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Transit Mapping
This section is under development. If you have expertise in transit mapping, please reach out to the admins at omcadmin@ccom.unh.edu to become a contributor today!
Vessels in transit routinely cross unmapped (or poorly mapped) regions of the planet. Transits offer important opportunities to map the gaps and verify sonar performance prior to science missions.
Whenever possible, it is helpful to run the mapping systems and collect data for these purposes. Details of the processing and archiving can be addressed after acquisition, if they have not been considered yet, but none of this is possible without the raw data!
This section provides resources for collecting high-quality transit mapping data with limited personnel or experience on board.
There are several reasons to collect transit mapping data:
- Contribute to the global grids, especially in areas without modern multibeam data
- Verify sonar performance through opportunistic testing with minimal impact on science mission scheduling
- Build experience with a vessel's specific mapping systems (and their effects on each other) in a low-risk environment
- Opportunistically document changes in seafloor that may have occured
Typical constraints during transits include:
- limited availability (or over-scheduling) of marine technicians and experienced multibeam operators
- limited route planning control for scientific objectives between ports
Evaluating global bathymetry data gaps and establishing mapping priorities relies on geospatial information and descriptive parameters that can inform decision-making processes. Geospatial representations that delineate where data have been collected offer first-order information, but additional metadata is necessary to meet use-case and mission priorities. Data availability, data quality, data resolution, and data density are important considerations that may have variable relevance based on use-case. The IHO Data Center for Digital Bathymetry (IHO-DCDB), operated by NOAA on behalf of the IHO, offers an interactive map-based data viewer that combines data coverage information from multiple international data sources to help suport the discovery and access of bathymetry data. These coverage layers are continually expanding as new data are acquired, and provide the most comprehensive information about global bathymetry data coverage. Information about the extent of data that have been integrated into various bathymetry compilations, such as GEBCO, GMRT, EMODnet, and AusSeabed is available directly from each synthesis and represents data that have been reviewed, vetted and integrated.
The GEBCO Technical Sub-Committee for Undersea Mapping (TSCOM) has been working to further unite data coverage layers to help support transit and opportunistic mapping activities. A working group report, available on the TSCOM webpage, describes some of the complexities and community needs with respect to these data coverage layers. Work is ongoing to simplify access to and use of this information.
GeoMapApp is a freely available geospatial data discovery and visualization application that offers access to a variety of data layers. The default basemap in GeoMapApp is the Global Multi-Resolution Topography (GMRT). In order to help support gap filling, GeoMapApp makes the GMRT mask layer available and also offers 2 additional coverage layers that show the geospatial extent of known bathymetry data. These layers are sourced from GEBCO, based on its most recent release, and the holdings of the IHO Data Center for Digital Bathymetry which includes the US multibeam archive. These layers can be found under the DataLayers menu under Bathymetry and Land Topography. With these layers turned on, one can rapidly identify unmapped portions of the ocean.
Route planning functionality is offered as a tool entitled "Waypoints and Survey Planner" which can be found under the Portals menu. This feature allows the user to click within the map interface to define a route and/or create parallel survey lines at a set distance apart. The resulting waypoints can subsequently be exported for use in a variety of other software packages. More information describing the waypoint and survey planner tool can be found in the GeoMapApp User Guide
Bathy Globe Gap Filler is a software tool designed to support planning for transit and area mapping. Gap filler provides the latest versions of GEBCO bathymetry as context for planning. The tool offers automatic overlap adjustments, polygon filling, plan statistics, and automatic transit planning. More details can be found in the Gap Filler Manual
Considerations for mapping data quality vs. vessel speed based on RX noise testing, sea state, and scheduling
Optimizing sonar settings when round-the-clock watchstanding is not possible
Avoiding the most common pitfalls of transit mapping
Setting expectations for acquiring sound speed profiles when needed and relying on atlas data when necessary. Sound speed corrections can be performed in post-processing and concerns about inadequate monitoring of sound speed during acquisition should not deter opportunistic mapping opportunities during transits.
Considering the relatively low cost and high impact of sound speed profiles on data quality
Frequent and simple checks to catch data quality issues as soon as possible
Let the computer do the work!
Quick and easy processing to show daily progress and check sonar performance
Minimal data quality standards for contributing to the global grids, and resources to achieve or exceed these. GMRT Tools are especially well suited for processing transit data because it enables the comparison of data with underlying QA/QC'd data.
Any transit data acquired aboard US Academic Research Vessels will be delivered to the NOAA/NCEI archive through the R2R Program. Once data are made publicly available, they will be processed by one (or many) groups interested in integrating the data. Once data are processed, it is recommended that processed data are shared in GSF (Generic Sonar Format) files which will enable additional processing and/or corrections if necessary.
The following resources provide some background information how and why transit data is useful:
Opportunistic Multibeam Surveying, Hydro International
Supported under NSF grants 1933720 and 1933776