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The relatively low purchase price and operating cost, coupled with automated flight capability, opens up the possibility of using several UAVs at the same time but sufficiently spaced to minimise the perturbation to the magnetic fields, to perform a task, such as a geological survey.

In order to minimise the extent of the necessary overlap regions in visual and thermal images, advantage is taken of the capability of the UAV to follow a precision flight path in both altitude and position.

To reduce the number of telemetry channels required when many UAVs are in the air, the UAV uses the on-board wireless LAN to communicate with nearby UAVs, in a wireless mesh network, with only a minimum number of UAVs maintaining either satellite, or, mobile phone based communication links.

• The advantages of using a swarm of UAVs are
• UAV altitude control
• Synthesis of macroscopic flying structures...
• The flying GridSwarm and the UltraSwarm
• Real Time Multi-UAV System

• that it will greatly reduce the time taken to perform a survey , or, task, with parallel operation of imaging and sensor systems, with a combined data bandwidth of 4 GBytes / sec for ten UAVs, all operating at maximum data transfer rates

• increased fault tolerance, in that should a UAV, or, a sensor on a UAV develop a fault, requiring it to return to base, then, another UAV could continue with the work, with minimal interruption, always to ensure the survey work is completed on time

• UAVs can repeatedly cover the same area, enabling the build up of an average time dependent representation for an image, that might be slowly changing with time

• the repeated scanning of the same region will allow the use of averaging techniques, to achieve a reduction in data noise levels. Typically, one realises a noise reduction equal to the square root of the number of samples taken.

• The ability to identify and compensate for any drift, or, errors in any of the magnetic, or, gravitational field sensor systems, due to the use of more than one UAV, to measure field strength in nominally the same location

• one can synchronise time for each UAV from a combination of highly accurate, temperature controlled, 10 MHz quartz crystals and precision GPS time signals. The UAVs can then synchronously detect electromagnetic signals, effectively forming a large synthetic antenna, enabling very high resolution imaging.

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Plot showing the stabilisation of height control to within +/- 6m.

From www.google.com/univ/stanford search term = “UAV” to locate AIAA035592.pdf

The Stanford University DragonFly UAV height control at nominal height of 120 m. The excellent control of height allows many UAVs to be flown in one area, if need be.

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A swarm of UAVs ready for a mission. From www.cloudcaptech.com wasco_5RnR_uavs.jpg.

A swarm of UAVs, including some back-up planes, could be used in one, or, in a combination of any, of the following flight configurations, due to their excellent speed and precision flight path control, to complete a high resolution aerial survey in record time:

• all abreast in a large wing-like formation , forming effectively a very wide wing (for example, 11 UAVs flying 400 m apart would form a 4 Km wide “wing” containing distributed sensors). Such a “wing” could cover a wide swathe of land to be surveyed at a very high resolution, with a massive combined data bandwidth.

• in a planar matrix formation (such as a 3x3 square or a 1+6+12 plane hexagon formation), forming in effect, a large planar antenna, with the UAV at the centre of the formation emitting the electromagnetic stimulus signal, with all the UAVs sensing the reflected signals. The very large synthetic aperture of the UAV matrix, will contribute to an increased resolution.

• in a vertical stack formation , enabling both near field and far field measurements of magnetic and gravitational fields and field gradients. Excellent speed and height control means the UAVs can fly very close to each other, if necessary.

• in a 3D cube formation , such as one formed by 27 UAVs flying in a 3 x 3 x 3 configuration, with a 100 m … 400 m spacing. Such a formation can:

• act as a large volume antenna

• derive X, Y and Z magnetic and electromagnetic field gradient information

• perform averaging of measured results, to reduce measurement noise

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Here is some very interesting work on UAV swarms by Dr Owen Holland, at the University of Essex, as described on his web site...

The above image and the text below from http://cswww.essex.ac.uk/staff/owen/research.htm

These two projects are exploring ways of getting a group of small aircraft to fly like a flock of birds, while at the same time performing non-trivial task-related distributed computation across a wireless network. The UltraSwarm is the indoor version the initial development used Proxflyer miniature helicopters. This work is in collaboration with John Woods and Adrian Clark from the Electronic Systems Engineering Department, and with computer science PhD student Renzo de Nardi who does most of the work, and it was initially funded by the University of Essex Research Promotion Fund.

The construction of the first prototype UltraSwarm node has been successfully completed - it is fitted with a Gumstix miniature Linux computer and a Bluetooth module, and we believe it is currently the smallest flying web server in the world - in the picture it is serving up the project web page over the Bluetooth link! We're now evaluating a new aerial platform - the Hirobo Lama XRB SR . When the flock has been completed, the Bluetooth modules will be configured as a single Piconet with the master on the arena-based computer system. Like the prototype, each helicopter will also carry a stripped-down colour video camera (a spycam) which will be used both for flight control, and for gathering data for a cooperative visual task. The background of this project is described here , in a paper presented at the IEEE Swarm Intelligence Symposium in June 2005. There is a more up to date version featuring the new platform here .

For the Flying Gridswarm, I am again working with several members of the Electronics Systems Engineering Department at the University of Essex (John Woods, Adrian Clark, Martin Fleury, and others). The project is based around a commercially available model aerobatic trainer - a very powerful machine capable of 120m.p.h. We have fitted the first aircraft with an autopilot system, and are currently evaluating its performance. The next stage will be to add a Linux-based miniature computer system, such as Gumstix , along with an 802.11 wireless LAN, and then to explore appropriate methods of enabling and controlling flocking, but first we have to find somewhere safe to do it... For some details of this project, and some useful links to related projects, see gridswarms.essex.ac.uk .

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The Brumby III Unmanned Aircraft developed by Ali Goktogan and his colleagues at the University of Sydney have been used in multiple UAV studies, as outlined in the following paper:

The following diagrams were copied from the above paper

Download a copy of the paper by Ali Goktogan.

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