This is a wonderful description by Dr. Renske Gelderloos of Oxford University of what mooring recoveries are all about, taken from her blog.
Today is mooring day! My function on board has officially been changed from scientist to full-time photographer for the day. We want as many photos as we can get from the equipment as it comes out of the water, so that we can always go back later and see if something happened before, during or after the recovery. And it is a beautiful sunny day; very photogenic!
Recovering the moorings is really our number-one priority on this field trip, so everyone is both excited and anxious whether we will be able to recover all of the seven moorings in this section. Ron has already contacted three of them yesterday evening, so that is a very good start. Contacting a mooring works as follows: Ron sends out a signal to the mooring at a given frequency. If the mooring receives this signal it will respond with another signal. Because these moorings are in the water for a very long time (three years in this case), the release switches are programmed to be asleep two thirds of the time and awake only one third of the time to save battery. The mooring only responds if it is awake, so it may take a few minutes to get a response. Once the mooring has confirmed that it is still in the position where it was left three years ago and awake, we go towards the mooring and check that there is no ice overlaying the site (or if there is a little and it is not too thick, ‘just push it away a little bit’ with our icebreaker). Then Ron sends out another signal to lure the mooring to the surface. This signal opens the acoustic release that holds the mooring down to its anchor. The floatation devices that are attached to the mooring line rush upwards to the surface. At this point everyone stares over the railing to try and be the first one to spot it. Today the weather was so calm that we could actually hear them come up, so it was easy. When the mooring is spotted, the FRC is launched with two crew members, who tow the mooring to the boat and attach the heavy things one by one to the crane. Then the crane tows them up to the deck.
Recovering an Acoustic Doppler Current Profiler (ADCP) mooring in 2009.
The first four moorings were recovered before lunch (which is from 11.30 to 12.30 here) and it looked like we were going to set a new record today. The fifth mooring after lunch also came in according to plan, but then our luck had run out. The sixth mooring refused to respond, no matter how long we tried. After a while we decided to try and contact the seventh mooring, but again without success. We steamed to the location of the seventh mooring in the hope of getting a response, still with no success. Then suddenly the sixth mooring decided it was willing to communicate after all. Apparently it had just been having some puberty issues refusing to wake up, but now it responded to our mating call. Quickly we steamed back to the site of the sixth mooring, opened the released and successfully recovered the mooring. We tried to get into contact with the last mooring, but unfortunately it was all in vain. We will probably try again on the way back, but we may need to accept that the mooring is just not there anymore.
The scientific successes and endavours of this day were celebrated at the bar that night with a drink. It was a long, eventful and in the end scientifically successful day.