Ground testing of space and airborne imaging sensor systems is supported by visible-to-long wave infrared (LWIR) imaging sensor calibration and characterization, as well as hardware-in-the-loop (HWIL) simulation with high-fidelity complex scene projection to validate sensor mission performance. To accomplish this successfully, there must be the development and evaluation of technologies that are used in space simulation chambers for such testing, including emitter-array cryotesting, silicon-carbide mirror cryotesting, and flood-source development. This paper provides an overview of the efforts being investigated and implemented at Arnold Engineering Development Complex (AEDC).
Experiments presented in a previous paper established proof-of-principle that water, the most prevalent contaminant in
high-vacuum cryogenic systems, initially collects on the surfaces of optical components as a thin film of ice, and thus
can be detected and its thickness measured via multiple-beam thin-film interference phenomena. In those earlier
experiments, a molecular sieve zeolite in a canister external to a vacuum chamber served as a water source, while the
buildup of ice was measured using a HeNe laser beam reflected off the surface of a mirror with a quartz crystal
microbalance (QCM) used for verification of the mass accumulation. Additional experiments have improved upon the
techniques used earlier and provided further insight into the ice accumulation process. Use of a shorter wavelength (450
nm) laser in conjunction with a first-surface gold mirror produced greater depth of modulation and thus increased signal-to-
noise ratio in the light interference. Data reduction using cross-correlation analysis over single-period interference
records provided more accuracy and precision in the ice thickness measurements. Ice buildup under varying pressure
and temperature ranges established baseline conditions for transparent thin-film deposition, and the transition to ice
fracture and specular reflection. These recent experiments have demonstrated that the optical monitoring of ice
accumulation via multiple-beam interference is applicable over a wider range of mass and thicknesses than the
conventionally-used QCM method.
Ground testing of space- and air-borne imaging sensor systems is supported by Vis-to-LWIR imaging sensor calibration and characterization, as well as hardware-in-the-loop (HWIL) simulation with high-fidelity complex scene projection to validate sensor mission performance. To accomplish this successfully, there must be the development of tools, technologies, and methodologies that are used in space simulation chambers for such testing. This paper provides an overview of such efforts being investigated and implemented at Arnold Engineering Development Complex (AEDC).
Standard vacuum practices mitigate the presence of water vapor and contamination inside cryogenic vacuum chambers. However, anomalies can occur in the facility that can cause the accumulation of amorphous water ice on optics and test articles. Under certain conditions, the amorphous ice on optical components shatters, which leads to a reduction in signal or failure of the component. An experiment was performed to study and measure the deposition of water (H2O) ice on optical surfaces under high-vacuum cryogenic conditions. Water was introduced into a cryogenic vacuum chamber, via a hydrated molecular sieve zeolite, through an effusion cell and impinged upon a quartz-crystal microbalance (QCM) and first-surface gold-plated mirror. A laser and photodiode setup, external to the vacuum chamber, monitored the multiple-beam interference reflectance of the ice-mirror configuration while the QCM measured the mass deposition. Data indicates that water ice, under these conditions, accumulates as a thin film on optical surfaces to thicknesses over 45 microns and can be detected and measured by nonintrusive optical methods which are based upon multiple-beam interference phenomena. The QCM validated the interference measurements. This experiment established proof-of-concept for a miniature system for monitoring ice accumulation within the chamber.
An experiment was performed to study and measure the deposition of water (H2O) ice on optical component surfaces
under high-vacuum cryogenic conditions. Water was introduced into a cryogenic vacuum chamber via a hydrated
molecular sieve zeolite housed in a valved external chamber, through an effusion cell, and impinged upon a quartz-crystal
microbalance (QCM) and first-surface gold-plated mirror. A laser and photodiode setup external to the vacuum
chamber monitored the multiple-beam interference reflectance of the ice-mirror configuration while the QCM measured
the mass deposition. Data acquired and analyzed from this experiment indicate that water ice under these conditions
accumulates on optical component surfaces as a thin film up to thicknesses over 45 microns and can be detected and
measured by nonintrusive optical methods based upon multiple-beam interference phenomena. The QCM, a well-established
measurement technique, was used to validate the interferometer.
Arnold Engineering Development Center (AEDC) is tasked with visible-to-LWIR imaging sensor calibration and
characterization, as well as hardware-in-the-loop (HWIL) testing with high-fidelity complex scene projection to validate
sensor mission performance. They are thus involved in the development of technologies and methodologies that are
used in space simulation chambers for such testing. These activities support a variety of program needs such as space
situational awareness (SSA). This paper provides an overview of pertinent technologies being investigated and
implemented at AEDC.
