principle of seismic survey - … principle of seismic survey objective of seismic survey...

PRINCIPLE OF SEISMIC SURVEY

MARINE INSTITUTE Galway, Ireland – 29th April 2016

Laurent MATTIO

2 Contents

Principle of seismic survey

Objective of seismic survey

Acquisition chain

Wave propagation

Different technologies

Acoustic sources

Acoustic receivers

Navigation and positioning

Parameters to take in account

Signal processing: CHIRP technology

Data processing

Data interpretation

3 Principle of seismic survey

Objective of seismic survey

Acquisition chain

- Understand the geology

- Determine the nature and characteristics of the ground

- Determine the nature and quantity of the fluids / sediments

- Evaluate and optimize pre/post dredging work

4 Principle of seismic survey

Wave propagation

The speed of sound depends of the density of the environment:

When the acoustic impedance changes,

the transmitted acoustic waves is:

- Reflected

- Refracted

- Absorbed

A better penetration is achieved by

sending more energy using:

- A stronger acoustic source

- Lower frequencies

Water Sand Hard bottom (rock)

Sound velocity ~1500 m/s ~2000 m/s ≥ 3000 m/s

5 Different technologies

Reflection

E M I S S I O N ⇨ Refraction ⇨ R E C E P T I O N

Absorpsion

Bi-static

- Source: air, water, mechanical,

electrical, piezo

- Receivers: piezo

Mono-static

- Source and receivers: piezo

6 Acoustic sources

AIRGUN / WATERGUN

Seismic source + -

Airgun / Watergun

Deep water

High penetration

Robust

Heavy installation

Tuning

Coarse resolution

- Quick release of compressed air or water volume

- 2000 to 3000 psi

- Involve using:

• Very large vessels

• Compressors

• Up to 48 guns

• Multiple kilometre-long separate receivers

7 Acoustic sources

SPARKER

Anodes Cathode

Seismic source + -

Sparker

Light

Medium / High resolution

Cheap

Repetitive pulse

High voltage (3000V)

Does not work in fresh water

Consumable

Uncertain geometry

Not to be used when gas in sediments

- Energy is stored in capacitors

- Discharged through a copper cathode

- Electric arc between cathode and anodes

- Reception on a different sensor

8

BOOMER

Acoustic sources

Seismic source + -

Boomer

Light

High resolution

Cheap

Low towing speed

High voltage (3000V)

Uncertain geometry


- Discharged through a coil

- Flex of copper a plate or hit of two plates

- Reception on a different sensor

9 Acoustic sources

Ceramics transducer

Seismic source + -

Ceramic transducer

Shallow to deep water

Wide frequency range

Hull, pole & towed installation

Compact systems amplifiers

Integrated receivers

Low penetration of high frequency

models


- Emission through a ceramic

- Reception on the same sensor possible

10 Acoustic sources

Low frequency sources are less sensitive to absorption and can accommodate

greater water depth & harder seabed types

High frequency / wide-band sources bring better vertical resolution

The use of one or multiple seismic receivers allow velocity analysis but very

sensitive to navigation, type of vessel and weather

Seismic source Bandwidth Water depth Penetration Resolution

Water gun 20 Hz – 300 Hz Deep Very good Poor

Air gun 10 Hz – 300 Hz Deep Very good Poor

Sparker 500 Hz – 5 000 Hz Shallow Good (soft) Good

Boomer 1 000 Hz – 4 000 Hz Shallow Good (soft) Very good

Chirp 500 Hz – 20 000 Hz Shallow - Deep Good (soft) Very good

11 Acoustic receivers

Streamers

Streamers are passive sensors/hydrophones in a row from few meters to several

kilometers long. The longer they are the more critical is their positioning (accessories:

birds, GPS, tail buoy, etc.)

Streamers are generally towed at the sea surface and so are very sensitive to sea

state

Ceramic transducers

Piezo-electric effect transforms electric pulses into compression waves (ie. sound)

and the same the other way.

12 Navigation & Positioning Survey vessel is commonly positioned using a GNSS device (differential / RTK)

When a streamer is used, it may be:

A short streamer that is simply positioned using the layback method

A longer streamer with positioning sensors (GNSS / beacons, etc.)

