Kite aerial thermography (KAT)

Kite aerial thermography (KAT)

Currently, commercial low-level aerial thermography is usually carried out using helicopters. PDG Helicopters (Locations) fly a gyro-stabilised Flir Polytech Kelvin 350III (2).

This camera contains a high definition 640×480 pixel detector that allows temperature readings either in real time or from a stored image. It has a 0.04°C sensitivity and ±1°C accuracy. The primary advantage of this platform is that large areas can be surveyed with precision.

For smaller areas, light UAVs can be employed using the small Flir Tau imager range.

Our simple kite system (November 2011) is built around a waterproof 320 x 240 pixel microbolometer with a 19 mm wide angle lens, giving a field of view of 36 x 27 degrees.

Flir PathFindIR 320 x 240 pixel thermal imager.

This provides a resolution of a little less than the 352 x 288 pixel, conventional Pencam image of Cairnpapple, taken by James Gentles in 2003. The sensitivity of the camera is 0.1°C but it is not calibrated for temperature readout. The advantage of our system is that it is relatively cheap and light. However, the total weight of the prototype rig (including camera) is 1.5kg!

Cade and John with the sandwich box housed thermal camera and KAP rig.

AVI still

Our first KAT image. John on wet grass at night.

10 Sept 2011 (HQ Flowform 2.0 kite)

Few aerial images are as boring as this, except possibly our first KAP image.

Configuration 2

Flir PathFindIR auto-ranging thermal IR camera unit (£1,900 inc.VAT (2011), incorporating a window heater - 6w/2w on/off), 12v/4800mAh lithium-ion battery (£15 from e-Bay), 12v/60w voltage stabiliser (£30 - this is power over-rated by an order of magnitude) and PVR (£57). The original, digital recorder was replaced by a PVR, 23 September 2011.

The rig with the new PVR (the battery is external for safety).

Half frame crop of image from the new PVR, 23 September 2011. (MP4 still)

The price of this camera is outside the remit of our normally cost-conscious work. However, we expect the price (and weight) of handheld, thermal imagers to continue to fall in the near future.

For simplicity, we considered the available handheld, thermal IR units (1, 2, 3 etc), but none offered this resolution, robustness and field of view, at this price (August 2011).

Is such an approach a useful and viable option for archaeological KAP, as the near infra-red has already proved to be? That is the question we hope to answer. The two main considerations are (1) The slow speed of capture of individual frames and (2) The optimal environmental conditions for camera deployment.

VirtualDub is available as a free download for stabilising videos using the plugin Deshaker filter (Download), but we have not used it so far.

A HQ FF4.0 kite has been purchased to cope with the rig over a wider range of wind speeds. We also have a Power Sled 81, but we are more trusting of the consistency of performance of HQ flow forms in strong winds. Although we have not lost a camera since we started KAP in 2007, infrequently, sleds can shear out of the sky. Normally, this is not a problem, but it would be a disaster and dangerous with a £2k, 1.5kg payload.

A second PathFindIR camera was ordered in April 2012 for work on the DART Project. This camera will now be used for pole work on an aluminium mast.

Configuration 3 July 2012

To reduce weight, the 60w input voltage stabiliser (235g) has been replaced with one rated at ~10w (22g). Specifications:

Input Voltage: 11.5 to 35.0 Volts

Output Voltage: 10 Volts +/-5%

Line regulation: 10 mV (typical)

Load Regulation: 12 mV (typical)

Operating temperature: 0 to 125°C

Storage temperature: - 65 to 150°C

The unit (CCVS3 from e-bay) has thermal overload and short circuit protection.

Moisture-proof enclosure.

Several off-the-shelf voltage stabilisers are available for around £10 each. These are solid state replacements for electro-mechanical devices used on older cars to regulate the voltage to the control panel. The 4800mAh battery (176g) has also been replaced with a smaller one rated at 1800mAh (80g). The PVR (149g) has been replaced with a smaller, lighter model (82g). The total weight of the rig is now 1.16kg.

Configuration 3 July 2012

24 September 2011

Second flight, Wood Park, Armadale.

HQ Flowform 2.0 kite

Images are stills from an MP4.

Launching the KAT rig with the new PVR. Note the footprints in the wet grass.

A man and a dog.

30 September 2011

Third flight, Cairnpapple.

HQ Flowform 2.0 kite

Rosie (flying the kite) and John

Bringing down the kite.

Inverted image (Heavily sharpened and high contrast)

Bringing down the kite.

Images are stills from an MP4.

The camera is now ready for archaeological field trials, which will be carried out by group members John, Jim and Rosie.

We have lost the best part of the year for crop work (Kiescow pdf). However, we will continue to image sites thermally, especially to see if anything new appears at locations which we have already photographed in the visible and near infra-red parts of the spectrum.

Kite aerial thermography is not an easy technique. We have a long way to go before we will know if the effort and expense is worthwhile archaeologically......but it is looking very promising.

1 Nov 2011

Blackness

HQ Flowform 2.0 kite

Images are stills from an MP4.

Thermal image of Jim and Rosie kite flying at Blackness.

A small feature seen at Blackness on wet, short-cut grass.

(Approximately the area where Jim and Rosie are standing in the image above - the camera auto-ranges on the thermal field of view)

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Others Locations

Cairn South of Broomy Knowes.

18 December 2011

Ogilface, Woodend, Armadale.

29 March 2012

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Other Kite Aerial Thermographers

Kite aerial images of a soybean crop by Larry C. Purcell

Cropped aerial photo in the visible spectrum (GoPro). Not the same part of the field as shown on the right.	Kite aerial thermogram (33°C, RH ~33%, wind 10-12mph).
As above (right) but mapped with a three colour gradient. Blue = colder = better irrigation. Less water, less transpiration = higher temperature.
© Larry C Purcell 1st August 2012