Last Mission

December 25, 2008

Based on the data from previous missions and what we saw yesterday, we identified a section of the glacier face that was reasonably flat, and the water near it was deep enough for the robot to approach it safely. We decided to drive up close to this part of the face, and try to get some  images. The robot managed to follow the wall closely at a distance of about 2.5 m and we got some images of the glacier face. The visibility was poor and  the images were not very crisp, but we were still able to see the glacier face.

Image of the glacier face taken during our wall-following mission. Thanks to Kristof for this image.

Image of the glacier face taken during our wall-following mission. Thanks to Kristof for this image.

We are done with our missions today – we got all the data we wanted and we will start packing up tomorrow. We celebrated our success with champagne and raised a toast to everyone who had contributed to this project. This list is very long and I have mentioned some of the people in my previous blog entries, but I will try to make a more comprehensive list later.

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Glacier Mission 4

December 25, 2008

Dec 23

We performed two more glacier missions in the past two days and have explored most of the glacier face. Bill and I had been working on extracting and plotting the Delta T data from the past few days to see how the glacier looks like. The data from each mission consists of approximately 25 million (x,y,z) points that correspond to the sonar returns. Bill plotted up the points in 2D, and we used this to plan today’s glacier mission so that we would cover parts of the glacier face we had missed in the previous missions.

2D model of the glacier face from the Delta T data. The points represent the Delta T renage returns. The grey line was our approximation of the glacier face. Thanks to Bill for the plot.

2D model of the glacier face from the Delta T data. The points represent the Delta T range returns. The grey line was our approximation of the glacier face. Thanks to Bill for the plot.

Today’s mission consisted of scanning the entire glacier face with the Delta T – we had the robot facing the glacier wall at all times while moving sideways. This was a relaxed mission for us since we ran the entire mission as an automated script and all we had to do was sit back and watch the data and the visualizers.

Bill plotted the data from all the missions to get an amazing view of the glacier face and lake bottom near the glacier.

2D model of the glacier face. The data from today's mission was added to the previous model. This shows that we obtained converage of the areas that we had previously missed.

2D model of the glacier face. The data from today's mission was added to the previous model. This shows that we obtained coverage of the areas that we had previously missed.

A plot of the Delta T data showing the lake bottom, lake ice and glacier face. The lake ice is seen on the top in dark blue while the green points at the bottom show the lake bottom. The glacier face does not come all the way to the bottom at all places but floats.

A plot of the Delta T data showing the lake bottom, lake ice and glacier face. The lake ice is seen on the top in dark blue while the green points at the bottom show the lake bottom. The glacier face does not come all the way to the bottom at all places but floats.

We also took a picture of lake bottom with our profiler camera.

Picture of the lake bottom in a shallow region near the glacier taken by the profiler camera. It appears that this is the interface between sand and ice.

Picture of the lake bottom in a shallow region near the glacier taken by the profiler camera. It appears that this is the interface between sand and ice.


Transformations in water and ice

December 25, 2008

Dec 20

The water and ice have undergone significant changes in the past week. The water is very cloudy and murky now and the visibility is very low. The upward looking camera of the robot is unable to see the blinking light even from a depth of 2 m. This means that the chances of obtaining good images of the glacier face are slim since we will have to approach the face closer than 2 meters.

The stream next to our campsite is now roaring, and a waterfall is flowing down the glacier. The lake water is probably murky because of all this inflow.

The lake ice has also transformed since we came here. It used to be very smooth and it was hard to walk on the ice without stabiliziers. All the water flowing in has made the ice very thin at places, and Maciej fell in through the ice at one place. The ice is now much rougher with many ditches and protrusions that make a glassy sound as they break when we walk on them. Driving the ATV has become very interesting since we have to avoid the bigger  and deeper ditches.


Glacier Mission 1

December 25, 2008

Dec 19

We ran our first glacier mission today. We want to use sonar data to develop a profile of Taylor Glacier where it descends into Lake Bonney and to build a mosaic of glacier face images taken by the forward-looking camera.

Picture of the glacier. We want to profile part of this glacier that is underwater. Thanks to Vickie for this picture.

Picture of the glacier. We want to profile part of this glacier that is underwater. Thanks to Vickie for this picture.

