Computer Watch . . . logging CTD data.
The system I looked after on this cruise was a Digital Electronics MicroVAX minicomputer. We monitored most of the routine data collection with a Decwriter, which is a glorified teletype, attached to the VAX at 300 baud. Any programming was done with a CRT terminal . . . the old RS-232 serial type set at 19,200 baud for writing FORTRAN programs and the like. Like everyone else, I stood a "watch." At sea, we did a lot of things, but one of the primary measurements done is with an instrument called a CTD.
CTD stands for Conductivity, Temperature and Depth. The ship is stopped at various locations and the CTD is lowered over the side of the ship and down to within a few metres of the ocean floor (water depth varies from less than a hundred metres to up to 6000 metres, depending on where the ship is.) There are sensors that measure the water's conductivity (which tells how salt it is), its temperature, and the depth of the instrument (derived from the water pressure.) All this is sampled 25 times a second, sent up through an insulated conductor in the centre of the cable holding the instrument and logged to the hard disk on the MicroVAX. The person on watch monitors the readings and ensures everything is running properly, that we don't lower the instrument into the ocean floor, etc.
I used to write and maintain a lot of the software that did this, but since 1993-94 commercially written software is supplied by the company that makes the CTD. Now, it runs on a Pentium based PC, not a MicroVAX.
Deploying the CTD . . . one of the few calm days!
And after the CTD, we collect water samples . . .
Here I am filling a glass bottle from an array of larger grey bottles on the CTD. The CTD itself is in the centre of the grey bottles. They are all open when the CTD is first deployed and each one is closed at a different depth on the way back up. Thus a water sample is taken at the bottom and at various depths all the way up to the surface. These samples are then further analyzed for trace amounts of chemicals like Freon, tritium (a by-product of the nuclear testing in the 50-60's) etc.
Last updated on Thursday, 12 April 2007