Kite Aerial Photography: low cost aerial cover or just blowing in the wind?

This is an article which first appeared in the Sept/Oct 2012 edition of Geomatics World magazine. Given the current level of interest in UAS I thought this might be a useful overview of the options as I see them. I am aware I have said much of this is in various posts to date but this article joins up the pieces and represents a fairly complete summary. I have taken the opportunity to add some images which were not possible to include in the original publication.

Origins of KAP

Aerial photos have been taken using a kite ever since 1887 when Arthur Batut took shots of his hometown of Labruguiere in France with a self-built light weight miniature camera attached to a bowed diamond kite. He shot sheet film negatives of his own manufacture one at a time with shutter tripped by a burning fuse.

Batut 1888Fig 1 Athur Batut KAP of Labruguière 1887

He quickly adapted his technique along the lines of modern practice where the camera is suspended on the flying line below the kite and triggered by a remote device. Between now and then much has changed but Batut’s method remains a standard practice in kite aerial photography (KAP). Both cameras and kites have improved since then so that today, a keen kite flyer, with a little practice, can capture reasonable resolution imagery of open sites provided wind and light oblige.

KAP got underway in the UK when Fletcher Baden Powell took a vertical of Middleton Hall in Staffordshire in the early 1890s.

F B Powell KAP 1897Fig 2 Middleton hall 1897

KAP in Archaeology

Early successes with KAP were in topographic recording and archaeology, famously George R. Lawrence recorded the devastation after the fire and earthquake at San Francisco in 1905 by lifting a massive 12kg panoramic camera beneath a train of 17 of Silas J. Conye’s kites and in 1913 Henry Welcome used kite captured imagery to successfully record excavations at Segadi, Jabel Moya, Sudan with a hefty wooden box camera. He began a practice which is continued to this day in archaeology as KAP is a good method of capturing excavation sites in open country where the low altitude pays off in terms of image resolution at close to the scales (1:50) used in excavation records.  Jebel Moya Sudan 1913Fig 3  Jabel Moya Sudan, Henry Wellcome 1913

A kite is a good low cost aerial platform for photography but it suffers from poor reliability in terms of accurate camera positioning on any given day. Although the number of windless days are few in the UK wind direction has a large bearing on the outcome:  getting the camera over the target area is a matter of wind direction and speed, neither of which are under the control of the flier! Photography by kite is more often a case of shooting what can be shot rather than what is wanted. Results take patience to achieve and careful reconnaissance of obstructions in the flying zone is a must. It is often possible to achieve oblique aerial cover but vertical cover of a given subject can be a tough call. KAP is best suited to sites with open access in a down wind direction.

Effectiveness of method

Reliable and repeatable photo-cover by kite is not often possible and there are alternatives to a kite as a low level aerial platform.  A balloon or powered UAV such as a radio controlled (RC)  aircraft or helicopter are all good means of raising a camera but they too have their limitations in terms of set up costs, pilot skills, flying time and CAA certification.  A kite can be a handful but it is simple, cheap and fairly easy to fly. The flying height of a kite in the UK is restricted by CAA regulation to 60m above ground level (AGL) and this is a significant constraint on photo-cover by kite. So given there’s more than one way of getting a low level aerial photo (Table 1) and that managing a kite is a bit of an awkward business why use one? The answer is two-fold.  First it must be said that KAP has an immense satisfaction value for the kite flier, the achievement in the successful balance of wind, lift, light and load is unique. Second is the impact of the viewpoint, the world seen at 60m AGL is captivating, the low height means that human scale features like foot prints and often material condition in buildings can be seen.  There is a sense of connection between land and sky experienced by kite fliers which is very different from other aerial photographers who move at speed though the air.  A kite photographer becomes immersed in the landscape whilst viewing it at bird’s eye height.  Tethered to both the sky and the ground a kite photographer has an awareness of landscape which is unique.

Table 1 : Low Elevation Aerial Photography (LEAP) options
Lifter Benefit Approximate Cost* Constraints
UAVs
Multi rotor semi autonomous RC helicopter
Rapid, stable, camera positioning. Up to 1kg payload.
€3,000
11mins flight time per battery
400’ limit (US)
Fixed wing drone or  autonomous RC aircraft
Programmable flight path for stereo swath cover.
€20,00
High altitude (600m+), high flying speed.CAA certification status ‘unresolved’ at present.
Manual RC helicopter
Rapid camera positioning
€3,000
11mins flight time per battery.High pilot skill level
Manual RC ‘plane/Glider
Rapid camera positioning20-30 mins flight duration
€300
high flying speedhigh pilot skill level
RC fan assisted dirigible balloon
Indoor flights possible.20-30 mins flight duration
Cannot operate in windy conditions.Cost of helium
 Un-powered tethered lifers
Balloon
Flight duration Stable no- wind
€300†
Limited to 60 m cost of Helium per flight. Cannot operate in windy conditions Clear line zone handling required.
Kite. In practice a selection of 3 or 4 kites is needed to meet wind conditions between Bft 2 and  Bft 4
Flight duration
€250
Limited to 60 m.
Clear down wind line zone required.
Weather dependent
HeliKite/ kitetoon A hybrid design of kite stabilised balloon
Flight duration, zero wind capacity.
€2000
Limited to 60 m.
Clear line zone handling required. Cost of Helium per flight.
†cost per filling of 3m3 helium
*excluding cost of 1kg camera payload with video relay

