ENDURANCE

West Lake Bonney, Taylor Valley, Antarctica
Reporting from East Lake Bonney Basecamp

Prior to commencing production science missions this year we needed to conduct a navigation calibration. There were also further questions about the presence of hanging cables under the ice near the traditional LTR limnological research station located about 200 meters east of the ENDURANCE lab, so plans were made to incrementally approach that zone and perform multibeam sonar scans now that we had calibrated our obstacle avoidance system (see November 5 images).

East Lake Bonney camp is located about 20 minutes by six-wheeled ATV from the ENDURANCE site. Each day begins with a cold trip in the wind.

A software bug discovered this morning required a hardware reset in the motor controller pod. Vickie prepares to close up the housing after the fix is in place.

Bill aligns the forward-looking glacier imaging camera (one of three on the vehicle).

A rectangular navigation course—see figure—was established along a true north-south grid centered on the lab with the designations N1 through N8. As with the 2008 ENDURANCE mission the method by which we established the calibration was through the use of RTK GPS. Before that could take place, however, it was necessary to locate the bot. The procedure there was to use a low frequency magnetic beacon that was pendulum-mounted inside the vehicle. The null (vertical) axis of the field can be detected at considerable distance (we were able to achieve a positive location out to 150 meters radius this season through 3 to 5 meters of ice cap) using phase-locked loop ring antennas. This is somewhat of an art form to do in real-time but we developed a procedure using two individuals (Vickie and Bill) with two receiver sets. This year the bot moved considerably faster (nearly double) than the previous year, following further power consumption tests that refined the lowest dynamic drag velocity of the vehicle. Thus, the field tracking team had to move fast and keep a location lock, otherwise we would end up burning power while the bot waited at a sonde cast (chemistry) location.

Vickie and Bart generate today’s vehicle trajectory using the ENDURANCE mission planner.

We spent a considerable amount of time scanning the limnology site, finding one full-depth sediment trap and another cable structure, which allowed us to more precisely define the “no fly” zone for our data fiber on normal missions (special missions will sample the “no fly” zone later in the season by using a diversion pole—a smooth tube with a radius larger than the minimum data fiber bend radius).

Shilpa, Vickie, Chris, and Bart check out a replay from the ENDURANCE Situational Awareness 3D visualizer, developed for this year’s missions.

Following the obstacle location runs we returned to the “N-series” calibration test course. At each designated location the vehicle was put into “ice picking” mode where it was allowed to float up and stabilize under the ice cap. We then localized the vehicle on the surface using the magnetic beacon, drilled a hole, and placed a numbered flag so that we could return to the location. Later in the day GPS measurements were taken at these same locations and the data were reduced to UTM coordinates that could be compared with the vehicle navigation record. With these data, fine-tuning corrections were made to the onboard dead-reckoning navigation (one of four nav systems used by ENDURANCE).

The navigation calibration test course for today. The small blue circles to the right are obstacles detected by ENDURANCE. The larger blue circles are “keep out” zones to avoid contacting the vehicle data tether with these hanging obstacles.

Reporting by Bill Stone

West Lake Bonney, Taylor Valley, Antarctica
Reporting from East Lake Bonney Basecamp

Today we tested the obstacle avoidance system. This year we have the high resolution Delta T sonar pointing forward for our sonde drop missions to identify objects, such as other science projects, hanging in the lake that may snag our fiber optic link to the bot. This is a change from last year, where had the Delta T facing down to map the lake bottom, so we wanted to see just what kind of objects the Delta T could resolve. Below are some of the results from our tests.

In this augmented reality visualization (part of the newly developed “situational awareness” system for ENDURANCE) the forward looking multi-beam sonar is swept under the ice cap at West Lake Bonney in the vicinity of the melt hole. We lowered three test “obstacles”—a steel ice chipper bar on a 10mm diameter rope; a 50 mm diameter pvc pipe; and a sack of lead weights on a 10mm diameter rope. At 15m radius we were easily able to detect them. The overhead red points are reflections off the underside of the ice cap. Interestingly, we also got returns from the surface of the super-saline chemocline at -14m depth (the yellow vertical lines near the bottom).

In this oblique image of the underside of the ice the bot is about 7 meters east of the melt hole—the underside edge of which can be clearly seen along with a long yellow vertical line on its west edge. This yellow stripe is the sonar return signature from a 50 mm diameter pvc tube that we lowered to a depth of 5 meters below the melt hole—so ENDURANCE is also able to detect plastic materials.

In this final test of the obstacle avoidance and detection system for ENDURANCE we maneuvered the vehicle to 50m radius and 7 meters depth. We removed all obstacles but the steel ice chipper bar (to simulate cables) and the vehicle was able to clearly detect it, along with the western side of the melt hole (the beam pattern from the vehicle was able to “illuminate” the back side of the hole and hence obtain ranges which show up as red vertical lines to the left of the image). The chipper bar shows up as the bright yellow vertical line projecting below the ice cap at the left of the image.

