Teacher Logbook:
Thursday, July 7, 2000 1600 hrs.

Location, location, location. Not just a real estate clich‚. Out at sea there are no landmarks, so technology plays a big part of determining one's position. There are two navigation systems in operation for NeMO. The first one, GPS (Global Positioning System), is used to determine the location of the ship. Every second at least three satellite fixes are recorded and used by a computer to calculate the ship's latitude and longitude, in much the same way that earthquakes are triangulated by seismologists. With the cold war over, President Clinton was instrumental in declassification of GPS data, improving the location accuracy. Your position anywhere on the globe is now accurate within the size of a tennis court, as opposed to a football field before declassification.

The second navigation system locates the position of our ROV, ROPOS. The ROPOS pilot often flies through the water where visibility is restricted to a few feet. Any time ROPOS is in the water one of our navigators, Susan Merle, Julia Getsiv, or Lisa Crowder are in the ROPOS control room continually updating the pilot on the position of ROPOS and any cataloged bottom features, such as a vent. Setting up the system for ROPOS navigation goes something like this: Long-baseline transponders are deployed at specific positions, creating an ocean floor "satellite system" that triangulates the position of ROPOS. Transponders are triggered by, and talk back with sound, and each has a unique frequency that identifies it. They are strung on a 200-meter-long tether anchored to the seafloor. Since we know the speed of sound in water, we use the length of time the sound takes to travel through the water and convert it into a distance, called a range. ROPOS is equipped with a relay transducer that talks to, and listens to, the transponders. The time it takes for the sound to travel from the transponders to the transducers is converted into distance (range) and the navigation software triangulates these ranges to determine the position of ROPOS within the net of transponders.

Location is not only important for ROPOS. Samples taken from the ocean floor are all labeled with the appropriate latitude and longitude. A great rock core does you absolutely no good if you don't know where it came from. Most of the scientists on board have a personal log book to record locations, times, and any other pertinent information that will help in further analysis of NeMO data. Six months down the road that log book is going to pay off.

Gotta go. There's only a few cups of coffee left.

Jeff

Navigation team (Susan Merle, Lisa Crowder and Julia Getsiv, l-r) pictured with one of the long baseline transponders.

Soft coral on older lava flows.