AVR Freaks

The Panasonic sensors from Digikey work well, and are reasonably priced. They have analog and digital output versions. A simple window comparator in software can be set up to track slow variations in the output, but trigger on sudden events. I wouldn't recommend a hardware implementation of the floating window comparator, since it's so easy to do in software, and much less power/components.

I'll be interested to see how you handle the camera, I haven't found any hobby-friendly cameras yet. Micron/Aptina imagers are nice, but their support is pretty awful unless you buy 1,000,000 chips up front.

On a recent project, I did my own imager, but I had an FPGA to deal with the 27MHz LVDS streams from the cameras. 30fps from four imagers is NOT gonna happen on an AVR :)

You won't have very good color performance without the NIR filter, and you're sacrificing low light performance if you're using a color imager.

Consider using a color imager AND a monochrome one, and using no NIR filter on the monochrome one. Best of both worlds, as long as you can handle the data.

I've seen that in Wisconsin and Indiana, at least -25F.

I went out with a friend playing a ham radio game called "foxhunting" at -25F. It was interesting. The coax cable was like a spring, and wouldn't unwind, and we needed handwarmers in the transmitter box to keep it on-frequency.

Definitely NOT an environment to rely on the internal RC clock. Even a crystal may have problems at lower temperatures. I've seen a badly designed oscillator (wrong cap values...) stall around +32F.