The methods we have been looking in to for taking air images have apart from the kite, so far been highly technological advanced, expensive and still a progressive field. There are some occasions where money will not allow, or the scope of such equipment is simply not necessary, and there for methods like the kite are more suited. So we used a helium balloon to capture images from above ground, in order to be able to mosaic them to ascertain and accurate, detailed, and well presented image of the surveyed land. For the first part we were concentrated on how the fieldwork was carried out, with the idea to spend an extended period of time looking in to and putting in to practice methods of putting together and displaying the images.
We were also able to go out to the field for a second time with the unmanned aerial vehicle (UAV), as the first time was pretty much a test for the new machine. So now, were were able to witness the drone in it's full flight and the technology and preparation it takes to achieve data collection over a period of time, in order to collect images over a specified area.
Study Area
We used the same study area as was used in the previous exercise where we were introduced to some Unmanned aerial systems, in Eau Claire's soccer park, because of the open green space.
Methods
The initial equipment set-up was to do with the balloon itself. A large strengthened rubber balloon (obviously significant;y larger and more durable than your every day balloon) was inflated using a helium tank. This was then tied at the bottom and attached to the same spool that we attached to the kite in a previous exercise. The balloon after inflation and before being launched is shown in figure 1.
Figure 1: The balloon we would be using to gather aerial imagery, post-inflation and before any imaging equipment was attached.
We then need to attach cameras to the balloon in order to take photos of the terrain. The same "harnessing" device was used as we did for the kite. This involved two digital cameras being attached to stabalisers, and then string to be attached to the cord of the spool on the balloon. Unlike the kite, this did not require a significant amount or height to the balloon first, as it was not going to be diving down to the ground as can happen with a kite. The balloon with the camera harness attached is portrayed in figure 2.
Figure 2: The balloon in the air with the two digital cameras attached for taking images using a stabalising device.
We then as a class walked with the balloon around or field site, taking it in turns to hold the balloon and direct, so that we covered the majority of the field site and would acquire multiple images. The balloon was then reeled in and the cameras and stabalisers attached, the SD card from the camera was then used to import the images taken on to a computer system, ready to be used for the mosaic.
The Unmanned Aerial vehicle (shown in figure 3 below) is out of the skill range of the majority of those in the class and so the flight and data collection was very much lead by the class professor, and we were observing and taking notes. We were able to see the laptop (Shown in in figure 4 below) that was used at the control section and it was explained to us how a designated checklist should be made prior to the flight so as to minimise the room for error and make sure everything is working as it should, especially when you are working with such expensive equipment.
Figure 3: The Unmanned Aerial Vehicle at it's starting (and finishing) point before taking flight over the field you can see.
Figure 4: The Laptop set up during the flight of the unmanned aerial vehicle used to observe the flight path to make sure it matches with the pre-set path.
We learned the importance of looking in to the topography of the area whilst setting up the flight, as the vertical GIS on the device is not great, and you want to make sure you are going to clear trees etc. On the laptop there is a survey grid so you can follow the path of the device and make sure it is going the same way as the pre-set course. The importance of having two people was emphasised and displayed, so that one person to watch the flight and keep control from the laptop and another to be watching the device int he air and ready with the remote control if necessary.
As part of the follow up to the fieldwork the class was to look in to and play around with ways of collaborating all the images gathered, so that we could see the whole study area, which is ultimately what you are aiming to do with this sort of fieldwork. We found that Photoscan, a program used by 3D artists and graphic designers, worked well. When adding the images we had to eliminate those that were of poorer quality of were of the cameras initially reaching it's desired elevation, if you were to have taken many more photos over a much larger area then we had, the process of putting them all together could run for a very long time. The images were then aligned, which created a point cloud, which I have previously talked about in the UAV mission planning assignment. Building a "Mesh" of these images created a TIN, which we have created from our own data modes before. IN order form images to be georefferenced, we would have to export the TIFF in to ArcMap, then alongside the base map of the are you studied the georeference tool would be used, where you would add control points. Figure 7 below, shown the result that a class member ( http://fieldmethodreports.blogspot.com/ ) managed to put together form our images. You can see now how we can cover a much wider are. However there are some slight distortions, particularly if we look at the outer parts where it appears more curved.
Discussion
In figures 5 and 6 below you can see two of the images that were taken using the cameras attached to the balloon. Figure 5 in many ways can be used to compare and contrast with the image that was taken using the kite over the same area, except that this time it is not covered in snow. We ca also see how much higher up in the sky the camera was able to go. Figure 6 shows that with elevated height you can see more of a wider frame, but the slight angle of the photograph does also highlight the problem with using a more basic piece of equipment like the balloon, as the cameras may not stay as stable when attached using the harness and with the effect of the wind.
Figure 5: The study site from above using the camera attached to the balloon.
Figure 6: The study site and surrounding area from the camera attached to the balloon.
Figure 7: The images taken from the cameras on the Balloon, put together as a mosaic in the form of a TIFF.
Before we were even able to start the exercise I feel it is worth noting that with such big heavy equipment it required a few people to be able to get the equipment to the field site. The SD card for one of the cameras was also left out and so once we were all in the field, someone had to go back and retrieve it before we could begin, which in the work force could cost time and money.
When the balloon and camera were being deployed, the camera attachment rope was winding and twisting around the balloon string, so the cameras were less stable, and consequently affecting the quality of those initial images. When we were walking the balloon around the site, the method was not really set before hand, and so the route did not really follow and order. Which will probably result in an unequal covering of areas.
We were also only able to carry out the survey for about 30 minutes, due to the battery life of the cameras with the system overrides. We were covering a fairly small area, and still felt we needed a little more time t cover it efficiently, so in larger problems this could be problematic.
The UAV had a similar flight time to the time of the balloon, for battery purposes. It flew very well and matched it's pre-set course and was surprisingly fast when it needed o be and went quite high, it also landed nicely back to where is started from.
Conclusion
Balloons can be used to take aerial images in a field if money is a factor in a project. The equipment is more basic and easier to use, but may be tricky to transport and handle. Some images may not be very clear due to the effect of the weather on the balloon, this method can not be used in particularly windy unstable conditions. A clear path for taking the balloon over the area you are examining may be needed in order to ensure accuracy and clarity across all areas. The UAV gathers a clearer picture through the use of the stablisers on the vehicle, and can be observed and carried out from a distance and does not require you to physically follow the course yourself, unlike the balloon. But for a much higher price you do get the same amount of time to gather footage. The images you collect can be meshed together using software applications, in order to make use of all the data you created. This can then create an image platform for yuo to perform a number of tasks from.
