Friday, 17 August 2012

Day 4 - Preparing to dive

Today the RRS James Cook  arrived on station, 200 nautical miles SW of Land's End and switched on the Dynamic Positioning (DP) system which enables the ship to remain very stable whilst our teams deploy equipment, for example, the Isis  ROV.

Part of the mission for today involved deploying a Sound Velocity Probe on a vertical wire in a water depth of approximately 1500m. This probe observes the speed of sound at different depths as it is lowered in the water. In order to make use of the acoustic navigation and seabed mapping sensors onboard James Cook, the speed of sound in water must be known.

Acoustic beacon
Weather conditions remained adverse for deploying the ROV so the decision was made to reposition to deeper water in approximately 4000m to complete the calibration of the Cassius USBL. This involves deploying an acoustic beacon to the seabed and manoeuvring the ship around the beacon whilst collecting acoustic range, ship position and ship orientation data in order to calibrate the USBL positioning system. The calibration started at 1800 this evening and is expected to last through to 0800 tomorrow morning.

Jon Martin from Sonardyne who is working on the USBL calibration is here to support TOBI2, a deep towed body used for side-scan sonar. Jon’s responsibility is to position TOBI2 and ensure that the Sonardyne systems are working correctly. Usually, when positioning a subsea vehicle (such as a ROV) from the surface, he would use a vessel mounted USBL system but because TOBI2 is so deep and a long distance behind and the vessel, Jon is using a system called iUSBL which entails putting the USBL transceiver on TOBI2 itself. This approach is not used often so more challenging. The TOBI2 launch is set for Sunday.

Elsewhere on deck, the ROV team continued working in the control van, calibrating the manipulator claw arms on Isis  and checking the multiple control and computer systems. The vehicle was switched on towards the end of the afternoon so that the predator manipulator claw arms could be tested. All is ready now for the first test dive of Isis  in the open ocean tomorrow.