KEYWORDS: Space operations, Stars, Data compression, Sensors, Receivers, Data communications, Optical tracking, Detection and tracking algorithms, Jupiter, Sun
The goal of a realistic interstellar mission to the nearest star recently announced by NASA as a new space exploration objective targeted for circa 2069, presents a daunting but exciting prospect for creating a pragmatic but visionary mission design. For such a long-range mission goal, mission enabling technological developments need to be developed and evaluated in precursor missions beyond the edge of the solar system. NASA is stimulating such a pathfinder mission starting this year to promote efforts that could build upon what has been accomplished by New Horizons, and for which APL can leverage heat shield technology used on the Parker Solar Probe. An academically-inspired graduate-student supported study at Johns Hopkins University reported on our progress presented at the 2018 Committee on Space Research meeting (COSPAR 2018) in assessing and evaluating several critical subsystem issues and fruitful lines of innovation to improve dual-band downlink performance for a 1000 AU (1.5 × 1011 km) mission. This work recapitulates and extends some work done much earlier at APL. We propose to quantify several critical subsystem trades essential to interstellar spacecraft communications, command and data handling, and critical guidance, navigation, and control (GNC) functions. These include the following: optimizing trajectories during transit and arrival in the targeted system, acquiring a quality mix of relevant highly-compressed scientific data, providing an accurate navigation capability at sub-relativistic speeds, insuring a robust communication system over extraordinary distances, and maintaining an effective command and data handling subsystem, while acknowledging the criticality of a survivable spacecraft bus in an illdefined, harsh and very long duration environment.
Optical beam spread and beam quality factor in the presence of both an initial quartic phase aberration and atmospheric turbulence are studied. We obtain the analytical expressions for both beam radius-squared and the beam quality factor using the moment method, and we compare these expressions with the results from Monte Carlo simulations, which allow us to mutually validate the theory and the Monte Carlo simulation codes. We then analyze the first- and second-order statistical moments of the fluctuating intensity of a propagating laser beam and the probability density function versus intensity as the beam propagates through a turbulent atmosphere with constant Cn2. At the end, we compare our analytical expression and our simulations with field test experimental results, and we find a good agreement.
We simulate the propagation of both a partially spatially coherent infra-red (IR) and a visible laser beam through a turbulent atmosphere, and we compare the intensity fluctuations produced in the simulation to the intensity fluctuations that are observed in both maritime and terrestrial environments at the US Naval Academy. We focus on the effect of the level of turbulence and the degree of the beam's spatial coherence on the receiver scintillations, and we compare the probability density function (PDF) of the intensity in our simulation to the experimental data. We also investigate the effect of optical beam spreading on the coherent and partially coherent laser beams along the propagation path.
KEYWORDS: Digital signal processing, Monte Carlo methods, Atmospheric turbulence, Turbulence, Atmospheric optics, Atmospheric propagation, Gaussian beams, Solids, Free space optical communications, Laser beam propagation
Optical beam spread and beam quality factor in the presence of both quartic phase aberrations and atmospheric turbulence is numerically analyzed. We obtain analytical expressions for both the mean-square beam radius and the beam quality factor using the moment method, and we compare these expressions to the results from Monte Carlo simulations, which allows us to mutually validate the theory and the Monte Carlo simulation codes. We also discuss the reason for the discrepancy between the classical approach for calculating the ensemble-averaged mean-square beam radius in a turbulent atmosphere that is described by Andrews and Phillips and by Fante versus using the moment method.
Recent progress at the Applied Physics Laboratory in high data rate communications technology development is
described in this paper. System issues for developing and implementing high data rate downlinks from geosynchronous
earth orbit to the ground, either for CONUS or in-theater users is considered. Technology is described that supports a
viable dual-band multi-channel system concept. Modeling and simulation of micro-electro-mechanical systems (MEMS)
beamsteering mirrors has been accomplished to evaluate the potential for this technology to support multi-channel
optical links with pointing accuracies approaching 10 microradians. These models were validated experimentally down
to levels in which Brownian motion was detected and characterized for single mirror devices only 500 microns across.
