1. Woods Hole Science Center
Advances in Data Processing Techniques and Base Surface Generation: Interferometric Sonar and Multibeam Echo Sounders
Title – Data processing techniques for interferometric sonars and multibeam echosounders.
William Danforth, Tom O’Brien, Emile Bergeron, Chuck Worley, Barry Irwin
U.S. Geological Survey
Woods Hole Science Center

2. USGS Coastal & Marine Geology Program National Science Field Centers
Woods Hole, Massachusetts
(Woods Hole Science Center)
Menlo Park / Santa Cruz, California
(Western Coastal & Marine Geology)
Describe national program; 3 offices throughout the US; small part of overall USGS
St. Petersburg, Florida
(Center for Coastal & Watershed Studies)

3. USGS Coastal & Marine Geology Program
Mapping Activities: Lacustrine – Estuarine – Nearshore - Offshore
* Habitat Geoscience
* Coastal Erosion and Geologic Framework
* Climate Change
* Nearshore Sediment Dynamics
* Ecosystems and Coastal Ground Water
* Predicting Effluent Pathways
* Coastal and Marine Sediment Contaminants
* Gas Hydrates
* Marine Aggregates (sand & gravel)
* Earthquake and Tsunami Hazards
Range of research within CMGP – onshore to offshore, show map with areas of study
Talk about the predictability in this section…can we predict the vulnerability of coast to erosion? Predict response to sea-level rise? Effects on sea floor of continued use (mining, aggregates, effects to habitat)

4. Scientific & Technological
WHSC Sea Floor Mapping
Scientific & Technological
Advances
South Carolina ( )
Continued focus geologic framework & nearshore surface processes
Systematic Mapping of inner continental shelf
Multibeam USGS/CHS/ UNB/NOAA (1994)
Gulf of Farallones (1989)
CMGP Research Deep to Shallow
Significant system developments (expand shallow water capability)
Now give a brief history of the build up of sea floor mapping technology the WHSC and how it has enabled expansion of our mapping capabilities, especially in shallow water / coastal environments. Brought in the SEA system in 1999 to augment the geologic interpretation of the geophysical data, NOT AS A CHARTING TOOL.
R/V Rafael, Vans & Swath Bathymetry
GLORIA (EEZ)
Real-time Processing (1989)
Digital Data Acquisition
High-Resolution Data Acquisition
Development & Growth of WHSC Sea Floor Mapping

5. Swath Bathymetric System
WHSC Sea Floor Mapping
Swath Bathymetric System
Incorporation of high-resolution swath bathymetry augments geologic framework studies by defining sea floor morphology
System operation: < m water depth 5 15
meters
R/V Rafael with bathymetric sonar deployed
SEA, SwathPlus bathymetric sonar (117 kHz & 234 kHz)
Angle
Range θ

6. Swath Bathymetric System
WHSC Sea Floor Mapping
Swath Bathymetric System
Shallow water surveying (< 30 m)
Interferometric Sonar – wide swath system
Multibeam Echo Sounder
Interferometric Sonar
Swath Width

7. Swath Bathymetric System
WHSC Sea Floor Mapping
Swath Bathymetric System
SEA, Ltd’s
SwathPlus
Bathy
Sonar
Coverage
Profile
Targets
Co-located bathymetry and backscatter. Huge data volume, generally collect 3072 samples / channel. How to clean this?

8. Swath Bathymetric System and the Common Data Set
WHSC Sea Floor Mapping
Swath Bathymetric System and the Common Data Set
OBJECTIVES:
Map the common data set area using a 6x water depth trackline spacing (twice the IHO order 1 spec).
Compare/contrast the resulting swath coverage and final grids with Multibeam Echo Sounder (MBES) coverage after using a single processing package on the raw data- CARIS.
Attempt to streamline the data processing flow and DTM surface generation using new algorithms such as the Combined Uncertainty and Bathymetry Estimator (CUBE).
Attempt to quantify Total Propagated Error (TPE) of the soundings using a preliminary sonar model for SwathPlus.
Compare the TPE statistics with those of the MBES systems.
Visually and statistically compare the SwathPlus surface to those created using the MBES data.

