GeoResJ 3-4 (2014) 1–8

Contents lists available at ScienceDirect

GeoResJ

journal homepage: www.elsevier .com/locate /GRJ

Compact and inexpensive kite apparatus for geomorphological fieldaerial photography, with some remarks on operations

http://dx.doi.org/10.1016/j.grj.2014.06.0012214-2428/� 2014 The Authors. Published by Elsevier Ltd.This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

⇑ Corresponding author. Tel.: +1 443 778 2903; fax: +1 443 778 8939.E-mail address: Ralph.lorenz@jhuapl.edu (R.D. Lorenz).

Ralph D. Lorenz a,⇑, Stephen P. Scheidt b

a Space Department, Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, USAb Center for Earth and Planetary Studies, Smithsonian Institution, 6th St. and Independence Ave. SW, PO Box 37012, MRC 315, Washington, DC 20013-7012, USA

a r t i c l e i n f o

Article history:Received 2 October 2013Revised 1 June 2014Accepted 6 June 2014

Keywords:KiteAerial photographyGeomorphologySand dunes

a b s t r a c t

Equipment for performing low-altitude aerial photography for geomorphological studies on 10–1000 mscales is described, with particular reference to study of sand dunes. An automatic digital camera is loftedby a parafoil kite: the arrangement costs around $400, collapses into a volume of �2 l and can bedeployed in a few minutes, making it convenient for field use when wind conditions (>4 m/s) permit.Some operational considerations are discussed and we demonstrate two scientific applications – changedetection to show a dune at White Sands has not advanced in an 11-month interval and the generation ofa digital elevation model of Bruneau Dune.� 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/3.0/).

1. Introduction

An aerial perspective is often useful in geomorphologicalstudies, either in its own right or as a bridge between the remotesensing view from orbit and that afforded from the ground. Beyondflying an observer in an aircraft in the classic mode of aerial pho-tography, an array of platforms exist for so-called small-formataerial photography (reviewed in detail by Aber et al. [1]) whereinan imaging capability is deployed from the ground on-site.

Such approaches are facilitated by the ever-growing capabilitiesof lightweight digital cameras. Other technologies includesolid-state gyroscopes that facilitate flight of slow-moving radiocontrolled vehicles such as quadcopters, and GPS guidance whichallows autonomous survey flights by small airplanes. However,these techniques (and the use of balloons, which typically requiresthe conveyance of heavy helium cylinders to the field) all entail acertain amount of expense and complexity.

Kite aerial photography (KAP) has a rich history, notably fromthe dramatic view of the destruction of San Francisco by the1906 earthquake. The field has experienced a renaissance withthe availability of lightweight digital cameras, and a web searchwill reveal many examples. A wide range of systems can be used,from large kites suspending radio-controlled steerable platformswith video viewfinders used in an interactive manner, to simpletimelapse devices. This paper focuses on the latter type, with

specific application to the geomorphological study of sand dunes,for which kite images were used in a recent book [7]. Since sanddunes tend to be found in windy locations, kiteborne photographyis particularly well-suited to this application, and modern parafoilkites (Fig. 1) can be readily packed into a small rucksack for conve-nient deployment in the field. More particularly, the relatively lowcost, mass and volume, and quick deployment and retrieval, meansthat aerial photography can be attempted with little effort, and canbe considered an opportunistic augmentation to other field activi-ties, rather than needing to be a premeditated enterprise.

While aerial photos, or high resolution (<5 m) satellite imagingmay be readily available for some locations (notably the continen-tal USA), many desert areas worldwide do not have such coverage.Such data may in any case be years old. KAP with wide-anglemegapixel cameras offers the ability to obtain resolution of about1/1000 of the altitude: thus typical flights to �10 to �200 m alti-tude offer centimeter to decimeter resolutions, in geometries thatcan be near-vertical, oblique, or near-horizontal. For a range ofapplications, KAP may be more timely and/or more cost-effectivethan obtaining spaceborne or commercial aerial photography,and for other applications may provide resolution or view anglesthat are not otherwise available.

