Digital Control Design of a CCD-Based Tracking Loop for Precision Beam Pointing
A tracking control loop was designed for an optical communication package that will use a high frame rate CCD array for precision beam pointing.
discrete↗
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Detection and Tracking of Aircraft in the Far-Field from Small Unmanned Aerial Systems
Onboard far-field aircraft detection is needed for safe non-cooperative traffic mitigation in autonomous small Unmanned Aerial System (sUAS) operations. Machine vision systems, based on standard optics and visible light detectors, possess the ideal size, weight, and power (SWaP) requirements for sUAS. This work presents the design and analysis of a novel aircraft detection and tracking pipeline based on optical sensing alone. Key contributions of the work include a refined range inequality model based on sensing and detection with FAA well-clear separation assurance distances between aircraft in mind, a detector fusion method to maximize the benefit of two image detectors, and a comparative analysis of Linear Kalman-filtering and Extended Kalman-filtering to seek optimal tracking performance. The pipeline is evaluated offline against multiple intruder platforms, using two types of flight encounters: multirotor sUAS vs. fixed-wing sUAS and multirotor sUAS vs. general aviation(GA)plane. Analysis is restricted to the rate-limiting head-on and departing collision volume cases vertically separated for safety. Results indicate that it is feasible to use the proposed optical spatial-temporal tracking algorithm to provide adequate alerting time to prevent penetration of well-clear separation volumes for both sUAS and GA aircraft.
Unmanned Aerial System↗
Preliminary greenhouse design for a Martian colony: Structural, solar collection, and light distribution systems
The design of a greenhouse that will be a component of a long-term habitat on Mars is presented. The greenhouse will be the primary food source for people stationed on Mars. The food will be grown in three identical underground modules, pressurized at 1 atm to allow a shirt-sleeve environment within the greenhouse. The underground location will support the structure, moderate the large environmental variations on the surface, and protect the crops from cosmic radiation. The design effort is concentrated on the outer structure and the lighting system for the greenhouse. The structure is inflatable and made of a Kevlar 49/Epoxy composite and a pipe-arched system that is corrugated to increase stiffness. This composite is pliable in an uncured state, which allows it to be efficiently packaged for transport. The lighting system consists of several flat-plate fiber optic solar collectors with dual-axis tracking systems that will continually track the sun. This design is modeled after the Himawari collector, which was designed by Dr. Kei Mori and is currently in use in Japan. The light will pass through Fresnel lenses that filter out undesirable wavelengths and send the light into the greenhouses by way of fiber optic cables. When the light arrives at the greenhouse, it is dispersed to the plants via a waveguide and diffuser system.
Source record↗
Optical pattern recognition; Proceedings of the Meeting, Los Angeles, CA, Jan. 17, 18, 1989
Papers on optical pattern recognition are presented, covering topics such as the estimation of satellite pose and motion parameters using a neural net tracker, associative memory, optical implmentation of programmable neural networks, optoelectronic neural networks, dynamic autoassociative neural memory, heteroassociative memory, bilinear pattern recognition processors, optical processing of optical correlation plane data, and a synthetic discriminant function-based nonlinear optical correlator. Other topics include an interactive optical-digital image processor, geometric transformations for video compression and human teleoperator display, quasiconformal remapping for compensation of human visual field defects, hybrid vision for automated spacecraft landing, advanced symbolic and inference optical correlation filters, and a rotationally invariant holographic tracking system. Additional topics include the detection of rotational and scale-varying objects with a programmable joint transform correlator, a single spatial light modulator binary nonlinear optical correlator, optical joint transform correlation, linear phase coefficient composite filters, and binary phase-only filters.
Liu, Hua-Kuang↗
Comparison of Sunphotometric Measurements During the Fall 1997 ARM Intensive Observation Period
In the Fall of 1997 the Atmospheric Radiation Measurement (ARM) program held an intensive observation period (IOP) to study atmospheric aerosols using in situ and remote sensing techniques at its Southern Great Plains (SGP) site near Lamont, Oklahoma. As part of this experiment five automated, tracking sunphotometers were present to measure total column aerosol optical depth over the three-week period. which included many clear days or parts of days that were clear. The World Meteorological Organization (WMO 1993) has recommended a comparison of tracking sunphotometers to assess the ability of different instruments to arrive at similar aerosol optical depths. It was further recommended that the comparison be staged at a clean mountain site. In fact, this comparison has not occurred, but the comparison that we describe in this paper is representative of what contemporary instruments may accomplish in an environment more typical of sites where aerosols measurements will be required. The measurements were made over the period 15 September to 5 October 1997. The aerosol loading varied from extremely clean to moderately turbid conditions. In the next section the instruments will be described along with a brief explanation of the calibration techniques. The third section contains the results compared graphically on moderately turbid and fairly clean days and in a table representing the whole period. The paper ends with a section of discussion and a summary of the results.
