Focal plane array and general questions about Thermal Imaging

[EnonimusTransmission]

I'm looking into purchasing a Thermal Imaging unit. Information on the internet is very complex for a newcomer. Additionally, there seems to be an extremely wide range of thermal imaging devices for various applications. At this point I'm very confused about what sort of unit I should get.

First of all, I'm investigating the purchase of TI for use in private security, and I realize this is a forum for firefighters, but there is almost no online TI community so I've end up here.

Here's a specific question:
FLIR VSR-6 -

http://thermalvideo.com/thermal-imaging-systems/flir_vsr-6.htm

vs.
Thermal-Eye X-150 -

http://www.morovision.com/thermal_imagers/x200xp.htm

The VSR-6 says it has a "640x480 InSb focal plane array" while the X-150 says it has a "Focal Plane Array Pixel Count (Resolution) 160 x 120", yet the X150 is more expensive and says it has a much greater range. Can anyone explain what this means?

Thanks!

 

[IRstuff]

As with normal cameras, pixel count means more resolution, so a 640x480 has about 300K pixels, while a 160x120 has only about 20K pixels.

Again, as with normal cameras, field of view drives range; the narrower the field of view, the higher the magnification, so more detail can be discerned.

Your first link gives conflicting information. While the website uses 640x480, the datasheet does not, and refers to a 160x120 FPA, while a substantially wider field of view than the other link.

TTFN

FAQ731-376

 

[EnonimusTransmission]

Thanks for the reply.

Looking at the datasheet, you're right. That explains a lot, actually. I was baffled how the Thermal-Eye could claim a better range when the resolution was much less, but now it appears the resolution is comparable to the VSR-6.

Are the ranges reported by these companies really accurate? 160x120 seems awfully low to me.

 

[IRstuff]

That's what we call "proposal land." "We have a car that gets 100 mpg and can go 200 mph." "Oh, you want BOTH at the same time? Well, that's a different story."

The only way that you can realistically compare two disparate systems is to do the analysis yourself, or to get someone with the appropriate analysis tools to do that for you.

Other than that, you can certainly talk to sales reps into bringing in a demo system for you to touch and feel and run against some sort of canonical target or scenario. For that, you should have some sort of controlled environment, like a collimator, and a controlled(controllable) target that you can image with each sensor and see what you can see.

My vote would be for the latter, since you're actually talking about buying a bunch of them for some user who may, or may not, have adequate understanding or expertise in the usage or interpretation of infrared imagery and cameras. Additionally, the actual performance and behavior of cameras, such as display quality, noise characteristics, etc., cannot be adequately gauged from analytical models. Some systems look good on paper, but suck in actual implementation.

I'm not sure what your very last comment refers to; you mention range and pixel format in the same phrase. Hypothetically, any halfway decent pixel resolution can do something, the question really boils down to what your specific requirements and concept of operations are:

> How are the sensors to be deployed?
> Coverage area?
> YOUR range requirement?
> Displays?
> Zoom capability?
> Anticipated threats?
> OPFOR countermeasures against detection?
> Complementary sensors: motion, sound, vibration, etc.?

My suggestion would be to formulate a specification for the system you're looking for, and then talk to the suppliers. The VSR-6 webpage gives a nice, brief tutorial on DRI (Detection, Recognition, Identification) and the resolution requirements needed for DRI. That's a good start for your own understanding of what type of pixel angular resolution is needed, which then determines the total angular field of view provided by the pixel format. Do be aware that diffraction limit for LWIR (8-12 um) can make a big impact on range performance, f/2 optics will "look" sharper than f/6 optics, because of diffration blur.

Note also, that LWIR will ALWAYS look "fuzzy" or out-of-focus, because of diffraction blur effects, and you should not expect the same level of image sharpness that you'd get from visible cameras.

TTFN

FAQ731-376