An example of mapping coverage achieved

It is quite possible to use KAP imagery for survey purposes but the consistency of coverage required for good photogrammetric results can be hard to achieve. In this example a simple photomap to show the condition of the monument was prepared. The coverage achievable at the permitted flying height of 60m is demonstrated. 2 cameras were used; a lightweight APSC sensor compact (Leica x1) and a DSLR with a 10.5mm lens (Nikon D5100). The kite was a Sutton Flowform 30 (2.7m2) flown in Bft3, the flying line used was a 250m length of 250DaN Dacron.

Fig 11KwideFig 4: Kite aerial photo-mosaic of the Earith Bulwark, Cambridgeshire. The photography was achieved at heights varying from 15 to 60m AGL using a LeicaX1 compact camera suspended from a Sutton Flowform 30 kite. The photo-scale achieved is approximately 1: 2000. The control for the mosaic is a graphical fit from the published Ordnance survey1:25000 scale map.

The photo-mosaic of the Civil War fort at Earith (Fig 4) shows the problem. At a maximum of 60m flying height the nadir coverage achieved with a 35mm equivalent lens is approximately 2500m2 per photo. The height of the camera is variable (dropping down to 15m in lull) and the 8 images used are on a variety of orientations caused by manoeuvring around obstructions to the kite line; the aspect of each shot is constrained by the position of the kite, access to open ground and the available sunlight.

The Bulwark layers 1kwFig 5 Kite aerial photo-mosaic of the Earith Bulwark. Showing the orientation of the image components of the mosaic.

10mm vs 35mm 1kwideFig 6 Comparison of 35mm (inset) and 10.5mm lens coverage at 60m AGL.. A photoscale of approximately 1:6000 is achieved with the 10.5mm lens.

The coverage at 60m AGL by 10.5mm fisheye (shown corrected to perspective projection in Fig 6) and 35mm (inset) lenses. Using a wider lens (10.5mm fish eye) the coverage is improved by about 3x but the resolution is reduced, the cover achieved at 60m AGL for each image is approximately 20,000m2 once the spherical distortion is removed.

Stereo capture

Earith Stereo Model copy 1k high

Fig 7 KAP Stereo pair, textured model and contour plan of part of the NE Bastion at Earith Bulwark Cambridgeshire. Processed in AGIsoft ‘Stereoscan’. Contours generated in TheoContour by LatimerCAD.

Stereo capture can be achieved by use of a stereo-metric rig or by the natural movement of the kite providing a base offset, this can be used photogrammetrically.  Fig 7 shows a stereo pair processed into 3d data. The orientation of the images and separation of the base can be problematic to control with a kite.

Equipment

KAP requires 3 components, a camera, the means to control it and a kite.

Camera

Digital capture is a great benefit to KAP as the image count can run on until the card is full without incurring the cost of developing a 36 shot roll of film because KAP can generate a lot of unwanted material.

The weight of the camera is a big consideration, in theory the load of the camera can be lifted by a kite of appropriate size but in practice the lift needed in light winds is often marginal, with patience DSLRs can be flown successfully but the compact cameras weighing less then 300g work well with manageable kite sizes. The new generation of APSC sized sensor compacts offer good resolution for their weight.  Examples being the Leica X1(lightest in the class at 283g), FujiX100,  Canon EOS M,  Sony NX and Samsung Nx200.