Today’s mission was mostly exploratory – we had absolutely no idea what we would find. Many icebergs were visible on the surface and we were wary of running the robot into them while appproaching the glacier. We approached the glacier slowly while stopping at places to rotate the vehicle to do a full scan. The robot has a multi-beam sonar, Delta T mounted at its front. The Delta T consists of 480 sonar beams forming a two dimensional “fan”.  Each ping consists of the range returns and intensities of 480 beams. The ping rate is 3-4 Hz.  Thus, the Delta T returns can be used to visualize a wall or an obstacle in front of the robot. We can rotate the robot to get a 3D view of the surroundings.  The Delta T visualizer along with  a simulator developed by Shriram Ayer with Andy Johnson  at the Electronic Visualization Laboratory form excellent visualization tools that help us in decision making.

We had plenty of excitement today. Bill and Vickie were out tracking the robot with a radio beacon and flagging specific locations to obtain their GPS coordinates. The ice near the glacier had gotten thin and uneven due to the warming  effect of the waterfall created by glacier meltwater.  A wheel of their ATV went into an ice ditch, the ATV rolled over and Bill’s leg got stuck under it. The ditch had a thin layer of ice on it with water underneath it and Bill’s leg got soaked. Bill had to come back to the Bot-House to change into dry clothes.

We did not find any icebergs under-water, but we found that the  glacier face had a cleft with a cavernous region beneath.  Below is a screenshot of an image from the Delta T visualizer.

Glacier face as seen in the Delta T visualizer. Thanks to Chris for this screenshot.

Glacier face as seen in the Delta T visualizer. Thanks to Chris for this screenshot.

We drove the vehicle close to the  glacier face in  the expectation of getting good images, and we ended up driving the vehicle into the cleft. The depth of water below the vehicle was about one meter and this led to loss of DVL lock. DVL (Doppler Velocity Log) is one of our primary navigation sensors and is crucial in estimating the position of the robot. If we lose DVL lock, the position estimate quickly drifts and the vehicle loses track of its correct position. We had discussed this situation before the mission and took swift action. We switched the mode to joystick control and Chris used the joystick to drive the vehicle back off the ledge. The position estimate had drifted by about 20 meters during that time. We then drove the robot back to a known location that Bill and Vickie had previously marked. We used the GPS coordinates of this location to reset the robot’s pose estimate and the robot was able to drive back to within 2 meters of the melt-hole.

Below is a snapshot of the visualizer taken when the vehicle was moving away from the glacier face.

Screenshot of the run-time visualizer. The robot is in the center of the screen with sonars shooting off of it. The glacier face is seen as the wall of green dots to the left. The line of yellow dots is the lake ice. The circles are locations where the robot rotated to perform a scan.

Screenshot of the run-time visualizer. The robot is in the centre of the screen with sonars shooting off of it. The glacier face is seen as the wall of green dots to the left. The line of yellow dots is the lake ice. The circles are locations where the robot rotated to perform a scan.

Below is a picture of the glacier face taken by the forward looking camera when the robot was very close to the nose before getting into the cleft.

Photo of the glacier face taken by the forward looking camera.

Photo of the glacier face taken by the forward looking camera. Thanks to Kristof for this image.

I extracted the DeltaT data and plotted it up after some cleaning up.

Plot of the Delta T data. The lake bottom is seen curving into the glacier face at the right.

Plot of the Delta T data. The lake bottom is seen curving into the glacier face at the right.


Profiling Missions Complete

December 25, 2008

Dec 18
We finished our seventh and final profiling mission today. Below is a picture of a rock on the lake bottom taken by the profiler camera. Thanks to Kristof for sorting through the pictures.

Picture of a rock at lake bottom taken by the profiler camera.

Picture of a rock at lake bottom taken by the profiler camera.

Below is a picture of west-lake Bonney that shows the grid points at which we have finished profiling. Thanks to Vickie for this picture. The interesting results will emerge after  John and Peter have analyzed the data. If you are interested, you can keep track of their work  here and here.
Picture of west-lake Bonney showing the grid points at which we have finished profiling.

Picture of west-lake Bonney showing the grid points at which we have finished profiling.