Tonga receives high-tech data from NZ underwater survey

10 October 2019

Kingdom of Tonga receives high-tech data from New Zealand underwater survey of main islands

The New Zealand High Commissioner in Tonga HE Ms Tiffany Babington has today delivered a massive thirty thousand gigabytes of data featuring never-before-seen images of the undersea world around Tonga to the Tongan Government.

The hydrographic surveys, undertaken as part of the Pacific Regional Navigation Initiative (PRNI) between Pacific governments, the Ministry of Foreign Affairs and Trade (MFAT), and Land Information New Zealand (LINZ) were carried out by marine survey company iXblue between November 2017 and December 2018.

The surveys were primarily undertaken in order to update Tonga’s nautical charts to improve navigation safety and to assist the expansion of Tonga’s shipping and tourism industries.

Data gathered will also support marine research and can be used to model the effects of sea level rise and flooding, and better understand the marine habitat.

Ms Babington said the data would provide Tonga with “modern, accurate and up-to-date charts to improve navigation safety, and build Tonga’s marine economy.”

LINZ designed the surveys to take advantage of innovative technologies using satellites, planes, lasers and autonomous technology to measure Tonga’s clear and pristine tropical waters.

The data gathered shows previously uncharted rocks and reefs along with a number of interesting geological features including a small underwater volcano.

LINZ is now beginning work to update Tonga’s existing nautical charts and produce six new charts covering the Ha’apai Group, Nuku’alofa, ‘Eua, Tofua and Kao.

These are expected to be available from March 2020.

New Zealand, through LINZ, is responsible under international conventions for the production and maintenance of nautical charts for the Kingdom of Tonga, Niue, Tokelau, Cook Islands and Samoa.

Since the PRNI began in 2015 hydrographic surveys have already been completed in Niue and Tonga and will be underway in Samoa in late 2019.

Technical summary of PRNI hydrographic survey around Tonga

In early 2017 the Tongan Government’s Marine and Ports Division worked with LINZ to identify where hydrographic surveys were needed.

Using tracks from ships moving in the area the agencies agreed on a programme of work which included a focus on the Ha’apai Group of islands where existing charts are still in fathoms and use data from the late 1800s.

The latest survey employed satellites and state-of-the-art bathymetric (seabed) and topographic (land) LiDAR (laser imaging) and multi-beam echo sounder technologies.

Two vessels, including one unmanned vessel collected data over three months.

The surveys started in 2017 using high resolution satellite images to derive bathymetry of the entire Tongan archipelago – thought to be one of the largest areas ever covered by this technology. This provided information about the seafloor to a depth of 15 metres.

The results from the satellite phase were used to confirm where the airborne laser technology (i.e. taken from an aeroplane) would be used most efficiently.

Airborne laser technology is used as it allows data to be collected in very shallow water where it’s dangerous and difficult for a survey boat to go. The LiDAR collected information to a depth of 20 metres.

Taking advantage of the plane equipped with laser technology, data was collected over Tonga’s islands as well as the seafloor, so it can be used for more than just improving the nautical charts.

As a result, the data being provided to Tonga contains information about vegetation cover, buildings, as well as information about the seafloor.

The final phase used two boats, one unmanned – a first for LINZ and Tonga. The boats were fitted with echo sounders capable of collecting a corridor of data up to five times wider than the depth of water. The boat survey focused on the domestic shipping routes through the Ha’apai Group and collected data to depths of 300 metres.

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