The Space Chambers at the Arnold Engineering Development Center (AEDC) are continually exploring new
technologies to improve their characterization, calibration, and mission simulation testing capabilities for imaging
sensors. Part of this task is to develop and integrate methods to simulate high-temperature sources (on the order of 3,000
K) while maintaining the integrity of the low radiometric background within the cryovacuum chambers. The High
Temperature Source Simulator project at AEDC is exploring the use of laser diodes, LEDs, and resistive sources of
varying IR wavelengths to simulate these high-temperature sources within AEDC's Space Chambers. A brief summary
of previous work will be presented with a more detailed discussion of the recent cryospectral shift of the tested sources.
We found that the IR LEDs spectrally shift up to about 20% from their ambient center wavelength while the resistive
sources do not shift at all (as expected). Several different resistive sources as well as LEDs of varying wavelengths have
been procured and will continue to be tested.
Polarization signature information is becoming more useful as an added discriminant in a variety of signature analysis applications. However, there are few infrared scene projection systems that provide the capability to inject object simulation images with polarization content into an imaging sensor. In this paper, we discuss a polarization scene generator that is applicable to testing polarimetric sensor systems. The system was originally designed for operation in cryogenic-vacuum environments to test sensors subject to cold operation. However, it is also applicable to testing warm sensors that are sensitive to polarimetric signatures. This polarization scene generator is currently designed for mid-wave infrared (MWIR) operation. It includes two table-top sparse emitter arrays with individually addressable pixels, polarizers, a beam combiner, and filters to provide flexibility in spectral content. The emitter arrays are combined to generate an output with independent linearly polarized content. The current system generates S1 polarization states, S2 polarization states, or a linear combination of the two. The concept is robust because it is relatively unconstrained by the infrared (IR) scene generators used or the sensors tested.
Performance testing of space imaging systems is crucial to meeting the requirements of such systems for all types of
space applications. For over 30 years, the space chambers at the Arnold Engineering Development Center (AEDC)
have performed space sensor characterization, calibration, and mission simulation testing on space-based, interceptor,
and airborne sensors. The use of infrared scene projection systems in the cryovacuum ground-test environment is
essential to this testing and is a challenging task. Experiences from the space test facilities at AEDC offer lessons
learned from its experience in projection technologies, optical system design, optical material characteristics and
measurement (including cryodeposition), and positioning systems involved in performing ground testing of a sensor
system under flight conditions.
Arnold Engineering Development Center (AEDC) is involved in the development of technologies that enable hardwarein-
the-loop (HWIL) testing with high-fidelity complex scene projection to validate sensor mission performance.
Radiometric calibration with National Institute of Science and Technology (NIST) radiometers has improved radiometric
and temporal fidelity testing in this cold background environment. This paper provides an overview of pertinent
technologies being investigated and implemented at AEDC to support a variety of program needs such as HWIIL testing
and space situational awareness (SSA).
Polarization signature information is becoming more useful as an added classifier in a variety of signature analysis
applications. However, there are few infrared (IR) scene
projection systems that provide the capability to inject target
simulation images with polarization content into a seeker, or
other imaging sensor. In a previous paper1 we discussed
experimental results for an infrared (IR) polarized scene
generator (PSG) concept demonstrator. The concept
demonstrator operated in ambient environmental conditions and
displayed polarized scenes of resolved targets. The IR PSG
demonstrator that is the goal of this research must be capable of
testing sensor systems operating in cryogenic-vacuum (cryo-vac
or CV) environments. The IR PSG must also be able to
accurately project scenes with unresolved polarized targets. As
part of the development process, several potential PSG
components are being tested in ambient and liquid nitrogen
(LN2) environments to verify functionality and changes in
behavior at ambient, vacuum, and cryovac conditions. This
paper presents test data for several of the components.
Components tested were an IR source, a polarizer, and motion
control components. We also present test data for an imaging
polarimeter being developed to validate the PSG.
KEYWORDS: Calibration, Data modeling, Sensors, Data acquisition, Mirrors, Projection systems, Light emitting diodes, Systems modeling, Black bodies, Cryogenics
The characterization, calibration, and mission simulation testing of imaging sensors require continual involvement in the
development and evaluation of radiometric projection technologies. Arnold Engineering Development Center (AEDC)
uses these technologies to perform hardware-in-the-loop (HWIL) testing with high-fidelity complex scene projection
technologies that involve sophisticated radiometric source calibration systems to validate sensor mission performance.
