Factors which affect the pulse performance and frequency resolution of the acousto-optic fm demodulator are investigated. Formulae are developed which allow prediction of both the pulse response and frequency resolution. Suggestions are made to improve performance of such systems in the laboratory.

This paper describes a series of new solid state ultraviolet detectors based on gallium nitride (GaN) material. Data will be presented on photoconductive type devices. These devices have a high responsivity between 200 to 362 nm with a sharp long wavelength cutoff at 362 nm. The photoconductive detectors have measured gains of over twenty thousand with proper doping. Data is given on two different detector configurations. Devices will be shown that can be utilized in the development of a focal plane array for UV imaging.

The design of a low-light-level CMOS active-pixel-sensor (APS) with on-chip, semi-parallel analog-to-digital (A/D) conversion is presented. The imager consists of a 128 X 128 array of active pixels at a 50 micrometers pitch. Each column of pixels shares a 10-bit A/D converter based on first-order oversampled sigma-delta ((Sigma) -(Delta) ) modulation. The 10-bit outputs of each converter are multiplexed and read out through a single set of outputs. A semi-parallel architecture is chosen to achieve 30 frames/second operation even at low light levels. The sensor is designed for less than 10 e^- rms noise performance. A 28 X 28 active-pixel-sensor (APS) with 40 X 40 micrometers ² pixels as well as individual elements of the sigma-delta modulator have been fabricated and tested using MOSIS* 2 micrometers CMOS technology.

A versatile high performance Frame Transfer and Storage imaging device has been demonstrated using tin oxide gates and Open Pinned Phase (OPP) technology. The device consists of a 512 X 512 imaging array and integral 512 X 512 frame buffer. The detector size is 18 micrometers X 18 micrometers , however, pixel size is electronically controllable by detector aggregation in the X and Y directions. The use of tin oxide gates and OPP technology provide a front side illuminated device with high Quantum Efficiency and low leakage. This combination of features yields a mechanically robust high resolution imager, ideally suited for military, scientific, and commercial applications requiring high sensitivity and/or long stare times.

An 8 micrometers pixel 1152 X 64 stage time delay and integration scanning visible imaging CCD which uses transparent tin oxide gates has been fabricated. The tin oxide gates provide a front side illuminated device with a peak quantum efficiency of greater than 80%. The chip features forward and reverse scan, variable TDI and commandable pixel size by the use of aggregation wells. The 1152 detector columns are subdivided into 8 subchips of 144 detector columns each. Buried Channel Charge Handling Capacity (CHC) of 100 ke- and Charge Transfer Efficiency (CTE) of 0.99999 has been measured. It is designed to operate at variable scan rates up to 52,000 lines per second.

This paper reports recent progress by the authors in two distinct charge coupled device (CCD) technology areas. The first technology area is high frame rate, multi-port, frame transfer imagers. A 16-port, 512 X 512, split frame transfer imager and a 32-port, 1024 X 1024, split frame transfer imager are described. The thinned, backside illuminated devices feature on-chip correlated double sampling, buried blooming drains, and a room temperature dark current of less than 50 pA/cm², without surface accumulation. The second technology area is vacuum ultraviolet (UV) frame transfer imagers. A developmental 1024 X 640 frame transfer imager with 20% quantum efficiency at 140 nm is described. The device is fabricated in a p-channel CCD process, thinned for backside illumination, and utilizes special packaging to achieve stable UV response.

Predicting emissions under rarified flow conditions remains a challenge. Two rocket experiments (at 3.5 and 5 km/s) obtained the UV data under flight conditions using onboard instruments; the greatest discrepancies in the predictions occurred at the higher altitudes. An additional experiment is being planned to extend the velocity to 7 to 8 km/sec using instrumentation onboard a small satellite with a highly elliptical orbit. Scanning spectrometers and photometers will observe the periodic bow shock interactions. The periodic bow shock re- immersion to low altitudes (200 to 120 km) coupled to the orbital decay of the satellite, provide an opportunity to progressively map a broad region of rarified aerodynamics. The paper discusses the flight regime of the planned experiment, provides examples of the anticipated phenomena and calculations, and gives an indication of the preliminary sets of instruments and measurements planned.

