It may come as a surprise to many to learn that much of the South Pacific is poorly charted, despite being heavily serviced by ships.
Maritime trade operating on old and poorly surveyed charts is less than ideal from a navigational safety and environmental safety perspective.
The New Zealand Government’s PRNI Initiative
To rectify this situation around the Tonga region, the New Zealand Government instigated a project termed the Pacific Regional Navigational Initiative – or PRNI for short. In 2017, Land Information New Zealand (LINZ) awarded iXblue a contract to improve the quality of Tongan nautical charting.
Due to the huge area in need of modern survey and charting, and a relatively small budget, LINZ needed a clever, multi-sensor approach to yield maximum return on investment with the project.
Their proposed approach had never before been adopted on such a grand scale anywhere in the world.
With the results generated to date, it is likely to be an excellent test case for many projects of its kind in the future.
The method used to keep survey costs down
For this large-scale project, we used Satellite Derived Bathymetry (SDB) to survey a large area, to a depth of approximately 20m. This is a very effective tool to map and plan a large area, at minimal cost.
As a result of the SDB work, we prepared a detailed plan using an airborne bathymetric Lidar (ALB) campaign.
- This sensor package allowed us to survey navigationally significant areas to IHO Order 1a to depths exceeding 20m.
- It also allowed us to capture significant information on the land/sea interface and topography of the region which may assist in future sea-level rise and flood inundation modelling.
Perhaps the most significant and valuable use of the ALB data though, has been the contribution it has made to the safety of the two vessels undertaking the third phase of the survey – the Multibeam survey.
The technical equipment
The ALB survey was flown in mid-2018 and employed the latest ALB technology from Leica.
The Chiropter system owned and operated by US firm Geomatic Data Solutions Inc. (GDS) delivered full coverage IHO Order 1a bathymetry to depths comfortably exceeding 20m across the full area of operations.
Most importantly, the latest version of the system generates four times the sounding density of the previous version which has seen an average of 36 discreet soundings per two square metres. This comfortably and reliably ensures that full feature detection is achieved to depths of 20m.
With complete knowledge of all navigationally significant features, the vessel operation could be planned and undertaken in complete safety and at maximum efficiency.
For the third and final stage of the PRNI project, we are using a 30m host vessel named the SILENT WINGS and DriX - our Unmanned Survey Vessel (USV) named DriX.
Live update from Tonga maritime survey
As I sit and type this update, a vessel crew of five and a survey crew of six have been working around the clock to complete the survey.
The project is proving to be a valuable learning opportunity to refine how USV technology can be employed to improve rate of effort, value for money and navigational safety during nautical charting surveys.
We are all very pleased that the experience has been extremely positive, and that the survey is currently running ahead of schedule.