This multi-channel beamsteering technology can be designed to address environmental compromises to free-space
optical links, which derive from turbulence, clouds, as well as spacecraft vibration. Another technology concept is being
pursued that is designed to mitigate the adverse effects of weather. It consists of a dual-band (RF/optical) antenna that is
optimally designed in both bands simultaneously (e.g., Ku-band and near infrared). This technology would enable
optical communications hardware to be seamlessly integrated with existing RF communications hardware on spacecraft
platforms, while saving on mass and power, and improving overall system performance. These technology initiatives
have been pursued principally because of potential sponsor interest in upgrading existing systems to accommodate quick
data recovery and decision support, particularly for the warfighter in future conflicts where the exchange of large data
sets such as high resolution imagery would have significant tactical benefits.
Recently developed MEMS micromirror technology provides an opportunity to replace macroscale actuators for laser beamsteering in lidar and free-space optical communication systems. Precision modeling of mirror pointing and its dynamics are critical to the design of MEMS beamsteerers. Beam jitter ultimately limits MEMS mirror pointing, with consequences for bit error rate and overall optical system performance. Sources of jitter are platform vibration, control voltage noise, and Brownian motion noise. This work relates the random jitter of the mirror facet to its originating sources via a multidimensional first-order Taylor expansion of a first-principles-derived analytic expression for the actuating torque. The input torque, consisting of deterministic and stochastic components, is related to the 2-D jitter through a pair of coupled damped harmonic oscillator differential equations. The linearized 2-D jitter model for the mirror is simulated using Matlab, while the full nonlinear torque model was simulated using Simulink. The work describes an experimental setup and methodology that is used to make precise micromirror measurements. Experimental measurements are in agreement with the jitter model, i.e., the linearized model is able to predict mirror facet jitter based on the measured power spectral densities for the sources of jitter.
The availability of recently developed microelectromechanical system (MEMS) micro-mirror technology provides an opportunity to replace macroscale actuators for free-space laser beam steering in light detection and ranging and communication systems. Precision modeling of mirror pointing and its dynamics are critical to the design and control of MEMS beam steerers. Beginning with Hornbeck's torque approach, we present a first-principles, analytically closed-form torque model for an electrostatically actuated two-axis (tip-tilt) MEMS mirror structure. The torque expression is a function of the mirror's physical parameters, such as angles, voltages, and size. An Euler dynamic equation formulation describes the gimballed motion as a pair of damped harmonic oscillators with a coupled torsion function. Static physical parameters such as MEMS mirror dimensions and voltages are inputs to the model as well as dynamic harmonic oscillator parameters, such as damping and restoring constants, which are calculated or fitted to measurements. A Taylor series expansion of the torque function provides insights into MEMS behavior, including operational sensitivities near "pull-in." MATLAB and SIMULINK simulations illustrate performance sensitivities, controllability, physical limitations, and other important considerations in the design of precise pointing systems. Commercial-off-the-shelf micromirror measurements confirm the model's validity in steady state and dynamic scanning operations.
NASA is planning missions to small planetary bodies in which low-risk high-accuracy soft-landing must be
accomplished independent of ground control. Accurate estimates of range, descent rate, attitude, and translational drift
rate are needed for precision landings (< 1 m CEP) in low gravity. Operational ranges for the landing phase are
expected to vary from a kilometer down to one meter. Poorly characterized landing sites may require real-time obstacle
avoidance. Although passive sensors are being considered, active sensors enable the spacecraft to exploit more optimal
measurement techniques in which surface illumination is controlled by design rather than accommodated by default.
This paper addresses the development and validation of a robust combination of sensors, which reduce risks while
minimizing spacecraft mass and power. This paper describes the design, test, and evaluation of two sensors: a miniature
pulsed Nd:YAG lidar and a Ka-band CW Doppler radar. These sensors are co-bore sighted on a two-axis gimbal, along
with an inertial measurement unit and a data acquisition PC on a mobile test-bed. Test results will be presented and
discussed for conditions that emulate appropriate landing operations. Fixed test structures with corner reflector targets
are used to validate this approach and calibrate sensor sensitivity to different geometries and kinematics.
The availability of recently developed MEMS micro-mirror technology provides an opportunity to replace macro-scale
actuators for free-space laser beamsteering in lidar and communication systems. Such an approach is under
investigation at the Johns Hopkins University Applied Physics Laboratory for use on space-based platforms.
