SAS on tow vehicle

An overview of a tow vehicle mounted synthetic aperture sonar system : 

An overview of a tow vehicle mounted synthetic aperture sonar system Kathryn H. Ford, Ph.D. Massachusetts Division of Marine Fisheries

MarineFisheries Habitat Objectives : 

MarineFisheries Habitat Objectives Map extent of fish habitats in Mass waters Examining existing datasets Collecting and analyzing additional acoustic, video, and grab data Examine impacts of fishing and coastal alterations Scale relevant

Tools : 

Tools EM3002 multibeam sonar (NOAA NMFS) Focus-2 tow vehicle Video, lights EM-3002 Video drop-frame (MarineFisheries lobster investigations) Collaborations: USGS SeaBoss AST (DTI) SAS EPA SPI (Sediment Profile Imaging Camera)

Focus-2 Remotely Operated Towed Underwater Vehicle : 

Focus-2 Remotely Operated Towed Underwater Vehicle Made by MacArtney A/S in Denmark ROTV and TUV are common acronyms Propulsion from vessel Flight surfaces control pitch and roll; yaw flaps allow horizontal adjustments Manual or automatic control of depth/altitude/undulation/horizontal

Focus-2 System Description : 

Focus-2 System Description Top-side control system -flight controls -displays/records Focus data -serial/ethernet demux to payload computers 2-fiber cable, 750 m -1:vessel speed layback; 5-250m depth capable -speed 3-10 kt Focus with payload Payload top-side -displays/records payload data

Synthetic Aperture Sonar Payload : 

Synthetic Aperture Sonar Payload Why SAS? Opportunity Resolution & Efficiency: SAS overcomes traditional tradeoffs SAS Wide swath Narrow swath (125 kHz, 200 m swath, 10 m water depth, <10 cm resolution)

Synthetic Aperture Sonar : 

Synthetic Aperture Sonar SAS signal processing concept Sonar emits series of pulses; single point imaged multiple times Results from the pulses are combined – fancy algorithms This process creates a synthetic aperture as long as the distance traveled while illuminating that point Hardware Sidescan multi-element array; each element is TX/RX; CHIRP signal SAS-capable arrays often combine multibeam techniques for phase-differencing bathymetric analysis From: SENSOTEK project, Forsvarsnett & Kongsberg

Main Drawbacks : 

Main Drawbacks Speed dependent (3-5 kt is best) It’s complicated & expensive: Navigation is critical It needs a very stable platform to line up the pulses TUVs with measured and controlled pitch and roll AUVs Careful seafloor tracking/positioning Onboard INS/DVL sensors USBL system integrated with vessel for TUVs Sophisticated arrays; intensive processing

Main Goals : 

Main Goals Setting up arrays on Focus-2 Physical constraints Communications constraints Measure the accuracy of the navigational systems USBL-LBL comparison XTE tests Conduct SAS processing Conduct habitat mapping

Focus-2 SAS System Schematic : 

Focus-2 SAS System Schematic Boat GPS Nav PC GeoDas PC Gyro USBL Focus PC SeaDevil INS, DVL Transponder (trigger) Sonar data Response Heading ProSAS Opterons Minescout Focus console Nav, motion Electronics pod Focus vehicle Focus I/O Nav, motion Nav updates, tracking Tracking Cross-track error Waypoints

Navigational Accuracy : 

Navigational Accuracy

SAS Processing : 

SAS Processing Sidescan SAS

Habitat Mapping : 

Habitat Mapping Applications in Buzzards Bay (See abstract!) Compare the biological predictive power of acoustic datasets in shallow soft seafloor, deep soft seafloor, and deep hard seafloor (Eastwood, et al. 2004 Mapping sediment biotopes. ICES CM 2004) Groundtruthing via video and SPI

Acknowledgements : 

Acknowledgements MarineFisheries Focus-2 co-pilot (Steve Voss) Applied Signal Technology (Andy Wilby, Dan Sternlicht, Randy Patton) R/V Quest (Eric & Lori Takakjian and crew)