Camera and thermal drone detection
Cameras confirm what another sensor has found. They provide identification and evidence that radar and RF cannot, and they are poor at searching open sky without cueing.
Key facts
- Electro-optical and infrared cameras are used in counter-drone systems mainly to confirm and identify an aircraft that another sensor has already detected.
- A camera produces a recorded image, which is the form of evidence most useful for reporting, prosecution and insurance.
- Cameras are poor at searching open sky without cueing, because the field of view needed for detail is narrow and the sky is large.
- Thermal imaging works in darkness and can pick out motor heat, though a small electric aircraft presents a weak thermal signature at distance.
- Optical performance is limited by weather, light and background clutter, and a camera aimed into bright sky or against a complex background performs worse than a datasheet suggests.
- Cameras raise privacy considerations that other detection methods do not, since they record the surrounding area as well as the aircraft.
What cameras are for
In a counter-drone system, cameras are usually the confirmation layer. Radar or RF detection establishes that something is there and roughly where. A camera slews to it and answers the questions the other sensors cannot: what kind of aircraft is it, is it carrying anything, which way is it facing, and is this the same aircraft as last week.
That answer matters operationally, because a response is easier to justify when someone has seen the thing. It also matters afterwards, because the image is the part of the record that other organisations accept.
Why they are poor at searching
The difficulty is geometry. Identifying a small aircraft at several hundred metres requires magnification, magnification narrows the field of view, and a narrow field of view covers very little of the sky at once.
A camera searching unaided is therefore looking at a small patch and hoping the aircraft is in it. Against a moving target and a short response window, that rarely works.
Systems that appear to detect optically are usually doing something narrower than it appears, such as watching a specific approach line or a fixed sector where an aircraft would have to pass.
Daylight, thermal and their limits
Daylight optics give the best detail and depend on light and weather. Bright sky behind the target, low sun, haze and rain all reduce what can be resolved.
Thermal imaging removes the light dependency and introduces a different constraint. A small electric aircraft produces limited heat, mostly at the motors and the battery, and that signature weakens quickly with distance. Thermal is genuinely useful at close and medium range, and it is not a night-time equivalent of a daylight camera at long range.
Background clutter affects both. A camera looking across a built environment has far more to separate the aircraft from than one looking at clear sky.
Practical points for a specification
A camera in a counter-drone system should be specified around the cueing that will drive it, not on its own. The useful questions are how quickly it slews to a cue, how accurately it stays on a moving track, what identification range it achieves against an aircraft of the size you actually expect, and how the footage is retained.
Retention deserves attention. The value of the image is largely in what happens after the incident, and a system that records nothing, or overwrites within hours, gives up most of that value.
Related work
FAQ
▸Can a camera system detect drones on its own?
In principle yes, and in practice it is inefficient. To identify a small aircraft at useful range a camera needs a narrow field of view, and searching a wide area with a narrow field of view takes time the incident does not allow. Cameras work far better when radar or RF tells them where to look.
▸Does thermal imaging solve the night problem?
It addresses darkness, which is a real advantage. It does not make a small electric aircraft easy to see at distance, because the heat signature from small motors and batteries is modest. Thermal is best treated as an addition to daylight optics rather than a replacement.
▸Why does the recorded image matter so much?
Because it is what other people accept. A radar track is convincing to an operator and hard to explain to anyone else. A clear image of the aircraft supports a report to an agency, a regulatory notification, an insurance claim and, where it comes to it, a prosecution.
▸Are there privacy issues?
Yes, and they should be considered before installation rather than afterwards. A camera positioned to watch the sky will also record the ground, and in some sites that raises obligations regarding staff, neighbours or the public. This is an ordinary surveillance question and should be handled with the same policies that already apply to CCTV.