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.
Bill and John cleaning the dirt from the profiler pump's impeller blades.
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.
Top view of the underwater part of Taylor glacier (North up, East right). The light blue cloud at the right is the glacier. The green cloud is the lake bottom.
There is morain on the north side of the glacier. This cross section of the glacier shows the moraine.
The middle part of the glacier has a "lip" or a protruding part at a depth of about 16 m. I posted some images in my previous post. We do not what is beneath the lip. It could be a cave. The grounding line may be beneath the lip. We will explore this in a couple of days by ballasting the bot heavy enough to get below the halocline.
Image taken by upward looking camera on the bot. The lake ice in some parts near the glacier was thin and sunlight penetrated through it. Our melt-hole detector algorithm, that identifies potential light sources for visual homing, had a field day finding so many light sources.
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.
Bill, John and Peter mounting the winch for the gantry at the glacier melt-hole.