|
DeepWorker Tracking
Surface tracking and navigation are important support functions for any submersible dive. Additionally, geographic information systems (GIS) provide the ability to use bottom topography, imagery, and habitat information in real time during a dive. Once a submersible leaves the surface, it can be tracked acoustically using an ultrashort baseline (USBL) tracking system. A hydrophone mounted on the surface ship sends a low frequency "ping" into the water column. A transponder mounted on the submersible hears the ping, then sends two reply pings on different frequencies. The first ping gives range and bearing information, and the second ping gives water depth. This occurs about every two seconds throughout the duration of the dive. The information from these acoustic signals are then converted into horizontal distance and bearing points indicating the position of the submersible in relation to the support ship. The tracking system lets the surface support team know where the submersible is in relation to the ship; however, it cannot provide information as to the submersible’s location in relation to the Earth (i.e., latitude and longitude). To derive this type of information, a second computer, running a software program known as WinFrog, is tied into the support ship's global positioning system(s) and gyrocompass (a highly accurate, stabilized compass). The combination of these two navigational systems allows the submersibles to be positioned in real time on the Earth. This information is important for safety, for quickly returning to important sites in the future, and for long-term research projects. Once the ship knows the submersible’s exact location, the ship's echo sounders (essentially a sonar that finds the bottom) and global positioning systems, can accomplish bottom mapping at dive sites for which current data is limited. Ideally, a grid system is set up so that the support ship's echo sounders can sweep back and forth over the bottom on proposed dive sites. The ship's crew often refers to this activity as "mowing the lawn". An ideal time to "mow the lawn" is when the sub batteries are being recharged and while the support crew is resting. The depth information is then reconstructed as a bathymetric map for use during DeepWorker dives. The navigation information (both real-time and post dive) can be fed into a software program known as ArcView GIS*, which allows the support team and researchers to access other data layers (e.g., bathymetry, sidescan, and multibeam bottom imagery). The GIS is also used for predive planning and postdive analyses. * ArcView is a proprietary desktop GIS software application of the Environmental Systems Research Institute (ESRI). |