Testing with the National Institute of Standards and Technology (NIST) Ballistic Missile Defense Organization
(BMDO) transfer radiometer (BXR) and Missile Defense Agency (MDA) transfer radiometer (MDXR) offers improved
radiometric and temporal fidelity in this cold-background environment. The development of hardware and test
methodologies to accommodate wide field of view (WFOV), polarimetric, and multi/hyperspectral imaging systems is
being pursued to support a variety of program needs such as space situational awareness (SSA). Test techniques for the
acquisition of data needed for scene generation models (solar/lunar exclusion, radiation effects, etc.) are also needed and
are being sought. The extension of HWIL testing to the 7V Chamber requires the upgrade of the current satellite
emulation scene generation system. This paper provides an overview of pertinent technologies being investigated and
implemented at AEDC.
The application of infrared scene projection systems in the cryovacuum ground-test environment is a very challenging
process. Work performed at Arnold Engineering Development Center (AEDC) in the past few years can offer lessons
learned from its experience in projection technologies, optical system design, optical material characteristics and
measurement (including cryodeposition), positioning systems, and pertinent analytical tools involved in performing
ground testing of a sensor system under flight conditions. Such testing is fundamental to characterizing its performance,
and should be accomplished early and often in order to manage operational uncertainty and reduce system life-cycle cost.
AEDC provides a comprehensive capability that strives to ensure system performance evaluations that are not limited by
test infrastructure. For over 30 years, the space chambers at AEDC have performed space sensor characterization,
calibration, and mission simulation testing on space-based, interceptor, and airborne sensors. This paper describes recent
efforts at AEDC to enhance this cryovacuum test capability.
KEYWORDS: Data modeling, Sensors, Calibration, Light emitting diodes, Black bodies, Optical components, Data conversion, Mirrors, Projection systems, Data acquisition
The characterization, calibration, and mission simulation testing of space-based, interceptor, and air-borne sensors
require a continual involvement in the development and evaluation of radiometric projection technologies. Activities at
Arnold Engineering Development Center (AEDC) include Hardware in the Loop (HWIL) testing with high-fidelity
complex scene-projection technologies as well as improvements in the radiometric source-calibration systems. These
technologies are integrated into a low cryo-vacuum (~20 K) environment. The latest scene simulation and HWIL
projection technologies are being investigated that can produce desired target temperatures and target-to-sensor ranges
such that sensor mission performance can be evaluated. These technologies include multiple-band source subsystems
and special spectral-tailoring methods, as well as comprehensive analysis and optical properties measurements of the
components involved. Emphasis areas include the development of methodologies to test wide field of view (WFOV),
polarimetric, and multi/hyperspectral radiometric imaging systems.
Polarization is increasingly being considered as a method of discrimination in passive sensing applications. In this paper
the degree of polarization of the thermal emission from the emitter arrays of two new Santa Barbara Infrared (SBIR)
micro-bolometer resistor array scene projectors was characterized at ambient temperature and at 77 K. The emitter
arrays characterized were from the Large Format Resistive Array (LFRA) and the Optimized Arrays for Space-Background Infrared Simulation (OASIS) scene projectors. This paper reports the results of this testing.
Polarization signature information is becoming more useful as an added discriminant in a variety of signature analysis
applications. However, there are few infrared scene projection systems that provide the capability to inject target
simulation images with polarization content into a seeker, or other imaging sensor. In this paper, we discuss a
polarization scene generator (PSG) concept that is applicable to testing sensor systems operating in cryogenic-vacuum
environments. This polarization scene generator concept demonstrator system was constructed from off-the-shelf
technology using commercially available mid-wave infrared (MWIR) scene projectors based on micromirror device
display technology, standard infrared polarizers, and standard IR cameras. The demonstrator system used two digital
micromirror device (DMD)-based displays, each projecting orthogonal polarization states, which were then combined to
generate images with pixels having independent S1 or S2 polarization content. This concept is robust because it is
relatively unconstrained by the IR scene generators used or by the seekers tested. This paper discusses the test results of
the concept demonstrator system with regard to sensitivity to misalignment, radiance mismatch, and display uniformity.
The characterization, calibration, and mission simulation testing of space-based, interceptor, and airborne sensors require a continual involvement in the development and evaluation of radiometric projection technologies. Recent efforts at the Arnold Engineering Development Center (AEDC) include hardware-in-the-loop (HWIL) testing with high-fidelity, complex scene projection technologies integrated into a low-cryovacuum (~20 K) environment as well as improvements in the radiometric source calibration systems. The latest scene simulation and projection technologies are being investigated, technologies that can produce desired target temperatures and target-to-sensor ranges that will make it possible to evaluate sensor mission performance. These technologies include multiple-band source subsystems and special spectral tailoring methods, as well as comprehensive analysis and optical properties measurements of the components involved. This paper discusses the implementation of such techniques at AEDC.
