We took Saturday off to celebrate Thanksgiving. I woke up around noon to see almost everyone already up and to be greeted cheerfully by Emma. Peter was cooking turkey (apart from other stuff) , and Kristof was working on a veggie casserole. After breakfast, I decided to hike down valley to the east end of the lake. Emma decided to accompany me and we had a great time. It was very beautiful and quiet there – it was as if we had traveled back in time. It is rare to get such a sense of solitude and freedom. We came back and enjoyed a very nice Thanksgiving meal and desserts cooked by Bill and Emma.
We finished our major science missions – profiling and glacier exploration. Our next goal is to obtain reasonably good bathymetry of the lake bottom. We obtained partial coverage last year, and we will attempt to fill in the gaps this year. We ran fully autonomous missions with zero manual intervention during the missions. These missions are easy for all of us and it was nice to relax and just watch the data flow. More on this later.
We had an awesome day today. The first mission of the day was to try and get pictures of the grounding line of Taylor glacier. We had attempted this yesterday, but were not able to get the bot close enough to lip of the glacier to take pictures. We still could not get close enough to get pictures of the grounding line, but we were able to take pictures of the lip and confirm that it was ice, and of the lake bottom and confirm that it was sediment. In addition, we saw some interesting low temperatures (less that -4 degree Celsius) during our sweep, indicating fresh water inflow from the glacier. The second mission was an automated bathymetry mission where the robot performed a side sweep of the shore. This mission was entirely automated and worked perfectly. It was very nice to sit back and watch the data flow and the visualizations. I will let the pictures do the rest of the talking.
If you are interested in the details of the visual homing algorithm below, please visit my publications page.
We did not have internet for the past week. I will slowly post the happenings from last week in the next few days.
In the current implementation, we spool the profiler down manually using reading from an altimeter. The altimeter tells us the height of the profiler from the bottom of the lake. Altimeter readings are not received continuously – sometimes we do not get readings for many seconds. This is possibly because of the changing reflectivity of the bottom, though the real cause is still a mystery to us. Hence, spooling down the profiler is partly an art. We need to remember what the starting height was and how much we have spooled. We also used the camera images of the bottom to estimate how far we are from the bottom. Our estimates were a little off at one grid point yesterday, and we spooled the profiler down too much. This caused it to run into the ground. The pump on the profiler ended up pumping a lot of mud through the rest of the mission, making the scientific data useless.
Hence, we repeated much of the mission from yesterday. We cleaned up the dirt from the impeller blades of the profiler pump in the morning.
We again worked a 14 hour day, but this time we were successful in getting good data. Peter watched the data all day and pointed out some interesting facts. The temperature showed a dip at a depth of 20 m, indicating an inflow of fresh water from the glacier at that depth. Further, the inflow has now reached as far as the bot-house.
Bill made some visualizations of the glacier from the sonar data. No one has ever seen the underwater of the glacier in this detail, and it was very exciting for us to see this. I will let the visualizations speak from themselves.
John, Peter and Bill mounted the winch for lifting the bot on the gantry at the new met-hole. John left for McMurdo in the evening.
One of the science objectives of this year’s mission is to perform exploration of Taylor glacier, including sonar and visual imaging. This will require the robot to operate below the halocline. The halocline is at about 16 m depth and forms the dividing line between the freshwater lens at the top and the highly saline water at the bottom. The higher salinity of the water below the halocline means that the robot has to be ballasted with about 200 lbs of extra weight to be neutral in this layer. Since we do not want to unnecessarily disturb the halocline, the robot will start above the halocline from the bot-house. It will then drive to another melt-hole near the glacier another melt-hole close to the glacier, where we will lift it out partially with a gantry and ballast it.
Maciej, John and Peter have been working on getting this melt-hole ready for the past few days. They are almost done, and have the gantry installed today. The gantry will be used for partly lifting the bot out of the melt-hole.
We performed a profiling mission on a high resolution grid near Taylor glacier. The hope is that a detailed analysis of water properties will help reveal the source of fresh water inflow into the lake. We worked a 17 hour day. It was an exhausting but exhilarating day and moved us one step to closer to finding the source.
Below are some pictures from this year. For a complete visualization of the glacier face, see my entry from last year.