2. Apparatus

Some initial experiments were carried out with a small parafoilkite and a homebuilt timelapse camera using a simple timing cir-cuit ‘hotwired’ via an optocoupler across the shutter switch of a

Fig. 1. Experiments with an early kite camera variant – a homebuilt timer driving akeychain camera, at White Sands National Monument, New Mexico, USA. Firstauthor is at left, with Jim Zimbelman at right. Note the curved upper surface of theparafoil kite. Note also that the installation shown here has the camera too close tothe kite to fly stably – 10 or meters would perform much better. Photo courtesy ofJason W. Barnes.

2 R.D. Lorenz, S.P. Scheidt / GeoResJ 3-4 (2014) 1–8

small keychain digital camera (see [5]) attached to a bar or smallboard suspended a couple of meters below the kite bridle attach-ment point. Reiche et al. [9] describe a similar arrangement forsuspending meteorological instrumentation from a parafoil kite.Although a few good results have been obtained (Fig. 2), thisapproach was unsatisfactory in a number of ways, most particu-larly because the majority of frames were motion-smeared. Thisresulted primarily from the slow readout of the cheap detector inthe ‘keychain’ cameras used (such small cameras lack a mechanicalshutter), but also because initial experiments tended to attach thecamera too close to the kite, leading to higher angular rates. Eventaking hundreds of pictures in a flight, not infrequently it wasfound that no images were useable.

A dramatic improvement is obtained with a more modern cam-era, optimized for documenting fast-moving sports activities suchas surfing and mountain-biking. Such cameras, the example beingused here is the HERO GoPro2, have optics and detectors thatpermit short exposure times and thus much reduced susceptibilityto blur. They are furthermore marketed with robust protectivehousings (see e.g. Fig. 3), and convenient controls to set imageacquisition at regular intervals. The image format is large enough(e.g. 2840 � 2880 pixels) that images can be cropped substantiallyto show regions of interest with acceptable resolution.

The kite dynamics can also be improved with some care. Ineffect the camera suspension can be considered as a pendulum. Avital consideration, learned unfortunately by experience, is thatthe pendulum should have a long period to prevent couplingbetween the swinging camera and the kite dynamics which can

in turn reinforce the swinging. This is avoided by the simple pre-caution of attaching the camera to the line about 10 m away ormore from the kite. This effectively lengthens the swing periodto a point where resonant interactions are reduced acceptably.

More elaborate KAP apparatus uses a Picavet suspensionwherein a platform is suspended on 4 pulleys, through which acord passes to attach at two locations on the kite string. Thissuspension allows the platform to maintain a constant horizontalorientation even when the suspension points move rapidly inspace. Such an arrangement is important to avoid rapid scenemotion in video, but is generally unnecessary for terrain photogra-phy and is somewhat prone to tangling. Simply passing a loop ofcord through four holes in the camera platform (for which the plas-tic display mount for the GOPRO was used) is generally adequate toensure a generally-horizontal orientation when wind turbulence isminimal. The system used by the author has a �1.5 m loop of cord,such that the suspension forms 2 legs of about 40 cm length (seeFig. 4).

The suspension cord is attached at two points onto the kitestring – most conveniently after the kite has been launched.Remarkably, the weight of the camera and the tension on the lineis enough to hold the system on the line even with only a couple ofloops of the line around a rigid element such as a carabiner or swi-vel hook. These elements allow the rapid attachment and removalof the suspension from the line.

The camera mounting itself in this instance is simply the plasticsupport plate supplied with the camera, onto which the waterproofprotective case is attached on a hinge which allows the tilt angle tobe adjusted. The plastic plate was trimmed by �2 cm on 2 sides,and four holes drilled through which the suspension cord isthreaded. More elaborate arrangements can be introduced: anautomatic mechanism to scan the camera in azimuth increasesobserving efficiency substantially, although full radio-controlpan-tilt mounts with video viewfinders can be obtained commer-cially. The latter arrangement is significantly more massive (andexpensive) than that shown here, and also requires rather higherwinds and/or a larger kite.

The distance between the suspension points determines the azi-muthal stiffness of the mount. If a rigid mounting is desired (suchthat the camera platform always points downwind or upwind,along the kite string direction) then the mounts should be far apart(here, about 60 cm), with the suspension forming a right angle.Alternatively, mounting the suspension points close togetherallows the suspension to swing (or even wrap around) whichmay be desirable for a wider range of azimuths.

