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Voyage to the Gulf of Carpentaria

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Report 7 – Outwitting Cyclone Ingrid

11 March 2005

Lat	S 15º 40'
Long	E 138º 5'

Sampling operations were moved nearer to the shelter of Groote Eylandt on Thursday as Cyclone Ingrid advanced west across the Gulf of Carpentaria. Quantitative ecologist Wayne Rochester explains how he 'adaptively updates' the voyage track and associated work plan.

We have just completed sampling at our first 42 sampling stations in a region north of Mornington Island. Our cruise track for Mornington looks like spaghetti and was updated four times in the seven days we took to complete it. Are we nuts?

Actually, there is method in our apparent madness. So far the results have been positive: we are on schedule with sampling and the response of the skipper and crew has for the most part been bemusement rather than irritation.

The spaghetti and the updates arise from our need for an optimised, but adaptive, cruise track to accommodate the survey design, operational requirements and hiccups.

The spaghetti arises because we require a track with a reasonably consistent 11 nautical mile steaming distance between sampling sites, rather than one following the shortest path.

This is for operational reasons such as keeping the ship moving, sorting the catch and maintaining a rhythm onboard. As a bonus, it also scatters the samples for nearby sites in time.

The need to adjust the track during the survey arises because our sampling sites are stratified by day and night in addition to trawling intensity. Whenever we complete more or less samples than planned, day sites get pushed into the night or vice versa. We must then recalculate the cruise track to ensure that we visit day sites in the daytime and night sites at night.

The cruise track is calculated with a simulated annealing optimiser. Importantly, the optimiser can be applied to a partly completed cruise track so changes can be made during the voyage.

The optimiser is integrated with the operational geographic information system (GIS) that is used to design and monitor the survey. So we can adaptively update the sampling site locations and cruise track in real time in response to operational hiccups or new knowledge, and print tables and maps of the updated track for distribution to the skipper, crew and scientists onboard.

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Updated: 29/03/07