(K)-AP as a tool in science

Applications

Case-study: Geomatics

(Kite) Aerial Photography as a tool in science

Aerial photography has long since been a very valuable tool in science. Aerial photography, starting from the first aerial images of San Fransisco after the earthquake in 1906 made by George Lawrence, up to the free high quality Google Earth database accessible by everyone today, has changed a lot.

Today high quality and often very recent imagery is available free of charge to everyone and everywhere on the Internet. But certain research requires even higher resolution imagery or more recent or frequent imagery. The choice then arises to rent an airplane to get the needed imagery. The quality of the images produced by professional aerial photography companies is in general perfect but this comes to a, sometimes significant, cost.

Here the possibilities and impossibilities of alternative methods of obtaining aerial photography will be described. The focus will be on kite aerial photography (KAP), other methods as balloon-, pole- and RC-airplane- aerial photography will also be discussed. The costs of the different methods we'll be reviewed and some examples of results are shown.

Alternative methods for aerial photography

K-AP (Kite Aerial Photography)

The camera is fixed to a platform which is suspended from the kite line at some distance from the kite. The kite used is in general a single line kite. These kites do not need controlling from the ground but fly stable autonomously. The position of the camera can only be controlled by walking around with the kite line.

B-AP (Balloon...)

Balloon aerial photography is similar to KAP but instead of a kite to lift the camera a helium filled balloon or blimp is used.

P-AP (Pole ...)

Pole aerial photography is a technique where the camera is lifted to a height by fitting it on top of a pole. Often a carp-fishing rod is used, these rods can be up to about 13 meters long. Specialized telescopic tripods are also commercially available which can safely lift the camera up to about 25 meters.

RC-aircraft -AP

Cameras are often attached to remote controlled helicopters or airplanes. A large variety of specialized aircraft exist and can be bought from loads of suppliers.

Other -AP

There are cross-overs between for example kites and balloons, a good example is the Helikite.

 

 

	KAP	BAP	PAP	RC-AP
Altitude (m)	Ground - limited by law	Ground - limited by law	Up to 30 meter	30 - limited by law
Weather dependent?	Yes, stable wind needed	Less, not too much wind	Not really	Yes, in general low wind speeds needed
Reliability	In good wind good	Good	Great	Often poor
Operational risks	Even good kites crash when the wind is unstable.	Balloons are prone to leaks, wind gusts can blow the balloon down	Few	There are 2 kinds of RC-aircrafts: the ones that have crashed and the ones that will.
Problems related to: photography	In most cases the camera swings, causing blur in long exposures.	Motion blur is often less than with KAP	Straight down images difficult because of the pole	Vibration and movements of the aircraft cause motion blur.
Location	Only in places with enough open space. Kite only flies downwind of the point it is fixed to. Wind is mandatory.	Needs less space than KAP, only downwind of tie-point.	For large poles a few square meters are needed. Large poles can be difficult to transport	Aircraft can fly anywhere, but space is needed for launch and landing.
Camera weight	Can be over 2kg, but low weight is preferred.	In general only compact cameras are suitable.	Only limited by the stiffness of the pole.	Large cameras can be lifted by large aircraft.
Experience needed	Intermediate.	Common sense	None	A lot, especially when flying large aircraft
Time to setup	20 minutes	1 hour (inflation of balloon)	10 minutes	Hours
Basic equipment (ex camera)	€200,-	€500,-	€100,-	€400,-
Pro equipment	€1000,-	€5000,-	€1500,-	€5000,- and up
Operational costs per session	€10,- (batteries)	€100,- (batteries, helium )	€5,- (batteries)	€100,- (batteries / fuel, repairs )

 

Camera s and lenses

For all methods described here it is an advantage if the camera has a low weight. When a lightweight camera is used kites and balloons can be much smaller and are therefore much easier to handle, also PAP and RC-AP is much easier. Because helium is an expensive gas a lot of money is saved too in the case of BAP. In general “better” cameras are bulkier and heavier than simple compact cameras. Depending on the aim of the research one should find a balance between camera weight and image quality. New and more advanced cameras get on the market every month so only a few remarks on suitable cameras can be made here.

Wide angle lens - In general wide angle lenses are preferred. Aerial photography is aimed at getting an overview, with wide angle lenses the altitude can be smaller to cover the same ground area.

Image stabilization – A camera which has this feature corrects for movements of the camera, either by moving a lens-element or the image recording chip. The motion blur is much less compared to cameras which lack this feature. Longer exposures and or lower ISO values are possible.

Fixed focal length – If measurements are to be performed on the images it is nice to have a lens which has an fixed focal length.

Long battery life – Nothing is worse than an empty battery in flight. Most cameras perform much better when the LCD is turned off.

Low noise – Although most cameras perform really well with low ISO values, there are a lot on the market which perform terrible with high ISO values. Because of the very dynamic nature of aerial platforms it is sometimes necessary to use higher ISO values in low light conditions. It is better to have a 5-megapixel noise-free image than 12 mp of noise.

Remote control or interval function – As there is no-one to trigger the shutter by hand, these functions come in handy. In case they are not available it is possible to use a servo to push the button.

Geometric measurements on the images

Aerial images are often used for mapping, in that case it is important that the camera produces distortion free images. Sadly most compact camera suffer from a lot of lens distortion, but it is quite simple to calibrate the camera and digitally correct the images. With these few extra steps any camera is suitable to use for photogrammetry or mapping. On the Internet and on this site more information and tools can be found on this subject.