ABSTRACT
The essential elements of an original form of thermal imager are illustrated as a block diagram in Figure 2.1. They are:
An optical system that can form an image of an external scene using radi-• ation in the thermal wavelength range. One or more detector elements that can convert this radiation into electri-• cal signals proportional to the radiation falling on them. Some systems require a scanning mechanism that scans the thermal image • in a regular pattern across the detector element(s), although most modern imagers do not require this, since they use large detector arrays that completely cover the field of view of the imager (see below). An electronic processor that can process the detector outputs, in conjunc-• tion with data from the scan mechanism (where this is used), and can convert them into a video signal. A display unit that generates a visual image from the video signal.•
As will be shown in Sections 2.5.3 and 2.5.4, the greater the proportion of the area of the complete image plane that is occupied by detector elements, the better will be the performance of the imager in terms of sensitivity to temperature differences. The ultimate arrangement is to completely fill the image plane with detector elements and to do away with the scanning mechanism, as illustrated in Figure 2.2. Most modern imagers conform to this arrangement where and when technical and economic consideration allow the construction of large two-dimensional (2D) detector arrays. This type of imager is often referred to as a staring array imager.