Some of the ultraviolet radiation detectors elaborated at TSNIIMASH and intended to examine ultraviolet emissions from various aerospace sources are described in this paper. The basic features of these detectors are high sensitivity and high selectivity. These features make it possible for the detectors to sense very weak ultraviolet radiation in the presence of intense background in the visible and infrared region of spectrum. Some applications of these detectors for surveillance of Earth atmosphere and aerospace objects are discussed.

This paper describes the design of a low power, lightweight, three-axis, high accuracy, wide field of view (WFOV), CCD based Star Tracker System. The autonomous system will provide an inertial attitude reference for several lightweight, lowpower satellite programs underway at TRW. The paper includes the trades which led to the current design. Product performance, description, and verification are provided. The paper concludes with a development schedule, which includes a flight unit acceptance in January 1994, and closing comments regarding increased functionality and improved integration ease.

Hybrid fiber-optical/silicon micromechanical sensing technique is a new technique which is recently developed in the world. In this paper, a new type of sound-optical array of microvibrators used as band pass filter gang is presented. The oscillating characteristic of microvibrators and the technique of detection has been analyzed by means of the fiber-optic intensity modulated microphone. The technique can extract sound spectrum features directly for the system of speech chinese recognition.

This paper discusses some of the techniques and results of the calibration of a visible sensor which is to be placed on a space-based satellite. The sensor consists of a set of four 420 by 420 pixel imagers in a f/3 off-axis reimaging telescope with a 6.6 degree(s) by 1.4 degree(s) field of view 1. The sensor has been designed to perform a wide variety of surveillance missions, including; metric and radiometric measurements of resident space objects, the demonstration of a high degree of Out-of-Field of View Radiance Rejection (OFVR), and background radiance measurements. This broad range of applications impose stringent requirements on the sensor calibration and characterization.

NASA's Mission to Planet Earth is a multi-platform, multi-orbit remote sensing and data distribution program designed to increase our understanding of both the Earth's environment and our potential impact on it. A preliminary Geostationary Earth Observatory (GEO) remote sensing instrument complement has been defined, based on the scientific requirements for this mission. These instruments include optical imagers, atmospheric sounders, passive microwave sensors and others. This paper discusses on-going studies which are focusing on advanced technologies to relieve the severe environmental and optical constraints experienced by earth- sensing instruments on a three-axis stabilized spacecraft in geostationary orbit.

The Geostationary Microwave Precipitation Radiometer will be a passive microwave radiometer system to be flown on the NASA Geostationary Earth Observatory. This instrument will provide microwave images for meteorology. It will measure radiation from the Earth and its atmosphere in seven frequency bands from 37 to 220 GHz. The instrument will have a 4 m Cassegrain antenna which will be mechanically scanned to provide images of the Earth in approximately equals 2 hours.

In this paper we focus on the status and development of critical detector and cooler technology in support of our instrument concept for a Geosynchronous orbiting Nadir Etalon Sounding Spectrometer (GeoNESS) for temperature, moisture and trace species. The concept is a technology derivative of the Cryogenic Limb Array Etalon Spectrometer (CLAES) which is deployed on the NASA Upper Atmospheric Research Satellite (UARS).

Many satellite-borne measurement applications require lightweight, reflective near diffraction limited telescopes with wide spectral bands (UV/visible to LWIR), for operation in space environments and over wide temperature ranges. Emerging silicon carbide (SiC) technology provides an attractive material for these telescope applications. The present paper describes the design and analysis of a 50 cm dia. aperture on-axis three mirror re-imaging SiC telescope, including the structure and a 'GOES like' scan flat for the GEO application. Optical, thermal and structural design and analyses are described for the demonstration hardware. Demonstration mirrors and structural hardware have been fabricated, tested and compared to design analyses with excellent agreement.