Reporting by Vickie Siegel

West Lake Bonney, Taylor Valley, Antarctica
Reporting from East Lake Bonney Basecamp

This morning we set straight to work on the ballast and got the bot neutrally buoyant pretty quickly. After the pre-dive check we lowered the bot into the water, ready to swim and perform some tests away from the hole. As the bot descended to the lower reaches of the hole for the first time this year it unexpectedly stopped just before it reached open water. We pulled out Maciek’s “fish cam”—a small underwater camera, camouflaged to look like a perch, with a live feed to a black and white monitor—and confirmed our fear. The bot was stuck. The hole had started to refreeze and now the last half meter was too narrow.

Rachel lowers the bot, complete with syntactic this time, into the melt hole for its first real swim this year.

Fortunately, it was only stuck in one direction, that is, it could not go down but it could still come up. So we brought the bot back to the surface, put the hotsies back in to work on the worst spots and ate lunch while debating our next move. It was decided that Bill would dive in and try to chisel the bottom edge with an ice chipper bar. After some hard work on Bill’s part, sure enough, good sized ice chunks started to float up and bob on the surface of the hole. After he made a couple circuits around the bottom edge, he came back up and we pulled him and the new ice chunks out.

The products of Bill’s underwater chipping efforts float to the surface to be scooped out.

Hopeful that Bill’s efforts widened the hole enough for the vehicle to pass, we dunked the bot again. Luck was with us and the bot made its way through the hole and down and under the ice. We proceeded to set up the visual homing beacon, a flashing light suspended over the melt hole. With the light in place, we ran some visual homing tests (for more on Endurance’s visual homing feature, see last year’s blog) and tested other basic behaviors: navigation, station-keeping and ice-picking. Everything is up and running!

Bill adjusts the visual homing light so that it points straight down the melt hole.

Shilpa inspects the placement of the visual homing light. The bot sees the blinking light with the upward looking camera at the top center and uses this light to navigate its way straight up the narrow hole.

Reporting by Vickie Siegel

West Lake Bonney, Taylor Valley, Antarctica
Reporting from East Lake Bonney Basecamp

To our delight, a large, irregularly shaped chunk of ice was floating on the surface of the melt hole this morning—the trombone melter had cut off the large flake Vickie had seen underwater yesterday. Removing this 1 meter long by half meter tall by 10 centimeter thick chunk of ice was a little tricky. We ended up screwing an ice screw into each end and lifting it out of the hole with the bot hoist.

This chunk of ice is all that remains of a large lump that was one of our problem spots around the bottom of the melt hole. We were able to saw it off with a trombone melter over night and it floated to the surface.

A close-up view of the ice chunk we sawed off, showing the elongated air bubbles that are present in most of the lake ice.

Once the rest of the morning ice crust had been broken up and hauled out of the hole, Rachel did some final adjustments with the syntactic mounts, Shilpa, Kristof, and Chris started going through the daily pre-dive procedures, and Bill and Vickie went out to get GPS coordinates of the Bot House for the programmers to use for the vehicle’s navigation. At some point in the middle of all this a helo landed and delivered our new, 2000 meter-long fiber optic cable.

A technician from McMurdo tests our new 2 kilometer long fiber optic cable. We will use this longer line for our missions to the far east end of the lake.

Our morning tasks completed, we regrouped after lunch and worked together to put the bot in the water and work on the ballast. Like last year, it was difficult to nail down how much lead we need to put on to achieve neutral buoyancy because of the microbubbles that form on the robot’s surfaces (see last year’s blog entry on microbubbles). Eventually we got it narrowed down and left the fine tuning for tomorrow.

Reporting by Vickie Siegel

West Lake Bonney, Taylor Valley, Antarctica
Reporting from East Lake Bonney Basecamp

After some hard work by our night shift melters, the hole looked much more promising this morning. We kept the Hotsies running as we got down to work. We ran through the pre-dive checklist and hoisted the vehicle, again without syntactic, above the melt hole. This time, instead of doing a full-vehicle dunk we kept the bot hanging above the hole and ran sonde up and down to check that we had successfully troubleshot the sonde camera communications problem. We had, and the profiler was functioning well, so we turned attention back to working on the hole.

We suspended the bot above the water and ran the sonde down into the water for testing.

The lake water is typically crystal clear but it is also super-saturated with gases. The vibrating Hotsies knock some of that gas out of solution, making the water in the melt hole very fizzy like a glass of soda, as tiny bubbles of gas escape the water. While interesting, the effervescence decreases the visibility such that we cannot see the bottom of the ice hole. In order to get a better feel for how the lower reaches of the hole were progressing, we decided to send a human diver into the water. Vickie and Bill assembled the surface-supply diving equipment and suited up in their drysuits. Vickie did the dive and found a few hook-shaped knobs of ice sticking around the bottom and chopped these off with an ice axe, helped the people on the surface measure the diameter of the hole along the bottom, and strategically placed a trombone melt finger so that it would cleanly cut off a particularly large flake of ice.

Suited up for the cold water, Vickie is lowered into the melt hole. She is the first woman to dive in Lake Bonney.

Vickie inspects the lower reaches of the melt hole.

Satisfied with our new melting strategy, after Vickie’s dive we spent the remainder of our time this evening installing the bot’s syntactic blocks so that we are ready to go with the next steps first thing in the morning.

Reporting by Vickie Siegel