Conclusion of 2009 Expedition

February 9, 2010

Thank you for following my blog and for your comments and questions. I have been aiming to write a wrap-up/summary post since long but other tasks have kept me from it. Here I  summarize our achievements for 2008 and 2009.

ENDURANCE (Environmentally Non-Disturbing Under-ice Robotic Antarctic Explorer)  is a hovering autonomous underwater vehicle.  It was developed under NASA’s ASTEP (Astrobiology Science and Technology for Exploring Planets)  program by Stone Aerospace as a platform for developing and testing technologies for discovery of life forms on watery moons such as Europa.

The robot ENDURANCE.

Europa is one of Jupiter’s satellites and there is strong evidence that it has a rocky core separated by saline liquid water from an ice/water crust about 80-170 km thick.

A visualization of Europa showing the ice crust (white), metallic core (brown) and liquid water (blue). Photograph available under public domain from http://photojournal.jpl.nasa.gov/catalog/PIA01130.

Some of the closest analogues to Europa’s  ice-covered saline ocean on earth are the lakes in the McMurdo Dry Valleys in Antarctica. The McMurdo Dry Valleys are the largest ice-free region in Antarctica with a total area of about 4800 square kilometers.  These dry valleys are a polar desert environment with mean annual temperatures of the valley floor between -30 Celsius to -14.8 Celsius and precipitation of less than 10 cm per year.  There are about 20 lakes in the Dry Valleys almost all of which maintain a perennial ice-cover (2.8-6.0 m) over liquid water. The low temperatures, the perennial ice-cover, and the presence of microbial life make the lakes in the Dry Valleys an ideal environment for testing the concepts and technology for discovering life-forms on Europa.

Map of the McMurdo Dry Valleys. Map available under public domain from United States Geological Survey. http://wy.water.usgs.gov/projects/antarctica/htms/map2.htm

One such lake, Lake Bonney, was chosen for field testing of ENDURANCE.

Photograph of Lake Bonney. The large body of snow at the back is Taylor glacier.

Aerial view of Lake Bonney. Lake Bonney is located in Taylor valley and consists of two lobes - the west lobe and the east lobe connected by a channel. The dimensions of the west lobe are approximately 3 km x 1.5 km, with a maximum depth of about 40 m. Under the ice cover lies a freshwater lens which extends down to a sharp halocline (a sharp salinity gradient) at a depth of about 12 m. Below the halocline is a salty body of water which reaches a salinity of about four times seawater at its greatest depths. Taylor Glacier, an outlet glacier of the east Antarctic ice sheet, flows into the west end of the west lobe.

ENDURANCE performed scientific missions over 10 weeks ( 4 weeks in 2008 and 6 weeks in 2009) in Lake Bonney. With ENDURANCE we  developed and demonstrated the technology for exploring under-ice lakes for life-forms.

1.  Our vehicle was able to reach within five meters of a specified target and came back to within five meters of the melt-hole after traveling a distance of as much as 3.2 km.

2.  We developed a visual homing algorithm that allows the robot to distinguish a blinking light source and  use it to rise through a melt-hole with tight clearances.

3.  We developed a profiling system that can collect bio-geochemical data and take lake-bottom images along the entire depth of the lake and at any specified location in the lake.

4.  We obtained bathymetric maps of the underwater part of Taylor glacier and the lake bottom using sonars. This is the first time that such a detailed map has been constructed.

5. We obtained close-up visual imaging of the underwater part of  Taylor glacier at selected locations.

If you are interested in more details, please visit my publications page.


Dec 2 – Profiling the narrows again

December 10, 2009

John thought that it would be a good idea to profile the narrows again so that he could see the variation in properties with respect to time. We profiled the narrows again yesterday. This time, the mission seemed very easy and went very smoothly. Below is a plot of the narrows (from Bill) using the data from the previous run.

Plot of the narrows from sonar data. The narrows refers to the narrow channel that connects the east lobe to the west lobe. In this view, we are looking from the east side. The points are color coded, so the green points are at a lesser depth than the blue ones. About 100 years back (1903), Scott's team travelled through this region and took various measurements. This channel was much narrower back then. (Sorry no numbers, Peter mentioned their values, but I don't remember them anymore).


Nov 26-27 – Fully autonomous missions

December 4, 2009

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.

Bathymetry coverage of West Lake Bonney obtained during 2008 missions.


Nov 25 – Exceeding expectations!

December 1, 2009

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 start every day with a short meeting. Everyone was looking forward to new discoveries.

The bot drove to the glacier melt-hole and surfaced up using visual homing. We added weights to the bot here to enable it to descend and be neutrally buoyant at a depth of about 22 m.

Images taken by the upward looking camera on the bot during visual homing to rise up the glacier melt-hole. During visual homing, the bot moves in a spiral pattern to search for a light source, finds potential targets, identifies a blinking light as the target, centers on it and then rises up the melt-hole. The water was turbid and the collimated light was barely visible unless the bot was right underneath it. The first image shows how the algorithm identified the light but failed to lock on to it since the bot was not directly underneath the light. On the arm of the spiral, the bot was underneath the light and locked on to it. The light appears bigger as the bot ascends the melt-hole.

After ballasting, the bot drove underneath the halocline to the glacier lip. A visualization showing the bot approaching the lip. The beams radiating from the bot are sonars whose returns help us construct this visualization.

The bot underneath the lip of the glacier. This mission kept us on edge all the time because we had to be very careful to not let the bot get wedged in the narrow cavity, yet get enough close enough to capture images.

Image of the glacier lip captured by the forward-looking camera.

Image of the lake bottom beneath the lip showed sediment. This confirmed that the glacier does not go down all the way to the bottom but floats.


Nov 23 – Amazing Taylor Glacier

November 25, 2009

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.


Nov 21 – Here we come Taylor Glacier!

November 22, 2009

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.

A view of Taylor glacier seen in the visualizer. This visualization is continuously updated as the robot moves, using the data from the robot's sonars. The red cloud at the top is the lake ice. The green cloud is the lake bottom. The vertical wall is the glacier face. It looks as if the glacier is floating on water with a 'lip' extending outwards. For visualization of the entire glacier face, see my entry from last year.

An image of the 'lip' of the glacier taken by the forward looking camera on the bot.


Nov 18 – To boldly go where no robot has gone before

November 22, 2009

Last few days were very successful for us. We fixed most of the hardware and software  problems and were able to finish profiling all the points in the lake. This was the main scientific objective of our mission and we were very happy to be done.

The weather cleared up and and Peter had arrived. John and Peter decided that they would like to get profiling data and bathymetric imaging of the narrows. The mission involved traveling all the way from the bot-house to east lobe of Bonney through the narrows. This was a bold mission and we executed with textbook perfection and efficiency.

We are working on data visualization and I will post pictures here when we have them done.

In today's misison, the bot drove all the way to east lobe of Bonney through the narrows.

Microbial mats at lake bottom in the narrows.

Rocks covered with microbial mats at lake bottom in the narrows.