Saturday, December 1, 2007: A shorter list
With SCINI almost completely rebuilt and tested, and only 2 weeks left, it’s time to reevaluate what we can achieve in the remaining time, without making ourselves too crazy. We have been remarkably successful so far, and we’d like to keep that high note.
SCINI beginning underwater explorations, with the hole in the ice visible in the background.
Our engineering goal for the season was to fine tune the navigation system. We were concerned before we arrived that echoes between the underice surface and the seafloor would confuse the positioning system. The software settings gave an option that helped us minimize the underwater noise, giving us positioning accuracy down to 10 cm. However, we learned that topside noise is a problem. The generator needs to be grounded, even if it has a noise filter. This has led us to consider solar power rather than petroleum-based engine power. More difficult to deal with is noise from undefined radio frequency sources, which is intense and sporadic around McMurdo. Unshielded cables function as giant antennas, picking up the noise and relaying it into the navigation system as error. Thus, shielded cables must be run across the ice. We also learned that it is easy to get transducer cables stuck in the ice, because they are running through small holes that refreeze quickly. Our solution has been to start with larger holes, place insulative plugs in them, and rigorously maintain them every half hour by dipping out the forming ice with a soup ladle. Next year, our approach will include placing small heating coils in the holes (like aquarium heaters) that can also be run off the generator or solar. This should keep us from having to run any more ‘ducer rescue missions! So we have two things we can improve for next season (longer shielded cagles, and heaters) but we are overall pleased with the performance of the navigation system. We have demonstrated consistent, accurate underwater navigation, a success!
Our science goal for 2007 was to find “the Lost Experiments”, and map and survey them. Up to 40 years old, these structures include experiments on predation, succession, larval dispersal, and substrate selection. Initially set up by Dr. Paul Dayton, their locations were based on visual lineups, and their depths sometimes exceed current safe diving limits. The ROV allowed us to overcome both of these issues, by letting us search safely at depth for hours, and by tying the underwater navigation net into GPS to get positions we can easily return to. We are enormously pleased that we found all of the sites, and one of our goals for the remaining time here is to complete the mapping on two of them.One of the many experimental structures showing remarkable colonization and growth.
Other progress that we have made is harder to quantify - or at least, harder to define as completed. In our work at New Harbor, we proved that we can deploy SCINI in remote areas with limited support…but can we get even more remote, and with less support? The operational limits for successful missions have not yet been set, or even pushed. We have shown that we can overlay data collected under different navigation nets, but can we overlay data collected from different dive holes, expanding the area of seafloor that is known? We can exceed diving depth limits – but how far can we go? Different modeling calculations for pressure vessels give us different results, and tether constraints on mobility are as yet unknown, so the only true test will be a real world one. We can use sonar to map hard manmade structures; can we also identify biological targets such as giant sponges?A sponge, such as the Calyx arcuarius shown here, is soft bodied, but has silica spicules and a different density that seawater. We won't know until we try how "visible" sponges are to sonar.