POLDER is a radiometer dedicated to the observation of the polarization and directionality of the Earth's reflectances. It images the Earth with a large field of view (115 degrees) in 8 spectral bands from visible to near infrared. The instrument, developed by CNES will be installed on the ADEOS Japanese satellite to be launched in August 1996. This paper deals with the preflight radiometric and geometrical calibrations of the instrument. It presents the radiometric and geometrical models of the instrument, in relation with its physics. The geometrical calibration consists in determining for each spectral band the mathematical model relating each viewing direction within the instrument field of view to a pixel location in the focal plane. The requirement is to determine the absolute location of the image point with 0.05 pixel accuracy. The radiometric model takes into acount the different characteristics of the instrument, including the polarization capability and the bidimensional detector array. The scientific objectives of POLDER lead to severe radiometric calibration requirements (for instance, +/- 1% on relative low spatial frequency calibration or +/- 0.1% on relative high spatial frequency calibration). The dedicated ground equipments are described (integrating spheres, polarizers, reference radiometer, optical directional reference generator...), as well as the procedures and the first results with their related accuracies.

This joint article presents the POLDER-OCTS preflight cross-calibration procedure and data set. POLDER is a radiometer developed by CNES devoted to the measurement of the polarization and directionality of the Earth's reflectances and OCTS is an ocean color and temperature scanner developed by NASDA. Both radiometers are onboard the ADEOS satellite to be launched in 1996. The preflight POLDER-OCTS cross-calibration experiment was carried out by NRLM, NASDA, and CNES from March to April in 1994 using round- robin radiometers. The cross-calibration results show the agreement between NRLM/NASDA and CNES radiometers better than 6% regarding POLDER integrating sphere at CNES in Toulouse and better than 5% regarding OCTS integrating sphere at NEC in Yokohama. Calbration of OCTS integrating sphere by NEC agreed with cross calibration by NRLM/NASDA within 3%. The calibration of CNES round-robin radiometer is guaranteed at 3.5%.

The MARS '96 spacecraft is devoted to a mission to planet Mars with a lifetime of three years. This paper presents the characteristics of the IR detection modules for the OMEGA IR spectrometer. SAT has developed the identification model, development model, and flight models of detectors, each having 2 arrays and IR filters in a dedicated space housing equipped with a flexible electrical line and a connector. An array is composed of 128 multiplexed InSb photovoltaic detectors surrounded by a specific IR filter. Each filter is divided into 2 zones. The multiplexed read-out is obtained with a Si CCD device. Space-designed and qualified for SPOT IV, it has not been modified for our 77 K operating condition, only the drive electronics, bias conditions, and phase clocking have been adapted to the 128 detectors. An evaluation program has been applied, according to ESA requirements, with environmental tests and the results are reported including mechanical tests. thermal cycling, ESD testing, and irradiation. Complete measurements have been performed with IR filters, specific packaging, and cold line integrated in the equipment.

Results of conceptual design study of a solar occultation infrared sensor, improved limb atmospheric spectrometer-II (ILAS-II) which will be onboard ADEOS-II spacecraft, is discussed. The ILAS-II will have four grating spectrometers for solar occultation measurement: two are identical to the spectrometers of the ILAS onboard ADEOS to be launched in 1996. To observe ClONO₂, which is a key species that controls catalytic destruction of ozone, an echelle grating spectrometer with 0.14 cm^-1 resolution for the 780.2 +/- 1 cm^-1 region will be added to the ILAS-II. Another new spectrometer will cover the 3 to 5.7 micrometers region to characterize the aerosols such as sulfuric acid aerosols and PSCs as well as to observe the chemical species.

A PtSi Schottky-barrier infrared focal plane array (FPA) has been developed for the short wavelength infrared radiometer (SWIR) of the advanced spaceborne thermal emission and reflection radiometer (ASTER). Six linear image sensors, which correspond to six observation bands, are integrated on the FPA to simplify the cooling system and the optics. Each linear sensor has a stagger layout of 2100 PtSi Schottky-barrier detectors and has an effective fill factor of 100%. The detector size is 20 micrometers by 17 micrometers with a cross-track pitch of 16.5 micrometers and a spacing between adjacent sensors of 1.33 mm. The charge transfer in each linear sensor is carried out by two 4-phase buried-channel CCD shift registers. The driving clock and structure of the CCD are optimized to achieve a large charge handling capacity and low transfer inefficiency. To assure a high reliability and a focal plane flatness, we have developed an original multilayer ceramic package with a filter holding structure. A focal plane flatness less than 14 micrometers and a heat shock endurance over 4000 cycles are achieved by using this packaging technology. The wavelength region between 1.5 micrometers and 2.5 micrometers is separated into six bands by optical band-pass filters attached to the package.

In support of the Canadian Space Plan, the R&D branch of the Department of National Defence initiated a technical study to identify satellite system options that would improve the national surveillance network. Space-based infrared and visible-light sensors and real and synthetic-aperture radar systems were considered. This report summarizes the findings of the study, starting with a general discussion of surveillance requirements and a description of the 'case-study' approach used to formulate a surveillance concept. Applicable technolgoy is described, with emphasis on concepts that address specific surveillance deficiencies. Current fiscal realities and the high cost of space technology are addressed in a discussion of near-term options using data from commercial satellites, accessed through an improved dissemination network.