Michalsky, J. J.↗
An optical study of grain formation: Casting and solidification technology (2-IML-1)
By studying the unidirectional growth of a metal-model material in microgravity, an attempt is made to characterize alloy solidification. Using holograms and supporting temperature measurements obtained during processing in the Fluids Experiment System (FES), the solute and thermal fields associated with the dendrite growth front and extraneous nucleation will be measured and compared to a theoretical (computational) model. Ground based supporting experiments include particle tracking to measure the velocity fields, and optical phase shift techniques (confocal optical signal processing, interferometry, and Schlieren) to study thermal and solutal fields.
Mccay, Mary H.↗
Optimetrics for Precise Navigation
Optimetrics for Precise Navigation will be implemented on existing optical communication links. The ranging and Doppler measurements are conducted over communication data frame and clock. The measurement accuracy is two orders of magnitude better than TDRSS. It also has other advantages of: The high optical carrier frequency enables: (1) Immunity from ionosphere and interplanetary Plasma noise floor, which is a performance limitation for RF tracking; and (2) High antenna gain reduces terminal size and volume, enables high precision tracking in Cubesat, and in deep space smallsat. High Optical Pointing Precision provides: (a) spacecraft orientation, (b) Minimal additional hardware to implement Precise Optimetrics over optical comm link; and (c) Continuous optical carrier phase measurement will enable the system presented here to accept future optical frequency standard with much higher clock accuracy.
Precise↗
Linear laser diode arrays for improvement in optical disk recording
The development of individually addressable laser diode arrays for multitrack magneto-optic recorders for space stations is discussed. Three multi-element channeled substrate planar (CSP) arrays with output power greater than 30 mW with linear light vs current characteristics and stable single mode spectra were delivered to NASA. These devices have been used to demonstrate for the first time the simultaneous recording of eight data tracks on a 14-inch magneto-optic erasable disk. The yield of these devices is low, mainly due to non-uniformities inherent to the LPE growth that was used to fabricate them. The authors have recently developed the inverted CSP, based on the much more uniform MOCVD growth techniques, and have made low threshold quantum well arrays requiring about three times less current than the CSP to deliver 30 mW CW in a single spatial mode. The inverted CSP is very promising for use in space flight recorder applications.
Alphonse, G. A.↗
A comparison of optical technologies for a high data rate Mars link
Several optical systems, based on Nd:YAG, GaAs, and CO2 laser sources and employing both direct and heterodyne detection, are analyzed in order to assess their feasibility in providing high data rate (10-1000 Mbps) Mars-to-earth communications. The rms pointing/tracking accuracy is shown to be a critical parameter in defining the Mars-earth optical link. Data obtained reveal that unless, extremely small rms pointing and tracking errors can be achieved (sigma less than .2 microrad), the most promising optical implementation appears to be the Nd:YAG laser using direct detection and high order PPM modulation.
Spence, Rodney L.↗
Study of optimum methods of optical communication
Optimum methods of optical communication accounting for the effects of the turbulent atmosphere and quantum mechanics, both by the semi-classical method and the full-fledged quantum theoretical model are described. A concerted effort to apply the techniques of communication theory to the novel problems of optical communication by a careful study of realistic models and their statistical descriptions, the finding of appropriate optimum structures and the calculation of their performance and, insofar as possible, comparing them to conventional and other suboptimal systems are discussed. In this unified way the bounds on performance and the structure of optimum communication systems for transmission of information, imaging, tracking, and estimation can be determined for optical channels.
Harger, R. O.↗
Per-Pixel, Dual-Counter Scheme for Optical Communications
Free space optical communications links from deep space are projected to fulfill future NASA communication requirements for 2020 and beyond. Accurate laser-beam pointing is required to achieve high data rates at low power levels.This innovation is a per-pixel processing scheme using a pair of three-state digital counters to implement acquisition and tracking of a dim laser beacon transmitted from Earth for pointing control of an interplanetary optical communications system using a focal plane array of single sensitive detectors. It shows how to implement dim beacon acquisition and tracking for an interplanetary optical transceiver with a method that is suitable for both achieving theoretical performance, as well as supporting additional functions of high data rate forward links and precision spacecraft ranging.
