Data Acquisition

= Seeking Contributors =

This section is under development. If you have expertise in multibeam data acquisition, please reach out to the admins at [mailto:omcadmin@ccom.unh.edu omcadmin@ccom.unh.edu] to become a contributor today!

= Overview =

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.

= Planning =

Where do you want to survey?

Finding existing data
Links to data repositories and planning resources


 * 1) GMRT resources - only processed data is published to this grid; GMRT includes much more than bathymetry
 * 2) GMRT Map Tool - select subsets of GMRT data for download in a variety of formats
 * 3) GEBCO - download grids with or without satellite altimetry mask
 * 4) Seabed2030 - a global effort to map the seafloor in high resolution
 * 5) IHO Data Centre for Digital Bathymetry - find out where industry and other non-public data exists
 * 6) NCEI Bathymetry Viewer - most of the data in this mosaic is not processed - user beware
 * 7) EMODnet Bathymetry - European data portal, including access requests for non-public data
 * 8) AusSeabed Data Portal - Australian marine data resources, including national compilations and regional surveys
 * 9) SCUFN - find a seafloor feature name, or submit a name for a new seafloor feature!

Planning surveys

 * 1) NOAA Tides &amp; Currents -
 * 2) SmartMap - sound speed forecasting and line planning web service
 * 3) UNH Map Portal - web map apps for CCOM-related data products; also available to integrate with ESRI Arc Pro/Online
 * 4) AusSeabed Survey Coordination - identify areas of interest and coordinate survey plans within Australian waters

Creating line plans
Helpful tools for converting and translating waypoints


 * 1) Coordinate Systems - find the EPSG code for a given coordinate system (useful for QPS, ESRI, etc.)
 * 2) Coordinate Conversion - handy for converting between geographic and UTM for single points
 * 3) Mapshaper - quick conversions of line planning file formats
 * 4) ECDIS converter - convert waypoints into ECDIS files for the bridge

Finding ancillary information

 * 1) NOAA Tides &amp; Currents - predicted, observed, and verified tides in US waters

= Coverage =

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 (see [Assessment Tools]). This will allow you to see the expected swath for a given depth, pick an overlap percentage and then calculate the recommended line spacing.

= Acquisition =

Sound speed
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.


 * 1) While offshore, working in the deep ocean, it is common to plan for four profiles per day. XBTs and UCTDs are helpful because you can conduct a profile while underway, not having to stop mapping.
 * 2) While inshore, you may need significantly more profiles to characterize the highly variable sound speed environment.  Moving vessel profilers are common on hydrographic survey ships/launches as they do not require the vessel to stop.
 * 3) 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 while moving across steep gradients, eddies, and areas of turbulent mixing.

It is important to monitor the data as it is coming in. For instance, the Kongsberg SIS software allows the user to see when there is &quot;too great&quot; 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.

Runtime parameters
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.

Filters
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.

Watchstanding
Number ONE priority 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 fail to complete 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.

= Processing =

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 to verify that what you are seeing in acquisition is reflected in processing. Some examples include:


 * 1) No holidays
 * 2) No gaps between lines
 * 3) Sound velocity alignment
 * 4) No major navigation/motion issues
 * 5) Data density is as expected
 * 6) No major or concerning outliers (which may be related to acquisition settings such as filters)

Some vessels will perform other operations and require products to select locations for deploying other equipment. See the Data Processing page for suggestions.

Metadata
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.

Examples

 * 1) EX-21-01 Mapping Data Acquisition and Processing Summary Report
 * 2) Ocean Exploration Cooperative Institute Data Management Plan