Polarization signature information is becoming more useful as an added discriminant in a variety of signature analysis
applications. However, there are few infrared scene projection systems that provide the capability to inject target
simulation images with polarization content into a seeker, or other imaging sensor. In this paper, we discuss a
polarization scene generator (PSG) concept that is applicable to testing sensor systems operating in cryogenic-vacuum
environments. This polarization scene generator concept demonstrator system was constructed from off-the-shelf
technology using commercially available mid-wave infrared (MWIR) scene projectors based on micromirror device
display technology, standard infrared polarizers, and standard IR cameras. The demonstrator system used two digital
micromirror device (DMD)-based displays, each projecting orthogonal polarization states, which were then combined to
generate images with pixels having independent S1 or S2 polarization content. This concept is robust because it is
relatively unconstrained by the IR scene generators used or by the seekers tested. This paper discusses the test results of
the concept demonstrator system with regard to sensitivity to misalignment, radiance mismatch, and display uniformity.
The Arnold Engineering Development Center (AEDC) has performed characterization and calibration of space-based,
airborne, and interceptor sensor systems for over 35 years. The 7V and 10V Chambers provide a suite of IR and visible
target systems that operate in a simulated space background (< 20K) and allow complete evaluation of sensor
performance within a single test installation. Test facility upgrades are continuously pursued to keep pace with evolving
sensor technologies.
This paper describes the methodology used to perform calibration and characterization of sensor systems in the AEDC
7V and 10V test chambers. Complex target systems that provide the ability to evaluate system performance against
representative mission scenarios are included in both test chambers. Representative results associated with the
calibration and mission simulation capabilities are shown. The overall status of the 7V and 10V Chamber facilities is
described, and plans to implement improved calibration capabilities are discussed.
Results from analysis performed on data collected during checkout testing of source systems included in both sensor test
chambers are presented. The results illustrate the ability of the 7V and 10V Chambers to facilitate complete
characterization of sensor performance with a high degree of accuracy in a representative mission operating
environment.
The space simulation chambers at the Arnold Engineering Development Center (AEDC) have performed space sensor
characterization, calibration, and mission simulation testing on space-based, interceptor, and air-borne sensors for more
than three decades. A continual effort to implement the latest scene simulation and projection technologies into these
ground-based space sensor test chambers is necessary to properly manage the development of space defense systems.
This requires the integration of high-fidelity, complex, dynamic scene projection systems that can provide the simulation
of the desired target temperatures and ranges. The technologies to accomplish this include multiple-band source
subsystems and special spectral tailoring methods, as well as comprehensive analysis and optical properties
measurements of the components involved. Implementation of such techniques in the AEDC space sensor test facilities
is discussed in this paper.
The ground testing of a sensor system under flight conditions is fundamental to characterizing its performance. It should be accomplished early and often in order to manage operational uncertainty and reduce system life-cycle cost. As a DoD Major Range Test Facility Base (MRTFB), the Arnold Engineering Development Center (AEDC) provides a comprehensive capability that strives to ensure system performance evaluations that are not limited by test infrastructure. For over 30 years, the space chambers at AEDC have performed space-sensor characterization, calibration, and mission
simulation testing on space-based, interceptor, and airborne sensors. In partnership with Missile Defense Agency (MDA), capability upgrades are continuously pursued to keep pace with evolving sensor technologies. A critical aspect of these chambers is the quality of the mirror coatings used to project simulated target scenes to the unit under test in low-background cryogenic conditions. This paper discusses the recent effort at AEDC to refurbish and/or replace the
mirror collimating systems in their 7V and 10V Aerospace Chambers and the coating choices that have been considered.
Testing system performance early and often under flight conditions is fundamental to managing uncertainty in system performance predictions and reducing system life-cycle cost. As a Department of Defense (DoD) Major Range Test Facility Base (MRTFB), Arnold Engineering Development Center (AEDC) strives to ensure that DoD system performance tests are not limited by test and evaluation capabilities. For over 30 years, the space chambers at AEDC have performed space sensor characterization, calibration, and mission simulation testing on space-based, interceptor, and air-borne sensors. In partnership with the Missile Defense Agency (MDA), AEDC continuously pursues capability upgrades in order to keep pace with evolving sensor technologies. Upgrades to sensor test facilities require rigorous facility characterization and calibration efforts, all of which are routinely included in AEDC's annual activities to ensure quality test data. This paper discusses the status of such upgrades especially with regard to scene projection.
