Seafloor mapping using interferometric sonars

Seafloor Mapping Using Interferometric Sonars:
Advances in Technology and Techniques
Tom Hiller, Advanced Products Manager, GeoAcoustics Ltd.
WORLD CLASS – through people, technology and dedication
Brest, France. 30 November 2009
Presentation Outline
/2/
•
Summary of the key attributes of interferometric
technology
•
Requirements for high accuracy surveys
•
Examples of interferometric technology capabilities
•
Use of interferometric technology in ROVs and AUVs
30-Nov-09
Introduction to Interferometric Sonar Concepts and Technology
/3/
30-Nov-09
How does an interferometer work?
•
•
•
•
•
/4/
Transmitted pulse geometry similar to side scan
Multiple receive staves (typically 4)
Phase of returned sonar signal is measured on each stave
Differential Phase is used to determine return angle
Data is a time series (of angles, amplitudes, and other
attributes)
30-Nov-09
The data products:
Side scan transmit geometry
Simultaneous bathymetry and
amplitude data (range series of
angles and amplitudes)
/5/
30-Nov-09
Principles of operation
Transmit is short in time (a few cycles), wide across track
and narrow along track (like a side scan)
Multiple receiver staves within each transducer
Phase measurement based on differential time
Phase difference (Ф)
/6/
30-Nov-09
Limitation: Interferometric Noise Sources
Phasor diagrams illustrating sliding footprint and sea noise effects
Result: interferometric raw data has angle noise
/7/
30-Nov-09
Looking at the Raw Data in Detail:
key feature: 1000s of data points/ping
Accurate range, noisy angle
/8/
30-Nov-09
Basics of Interferometric Data Processing
Key steps:
Amplitude filtering
▼
Statistical filtering
▼
Binning
/9/
30-Nov-09
Summary of interferometer attributes:
•
•
•
•
•
•
•
•
Wide field of view (>240degrees)
Data density similar to digital side scan
Simultaneous bathymetry and side scan
Swath width is insensitive to roll
Higher data density away from nadir
Limited range due to signal to noise requirement for phase
measurements
High data density but phase noise means processing is needed
to get accurate seafloor depths
Able to be implemented in compact, robust, low power form
- Particularly suitable for shallow water surveys from small vessels
/ 10 /
30-Nov-09
The GeoAcoustics GeoSwath Plus
/ 11 /
30-Nov-09
GeoSwath Technology Timeline
•
GeoSwath 32 was introduced in 1998 by GeoAcoustics Ltd of
Great Yarmouth, UK
•
GeoSwath Plus was launched Q4 2003
•
Continuous improvements in hardware and software have
been improving data quality and swath width
•
Data has been accepted as meeting IHO standards, and been
included in UKHO Nautical Charts since 2005
Other
Military
•
By mid-2009 over 120 systems
in use worldwide
Oil&Gas
Ports &
harbours
Environment
Scientific/
geological
General
Hydrographic
Dredging
/ 12 /
30-Nov-09
GeoSwath Transducer Specifications:
Frequency:
125kHz
250kHz
500kHz
Txd dims:
60x25x8cm
30x15x6cm
25x11x6cm
Max depth:
200m
100m
50m
Usual use:
0m – 200m capability
0m – 100m capability
0m – 50m capability
10m-200m
2m-50m
1m-40m
Typically found
on:
Larger Survey
Ship
Smaller Vessel and
larger AUV/ROV
Small vessel &
small AUV/ROV
/ 13 /
30-Nov-09
GeoSwath Deployment Examples
Large and small vessels.
Fixed, semi-permanent and temporary.
Pole mount, hull mount.
AUV and ROV mount.
/ 14 /
30-Nov-09
Suitable for very small survey vessels:
/ 15 /
30-Nov-09
Achieving High Accuracy with Interferometric Data
/ 16 /
30-Nov-09
GeoSwath Data Processing summary
/ 17 /
30-Nov-09
Alternative Third Party Processing Routes
Real-time
control
GeoSwath Plus
On-line
processing
Transfer of flagged
raw data via
Ethernet
Hypack
QINSY
(real-time)
GeoSwath Plus
Acquisition
Hardware
Fledermaus
Data
storage and
transfer
GeoSwath Plus
Off-line
processing
Data
Flagging
and
conversion
to GSF
Data
filtering and
conversion
to ‘reduced’
raw file
Further GS+ processing
and export as xyz
/ 18 /
30-Nov-09
SABRE
Other GSF
reader
CARIS
Other vendors
Unfiltered and filtered raw data
/ 19 /
30-Nov-09
19
All data view of single swath, 50m per side range
setting, 5 Knots vessel speed
/ 20 /
30-Nov-09
20
Single swath binned at 50cm without interpolation or
smoothing, and sun illuminated
/ 21 /
30-Nov-09
21
High Data Density Ensures Survey Quality
1m
Grid
Raw Data
Bin size ≈ sonar footprint ≈ min. feature size. Data density > (or >>) 10 per bin.
