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Monday, April 15, 2013

Lab 9: Balloon Mapping

Introduction
Due to the complex nature of balloon mapping, the task was broken up into two parts that spanned over two weeks of class. The first week, outlined by this blog, entailed experimentation with the mapping rigs created in week three. The purpose of experimenting with the different rigs prior to collecting the final imagery that would be used to create a seamless, mosaicked map of campus was to observe how the rig behaved when deployed to 400 feet and troubleshoot any problems that may arise. Preliminary methods of how images generated from the balloon mapping rig are to be processed and mosaicked will also be outlined and discussed.
Methods
            Because of the short window of time that spanned our three hour class period that required the assembly, transport, launch and retrieval of the rig; delegation of duties was essential. The class was broken up into small groups (one-four people) who were assigned to be responsible for a single element of the rig launch. To document all aspects of the experimentation day, fellow classmate Tonya O. was outfitted HD video camera to provide video footage.
            The rig used for balloon mapping would resemble the HABL platform. The Styrofoam box would hang from the helium filled weather balloon and would house a Lumix digital camera that was set to continuous shoot mode. Also tested within the same rig housing was a Flip Camera that was set to shoot video. Connecting the balloon/ camera rig to the pilot on the ground would be 400 feet of rope that was marked off in 50 foot increments to allow for observation of the balloons altitude. Once the balloon reached its service altitude of 400 feet, the time was observed to be compared to date stamps on the pictures to confirm the camera rig was shooting imagery at the correct altitude. Once deployed the pilot controlling the balloon from the ground was to experiment with different flight paths by walking around the campus courtyard.
Figure 1: Shown here are teammembers inflating the weather balloon used for the mapping of campus with helium.
Figure 2: Shown here is the balloon mapping rig suspended from the helium filled weather balloon.
Figure 3: Shown here is the balloon mapping rig at its maximum altitued (around 100ft). Notice its horizontal drift from being directly overhead due to the wind out of the NW.  
 
            Imagery generated by this experimental launch were to be mosaicked using three different approaches outlined by Dr. Hupy. The methods to be tested were a freeware website called Mapknitter, a geospatial raster processing software program called ERDAS Imagine, and ArcMap Image Processor. For each of the programs, imagery was uploaded as .jpeg files.
            Our Team consisting of Tonya O. and Chuck P. stitched the balloon imagery together using Mapknitter. After uploading an image into Mapknitter, tools within the program allowed for image manipulation. Once uploaded and projected over a  Google Earth basemap of the UWEC campus tools such as rotate (to scale the image), distort (to shift the image by dragging the corners), and toggle (to adjust image transparency) were used to manipulate the image to mimic that of the basemap.
Discussion
            After much discussion as a class, we decided to use a rig similar to the HABL platform instead of the plastic bottle prototypes generated for lab three in class. By incorporating the HABL rig into the balloon mapping exercise, testing for both could be done simultaneously. The first observation that was made was that the camera would have to be firmly secured within the Styrofoam rig housing to prevent the lens from slipping out of the slot cut into the bottom of the rig due to any turbulence encountered at 400 feet. The second observation made was that nearly windless conditions would be necessary to both get the balloon to reach 400 feet directly overhead, and to also keep the camera steady to prevent it from swinging like a pendulum. Although the line connecting the balloon to the ground snapped from such high winds, we decided that higher pound test line would not be necessary when flying it in calmer conditions. Any image that was taken as the camera was swinging would obviously be blurry, but also it would be oblique because it was not pointed directly downward; thus useless for image mosaicking. Although windless conditions would be optimal for image collection with the balloon, we observed that the addition of some sort of fin on the bottom of the rig would help mitigate its effect and allow us to fly the rig even if there was a slight breeze. It was also decided that the Lumix digital camera would be used because after processing the images from both the Flip camera and the Lumix, the Lumix took higher quality imagery.
Figure 4: Shown here is a low oblique image of UWEC taken by the rig as it swung out of control underneath the balloon.
 
            Aside from observations made from the experimental flying of the balloon, many were also made in regard to image processing. I found Mapknitter to be extremely straightforward and user friendly but I was not able to achieve the level of accuracy needed for this project by using it to mosaic the images. Although it generated cartographically pleasing maps, it lacked the georeferencing component needed to tie our imagery to ground control points which is our end goal, so either ERDAS Imagine or ArcMap Image Processor will be used for mosaicking the second time. Both programs allow for georeferencing so either will suit our needs.
Figure 5: Shown here is the mosaic output from MapKnitter overlayed on a Google Earth base map.
 
Conclusion
            Even though Mother Nature won out and snapped the line at the base of the balloon due to such extreme wind conditions, we were able to gather valuable data that will be applied to the final launch of the balloon mapping rig. By applying the knowledge gained by this experimental day, I have no doubt that a seamless, high resolution mosaicked map of campus will be generated.
Shown in the video above is the balloon rig plummeting into the river when the 400 foot tether snapped at the base of the balloon.
 

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