Field Activity 10: Balloon Mapping II

Introduction
This follow-up activity is very much the same as the previous activity. Using a balloon and a constructed rig, aerial photos were taken of the UW-Eau Claire campus. Once the data was collected, the images were went through and georeferenced, to be put into a mosaic and thus creating an aerial map of the campus. There was much more work put into this activity, as the last activity was just a test run of sorts.

Methodology
Much of the preparation for this activity was just as it was in the previous activity, however there are a couple noteworthy alterations. The first is that there was essentially no rig for this balloon mapping launch. It was decided that the rig contraption was not essential to the quality of the image collection (merely a very weak backup for a crash landing) so the camera was just secured to the balloon with tape and string, hanging just below the balloon. Another addition to this launch was a stabilizing wing, which was taped to the camera. This addition ensured that the camera would stay at a relatively stable position, and wouldn't be rotating constantly. One final difference was that we filled the balloon with more helium, to ensure that it would rise faster and stay more stable in the air.

After making these revisions and preparing the activity just as before, the image collection began. The balloon was released in the middle of the campus mall, and the length indicators on the string was observed to make sure the balloon reached the desired height (400 meters). Once the balloon was at the correct altitude, the class began leading the balloon around campus as the camera snapped aerial images every second (Figure 1 shows an aerial photo of our starting location). The weather was much more cooperative, with much less wind. Because of this, the class was able to collect aerial photos of the entire campus without much difficulty. We started in the middle of the campus mall, walked around the new Davies Center, walked around Phillips Hall, cut back through the mall to the footbridge, and then walked around the Haas Fine Arts Center. Once that was completed, the balloon was brought down and taken back across the footbridge, where it was once again launched to continue data collection. Because the weather was so favorable, the team lead the balloon from the footbridge to Upper Campus, collecting aerial images the entire time.

Figure 1: Campus mall starting location (note the string on the right side of the image)

Once the data collection procedure was completed, we began to go through the images and pick out suitable images for georeferencing. Georeferencing is a procedure that positions the aerial image in the correct geospatial location by referencing a previously projected raster image (or by using Ground Control Points). For this activity, we collected several Ground Control Points, which are points that can be easily spotted on an aerial image. A team of students went around the campus with GPS units and collected the coordinates of suitable Ground Control Points (in this case, light poles were the most reliable object). We would then use these points and reference them with the corresponding objects on the aerial images so that an accurate aerial map can be created by making a mosaic. This is merely the process of forming one large image of several overlapping georeferenced images. Because the class covered such a large area, it was decided that the campus be split up into six different sections to be georeferenced by the different teams within the class (Figure 2 displays these six different sections). Each team would then submit their mosaic to create the campus aerial map.

Figure 2: The six different sections to be georeferenced

Results
Overall, it was a very successful activity. The images that were gathered were all great, all that was required was to sort through them to find the best ones to be georeferenced. Figure 3 shows the mosaic that was created for section four (the section that my team was to georeference). Though the mosaic isn't perfect, I think that it turned out quite well considering the resources and procedures that were used to produce this result.

Figure 3: The completed mosaic of section four

Discussion
I thought that this activity was a great success, especially after comparing it to the previous week's activity. The weather was perfect for what we were trying to achieve (there was no wind pushing the balloon around), and there were no other set backs to be fixed. We were all very satisfied with our results.

Field Activity 9: Beginning Balloon Mapping

Introduction
This activity continues the work that was started in a previous activity (Activity 3). In that activity, we planned and created rigs to collect aerial photos of UW-Eau Claire's campus via balloon. Using the careful planning and constructing that was achieved during that activity (and after waiting for it to warm up a little) we were then able to finish our project.

