Balloon Mapping I

Introduction

This week we had the goal of launching our first balloon to begin learning a bit more about aerial photography and the processes behind aerial mapping. This was actually a project that we had been working on for some time now. Earlier in the semester we worked to design a housing to attach the camera to the balloon. With that exercise we took care to keep our payload low so our balloon would have no problem carrying it to the proper height. The class was excited to get started with balloon mapping and take a break from priory activities. The day we chose to launch our balloon wound up being pretty windy and it would be interesting to see how this affected our mapping exercises.

Methodology

As stated earlier, we spent some time earlier in the year creating our camera housing so that was ready to go right away. We met during our normal class period and then split out into different smaller groups in order to get the launch going. One group got the helium, one group measured the string in 100 foot increments, another got the camera ready. Once we all met in the garage with our tasks complete we spent about 15 minutes filling the balloon with helium (Figure 1). Then we attached the camera housing and the balloon was ready for launch (Figure 2). Included in the housing was a GPS tracking unit so that we could georeference the photos after they were compiled on the computers.

Figure 1: The filling of the helium balloon

 

Figure 2: Balloon with the camera housing and gps attached

 

We walked out to campus mall and got the full effect of the wind on the ground and could only wonder what was going on 400 feet above us. When we were ready to launch we had to pay close attention to the string as we let the balloon out. The string attached to the spool was marked at 50ft intervals with a black mark, and then at 400 feet there was a red mark to signify the end. This was helpful, as it could tell us just how high the balloon was (assuming it went straight up).

We released the balloon into the air and found that the winds were a large hindrance to the balloon gaining altitude. I think the balloon was only about 100 feet in the air and was nowhere near directly above us (Figure 3).

Figure 3: Balloon moving more laterally than vertically.

 

Despite the lack of altitude we still walked the balloon around campus mall and along the river front. When we decided to walk the balloon across the bridge is when issues began to arise. The wind was battering on the balloon and eventually it was too much for the string to handle and our string snapped. Luckily for us though, the camera housing and gps also came detached from the balloon and fell into the river. The camera housing kept it afloat however, and we were able to retrieve it from the river with little issue.

Results/Discussion

When we got back indoors it was time to upload our photos to see if any were usable. The good news is that we got over 2,000 photos from the mapping exercise. However, a very limited few were usable. Photos that were taken at too much of an angle provide too much distortion for photo stitching. But with a sample size of 2,000 we were able to attain a good sample of usable images (Figures 4, 5).

Figure 4: One of the pictures I used to stitch the map

Figure 5: One of the pictures I used to stitch the map

 

When it came to mosaicking our images, a large portion of the class decided to use the freeware website called MapKnitter. This is supposed to be a very user friendly, easy to use website. After viewing a few tutorials I was able to get the hang of it and was able to stitch a few photos together. However, with MapKnitter you have no way of georeferencing your photos, so adding a true location becomes very inaccurate/un-reliable. Your resulting photo stitching image will be a pretty image but will not be up to reference standards (like an orthophoto would be) (Figure 6).

Figure 6: The resulting map from stitching three photos together.

 

Conclusion

Overall this was a great introductory exercise for many reasons. We learned the basics of photo mapping, map stitching, and most importantly the importance of wind and weather forecasting when conducting an exercise like this. Next week we are planning on launching the balloon again, hopefully in better conditions to get some more height, and more usable photos.