Abstract
A novel system to measure the time constant of microbolometer cameras per-pixel to create a 2-D time constant map is presented. The measurements take place at the camera level and do not require any special control of the camera beyond the ability to capture raw data. Detailed simulations are run for a broad range of variables and values to demonstrate the usefulness of the system in extracting even extremely fast time constants with high accuracy and repeatability. Measurements are taken on a proof of concept system with an example camera, and a 2-D time constant map is reported. These results are compared with measurements from a linear motion stage system.
Highlights
M ICROBOLOMETER sensor performance is frequently quantified by a figure of merit (FOM)
FOM is the product of the noise equivalent difference temperature (NET) and its thermal time constant (τ ); it is expressed in units of mK·ms
One can typically achieve a given FOM with certain process technology, and NET and τ can be traded against each other to get a more sensitive or faster responding detector. (Since FOM roughly scales with the area of the pixel, an alternate FOM would include pixel area in its product [1].) Different applications may put a premium on either NET or τ ; a lower τ detector is useful for on-the-move applications, such as an unmanned aerial system payload, while greater sensitivity is useful for finding low-contrast targets at greater range
Summary
M ICROBOLOMETER sensor performance is frequently quantified by a figure of merit (FOM). The pixels are excited by the blackbody when the aperture is open and cool when it is closed These methods all fundamentally suffer from the same problem: they all are attempting to gather enough data to fit a curve to (1), but the frame rate of the camera is too slow to populate more than a point or few along the characteristic exponential curve. All known current system-level measurement apparatuses report τ for the entire array, typically based on some subsets of the pixels that are measured This is a fundamental limitation for slow aperture systems that require a spatial fit. Since NET is already reported per-pixel, this will allow a per-pixel FOM map to be generated for the entire FPA
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