Bathymetric Mapping in Tonga

As part of the Australian Government’s AusAID sponsored project to examine tsunami risk in the South-West Pacific Ocean, bathymetric models are being completed for the shallow-water coastal areas of Tonga and the Solomon Islands. The high resolution bathymetry models will be used to assist accurate inundation modelling as part of a comprehensive tsunami risk assessment of these island nations.

Geoscience Australia is using high resolution (2.4m) multispectral data from the Quickbird satellite to produce detailed bathymetric maps for these areas. The use of a physics-based remote sensing technique enables water depth in shallow coastal areas (0 - 20m depth in clear waters) to be estimated without the need for extensive field-work, and at a much lower cost than other surveying methods such as multi-beam sonar and laser airborne depth sounding. This methodology offers advantages over empirical, image-based remote sensing bathymetry techniques, including the ability to:

  • offer an objective, repeatable analysis (which is particularly important for time-series data)
  • operate across a range of sensors
  • provide model-based error and confidence maps.

Using a physics-based remote sensing approach, Geoscience Australia has improved the resolution of the existing bathymetric model in Tonga.

Image-based remote sensing bathymetry has been derived previously for some of the areas surrounding these islands but it has limited applications because of the coarse resolution (30m). The method used by Geoscience Australia has been assessed against the existing model and shows good potential for improving existing bathymetry and mapping unknown areas.

Physics-based remote sensing approach, Geoscience Australia.

The left image is the existing
Image-based bathymetric model,
the centre image is the bathymetry
derived by Geoscience Australia,
and the right image is a true colour
image of the region.
© Geoscience Australia

Bathymetric model of reef area, Geoscience Australia. 

A bathymetric model of reef areas
to the north of Tongatapu,
Tonga-derived from the physics-based
remote sensing techniques at
Geoscience Australia.
Reproduced with permission from
QuickBird Image © Digital Globe Inc.

Topic contact: earth.observation@ga.gov.au Last updated: February 5, 2014