Steven Arthur Marlow

Procedures and recent results for two-color infrared projection

Testing of two-color imaging sensors often requires precise spatial alignment, including correction of distortion in the optical paths, beyond what can be achieved mechanically. Testing, in many cases, also demands careful radiometric calibration, which may be complicated by overlap in the spectral responses of the two sensor bands. In this paper, we describe calibration procedures used at the Air Force Research Laboratory hardware-in-the-loop (HWIL) facility at Eglin AFB, and present some results of recent two-color testing in a cryo-vacuum test chamber.

Advances in cryo-vacuum test capabilities for dual-band sensors at the kinetic kill vehicle hardware-in-the-loop simulation (KHILS) facility

The KHILS Vacuum Cold Chamber (KVACC) has formed the basis for a comprehensive test capability for newly developed dual-band infrared sensors. Since initial delivery in 1995, the KVACC chamber and its support systems have undergone a number of upgrades, maturing into a valuable test asset and technology demonstrator for missile defense systems. Many leading edge test technologies have been consolidated during the past several years, demonstrating the level of fidelity achievable in tomorrows missile test facilities. These technologies include resistive array scene projectors, sub-pixel non-linear spatial calibration and coupled two-dimensional radiometric calibration techniques, re-configurable FPGA based calibration electronics, dual-band beam-combination and collimation optics, a closed-cycle multi-chamber cryo-vacuum environment, personal computer (PC) based scene generation systems and a surrounding class-1000 clean room environment. The purpose of this paper is to describe this unique combination of technologies and the capability it represents to the hardware-in-the-loop community.

Measurement of the wideband infrared scene projector (WISP) radiometric and thermal resolution

The third generation of the Wide-band Infrared Scene Projector (WISP) resistor arrays has been delivered to the Air Force Research Laboratorys Kinetic Kill Vehicle Hardware-in-the-Loop Simulation facility. A critical parameter in determining the extent with which the thermal arrays simulate the real world is the radiometric and thermal resolution. The measurement of the resolution is dependent upon several factors including the input data word resolution, drive electronics resolution, system noise factors, and the measurement sensor. Several measurements were made to quantify the noise components of the WISP array and the measurement sensor to determine the limiting factor for the measurements. Due to the nonlinear transfer function between the command voltage and the projected radiance, measurements were made at several input levels to determine how the resolution varies as a function of command voltage level. Measurements were performed both with and without the spatial non-uniformity correction (NUC) applied to determine the impact of the NUC on the radiometric resolution. Based on the results of these measurements the resolution of the WISP arrays is defined in both radiometric and thermal units.

Characterization of the multiwavelength Scophony infrared scene projector

A Scophony Infrared Scene Projector (IRSP) was developed for use in evaluating thermal- imaging guidance systems. The IRSP is a very high frame rate, laser scanned projection system incorporating Scophony modulation. The Scophony IRSP serves as the image projection system in the Kinetic Kill Vehicle Hardware in the Loop Simulator (KHILS) terminal guidance simulation. It is capable of projecting multiband target engagement scenarios with high fidelity using Auras proprietary software/electronic control system. The Scophony IRSP utilizes acousto-optical (AO) devices to produce the required imagery at separate wavelengths, simultaneously. The separate scenes are combined and projected into the imaging guidance system. The Scophony IRSP has been installed and integrated into the KHILS facility at Eglin Air Force Base, Florida. Some performance characteristics of the IRSP have been measured. The current presentation provides a brief description of the Scophony IRSP and a performance evaluation. The performance characteristics measured are spot size, dynamic range, and field of view. Further characteristics may be reported as they become available.

Development of a two-color projection system for the KHILS Vacuum Cold Chamber (KVACC)

The KHILS Vacuum Cold Chamber (KVACC) was developed to provide the capability of performing hardware-in-the-loop testing of infrared seekers requiring scenes involving cold backgrounds. Being able to project cold backgrounds enables the projector to simulate high-altitude exoatmospheric engagements. Previous tests with the KVACC projection system have used only one resistive-array projection device. In order to realistically stimulate a 2-color seeker, it is necessary to project in two, independently controlled IR bands. Missile interceptors commonly use two or more colors; thus, a 2-color projection capability has been developed for the KVACC system. The 2- color projection capability is being accomplished by optically combining two Phase 3 WISP arrays with a dichroic beam combiner. Both WISP arrays are cooled to user-selected temperatures ranging from ambient temperature to below 150 K. In order to test the projection system, a special-purpose camera has also been developed. The camera is designed to operate inside the vacuum chamber. It has a cooled, all- reflective broadband optical system to enable the measurement of low radiance levels in the 3 - 12 micrometer spectrum. Camera upgrades later this year will allow measurements in two independent wavebands. Both the camera and the projector will be described in this paper.

