Advanced Techniques For Measuring Temperature Or Radiance Of Thermally Dynamic Events

Each infrared focal plane array pixel is a photo conductor that converts photons into electrons. As infrared radiation is absorbed by the pixel it is converted into electrons which are collected in the pixel's charge capac-itor. By adjusting the time the capacitor collects charges, the integration time (IT), we can alter the system's dynamic range and the scene temp-erature that the system is optimized for. Shortening the integration time enables the imaging of hotter objects, while increasing the integration time enables the imaging and measurement of colder objects.

The dynamic range of an infrared camera can be specified in numerous ways. However for the purpose of this paper we will refer to dynamic range as the range of apparent blackbody temperature that a single infrared image frame can quantify without being saturated. Because the systems are designed for high sensitivity their dynamic range is typically limited to about 50°C (nominal integration of 2 milliseconds). Refer to Figure 4 for an example of the target temperature ranges of an InSb-based system at different integration times.

There are many applications in which targets heat (or cool) very rapidly and span a temperature range that exceeds the system's nominal temperature dynamic range. Using a single integration time in this instance will potentially result in saturated data. To overcome this a camera feature called Multi-IT enables the camera to automatically cycle through up to four user-selected integration time settings in sequential frames to build a data set that software can process to create a single data set in which each pixel in every image of a recorded sequence is optimized.