Canada recently approved a new long term space plan (LTSP). It involves continuation of international collaboration in space science, continued participation to the International Space Station project and sustained support to the Earth Observation RADARSAT program. Optical technologies, in particular infrared technologies, are at the core of many of the ongoing and planned missions. Areas of interest include imaging doppler-shift and Fourier transform interferometry, correlation spectroscopy, and space vision systems. The LTSP also sets the major thrusts for the developement of new space missions and supporting technology programs, emphasizing the role of international collaboration and Canadian industry involvement. Communications, earth observation, and space science will constitute the essence of future space applications. Notably, two science small satellites are proposed. To allow implementation of future projects to proceed effectively, a technology developemnt program is being defined. It is based on continued improvement of space demonstrated systems and on investigating advanced optical technologies.

A surveillance concept is formulated for the detection and localization of large aircraft in the outer zone surrounding Canada, based on a cued sensor in a one-meter aperture satellite- mounted camera, working in the 8 to 12 micrometers spectral band, surveying a narrow fence enclosing the north of Canada from the Pacific to the Atlantic via the Arctic. This surveillance task can be achieved by three satellites in inclined elliptical orbits for the Arctic zone above the 50th parallel or by six satellites for a zone of surveillance extended up to the 40th parallel.

Small, incipient wildfires in the boreal forest can be detected with a space-based infrared sensor that uses currently available technology. At night, wildfires with a temperature of 700 K or more and an area of 1 m² should be visible if there is a clear line of sight to the sensor. Sensor refinements and signal processing could enhance this level of detection. Clouds, topographical variations and the forest canopy may obscure the line of sight, so that multiple looks would significantly improve the probability of detection of a small fire. The relatively long revisit time of a satellite-based sensor is a constraint of the fire management application. Although the cost and revisit time of a spaceborne sensor are currently too high for it to replace airborne sensors, there is an important role as an adjunct sensor operating at night. Many of the specifications of an infrared sensor for wildfire detection are similar to those for space-based surveillance applications, so that useful infrared imagery from space may become available to the forest management community at relatively low cost.

The portable hyperspectral imager for low light spectroscopy (PHILLS) is a modular system incorporating panchromatic and spectroscopic imagers. PHILLS was designed to be a low cost, versatile hyperspectral imager using primarily commercial off-the-shelf parts that could be used as a ground based or airborne imager. The goals fo the PHILLS program are to allow collection of high quality broadband hyperspectral data, to develop methodology for near real time spectral unmixing, to make deployment of hyperspectral imagers feasible in airborne or spaceborne scenarios. Presently PHILLS combines high resolution color video cameras with intensified UV, visible, and NIR spectroscopic modules with wavelength resolution of 0.5-2 nm over the 0.2-1.1 micrometers band. The system offers analog and digital data recording capability with GPS annotation. The instrument has been successfully deployed on NRL's P-3 aircraft in missions from the North Pole to the Florida Keys. The PHILLS system is controlled by a personal computer and is integrated with an adaptive hyperspectral data analysis system that provides very fast end member determination and subpixel spectral unmixing using an orthogonal projection based method known as the filter vector algorithm.

The portable hyperspectral imager for low light spectroscopy (PHILLS) instrument consists of several modules containing analog and digital imaging spectrometers, two of which are intensified, covering the 200 nm to 1100 nm wavelength range with over 100 wavelength bands. The PHILLS instrument is usually flown aboard P-3 Orion aircraft at altitudes from 500 feet to 10,000 feet. PHILLS ground images are acquired with > 70 degrees FOV and 2-5 meter spatial resolution, and 0.5-1 nm wavelength resolution. Hyperspectral data cubes are processed using a combination of spectral matching techniques and the filter vector algorithm, to produce terrain separation and spectral dimensionality; i.e. variability of the spectral signatures for individual 'substances' in the image. Data obtained on flights over the Florida Keys showing land and underwater features are presented.

We report recent progress using a filter vector technique to analyze the data from a hyperspectral image. The filter vector technique finds the optimal filter vectors for demixing the complex patterns found in the hyperspectral image. The method has the potential to be implemented in real time since it is fully parallel. Computation of the filter vectors for a given family of known species vectors is fast and direct and improved algorithms for developing of the algorithm which may be updated as conditions change is possible. Advantages of using the filter vector techniques over the technique of pattern matching will be discussed. The portable hyperspectral images for low light spectroscopy (PHILLS) instrument has been used on a number of depolyments in the last year. Typically, the instrument files on the Naval Research Laboratory's P-3 Orion aircraft. Currently, the PHILLS instrument records over 1000 wavelength bands between UV and near IR. Results from a number of deployment and test situations is shown.

In this paper, we study the effects of orthogonalization on sequential, multisensor, and multispectral satellite images for CFAR point target detection incorporting fusion techniques. Although the K-L orthogonalization offers the best CFAR detection performance, it requires central fusion. A version of the G-S orthogonalization method, which preprocesses data in a pipeline form, offers a comparable CFAR detection to that of the K-L method. Point target CFAR detection is carried out by employing various fusion approaches on the orthogonal data. Sensor level fusion with quality information is shown to be preferable when the proposed sequential G-S orhtogonaltization is applied. The proposed CFAR approach is applied to dissimilar sensors and avoids overloading the communication channel transmitting only in the case of target detection. Trade-off studies and experimental results on real and simulated data are presented.

In this paper, we present a new statistical model to describe infrared images. The proposed pdf is a compound model derived from the Gaussian and the GT-pdf. Closed form expressions for the statistical moments of the model are derived. For specific values of its parameters the model ends up to be simpler pdfs. The proposed compound pdf models the thermal radiation from the background, the sunlight scattering as well as scintillating effects. We propose a parameter estimation technique which is based on the equivalence of experimental and theoretical moments. Experimental results are provided for model validation in real data as well as for demonstration of the segmentation procedure.