Precision modeling of mirror pointing and its dynamics are critical to optimal design and control of MEMS
beamsteerers. Beginning with Hornbeck's torque approach, this paper presents a first-principle, analytically
closed-form torque model for an electro-statically actuated two-axis (tip-tilt) MEMS structure. An Euler dynamic
equation formulation describes the gimbaled motion as a coupled pair of damped harmonic oscillators with a
common forcing function. Static physical parameters such as MEMS mirror dimensions, facet mass, and height
are inputs to the model as well as dynamic harmonic oscillator parameters such as damping and restoring
constants fitted from measurements. A Taylor series expansion of the torque function provides valuable insights
into basic one dimensional as well as two dimensional MEMS behavior, including operational sensitivities near
"pull-in." The model also permits the natural inclusion and analysis of pointing noise sources such as electrical
drive noise, platform vibration, and molecular Brownian motion. MATLAB and SIMULINK simulations illustrate
performance sensitivities, controllability, and physical limitations, important considerations in the design of
optimal pointing systems.
KEYWORDS: Stars, Sensors, Space operations, Scanners, Digital signal processing, Light emitting diodes, Signal to noise ratio, Silicon, Domes, Detection and tracking algorithms
The Johns Hopkins University Applied Physics Laboratory (JHU/APL) is currently developing a prototype star scanner design incorporating a variation on the V-slit design concept, called the N-slit, which is intended for deployment on future NASA spacecraft missions, such as the Radiation Belt Storm Probe (RBSP). In order to effectively test and evaluate alternative designs, including optics, sensors, and tracking algorithms, we have developed a laboratory testbed that simulates celestial objects, including stars down to a specified magnitude. We do this by creating a light-hermetic dome-shaped projection environment using light emitting diodes of specified brightness coupled to the dome exterior via fiber-optic patch cords, which can be adjusted by current bias and selected for color, if necessary, to simulate stars over a particular range of magnitudes required for the desired system accuracy. We also simulate the spacecraft platform spin dynamics using a two-axis servo-actuated mount for the star tracker test unit within the dome. This same actuator or a similar assembly can then be transitioned to actual field tests for sensor down-select and full functionality demonstrations prior to follow-on spacecraft-qualified design. We will describe the design, construction, calibration, and operation of this simulator and preliminary results of star scanner sensor evaluation using a photomultiplier-based N-slit sensor.
KEYWORDS: Micromirrors, Mirrors, Microelectromechanical systems, Oxides, Digital signal processing, Transmitters, Space operations, CMOS cameras, Charge-coupled devices, Imaging systems
MEMX Corporation in collaboration with Johns Hopkins University Applied Physics Laboratory (JHU/APL) has developed micro-mirror technology applicable to free-space multi-access optical communications terminals. Based on their previously developed micro-electro-mechanical systems (MEMS) optical switches, these new units are being evaluated for applications on spacecraft. These devices must operate within very accurate digitally-controlled pointing and tracking subsystems, which are an essential adjunct to the long-haul optical communication channels that would be operated potentially from geosynchronous earth orbit (GEO) to ground. For such spacecraft applications high-powered laser diodes are likely be the required transmitter. Coupled with their potential operation in a vacuum or at partial atmospheric pressures, MEMS mirror shape stability and fabrication tolerances are of key concern to a system designer. To this end we have measured the performance of preliminary micro-mirror units in terms of angular jitter, focal spot stability, and open and closed-loop response versus laser transmitter power in both ambient air and at low partial pressures. We will describe the fabrication process as well as the experimental test configurations and results in the context of optical beamsteering. We will also discuss the applicability and scalability of this technology to multi-access terminals.
KEYWORDS: Mirrors, Composites, Telescopes, Digital signal processing, Space telescopes, Space operations, Signal processing, Actuators, Control systems, Telescope design
The National Aeronautics and Space Administration (NASA) is planning future deep space missions requiring space-based imaging reconnaissance of planets and recovery of imagery from these missions via optical communications. Both applications have similar requirements that can be met by a common aperture. The Johns Hopkins University Applied Physics Laboratory in collaboration with commercial and academic partners is developing a new approach to deploying and controlling large aperture (meter-class) optical telescopes on spacecraft that can be rapidly launched and deployed. The deployment mechanism uses flexible longeron struts to deploy the secondary. The active control system uses a fiber-coupled laser array near the focal plane that reflects four collimated laser beams off of the periphery of the secondary to four equally-disposed quad cell sensors at the periphery of the primary to correct secondary-to-primary misalignments and enable motion compensation. We describe a compensation technique that uses tip/tilt and piston actuators for quasi-static bias correction and dynamic motion compensation. We also describe preliminary optical tests using a commercial Schmidt-Cassegrain telescope in lieu of an ultra-lightweight composite Cassegrain, which is under development by Composite Mirror Applications, Inc. Finite element and ray trace modeling results for a 40 cm composite telescope design will also be described.