In this paper we put forward some conceptual designs for liquid crystal tunable filters (LCTF's) that offer improved wavelength flexibility, tuning speed, power consumption and reliability, over the mechanical filter wheels presently baselined for the High Resolution Earth Processing Imager (HEPI) and Advanced Lightning Mapper (ALM) geosynchronous remote sensing experiments. We also point out advantages that accrue from the extremely wide acceptance angle (F 1) achievable with birefringent filters. Thermal vacuum testing and radiation damage analysis will be required to investigate the space hardening of these new filters.

Diffractive (or binary) optics offers unique capabilities for the development of high- performance, low-weight optical systems for space-based sensors. The basic operating principles of diffractive optical elements along with fabrication methods suitable for production of diffractive elements for space-based applications are described. Several potential applications where diffractive optics may serve as a key technology for improving the performance and reducing the weight and cost of sensors for the Geostationary Earth Observatory will be discussed. These applications include the use of diffractive/refractive hybrid lenses for the Lightning Mapper Sensor, diffractive telescopes for narrowband imaging and subwavelength structured surfaces for antireflection and polarization control.

The physical and spectral characteristics of refractory oxide narrowband optical filters, fabricated with an ion-assisted deposition process are investigated. The properties of tantalum pentoxide (Ta₂O₅) and silicon dioxide (SiO₂) are compared with more conventional zinc sulfide (ZnS) and cryolite (Na₃AlF₆) optical interference filters, for effects of radiation, moisture and abrasion, as well as thermal stability. Filter longevity and thermal properties are dramatically improved, which can have a significant impact on the performance of space-borne optical systems.

Attainment of critical low noise performance of integrated focal plane subsystems (FPS) has been a difficult challenge, particularly the electrical interface between cryogenic and room temperature components. This paper presents a focal plane architecture for high performance scanning HgCdTe sensors which simplifies this interface and uses optical interconnects for improved noise immunity. Hardware testing has demonstrated operation at both component and integrated levels. Integrated FPS tests established noise as low as 50 (mu) V which is our goal. Our next step will be to evolve the FPS to demonstrate a fully flight compatible configuration.

Optically interfacing a modern focal plane to its processing system requires technologies and methods with which many may be unfamiliar. This paper discusses some of the alternatives available among light emitters, detectors, and conduits. We also describe AESD activities in using these devices to provide power and clock signals to a cryogenic focal plane.

Autonomous wildfire detection systems may help to reduce hazards resulting from large wildland fires. In many situations wildfires start in the duff below trees and shrubs, which are hidden from direct view by groundbased sensors overlooking forests and wildlands. Mid- and thermal infrared measurements only detect wildfires when the fire has become a crownfire, and, by then, it usually has developed into a large wildfire. Therefore, the early discovery of wildfires using groundbased, autonomous sensors should be performed by detecting smoke clouds rather than the heat of the fire, since smoke becomes earlier visible above the trees as a result of convection than the heat of the fire. A demonstration sensor is being developed to show the feasibility of an affordable system for autonomous wildland fire detection. The system is designed to minimize false alarms by simultaneously analyzing the temporal, spatial and spectral information in the acquired imagery. The groundbased sensor will be horizon scanning and will employ linear CCD's for better contrast sensitivity in three different spectral bands.

A patented camera system for omnidirectional image viewing applications that provides pan, tilt, zoom, and rotational orientation within a hemispherical field-of-view utilizing no moving parts has been developed. The imaging device is based on the effect that the image from a fisheye lens, which produces a circular image of an entire hemispherical field-of-view, can be mathematically corrected using high speed electronic circuitry. More specifically, an incoming fisheye image from any image acquisition source is capture in memory of the device, a transformation is performed for the viewing region-of-interest and viewing direction, and a corrected image is output as a video image signal for viewing, recording, or analysis. As a result, this device can accomplish the functions of pan, tilt, rotation, and zoom throughout a hemispherical field-of-view without the need for any mechanical mechanisms. A programmable transformation process provides flexible control over viewing situations. Multiple images, each with different image magnifications and pin-tilt-rotate parameters, can be obtained from a single camera.