3. Operating considerations

General safety considerations pertaining to kites should befollowed – e.g. do not fly near power lines, roads etc. and pay atten-tion to applicable regulations (see [1]) Beyond the camera, kite andline, a few accessories have been found to be useful. First, protec-tive (e.g. leather) gloves are all but essential, as severe abrasionof the hands will occur when winding the kite back in. With suit-ably close-fitting gloves, the camera can be operated and attachedwithout their removal. A handheld anemometer may be useful inassessing wind conditions, although with practice the wind pres-sure felt on the face or wind noise can become an adequate guide.

The GoPro cameras have a variety of operating modes, fromindividual stills to high-speed movies. Most useful in this applica-tion is the timelapse setting, where still images at a cadence ofunder a second to minutes can be automatically acquired. The bestcadence is a compromise between acquiring enough images toensure the available views are obtained, while not oversampling(i.e. obtaining multiple near-identical images, which will fill the

Fig. 2. Example results with a ‘keychain’ digital camera. (A) Dumont Dunes, in California. This image looks towards the sun (which has saturated the upper part of the image)and so has strong contrasts. (B) Barchanoid dunes on the Chott El Gharsa, Tunisia. Contrasts in this noontime image are rather muted, but the presence of personnel andvehicles adds thematic interest to the image. (C) A linear dune in Quattaniya, west of Cairo, Egypt. The image shows the wavy (seif) crestline of the dune, and the fact that theeastern (right) plinth on which the main dune sits is narrower than at the left. Note that the presence of the horizon in the image facilitates interpretation. (D) A downlookingimage from relatively low altitude at Kelso, California. Note the smearing in the lower part of the image, due to violent kite motion. This smear is a particular problem with(typically inexpensive) cameras where the longer exposure times increase the chance of scene motion.

Fig. 3. Apparatus is compact. (A) The packed Parafoil-10 kite with a hoop of 100 lbline (B). Gloves (C) are essential to prevent abrasion injury to the hands. (D) is asmall hoop of 3000 of 30 lb line. (E) is the GoPro2 camera used for the later images inthis paper. (F) is a handheld anemometer, useful to gain familiarity with the windconditions. (G) is the GoPro camera housing, on a small plate suspended from a loopof heavy string. (H) is a smaller Parafoil-5 kite.

Fig. 4. Suspension arrangement.

R.D. Lorenz, S.P. Scheidt / GeoResJ 3-4 (2014) 1–8 3

memory card on the camera more rapidly and take longer toinspect). With the arrangement described here in somewhatsteady conditions, a five-second cadence is usually more thanadequate. If the kite is undergoing rapid motions in turbulentconditions, faster sampling might be preferred.

The GoPro camera used has a very wide field of view (FOV),which leads to fisheye distortion. When the camera views horizon-tally, with the horizon in the center of the frame, this distortiondoes not appear to be severe, however. This distortion is inherentin the lens unfortunately, but the benefit of the GoPro camera isthat a very large area can be imaged without extreme altitude. Ifa rectilinear image is desired or needed for the photogrammetriccalculations described below, the lens on the GoPro can be

4 R.D. Lorenz, S.P. Scheidt / GeoResJ 3-4 (2014) 1–8

replaced with a lens that has a narrower FOV. The GoPro modelused here is a 2nd generation model, whereas the now releasedGoPro Hero3 has a widely distributed lens model (or lens profile)that adequately describes the distortion parameters. There are afew choices of software packages that can be used to remove dis-tortion, such as Adobe Photoshop, Adobe Lightroom and AdobeCloud. Likewise, tools such as Adobe Profile and OpenCV allow auser to create their own lens profile for later removing distortionfrom images taken by any camera imaginable.

One camera alternative to the GoPro is the Pentax Optio WG-2GPS. The Bruneau Dunes case study below utilized this lightweight(0.198 kg), ‘‘adventure-style’’ compact camera for its durability,marketed as waterproof, dustproof and crushproof. This model isable to withstand a freefall drop of 2 m, which buffers against smallbumps, poor landings and possibly a slightly better level of protec-tion over a standard camera in the event of a catastrophic kitecrash. Although this camera produces 16 megapixel images(4608 � 3456 pixels), the true or effective resolution of theseimages is 9.7 megapixels because of its 6.2 � 4.6 mm back-illumi-nated CMOS image sensor (standard for most point-and-shoot dig-ital cameras). This digital camera, as well as the GoPro, lacks theideal, full range of manual exposure settings. As few auto settingshould be used as possible when applied for a given set of fieldconditions. This allows images to have comparable exposure, whitebalance, color and contrast, and it can allow images to be mosa-icked into panoramas or composite image maps of the field area.

