.

7.2.1 Deck equipment.

The deck equipment consist of a high voltage a) pulsed power supply, b) Geo-

Trace 24-2 data acquisition, monitoring and processing unit, and, c) Post Processing

computer with Plotter.

a) Pulsed Power supply

The power supply comprises two modules a) Controlling panel that works with

230 volts at 50 Hz, b) a high voltage pulsed corona plasma unit which generates high

voltage up to 5600 volts with peak out put of 10 K Joules by step up through a

Capacitor bank of 5 racks of 32 µF capacitance each. If necessary it can also function

at other voltages and Hertz values. It has a maximum charge rate of 2500Joules/sec

and maximum shooting rate at full power of 1 shot per 4 seconds. Inside the entire

system the following power supply exists. They are 2ATXPC power supply, 2flat-panel

power supplies, Touch screen/analogue front-end unit power supply,

b) Geo-Trace 24-2 data acquisition, monitoring and processing unit

The Acquisition System mainly consists of a) Geo-Trace 24-2 software b)

Analogue filter interface, c) DigiBird Controller System, d) DigiBird Components and e)

Online OYO Geospace Plotter.

c) Post Processing computer with plotting facility

The processing PC comprises of a HP Designjet 500 plotter. The PC is

interfaced with the Acquisition PC System through the LAN.

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7.2.2 Sub sea equipment:

The sub sea equipment mainly consist of i) Sparker, ii) Streamer, iii) Birds and

iv) an auxiliary hydrophone to receive source signal.

i) Sparker.

This is the high voltage electrical energy-discharging unit. It consists of 800 tips

through which the energy released in to the seawater. The High voltage pulsed corona

plasma unit and the sparker is connected through high voltage transmitting cables.

ii) Streamer

This is the sensor unit of the system. It consists of hydrophones housed in a

rubber tube of diameter 50-mm, filled with paraffin. It contains 24 channels; each

channel is an array of 8 elements. The actual length of the streamer is 200 m. The first

50 m is dead section (two sections of 25m length each) followed by 150 m of active

section (two sections of 75 m length each), 50 m of lead in sections and 50 m of deck

cables.

iii) Birds

The birds are microprocessor-based control and monitoring devices that mount

externally on a marine seismic streamer. The Geospark-800 system uses 2 Digi-

birds, model 5010 c/w collar set and D-cell battery set. Using internally mounted

transducers they can monitor depth over a range of 0 to 400 ft with a resolution of 0.1

ft and an accuracy of +/-0.5ft. Once programmed with an assigned operating depth the

bird operates independently to control streamer depth by adjusting its wings. The

assembly is housed in a non-corroding and non-magnetic molded polyurethane body

that is streamlined to minimize flow induced noise. Each unit is powered by 4 high

energy density lithium cells packed in a dual battery pack.

7.3 LEICA DGPS

Leica DGPS is one of the most reliable positions fixing navigation equipment,

especially to carryout Geo-physical surveys of this magnitude, which seldom gave any

problem to the user. The position data transfer (at every second) to the interfaced

Geo-physical instruments was quite effective and was easy to handle, while post-

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processing the data. The position update of the system is 10 Hertz and the data

transmission rate to the geophysical equipment was of every second.

Principle:

Each GPS satellite has several very accurate atomic clocks on board. The

clocks operate at a fundamental frequency of 10.23MHz. This is used to generate the

signals that are broadcast from the satellite. Many of the errors affecting the measure-

ment of satellite range can be completely eliminated or at least significantly reduced

using differential measurement techniques. DGPS allows the civilian user to increase

position accuracy from 100m to 2-3m or less, making it more useful for many civilian

applications. GPS is the shortened form of NAVSTAR GPS. This is an acronym for

NAVIGATION System with Time And Ranging Global Positioning System. GPS is a

satellite-based navigation system that uses a constellation of 24 satellites that enable

users to accurately determine three dimensional position, velocity and time.

Differential Global positioning system was used throughout the cruise and

obtained the accurate position of the ship along the pre-planned survey tracks. The

Leica SR 520 differential GPS receiver was used to achieve this. Using the Tsunami-

Electronic chart/navigation software, the vessel movement along the predetermined

survey track was monitored.

