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Marine Geophysical Research

, Volume 32, Issue 1–2, pp 25–35 | Cite as

Cautionary considerations for geohazard mapping with multibeam sonar: resolution and the need for the third and fourth dimensions

  • David C. Mosher
Original Research Paper

Abstract

Most modern submarine geohazard investigations rely heavily on multibeam sonar data, yet there are limitations to these data that must be respected. Disregard of fundamental aspects of spatial sampling, averaging and interpolation, and statistical parameters that accompany all forms of measurement, can lead to over-interpretation of data. Beam spreading and sounding density govern spatial resolution and therefore limit seafloor features that are resolved and interpreted as indicative of geohazards. These resolution limitations are shown with a synthetic model of the seafloor convolved with a spherically spreading wavefront approximated with a spherical smoothing algorithm. This simulation shows the inability to resolve metrics of objects, as well as determine critical parameters such as slope angles with increasing water depth. As well, real case examples are presented showing these effects on identification of targets, slope angles and pockmarks. Misinterpretation of seafloor features is common in multibeam data, particularly without the benefit of coincident subbottom data. Thus it is critical to image the third dimension below the seafloor. Finally, seafloor mapping for geohazards is just one step in a geohazard assessment: it is critical to know frequency of recurrence of geohazard events and their modern geologic context in order to appropriately assess risk.

Keywords

Multibeam Resolution Marine geohazard Seismic reflection Aliasing 

Notes

Acknowledgments

The author would like to thank F. Chiocci and organizers of the “Seafloor Mapping for Geohazard Assessment” conference for stimulating discussion about this important subject, as well as project MAGIC and IGCP 511 for sponsoring the event. The author’s work and participation in the conference was sponsored by NRCan Earth Science Sector Offshore Geoscience Program. Data for this paper were drawn from many sources and the author would like to thank industry (particularly Encana) and GSC data contributions. P. Fraser was of great assistance in the ArcGIS component of this project. G. Sonnichsen, B. Todd and J. Shaw reviewed the paper prior to publication and I thank the two anonymous reviewers and the editors who supplied helpful comments to greatly improve the manuscript. Natural Resources Canada, Earth Science Sector contribution number 20100123.

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Copyright information

© Her Majesty the Queen in Right of Canada 2010

Authors and Affiliations

  1. 1.Natural Resources Canada, Geological Survey of Canada—AtlanticBedford Institute of OceanographyDartmouthCanada

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