Thermal imagers are the most important type of electro-optical imaging systems that have found a long  series of both military and civilian applications. Performance of thermal imagers (understood as ranges of effective surveillance: detection, recognition, identification) can be relatively accurately estimated on basic of measured three important parameters like MRTD, MTF, NETD (or at least MRTD). Measurement of these parameters can be carried out using different test systems offered on the market (including systems offered by Inframet described at section Thermal imagers ). However, the problem is that typical test systems offer testing thermal imagers only at laboratory conditions. Both imager ambient temperature and target background temperature at laboratory tests are at level about 20C when in real work conditions of surveillance thermal imagers both temperatures can vary from about -40C to about +60C or more. It means that a near perfect imager at laboratory conditions can perform very poorly at extreme ambient/background temperatures. It can also occurs that imager of modest performance at laboratory conditions can keep this performance nearly the same at extreme ambient/background temperatures.

In such a situation Inframet has developed three test systems that enables testing thermal imagers at simulated real work conditions: EXIR-1, EXIR-2, EXIR-3 (Fig.1).

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Fig.1. Cross section of a)EXIR-1, b)EXIR-2, c)EXIR-3

EXIR-1 system is a test system built from two blocks: 1) CHI special translucent temperature chamber where the tested imager can be inserted; 2) typical laboratory class  DT system for testing thermal imagers.

EXIR-2 system is a set of two blocks:1) special ADT athermal  image projector, 2)CHP projector chamber. Both tested imager and the image projector are inserted to the CDP projector chamber.

EXIR-3 system is build from a set of three blocks: CHI translucent imager chamber, CHP projector chamber and ADT athermal image projector.The tested imager is inserted to the CHI imager chamber. The ADT athermal image projector is inserted to the CHP projector chamber. The tested imager can see athermal projector via the translucent window in the first chamber and hole in the second chamber. This concept enable independent regulation of both imager ambient temperature and background temperature. It is the first reported test system in the world of such simulation capabilities.   Design of EXIR-3 system is based on patent pending solution.

All three test system enable measurement of all important parameters of thermal imagers at variable work conditions. EXIR-1 and EXIR-2 enable simulation of most typical work  scenarios when imager ambient temperature and target background temperature  are approximately equal. Only in case of EXIR-3  system both temperatures can be regulated fully independently in range from about -40C to at least +60C and all possible work scenarios can be simulated (Table 1).

Table 1. Imager ambient temperature and target background temperature at different surveillance scenarios

Applications of these new tests systems in process of evaluation of surveillance thermal imagers can bring revolution in thermal imaging metrology. The new test systems enable much more accurate evaluation of performance of thermal imagers at real work conditions comparing to typical test systems capable only to simulate laboratory conditions. The new test systems can also show new ways of technical modifications to improve performance at extreme conditions. Therefore the new test systems can become in near future a very valuable tool for both users and manufacturers of thermal imagers.

The test systems presented in this section (EXIR-1, EXIR-2, EXIR-3)  have been basically developed for testing thermal imagers operating at MWIR/LWIR spectral bands. However, they can be modified (new radiation source and broadband window ) to enable testing VIS-NIR cameras, SWIR imagers or multi-sensor systems. Testing the latter systems is of particular importance because these test systems enable not only to measure image quality but also to measure boresight errors at simulated real work conditions. 

Due to high potential of new EXIR systems  Inframet organizes special international exhibition EXTRIMUS to present this new  test  system. Detail can be found at EXTRIMUS webpage.