Although post-processing to enhance contrast can improvematters, images in the middle of the day can often be disappoint-ing. However, for high-contrast scenes, such as red barchan duneson a mud pan (Fig. 5), good images can be obtained even with highsun.

Much more generally appealing results can be obtained within acouple of hours of sunset, when topographic shading becomesmuch more prominent (Fig. 6). Images taken facing somewhattowards the sun can be particularly dramatic (e.g. Fig. 7).

Fig. 5. A chain of reversing barchans in the eastern United Arab Emirates. While thewide field of view of the kite camera (A) introduces some distortion to the scene,the utility of the image in showing the morphology is evident. Note that at thislocation there is good contrast between the gravel plain and the sand. The bestavailable satellite view in Google Earth is of much lower resolution, and the verticalview makes it difficult to assess the dune height and morphology.

Fig. 6. Barchans at the Salton Sea, in southern California, USA, in the late afternoonwith winds from the west. (A) With the camera mounted down-sun, the view is tothe East, and shows the Salton Sea in the background. Although the low sungenerates a shadow behind the slip face, the overall image contrast is quite poor.The first author, holding the kite, is just upwind of the barchan slipface (B) tenminutes later, with the camera mounted to view towards the sun. The surfacecontrasts are much more dramatic and show the morphology much better. The kitewith its two stabilizing streamers is visible at the top. Also noticeable are patches oflight due to sand grains on the lens cover – viewed down-sun these would not beapparent, but at this phase angle, they scatter light strongly. A satellite view inGoogle Earth (C) has rather poor contrast between dunes and substrate, and it isdifficult or impossible to assess the dune heights.

The most efficient procedure for launching the kite, which canbe accomplished easily by a single operator in the field, is as fol-lows. Lay out the kite string, and the camera mount, on the ground,keeping the kite itself in one’s rucksack. Turn on the camera, adjustits pointing as desired and verify that it is taking pictures every fewseconds as desired. Then remove the kite and unfold, attaching anytail or streamers (in fact, it has been found that a streamer tail canbe efficiently left attached and wound around the kite envelopeafter flight) and attach to the swivel on the kite string – the kitecan be kept from blowing away by kneeling on it if necessary.Put on gloves and launch the kite, then allow the line to pay outby 10 m or more. Then the camera suspension can be attached,and the kite then paid out to its operating altitude (usually as highas the string will allow, subject also to time constraints).

Fig. 7. Image from about 200 m altitude (10000 line fully paid-out) at White SandsNational Monument, New Mexico, USA. The low sun dramatically illuminates thebarchanoid ridges, and highlights the normally rather subtle elemental duneformson the stoss slopes. At center left there is a vehicle for scale – a flat area bounded bya narrow berm is bulldozed as a road and parking area.

R.D. Lorenz, S.P. Scheidt / GeoResJ 3-4 (2014) 1–8 5

Releasing the kite can be rather quick in strong winds, but witha hoop it is practical only to winch in the kite at about 0.3 m persecond. Thus a deployment to the full altitude permitted by a300 m line may take 10–15 min to wind back in. Parafoil kites tendto fly at somewhat shallower angles than some rigid kites, and itwill be observed that often (especially in marginal conditions)releasing more kite string does not lead to a substantial increasein altitude, but the kite simply flies further downwind. This isbecause the weight of (and more importantly, the aerodynamicdrag on) the kite string progressively loads the system. Indeed,the fact that a kite string forms a curved (catenary) shape was doc-umented very early [8]. At the point of suspension, the angle of thekite string with respect to the horizontal is determined by the tan-gent of (lift minus weight of the kite) divided by the kite drag,whereas the angle of the string at the operator is defined by thetangent of (lift minus weight of the kite, minus weight of the kitestring) divided by the drag of the kite and the string. The kite stringdefines a smooth curve linking these asymptotes.