The overall system consists of three major segments; the space segment, the

ground control segment and the user segment. The space segment is a constellation

of 24 satellites, operating in 12-hour orbits at an altitude of 20,183 kms. (10, 898

Nautical miles). This constellation contains 24 satellites in 6 orbits, each orbital plane

equally spaced about the equator at an inclination of about 55 degrees. The User

Segment comprises of anyone using a GPS receiver to receive the GPS signal and

determine their position and/ or time. Typical applications within the user segment are

land navigation for hikers, vehicle location, surveying, marine navigation, aerial

navigation, machine control etc. The space segment is so designed that there will be a

minimum of 4 satellites visible above a 15° cut-off angle at any point of the earth’s

surface at any given time. Four satellites are the minimum that must be visible for

most applications.

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Principles of DGPS :

In DGPS operation, two receivers operate simultaneously, one at reference

station and other at a mobile unit (Ship, Boat, etc.). The reference station generates

corrections to all visible satellites and transmits to mobile by a radio link. The mobile

receiver combines its observed ranges from satellites and the corrections received

from the reference station, to arrive at differentially corrected ranges – that are almost

free from all errors common to both the receivers. This way the accuracy of the

mobile’s position can be improved to about 1 meter, which otherwise would have been

up to 100 meters. That is, by measuring the time taken for a signal to travel from

satellite to receiver, the distance is computed. To measure the travel time, however,

the receiver clock needs to be synchronized with GPS time frame. Since the GPS is a

passive system, an individual receiver cannot interrogate the satellite. Hence the

difference between the satellite clock and receiver clock, are treated as an unknown

quantity (T). Thus we have four unknowns to solve to get a fix. They are the position

co-ordinates (X, Y, Z) and time offset of user clock (T).To solve an equation system of

4 unknowns, 4 ranges are measured to different satellites simultaneously. After

applying the correction (for the measured ranges) received from the reference station,

the position of the survey vessel is determined by the geometric intersection of those

ranges. Experience shows that there are usually at least 5 satellites visible above 15°

for most of the time and quite often there are 7 or 8 satellites visible.

Differential Global positioning system was used throughout the cruise and

obtained the accurate position of the ship along the pre-planned survey tracks. The

Leica SR 520 differential GPS receiver was used to achieve this. Using the Tsunami-

Electronic chart/navigation software, the vessel movement along the predetermined

survey track was monitored. More commonly known as DGPS, this system gives

accuracy between 0.5 and 5 meters. The Reference receiver antenna is mounted on a

previously measured point with known co-ordinates. The receiver that is set at this

point is known as the Reference Receiver or Base Station. The moment, the receiver

is switched on, it starts tracking the satellites. It can calculate an autonomous position.

Because it is on a known point, the reference receiver can estimate very precisely

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what the ranges to the various satellites should be. The reference receiver can

therefore work out the difference between the computed and measured range values.

These differences are known as corrections. The reference receiver is usually

attached to a radio data link, which is used to broadcast these corrections. The rover

receiver is on the other end of these corrections. The rover receiver has a radio data

link attached to it that enables it to receive the range corrections broadcast by the

Reference

8.0. RESULTS

The geophysical data (Deep tow digital side scan sonar, chirp sonar and 3.5

KHz echo sounder) along the pre determined SE-NW, NE-SW trending cruise tracks

in the Goa offshore basin were collected as per the plan onboard AA Sidorenko.

Some selected records of side scan sonar, chirp sonar were shown in this report

9.0. WEATHER DURING THE CRUISE

The weather during the cruise was favorable with Sea State varying between 1

and 3 with weak wind force.

10. 0 SHIP’S GENERAL PERFORMANCE

Ship’s staff was cooperative during the entire survey. Cook‘s hospitality and

catering is very good throughout the cruise.

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Figure captions

Figure.1. Photograph showing the Ocean Research Vessel AA Sidorenko (chartered

from NIOT, Department of Ocean Development, Government of India)

Figure. 2. Cruise track map of the Goa offshore

Figure.3. Deep tow telemetry system comprised of Side scan sonar, Chirp sonar,

recording unit and accessories.

Figure.4. Block diagram showing various components of the deep tow telemetry

system.

Figure.5. High resolution sparker system and accessories

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Fig 1 Ocean Research Vessel AA Sidorenko.

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Fig 2. Cruise Track Map.

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Acquisition System

Thermal Printer

Fig 3 Deep tow Telemetry recording unit and acces

Tow Fish

GeoPro Processing Unit with Display

system comprised of Side scan sonar, Chirp sonar, sories

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25

10 K Joule Spark

Power

High Resolution Sparker System

Power A A SIDORENKO 24 Channel seismic 10 K Joule

Front-end-module HRS data acquisition&Processing unit

Front end module HRS data acquisition unit S

Sparker source in th

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parker source in th