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

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)

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)

Scientific & Technological WHSC Sea Floor Mapping Scientific & Technological Advances South Carolina (1999-2003) 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 1980 1990 2000 2008

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: < 5 - 200 m water depth 5 15 meters R/V Rafael with bathymetric sonar deployed SEA, SwathPlus bathymetric sonar (117 kHz & 234 kHz) Angle Range θ

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

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?

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.

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

Common Data Set Processing Flow WHSC Sea Floor Mapping Common Data Set Processing Flow SwathPlus SXP data - 234 kHz Simrad EM3002D “raw.all” data - 307 kHz Reson 7125 XTF data - 400 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

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

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

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

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

Further CUBE processing WHSC Sea Floor Mapping Further CUBE processing

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

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

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

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

WHSC Sea Floor Mapping Drilling down….

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

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

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

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…

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

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