KEYWORDS: Sensors, Transducers, Digital signal processing, Actuators, Control systems, Mirrors, Space operations, Signal processing, Photodiodes, Optical communications
The National Aeronautics and Space Administration (NASA) plans to develop optical communication terminals for future spacecraft, especially in support of high data rate science missions and manned exploration of Mars. Future, very long-range missions, such as the Realistic Interstellar Explorer (RISE)1, will need optical downlink communications to enable even very low data rates. For all of these applications, very fine pointing and tracking is also required, with accuracies on the order of ± 1 μrad or less and peak-to-peak ranges of ± 10 mrad or more. For these applications, it will also be necessary to implement very compact, lightweight and low-power precision beam-steering technologies. Although current commercial-off-the-shelf devices, such as macro-scale piezo-driven tip/tilt actuators exist, which approach mission requirements, they are too large, heavy, and power consuming for projected spacecraft mass and power budgets. The Johns Hopkins University Applied Physics Laboratory (JHU/APL) has adopted a different approach to beam-steering in collaboration with the National Institute of Standards and Technology (NIST). We are testing and planning to eventually package a highly accurate large dynamic range meso-scale position transducer under development at NIST. In this paper we will describe a generic package design of an optical communications terminal incorporating the NIST prototype beam-steerer. We will also show test results comparing the performance of the NIST prototype meso-scale position beam-steerer to a commercial macro-tip/tilt actuator using a quad-cell tracking sensor.
Beam steering accuracy is critical to the successful operation of optical communications systems, especially those which take place over extreme length scales, such as for an interstellar spacecraft. In this paper, a novel beam steering mechanism and several control system approaches for ultra-precision beam steering are discussed. The beam steering mechanism is a nanopositioning device which utilizes a parallel cantilever configuration and a piezoelectric actuator to obtain extremely high positioning accuracy with minimal parasitic errors. A robust motion controller is presented for this mechanism which is designed to compensate for modeling uncertainty. This controller is intended for use with feedback from the nanopositioner’s built-in capacitance probe. Due to the need to track the trajectory of the steered beam, two additional control approaches are presented which combine the robust motion controller with additional feedback for the actual beam displacement. These multi-loop control approaches provide a level of robustness to thermal effects and vibrations which could not be obtained from a single sensor and feedback loop. Simulation results are provided for each of the control designs.
The National Aeronautics and Space Administration (NASA) continues to plan and anticipate the development of high data rate communications for future deep space missions. The Johns Hopkins University Applied Physics Laboratory is responding to this challenge by developing a breadboard laser transceiver package using commercial off-the-shelf components. We plan to demonstrate a breadboard transceiver unit, integrated with a fine pointing and tracking capability by the end of FY-03. A potential mission application is to ultimately demonstrate a live video link from Mars. Our near-term demonstration goals are to achieve a modest 5 Mbps data rate over an equivalent range of 2 AU. To achieve this we are modeling and testing the components for a hybrid analog/digital receiver in conjunctino with semiconductor laser diodes and silicon PIN and avalanche photodiodes. Our efforts leading up to hardware implementation and test have consisted of a trade-of between coherent and direct detection receiver architectures, and a link analysis for deep space applications, which established the laser power requirements for supporting a real-time video link from Mars as well as other missions, where the encoded bit error rate is from 10-6 to 10-9. Current efforts include the development of a direct-detection 4-ary pulse position modulation scheme using a FPGA-based modulator/demodulator as well as a separate quadrant photodiode receiver for tracking. We plan to integrate this transceiver with lightweight diffractive optical elements for beam-forming. The design and initial testing of the transceiver components will be discussed.
