“Hey Pete, you mind if you watch the Acrobat for a little bit? I need to fill up my coffee and splash some water on my face.”
The time was 2:45 AM, and Pete Shipton, marine technician for UAF/CFOS, was still awake, downloading data from a mooring recovered from a year-long stint on the Chukchi Sea seafloor. Despite the seeming triviality of my request, he drops everything and meets me in the computer lab. Pete is one of the few people on the ship that knows the perils of taking your eye off the Acrobat. Lapsing even for a brief moment of attentiveness could result in an expensive scientific instrument crashing into the seafloor.
After a few moments, I return to my post in the computer lab. Pete finishes the data download and heads to bed—it was an unusually long day for him. Only one scientist remains in the science lab across the hallway. I am left to my own devices amongst the 30 computer monitors hinged along the perimeter of a room. Even on the busiest of science days, ship operations tend to wind down before midnight. The ship is eerily quiet except for the melodic tones of Vitamin String Quartet coming from the Bluetooth speaker to keep me awake.
Adjusting to an 8 PM-8 AM schedule is rough. Everyone has finished experiments for the day by the time you are waking up, and those same people are asleep when you are awake. You feel like you miss everyone and everything. People say good morning to you in the afternoon and chuckle. While it is funny, feelings of isolation and separation undoubtedly have seeped into my conscience.
But the Acrobat abides…well most of the time. It continues to fly through the water with alacrity and grace paying little heed to operators' watch schedules or emotions.
Developed by Sea Sciences Inc., the Acrobat is a scientific instrument that is towed at about 7 knots through the water behind R/V Sikuliaq on a tether that is between 150 and 220 meters long. It has wings, a motor, and can be fitted with various payloads. This particular Acrobat is equipped with sensors that measure temperature, conductivity, salinity, pressure, chlorophyll, particle concentrations, and colored dissolved organic matter. The Acrobat’s tether provides power and data transmission directly to a series of computers that store the data in real-time and control the flight pattern.
Once the Acrobat is deployed, an operator in the ship’s computer lab can control the pitch of the wings thereby adjusting the altitude (depth). As a result, the flight path of the Acrobat resembles that of a chain of waves or a yo-yo pattern oscillating through the water. The operator can control how close to the surface and seafloor the Acrobat “yo’s” in the water column either manually or through an automated process. In the ship’s lab, an Acrobat control station digitally displays the flight path and seafloor depth linked from the ship’s depth sounder. It is at the control station where quick decisions to alter flight path patterns are performed based on seafloor depth, current, speed over ground, etc.
Unlike other scientific instruments on R/V Sikuliaq, the Acrobat can obtain fine scale resolution measurements of subsurface water properties while the ship is underway. There are instruments on the ship’s hull measuring surface parameters, but the Acrobat has the ability to sample throughout the entire water column—something that the ship's acoustic transducers can do, but not most of the other pieces of equipment on board while underway. The data obtained through the Acrobat tell a much richer story about what is happening in the water column than the CTD. The Acrobat data provide contextual dimensionality to the other types of data being collected. No longer are scientists confined to surface CTD sampling for spatial high-resolution data or stopping the ship for a full CTD rosette deployment that only gives a snapshot in time - the Acrobat provides a full transect of linear data from surface to seafloor.
Imagine, if you will, a layer cake with several alternating layers of strawberry and chocolate—but somewhere in the cake is a small section of vanilla frosting. If you slice into the cake, all the layers of strawberry and chocolate would be revealed. Only certain slices of cake might contain the vanilla layer, however. The Acrobat slices through the ocean water column as the ship makes a transect line, much like slicing a cake. Despite all of the fine-scale structure the Acrobat data reveal, there still could be other oceanographic features not being expressed. After all, the northern Bering and Chukchi Seas are vast ocean seascapes.
A couple hours later… the Acrobat sends a pressure spike anomaly through the data stream. And another. Sequentially, the spikes cause the Acrobat to alter course through the water. Sikuliaq is entering deeper water, causing strain on the cable wire. I have to begin manually controlling the flight path. Reluctantly, I wake the chief scientist, Dr. Seth Danielson, from a snoring slumber to assess the situation. Both of us strain anxiously as each yo approaches the surface and seafloor. Somehow Pete is still awake after all this time.
Eyes are glued with trepidation…will the oscillation return to normal?
Seth realizes that there is perhaps too much tension on the tether cable and the Acrobat is descending deeper than it should at the speed we were traveling. A phone call to the ship’s bridge quickly ensued and we lowered our speed over ground. The flight path was adjusted for a shallower yo, putting less strain on the tether cable. After saving the day and a few yawns later, and Seth returns to his rack, and Pete follows. Slowly the spikes abate and the Acrobat returns to normal.
Only a couple hundred more yo’s before the watch ends and the Acrobat is hauled in. Once again, the Acrobat abides for the science team collecting valuable data across the Chukchi Sea.