Digital aerial images from kites or balloons


Kite and Balloon Aerial Imaging

by: Paul Illsley



Author (lower right) flying a kite camera (upper left) over a glacier in Alaska.



Resulting image of a research camp in Alaska using the kite camera shown above.



Close-up of the camera system used for the previous images. This image shows a simple box container with foam pads
to hold the camera and the cameraís remote control unit which was modified to fire every 10 seconds. Notice the 4 pulleys attached
to the top of the container, these were used to create the Picavet leveling system. A hole was cut in the bottom of the container
in front of the lens to allow for unobstructed vertical shooting.




View of the gondola (a plastic crate for holding CDís) and a shortened Picavet pulley system.
Threading sequence: A Ė X Ė 1 Ė B Ė X Ė 2 Ė A Ė 3 Ė B Ė 4 Ė A (the lines go through a small smooth washer at X).
Pulleys can be purchased at a local hobby shop or you can simply use smooth metal rings instead.
The actual length of line used in the full pulley system will measure about 10 meters.




Gondola and Ricoh Caplio R4 camera. This camera is almost perfectly suited for vertical aerial photography due to its
6 megapixel sensor, low weight (264 grams), wide angle lens, ability to set the focus to infinity and a built in intervalometer.
The entire camera and gondola weigh in at 416 grams.




An image of an earlier more elaborate remotely controlled camera platform system. This system proved to be too delicate
and complex for continuous use in remote conditions. A simpler box design (shown previously) proved to be a better choice.




Diagram showing a method of suspending the camera system from a balloon using one tether line.




Diagram showing a method of suspending the camera system from a balloon using two tether lines.





    How do I get the camera airborne?
    Now that you have your camera ready, you need a way to get it up in the air. There are 4 options Iím going to chat about: hot air balloons, hydrogen balloons, helium balloons and kites.

    Hot Air Balloons: There are two types of hot air balloons: solar heated and combustion heated. The solar balloons rely on the solar radiation from the sun to heat the air inside the balloon. Believe it or not, they actually work; in fact they can be big enough to lift people (http://perso.orange.fr/ballonsolaire/en-index.htm). You need a pretty calm day and bright sun but if you have these conditions itís a pretty neat trick to get a camera in the air without any additional fuel source. The other option is a fuel powered hot air balloon. A simple lightweight camping stove suspended under a nylon envelope can heat enough air to get a light weight camera off the ground. I donít go this second option because I donít really like the idea of having a burning object floating around above me. The important thing to remember about hot air balloons is the lifting capacity depends on the difference in the warmth of the air inside the balloon compared to the outside air. The larger the difference in relative temperatures the better the lifting capacity of a given volume. So, hot air balloons have more lifting potential in cooler days than they do on hot days.

    Hydrogen balloons: (donít even go down this road). Although hydrogen is a safe fuel when handled properly and has great lifting potential, the safety concerns far outweigh the slight increase in lift compared with helium. I choose not to go the hydrogen route and I donít endorse it.

    Helium Balloons: Now this is the way to go. Helium has nearly the same lifting potential as hydrogen but is much safer to handle. To calculate the volume (in liters) of helium required to lift a certain weight (in grams) simply multiply the weight by 0.9743640 . Itís always good to double, triple or even quadruple the amount of helium required to lift the entire camera assembly and balloon in order to make sure the balloon can fight against slight breezes. Helium can be purchased wherever compressed gas cylinders are sold, contact your local automotive parts dealer for the nearest compressed gas distributor. Be wary of the helium thatís designed for filling party balloons, these tanks may include other gasses in addition to the helium which will decrease the lifting potential. Check out: http://www.balloondealer.com/skybuster.asp or http://www.kaymont.com for large balloons.

    Kites: These work great when you have steady wind. This statement might sound obvious but youíd be surprised how much wind it takes to get a camera up in the air. Gusting wind isnít what youíre looking for; itís the continuous sustained winds that work best. Thereís nothing worse than having your kite and expensive camera lost in the forest or even worse having string draped from rooftop to rooftop or disappearing over the edge of a cliff with no camera and kite in sight due to the wind quitting mid flight (I speak from experience). Not only is this a huge headache, itís a definite safety issue for all concerned. There are special kites like the Sutton Flowform (to name only one) which are used for lifting cameras and instruments. Here is a site that is probably the best resource on the web for aerial photography from kites: http://arch.ced.berkeley.edu/kap/ . Remember that the weight of the camera will effect the amount of wind it takes to lift the rig, if the specifications say it takes a certain amount of wind to fly the kite, be assured that it will take a lot more wind to get it in the air with the camera attached.



Author directing the positioning of the kite aerial camera system during the imaging
of a glaciological formation on an Alaskan glacier.



A resulting image of a rock outcrop with GPS referenced ground control markers (circled in red)
which were used for determining scale and orientation for subsequent mapping analysis.



Ricoh GX200 camera (234 grams)



Bench Test setup



Calculated results from the test procedure



4 balloons and camera



Distribution of images used



Point cloud generated from the overlaping images



3D model created from the point cloud



Mosaic created from draping the images over the 3D model



GoPro Hero HD camera (128 grams with LCD screen, 97 grams without)



Image from GoPro camera showing distortion due to its extreme wide angle lens



The same image after the lens distortion has been corrected



Software used to correct the lens distortion ( PTLens ).



Balloon and GoPro setup: 0.953 m balloon diameter with 247 g of lift



About as simple an attachment system as you can get, but it worked (see image below)



Vertical aerial image of the Centre of Geographic Sciences taken with the GoPro HD camera and balloon (lens distortion corrected)



Chart showing the lift values for Helium (remember to subtract the weight of the balloon itself)
Assuming standard temperatures and pressures and no significant overpressure.
Source: University of Hawaii, Manoa, Department of Chemistry (http://www.chem.hawaii.edu/uham/lift.html)



Shot of a simple homemade reel holding 1000 feet of 130 pound test fishing line used in the Sutton Flowform kite system.



An inexpensive reel ($12.00) for light weight systems (originally intended for wrapping electrical cords).
This is great for balloon systems because it holds a huge amount of line and is easy to use and transport.



An fishing reel with 20 pound test line for light weight balloon systems (like the one shown above).



A fishing reel on a broomstick will do the job just fine (for a balloon system).