When no streamer is used, it may be:

A tow-fish chirp that is positioned using layback or better USBL/acoustic positioning

A hull/pole mounted SBP that must be compensated from the vessel motion using

a motion reference unit (gyros, Inertial Navigation System)

In all cases, rigid offsets are involved and must be defined for the survey

GNSS antenna offsets

Motion sensor offsets

Tow point / pole offsets

A motion sensor can be used to compute fix equipment positions

13 Parameters to take in account

Some parameters are adjustable, but most depend on the chosen equipment

The most appropriate equipment must be selected to achieve the survey goals

Requirement / Constraints will determine:

Water depth ⇨ Power / Shooting rate / Recording length

Penetration ⇨ Power / Recording length / Frequency

Shooting rate ⇨ Power / Recording length / Frequency

Source power ⇨ Frequency

Resolution ⇨ Power / Frequency

Vessel speed ⇨ Shooting rate

Vessel size ⇨ Power / Frequency

14 Signal processing: CHIRP technology

Only possible with ceramic transducer sources

The emitted acoustic wave is characterized by:

A frequency band width

A signal modulation

A duration

Matched filtering: a mathematical correlation compares and matches the

emitted pattern with the received signal

CHIRP processing improves the vertical resolution and filters the noise out

Received pulse + Noise Transmitted modulated pulse

Processed signal

15 Data processing

Low-frequency sound is impacted by:

Various noises (vessel, environment, weather, etc.)

Propagation effects (acoustic multiples, acoustic blanking, diffraction, etc.)

Prior to interpretation, data must be processed:

Filters

Band-Pass filters for impulsive acoustic sources (sparkers, boomers, etc.)

Matched filtering for chirp systems

Gains

Increase the received signal level to compensate the attenuation

Filter OFF Filter ON

16 Data interpretation

Sub-bottom profiling is an indirect mean to observe the sub-soil acoustic

interfaces and can not determine the seabed type.

Only correlation between ground-truthing data and acoustic profiles can be

used to caracterise sediment types & geological features

Any questions ?

Thank you.

ECHOES PRODUCT LINE


Laurent MATTIO

2 Contents

Overview A wide range of frequencies

Echoes 1500: Low frequency sub-bottom profiler

Echoes 3500 T3: Shallow to medium ocean depth

Echoes 3500 T7: Full ocean master class sub-bottom profiler

Echoes 5000: Cutting edge AUV-mounted sub-bottom profiler

Echoes 10000: Ultra compact, ultra high resolution

Typical applications

3 Echoes products line - Overview

• Very compact Topside Unit • Unrivaled low-distortion amplifier • Full control over the chirp signal • Ethernet link to topside computer • Embedded 24-bit signal digitizing • DELPH Seismic Acquisition Included

• Full bandwidth efficiency • The best data quality • Easy installation & operation • Reduced maintenance • Permanent or mobile solution

ECHOES is a complete range of low-frequency to ultra-high resolution

sub-bottom profilers

1500 3500 5000 10000

4 Echoes products line - Overview

ECHOES models cover:

A broad range of frequencies

All types of integration

All types of applications

1.7 – 5.5 kHz

5 Echoes products line - Echoes 1500

Low frequency sub-bottom profiler

• Wide band and flat spectrum • 0.5 to 2.5kHz user-selectable chirp • 40cm resolution • 2 to 4kVA compact power amplifier

• Up to 6000m water-depth • Penetration up to 240m • Tow fish or AUV integration • Alternative to Sparkers & Boomers

6

Echoes products line - Echoes 1500

3km

approx. 40 cm

82.5m

(110ms)

7 Echoes products line - Echoes 3500 T3

Shallow to Medium water depth


• Shallow to Medium ocean depth • Up to 2000m water-depth • Penetration up to 120m • Hull-mounted or pole-mounted integration


Shallow to Medium water depth

100 m

135 m

35

m


Full ocean master class sub-bottom profiler


• Shallow to full ocean depth • Up to 11000m water-depth • Penetration up to 200m • Hull-mounted integration


Balanced penetration and resolution

330ms

247 m

490ms

367 m

12

0 m

11

Cutting edge AUV-mounted sub-bottom profiler

Echoes products line - Echoes 5000

• Wide band and flat spectrum • 2.0 to 6.0kHz user-selectable chirp • < 25cm resolution • 1 to 2kVA compact power amplifier

• Shallow to full ocean depth • Up to 6000m water-depth • Penetration up to 100m • Tow fish or AUV integration

12 Echoes products line - Echoes 5000

AUV

795m

13 Echoes products line – Echoes 10000

Ultra-compact & ultra-high resolution

• Wide band and flat spectrum • 5.0 to 15.0kHz user-selectable chirp • < 10cm resolution • 2 to 4kVA compact power amplifier

• Shallow water and inland waterways • Up to 100m water-depth • Penetration up to 70m • Compact pole-mounted integration


Meeting both penetration and resolution

25ms

2km

20 ms

15 m

15

ms

11

.25

m

5 ms

3.75 m


Meeting both penetration and resolution

16 Echoes products line - Typical applications

Commercial Institutional

Geophysical survey

Dredging Scientific Hydro Archaeology

ECHOES 1500 (towed) X X

ECHOES 1500 (AUV / ROV) X X

ECHOES 3500 T3 (pole-mounted) X X X X

ECHOES 3500 T3 (hull-mounted) X X X X

ECHOES 3500 T7 (hull-mounted) X X X

ECHOES 5000 (towed) X X X X

ECHOES 5000 (AUV / ROV) X X X

ECHOES 10000 (pole mounted) X X X X X

Any questions ?

