Scene projection for HITL testing of LADAR seekers is unique because the 3rd dimension is time delay. Advancement in AFRL for electronic delay and pulse shaping circuits, VCSEL emitters, fiber optic and associated scene generation is underway, and technology hand-off to test facilities is expected eventually. However, size and cost currently projected behooves cost mitigation through further innovation in system design, incorporating new developments, cooperation, and leveraging of dual-purpose technology. Therefore a concept is offered which greatly reduces the number (thus cost) of pulse shaping circuits and enables the projector to be installed on the mobile arm of a flight motion simulator table without fiber optic cables. The concept calls for an optical MEMS (micro-electromechanical system) steerable micro-mirror array. IFOV’s are a cluster of four micro-mirrors, each of which steers through a unique angle to a selected light source with the appropriate delay and waveform basis. An array of such sources promotes angle-to-delay mapping. Separate pulse waveform basis circuits for each scene IFOV are not required because a single set of basis functions is broadcast to all MEMS elements simultaneously. Waveform delivery to spatial filtering and collimation optics is addressed by angular selection at the MEMS array. Emphasis is on technology in existence or under development by the government, its contractors and the telecommunications industry. Values for components are first assumed as those that are easily available. Concept adequacy and upgrades are then discussed. In conclusion an opto-mechanical scan option ranks as the best light source for near-term MEMS-based projector testing of both flash and scan LADAR seekers.
Addressing scene display noise problems in a manner consistent with real-time, hardware-in-the-loop testing requirements is an important issue. Measurements and analysis of different type noise problems in the WISP thermal array, an LCD visible projector and a dynamic laser spot projector have been undertaken. Solutions are offered, some of which are identical for very different kinds of noise. Trade-offs between noise reduction and other display features are discussed. This work originated at Eglin Air Force Base in the Guided Weapons Evaluation Facility.
Theory and data were used to characterize apparent blackbody temperature spatial variation for a thermal emitter array and determine its dependence on sensor wavelength. The effect of inactive resistor cells was also explored. Two kinds of spatial variations are (1) nonuniformities between the operating characteristics of different thermal array cells and (2) periodic variation due to spatially varying temperature within each cell. Essential developments were (a) curves for determining how thermal effects measured in one sensor band translate to that for another spectral band, (b) analysis of measured data in a one-temperature model and a two-temperature model, and (c) quantification of a defocus remedy for decreasing contrast between inactive and active cells. It is concluded that (A) apparent blackbody temperature and spatial variations thereof are lower for high wavelengths than at 2 microns, (B) use of a uniform, one-temperature blackbody model leads to the consequence of an exaggerated effective emissivity decrease at higher wavelengths, and (C) defocus circle diameter of 1.75 times the array cell spacing promotes optimum operation. This work was performed in Eglin's Guided Weapons Evaluation Facility (GWEF).
Members of the electro-optics community have essentially redefined the modulation transfer function (MTF) for focal plane arrays in different ways. Although these particular discrepancies make little difference below the Nyquist frequency, they are significant for system which push limits and process above-Nyquist frequency data. This issue is briefly reviewed, and it is shown that consistency with the Fourier method of defining MTF for focal plane arrays implied sample phase averaging, separation of the transferred sinusoid remnant with the input frequency from those of alias frequencies and recognition that the contrast ratio expression for MTF is a special case. Differences in the implications of discrete sampling analysis and the sample- and-hold operation are presented. In this approach MTF and alias effect are separated so that MTF represents a single-valued, global transfer entity and alias is defined by two different characterization metrics.
A method based on the line scan of a narrow slit pattern is described for MTF and MRTD determinations. A digital signal analyzer and automatic computer worksheet are utilized for executing this methodology. This single-scan procedure can replace a series of measurements with different sized bar patterns, and it facilitates rapid imaging system characterization for weapons scheduled for intensive hardware-in-the-loop testing. The challenge of this method was to overcome the practical data processing problems encountered. MRTD determinations using the slit-scan method agree very well with conventional bar pattern measurements and has been validated for a variety of imaging sensors. The automatic worksheet analysis determines MTF and both the objective, line scan MRTD as well as the 'eye-brain MRTD' based on a human vision model.