Currently, both the off shore survey vessel and the in shore survey vessel are conducting magnetometer surveys. A magnetometer is a scientific instrument used to measure the strength and/or direction of magnetic fields within its vicinity. The inshore magnetometer survey is searching for the location of other cables within the region, so we can map where PPC-1 will lie close to, or on top of, existing cables.
For the inshore survey, two existing cables within the survey corridor run approximately parallel to the survey centreline. This is in water depths from 30m to 50m.
The alignment of the magnetometer traverses will be surveyed obliquely to approximately perpendicular to the mapped alignment of the existing cables, to best suit sea conditions on site. The magnetometer traverses will be at intervals of 500m along the route, with one traverse at the position where there is a planned crossing between the existing APNG-2 cable and the main survey centreline.
At the inshore end the two existing cables are approximately 150m apart, and the magnetometer traverses will be extended to cover both cables in each pass. The existing cables diverge from one another towards the 50m depth contour, with a 1km separation as they exit the corridor. The inshore survey equipment used will be a Marine Magnetics SEASPY Magnetometer and a Magnetometer Logging computer. Along the traverses, the magnetometer will be deployed within 20m of the seabed where it is safe to do so. Clearly this depends on seabed terrain and seawater currents.
The above map illustrates the proposed inshore survey. The red line represents the proposed PPC-1 cable, and the purples lines represent other existing cables. The shaded area highlights the proposed cable crossing with APNG-2.