A stereoscopic approach for 3D terrain reconstruction from IR aerial image sequences is presented. The image sequence is captured in the so-called push-broom mode in which the same terrain is viewed by the aircraft from two different locations with two opposite viewing angles. Furthermore, a high frame rate IR imaging system mounted on a relatively slow speed aircraft allows the acquisition of a sub-pixel resolution image sequence, in which one physical point in the scene appears in several consecutive images at the same location. The proposed terrain reconstruction is carried out in three steps: first, two superimages (SI), representing an extended area of the viewed scene, are constructed from the forward and backward sequences. Each line of a SI is a weighted combination of a series of lines, each one extracted from a different image, at locations corresponding to the same scene elements. The determination of the set of lines in consecutive images to be combined into one line of the SI is accomplished through a correlation-based global matching procedure between images. In the second step, a multiresolution matching technique is applied on pairs of images extracted from the SIs, using a matching approach which relies on multiple matching cues in the infrared images. The final step consists of the absolute depth map computation, making use of the previous matching results and the prior knowledge about the geometrical configuration of the sensor at the two viewing locations.

The Marshall Space Flight Center, Alabama, in a teaming arrangement with the University of Florida, Gainesville, and the Joint Astronomy Center, Hawaii, has completed a comprehensive investigation into the feasibility of a low-cost infrared space astronomy mission. This mission would map the emission of molecular hydrogen in our galaxy at two or three previously inaccessible mid-IR wavelengths, and provide information on the temperatures. The feasibility of the low-cost mission hinged on whether a thermal design could be found which would allow sufficient passive cooling of the telescope to elimiate the need for a large, expensive dewar. An approach has been found which can provide telescope temperatures on the order of 50 K, which makes the mission feasible at low cost in low-Earth orbit.

A 1-5 micrometers astronomical infrared imaging camera, COMIC, is currently being developed for the ADONIS adaptive optics system, as a collaborative project of Observatoire de Paris and Observatoire de Grenoble under ESO (European Space Observatory) contract. This camera is based on a 128 by 128 HgCdTe/CCD array built by the CEA-LETI-LIR (Grenoble, France). Among its main characteristics, this detector offers a very high storage capacity of 3 10⁶ e- with a total system read-out noise of about 600 e- which makes it particularly optimized for the 3-5 mum. COMIC will be installed in the fall of 1995 at the output focus of the ADONIS AO system on the ESO 3.6-m telescope at La Silla (Chile).

The wide-field infrared explorer (WIRE) is a cryogenically cooled infrared telescope being prepared to study the evolution of starburst galaxies. The WIRE instrument will measure the infrared energy in two broad bands. Two 128- by 128-pixel arsenic-doped silicon focal plane arrays detect the galactic emissions. We provide a sensitivity analysis for the long wavelength band, 21 to 27 micrometers , including NEP for a single element. Ultimate flux sensitivity is limited by imaging resolution which includes the effects of diffraction, spacecraft jitter, and sampling of the point spread fuction. Observation times to obtain these confusion limited measurements are provided. Ground characterization and on-orbit calibration measurements are outlined, as is the simulation plan.

Very high precision, lightweight optical pointing devices, in conjunction with ultra lightweight telescope assemblies are enabling technolgies for small, low cost space satellite platforms. These platforms do not provide a stable pointing platform. High bandwidth, servo controlled pointers compensate for the platform instabilites. A new generation of high bandwidth, very precise pointers are possible because of very low mass mirrors made from silicon carbide (SiC), aluminum or beryllium and ultraprecise optical fringe counting encoders. Silicon carbide pointing mirrors are very attractive because of their extreme thermal stability. This allows operation over large temperature ranges and gradients. SSG, Inc. has developed a range of very lightweight telescope systems for DOD and NASA missions. These systems are applicable to small space platforms with minimal weight impact, thus enabling a new generation of very cost effective missions not yet achieved.

This paper describes the design of a 10-channel infrared (1.27 to 16.9 micrometers ) radiometer instrument known as SABER (sounding of the atmosphere using broadband emission radiometry) that will measure earth-limb emissions from the TIMED (thermosphere- ionosphere-mesosphere energetics and dynamics) satellite. The instrument telescope, designed to reject stray light from the earth and the atmosphere, is an on-axis Cassegrain design with a clam shell reimager and a one-axis scan mirror. The telescope is cooled below 210 K by a dedicated radiator. The focal plane assembly (consisting of a filter array, a detector array, a Lyot stop, and a window) is cooled to 75 K by a miniature cryogenic refrigerator. The conductive heat load on the refrigerator is minimized by a Kevlar support system that thermally isolates the focal plane assembly from the telescope. Kevlar is also used to thermally isolate the telescope from the spacecraft. Instrument responsivity drifts due to changes in telescope and focal plane temperatures as well as other causes are neutralized by an in-flight calibration system. The detector array consists of discrete HgCdTe, InSb, and InGaAs detectors. Two InGaAs detectors are a new long wavelength type, made by EG&G, that have a long wavelength cutoff of 2.33 micrometers at 77 K.

The stray light analysis of the sounding of the atmosphere using broadband emission radiometry (SABER) instrument on the thermosphere-ionosphere-mesosphere energetics and dynamics (TIMED) mission is discussed. Relevant mission objectives and operating conditions are stated to define the stray light problem. Since SABER is an earth limb viewing sensor, the telescope must be designed for large off-axis rejection. Described are the key design features which make the instrument well suited for its mission. Representative point source transmittance (PST) curves computed using the commercial stray light program APART are presented. Nonrejected radiance (NRR) values computed using APART generated PST curves and LINEPACK generated curves for the total radiance from the earth and the atmosphere are given. A method for computing NRR from the earth and the atmosphere using line-of-sight radiance profiles versus tangent height is described. Computed NRR values demonstrate that the effect of stray light on SABER's measurement capability is negligible.