The concept of a realistic interstellar explorer has been addressed by the Johns Hopkins University Applied Physics Laboratory with support from the NASA Institute for Advanced Concepts. This paper discusses the requirements, conceptual design and technology issues associated with the optical and RF communications systems envisioned for this mission, in which the spacecraft has a projected range of 1000 AU. Well before a range of 100 AU interactive control of the spacecraft becomes nearly impossible, necessitating a highly autonomous craft and one-way communications to Earth. An approach is taken in which the role of the optical downlink is emphasized for data transfer and that of the microwave uplink emphasized for commands. The communication system is strongly influenced by the large distances involved, the high velocities as well as the requirements for low-mass, low prime power, reliability, and spacecraft autonomy. An optical terminal concept is described that has low mass and prime power in a highly integrated and novel architecture, but new technologies are needed to meet the range, mass, and power requirements. These include high-power, 'wall-plug' efficient diode-pumped fiber lasers; compact, lightweight, and low-power micro-electromechanical (MEM) beam steering elements; and lightweight diffractive quasi-membrane optics. In addition, a very accurate star tracking mechanism must be fully integrated with the laser downlink to achieve unprecedented pointing accuracy. The essential optical, structural, mechanical, and electronic subsystems are described that meet the mission requirements, and the key features of advanced technologies that need to be developed are discussed. The conclusion from this preliminary effort is that an optical communications downlink out to 1000 astronomical units is within the realm of technical feasibility in the next 5-10 years if the identified technical risks for the new technologies can be retired.
The National Aeronautics and Space Administration is planning high data rate optical communications for future deep space missions. The Johns Hopkins University Applied Physics Laboratory (JHU/APL) is responding by developing concepts for implementing optical communications terminals that are more compact and lightweight than heretofore. An essential requirement for these long-range optical links is a high-precision pointing and tracking system. Focal plane array (FPA)-based star trackers that enable open-loop pointing and tracking are necessary. Spacecraft attitude instabilities, emphemeris errors, tracking sensor noise, clock errors, and mechanical misalignments are among the error sources that must be minimized and compensated for. To achieve this JHU/APL has developed an imaging star tracker concept using redundant multi-aperture FPA's symmetrically disposed about the laser downlink. Centroid estimation and pattern matching techniques account for aberration and motion errors. Robustness, sensitivity to detection thresholds, field-of-view sizing, number of stars per frame, missed detections, false alarms, and position biases, as well as stellar catalog size and star selection, will be described. Finally the conceptual design of a frame-to-frame integration method and sensor fusion algorithm (such as a Kalman filter) will be considered. The goal is to achieve a system pointing and tracking error significantly less than 1 μrad.
Nanosatellites operating singly or in clusters are anticipated for future space science missions. To implement this new communications paradigm, we are approaching cluster communications by first developing an infrared (IR) intra- craft wireless bus capability, following initially the MIL- STD-1553B protocol. Benefits of an IR wireless bus are low mass, size, power, and cost, simplicity of implementation, ease of use, minimum EMI, and efficient and reliable data transfer. Our goals are to maximize the reliable link margin in order to afford greater flexibility in receiver placement, which will ease technology insertion. We have developed a concept demonstration using a high-speed visible-band silicon PIN photodiode and a high-efficiency visible LED operating at a data rate up to 4 Mb/sec. In designing an internal IR wireless bus, we have characterized various candidate materials, emitters, and geometries, assuming a single reflection. Thus, we have measured the bidirectional reflectance distribution function (BRDF) for five different materials characteristic of typical spacecraft structures, which range from nearly Lambertian to highly specular. We have fit our data to empirical BRDF functions and modeled the detected irradiance anywhere in the plane of incidence for a divergent emitter. We have also determined the angular limits on the link geometry to remain within the required bit error rate by determining the received signal-to-noise ratio for minimum values of irradiance received at the detector.
We report here a model of a high temperature superconducting detector response to microwaves. The goal of the model is to approximate, based on microscopic theoretical results, the measured response of a superconducting detector to microwave frequency over a wide temperature range (from zero up to the critical temperature of the superconductor, Tc). In this work, the nonbolometric response is emphasized because its detector performance is better than the bolometric response. The nonbolometric response model is based on microwave enhancement of a thermal fluctuation voltage occurring in the networks of inherent Josephson junctions. Modeling the film as a distribution of granular connections with varying critical currents and temperatures yields results similar to those observed in microwave response measurements in granular Bi-Sr-Ca-Cu-O thin films. We also report here initial measurements and modeling of the microwave (9 GHz) response of a bi-epitaxial thin film showing the simultaneous presence of bolometric and nonbolometric response peaks in the same sample. The response in this Y-Ba-Cu-O thin films gives further evidence of microwave detection in the networks of inherent Josephson junctions presented at the grain boundaries of two epitaxial layers.