For over 30 years, the Space Systems Test Facility and space chambers at the Arnold Engineering Development Center (AEDC) have been used to perform space sensor characterization, calibration, and mission simulation testing of space-based, interceptor, and airborne sensors. In partnership with the Missile Defense Agency (MDA), capability upgrades are continuously pursued to keep pace with evolving sensor technologies. Upgrades to sensor test facilities require rigorous facility characterization and calibration activities that are part of AEDC's annual activities to comply with Major Range Test Facility Base processes to ensure quality metrology and test data. This paper discusses the ongoing effort to characterize and quantify Aerospace Chamber 7V measurement uncertainties. The 7V Chamber is a state-of-the-art cryogenic/vacuum facility providing calibration and high-fidelity mission simulation for infrared seekers and sensors against a low-infrared background. One of its key features is the high fidelity of the radiometric calibration process. Calibration of the radiometric sources used is traceable to the National Institute of Standards and Technology and provides relative uncertainties on the order of two to three percent, based on measurement data acquired during many test periods. Three types of sources of measurement error and top-level uncertainties have been analyzed; these include radiometric calibration, target position, and spectral output. The approach used and presented is to quantify uncertainties of each component in the optical system and then build uncertainty diagrams and easily updated databases to detail the uncertainty for each optical system. The formalism, equations, and corresponding analyses are provided to help describe how the specific quantities are derived and currently used. This paper presents the uncertainty methodology used and current results.
A continual effort to develop the latest scene simulation technologies into actual space simulation test chambers is necessary to ensure that the U.S. has the proper ground test capabilities to test space defense systems. This involves the integration of high-fidelity, complex, and dynamic scene projection systems, including multiple-band source subsystems and the spectral tailoring methods used to simulate the desired target temperatures. Comprehensive analysis and measurement of the properties of the optical components involved are also required. This paper discusses implementation of these techniques in the space sensor test facilities of the Arnold Engineering Development Center (AEDC).
The process of integrating high-fidelity, complex dynamic scene projection systems into space simulation test chambers is a continual challenge which requires comprehensive analysis and measurement of the properties of the optical components involved. This includes the multiple-band source subsystems and the spectral tailoring methods invoked to represent target temperatures. Techniques currently employed in the AEDC space sensor test facilities will be discussed in this paper.
The 10V Chamber Test Facility at the Arnold Engineering Development Center (AEDC) is being upgraded to provide a closed-loop capability to assess multi-band electro-optical sensor performance under realistic operational scenarios against evolving threats. This test facility will leverage existing facilities and expertise from several Government agencies including AEDC, Army/AMCOM, and USAF/KHILS to investigate performance issues during ground testing at cryogenic conditions. Radiometrically accurate simulated scenes will be presented to the test article using dual-band infrared point sources, a dual-band infrared emitter array projector, and a visible array projector. Various optical assemblies will be required to project the images from these radiometric source systems onto the sensor aperture.
The infrared point sources will be positioned in the XY plane using two-stage linear translators, which must meet stringent spatial coverage and position accuracy requirements to create realistic closed-loop target motion. A large two-axis steering mirror will simulate sensor line of sight movements for the blackbody sources. A high-speed jitter mirror will simulate high frequency image motion for the emitter arrays. These mirror systems must be vibrationally isolated to minimize the jitter induced in other optical elements.
Narcissus and ghost image effects will be minimized using appropriate fabrication, shielding, and calibration techniques. A multi-spectral calibration and alignment system will be integrated into the facility to ensure proper radiometric and goniometric operation of the various target sources.
The target and optical systems must all meet performance specifications at cryo-vacuum conditions. Code V will be the primary tool used to evaluate wave front error and distortion coating performance for ghosting/polarization/transmission effects, optical manufacturing errors, and energy-on-detector (EOD). Finite element models of the facility will be used to analyze the structural rigidity and dynamics of the components due to the cryogenic environment.
The continuing effort to provide a complex, broad-based (low-background, complex dynamic scene projection) sensor test capability at Arnold Engineering Development Center involves the development of scene projection technologies and their integration into existing space chambers. New radiometric source concepts are being investigated that will allow greater flexibility in simulating multiple target scenarios for space sensor testing. Alternate sources, filtering techniques, beam combining methods, and optical power delivery systems are being investigated for possible use in meeting the ultimate objectives of current and anticipated testing programs.
In order to provide multiple radiometrically characterizable targets for testing in Arnold Engineering Development Center's (AEDC's) 10V chamber, an extension of current scene generation methods is required. New concepts are also being investigated that will allow more flexibility in reaching the desired simulation parameters. Alternate sources, filtering techniques, beam combining methods, and optical power delivery systems may prove useful in meeting the ultimate objectives of the testing program. This paper presents the results of this effort.
The operation of the Direct Write Scene Generator (DWSG) at the Arnold Engineering Development Center (AEDC) to drive a fiber array projection system is reported. The fiber array absorbs the input radiation from the laser-based system and produces broadband infrared output through blackbody cavities fabricated on the ends of the optical fibers. A test program was accomplished to quantify the performance of the fiber array with respect to input laser power and optical pulse width. Static and dynamic scenes were also projected with the device and recorded with an IR camera system. This paper presents the results of this work.