It will be observed that when applying tension to the kite string(as when winding in) the kite tends to fly higher, i.e. the kite stringbecomes more vertical (see Fig. 8). This effect can be exploited toobtain a different set of viewing angles, or by periodic wind andrelease, to gain altitude. In fact, this phenomenon deserves closerstudy from a purely dynamical perspective, in that simple models

Fig. 8. Paying out more line after launching a kite in weak winds typically results init flying further downwind with only modest increase in altitude, with the kitestring being near-horizontal at the operator. Winding the string back in, applyinghigher line tension, often makes the kite fly at a steeper angle, with higher lift andlift/drag ratio. This effect can be exploited to derive a range of positions forphotography from a single operator location.

of a kite system can be bi-stable (e.g. [2]), and real-world flightdata may elucidate this bifurcation. It presumably results fromthe curves of lift, drag and moment coefficients as a function ofangle of attack, and the moment applied by the kite suspensionbridle, such that two moment equilibria exist. One of these is ata higher lift/drag ratio (L/D) and thus steeper kite string, and corre-sponds to a higher lift and a higher line tension.

It is tempting to launch the kite from the crest of a dune understudy. Such a location is clear of obstructions, and has the aestheticadvantage of placing the observer in the center of the scene understudy. However, this temptation should be avoided for tworeasons. First, the observer may be deceived into launching intomarginal conditions – the streamline compression near the brinkof the dune means windspeed is at a local maximum, and thus inmarginal winds the kite will fly adequately there, as soon as itattempts to gain height it enters slower-moving air and fails toclimb. The operator may spend some time in such an environmenthoping in vain for the situation to improve. The other difficulty isthat flow separation at the brink can often occur (leading, whensaltation is active, to the classic ‘smoking dune’ behavior). Thiscauses a recirculating flow region (see Fig. 9) in the lee of the dune,with a vortex bound to the slip face. This region, which may extendsome way above the crest, is characterized by weak and oftenhighly turbulent winds, in which the kite may fly very erratically,or (as the author found at a large dune in Sossusvlei, Namibia) itmay lose lift entirely and fall to the ground.

What the operator can get away with is best learned by experi-ence, but a rule of thumb for dunes may be that the recirculatingregion extends from the brink at about 45� downwind, up to aboutone dune height above the crest. The airflow may be disturbed,however, rather further downwind than that (a rule of thumb inthe kite literature is that a wake behind a building extends about7 times the height of the building, although this is a particularlysharp-edged obstacle). It may be easiest to explore these regions(and in fact kites may be a useful means of quantitatively mappingthe airflow around a dune – e.g. Walesby and Harrison [12] showthat the kite string tension measured by a strain gauge can be auseful proxy of windspeed) by launching the kite upwind of thedune and marching around, than by attempting to launch the kiteat the crest itself.

Aeolian geomorphology is comparatively forgiving for KAP –not only is the topography somewhat subdued with relativelysimple airflow patterns, but the ground is fairly soft so that whenimpact of the camera with the ground occurs, it is not fatal. Theusual effects of impact, namely deposition of sand, abrasion ofthe lens cover and/or dislodging of the memory card, can be

Fig. 9. Inexperienced operators should avoid launching at dune crests – winds maydecrease aloft and downwind leading to ‘trapped’ flight or loss of lift as the line ispaid out, and/or erratic flight in the vortex region. Launch upwind of the dune isrecommended, where wind may be slightly weaker, but is steadier and does notdecrease with height or distance downwind.

6 R.D. Lorenz, S.P. Scheidt / GeoResJ 3-4 (2014) 1–8

repaired easily in the field. Kite photography at volcanoes, in con-trast, can be very challenging. Hazards encountered include impactwith hard rock surfaces, sharp lava surfaces on which the kitestring can be abraded, hazardous terrain making recovery difficult,and chaotic airflow. The latter can result not only from sharptopography e.g. at the crater rim where flow separation occurs,but also due to circulation driven by the volcano’s thermal output.This circulation can include strong downdrafts at the crater edge tomaintain flow continuity with a central updraft (much as the buoy-ant foam in a glass of Guinness beer drives a central upwelling butcauses a downward secondary flow at the glass edge). Such adowndraft caught the first author’s kite at the Mt. Marum lava lakein Vanuatu: although the kite recovered altitude, abrasion on thecrater lip weakened the kite string which subsequently failed andthe kite and camera were lost.