A variety of techniques have been previously developed for surface topography reconstruction using CCD video images and various image processing algorithms. These include passive stereo disparity estimation using sub-area image correlation, confocal imaging (depth from focus), as well as structured light techniques. These approaches are compared on the basis of theoretical height error and algorithm complexity. A simple post-processing scheme based on the use of Fourier phase of structured light is then described, and results are shown from height measurements of tens of microns over areas on the order of a centimeter. A diode laser source is used in conjunction with a fan-beam refractive element, appropriate optical filtering, microscope, and CCD camera. This approach has application to long working-distance microscopy, closed-loop numerical control of machining, and retinal surface topography for early disease detection. Our approach offers a simple, low-cost, and real-time method of surface topography visualization and closed-loop machine tool control. Reflected laser beam quality and associated digital image filtering are considered with respect to the nature of possible surface materials measured.
This paper describes two processing algorithms that can be implemented optically: the Radon transform and angular correlation. These two algorithms can be combined in one optical processor to extract all the basic geometric and amplitude features from objects embedded in video imagery. We show that the internal amplitude structure of objects is recovered by the Radon transform, which is a well-known result, but, in addition, we show simulation results that calculate angular correlation, a simple but unique algorithm, which extracts object length, width, area, aspect ratio, orientation and boundary from suitably thresholded images. In addition to being insensitive to scale and rotation, these simulations indicate that the features derived from angular correlation algorithm are relatively insensitive to tracking shifts and image noise. Some optical architecture concepts, including one based on micro-optical lenslet arrays, have been developed to implement these algorithms. We will discussed these architectures, stressing the micro-optical approach. Test and evaluation using simple synthetic object data will be described. We will also describe the results of a study that uses object boundary (derivable from angular correlation) to classify objects using a neural network.
In order to search for symbolically encoded sequences of DNA base information, we have constructed an incoherent optical feature extraction system. This approach uses video display, spatial light modulation, and detection components in conjunction with microlenslet replicating optics, to expedite the recognition of symbol sequences based on their symmetry properties. Multichannel operation is achieved through the replication of input scenery, making possible a higher throughput rate than for single channel systems. A notable feature of our arrangement has been the exchanged positions of input scenery and the filter set. The conventional treatment has been to display the input scene on a monitor for projection onto a set of feature extraction vectors realized as amplitude modulated LCTV devices or lithographically prepared masks. We have chosen instead to provide the filter set as input to the system and to correspondingly place the sequence data in the filter plane of the system, relying on the commutativity of projection to allow this role reversal. A class of DNA sequences known as palindromes are known to have special regulatory functions in biological systems; this class is distinguished by the antisymmetric arrangement of bases in palindromic sequences. We have designed our optical feature extractor to classify short (6 bases in length) sequences of DNA as palindrome or nonpalindrome. We note that this classification is made on the basis of the sequence symmetry, independent of base composition. We discuss the design of this architecture and the considerations that led us to the sequence representation. Initial results of this work are presented. Finally, the integration of this optical architecture into a complete system is discussed.
This paper describes the results of using video feedback to support the calculation of the radon transform and angular correlation. Application of this type of optical processor to the extraction of features from synthetic aperture radar imagery of ships is described. By theoretical analysis and experimental evaluation of the optical architecture outputs (using some digital post processing) it is shown that the internal structure of objects, their primitive dimensions, and even their boundary can be obtained. In particular, the power of angular correlation to extract object length, width, area, aspect ratio, orientation and boundary from suitably thresholded images is shown. Alternative techniques to extract the object boundary based on angular correlation are discussed, including direct optical computation as well as digital deconvolution. Simple optical shapes, such as squares, rectangles, and triangles were used to initially compare the optical architecture outputs with digital baseline calculations. In addition, the test and evaluation of the optical processor using simple synthetic models of ship data is discussed. The results of a study that uses object primitives (derivable from angular correlation) in conjunction with the Radon transform (along the longitudinal axis) to classify ships using a backpropagation neural network also are described. A discussion of these results is presented pertaining to their broader application to optical parts inspection and to feature extraction from imaging infrared surveillance sensors. The practical implementation of such a processor in compact form using lenslet array optics also is discussed.
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