The operation of the Direct Write Scene Generator (DWSG) to drive a fiber array projection system is reported in this paper. The fiber array absorbs the input radiation from the laser-based system and produces broadband infrared output through blackbody cavities fabricated on the ends of the optical fibers. A test program was begun to quantify the performance of the fiber array with respect to input laser, power, temporal response, spatial uniformity, IR output, and fiber-to-fiber crosstalk. Static and dynamic scenes will also be projected with the device and captured with a camera system. Preliminary projection of a simple scene has been accomplished.
An advanced sensor test facility, located at Arnold Engineering Development Center (AEDC) has been designed for sensor calibration and performance characterization of advanced infrared sensors for strategic and tactile systems. During the past few years a sensor test facility, known as the 7V Chamber, has been used to support the Army's Interceptor Programs. This chamber complements other focal-plane-array and sensor-test capabilities developed at AEDC to provide ground test support for strategic and tactical sensor systems. The 7V Chamber is a state-of-the-art cryo-vacuum facility providing calibration and high-fidelity mission simulation using complex backgrounds and targets. This paper describes a validation effort for determining the point spread function (PSF) and corresponding wavefront errors. A method is described for measuring a highly under-sampled PSF and determining the corresponding wavefront error. This method employs a knife- edge distribution inversion of Bessel-distributed densities with a Gaussian approximation to implement a nonlinear least- squares functional fit using a Levenberg-Marquardt method.
This paper describes the investigation and potential utility of using the Direct Write Scene Generator (DWSG) to project onto a sensor system's focal plane array (FPA) through its optical telescope. The test approach requires development of magnifier/collimator systems to expand the DWSG output to the sensor telescope. A lens system has been procured to facilitate the projection to the full array of a standard CCD with an attached lens system. A demonstration of operation of the DWSG through camera optics has been recorded. The capability of the DWSG system to measure FPA crosstalk has been examined in some detail.
Technology effects are underway at Arnold Engineering Development Center to extend closed-loop Direct Write Scene Generation capabilities to include advanced signal-injection and thermal-array optical projection capabilities. Laser- projection for sensor optics with or without optics installed, signal-injection, and thermal-array optical projection schemes provide direct simulation of dynamic electro-optic sensor systems. FPAs and electro-optic sensors are stimulated with simulated infrared scenes for optical diagnostics and evaluation of focal plane arrays or electro- optic sensor systems, and to simulate complex mission scenarios. Closed-loop operation can provide high-fidelity simulation of complex infrared scenes, sensor optical blurring, and other temporal effects such as jitter. Although all optical stimulation and testing methods have inherent advantages, compromises, and limitations, there is a common desire to not only maximize optical simulation and photonic stimulation fidelity through advanced verification and validation efforts, but to also minimize computational requirements for high-performance diagnostics. Computational and source-to-FPA oversampling have very similar fidelity defects and requirements for signal-injection, laser- projection, and thermal-array optical projection diagnostic- methods. This paper briefly describes scene generation and projection technology and corresponding research devoted to sampling issues and criteria related to FPA oversampling, corresponding fidelity defects, and performance trades.
The viability of extending the Direct Write Scene Generator (DWSG) to project to a sensor system with an optical telescope installed has been investigated. The test approach requires development of transmissive or reflective screens and/or collimator systems to expand the DWSG output to the sensor telescope. Several optical configurations have been examined to accommodate this capability. Measurements of the optical spot size on a camera with a zoom lens have been compared to CODE V predictions. Analysis has been performed to determine the practical limitations of this configuration with regard to testing sensors with a set field of view. A demonstration of operation of the DWSG through camera optics has been accomplished. The utility of this new capability to closed-loop operation has also been examined.
Arnold Engineering Development Center's (AEDC) Focal Plane Array Test Chamber (FPATC) is currently operational and has been involved in the testing and evaluation of focal plane arrays (FPAs) developed for interceptor applications. Testing included blackbody characterization, laser compatibility, and projection of AEDC test patterns and scenes. Efforts continue to be made to improve the capability of direct write scene generation (DWSG) to support the latest in FPA technology. A demonstration of closed-loop operation has been accomplished.
This paper describes recent research at Arnold Engineering Development Center to investigate aspects of using laser-based direct write scene generation photonics complementary to traditional blackbodies and thermal sources for focal-plane-array diagnostics. The equivalence of using lasers and thermal sources for photodetection and focal-plane-array evaluation depends not only on generating the same mean number of detectable photoevents, but also depends on generating the same photonic noise needed to accurately simulate photostochastic events representative of statistical ensembles and operational envelopes expected from normal focal-plane-array modes and sensor operation. Effective signal-to-noise ratios and photodetection equivalence also depend on the absence of signal artifacts or perturbations resulting from using laser-based photonics for optical diagnostics. The useful domain and relevance for using lasers complementary to thermal sources for photodetector and focal- plane-array diagnostics have been investigated to ascertain differences and similarities.
