A Design for a Trusted Community Bathymetry System

Abstract

Marine Volunteered Geographic Information (informally “crowdsourced bathymetry”) has raised much interest within the authoritative hydrographic community as a means to cheaply gather information to satisfy chart updating requirements. So far, however, a routine path to the official chart has been rare, mainly due to lack of calibration and other metadata that would satisfy liability concerns. As an alternative to these ideas, a data collection system is proposed which, by design, can auto-calibrate and provide other data quality guarantees, and thereby generate data that by construction should be qualified for hydrographic use. This idea is termed here Trusted Community Bathymetry (TCB). A design for such a system is outlined, and its performance demonstrated experimentally through a prototype system based on a low-cost, post-processed GNSS receiver and NMEA data logger. By comparison against NGS control and survey-grade GNSS equipment, it is shown that the TCB system achieves centimeter to decimeter-level positioning in 3D, auto-calibrates vertical offsets to the sonar transducer within a decimeter, and provides realtime uncertainty estimates for ellipsoid-referenced soundings. Additionally, in an underway field trial, the total vertical uncertainty of the soundings is shown to be within the limits required for IHO Order 1b (S.44, 5 Ed.) surveys.

Keywords:

• Bathymetry
• Crowdsourced Bathymetry
• GNSS volunteered geographical information ellipsoid-referenced survey
• Trusted Community Bathymetry

Acknowledgements

This work was supported through a collaboration with SeaID Ltd. (K.H. and A.S.), and funding from NOAA through grant NA15NOS4000200 to the Joint Hydrographic Center at the University of New Hampshire (B.R.C., S.J.D, and S.H.). The use of particular equipment here is not intended to imply endorsement on the part of CCOM/JHC, the University of New Hampshire, or NOAA. The authors would like to thank the Captain and crew of the R/V Gulf Surveyor, without whom the work could not have been completed, for their hard work, dedication, and willingness to put up with long hours during set-up and trouble-shooting. Thanks also to Emily Terry, Mike Tuttle, and Andy McLeod at CCOM/JHC for logistical support, Dave Shay and Nate Rennels at the UNH Judd Gregg pier facility for local support and hosting, and Dan Tauriello for GNSS post-processing.

Notes

1 See https://www.iho.int/srv1/index.php?option=com_content&view=article&id=635&Itemid=988\&lang=en for more details of the Crowd Source Bathymetry Working Group (CSBWG) and the status of the developing B.12.

2 For example, “innocent passage” sounding for safety of navigation is generally allowed even within territorial waters, but is this still “innocent passage” where the mariner knows beforehand that the data will be used for CSB purposes?

3 As with the Free Software movement, the intent here is “free” as in speech, rather than “free” as in beer.

4 See https://radionavlab.ae.utexas.edu

5 In 2017 dollars.

6 Antenna serial 60073787, receiver serial 0220358293, firmware 2.32.

7 Antenna model GPS-702-GG, rev. 1.03, serial NAE 16440036.

8 Trimble antenna serial 3620270396, NovAtel antenna serial NAE16440036, rev. 1.03.

9 Receiver serial 022036964, firmware 2.34.

10 See http://www.rtklib.com

11 Serial number 98139.

12 See https://vdatum.noaa.gov

13 Note that a different reference position was used from the static calibration experiment, which is easier to get to while underway.

14 See https://www.nodc.noaa.gov/OC5/woa13

15 See https://oceanservice.noaa.gov/facts/ofs.html

Additional information

Funding

National Oceanic and Atmospheric Administration (NOAA Grant NA15NOS4000200) for Calder, Dijkstra and Hoy.