We present the development of a near infrared image intensifier tube based on a Generation III configuration. The photocathode driving this tube is based on a negative-electron-affinity (NEA) InGaAs design. The surface and crystalline quality of the InGaAs active layer for this device is characterized by x-ray diffraction (XRD), micro-Raman spectroscopy, energy dispersive x-rays (EDX), and Auger spectroscopy. Room temperature and 77 K photoluminescence (PL) and transmission measurements indicate the near infrared responsivity (1.2 - 1.7 micrometers ) of the InGaAs active layer. Reflection mode measurements of the photoresponse (PR) in an ultra high vacuum environment produced white light sensitivities of 100 (mu) A/lumen and quantum efficiencies of approximately 1% for wavelengths of 1300 - 1600 nm at 300 K. Sealed image tubes were created, and early sealed tube results show low quantum efficiencies (approximately 0.1% 1550 nm) due to nonoptimized active layer thickness.

A 12 mm active diameter proximity focused MCP image intensifier tube has been developed having a typical limiting resolution of 45 lp/mm, and a luminous gain of 1E4 fL/fc at 960 V, and a mass of 24 g. In produces about the same number of pixels in its active area as an 18 mm active diameter image tube having a limiting resolution of 32 lp/mm and a mass of 51 g. Its equivalent background input at 23 degree(s)C is essentially the same as an 18 mm tube; i.e., 2E-11 lm/cm². This 12 mm tube is well suited for use in small and lightweight low light level direct-view systems and TV cameras.

There are subtle effects on the MTF of any optical device when 'stray light' is present along with the test pattern (usually a slit). Reported here are observations on image intensifiers, using the Ealing Solid-State MTF analyzer, which allows more detailed readout than with some prior systems. The shape of the MTF curve at low space-frequencies can yield clues about the effects of stray light.

Infrared response of multialkali photocathode is an important subject of the research for the improvement of the detecting objective distance ability of night vision system, some aspects for the possibility of the improvement of the infrared response of the multialkali photocathode in an image intensifier are studied theoretically in this article.

Bright and dark spots noise phenomena observed on the phosphor screen output of framing streak tube with Fiber Optic Plate (FOP) output window have been investigated and the mechanism of these phenomena has been attributed to undesirable accumulation of charge on the FOP because of nonuniformity of FOP resistance. In order to solve these noise problems, the transparent conductive layer (ITO) was inserted between the FOP and phosphor screen. It was shown that bright and dark spot noises were completely eliminated by this method. In addition to this improvement, the conversion gain of the phosphor was also shown to be improved. The improvement of conversion gain and spatial resolution were about 1.5 approximately 2.0 times compared to conventional values. This method could be effectively applied to all kinds of imaging devices with FOP in which the high quality of the image intensification is most important.

This paper describes one of the research projects currently in progress at C.A.R.S.O. The goal is to develop space qualified Intensified CCD detectors for applications in different wavelength bands, from the visual to the UV and EUV, and the related control electronics. The required performances, high sensitivity and flexibility, allow to obtain spectral images of faint extended sources and to operate, simultaneously, multiple detectors, in order to respond to different scientific and operational tasks.

The Multi-Anode Microchannel Array (MAMA) detector system is a true photon-counting imager which records the position and arrival time of each detected photon for post facto image reconstruction analysis. Imaging by time-tag photon detection with the MAMA is being used for image stabilization on sounding rockets, and for speckle interferometry and speckle image reconstruction at ground-based telescopes using the Stanford University Speckle Interferometer System (SUSIS). This paper describes the construction and mode-of-operation of the MAMA time-tag photon-detection system, including recent improvements to the data- handling system which permit a data-recording rate in excess of 1 M event s^-1. The intrinsic time resolution of the MAMA detector system is < 300 ns and the time resolution of the SUSIS used to date is 3.2 microsecond(s) for each detected photon. A number of examples of both laboratory data and visible-light speckle interferometric deconvolutions and two-dimensional speckle image reconstructions are presented.