The advanced spaceborne thermal emission and reflection radiometer (ASTER) is an instrument which was selected by NASA to fly on the EOS-AM1 platform in 1998. Two cryocoolers are required to cool infrared detectors for the short-wave infrared radiometer (SWIR) and thermal infrared radiometer (TIR). The mission lifetime of the EOS-AM1 platform is expected to be 5 years, and accordingly, an operation lifetime more than 5 years is required for ASTER cryocoolers. The goals in the development of the ASTER cryocoolers are realization of a operation lifetime of over 50,000 hours and mechanical vibration forces below 0.1 N in the frequency range from 40 Hz to 135 Hz in the driection of all three axes. A split- Stirling cycle cryocoolers with clearance seals and linear motors is employed for this purpose. The compressor design adopts a piston driving mechanism which has a twin-opposed piston configuration in one compression space. The mechanical vibration caused by a displacer in the expander unit is reduced by an active balancer. Cryocoolers for SWIR and TIR have cooling capacity of 1.2 W at 70 K with power consumption lower than 55 W without control electronics. Several engineering models (EM) have been fabricated and are presently undergoing performance and life tests. Results of cryocooler verification tests and effects of jitter of mechanical vibration on the ASTER instrument are described.

We have studied potential effects of the ISO spacecraft orbital radiation environment on the transmission of infrared interference filters and filter materials. To simulate the critical proton radiation within the earth radiation belts and its influence on the materials at cryogenic temperatures the samples were cooled to LHe temperature and subjected to an Am-241 (alpha) -radiation source (approximately 4.1 MeV) mounted inside a cryostat. The dose per hour absorbed in a 20 micron thick layer, the mean penetration depth for the (alpha) particles, was about 25 krad (Si). The substrates Ge, ZnSe, and CaF₂ and three tested ISOPHOT interference bandpass filters (3.21-3.37 micrometers and 2-50 micrometers even after a total dose of approximately 0.5 Mrad (Si), which is more than 100 times the expected total dose for ISOPHOT. The multilayer interference blocking coating on sapphire used on all ISOPHOT far infrared filters to block the wavelength range 1.7-6.7 micrometers showed no degeneration either. The organic far infrared antireflex coating materials polyethylene deposited on a quartz substrate, and a 15 micrometers thick parylene foil used as field lens coating, were investigated in the wavelength range of 16-300 micrometers . Our data suggests a slightly reduced transmission < 6% after 350 krad (Si) exposure.

Cassini/Huygens is a joint NASA/ESA planetary mission to the Saturnian system. Titan, the largest Saturn moon, is the major target of the mission. Cassini is the Saturn orbiter provided by NASA to be launched on October 1997. To reach planet Saturn in 2004 and to study the rings, the planet and its satellites, the Cassini/Huygens planetary mission, a NASA-JPL project, includes among 12 instruments, the composite infrared spectrometer (CIRS) with GSFC as prime contractor of this instrument. The French participants are the Service d'Astrophysique (SAp) of CEA-Saclay and the DESPA-Observatoire de Meudon. CEA/SAp is in charge of the focal plane 4 electronics (detector, cold preamplifier, and analog processing electronic). SAT has developed under a CEA-SAp contract the hybrid micro-circuit which ensures the preamplifying function. These transimpedance amplifiers operate at 170 K and consist of 10 channels. The input current from the detector is up to 60 nA (mainly background current, modulated by a signal in the pA-nA range) and is converted into voltage up to 1.2 V through a 20 M(Omega) feedback resistor. The noise is < 15 nV/(root)Hz. The stability of the resistors is expected to be 0.1% for a duration of 16 years. The lifetime reuqirement consists of: 1) ground storage: 3-4 years, 2) transfer orbit: 7 years (instrument not operating), 3) Saturnian orbit: 4-5 years (instrument operating) and more than 40 Saturn-centered orbits. The preamplifier hybrid is an operational amplifier using a resistor multichip substrate designed, manufactured, and selected according to ESA PSS and MIL applicable documents. This amplifier integrated circuit has been chosen taking into account its cold temperature electrical performance and on the basis of its radiation resistance to 100 krad (at 170 K and operating). The model philosophy includes 2 main deliveries: engineering models and flight/spare models. The evaluation program consists of the electrical testing of all component parameters at 293 K and 170 K, and lifetime tests (burn-in, thermal cycling). The preamplifier hybrids are mounted in packages, hermetically laser-sealed with dry gas atmosphere.

IASI is an infrared atmospheric sounding instrument devoted to the operational meteorology and to atmospheric studies and is to be installed on board the second ESA Polar Platform METOP-1 to be launched in 2001. The required operating lifetime is 4 years. An overall design of the Cold box, located at the focal plane interface level of the Michelson interferometer, has been performed for the mechanical structure and for the optical system taking into account the cold temperature requirement. This structure is interfaced with a passive cryogenic radiator. A thermal and modal analysis of this unit has been modeled to evaluate the thermal gradient and the eigen frequencies, by means of a finite-element software involving several thousands of nodes. Sinusoidal and random loads have been applied and the strains deduced. A thermoelastic model gives the relative position shift of the constituents when cooled-down. SAT is responsible for the subsystem Cold box and has been developing most of the critical elements of this unit. The role of this sub-assembly is to focus the IR signal onto the 3 detection arrays. It includes a spectral separation using 2 diochroic plates dividing the incoming flux into 3 spectral bands which are 3.6 to 5.0 micrometers , 5.0 to 8.26 micrometers and 8.26 to 15.5 micrometers . Each array stands behind an objective and a set of 4 microlenses. This unit defines the aperture and the field of view of the instrument and operates at 100 K with passive cooling. A specific optical ray tracer has delivered the optimization and the tolerancing of the optical system design. The results show that, with severe tolerances, the optical losses and cross-talk meet the requirements. The B-phase study is devoted to the preliminary design of the instrument and subsystems and to the manufacture of the critical components, among which the Cold box including all elements like IR detectors, optics, and packaging.