4. Interpretation and scientific applications

It may simply be desired to obtain oblique aerial views forillustration of papers or talks, and for this application the appara-tus described works very well. Repeat visits may permit changedetection (e.g. due to dune migration) although the importanceof making such observations in illumination conditions as similarlyas possible is stressed.

Quantitative photogrammetric interpretation can be compli-cated by the oblique view and camera distortion – as discussedat length in Aber et al. [1] and Verhoeven et al. [11]. On the otherhand, the oblique views that are readily attained are much moreuseful for evaluating topography. Images can be calibrated withan optical model and/or by using markers with known sizes and/or locations. Even when no known lengths are present, tools likeGoogle Earth may be used to compare satellite imaging with kiteaerial views to establish ground control points and achieve rela-tively good georeferencing of the data. For example at the WhiteSands dune field in Fig. 7, the parking area is 163 pixels wide,and can be measured with satellite imaging in Google Earth to be

Fig. 10. Change detection via kite imaging. (a) A low altitude image showing part of the sinterest (b) a medium altitude image acquired almost a year later. (c) A section of (a) zooridge. Note the set of bushes right at the foot of the slip face. (d) Zoom of image (b) – theadvanced significantly (<1 m) in this interval.

58 m across, indicating a local horizontal scale of �0.3 m/pixel.On the other hand, from the image itself, the author (1.8 m tall)subtends �7 pixels, indicating that the local vertical scale is aboutthe same (i.e. the camera has an elevation of roughly 45� seen fromthis location – obviously in the far field the horizontal pixel scale ismuch larger than the vertical due to foreshortening). The slip faceat this site, which cannot be seen well in the Google image, can bemeasured to be 30 pixels high, or 10 m. These and other simple cal-culations are extremely valuable in the field and can provide a firstorder assessment of dune geomorphology in multiple locationsthat have not yet been viewed from the ground.

Change detection can be performed with repeat imaging. Fig. 10shows two images taken almost a year apart at White SandsNational Monument with the same GoPro/kite rig. Despite some-what different viewing geometry, a section of the �km wide scenecan be zoomed into, and the dune shape and its position relative toindividual bushes can be determined. These bushes are only�0.5 m wide, and while a few changes in the dune shape can beseen, it is clear that the slip face of the dune has not overrun anybushes and thus its movement is less than �1 m. This movementof <1 m/yr is in some contrast to typical migration rates of dunesof this size (e.g. [6]) of >10 m/yr.

An intriguing possibility is that digital elevation models can beconstructed from a large set of oblique, overlapping imagesacquired from a range of angles and elevations using a computervision technique called ‘‘structure from motion’’ and has also beendescribed as multiview stereo photogrammetry (MVSP). MVSPuses only 2D images acquired from several 10 to 1000 s ofviewpoints of a target to reconstruct 3D points that are computerfrom the occurrence, correlation and triangulation of matching fea-tures in different images. Traditional photogrammetry requiresknowledge of camera position and pose, but the modern MVSPalgorithms simultaneously solves for the projection of each cameraimage, including exterior camera orientation (positional x, y and zand rotations j, u and x) parameters. In general, the computationof a sparse point cloud of 3D points is all that is needed todetermine the kite camera positions. The goal of this exercise is

cene imaged a few minutes later in Fig. 7 in May 2013. Arrow denotes the region ofming in on a collection of halophyte bushes in front of the slip face of a barchanoidsame bushes can be identified at the foot of the slip face, implying the dune has not

Fig. 11. DEM of Bruneau Dune, showing shape and reconstructed kite camera positions. The portion of the dune that was reconstructed measured to be 125 m. The color-classified 3D point clouds of the kite camera positions reflect the kite flying patterns of the two flights accurately. The flight on the west side of the dune ridge occurred duringturbulent, variable winds, likely due to flow separation occurring over the dune ridge. This resulted in several gains and falls in altitude, and it occurred over a large area as thesecond author would attempt to loft the kite by running. The flight on the east side of the dune occurred during a stronger, steady wind that carried the kite aloft directly. Atthe highest elevations, the delta wing kite encountered gusts that caused greater variations in azimuth viewing geometry. (This contains a rigid frame, different from theparafoil model described earlier.)

