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
- 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 - data for the European region; can also find out where non-public data exists and make inquiries for access
- SCUFN How to determine if a feature has already been named, or to submit a name for a new seafloor feature!
- NOAA Tides & Currents
- GMRT Map Tool - helpful for locating/downloading background data for planning maps, Fledermaus visualizations, etc.
- SmartMap - sound speed forecasting and line planning web service
- Coordinate Systems - find the espg 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 - a library of web map applications for background 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
Duties, checklists, things for watchstanders to... watch...
Recommendations for minimum required processing effort underway to ensure data quality
See the Data Processing page for further details on processing practices.
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.