Owen M. Williams

Dynamic infrared scene projection: a review

Abstract Since the early 1990s, there has been major progress in the developing field of dynamic infrared scene projection, driven principally by the need for hardware-in-the-loop simulation of the oncoming generation of imaging infrared missile seekers and more recently by the needs for realistic simulation of the new generation of thermal imagers and forward-looking infrared systems. In this paper the current status of the dynamic infrared projection field is reviewed, commencing with an outline of its history. The requirements for dynamic infrared scene projection are examined, allowing a set of validity criteria to be developed. Each class of infrared projector that has been investigated—emissive, transmissive, reflective, laser scanner and phosphor—together with the specific technology initiatives within the class is described and examined against the validity criteria. In this way the leading dynamic infrared scene projection technologies are identified.

History of resistor array infrared projectors : hindsight is always 100% operability

Numerous infrared scene projection technologies have been investigated since the 1970s. Notably, from the late 1980s the development of the first resistor array infrared projectors gained leverage from the strong concurrent developments within focal plane array imaging technology, linked by the common need for large integrated circuits comprising a 2-dimensional array of interconnected unit cells. In the resistor array case, it is the unit cell comprising the resistively heated emitter and its dedicated drive circuit that determines the projector response to its associated scene generator commands. In this paper we review the development of resistor array technology from a historical perspective, concentrating on the unit cell developments. We commence by describing the technological innovations that forged the way, sharing along the way stories of the successes and failures, all of which contributed to the steady if somewhat eventful growth of the critical knowledge base that underpins the strength of todays array technology. We conclude with comments on the characteristics and limitations of the technology and on the prospects for future array development.

Resistor array infrared projector nonuniformity correction: search for performance improvement III

Results from sparse grid and flood nonuniformity correction (NUC) obtained using the DSTO Primary Infrared Scene Projection at 1:1 mapping ratio are reported. Residual nonuniformities in the 0.5-1.0% range are currently being achieved, the flood results equating to noise equivalent temperature differences in the 50-100mK range within the low drive thermal imager and FLIR simulation region. The NUC techniques and results are discussed in the light of both their present applicability and scope for further improvement.

Search for optimal infrared projector nonuniformity correction procedures

A search is commenced directed towards understanding the fundamental elements that underlie the generation of nonuniformity correction information in dynamic infrared scene projection systems.

Infrared projector effective blackbody temperature

The effective blackbody temperature used to specify the radiant output from an IR projector is defined formally as the temperature assumed by the blackbody target that generates the same signal radiance as the IR projector characterized. Analytical expressions and graphical analyses are developed enabling the calculation of the blackbody temperature in terms of both the actual device temperature and a specified active zone attenuation coefficient, the latter quantifying the deviation from blackbody behavior. Both the projector signal radiance and the signal current developed in the imaging unit under test illuminated by the projector are shown to be readily calculable once the value of the effective blackbody temperature is known. The analysis is applied to the comparison of the thin film resistor, silicon bridge resistor, and suspended membrane resistor emissive IR projection technologies.

Performance characteristics of thin film resistor arrays for infrared projector applications

The thin film resistor array choice of infrared projector technology is characterized by the comparatively large values of pixel fill factor and emissivity that can be attained but is limited by materials and heat transfer constraints. In this paper, the characteristics and limitations of an infrared projector test device based on a 2 X 25 bilinear thin film nichrome resistor array are described. The steady state and transient performance characteristics have each been assessed by use of both analytical and finite element heat transfer techniques. Test devices based on the design that gave the best predicted performance have been fabricated on a silicon wafer substrate by application of the conventional techniques of photolithography, etching and vacuum deposition, each array being comprised of a patterned polyimide insulation layer sandwiched between the substrate and the nichrome heating elements. Initial characterization experiments have demonstrated a 200 degree(s)C operating temperature capability and 10 - 90% rise and fall times of the order of 100 - 200 microsecond(s) . It is shown that the risetime can be improved significantly by application of a tailored drive voltage waveform, as can the falltime of appropriate thermal connection of the substrate to a low temperature heat sink. Modes of device failure are also discussed.

Emissive infrared projector sparse grid nonuniformity correction

Results from application of the sparse grid nonuniformity correction procedure within the DSTO resistor array Primary Infrared Scene Projection system are reported. In particular, the techniques used to cover the full dynamic range and to combat camera drift are described. The effectiveness of the projector NUC procedure is assessed and discussed in terms of the scope for further improvement.

Infrared projector flood nonuniformity correction characteristics

The DSTO Primary Infrared Scene Projection (PIRSP) system has been used to investigate the practical application of the emitter array flood nonuniformity correction (NUC) technique. In the first instance the measurements have been limited to the special case of unity mapping ratio. The methods for achieving unity mapping at sub-pixel registration are described; in particular, the use of Moire fringes for accurately measuring the optical distortion across the field-of-view and for attaining the optimal mapping condition. Application of the flood NUC technique within the PIRSP system is discussed in terms of its convergence limitations. The latter include the presence of spatial and temporal camera noise, optical distortion, the mixing of neighbouring pixel information due to the finite point spread function and radiance-to-voltage transformation errors.

Resolution and dynamic range capabilities of dynamic infrared scene projection systems

It is shown that commercial-off-the-shelf (COTS) renderers can be used for covering the simultaneous fine temperature resolution and large dynamic range specifications associated with the demands of medium-wave infrared scene projection applications. Appropriate use of the RGB capabilities of the COTS renderer combined with redistribution of the binary scene data by using a nonlinear transformation enables the dual specifications for 0.1 degree Celsius small signal temperature resolution and > 400 degree Celsius range in simulated temperature difference to be simultaneously met.

Infrared projector scene data real-time processor design

A new infrared projector emitter response curve-fitting procedure suitable for generating nonuniformity coefficients capable of being applied in existing real-time processing architectures is introduced. The procedure has been developed through detailed analysis of a Honeywell Multi-Spectral Scene Projector (MSSP) sparse array data set, combined with an appreciation of the underlying physical processes that lead to the generation of infrared radiance.