R.D. Lorenz, S.P. Scheidt / GeoResJ 3-4 (2014) 1–8 7

to produce accurate CAD-like 3D models that can be analyzed in ageographic information system (GIS). Several online tools are avail-able to complete the entire process of generating a dense 3D pointcloud from images on remote servers. For example, Adobe123DCatch is free and can perform automatically the correlationand registration of such images, returning a phototextured, 3D‘‘mesh’’ from a small image set within an hour. 123D Catch hassome limitations as a free service, but the paid service, AdobeRecap, offers an ‘‘ultra’’ high resolution product, and will processan image set of up to 250 high resolution images. Such stereogram-metry requires a diversity of viewing angles, and so a combinationof walking the kite around with winding the line in and out may benecessary to have the kite move the viewpoint to a wide enoughrange of locations. For this application especially, adjusting theview azimuth relative to the wind (or allowing it to change, e.g.by narrow suspension points) may be necessary.

This process was attempted with a slightly different, moreelaborate kite aerial photography rig at the Bruneau Dunes StatePark [10]. This location is a test site for producing kite aerialphotography because of previously collected differential globalposition system (dGPS) surveys at the southern end of the dunecomplex [14,15]. This kite camera platform was suspended froma Picavet cross (described earlier), which is fixed to a lightweightrotating servo motor. The Pentax Optio WG-2 GPS was used asthe camera, angled downward at roughly 30� to capture a largerportion of the land surface (and dune) as opposed to sky. Thiscamera can be remotely triggered with an infrared LED. A timedelectronic emitting IR LED captured images every 5 s in tune withthe rotating servo motor, capturing a 360� view every minute.These images had a narrower FOV with the focal length set to28 mm, which simplifies the geometric considerations when usingMVSP software to produce 3D data. Images were captured from arange of altitudes and positions of the dune, but only 50% of theimages that pointed at the dune were needed. The 3D model wasconstructed using techniques described in Heller et al. [4] andWu [13] from a selection of 686 images. A high resolution DEMof the area was produced using sparse reconstruction [13] and asubsequent dense reconstruction [3], but only some 3D data ofthe dune was generated (Fig. 11). Exceptional, high quality 3D datawas produced in the area surrounding the dune because of thesurface texture provided by scrub, gravel patches and small, locallyvarying topographic relief. These image textures allow the MVSPalgorithms to find features that can be used to calculate 3D points.However, the dune’s sandy surfaces had surface features that were

smaller than ground sampling distance, a product of the high alti-tude and sensor resolution. Consequently, feature detection failedto provide enough points for triangulating a dense 3D point cloudof the dune. Despite the large areas without data, the general shapeof the dune, the dune height and the projection geometry of thekite images were produced with very good accuracy because ofsome vegetation and wet sand patches on the dune surface. Also,the dune crest was reasonable resolved. The image set of theBruneau Dune was also uploaded to Microsoft Photosynth, whichgenerates a 3D point cloud and embedded the images into a unique3D visualization. The camera positions and pose are used toprovide a multiview projection for each of the images, as if viewedfrom the kite. These aerial view can be explored through a webbrowser online. This 3D view of the Bruneau project can beviewed online at http://photosynth.net/view.aspx?cid=67c92721-73c6-4af9-b81d-955fef9d2ed7.

5. Conclusions

A compact and relatively inexpensive setup has been describedthat can provide aerial views up to altitudes of �200 m suitable forgeomorphological studies. Some considerations for safe andefficient operations have been discussed. The utility of using kiteaerial photography for simple photogrammetry calculations hasbeen shown. With the advancements in MVSP, the variability andunknown a-priori knowledge of the camera position is actuallyshown to be a benefit for quantitative field surveys.

Acknowledgements

Field visits to some sites where results are reported in thispaper were supported by NASA grant NNX13AH14G ‘Cassini RadarScience Support’. Colleagues Jim Zimbelman, Joseph Spitale, JaniRadebaugh, Jason Barnes and Brian Jackson are thanked for assis-tance in the field. NHK TV of Japan is thanked for the donation ofa battened foil kite and picavet suspension, and for alerting the firstauthor to the GoPro camera range.

Appendix

Apparatus details

The kite apparatus used here was obtained from Into the Wind(www.intothewind.com) and their part numbers are quoted for

8 R.D. Lorenz, S.P. Scheidt / GeoResJ 3-4 (2014) 1–8

convenience, although of course products and specifications (theImperial units used in their catalog are repeated here) can changeand other vendors may offer comparable products.

