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Re: An amateur fireball detection/tracking system

FERNLEA4@aol.com wrote:
> Hi Bill and List,

> I design electronics circuits for a living and have recently been
> experimenting with a simple low light CCD camera and a method to trigger it at
> the right moment.

The CCD camera module I've been considering costs US$100 which includes a very
wide angle 150 degree field of view lens.  It's highly sensitive to IR and
has 0.3 lux sensitivity.  As suggested in one of the papers that I've read
on the subject of video recording of meteors, I'll use a photographic R50
red filter to reduce the effects of ambient light while accentuating the near
IR part of the spectrum where meteors really shine.

> The camera itself seems capable, although the triggering is another matter!
> I've tried all manner of light sensing devices without success.....the light
> levels being far too low to give clean switching. It's a question of setting
> the sensitivity to just the right point, but so far, the only overnight
> automatically captured images I've managed show nothing of interest.

It sounds like you are using analog methods (i.e. your mention of setting 
sensitivity).  That's why I plan to use a small, cheap, onboard microcontroller 
which can intelligently analyze variations in light levels in real time.  With
multiple photodiodes, it could even detect and analyze any movement of a light 
source across the sky.  This is well within the capabilities of even the 
cheapest microcontroller (like a PIC).

> I guess it's time for a re-think because simple optical sensors don't seem to
> be of much use for anything but the brightest fireball....needless to say,
> there's been nothing in our UK skies recently, bright enough to allow
> calibration! The sensor could be focussed with a simple lens, but that could
> restrict the area of sky covered.

What sort of photo sensors are you using?  I plan to use IR photodiodes with 
external IR diffusing filters to allow wide angle rather than directional 
sensing.  The sensors will be shielded from direct sunlight to, hopefully,
allow the detection of daylight fireballs.  Once again, it takes a microcontroller
with the capability of intelligently analyzing changing light levels to do this.

> A more accurate method may be to switch the camera using it's own video signal
> as the reference.....any changes in the signal above a set threshold could be
> used to trigger the capture card.

Yes, this sounds promising!  Rather than analyzing video in real time for the
tracks of fireballs (very processor intensive), just add and average all of the 
pixels in each frame.  The average value of each frame could be compared with 
the next.  An analysis of average frame luminance values with time could then 
be used to command retention, when deemed appropriate, of the video buffer in 
a file stored on the system hard drive.

Many thanks for the input. Please keep me advised of your progress.

Bill Blair

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