Thank you.

ECHOES 3500 T7 Presentation


Laurent MATTIO

2 Contents

Overview

System components

Acquisition chain

Technical specifications

Wiring diagram

3 ECHOES 3500 T7 – Overview

ECHOES 3500 T7 is a low frequency CHIRP Sub-Bottom Profiler (SBP), based on

seven transducers. Designed for:

Geophysical surveys, hydrographic and scientific applications

From medium to full ocean depths

Bandwidth range from 1.7kHz to 5.5kHz (centered on 3.5kHz) providing:

Good penetration in sediment

Very good vertical resolution

CHIRP frequency modulation provides:

Important gain in signal to noise ratio (SNR) in deep water

Short pulses for shallow water

4 ECHOES 3500 T7 – System components

A workstation

Data acquisition

Data real-time & offline

processing (optional)

A topside unit

CHIRP signal generation

Power amplifier

Impedance matching

Data acquisition

A transducer array

Mono-static configuration

Acoustic beam emitting

Acoustic data receiving

ECHOES TopSide Unit

ECHOES Transducers

DELPH Software

Dig

ital

Eth

ern

et

An

alo

g

H

igh

V

olt

age

Digital Raw data Pulse selection

HYDRINS Hydrographic Inertial Navigation System

Heave

Position Position

GNSS

5 ECHOES 3500 T7 – Acquisition chain

A workstation

Data acquisition

Data real-time & offline

processing (optional)

A topside unit

CHIRP signal generation

Power amplifier

Impedance matching

Data acquisition

A transducer array

Mono-static configuration

Acoustic beam emitting

Acoustic data receiving

6 ECHOES 3500 T7 – Technical specifications

Workstation

Typical configuration

Windows 7 - 64 bit

4 GB of RAM for the complete interpretation package

500 MB of disk space for installation files

Enough storage space for data

DELPH package

DELPH Seismic Acquisition

DELPH Seismic Interpretation

(including DELPH RoadMap)

Each license on a separate dongle

IP address 20.0.0.2


Topside unit

CHIRP pulse generation

Impedance matching

Transmit / Receive amplifier

24-bit Digitization

IP address 20.0.0.1

Power 6000VA

Output voltage 0 to 700V RMS

Input AC sine wave 0 to 3.16 V RMS.

Settling time < 100ms

AC line 115/230VAC – 50 / 60Hz

Dimensions 6U x 486mm x 586mm / 6U x 19.2” x 23”

Weight 30kgs

Output connector 1 GES HTV connector to the transducer

1 BNC connector for the Synchro Out

1 BNC connector for the Auxiliary Out

1 Ethernet connector

Input connector 1 BNC connector for the Synchro In

1 BNC connector for the Auxiliary In

1 AC connector to the AC 220V

1 Banana connector for the ground


ON / OFF

button and indicator

Output

indicator

Acquisition

indicator

Alarm indicator High voltage indicator Fans

Status indicator

Fan


Fuse Computer

Aux IN

Power

Fans Ground High voltage indicator Transducer

Fan Aux OUT

Sync OUT

Sync IN


Transducer array

The directivity index is much better than the one of a single transducer

The bandwidth is obtained by coupling the two resonance frequencies of the transducers

The antenna has been designed to sustain rough weather

The output of each individual transducer is made with an underwater connector

Bandwidth 1.7kHz to 5.5kHz

Resonant frequency 2.1kHz – 5.1kHz

Max input voltage 700V

Directivity Unidirectional

Dimensions and weight

Height 0.38m Diameter 0.98m Weight in air 363kg Weight in water 265kg

12 ECHOES 3500 T7 – Wiring diagram

ECHOES TopSide Unit

ECHOES Transducers

DELPH Software

HYDRINS Hydrographic Inertial Navigation System

GNSS

Ethernet RJ45

GES

Subconn 3 pins

Serial DB9 Ethernet RJ45

Subconn 2 pins

Underwater

13 ECHOES 3500 T7 – Wiring diagram

Ethernet – RJ45 (topside unit / computer)

Serial – RS232 DB9 (external sensors / computer)

Serial / USB converter (external sensors / computer)

Power leads (computer and topside unit)

Grounding (topside unit)

50m deck cable – GES / Subconn (topside unit / octopus)

Octopus – Subconn / Subconn x 7 (deck cable / transducers)

Deck cable Octopus

Pin number GES SUBCONN SUBCONN

Pin 1 VT+ Signal + Signal +

Pin 2 VT- Signal - Signal -

Pin 3 - - N/A

Any questions ?

Thank you.

principle of seismic survey - … principle of seismic survey objective of seismic survey...

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