In case you didn’t know, a CTD is the tool that enables us to calculate the temperature, salinity and density of seawater. They are also very, very expensive. This is why the OpenCTD is so amazing. Now for a fraction of the cost, you can build your own if you need/want to. All the code and the instructions can be found on their GitHub site. And you can also build an adorable little niskin bottle for your ROV. WOOT for low cost, open source ocean observing!