/ 22 /
30-Nov-09
22
500kHz GeoSwath: bathymetry and side scan coverage plots
Water depth ~10m under the transducers
Bathymetry:
20cm grid
/ 23 /
30-Nov-09
80m swath width
Resolves 5cm high sand waves
Side-scan mosaic:
10cm grid
Standard deviation of filtered data
/ 24 /
30-Nov-09
Data density at different resolutions
/ 25 /
30-Nov-09
Interferometric data processing for high
accuracy:
•
Key Characteristic: lots of data with accurate range and
noisy angle
•
In each depth bin may be 100s of measurements with
approximately independent noise and random
distribution
•
Mean of this many depths gives a very repeatable and
reliable number
•
Standard Error of the Mean = Standard Deviation of data
divided by the square root of the number of data points
Accurate depths requires high data density, good data
filtering, and prudent binning
/ 26 /
30-Nov-09
Running a Survey: the side scan search pattern
/ 27 /
30-Nov-09
27
The side scan search pattern gives full coverage
high resolution interferometric surveys:
930m x 780m, 8m to 25m deep, 2h survey time
/ 28 /
30-Nov-09
28
High accuracy surveying also requires:
•Data Timing and Time Synchronisation:
• Sub-ms PPS timing and use of time stamped ancillary data.
•Navigation accuracy:
• RTK GPS, or postprocessed position and attitude
•
•
Accurate sound velocity profiles
Minimise possible offset error sources:
•
•
•
•
•
Minimise lever arms
Align reference frame axes
Accurately measured offsets
Accurate ancillary data
Good calibration: multiple patch tests, cross-checks
Using above have demonstrated <4cm repeatability re. geoid.
/ 29 /
30-Nov-09
Example of high accuracy river mapping:
/ 30 /
•
Example is from Rijkswaterstaat; part of the Dutch
Ministry of Transportation and Water Management.
•
Responsibilities including the construction and
maintennance of waterways and flood prevention.
•
Chose the GeoSwath because it is particularly suitable
for the shallow rivers, canals and seas in Holland.
•
All the GeoSwath installations on RWS vessels are
250kHz GeoSwath Plus configured with the QINSy real
time interface
30-Nov-09
Vessel and retractable mounts
/ 31 /
30-Nov-09
GeoSwath and QINSY
-real time interface
-into native QPS structure
/ 32 /
30-Nov-09
Data Comparison Tests by Rijkswaterstaat
• Same boat, same ancillaries, 2 fixed sonar mounts:
GeoSwath 250kHz and Reson Seabat 8101
• RTK GPS positioning and height control, Octans motion
sensor
• Surveys run alternately, same 4-line pattern;
GeoSwath-8101-GeoSwath-8101
• Processing separately:
• GeoSwath via GS+ software
• 8101 via QPS QINSY
• GeoSwath via QINSY
• Data compared in final grid
/ 33 /
30-Nov-09
Detailed comparisons of 300m profiles
GeoSwath1 vs GeoSwath2
Beamformer1 vs Beamformer2
GeoSwath1 vs Beamformer1
GeoSwath2 vs Beamformer2
Conclusion: GeoSwath and Beamformer results are as repeatable
as each other via either processing route (within ~3cm).
/ 34 /
30-Nov-09
Interferometer vs Beamformer Comparison on the
River Meuse (1m bins)
/ 35 /
30-Nov-09
Data suitable for
engineering surveys of
rivers, canals and ports
/ 36 /
30-Nov-09
Bathymetry and Sediment Classification Maps:
Example of monitoring slow changes in sediment dump area
Aivo Lepland, Reidulv Bøe, Aave Lepland, Oddbjørn Totland, "Monitoring the volume and lateral spread of disposed
sediments by acoustic methods, Oslo Harbor, Norway", Journal of Environmental Management 90 (2009) 3589–3598
/ 37 /
30-Nov-09
Another approach to height control:
• GPS height using postprocessed navigation solution
Combine with inertial data to obtain full 3D GPS solution remove effects of:
• Squat
• Vessel loading
• Tide errors
• Long period swell
• Errors in the concept of ‘vessel centre of
rotation’
/ 38 /
30-Nov-09
POS-MV SBET processing vs tide and heave
2km line off NW Australia; ±10cm swell artefacts with ~12s period
/ 39 /
30-Nov-09
Precise positioning allows multi-senor surveys of structures.
