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.