• Haleh

CTD logging

We deployed the first of our instruments yesterday, a CTD cast, on the way towards our research area.

CTD stands for Conductivity, Temperature and Depth.

Conductivity is the measure of how easily an electric current can pass through a material. Conductivity helps us derive salinity (saltiness of water). Temperature and Depth are also measured, where depth is derived from pressure data (the pressure will increase with depth).

These data are valuable as they give us insight about the physical properties of the water column, such as the speed of sound in water.

As shown in the following figure, the CDT cast is attached to a device known as a rosette (the white frame), which descends between 0.6-1 meter per second. The cable at the end of the rosette is connected to a computer on the vessel and provides online data streaming and visualization.

The CTD cast is winched over the edge of the ship and dropped into the water, sinking down to 2500 meters.

The rosette can also hold other probes too. Along with CTD logging, we performed a release test for the Ocean Bottom Seismometers (OBS) that will be deployed at a later stage.

You can see the 7 releaser probes in the figure (silver canisters attached to the frame). It is essential to run a test on the OBS releasers, to ensure that the OBS's can return to the surface after they have finised taking measurements. We will have separate posts regarding OBS deployment and retrieval. This way you will become familiar with different components of an OBS later on and the various stages of collecting geophysical data.

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