This paper presents the infrared atmospheric sounding interferometer (IASI) being developed at CNES Toulouse. IASI is a part of the operational meteorological payload managed by EUMETSAT. The baseline platform for the first flight model of the instrument is the METOP-1 polar platform to be launched during 2000/2001. IASI consists of a Fourier transform spectrometer (FTS) based on a Michelson interferometer coupled to an integrated imaging system which allows characterization of cloudiness inside the FTS field of view. This instrument will provide spectra of high radiometric quality at 0.5 cm-1 resolution from 15.5 micrometers to 3.4 micrometers , with global coverage twice per day at 25 km horizontal resolution.

The atmospheric infrared sounder (AIRS) is being developed for the NASA Earth Observing System (EOS) program with a scheduled launch on the first post meridian (PM) platform in the year 2000. AIRS is designed to provide both new and more accurate data about the atmosphere, land, and oceans for applications to climate studies and weather prediction. Among the important parameters to be derived from AIRS observations are atmospheric temperature profiles with an average accuracy of 1K in 1 kilometer (km) layers in the troposphere and surface temperatures with an average accuracy of 0.5 K. The AIRS measurement technique is based on very sensitive passive IR remote sensing using a precisely calibrated, high spectral resolution grating spectrometer operating in the 3.7 micrometers to 15.4 micrometers region. The instrument concept utilizes a passively cooled multiaperture echelle array spectrometer approach in combination with advanced state of the art focal plane and cryogenic refrigerator technology to achieve unparalleled performance capability in a practical long life configuration. AIRS is a key component of NASA's Global Change Research Program and is expected to play an important role in fulfilling the needs of the converged National Polar- Orbiting Operating Environment Satellite System (NPOESS) now under study. This paper provides a brief overview of the mission followed by a description of the instrument design and current development status.

AIRS is a key facility instrument on the first post meridian platform as part of NASA'a Earth Observing System (EOS) program. The Atmospheric Infrared Sounder measurement technique is based on passive IR remote sensing using a high spectral resolution grating spectrometer. The structure of the infrared focal plane for the AIRS instrument has been defined and is presented in this paper. The optical footprint of 8.1 mm by 36.3 mm along with the necessary support and interface components leads to a focal plane assembly of 53 mm by 66 mm, the largest ever built at LIRIS. With 4208 diodes and 274 photoconductors in the same focal plane to achieve the wide spectral coverage from 3.7 to 15.4 micrometers , a modular approach is required. Ten PV modules utilize silicon readout integrated circuits (ROICs) joined to the detector arrays as either direct or indirect hybrids while two PC modules cover the 13.7 to 15.4 mm range, optically chopped and led out to uncooled preamplifiers. The simultaneous operation of PV and PC devices in the same focal plane has required unique approaches to shielding, ROIC output design and lead routing. High D^*'s of 7E14 and 3E11 cm- Hz1/2/W are needed to meet the sensitivity requirements of the 4.2 and 15.0 micrometers regions respectively. The 35 micrometers by 800 micrometers PC detectors on a 50 micrometers pitch have necessitated modifications to standard delineation techniques, while the MW performance is nearly D^* BLIP for PV devices. Dispersed energy is presented to the modules through 17 narrow band filters packaged into a single precision assembly mounted within 0.18-0.25 mm of the focal plane surface. The more than 50 components comprising the focal plane in conjunction with the tightly spaced optical pattern presented by the grating add a high degree of complexity to the assembly process. This paper focuses on the architectural constraints derived from performance, interface, and reliability requirements. Key aspects of these requirements are presented and their impact on the partitioning of the 12 modules is discussed. The rationale for the spectral range assigned to each module is reviewed relative to PV and PC performance capabilites. ROIC design guidelines and physical contraints due to manufacturability and assembly. Results of structural and thermal analyses for the various module configurations and assembled focal plane to determine compliance with the stringent stability and positional requirements are presneted. Specific features of the module carrier/interface boards and the multilayered focal plane carrier/interface board are included as well as a review of the overall assembly sequence of the focal plane as influenced by repairability and reliability considerations. The comprehensive redundance strategy applied to the design of the FPA/dewar assembly will be reviewed, and the approach for operation/survival in the radiation environment is discussed. Key features of the ROIC, PV, and PC array designs will be presented along with results of analyses performed.

The Atmospheric Infrared Sounder (AIRS) is a space-borne high spectral resolution grating array spectrometer designed to provide improved global atmospheric temperature and humidity profiles to aid in climate studies and weather prediction. AIRS, which is a key component of NASA's Earth Observing System, is a complex cryogenic optical instrument with demanding ground operating constraints and calibration requirements which place significant demands on integration and test processes. The approach adopted for the integration of the instrument, is one designed to minimize/eliminate 'surprises' at the instrument level testing, where problems are difficult, time consuming, and costly to identify, isolate, and repair. This philosophy is not just limited to the integration and test of the instrument, but rather starts with the system's design synthesis and flowdown of the requirements to the lower level components, subassemblies, and continues with testability features designed into the instrument. Mathematical models and simulations are created to accurately predict critical performance parameters at various subassembly levels which are subsequently validated with subsystem and assembly level tests. Ground support equipment and a comprehensive test and calibration facility were also designed to support this gradual build-up of instrument performance knowledge taking into account tests to be performed, data acquisition, real time data processing and diagnostics, data analyses, data archival and dissemination. Presented in this paper are an overview of the instrument, the integration and test philosophy, the integration process/test flow, and the design approach for the ground support equipment and the test and calibration facility.

