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.