Breakwater with bathymetry and LIDAR data combined
Images from U.S. Army Corp of Engineers, Field Data Collection and Analysis Branch, Coastal Hydraulics Lab.
/ 40 /
30-Nov-09
GeoSwath Plus for ROVs and AUVs
/ 41 /
30-Nov-09
Why GeoSwath works well on AUVs and ROVs:
• Intrinsic advantages of interferometric
technology
• Wide coverage even at low fly heights
• Swath width insensitive to vehicle motion
• Simultaneous bathymetry and Side Scan
• Dimensions
• Small, light and rugged transducers
• Compact low power electronics
• Communications
• PC based - Windows XP
• Ethernet and serial interfaces
• Proprietary acquisition and processing
software package
/ 42 /
30-Nov-09
500KHz Transducers and Electronics
/ 43 /
30-Nov-09
GeoSwath ROV
Ethernet Interface
Timing, start, stop
Timing etc
Sonar Receivers
and controller
Sonar
Transmitters
Transducer
/ 44 /
30-Nov-09
Compact
PC
Sensor inputs
Attitude etc
Optionally also
to dry-end PC
Transducer
GeoSwath Plus on Minerva ROV
/ 45 /
30-Nov-09
GeoSwath Plus on ROV
/ 46 /
30-Nov-09
Sidescan and bathymetry
/ 47 /
30-Nov-09
47
ROV Survey Data Bathymetry: Subsea ridge
/ 48 /
30-Nov-09
GeoSwath AUV
Generic AUV application using
Standard GeoSwath Electronics Modules
Sonar Receivers
and controller
Sonar
Transmitters
Memory
Compact
PC
Ethernet Interface
Timing, start, stop
Timing etc
Sensor inputs
Attitude etc
Transducer
Transducer
Local controller
or self contained
/ 49 /
30-Nov-09
AUV module electronics and transducers
40cm
/ 50 /
30-Nov-09
GeoSwath on the Hydroid Remus 100 AUV
/ 51 /
30-Nov-09
AUV swath width capability: >100m at 5m fly height
/ 52 /
30-Nov-09
GeoSwath on the Gavia AUV
2.6m
Propulsion
/ 53 /
30-Nov-09
Control & Comms
INS
DVL
GeoSwath
Batt.
Nose
Resolution of objects using 500kHz GeoSwath on small
AUV at 5m fly height.
/ 54 /
30-Nov-09
Pre-lay pipe trench survey using AUV-mounted GeoSwath
1km
/ 55 /
30-Nov-09
Harbour post-dredge survey using AUV-mounted GeoSwath
100m
/ 56 /
30-Nov-09
Portable AUVs for difficult deployments: under-ice mapping
Location of APLIS ice camp: 73° N, 146° W in Beaufort Sea
/ 57 /
30-Nov-09
GeoSwath Plus on Gavia AUV
Under the Artic Ice
/ 58 /
30-Nov-09
Mission data
/ 59 /
30-Nov-09
Maps of the underside of the Arctic ice
(from M. Doble and P. Wadhams, University of Cambridge, UK)
•
•
/ 60 /
Doble M. J. and Wadhams P. (2009) “First Through- Ice Use Of A Small Auv For Mapping The Arctic Sea Ice Underside.” GeoPhysics
Research Letters
Doble M. J and Wadhams P. (2009) “Digital terrain mapping of the underside of sea ice from a small AUV” Journal of Atmospheric and
Oceanic Technology
30-Nov-09
GeoSwath Plus on Gavia AUV, Bonaire 2008
/ 61 /
30-Nov-09
Small AUV operations
Operations Centre
Vessel transit to site
/ 62 /
30-Nov-09
Survey area
The edge of the coral reef
/ 63 /
30-Nov-09
GeoSwath 500kHz SS from 2 lines at 15m fly height
/ 64 /
30-Nov-09
The AUV track lines down to 210m vehicle depth
/ 65 /
30-Nov-09
Wide swath width from a small AUV ….
/ 66 /
30-Nov-09
… with simultaneous co-registered side scan
/ 67 /
30-Nov-09
Summary:
• Interferometric technology has been shown to be suitable for
high accuracy surveys, given proper survey planning, ancillary
equipment and data processing.
• This technology is particularly suitable for small boat shallow
water applications and AUV/ROV deployment
/ 68 /
30-Nov-09
Kongsberg Maritime
/ 69 /
30-Nov-09