PRINCIPLE OF SEISMIC SURVEY MARINE INSTITUTE Galway, Ireland 29th April 2016 Laurent MATTIO
Contents 2 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
Principle of seismic survey 3 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
Principle of seismic survey 4 Wave propagation The speed of sound depends of the density of the environment: Water Sand Hard bottom (rock) Sound velocity ~1500 m/s ~2000 m/s 3000 m/s 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
Different technologies 5 Bi-static - Source: air, water, mechanical, electrical, piezo - Receivers: piezo Mono-static - Source and receivers: piezo Reflection E M I S S I O N Refraction R E C E P T I O N Absorpsion
Acoustic sources AIRGUN / WATERGUN 6 - 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 Seismic source + - Airgun / Watergun Deep water High penetration Robust Heavy installation Tuning Coarse resolution
Acoustic sources 7 Cathode SPARKER Anodes - Energy is stored in capacitors - Discharged through a copper cathode - Electric arc between cathode and anodes - Reception on a different sensor 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
Acoustic sources 8 BOOMER - Energy is stored in capacitors - Discharged through a coil - Flex of copper a plate or hit of two plates - Reception on a different sensor Seismic source + - Boomer Light High resolution Cheap Low towing speed High voltage (3000V) Uncertain geometry
Acoustic sources 9 Ceramics transducer - Energy is stored in capacitors - Emission through a ceramic - Reception on the same sensor possible 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
Acoustic sources 10 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
Acoustic receivers 11 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.
Navigation & Positioning Survey vessel is commonly positioned using a GNSS device (differential / RTK) 12 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
Parameters to take in account 13 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 Some parameters are adjustable, but most depend on the chosen equipment The most appropriate equipment must be selected to achieve the survey goals
Signal processing: CHIRP technology 14 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 Transmitted modulated pulse Received pulse + Noise Processed signal
Data processing 15 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
Data interpretation 16 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
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ECHOES PRODUCT LINE MARINE INSTITUTE Galway, Ireland 29th April 2016 Laurent MATTIO
Contents 2 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
Echoes products line - Overview 3 ECHOES is a complete range of low-frequency to ultra-high resolution sub-bottom profilers 1500 3500 5000 10000 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 products line - Overview 4 ECHOES models cover: A broad range of frequencies All types of integration All types of applications 1.7 5.5 khz
Echoes products line - Echoes 1500 5 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
Echoes products line - Echoes 1500 6 82.5m (110ms) approx. 40 cm 3km
Echoes products line - Echoes 3500 T3 7 Shallow to Medium water depth Wide band and flat spectrum 1.7 to 5.5kHz user-selectable chirp 20cm resolution 2 to 4kVA compact power amplifier Shallow to Medium ocean depth Up to 2000m water-depth Penetration up to 120m Hull-mounted or pole-mounted integration
35 m Echoes products line - Echoes 3500 T3 8 Shallow to Medium water depth 100 m 135 m
Echoes products line - Echoes 3500 T7 9 Full ocean master class sub-bottom profiler Wide band and flat spectrum 1.7 to 5.5kHz user-selectable chirp 20cm resolution 2 to 6kVA compact power amplifier Shallow to full ocean depth Up to 11000m water-depth Penetration up to 200m Hull-mounted integration
120 m Echoes products line - Echoes 3500 T7 10 Balanced penetration and resolution 330ms 247 m 490ms 367 m
Echoes products line - Echoes 5000 11 Cutting edge AUV-mounted sub-bottom profiler 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
Echoes products line - Echoes 5000 12 AUV 795m
Echoes products line Echoes 10000 13 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
15 ms 11.25m Echoes products line Echoes 10000 14 Meeting both penetration and resolution 5 ms 3.75 m 20 ms 15 m 25ms 2km
Echoes products line Echoes 10000 15 Meeting both penetration and resolution
Echoes products line - Typical applications 16 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
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ECHOES 3500 T7 Presentation MARINE INSTITUTE Galway, Ireland 29th April 2016 Laurent MATTIO
Contents 2 Overview System components Acquisition chain Technical specifications Wiring diagram
ECHOES 3500 T7 Overview 3 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
Analog High Voltage Digital Ethernet ECHOES 3500 T7 System components 4 GNSS A workstation Heave DELPH Software Data acquisition Data real-time & offline processing (optional) Position HYDRINS Hydrographic Inertial Navigation System Position Pulse selection Digital Raw data A topside unit CHIRP signal generation ECHOES TopSide Unit Power amplifier Impedance matching Data acquisition A transducer array Mono-static configuration Acoustic beam emitting ECHOES Transducers Acoustic data receiving
ECHOES 3500 T7 Acquisition chain 5 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 3500 T7 Technical specifications 6 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
ECHOES 3500 T7 Technical specifications 7 Power Output voltage Input Settling time AC line 6000VA 0 to 700V RMS AC sine wave 0 to 3.16 V RMS. < 100ms 115/230VAC 50 / 60Hz Dimensions 6U x 486mm x 586mm / 6U x 19.2 x 23 Topside unit CHIRP pulse generation Impedance matching Transmit / Receive amplifier 24-bit Digitization IP address 20.0.0.1 Weight Output connector Input connector 30kgs 1 GES HTV connector to the transducer 1 BNC connector for the Synchro Out 1 BNC connector for the Auxiliary Out 1 Ethernet 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
ECHOES 3500 T7 Technical specifications 8 Alarm indicator High voltage indicator Fans Status indicator Acquisition indicator Output indicator ON / OFF button and indicator Fan
ECHOES 3500 T7 Technical specifications Fan Aux IN Aux OUT 9 Power Sync IN Sync OUT High voltage indicator Transducer Ground Fuse Computer Fans
ECHOES 3500 T7 Technical specifications 10 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 Resonant frequency Max input voltage Directivity Dimensions and weight 1.7kHz to 5.5kHz 2.1kHz 5.1kHz 700V Unidirectional Height 0.38m Diameter 0.98m Weight in air 363kg Weight in water 265kg
ECHOES 3500 T7 Technical specifications 11
ECHOES 3500 T7 Wiring diagram GNSS DELPH Software 12 HYDRINS Hydrographic Inertial Navigation System Serial DB9 Ethernet RJ45 Ethernet RJ45 ECHOES TopSide Unit GES Underwater Subconn 2 pins Subconn 3 pins ECHOES Transducers
ECHOES 3500 T7 Wiring diagram 13 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
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