This paper describes recent technology at Arnold Engineering Development Center to provide real-time closed-loop image synthesis. Laser-based direct-write scene generation methods are used to simulate dynamic sensor operation and complex infrared scenes. New photonic image- synthesis methods employ image-to-object Whittaker-Shannon sampling, anisoplanatic optical convolution by quasi-isoplanatic spatial decomposition, and high-speed digital electronics for acousto-optic modulation.
The scene generation test capability (SGTC) has achieved an initial operating capability (IOC) at the Arnold Engineering Development Center (AEDC) using direct write scene generation (DWSG). This test tool will be able to present realistic mission scenarios directly to sensor focal plane arrays (FPAs) for developmental and operational test and evaluation (DT&E and OT&E), and will be integrated with the full-up sensor test capabilities at AEDC. The concept validation phase of this program is an operational system that is currently involved in sensor testing. The final phase provides scene projection at three infrared wavelengths and one visible wavelength. The facility is ready for FPA testing. This paper presents an overview of the current SGTC program, including a report of the hardware testing performed as part of the validation process.
KEYWORDS: Control systems, Electronics, Staring arrays, Signal attenuation, Sensors, Frequency conversion, Computer aided design, Digital signal processing, Clocks, Signal processing
The Arnold Engineering Development Center (AEDC) Scene Generation Test Capability (SGTC) program has completed the development of a laser based Direct Write Scene Generation (DWSG) facility that provides dynamic mission simulation testing for infrared (IR) Focal Plane Array (FPAs) and their associated signal processing electronics. The AEDC DWSG Focal Plane Array Test Capability includes lasers operating at 0.514, 1.06, 5.4, or 10.6 micrometers , and Acousto-Optic Deflectors (AODs) which modulate the laser beam position and amplitude. Complex Radio Frequency (RF) electronics control each AOD by providing multi-frequency inputs. These inputs produce a highly accurate and independent multi-beam deflection, or `rake', that is swept across the FPA sensor under test. Each RF amplitude input to an AOD translates into an accurate and independent beam intensity in the rake. Issues such as scene fidelity, sensor frame rates, scenario length, and real-time laser beam position adjustments require RF control electronics that employ the use of advanced analog and digital signal processing techniques and designs. By implementing flexible system architectures in the electronics, the overall capability of the DWSG to adapt to emerging test requirements is greatly enhanced. Presented in this paper is an overview of the signal processing methodology and designs required to handle the DWSG requirement. Further, electronic design techniques that enabled the system to be implemented within program cost constraints will also be presented. These electronic designs include a broad range of disciplines including digital signal processing hardware and software, programmable logic implementations, and advanced techniques for high fidelity RF synthesis, switching, and amplitude control. Techniques for validating electronic performance will also be presented along with data acquired using those techniques.
The Scene Generation Test Capability (SGTC) program at AEDC has completed development of the Direct Write Scene Generation (DWSG) test facilities which provide a dynamic mission simulation capability for Focal Plane Arrays (FPAs) and their associated signal processing electronics. The first phase of the program was completed in September 1991 and supplied a near-term test capability (designated for Transportable Direct Write Scene Generator, or TDWSG) to meet the test requirements of future early warning sensor systems. Over the last two years the TDWSG has been involved in test activities to validate the DWSG technique for meeting system mission simulation requirements. The DWSG approach is based on the ability to accurately control the position and amplitude of multiple laser beams through the application of radio frequencies to a set of acousto-optic deflectors. One of the primary concerns related to using the TDWSG for mission simulation is the system noise associated with the test facility. A system noise study was conducted using a low noise LWIR Si:As FPA and an optical power meter. Radiometric signal and noise measurements were acquired and used as a baseline for comparison with the TDWSG data to quantify the noise contributions of individual TDWSG subsystems. This paper presents an overview of the DWSG concept, results of the system noise study, and results of system precision measurements.
Scene generation systems which utilize laser radiation as a source must demonstrate the equivalence of focal plane array (FPA) response to this radiation as compared to the continuous radiation of realistic in-band scene. AEDCs Direct Write Scene Generation technique has been developed to provide mission scenarios for FPA testing. In the course of this development, radiative source issues have been examined in some detail to validate the technique. The purpose of this paper is to report the results of this investigation. In particular the response of a variety of FPAs to pulsed laser radiation is discussed.
