ALTEX Arctic Cruise
October 7 - November 7, 2001
Tromso, Norway to the Arctic Circle
October 13, 2001: Day #7
Mike Pinto writes: The mid-length AUV was back in open water ready to resume testing just after breakfast. We were looking for the first successful run of the trip. Conditions were favorable with calm seas and minimal wind. The AUV's strobe light was operating due to the lowered light levels caused by the high latitude and cloud cover. The first test was a 2-minute straight run at 15 meter depth. The vehicle performed exactly as planned and returned to the surface and transmitted data back to the ship flawlessly via the wireless modem. We had no problem spotting the vehicle from the bridge with the strobe operating.
The next series of tests added complexities with turns and varied depth commands. Continued successes!!! Acoustic tracking also performed well. The vehicle could be tracked reliably up to 800-900 meters as it moved away from the ship and up to 1400 meters as it approached the ship.
The doppler velocity log (DVL) integrated in the vehicle's inertial navigation system (INS) is normally oriented towards the sea floor to accurately measure velocity over ground and to correct errors in the INS. In deep water however, the doppler cannot pick-up the sea floor. Since the vehicle will be eventually working under the ice, the INS was flipped upside down to test its ability to use the underside of the ice to take its measurements. This caused a few minor data glitches while parameters were readjusted to take into account the change in equipment orientation..
The final test of the day incorporated an acoustic generated abort signal to see if the vehicle could be shut down in an emergency. Hans Thomas had earlier added this capability to the software but it had not been tested. As the vehicle approached, the signal was given using an acoustic transmitter hung over the side of the Healy. It worked as planned! Utilizing the acoustic tracking equipment we could see the vehicle slowing down, stopping and returning to the surface (as evidenced by the resumption of data collection from the vehicle). Later that evening at the science meeting, on-board data was reviewed and the team declared the vehicle was ready for the next set of tests - running under the ice. Our next stop will be an area where we have open water and solid ice.
Now things are getting interesting!
P.S.: While breaking ice later in the day moving north, several of us spotted large tracks on the ice. We later verified that we had the first evidence of polar bears!