Computer generated holographic and moire aspherical compensators are frequently regarded as two completely different devices to analyze interferograms. Here we will show that they have more in common than normally thought.

The Centro de Investigaciones en Optica is developing the AZTECA optical design program to exploit the full synthesis capabilities intrinsic to Delano's y-y method. Both the y- y diagram and its dual the (omega) -(omega) diagram, are manipulated in real time to introduce changes at any point or line in those diagrams. These changes result in altered new versions of the optical system by means of a specialized subroutine that incorporates the fundamental synthesis equations for those diagrams. To display results on the computer's screen as the optimization process progress, AZTECA makes wide use of the fact that the y-y and the (omega) -(omega) diagrams display graphically all the first order attributes of an optical system. This program adjoins to these features the calculation of Buchdahl's 3rd, 5th, and 7th order aberration coefficients to the output. This results in a real time display of the system's paraxial and aberrational behavior. Efficient graphic displays, the program's modular structure and an interactive mode of operation, also contribute to make the AZTECA a versatile platform. It will be further developed as a new tool for efficient optical system design.

The measurement of pollution in the troposphere (MOPITT), is an experiment on the earth observing satellite, scheduled for launch in 1999. The instrument is an infrared spectrometer which will measure concentrations of carbon monoxide and methane in the atmosphere. This paper describes the optical mechanical design for the MOPITT qualification model lens systems.

Evaluation of real-time IR imagers is usually based solely on quantitative factors such as SNR, MTF, nonlinearity, dynamic range, and detector nonuniformity. These imagers may come up to specifications for each parameter individually, but still be unacceptable to human observers because of cumulative effects. We have devised a method to evaluate and compare the overall performance of real-time imaging systems for which humans are the ultimate receivers of the images. We designed and built a real-time synthetic image generator (RTSIG) for simulating real-time thermal imagers, and for use in visual psychophysical testing of human observers. RTSIG is highly useful in determining the effects on humans of various combinations and levels of image degradation mechanisms. Primary considerations involve MTF, detector array configurations, detector noise, detector nonuniformity, and electronics transfer functions. We have discovered surprising differences in the performances of single-detector imagers and linear array imagers. For single-detector imagers with fixed total noise power, an imager with a higher knee frequency has a lower threshold of detectability than one with a lower knee frequency. For linear array imagers, varying the knee frequency within limits does not affect the threshold of detectability.

The thermal infrared radiometer (TIR) is one of the three radiometers of the advanced spaceborne thermal emission and reflection radiometer (ASTER). The TIR is a multispectral scanning radiometer for the thermal infrared region of 8 to 12 micrometers. This region is thought to be useful to identify stone and rock classification, investigate clouds, water evaporation, and volcano observation. The TIR and other radiometers are to be loaded to EOS-AM1 polar orbital platform, which is planned to be launched in early 1998 by NASA. At present, developement of the TIR subsystem engineering model has successfully finished and development of the proto-flight model has started. The developemnt of TIR detector has completed attaining high detector performances and high reliability simultaneously, by the developments such as improvements of detector-element structures and improvement of detector/dewar design. In this paper, we report the progres and status of the design and development of the TIR infrared detector.

Extrinsic photodetectors with implanted low ohmic contacts are used in ISOPHOT, which is one of the four focal plane instruments of the Infrared Space Observatory (ISO). If operated under the low temperature and low background conditions of ISO, such detectors show a highly nonlinear transient response to step changes of infrared illumination. For the Si:Ga detector arrays in PHT-S, the spectrometer in ISOPHOT, we are able to describe accurately the nonlinear photoresponse by a simple analytical function of time. Based on the theory, fundamental detector constants characterizing the dynamic behavior of such detectors can be extracted from experimental data. This allows the prediction of the steady state signals of short time measurements that have not stabilized after an illumination change. Results are presented on the dynamic effects of step-like flux changes and on the observed nonstationary injection of carriers due to temperature variations of the detector. The optimization of the in-orbit observation strategy is discussed using theory and experimental results.

ISOPHOT is one of the four focal plane instruments of the astronomical infrared space observatory (ISO). In its flight spare model the sensitivity of two photo-polarimeters could be significantly improved by replacing bulk Si:Ga and Si:B detectors by Si:As blocked impurity- band detectors. These detector elements were selected for low dark current to allow for low background observations in the LHe-cooled ISO telescope. Their operational parameters temperature and bias voltage were optimized for best sensitivity when operated with the ISOPHOT cryogenic readout electronics. At fluxes of about 10^-16 W/pixel and temperatures of 2.9-3.6 K, NEP_DET equals 5 X 10^-18 W/Hz and R equals 23-36 A/W were measured. Their dynamic flux response is much faster than in bulk Si:Ga. Radiation-hardness has been tested by simulating the passage through the radiation belts on the ISO-orbit with a gamma source.