The continuing effort to improve detectors for low light applications has resulted in the development of imaging photon counting detectors. One such device is the MAMA (Multi- Anode Microchannel Array) detector fabricated by Ball Aerospace. This paper provides a brief overview of the STIS (Space Telescope Imaging Spectrograph) MAMA detector and a detailed description of the analog signal processing electronics. The analog signal processing circuit is built using two unique Ball Aerospace and Communications Group (BACG) designed ASICs (application specific integrated circuits). Each MAMA detector analog signal processing channel uses a pair of the ASICs. The first is a charge to voltage amplifier and the second a voltage discriminator. The amplifier has lower noise and higher speed than previous BACG designs. Its first stage gain bandwidth is 10 GHz with an equivalent input noise voltage of about 1 nV per root hertz. It has a single ended input and differential output to drive the voltage discriminator. The voltage discriminator ASIC has differential input and single ended, CMOS compatible, output. The system has a 120 ns pulse pair resolution with 21 ns amplitude dependent timing uncertainty. Calculated false event rate, for prototype devices, is 1 count in 10⁷ sec with 100 pF detector capacitance and a 20,000 electron threshold. Counting rates greater than 1 million per second per channel can be accommodated. Both ASICs have much lower power consumption than previous discrete designs. The ASIC process used allows the fabrication of extremely robust devices while reducing the total number of parts.

Photomultiplier tubes (PMTs) making use of microchannel plate (MCP) electron multiplier assemblies are being developed. Both single anode and multianode designs are available having active diameters of 18 mm, 25 mm and 40 mm. A variety of spectral sensitivities is available in all sizes, and Blue GaAs, GaAs, or InGaAs photocathodes can be provided in the 18 mm active diameter size. Pulse height distributions having full-width half-maximum values of 59% and peak-to-valley ratios of 10 have been achieved.

A 16 mm active diameter photomultiplier tube (PMT) having an electron-bombarded silicon avalanche diode electron multiplier is shown to have promise as a replacement for PMTs with conventional discrete dynode or channel electron multipliers. Any type of conventional photocathode, e.g. uv-sensitive, bialkali or multialkali types, as well as negative electron affinity GaAs types can be used. The full potential of the high detective quantum efficiency of the GaAs cathode can be realized for the first time in a photoelectronic detector because of the nearly complete utilization of the photoelectrons. Key performance characteristics are gain to about 1E6 e/e, linear dynamic range for dc operation to about 1E6, insensitivity to strong magnetic fields, and a counting efficiency of about 80%.

Modern combat aircraft depend on high quality airfield surfaces for takeoff and landings (TOLs). This makes TOL surfaces a very attractive target to enemy attack. After an attack, the number one priority of the recovery forces at a combat air base is to restore the air base's war fighting capability; therefore, an accurate and expedient assessment of damage is the first step of the restoration process. At present a damage assessment system (DAS) that can accurately, rapidly, and safely characterize and evaluate the magnitude of damage from an enemy attack with conventional weaponry such as mines and bombs does not exist. Using the systems engineering approach, this paper develops a DAS based on the promising ATR technology for improving the conduct of the postattack air base DA function. This paper also examines and identifies the sensors and the sensor fusion techniques that form the core of this DAS. Furthermore, this paper ranks the exploitable technologies and recommends test-worthy systems for further analysis.

