Data Acquisition
This section is under development. If you have expertise in multibeam data acquisition, please reach out to the admins at omcadmin@ccom.unh.edu to become a contributor today!
Resources for planning and conducting a multibeam survey.
Add / modify topics as needed. This page is not going to be a one-size-fits-all SOP, as platforms, systems, and survey requirements vary wildly. These resources may be split into different pages as they grow.
See Transit Mapping for optimizing mapping opportunities on transits.
Where do you want to survey?
Links to data repositories and planning resources
- GMRT resources - only processed data is published to this grid; GMRT includes much more than bathymetry
- GMRT Map Tool - select subsets of GMRT data for download in a variety of formats
- GEBCO - download grids with or without satellite altimetry mask
- Seabed2030 - a global effort to map the seafloor in high resolution
- IHO Data Centre for Digital Bathymetry - find out where industry and other non-public data exists
- NCEI Bathymetry Viewer - most of the data in this mosaic is not processed - user beware
- EMODnet Bathymetry - European data portal, including access requests for non-public data
- AusSeabed Data Portal - Australian marine data resources, including national compilations and regional surveys
- SCUFN - find a seafloor feature name, or submit a name for a new seafloor feature!
- GeoMapApp - visualize a variety of geoscience datasets on top of the GMRT base map
- NOAA Tides & Currents - predicted and verified tides for planning and processing
- HydrOffice SmartMap - sound speed forecasting and line planning web service
- UNH Map Portal - web map apps for CCOM-related data products; also available to integrate with ESRI Arc Pro/Online
- AusSeabed Survey Coordination - identify areas of interest and coordinate survey plans within Australian waters
- Multibeam Survey Plan for Scientists - a template for helping science parties communicate their survey priorities (copy and modify for each ship)
Helpful tools for converting and translating waypoints
- HydrOffice SmartMap Survey Planner (Beta) - draw lines, fill areas, export, and import (Hypack .lnw and GeoJSON)
- Coordinate Systems - find the EPSG code for a given coordinate system (useful for QPS, ESRI, etc.)
- Coordinate Conversion - handy for converting between geographic and UTM for single points
- Mapshaper - quick conversions of line planning file formats
-
ECDIS converter - convert waypoints into ECDIS and other formats
- Need a different format? Submit a request (and example) to mac-help@unols.org and it could be added in a future version!
- NOAA Tides & Currents - predicted, observed, and verified tides in US waters
How much coverage do I need?
Coverage is typically specified in the Cruise/Mission Plan. In deeper water, during exploration operations, 30-50% is common. In the inshore environment, where tides, currents and sound speed are widely variable, more overlap is generally encouraged. For the purpose of making nautical charts, 200% coverage (100% overlap) is generally required.
If available, it is helpful to use a table or swath curve from the multibeam manufacturer to estimate how much coverage you should expect in a given depth. If one is not available (some companies hesitate to publish these as there are so many factors that contribute to swath width), then you may build one with your own data for future reference. This will allow you to see the expected swath for a given depth, pick an overlap percentage and then calculate the recommended line spacing.
Once you have compiled data for your system on your platform, you can create a handy visual diagram for reference by all mappers.
For Kongsberg EM systems, this information can be found in the Product Description for the EM system. The product description can be found in the EM system installation files on your workstation at C:\Program Files\Kongsberg Maritime\EMSystem\Doc\EM.
If you install Seafloor Information System (SIS) with an EM system, you can also access this document through the documents main page; this is found in the installation documents or through the SIS Help menu at C:/Program%20Files/Kongsberg%20Maritime/EMSystem/Doc/EM/EM_documents.html.
Each table notes which size array is used, warm or cold ocean, and the three main types of substrates for comparison. These figures are a GUIDE based on theoretical performance, and it is recommended to collect data with your system and observe the real-world performance of your system as results may vary between platform, installation, environment, and system maintenance.
[Future: insert Charlie's Okeanos Explorer coverage graphic]
See the Sound Speed page for details on this critical consideration.
It is imperative to collect sound speed at the transducers and profiles through the water column while conducting a survey. There are several different tools, many of which are described on the Sound Speed page.
- While offshore, working in the deep ocean, 4 profiles per day are common. XBTs and UCTDs are helpful because you can conduct a profile while underway, not having to stop mapping.
- While inshore, you may need significantly more--which is why moving vessel profilers are common on hydrographic survey ships/launches. They do not require the vessel to stop.