Farr, William H.↗
Improved accuracies for satellite tracking
A charge coupled device (CCD) camera on an optical telescope which follows the stars can be used to provide high accuracy comparisons between the line of sight to a satellite, over a large range of satellite altitudes, and lines of sight to nearby stars. The CCD camera can be rotated so the motion of the satellite is down columns of the CCD chip, and charge can be moved from row to row of the chip at a rate which matches the motion of the optical image of the satellite across the chip. Measurement of satellite and star images, together with accurate timing of charge motion, provides accurate comparisons of lines of sight. Given lines of sight to stars near the satellite, the satellite line of sight may be determined. Initial experiments with this technique, using an 18 cm telescope, have produced TDRS-4 observations which have an rms error of 0.5 arc second, 100 m at synchronous altitude. Use of a mosaic of CCD chips, each having its own rate of charge motion, in the focal place of a telescope would allow point images of a geosynchronous satellite and of stars to be formed simultaneously in the same telescope. The line of sight of such a satellite could be measured relative to nearby star lines of sight with an accuracy of approximately 0.03 arc second. Development of a star catalog with 0.04 arc second rms accuracy and perhaps ten stars per square degree would allow determination of satellite lines of sight with 0.05 arc second rms absolute accuracy, corresponding to 10 m at synchronous altitude. Multiple station time transfers through a communications satellite can provide accurate distances from the satellite to the ground stations. Such observations can, if calibrated for delays, determine satellite orbits to an accuracy approaching 10 m rms.
Kammeyer, P. C.↗
Convective Characteristics and GOES GLM Optical Energy in Hurricane Ian (2022)
Tropical cyclone (TC) track forecasts have improved greatly in recent decades, while intensity forecasts have struggled to improve at the same rate. As a result, there has been a focus in literature to attempt to better understand the processes that lead to TC intensification and especially TC rapid intensification (RI). Lightning has been studied as a tool to determine changes in TC intensity, but studied thus far have had conflicting results.
Hurricane↗
Scanning Lidar Transceiver Telescopes Using Holographic Optical Elements
Scanning enables remote measurements perpendicular to the ground track of airborne and spaceborne lidar systems, giving us three dimensional images of atmospheric backscatter or other measurable parameters. For ground based systems, scanning allows one to record a time series of data in multiple spatial dimensions. The large size and cost of scanning systems for atmospheric lidars using conventional scanning technologies is prohibitive for space based systems. By replacing the conventional reflective telescope with a holographic optical element (HOE) in the lidar, single axis conical scanning can be achieved with a mechanically simple system. Relatively inexpensive to produce, HOES can be used to satisfy a variety of scanning lidar applications. I will introduce the concept of the HOE and describe its production and use as a scanning lidar transceiver telescope. I will describe the advantages as well as the disadvantages and limitations of HOES in this application. Optical performance test results and two lidar systems currently using HOES will be described. Examples of data taken with these systems will be presented. Current and planned future developments will be described, including scanning without mechanical motion and wide field-of-view lidar imaging.
Schwemmer, Geary K.↗
Lasercom system architecture with reduced complexity
Spatial acquisition and precision beam pointing functions are critical to spaceborne laser communication systems. In the present invention, a single high bandwidth CCD detector is used to perform both spatial acquisition and tracking functions. Compared to previous lasercom hardware design, the array tracking concept offers reduced system complexity by reducing the number of optical elements in the design. Specifically, the design requires only one detector and one beam steering mechanism. It also provides the means to optically close the point-ahead control loop. The technology required for high bandwidth array tracking was examined and shown to be consistent with current state of the art. The single detector design can lead to a significantly reduced system complexity and a lower system cost.
Lesh, James R.↗
LaserCom System Architecture With Reduced Complexity
Spatial acquisition and precision beam pointing functions are critical to spaceborne laser communication systems. In the present invention a single high bandwidth CCD detector is used to perform both spatial acquisition and tracking functions. Compared to previous lasercom hardware design, the array tracking concept offers reduced system complexity by reducing the number of optical elements in the design. Specifically, the design requires only one detector and one beam steering mechanism. It also provides means to optically close the point-ahead control loop. The technology required for high bandwidth array tracking was examined and shown to be consistent with current state of the art. The single detector design can lead to a significantly reduced system complexity and a lower system cost.
Lesh, James R.↗
Optical imaging chamber for X-ray astronomy
The light emitted by electron avalanches in a parallel plate chamber can be used to image the tracks of photoelectrons liberated by the interaction of an incident X-ray with the gas filling the chamber. The differing morphologies of photoelectron tracks and high-energy charged particle tracks can be used for background rejection. The initial direction (before scattering) of the liberated photoelectron also contains information about the polarization of the incident radiation. We have built a small test chamber with which we have imaged photoelectron tracks using an intensified CCD camera. Our results show that optical imaging could be used in a hard X-ray imaging polarimeter useful for astronomy.
Austin, Robert A.↗
A 10, 6-micrometer laser receiver RF subsystem
A simplified laser receiver carrier tracking loop is described. The laser carrier is optically mixed with a locally generated 10.6 micrometer signal, thereby translating the received signal to an IF signal that varies between dc and GHz. This signal is fed to a second order carrier tracking loop that contains a transistor LC oscillator tuned by a varactor over a 1 GHz range; transistor shunt capacitance increases the upper frequency bound of the oscillator in a high Doppler environment.
Santarpia, D. E.↗