Low energy neutral atoms (LENAs) are produced in space plasmas by charge exchange between the ambient magnetospheric plasma ions and cold neutral atoms. Under normal conditions these cold neutrals come from the terrestrial geocorona, a shroud of few-eV hydrogen atoms surrounding the Earth. As a consequence of this charge exchange, it has become possible to remotely image many regions of the magnetosphere for the first time utilizing recently developed LENA imaging technology. In addition to the natural hydrogen geocorona, conventional explosions and maneuvering thruster firings can also introduce large amounts of cold gas into the space environment. In this paper we examine whether such potentially clandestine activities could also be remotely observed for the first time via LENA imaging. First, we examine the fluxes of LENAs produced in the space environment from a conventional explosion. Then we review the present state of the art in the emerging field of LENA detection and imaging. We conclude that the sensitivities for present LENA imager designs may be just adequate for detecting some mad-made releases. With additional improvements in LENA detection capabilities, this technique could become an important new method for monitoring for conventional explosions, as well as other man-made neutral releases, in the space environment.

The High ALtitude Observatory (HALO), is an instrumented Gulfstream IIb twin engine jet aircraft maintained by the United States Army Space and Strategic Defense Command as an optical data collection platform. Capable of operating above 50,000 feet, the HALO's diverse and flexible sensor suite has provided infrared, optical and ultraviolet data on numerous SDIO, NASA and DOD test programs. The HALO contains three optical platforms, the first of which contains the Infrared Instrumentation System (IRIS), the primary HALO sensor, while the second and third can be custom configured with a wide variety of UV, visible and infrared sensors. Included in the HALO sensor suite are calibrated UV/Visible ICCD imagers, spectrometers, high speed video cameras, uncalibrated film and video sensors and an infrared spectroradiometer. This paper describes in detail some of the ultraviolet and visible sensors employed on the HALO for the purpose of measuring and characterizing missile plume signatures and phenomenology and presents a representative sample of HALO plume data obtained from these sensors.

Photek manufactures a range of imaging photon counting tubes for resistive anode, centroiding CCD and wedge and strip readout systems. All three readout mechanisms have advantages and disadvantages. These are reviewed in this paper, by the way of examples of the various applications. All three systems can cover the electro magnetic spectrum from MeV photons to less than 1 eV and the means of doing so are briefly described. All three systems share similar limitations in count rate, counting efficiency and resolution. These limitations mainly stem from the micro channel plate structure and are the main area of development. Recent developments in the microchannel plate (MCP) tube technology have led to improvements in these aspects and are described in the paper.

Reconnaissance systems incorporating solid-state image sensors have advantages over film- based systems in their ability to provide real-time images and transmit digital data to a remote location. In this application area array sensors have advantages over linear and TDI type sensors in eliminating the need for the aircraft to travel in a straight line as is required for 'push broom' imaging. DALSA has previously developed a single output 2048 X 2048 area array which evolved to a four output high speed image sensor suitable for airborne reconnaissance. In this paper we discuss a four output 5120 X 5120 image sensor; this sensor is a prototype for an 8 output imager suitable to replace film recording media for airborne reconnaissance. We review the performance of the existing 5120 X 5120 array and discuss the design modifications implemented on the second generation device to match reconnaissance requirements, improve performance and enhance yield.

Over the past years, fiber optic temperature sensors have been constructed for a variety of applications. Some utilize bi-metallic transducers which are attached to the ends of Y branched bifurcated fiber bundle cables and operate much as proximity sensors, while others are based on blackbody radiation principles, such as those generated by a hollow sapphire tube. The latter type of sensor is typically used for high temperature ranges, (500 - 2400 F). As the sapphire tube is subjected to heat, it begins to radiate light which propagates through the cylinder and is detected by an optical meter at the opposite end of the tube. Thus, an optical- temperature relationship is generated. Additionally, other temperature sensors are also based on interferometric principles. It is proposed that a Hybrid Temperature sensor based upon the internal effect principle which, for experimental and proof-of-concept purposes, can be modeled utilizing a simple fiber-coupler assembly. It will be demonstrated that such a sensor can be operated efficiently in the 0 - 200 F range, (with upper and lower temperature range maximums being material limited). Theoretical documentation is presented for both single and multi-mode fiber sensor models. Experimental results are also presented for the multi-mode case utilizing an 850 nm laser source.