Advances in Data Processing Techniques and Base Surface

Advances in Data Processing Techniques and Base Surface Generation: Interferometric Sonar and Multibeam Echo Sounders 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 Menlo Park / Santa Cruz, California (Western Coastal & Marine Geology) Woods Hole, Massachusetts (Woods Hole Science Center) 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

WHSC Sea Floor Mapping Scientific & Technological Advances South Carolina (1999 -2003) Gulf of Farallones (1989) GLORIA (EEZ) High-Resolution Data Acquisition 1980 CMGP Research Deep to Shallow Digital Data Acquisition Multibeam USGS/CHS/ UNB/NOAA (1994) Real-time Processing (1989) Systematic Mapping of inner continental shelf R/V Rafael, Vans & Swath Bathymetry Continued focus geologic framework & nearshore surface processes Significant system developments (expand shallow water capability) Development & Growth of WHSC Sea Floor Mapping 1990 2008

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 θ e ng Ra Angle SEA, Swath. Plus bathymetric sonar (117 k. Hz & 234 k. Hz)

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

WHSC Sea Floor Mapping Swath Bathymetric System SEA, Ltd’s Swath. Plus Bathy Sonar Coverage Profile Targets

WHSC Sea Floor Mapping Swath Bathymetric System and the Common Data Set OBJECTIVES: Ø Map the common data set area using a 6 x water depth trackline spacing (twice the IHO order 1 spec). Ø 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. Ø Attempt to streamline the data processing flow and DTM surface generation using new algorithms such as the Combined Uncertainty and Bathymetry Estimator (CUBE). Ø Attempt to quantify Total Propagated Error (TPE) of the soundings using a preliminary sonar model for Swath. Plus. Ø Compare the TPE statistics with those of the MBES systems. Ø Visually and statistically compare the Swath. Plus surface to those created using the MBES data.

WHSC Sea Floor Mapping Data Acquisition, October 2007 Ø Survey Vessel R/V Rafael Ø Sea Swath. Plus 234 k. Hz transducers and data acquisition software Ø Coda Octopus F 180 R MRU Ø Ashtech RTK navigation Ø Applied Microsystems SVP (both hand deployed and mounted at the head for SSV) Ø Collected 6144 samples / swath

WHSC Sea Floor Mapping Common Data Set Processing Flow Swath. Plus SXP data - 234 k. Hz Simrad EM 3002 D “raw. all” data - 307 k. Hz Reson 7125 XTF data - 400 k. Hz CARIS ü ü 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 ü Statistical and Visual comparisons

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

WHSC Sea Floor Mapping Initial Grids using the TPE and CUBE approach Simrad EM 3002 D And there was NO swath editing performed!! Reson 7125

WHSC Sea Floor Mapping Initial Grids using the TPE and CUBE approach Swath. Plus 234 k. Hz

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

WHSC Sea Floor Mapping Further CUBE processing

WHSC Sea Floor Mapping Comparing TPE values Depth = 13. 6 m IHO Order 1: 5 m horizontal 0. 53 m vertical at 13. 6 meters

WHSC Sea Floor Mapping Comparing Swath. Plus soundings to the Simrad CUBE surface

WHSC Sea Floor Mapping Comparing Swath. Plus soundings to the Reson CUBE surface

WHSC Sea Floor Mapping Surface differencing: Swath. Plus compared to Reson and Simrad

WHSC Sea Floor Mapping Drilling down….

WHSC Sea Floor Mapping Visual comparison: Profile over a small feature Simrad EM 3002 D CUBE surface

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

WHSC Sea Floor Mapping Visual comparison: Profile over a small feature Swath. Plus 234 k. Hz CUBE surface

WHSC Sea Floor Mapping So what does all this tell us? Ø 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. Ø 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? Ø 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…

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

WHSC 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