Monday 10 November 2014

Technical talk...

Another weather chart. Red indicates bad weather on the way!

As the weather sets in again, it’s the perfect time to talk about the equipment that we have been using on this survey.

The main piece of equipment that we’ve been using is the drop-frame camera. This is a welded metal frame that supports the large amount of equipment needed to enable us to view and record images of the seabed many meters below.

The Drop-frame hub: 1 - Still camera, 2- Standard video camera
3 - HD video camera, 4 - Scaling lasers.
A high resolution still image camera provides photographs to be used as ‘quadrats’ later on, and alongside sits a High Definition (HD) video camera and a backup standard definition camera. The final piece in the 4-part ‘hub’ is the laser-scaling device: four lasers set to provide a reference box
of exactly 64 x 64 mm (the official smallest size of a cobble!) that enables us to estimate the size of features and fauna on the seafloor, especially as the equipment tends to move up and down in the current and swell.

Four LED lamps situated on corners of the metal frame shine a light on the passing sponges and other fauna, enabling the video camera to record clear images in these otherwise pitch black depths. An underwater flash gun provides a high-powered burst of light to enable the stills camera to produce crisp images such as those you have seen  in earlier blog posts. The whole rig is towed behind and below the Scotia by up to 200 meters of armoured cable attached to the ship’s winch.

Not playing Pong! MSS Engineer Chris guides
the Drop-frame through the water

Wires transmitting data and commands to the camera run through the cable itself, allowing a live stream to be viewed and the camera to be ‘flown’ above the seabed. This is skilfully handled by expert Marine Scotland engineers Chris and Neil, who keep the frame in the ‘sweet spot’ to provide as close a view as possible of the habitats and species present without creating an expensive wreck on the  seabed and reefs below...

On this survey,  the frame also carries extra equipment in the form of a CTD probe and Fluoro-turbidity logger. Sitting on the top of the frame, the CTD continuously records the Conductivity (salinity), Temperature and Depth, whilst the Fluoro-turbidity logger measures how ‘clear’ the water is. This allows us to collect environmental data which may influence the differing habitats and fauna below.

The Drop-frame being deployed, with the CTD visible
on the top of the frame.

All in all, some fairly hefty equipment! Graeme