Projector nonuniformity and spatial effects modeling

This paper presents mathematical models and measurements of the spatial noise a camera observes as it views a projection system with nonuniform emitter responses. The models account for the effects of the projector and camera spatial resolutions and of the alignment of the emitters with respect to the camera detectors. The models attempt to provide a better understanding of the spatial effects in a projection system and provide mathematical models for analyzing measurements and designing future hardware-in-the-loop tests. In previous work, one of the authors presented a model of the spatial, spectral, and temporal effects in a pixelized projector. In this paper, the previous model is simplified omitting the temporal effects (the scenes are assumed static). The model is then modified to describe random variations (noise) in the responses from one emitter to the next. This paper presents two different methods of modeling these effects. The first involves evaluating the spatial model directly. The second method involves performing a first order error propagation analysis on the spatial model and neglecting alignment effects. Measurements were performed to validate the models. The measurements are described in detail in a companion paper. In this paper, the spatial noise measurements are compared with model results. It was found that alignment effects were negligible, and the resulting predictions of the simplest model were in good agreement with the measured spatial noise.

Radiometric, noise, and spatial characterization of the wideband infrared scene projector

The Wideband Infrared Scene Projector (WISP) has been undergoing development for the AF Research Laboratory Kinetic Kill Vehicle Hardware-in-the-loop Simulator facility (KHILS) at Eglin AFB, FL. Numerous characterization measurements defining array dynamic range, spectral output, temporal response and nonuniformity have been performed and reported on in the past. This paper addresses the measurements and analyses performed to characterize the radiometric, spatial, and temporal noise errors induced by the array on a unit under test (UUT). An Amber camera was used as the UUT. The Amber camera spectral, spatial and radiometric response characteristics were measured. The camera spatial and temporal noises were measured by observing an extended blackbody. Similar measurements were then made on the WISP/UUT system by projecting uniform scenes. The WISP spatial and radiometric responses and the WISP-induced spatial and temporal noise were determined from the measurements. Although the measurements are unique to the UUT adopted, the WISP contribution to the system noise-equivalent temperature difference (NEDT) was determined. The spatial noise measurements provided data for validating a spatial noise model described in a companion paper. The measurements and models are useful for analyzing future measurements and predicting the impact of WISP on various test articles.

Laser scophony infrared scene project

A scophony infrared scene projector (IRSP) was developed by AURA Systems Inc. for use in evaluating thermal imaging guidance systems. The IRSP is a laser-scanned projector system incorporating scophony modulation with acousto-optical (AO) devices to produce multiband 96 x 96 image frames. A description of the system and preliminary test results with the Seeker Endo/Exo Demonstration Development (SEEDD) breadboard interceptor are addressed.

KVACC cryogenic complex scene test capability for 1 and 2-color sensors

The Kinetic Kill Vehicle Hardware-in-the-Loop Vacuum Cold Chamber (KVACC) has been a work in progress since its initial delivery in 1995. Originally delivered as a basic cryogenic test chamber with little real world capability, it has evolved over the years to a valuable test asset incorporating many leading edge test technologies. KVACC is now the centerpiece for the cryogenic complex scene test capability within the Air Force Research Laboratory (AFRL). The purpose of this paper is to describe the capabilities of KVACC as they have evolved since its initial delivery.

Accuracy of aperture irradiances from a resistor-array projection system

In seekers that never resolve targets spatially, it may be adequate to calibrate only with sources that have known aperture irradiance. In modern missile interceptors, the target becomes spatially resolved at close ranges, and the seekers ability to accurately measure the radiance at different positions in the scene is also important. Thus, it is necessary to calibrate the seekers with extended sources of known radiance. The aperture irradiance is given by the radiance integrated over the angular extent of the target in the scene. Thus radiance calibrations and accurately presenting the targets spatially produces accurate irradiances. The accuracy of the scene radiance is also important in generating synthetic imagery for testing seeker conceptual designs and seeker algorithms, and for hardware-in-the-loop testing with imaging projection systems. The routine procedure at the Air Force Research Laboratory Munitions Directorates AFRL/MNGG is to model and project the detailed spatial and radiometric content of the scenes. Hence, accurate depiction of the radiance in the scene is important. AFRL/MNGG calibrates the complete projection system (synthetic image generator and scene projector) with extended sources of known radiance, not unresolved sources of known irradiance. This paper demonstrates that accurate radiance calibrations and accurate spatial rendering do provide accurate aperture irradiances in the projection systems. In recent tests conducted by AFRL/MNGG, the projection system was calibrated in terms of radiance, and the aperture irradiances were determined both as they were observed in the synthetic images that drove the projection system and in the images of the projection system measured by the unit under test. The aperture irradiances were compared with the known truth data and errors were determined. This paper presents results of analyzing the errors associated with the observed aperture irradiances.