The Arnold Engineering Development Center (AEDC) has developed new test technologies and methodologies for realistic mission simulations testing of IR space-based sensors. These technologies and methodologies have been combined into an integrated approach for space sensor testing. Direct write scene generation plays a critical role in this integrated approach and is being applied in two new AEDC test facilities. Prior to performing the first test in such a new facility, a critical but often overlooked process must be completed. This critical process demonstrates that the test facility can indeed provide a realistic, NIST traceable simulation of a sensor's mission. This process is complex and must be uniquely tailored for each individual test facility and sensor mission. Such a process can be designed to address both developmental test and evaluation and operational test and evaluation concerns. A case study based on AEDC's direct write scene generation technology will be used to illustrate the issues related to the validation, verification, and accreditation process.
The scene generation test capability (SGTC) continues to be developed at Arnold Engineering Development Center (AEDC) using direct write scene generation. This test tool will be able to present realistic mission scenarios directly to sensor focal plane arrays for developmental and operational test and evaluation, and will be integrated with the full-up sensor test capabilities at AEDC. The concept validation phase of this program provided an operational system which is currently involved in sensor testing. Noise measurements have also been made in some detail on this system. The final phase of the program will provide scene projection at three infrared wavelengths and one visible wavelength. This paper presents an overview of the current SGTC program, including experimental data taken with the concept validation hardware.
The Arnold Engineering Development Center (AEDC) has developed new test technologies and methodologies for realistic mission simulation testing of infrared space-based sensors. These technologies and methodologies have been combined into an integrated approach for space sensor testing. This approach integrates component, subsystem, and system level tests. Computational models are used to address both sensor optic and chamber optics effects. Simulations and real-world phenomenology are used to generate scenarios tailored for each specific orbit, mission, threat, etc. The synergism of test technology and sensor design characteristics is evaluated and integrated into the test process in order that issues ranging from radiometric calibration to overall mission performance may be properly addressed. A case study based on AEDC's Direct Write Scene Generation (DWSG) test technology is used to illustrate this integrated approach.
In Direct Write Scene Generation (DWSG) a critical lens design parameter is the optical crosstalk, or the undesired energy incident on adjacent pixels (EOAD). Crosstalk must be minimized to obtain the proper scene projection fidelity. The laser scan lens systems used in this scene generation technique are typical f(theta) and can be optimized by adjusting the diameter of the input gaussian beam in relation to the entrance pupil. The optimum gaussian beam diameter is dependent on the resolution requirements placed on a system and the test article metrics. Optical cross talk calculations are used to gauge the performance of systems with square and circular entrance pupils. This paper will address the calculated relationship between crosstalk and the truncation of the Gaussian input beam.
A Scene Generation Test Capability (SGTC) is under development at Arnold Engineering Development Center (AEDC) which uses Direct Write Scene Generation (DWSG) as a tool to project realistic mission scenarios into sensors operating in a simulated space system environment. This capability can reduce the risk associated with developing advanced sensor systems. The second phase of this program, a Focal Plane Array Test Chamber (FPATC), is currently underway which expands the capabilities of the phase one Transportable Direct Write Scene Generator (TDWSG) reported previously. Projection wavelengths for the system include 0.514, 1.06, 5.4 and 10.6 micrometers . Multiple chamber configurations will be used to accommodate different types of test articles. The FPATC is also transportable. User testing has begun in the TDWSG. This paper will present an overview of the current SGTC program.
A Transportable Direct Write Scene Generation (TDWSG) test capability has been developed at the Arnold Engineering Development Center (AEDC) for visible and IR focal plane array (FPA) testing which utilizes laser sources and two-axis acousto-optic deflectors. The objective of this effort is to provide a test and evaluation facility which will help reduce space sensor development risks by testing FPAs with their data subsystems against realistic mission scenarios in a space environment. The TDWSG's performance envelope covers both high- speed (100 microsecond(s) frame time) scanning and slower staring formats. A modular concept is used to address large (512 X 512 pixel) FPAs. Scene inputs can be derived from various sources including the Strategic Scene Generation Model (SSGM). A continuance of this effort is being applied toward development of a fixed-site Scene Generation Test Capability (SGTC).
A scene generation capability is under development at the Arnold Engineering Development Center (AEDC)
for visible and lR focal plane array (FPA) testing that uses two-axis acousto-optic (AO) deflectors. A multifrequency
RF input creates a rake of output beams which is step-scanned across the face of the imaging
device. Each component of the rake is modulated independently, and the beams are blanked during the
shift from one row of pixels to the next. The expected maximum frame rate is 20 kHz, with operation
synchronized to the operation of the FPA. A modular concept is being investigated to address large (51 2 x
512 pixel) FPAs. This AEDC Direct Write Scene Generation (DW5G) technology is being applied toward
development of a transportable and a fixed-site Scene Generation Test Capability (SGTC).
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