Related Links:

  • Seafloor Mapping Seafloor Mapping
  • Natural Hydrocarbon Seepage Natural Hydrocarbon Seepage
  • Oil Spill Monitoring Oil Spill Monitoring

 

 

  • Oceanographic Studies Oceanographic Studies
  • Data Integration Data Integration
  • Chemosynthetic Studies Chemosynthetic Studies

Rotary Time-lapse Cameras: Part 1

June 19, 2007
Ian R. MacDonald
Texas A&M University – Corpus Christi
27° 25.00 N
88° 22.20 W

Using the remotely operate vehicle (ROV) Jason, scientists and observers are able to operate on the bottom for much longer than is possible with most human-occupied submarines. But the time still comes when the dive ends, and we move on to the next site or take our data back to the lab. Life in chemosynthetic communities goes on, of course, and we have to wonder what happens outside of the brief snapshot in time when we were there.


For many years, I have been deploying a variety of time-lapse cameras at hydrocarbon seeps and hydrothermal vents to try to address this question. I use the data these systems generate to understand how the physical environments change over time: how seeps increase or decrease in activity and how animals behave when they are not disturbed by the bright lights and noise generated by submersibles. These are questions that are difficult or impossible to answer unless you have long-term continuous information.

The basic idea is to have a camera along with a source of light that takes a picture at a fixed interval. For this to work, you need a pressure housing for the camera and lights, and a large and robust battery to supply power. You also need assurances that you will be able to come back in the not-too-distant future to retrieve your camera, which you hope will be full of fascinating images.


As with any deep-sea operation there are many challenges in trying to make equipment work when you cannot be there to check on it — especially under the pressure hundreds or housands of meters of water. Over the years I have had my share of disasters: housings that flooded, batteries that failed, and cameras that were out of focus. Even when everything works, you still are left with a single point of view. Looking at the pictures, you always wonder what was happening just outside the frame. On most deployments, I have had to leave the cameras out for about a year because the scheduling of ship operations rarely allows multiple cruises with a submersible in less than a year. Knowing you have a camera on the bottom and wondering if it is still working can be a source of worry in the time between cruises.

For this project, I wanted to try and solve some of the more common deep-sea time-lapse camera problems with a new type of camera. I worked with an electrical engineer named Mark Roberts and a company called AquaPix (of which I am part owner). Together we developed a time-lapse camera that rotates between frames and uses an energy efficient strobe as a light source. The idea is to be able to view a 360° area around the camera. (No
more wondering what was happening behind the camera!) To get around the problem of year-long deployments, I wanted a system that would let me recover the cameras without having to dive with a submersible.


Our solution has been to place the camera and light source inside a thick-walled (9 millimeter) glass tube. Using a glass tube as a pressure housing not only lets the camera aim in all directions, but it provides a significant cost saving over conventional titanium or aluminum housings. In adapting an off-the-shelf digital camera (Nikon CP5400) and creating a powerful custom strobe for light, our objective is to take high-resolution images with an affordable,
energy-efficient system.

I deployed a prototype rotary camera during last year’s Alvin cruise, but was obliged to leave it out for an entire year because no submersible was available until we returned with Jason. Sadly, when we recovered it from our Green Canyon 852 site, the stainless steel endcap had developed a pin-hole and the unit was half full of water. Although I may be able to recover the data from the compact flash card, the camera and electronics were a total loss.


The new design dispenses with stainless steel in favor of an all-glass housing. More important, I have attached the camera to a compact recovery platform that will return to the surface when it receives an acoustic signal. This time I should be able to get my camera back in a couple of months. For power, I use two lead-acid gel cells deployed in an oil-compensated container. The battery container is filled with mineral oil and covered with a flexible membrane. The pressure of the seawater can press in on the oil until the batteries are at the same pressure as the surrounding seawater. The pressure does not hurt the batteries, while the oil protects them from seawater. Best of all, the battery packs can be made light enough to lift with a single float having about 45 pounds of buoyancy.

Check back later in the cruise to see how things go during the first series of deployments for the new camera design.

 

Rotary Time-lapse Cameras: Part 2

June 29, 2007
Ian R. MacDonald
Texas A&M University – Corpus Christi
26° 21.25 N
94° 29.83 W

In the June 19 log, I discussed many of the advantages of using time-lapse cameras for science, as well as the challenges associated with building and operating them. In this log, which I've
entitled "Part 2," I want to update you on what happened with the new model of camera when we returned two weeks later to the Atwater Valley 340 (AT 340) site to retrieve the camera.


Everything started out quite well! Upon arrival, we discovered that the camera was still in place, right where we had left it. As the Jason remotely operated vehicle (ROV) pulled up close to the camera, I was slightly concerned to see that it had stopped taking pictures. But I breathed a big sigh of relief when I saw that the housing was still intact; the inside seemed dry and secure. Now all we had to do was get the camera safely back to the surface and onboard the NOAA research vessel Ronald H. Brown.

While the Jason rested on the sea floor, I hung a hydrophone over the side of the ship and beamed the release command — a strong acoustic signal — to the camera over 2,000 meters (m) below. This signal starts an electric current over a circuit below the camera housing. There is thin piece of wire on the positive side and grounding contact on the other. In between are six inches of seawater. When the current flows across this six-inch gap, it
causes the thin wire to corrode rapidly, eventually burning through the wire and causing a mechanism to drop an anchor. After sending the signal, I raced back to the control van to watch the release on video in the Jason control van. About 15 minutes later, the burn wire failed, the anchor dropped, and the 17-inch Benthos glass sphere began lifting the camera to the surface. Immediately, the bystanders in the van began laying bets as to when it would get to the surface. I helpfully provided information on the system’s weight in water and air and its positive buoyancy. (I failed to mention that I knew from previous experience that it should rise at about 40 m per minute.) So 49 minutes later, when the bridge watch spotted theyellow ball, my bet of 55 minutes won a round of beer when we get back to port in Galveston on July 6.

Better yet, the camera was in great shape and had taken over 1,300 pictures on the bottom. There do seem to be a few areas where I can make improvements. A lens cover I glued in place to cut back on glare had peeled off — partly obscuring the corners of the images. A high spot on a connector had rubbed against the inside of the glass — causing the rotation to stick in a few places.


The great news is that the camera recorded several resident fish that seemed to reappear after the ROV had left the site. The images also show numerous small fauna that came and went while the camera was on bottom. It will take my students and me several months to sort out all the information. For now, I am happy with a proof of concept and a chance to “immerse” myself in the seep environment. Hopefully, I’ll have a few more images to share once we get to Alaminos Canyon in a few days.


 
 
| Site Map | Contact Webmaster |
 

Follow us on