The generally accepted models for imaging and range performance modeling of thermal imagers have not been able to properly model under-sampled systems, i.e. staring focal plane arrays (FPAs). The ruling STANAGs 4349 and 4350 on measurement and modeling of Minimum Resolvable Temperature Difference (MRTD), by definition only deal with properly sampled systems and thus cannot address performance beyond the Nyquist frequency. This includes the FLIR92 model which is based on the models defined in STANAG 4350.
Range performance modeling, defined through STANAG 4347, is based on MRTD and thus likewise limits performance to below Nyquist frequencies. Practical experience has long shown that this limitation is not valid and development of new modeling techniques to address these problems has been performed e.g. in Germany, the TRM3 model, and in the US, with the NVTherm model. TRM3 addresses the under-sampled systems by introducing a concept of Minimum Temperature Difference Perceived (MTDP) which replaces MRTD for frequencies beyond Nyquist. NVTherm instead introduces a modified MRTD function through the concept of MTF squeeze. Typically, range performance predictions from NVTherm will increase ranges by some 15% over Nyquist resolution based predictions, and TRM3 based predictions exceed Nyquist ranges by up to 30%. A study is done to compare modeling results from these two models with laboratory measurements (MRTD) on QWIP long wave staring FPA based thermal imagers and finally relate these to empirical data from range performance field trials against actual targets.
Following on the success of the BIRC clip on thermal imaging sight for the BILL Anti-Tank Missile System, which was in fact the world's first military QWIP based thermal imager, and which has been successfully delivered to the Swedish Army in serial quantities, several new QWIP-based products from FLIR Systems AB in Sweden are now under contract for defense customers worldwide. These include the new Forward Observation Systems for Norway and Sweden, Airborne Search & Rescue Systems, and a new clip on thermal imager for the Bofors RBS 70 Air Defense Missile System. The latest of these products is the development of a High Resolution QWIP Thermal Imager, LIRC, under contract for an upgrade of a number of Swedish CV9040C Armored Fighting Vehicles for Swedish Army International Operations. The paper will focus on the rationale behind the system selection, the development of the military qualified QWIP Thermal Imagers and the current status of the program.
The Swedish Army is currently taking serial deliveries of a QWIP-based thermal imaging sight for anti-tank missiles. Two other applications of QWIP imagers are being evaluated for near time acquisition by the Swedish and Norwegian armies. This paper gives an overview of these programs and their background. Experience has been gained during field trials of these instruments, and highlights advantages and problems of this new technology and their solutions. One example is the low NETD of these imagers, which, while being a great advantage, also presents entirely new problems compared to older technologies. Reasons for the choice of QWIP technology for these programs are discussed. QWIP based thermal imagers are gaining ground in military applications and the Scandinavian countries are the early adopters
This paper discusses the different detector and systems technologies available today and in the near future, and how they measure up to these requirements. It is concluded that the only affordable alternative today and within the next ten years is QWIP technology. A system based on a Swedish developed and manufactured 320 X 240 QWIP has been demonstrated in the field. This and examples of other systems under development are presented.