Rig

There are 2 approaches to rig design, one is to simply automate camera control and let image capture occur at a fixed time interval. The other is to use radio control to direct the camera. Camera control is improved by use of a video relay to ground and by gyro stabilisation of the tilting axis of the rig. A radio controlled KAP rig is also suitable for use mounted atop a pole or hung under a balloon where weight considerations are also important. Rigs are available in kit form or assembled in a variety of configurations from www.kapshop.com

Kite and line

The basics are that the kite needs to be big enough to lift the load and stable enough to take a photograph from.  Not all kites behave well enough for photographic purposes, traction kites are not ideal with most kite photography being taken from single line kites. The majority of kites have quite a narrow wind range in which they will be stable, for example a kite big enough to lift a 1kg load in Beaufort (Bft) force 3 may well be at risk of either snapping its spars or being blown over in Bft 4. The quality of material and manufacture are important, a kite needs to be precisely symmetrical, flexible enough to absorb gusts and strong enough to take the forces acting upon it but at the same time light enough to create the maximum possible lift.  A good KAP kite will be stable across a wide wind range and be capable of lifting about 1kg in about 5mph wind speed, this works out at a minimum sail surface area of about 2.5msq. The quality of the airflow supporting the kite is important and smooth breezes are better than blustery. The variation in wind speed will produce a variation in flying height as well as the risk of either stalling the kite in a lull or being overblown in a gust. Large (3m wing span) delta kites, the classic Japanese Rokkaku and the recently developed flowform and parafoil types can be effective. Large kites (4m2 is a typical light wind lifter size) can be difficult to handle and ideally a balance between the kite, the load and flier should be achieved to enable the movement of the kite and rig across the landscape. Kappers flying heavy (DSLR) cameras tend to use a ground anchor to manage the forces involved in controlling the large kites required.

The best work is achieved in steady light winds of Bft 2 and 3. It is possible to work in higher wind speeds but the turbulence common in Bft 4 and 5 tends make positioning camera difficult as well as creating camera movements well beyond the range of image stabilisation.

KAP Applications

Applications for KAP are limited to sites which lend themselves to kite flying where good pictorial records can be captured of a site and its condition. The low view-point records site context without compromising detail and often provides useful visitor orientation images of heritage sites because of the ‘human scale’ effect of the low height.

Since Arthur Batut took his first image the new technologies of ripstop nylon, high tensile Dacron line, digital image capture and radio control have made photography by kite achievable by anyone who is happy flying a kite and is ready to capture a new perspective on the world around them!

Further info:

The principal source for information on KAP is the KAP forum hosted by Berkeley University: http://www.arch.ced.berkeley.edu/kap/

 A good selection of archaeological KAP applications in the UK is collected by the West Lothain Archaeology group at:

http://www.armadale.org.uk/kite.htm

 Selected publications

Rand Eppich, Antonio Almagro, Mario Santana, Ana Almagro: The view from above overview and comparison of low cost aerial photographic techniques. Raymond Lemaire International Centre for Conservation, KU Leuven, Belgium 2011

Mike J. Smith, Jim Chandler and James Rose  High spatial resolution data acquisition for the geosciences: kite aerial photography Earth surface processes and landforms. Landforms 34, 155–161. 2009

British Kite Flying Association:  Kite Flying and the law Version 1.0 23 September http://www.bkfa.org.uk/ 2008

David Wheeler: TIGHAR KAP Guide The International Group for Historic Aircraft Recovery July 8, 2007

Beaumont Newhall  A KAP Timeline : Aerial Photography in the Early Days Drachen Foundation Journal Summer 2007

Craig Wilson Hanging by a Thread (A Kite’s View of Wisconsin) Itchy Cat Press. USA . 2006.

James S. Aber and Susan W. Aber, Earth Science Department, and Firooza Pavri: Unmanned small-format aerial photography from kites for acquiring large-scale, high-resolution, multiview-angle imagery.  ISPRS Commission I/FIEOS 2002 Conference Proceedings, 2002.

Serge Negre  Vu du ciel (Eye in the sky)  Société d’études et de Recherches Archéologiques et Historiques de Labruguière 1999

Christian Becot Photographie Aérienne Avec Cerf-Volant, C. Becot, 108 Rue Médéric, 50110, Tourlaville, France. 1995

Andrea Georgopulos  Balloon and kite photography: an historical overview ISPRS Commision V ISSN 02528231 1982

Andrea Georgopoulos Low Altitude non metric photography using a kite ISPRS Commission V ISSN 02528231 1982

About billboyheritagesurvey

Heritage worker
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4 Responses to Kite Aerial Photography: low cost aerial cover or just blowing in the wind?

  1. z1ggur4t says:

    Great reference section at the end Bill, contents of the article aside.

  2. Brianne says:

    Hello to all, the contents existing at this web page are
    genuinely awesome for people experience, well, keep up the good work
    fellows.

  3. German Walton says:

    There were days with strong wind, and box kites handle wind well. However, any drop in the wind and a box kite will drop rapidly, as will any camera that it might be lifting.

  4. DV_Hugh says:

    We had excellent results at our dig last week using a variety of airborne devices including a kite.. http://digventures.com/2013/07/11/saints-secrets-day-ten/

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