Data Acquisition
How to run a survey!
Add / modify topics as needed. This page is not going to be a one-size-fits-all SOP--as different platforms have different systems, survey requirements, etc. the following are meant to be a best-practice guide.
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
- 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; can also find out where non-public data exists and request access
- SCUFN - find a seafloor feature name, or submit a name for a new seafloor feature!
- NOAA Tides & Currents
- GMRT Map Tool - select subsets of GMRT data for download in a variety of formats
- SmartMap - sound speed forecasting and line planning web service
- 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
- UNH Map Portal - web map apps for CCOM-related data products; also available to integrate with ESRI Arc Pro/Online
- Mapshaper - quick conversions of line planning file formats
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 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.
[Insert Charlie's sweet Okeanos coverage graphic]
See the Sound Speed page for all the nerdy details!
It is imperative to collect sound velocity 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.
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.
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 to verify that what you are seeing in acquisition is reflected in processing. Some examples include:
- No holidays
- No gaps between lines
- Sound velocity alignment
- No major navigation/motion issues
- Data density is as expected
- 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.
Data is only as good as it is described. 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.