First flights - problems and solutions
I wanted to share some basic problems and solutions we found in our first and second balloon flights for aerial surveys. These notes might help other first-timers and may also elicit input from those who are more experienced and have better solutions.
My attempt and results
Helium tank and regulator - since a regulator should not be used when filling the balloon, I ordered the helium delivery without one (it cost a little extra), but I recommend you get a regulator that includes a pressure gauge so you can keep track of how much helium you use. We will be getting one next time.
String reel - the Public Lab kit includes a basic reel, but we decided to get a wooden reel with handles ($30 from Into the Wind - http://www.intothewind.com/shop/Line_and_Accessories/Bulk_Line_and_Reels_for_Traditional_Kites/Windbreaker_Kite_Line_Reel ). This was worth every penny.
String markings - we decided to mark the string with a permanent marker every 10 meters (1 red mark each increment, and one - 9 black marks to represent multiples of 10). This helped us estimate altitude.
Zip ties - the reusable zip ties provided in the Public Lab kit worked fine on the first flight, but came loose on the second flight and our balloon slowly lost helium and altitude. We refilled it and tried with the reusable ties, but they were not getting a satisfactory seal and would sometimes open up one click or more after we tried to cinch them down. We decided to use standard single-use ties which worked great. We used wire cutters to cut them off.
Cones - we put orange traffic cones in the survey area at 20 meter intervals so we could 1) determine scale of the photos and 2) determine altitude that the image was taken (given a known FOV or AOV).
Picavet and balloons - since I had originally planned on doing a kite survey, I built a picavet system rather than the liter bottle pendulum system described in the balloon mapping kit. With a balloon and little wind, this system didn't work as well as I hoped. Because the tether was almost vertical, there was no horizontal distance between the two attachment points so it allowed the camera to spin. Many others probably had the sense to not try this setup, but the problem wasn't obvious to me until we launched. The result was that about a third of our images were too blurry to use because they were captured during a camera spin.
Questions and next steps
We wanted to measure the buoyancy of the balloon with a spring scale, but ours didn't arrive in time. We have them now and plan on finding the minimum buoyancy needed for a given payload so we can minimize the amount of helium needed. Others have probably done this so I'd appreciate any input.
We'll be conducting another survey of the site in a few days to compare the results of horse grazing on an urban prairie restoration of the site: http://goo.gl/maps/muPzD
I'll be posting a full writeup soon but for now, I'm adding our first stitched image of the survey. This was done using VisualFSM as shown on the tutorials at FlightRiot.com: http://flightriot.com/uav-mapping-post-processing-tutorial-1-visualsfm-cmvs/