Cryogenic telescopes in space offer dramatic reduction in thermal IR background flux. Outstanding performance in the areas of detector dark current, read noise, and radiation hardness are required to take full advantage of the sensitivity improvements possible with such facilities, especially in very low flux (2 to 100 photons/pixel/sec) applications such as the Infrared Spectrograph on SIRTF. We present our testing methods and our results on Si:As and Si:Sb block impurity band (BIB) detectors produced by Rockwell International for our SIRTF and WIRE applications. Remarkable recent results are the reduction of the multiple-sampling read noise to 30 electrons, reduction of dark current to 10 e^-/s for Si:As and 40 e^-/s for Si:Sb, the use of an antireflective coating to improve the detective quantum efficiency for Si:As, extension of the useful wavelength range of Si:Sb to 40 microns, and confirmation that lab data on a 50 s time scale can be extrapolated to integration times at least 10 times longer.

Development of a new spectral irradiance scale realization at the National Institute of Standards and Technology (NIST) requires a careful and complete calibration of a high- temperature blackbody between 1200 K and 2800 K. Filter radiometers have been calibrated to measure the spectral radiance (or radiance temperature) of the blackbody. Using a monochromator, the blackbody spectral radiance will then be used to determine the spectral irradiance distributions of primary and secondary spectral irradiance lamp standards at NIST. In this paper, a calibrated pyrometer and V((lambda) ) filter radiometer will be used to evaluate the high-temperature blackbody for determination of the optimum calibration method for the blackbody. The blackbody apparatus will be described in detail. When the power supply is the sole source of current control, the blackbody current is stable to within 0.056%, resulting in 0.72% for the uncertainty in the blackbody spectral radiance. To achieve our goal of 0.1% in the final blackbody radiance, a blackbody current stability of 0.007% is required. Due to the day-to-day variations in the current, calibrations of the blackbody msut be made frequently. Several feedback control options are recommended as possible solutions for improving both the short term and long term current stability.

Use of ta photoconductor array in the wavelength range from about 100 to 300 microns could add to the capability of the far-infrared imaging spectrometer in the model payload of FIRST (ESA's far-infrared and submillimeter space telescope). The GaAs detector array is a completely new development and will be included in an ESA-sponsored detector development program. The material offers the advantage of extending the wavelength range of photoconductors considerably. Essential improvement of material quality is required to bring dark current and NEP at operating temperatures around 1 K down to levels of state-of-the-art photoconductors. Recent progress has led to the production of extremely high purity GaAs layers using liquid phase epitaxy. Layers with a thickness of a few hundred microns were produced only a short time ago. They are considered good candidates to start investigations and preparation of detectors. This paper discusses recent results of the GaAs material research, detector design, and progress of array development.

The remote measurement of the emissivity of ground materials is of tremendous value in their identification and mapping. Traditional techniques use reflected solar radiation for this measurement for wavelengths shorter than 5 micrometers . With the development of new techniques, the 10 micrometers atmospheric transmission window might also be used for this purpose. Previous work using the multiangle data acquisition technique demonstrated its utility to determine source thermal emission. Here we find the multiangle technique can be used to determine the source specular reflectivity to approximately 0.05 if there is very good system performance.

An optical test Dewar has been constructed with the unique capability to test mirrors of diameter <EQ 1 m, f <EQ 6, at temperatures from 300 to 5 K with a ZYGO Mark IV interferometer. The facility possesses extensive thermometry throughout for characterization of the test chamber thermal environment and Dewar performance. Optical accesss is controlled with cryogenically cooled shutters. The entire Dewar is vibration isolated by 40 dB where the fundamental resonances of the Dewar structure are highest. The facility has been brought on line for its first user, the Infrared Telescope Technology Testbed for the Space Infrared Telescope Facility at JPL. The design requirements for this facility and the resultant design and implementation experiences and challenges will be presented.

Submillimeter-wave telescope on board S-520-17 was launched on January 23, 1995. The telescope is dedicated for observation of cold dust within Orion molecular cloud. In this paper, a brief description of the telescope system and review through the environmental test, preflight calibration, and flight performance is described. Also discussed in the last section is a development of array detectors for future space mission in far-infrared and submillimeter- wave.

MicroMAPS is a gas filter correlation radiometer capable of detecting trace atmospheric gases by remotely sensing their infrared absorption characteristics. While the method can be used to detect a number of trace species (including CH₄, SO₂, and NO₂), the current version of MicroMAPS detects CO and N₂O from a nadir viewing orbital platform. To do this, the instrument is equipped with CO and N₂O gas cells and configured to observe the earth's IR radiance in a band centered at 4.67 microns. It has been demonstrated that the synchronous detection of alternatively chopped signals through CO, vacuum and N₂O view cells can produce a quantitative measure CO in three tropospheric layers. The simplicity of the method affords a low cost technique for generating global maps of this important atmospheric species when viewing from space. MicroMAPS uses the sam method of detection of trace CO as an older instrument called MAPS. MAPS (the measurement of air pollution from satellites) has heritage from shuttle missions in 1982, 1984, and 1994 (STS-2, STS-41G, and STS68). There are two fundamental differences between MicroMAPS and MAPS. To give the correlation signal related to the CO column density in the atmosphere, MicroMAPS employs a rotating gas cell chopper and a single IR detector. MAPS employs fixed gas cells with more than one detector. MicroMAPS replaces the complex amplifier and synchronous detector analog signal processing system of MAPS with a microprocessor based signal processor. The effect of these two changes reduces the weight from 100 lbs plus (MAPS) to approximately 14 lbs (MicroMAPS) as well as reducing the cost of MicroMAPS by about the same proportion as its mass. On June 8, 1994 CTA Incorporated of Rockport, Maryland was awarded a NASA contract to build the Clark spacecraft as part of the small satellite technology initiative program. In March 1995 Resonance Ltd. received a contract to build a spacequalified MicroMAPS remote sensor for this small satellite.

