|CTD in its protective cage. c.50cm long|
Why do we need it? The CTD measures Conductivity, Temperature and Depth every 0.5s as it descends (the downcast), parameters need to to calculate the speed of sound through the water. This sound profile information is used to calibrate the multibeam echo sounders so that data taken over a period of time can be integrated into a single 'picture' of the seabed. Analysis of the sound backscatter can provide a broad scale analysis of the seabed type, which is then ground truthed with grab and camera samples.
Talking of which we're at our next station so I need to get back on duty!