Methods
There were several processes that had to be completed before we could actually begin the balloon mapping. First and foremost, the balloon had to be filled with helium. For this activity, we used a special weather balloon that was able to carry a payload of up to 3 lbs. While the balloon was being filled it was important to be sure that someone was always holding onto it, because it would be quite tragic if it floated away without even being used. As an extra precaution, we filled the balloon inside of the shed by Phillips Hall. Figures 1, 2, and 3 capture this process and display just how large the balloon is. Figure 3 also displays the next step, which was the securing of the balloon's opening. First, the opening is tied shut with a zip tie, then the remaining length is wrapped through a rubber ring, and then two more zip ties secure the extra length back to the original. The ring is necessary because the string will then be clipped to the balloon with a carabiner.

Figure 1: Preparing the balloon.

Figure 2: Filling the balloon with helium.

Figure 3: The balloon is filled, and the opening is secured with zip ties. A
rubber loop is also attached so that the string can be clipped on with a carabiner.

While the balloon was being filled, a team of students were required to measure out the string that would be secured to the balloon. Our target height for the balloon was 400 meters, so the team marked the string every 50 meters, and made the 400 meter mark a different color than the rest. Figure 4 shows their technique in this matter. After the string was measured, it was tied to a carabiner and then clipped on to the ring that was attached to the balloon. We then secured a GPS unit to the ring, and then tied the rig to on the string just under the balloon. After all of this preparation it was time to launch the balloon. In the middle of the campus mall the balloon was prepared for launch. The camera within the rig was set to continuous shot (so that it would take a picture every second), and then the rig was sealed. The balloon was then released, while the students holding the spool of string kept watch for the length markings (Figure 5).

Figure 4: The string is marked in this manner every 50 meters

Figure 5: After releasing the balloon, the string is observed to find the markings

Once the balloon was at 400 meters, it was pulled around campus so that images were taken of most of the campus mall (Figure 6 shows the balloon and rig in flight). It was important to keep an eye on the string, and navigate away from tall objects like light poles, trees, and tall buildings. The class did this entire process twice: the first time with a standard digital camera, and a second time with a flipcam that took video footage. After the entire process, all of the data was uploaded onto a computer. We were then required to go through all of the images and select several that were perpendicular to the ground (this creates less distortion on an aerial map). Once enough suitable photos were selected, they were georeferenced and then mosaiced using either ArcMap, ERDAS Imagine, or Mapknitter.

Figure 6: The balloon, rig, and GPS unit in flight.

Results

Because it was such a windy day, there were little suitable photos for the Mosaic process. There were several photos of Eau Claire's city horizon (Figure 7), but there was little to work with in regards to aerial mapping. However, each of us worked with what we had and a rough mosaic was created. Figure 8 displays  an elementary aerial map that was created using Mapknitter.

Figure 7: With so much wind, photos such as this were quite numerous

Figure 8: An aerial map using four aerial photos and Mapknitter. The faded background is a reference image.

This was merely the results of our first launch, however. Our second launch was even more eventful. While we were leading the balloon across the footbridge, the string that was attached to the balloon snapped. The rig fell into the river, and the balloon floated into the distance. Luckily, the rig was a Styrofoam case and the camera was waterproof. We were able to recover both, so the data was acquired (with similar results to the previous launch).

Discussion

I thought that this activity was very exciting and a great learning experience. It was really cool to go through all of this work and then finally see the fruits of our labor. Though the wind put a damper on our plans, and the balloon dropped its payload the second time, I think that this activity was quite successful. We will be continuing this work in our next activity, hopefully with even more great results.

Field Activity 8: Final Land Navigation

Introduction
This was the final activity in a large span of navigation activities. We began this learning experience by creating topographic maps of our study area. After this, we proceeded to learn how to navigate using the topographic map and a compass, and finally with a GPS unit. During this activity, we were to navigate to every single checkpoint on the property (15 points total), using a GPS and our maps with each checkpoint plotted. To add to the fun, each participant got an extra piece of equipment: a paintball gun. Throughout the activity we had to avoid being ambushed by other teams (or try to attack other teams), all while navigating to the checkpoints.

