Shallow Water Bottom Characterization from Single-beam Echosounders

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Bill Boyd Scripps Institution of Oceanography Collaborator
Thomas Lippmann UNH - Center for Coastal and Ocean Mapping Principal Investigator
Andy McLeod UNH - Center for Coastal and Ocean Mapping Co-Principal Investigator
James Irish UNH - Center for Coastal and Ocean Mapping Co-Principal Investigator
Jonathan Hunt UNH - Center for Coastal and Ocean Mapping Technician
Presently, remote acoustic systems for seafloor characterization and mapping (e.g., multi-beam echosounders or swath bathymeters) do not work well in shallow water environments because of operational, dynamical or cost limitations. As a consequence, there is a severe lack of field data to assess seafloor properties essential to establishing spatial maps of fish habitat, marine protected areas, or sedimentation rates. This research is focused on developing new acoustic capability to assess seafloor characterization specifically applicable to shallow marine environments. A newly fabricated single-beam echosounder with bottom characterization will be developed and utilized in local field tests this summer as part of planned surveys in the Great Bay using the existing Coastal Bathymetry Survey System (CBASS), a personal watercraft with survey capability in shallow water. The data will be interrogated with existing software, TracEd, developed at the Center for Coastal and Ocean Mapping (CCOM) specifically for vertically oriented single-beam acoustic echosounders. Successful development of the system will position the research team, as well as UNH in general, to be leaders in the field of shallow water seafloor characterization and mapping.
We propose to fabricate a new field measurement system with capability to characterize and map shallow water seafloor features. The system is based on a unique vertically-oriented single-beam echosounder (with digitally rectified signal) mounted on a highly maneuverable, shallow-draft personal watercraft. The system will allow classification and mapping of sediment type, bathymetry, seafloor morphology, fish habitat, and plant distribution and canopy height in shallow marine and fresh water environments. Presently, bottom characterization is limited to larger vessels with delicate, highly sophisticated, and (very) expensive multi-beam echo-sounding systems (MBES) or interferometric swath bathymeters that are limited to navigable waterways well away from many sensitive ecological environments (such as estuaries, rocky coastal waters, riverbeds and other shallow water regions). These shallow regions are often wrought with hazards, high dynamic vessel movements, and virtually no prior spatial coverage.
Funds will be used to fabricate a new sonar system to interrogate and characterize bottom features in shallow environments. The fabricated system includes microprocessor hardware to integrate into a custom single-beam echosounder (Bill Boyd, Sonora, Calif.) to produce a unique, shallow water bottom finding and characterization system. Digitized output from the system will be used with the TracEd software developed at CCOM specifically for remote seafloor characterization with vertical single-beam echosounders (Dijkstra and Mayer, 2000). The new system will enable seafloor characterization in regions not presently possible and in ways traditional systems (e.g., multi-beam) do not operate.
This research will enable the PIs (as well as other CCOM and UNH researchers) to pursue research funding related to essential fish and aquatic plant habitat, marine protected areas, and maintenance of navigational waterways and sedimentation. The system will be tested this summer as part of a larger effort to map the Great Bay region. Present efforts are limited to coarse bathymetric surveys without any abilities to characterize the seafloor properties.
Seafloor classification and environmental assessment in shallow marine waters is a critical need for establishing marine protected areas (MPAs), essential fish habitat (EFH), coastal management policies, and maintaining navigational waterways. Most commonly these assessments are done using software packages adapted for use with remote acoustic measurements obtained from various water-borne vessels. Unfortunately, capability to make appropriate measurements in shallow water in a timely manner does not presently exist, and thus the order one characterization of seafloor environmental properties in shallow marine environments is entirely lacking. As a consequence, development of shallow marine management practices has virtually no quantifiable data from which to base policies, and guidance from observations is thus limited to anecdotal evidence or historical maps whose relevance to the spatial variability today is not known.
This proposal is aimed at developing a new, low-cost, rapid sampling seafloor characterization system that can be used in a variety of shallow water environments, including marine estuaries, bays, river mouths and nearshore coastal zones (that may include rocky hazards and breaking waves). The system builds upon 10 years of experience making shallow bathymetric measurements onboard the Coastal Bathymetric Survey System (CBASS), and transitioning this system into a unique, shallow water system with full seafloor characterization capabilities. The new system will position UNH to be a leader in field capabilities for very shallow water mapping and seafloor characterization.
Budget and Budget Justification
Funds are requested to support the fabrication of a vertically-oriented, single-beam echosounder with bottom characterization capability for shallow water seafloor environmental assessment. The system components include a dual-transducer (1 transmit, 1 receive) 192 khz single-beam echosounder with auto-gain feature for bottom tracking (produced by Bill Boyd, a Scripps Institution of Oceanography Engineer with 25 years of field experience with shallow water sonar systems). The system will be modified at CCOM to allow for full-pulse post-processing interrogation, assessment, and seafloor classification using the TracEd software (designed in CCOM; Dijkstra and Mayer, 2000, MTS/IEEE, 2, 1211-1217). The modifications will be done by CCOM personnel (Lippmann, McLeod, and Irish) using microprocessor components reutilized from past field efforts. The fabricated system will be incorporated into the existing Coastal Bathymetry Survey System (CBASS), a shallow water mapping system consisting of Yamaha GP1200 Waverunner, differential GPS, sonic altimeter, and onboard navigation (Lippmann and Smith, 2009, Proc. US. Hydro 09, in press). (Note that the present sonic altimeter is 10 years old and cannot be modified to include full pulse digitizing and hence cannot be modified for bottom characterization).