Best results have been obtained with a ‘Parafoil 10’ kite(Product #5105) which inflates to 20900 � 30700 and will fly withthe camera in winds of �6mph or so. With strong winds this kitecan develop a strong pull, and so a 100 lb line is recommended(e.g. 10000 of Dacron line #138 wound onto an 800 hoop spool#1280). For attachment of the camera suspension lines, smallswivel clips (e.g. #4032) or carabiners (#6551) can be used.

If one is confident of encountering reasonably strong winds asmaller kite (e.g. ‘Parafoil 5’ #5752 inflating to 101100 � 20700 witha 50 lb line on a 600 spool #1265) will be slightly easier to handleand is more compact.

The consumer electronics industry is of course fast-moving,with products rapidly being retired in favour of new items, andthe GoPro2 cameras used in this paper are no longer offered forsale by the manufacturer directly (although aftermarket vendorsmay retain some stock). GoPro3 cameras likely offer comparableor superior performance, and the kite suspension described in thispaper can likely be constructed similarly, or using one of the man-ufacturers helmet or surfboard mountings, or with a simple boltand the tripod mount. An alternative might be to thread a smallrope through a PVC tube or similar element, perhaps 20–30 cmlong, and attach the camera using one of the handlebar mountssold for mountain biking video.

References

[1] Aber J, Marzolff I, Ries J. Small-format aerial photography; principles,techniques and geoscience applications. Elsevier; 2010.

[2] Adomaitis RA. Kites and bifurcation theory. SIAM Rev 1989;31:478–83.[3] Furukawa Y, Ponce J. Accurate, dense, and robust multiview stereopsis. IEEE

Trans Pattern Anal Mach Intell 2010;32(8):1362–76.[4] Heller J, Havlena M, Torii A, Pajdla T. CMP SfM Web Service v1. 0; 2010.[5] Lorenz RD, Jackson B, Barnes J. Inexpensive timelapse digital cameras for

studying transient meteorological phenomena: dust devils and playa flooding.J Atmos Ocean Technol 2010;27:246–56.

[6] Lorenz RD, Gasmi N, Radebaugh J, Barnes JW, Ori GG. Dunes on planetTatooine: observation of barchan migration at the Star Wars film set in Tunisia.Geomorphology 2013;201:264–71.

[7] Lorenz RD, Zimbelman J. Dune worlds: how windblown sand shapes planetarylandscapes. Springer; 2014.

[8] Marvin CF. A monograph on the mechanics and equilibrium of kites. WeatherBureau W.B. No.122, Department of Agriculture, Washington, DC; 1897.

[9] Reiche M, Funk R, Zhang Z, Hoffmann C, Li Y, Sommer M. Using a parafoil kitefor measurement of variations in particulate matter – a kite-based dustprofiling approach. Atmos Climate Sci 2012;2(2012):41–51.

[10] Scheidt SP, Zimbelman JR, Johnson M. Multiview stereo photogrammetry ofMars aeolian analogues, Lunar Planet Sci Conf #XLV; 2014 [abs. #1446].

[11] Verhoeven G, Sevara C, Karel W, Ressl C, Doneus M, Briese C. Undistorting thepast: new techniques for orthorectification of archaeological aerial frameimagery. In: Corsi C et al., editors. Good practice in archaeological diagnostics.Nat Sci Archaeol. Springer International Publishing Switzerland; 2013. http://dx.doi.org/10.1007/978-3-319-01784-6_3.

[12] Walesby KT, Harrison RG. Note: a thermally stable tension meter foratmospheric soundings using kites. Rev Sci Instrum 2010;81:076104.

[13] Wu C. Towards linear-time incremental structure from motion. In: 3DTV-Conference, 2013 International Conference on IEEE; 2013. p. 127–134.

[14] Zimbelman JR, Scheidt SP. Investigation of reversing sand dunes at theBruneau Dunes, Idaho, as analogs for features on Mars, Eos Trans., Fall Meet.AGU abs. # P21D–1870, presented at 2012 Fall Mtg., AGU, San Francisco, Calif.,3–7 Dec; 2012.

[15] Zimbelman JR, Scheidt SP. Precision topography of a reversing sand dune atBruneau Dunes, Idaho, as an analog for Transverse Aeolian Ridges on Mars.Icarus 2013;230:29–37.