Study Area
For each of these activities, the class met at the University's Priory. This property is off campus and is on a 112 acre plot of forested land, perfect for navigation activities. While this location was perfect to learn these navigation techniques, it is also home to the University's Children's Center. Because we were outfitted with a paintball gun and a full face mask, we had to be careful where we navigated during the activity. Even though all the necessary authorities were notified of this activity, we did not wish to start any panic or cause any concern. Our professor stressed how important it was to avoid any areas within sight of the priory during the activity. He also advised us to stay clear of areas within sight of the highway to the north of priory, and the house to the southeast (See Figure 1 for restricted zones). With all of this in mind, as well as the massive amounts of snow on the ground, it was quite a terrain to navigate.




Figure 1: Highlighted areas were the restricted zones during this activity

Methodology
Throughout this activity, we used skills that we had learned from the previous three weeks of field activities. We used navigation techniques learned from prior activities to navigate the terrain for one last time, this time trying to locate each checkpoint. For starters, we used the same map that we had made in the first navigation exersize, though it was slightly modified. This time we had to deal with restricted zones, but we also had the locations of each checkpoint on our map (Figure 2).



Figure 2: Our Starting Map

Just by looking at the map, it is easy to tell that each team would have a lot of ground to cover. After preparing for the trek (familiarizing ourselves with the paintball guns and the masks), we met up with our teams to try and come up with a strategy. Each participant used a tracklog feature on their GPS to track their navigation route once the activity was complete. Looking at Figure 2 for reference, each team started at point 1A. Our team decided to avoid traffic by going to point 6b first and then navigating around the priory to complete the course in a counter-clockwise direction. However, we were not the only team to come up with this plan. Our professor instructed us to wait 5 minutes before we could open fire, so we got to the first point with no conflict. However, after reaching that point our team lost our map so we negotiated with another team and began to work together. We then navigated by using our GPS units and our map. The basic navigation technique that we used was just looking at the lay of the land and comparing that with the topographic map to find each point. Once we were certain that we were close, we utilized the GPS units to compare more exact coordinates with the points on the map. At each checkpoint, we took a waypoint with our GPS units to mark that we had successfully navigated to that checkpoint. Figure 3 shows our teams route, as well as the waypoints at each checkpoint that we successfully navigated to. Figure 4 shows my individual tracklog, and Figure 5 shows the tracklogs of the entire class.

 

 

 

Figure 3: Team Tracklog

Figure 4: My Tracklog. As can be seen in the image, my GPS had some PDOP issues

because sometimes the points of the tracklog weren't quite accurate.

 

Figure 5: The tracklog of the entire class. Several different routes can be seen,

though they all seem to make the same loop.

 

Discussion
Throughout the activity, our team encountered several problems. The first and most significant problem was the loss of our map after reaching our first point. Without a map to use, we would have been quite hopeless. The map was so important because it marked where each point was, and it had a coordinate grid as well. With nothing but a GPS unit, we would have been clueless as to where to navigate. Luckily, another team agreed to help, and we continued the activity together. Not long after this, as we were navigating from point 2B to 6, we ran into another group and got into a firefight. Other than this, we ran into few other groups. Another big problem that occurred was that we were in a crunch for time towards the end of the navigation. As we navigated from point 3a to 3, we realized that there wasn't much time left. For some reason, we had trouble finding point 3 as well, so this didn't add to the situation. In the end, we decided to take a waypoint because we knew that we were quite close (this is why there is a waypoint between 3 and 2a in Figure 3). We then traveled to point 2a and then back to 1A just to find out that we still had a couple minute, and probably could have still made it to the remaining two points. I think that we relied too heavily on the map and didn't use the coordinate grid and GPS coordinates to their full potential. Also, if we had brought along the exact coordinates of the checkpoints, it would have been much easier to compare to the GPS location and we could have navigated more accurately.

Conclusion
Overall, I thought that this was a fun activity to be a part of. The addition of the paintball guns transformed the activity entirely. Not only were our navigational skills required, but we also had to stay alert for other teams that may cross our path. It added a little excitement, and I think the bruises and paint splatters that were compared afterwards can attest to that fact.