Satellite laser communication concepts have been under development for many years. The conventioanl approaches require sophisticated hardware and considerable spacecraft resources introducing concerns about cost, added weight, power consumption, and reliability. An optical tranceiver based on a modulating retroreflector is a relatively new concept which has not been explored for space communications. The majority of the hardware and complexity for such a communications link is located on the ground and only minimal spacecraft hardware is required. This technique can provide a modest telemetry link for spacecraft in low earth orbits while consuming negligible spacecraft resources when compared to a traditional RF system. A prototype for such a low power optical tranceiver has been constructed and tested over a 4 km ground path in preparation for a high altitude balloon demonstration. Presented here is an overview of the retromodulator communications concept, a link design, and results from prototype testing.

An extrinsic semiconductor IR field-effect transistor of a new type has been developed and studied. It operates in a spectral range corresponding to its bulk material extrinsic photoresponsivity and possesses a quantum efficiency on the order of that of the same material photoconductor detectors. Its principle of operation is based on the variation of the near- contact electric field on a change in the concentration of free charge carriers in the bulk. A low-frequency current responsivity of 10⁶-10⁷ A/W for experimental SI:Ga samples has been attained under a background intensity of 10¹¹ cm^-2s^-1. The low-frequency responsivity changes in inverse proportion to the level of background and can achieve a very high value with a decrease in it. The 3-dB cutoff frequency of photoresponse is close to the cutoff frequency of the low- frequency photoresponse plateau for the similar photoconductor detectors. A physical model has been developed which makes it possible to carry out approximate designing of such devices. Experimental samples of 16-element phototransistor linear arrays have been developed.

The first two indigenously developed communication satellites of India at Geosynchronous orbit (GEO) Insat-2A and Insat-2B have an oscillatory type earth sensor for providing the pitch and roll reference to the momentum biased, 3 axis stabilized control system. The sensor consists of an oscillatory resonant scan mechanism which provides a East-West scan field of +/- 25 degrees. The excellent on orbit performance of the above sensor and also its advantages such as simplicity and long life have given rise to explore the possibility of using such a sensor for low earth orbit (LEO) mission where the subtended angle is large, i.e. nearly 120 degrees. This paper presents a design approach and test results of a germanium wedge prism adapter which separates the scan in the North-South direction by +/- 45 degrees from the existing +/- 6.1 degrees in the GEO sensor and also extends the scan field in the East-West direction from +/- 25 degrees to beyond +/- 60 degrees providing the four horizon cross over points for the computation of pitch and roll errors of the spacecraft. Thus with a marginal change in the optics and a marginal reduction in the signal, all the advantages of the GEO sensor such as long life, higher update frequency, lower weight can be made use of for the LEO mission. A comparative study is also made with the conical type scanning horizon sensor using a motor driven mechanism with the above sensor and the advantages outweight the disadvantages. The development model results show the technical feasibility and confirm the advantages of the sensor for LEO application.

Stray light in an optical system is the radiation that is incident on the detector, but does not originate from the conjugate object point. Cool stops are placed at strategic locations to decrease the transfer of the thermal noise to the detector plane. We describe an approach to stray light management and control that may be performed simultaneously with the first order optical system design using the y, y-bar diagram.

The ways in which the knowledge gained from GIS can be incorporated into the satellite imagery classification process are analyzed. The problem of land cover types classification and land cover types annual changes detection is considered with respect to a particular area of Germany. The emphasis is given to the inland water bodies change detection, woodland development analysis and suburban development analysis. The possibilites of simultaneous manipulation over the raster (satellite images) and vector (map information) spatial data are demonstrated.

Principles of the theory of nonstationary processes in high-resistivity semiconductors are expounded with the following use of the theory as a base to analyze the problems of the operation of low-background IR detectors in space missions, to find the ways around these problems, to optimize the parameters and the operation of the detectors.

Errors in the thickness of the coating deposited on an optical component contribute to the fabrication-related performance deterioration of an optical system. We analyze the effects of systematic thickness errors, as might be generated during the coating fabrication process. The reflectivity changes only minimally from the nonperturbed values. However, the phase is very sensitive to the coating error. The effect of the coating thickness error on the performance of an optical element is two-fold. The layer thickness error results in a phase shift that differs from the design values for both the s- and the p-polarized light. The coating thickness error may additionally change the apparent surface figure of the optical component. Using the numerically-controlled diamond turning machines, a component may be fabricated intentionally with a requisite figure error to compensate for the coating thickness error.

An approximate analytic expression for the coefficient of optical extinction by a polydisperse plate crystal system is derived within the framework of physical optics. Numerical investigations of the extinction coefficient of a system of oriented ice plates in optical plane range is represented in the paper. Each wavelength dependence of extinction has a certain specific feature, which may be used to estimate the average size of the ice plates. It is shown that oriented ice plates can cause a noticeable wavelength dependence of the extinction coefficient of a crystal cloud.

Established telescope design methods used in the infrared-wavelength region are not responsive to the specific imaging requirements of this wavelength interval. A Gregorian telescope using off-axis mirror segments, and a real focus for the cold stop placement is proposed for the detection of faint IR sources. Exact ray trace equations are given for a general ray propagating through two coupled confocal spheroids. Relationships between the spheroid mirror parameters, and the object and image distances are presented in a graphical form to facilitate the first order telescope design.

An infrared, rotating, rotationally-shearing interferometer is proposed for the detection of a planet around a nearby star. The fringe visibility pattern is shown to depend only on the planet parameters. The expression for the interferometric pattern generated by a star and its faint companion detected by a rotationally-shearing interferometer shows that the planet may be detected only if the aperture rotates. Additionally, we show that the shearing interferometer does not suppress the star light--the interferometric pattern is proportional to the star intensity.