- While working offshore, but in a dynamic environment (e.g Columbia River, Chesapeake Bay, Gulf Stream), you may need to conduct profiles as much as once per hour or two.
It is important to monitor the data as it is coming in--the Kongsberg SIS software allows the user to see when there is "too great" a difference between the probe and the recent profile, which is very helpful to signal that a new cast is needed. It is also important to examine the data as it is being collected (where practicable!) to ensure that there are no significant velocity artifacts. By collecting lots of profiles, you then have the option to select different profiles (e.g. nearest in time or distance) in post-processing, according to whichever profile reduces artifacts the most.
For vessels with multiple navigation sources, it is imperative that the active position, attitude, attitude velocity, and timing sources are consistent during acquisition. See this example of selecting active navigation sources as an overview of the sources that must be valid and selected consistently.
Secondary or 'backup' navigation sources should be logged to the raw files, if possible. These data may be applied in post-processing if issues arise with the primary source that were not detected or resolved quickly during acquisition, potentially 'saving' the survey dataset. Note there are some components of the active source that are applied in real time and cannot be fully applied in post-processing, even if logged (e.g., attitude velocity for Doppler correction).
For this reason, it is important that all configurations and offsets for secondary or 'backup' navigation sources be fully reviewed and calibrated (patch tested) to the same standard as the primary navigation source. Given the challenge of finding suitable time and locations for emergency patch tests, it is often most efficient and least risky to patch test all navigation sources using the same site at the start of the field season or before major survey missions. See the MBES Test Site Database and Calibration sections for more information, and reach out to the OMC Admins with any feedback or questions on these topics.
Recommended settings for typical surveys will depend on the systems that are being run. It is generally recommended to start with a 'baseline' or 'automatic' setup for the particular system, then dial it in according to the depth, weather conditions, substrate, etc.
Penetration Filter Strength: Kongsberg recommends that you keep the penetration filter OFF unless you actually observe penetration issues. The penetration filter forces the bottom detector to look for a weaker signal shallower than the strongest and best bottom candidate. Penetration issues will be visible in the Water Column window -- the bottom detections around nadir will start tracking on subbottom layers. In areas without penetration, this filter may lead to detections above the bottom. This may show up as 'lifted' seafloor along nadir going up and down slopes; in this case, the penetration filter is leading to tracking on strong sidelobes from up-slope.
Example of penetration visible in the Water Column window. The bottom detections are 'latching on' to sub-surface layers.
Example of tracking on a weaker signal due to the penetration filter being on over a sloped area.
Example of a 'lifted' section of seafloor due to mistracking.
Number ONE is to WATCH the acquisition of data. Do not try to do too many things at once! It is highly recommended to have two separate people (when feasible) for acquisition and processing. If you get distracted, you can easily leave holidays in the data, miss logging cues, or completing regular system checks. The number one most important thing is to collect high quality data--processing always comes second.
It is important to either log your settings periodically, or provide a review of the settings during a watch handover. If you change the min/max depth, for example, and the next person doesn't notice, a holiday can be left in the survey which will take additional time to fill in.
Many vessels have developed watch-standing checklists. This is very helpful to lay out the specific things that need to be checked periodically. This not only helps you remember what to do, but is helpful in training new surveyors.
It is also helpful to log changes to the acquisition settings, observations in the acquisition screen, SVP casts, etc. Anything that a processor might need to know if they see anything questionable in the data.
Recommendations for minimum required processing effort underway to ensure data quality
See the Data Processing page for further details on processing practices.
In general, you want to do enough processing underway to verify that what you are seeing in acquisition is reflected correctly in preliminary bathymetry products.
Some basic data quality examples to check include:
- No 'holidays' (gaps in coverage)
- No gaps between lines (improper line spacing)
- Sound velocity alignment
- No major navigation/motion issues
- Adequate data density for desired resolution
- No major or concerning outliers
- These may be related to acquisition settings (e.g., filters) that can be modified or environmental factors (e.g., sea state, bubbles) that might be more difficult to avoid
Some vessels will perform other operations and require products to select locations for deploying other equipment (e.g., dredging or coring). See the Data Processing page for suggestions.
Data is only as useful as its description for downstream users. It is recommended to provide an Acquisition or Cruise Report with each survey that details information about the mission, what was completed, what was discovered or achieved.