9. Data Acquisition, October 2007
WHSC Sea Floor Mapping
Data Acquisition, October 2007
Survey Vessel R/V Rafael
Sea SwathPlus 234 kHz transducers and data acquisition software
Coda Octopus F180R MRU
Ashtech RTK navigation
Applied Microsystems SVP (both hand deployed and mounted at the head for SSV)
Collected 6144 samples / swath

10. Common Data Set Processing Flow
WHSC Sea Floor Mapping
Common Data Set Processing Flow
SwathPlus SXP data kHz
Simrad EM3002D “raw.all” data kHz
Reson 7125 XTF data kHz
CARIS
Create Vessel file for each data type
Apply motion and nav if necessary
Generate TPE sounding statistics for each line
Incorporate lines into a CUBE surface using default settings
Fledermaus
Statistical and Visual comparisons

11. TPE Computation for Hz and Dp values
WHSC Sea Floor Mapping
TPE Computation for Hz and Dp values
Takes into account:
RP placement (usually the MRU)
Offsets to sensors and transducers
Mounting offsets
Patch test results
Accuracy of MRU and system timing
Specifications from individual sonar models

12. Initial Grids using the TPE and CUBE approach
WHSC Sea Floor Mapping
Initial Grids using the TPE and CUBE approach
Simrad EM3002D
And there was NO swath editing performed!!
Reson 7125

13. Initial Grids using the TPE and CUBE approach
WHSC Sea Floor Mapping
Initial Grids using the TPE and CUBE approach
SwathPlus 234 kHz

14. Processing benefits using the TPE and CUBE approach
WHSC Sea Floor Mapping
Processing benefits using the TPE and CUBE approach
Semi-automates the DTM generation using very dense data sets (Interferometric and MBES)
Preserves significant bathymetric detail on a first pass
Auxiliary outputs can be used for further editing decisions based on error analysis and hypothesis testing
Helps to significantly reduce point by point editing traditionally used to eliminate spurious soundings

15. Further CUBE processing
WHSC Sea Floor Mapping
Further CUBE processing

16. WHSC Sea Floor Mapping Comparing TPE values IHO Order 1:
5 m horizontal
0.53 m vertical at 13.6 meters
Depth = 13.6 m

17. Comparing SwathPlus soundings to the Simrad CUBE surface
WHSC Sea Floor Mapping
Comparing SwathPlus soundings to the Simrad CUBE surface

18. Comparing SwathPlus soundings to the Reson CUBE surface
WHSC Sea Floor Mapping
Comparing SwathPlus soundings to the Reson CUBE surface

19. Surface differencing: SwathPlus compared to Reson and Simrad
WHSC Sea Floor Mapping
Surface differencing: SwathPlus compared to Reson and Simrad

20. WHSC Sea Floor Mapping
Drilling down….

21. Visual comparison: Profile over a small feature
WHSC Sea Floor Mapping
Visual comparison: Profile over a small feature
Simrad EM3002D CUBE surface

22. Visual comparison: Profile over a small feature
WHSC Sea Floor Mapping
Visual comparison: Profile over a small feature
Reson 7125 CUBE surface

23. Visual comparison: Profile over a small feature
WHSC Sea Floor Mapping
Visual comparison: Profile over a small feature
SwathPlus 234 kHz CUBE surface

24. WHSC Sea Floor Mapping So what does all this tell us?
Interferometric sonar data tend to have a higher standard deviation across the swath as compared to MBES systems, however the resulting bathymetric surface retains very closely the level of detail see in surfaces created using MBES data.
Semi-automated processing and generation of bathymetric surfaces from interferometric sonar data is viable and preserves the true nature of the seafloor, thus significantly reducing the post processing effort and time sink required to generate a reliable bathymetric surface from these data.
Where do we go from here?
The advantages of interferometric methods in waters shallower than 20 meters are numerous, but the question of vertical resolution and target detection, especially for hydrographic surveys, still needs further study .. And maybe…

25. Interferometry on an ASV ???
WHSC Sea Floor Mapping
Interferometry on an ASV ???
ASV: Autonomous Surface Vessel
Shallow water
Sidescan Sonar
Edgetech Chirp (4 – 24 kHz)
Single Beam EchoSounder
ADCP
Additional Sensors or Reconfigure
Modular
Numerous Sensors
Easily Modified
Autonomous or manual
Integrated Systems

27. Sea Floor Mapping Systems
WHSC Sea Floor Mapping
Sea Floor Mapping Systems
Surficial and Sub-bottom Systems
Sidescan-sonar
Seismic Reflection
Swath Bathymetry
Sampling
Video/photography
Core and Grab Samplers
Navigation
WAAS , DGPS, RTK