Aerosol blur, often referred to as the adjacency effect, is well-established as the primary and perhaps only source of atmospheric blur in remote sensing imaging from satellites. However, much of the propagation community considers turbulence blur only in interpreting experiments. Because of the complexities of atmospheric and meteorological processes a broad system engineering approach is called for, which includes aerosols, turbulence, absorption, and other atmospheric effects. In general, turbulence is most significant at low elevations up to a few meters above earth's surface, and aerosol blur is most significant at higher elevations, especially if optical depth is on the order of unity or more. However, turbulence and aerosol effects increase in the stratosphere.

Classical dispersive double monochromator systems generally provide high stray light rejection but the energy throughput is very low at higher wavelengths. The low throughput disables the characterization of high optical density samples. Spectral multiplexing, like in Fourier transform or array spectrometers, increases the throughput and improves the signal-to-noise ratio of the spectroradiometer/spectrophotometer but they show other shortcomings. To correct these shortcomings a new system based on a van Cittert monochromator is under construction. The van Cittert system consists of two identical monochromators coupled together as a subtractive system. The usual narrow slit, between the two monochromators, is replaced by a wide one and a part of this wide slit is covered by a lamella, mounted on a fine resolution translation stage. The wide slit transmits a wide spectral range but the lamella filters out a narrow range, it operates like a notch filter. The second monochromator collects and recombines the transmitted radiation at its exit slit. The sample can be positioned behind the exit slit and the beam forming elements in a spectrophotometer system. By the translation of the lamella the center wavelength of the notch can be shifted over the whole spectral range covered by the wide slit. Carrying out spectroradiometric/spectrophotometric measurements the total transmitted power is measured at every stop of the lamella. From this array of measurement results the transmittance, reflectance, emittance or absorptance of the sample can be calculated as a function of the wavelength. The theoretical basics and the first results will be shown.

The low level detection of photoconductive and photovoltaic detectors is influenced by their dark current and their impedance, by the change of these parameters during a measurement in connection with the attached electronic circuit. Photoconductive detectors are generally biased by a constant voltage through a resistance. Without radiation the voltage on the detector produces dark current by the help of thermally generated and injected carriers. When incident light falls on the surface of the detector carriers are generated either by band-to-band transitions or transitions involving forbidden gap energy levels. This changes the conductivity and by it the voltage drop on the detector which results in a change of the thermal load of the detector and that of the original dark current. This way a distinction between the change of the dark current the effect of impedance on the measuring circuit and the radiation-generated current can not be made. Photovoltaic detectors for radiometric quality measurements are used in the short circuit mode. Light absorption in a photodiode produces electron-hole pairs. Pairs generated either in the depletion region or in a region from where a carrier can eventually diffuse to the depletion region will produce a current flow in the external circuit. The same is produced by thermally generated carriers, too. Generally a non-ideal short circuit is used, a change in the measured current slightly changes the voltage on the photodiode resulting in a small deterioration of the field structure within the diode. This changes both the recombination rate at the different layers of the diode and the collection factor causing a change in the dark current. The change of the dark current means the change of the impedance and this deviation can strongly influence the measurement results. At low level measurements this change of the dark current and that of the impedance can at either type of detector be critical. The bootstrapping of the detectors practically eliminates this problem, this solution is analyzed.

This paper reviews general methodologies for hyper-spectra image processing and provides a systematic way of hyperspectra data exploitation. Although the paper reviews the most recent hyperspectra processing techniques, which are available in the open literature, it focuses on those that have been recently developed by the authors These approaches often complement work presented by others. Since the field of hyperspectra processing is relatively new, and is growing rapidly, it is a field rich of research areas with many unsolved problems. Its significance in military, and more generally in remote sensing applications, is tremendous. Furthermore, this paper has the objective to offer a quick look to the many approaches, to put in light the authors' recent developments in this field, and to serve as a background for new advances.

Laser beam measurement instruments have long been available for visible laser beams, but there is a growing need for such instruments in the near IR. This is especially true for the 1 - 1.7 micrometer region that is used for communication lasers. While a few cameras have been developed for this region, there are currently no instruments for measuring laser beam phase that operate in this regime. We have begun the development of an infrared wavefront sensor based on the Shack-Hartmann principal using an InGaAs IR camera. With this method, the laser beam is dissected into a number of focal spots, which are projected onto a detector. The focal spot position is related to the local wavefront slope. Through appropriate analysis, the laser beam intensity and phase distribution can be obtained.

We describe a radiometric model developed to simulate the transfer of time-dependent radiant and electrical signals through the High Resolution Dynamics Limb Sounder (HIRDLS). HIRDLS is an infrared limb-scanning satellite radiometer with 21 spectral channels defined by individual narrow band interference filters covering the spectral range from 6 to 18 micrometer. HIRDLS is scheduled to fly onboard the NASA Earth Observing System Chemistry platform to be launched early in the next century. The scientific objectives for HIRDLS place demanding requirements on instrument calibration and radiometric stability, particularly at low signal levels. The HIRDLS Radiometric Model (HIRAM) was developed to provide an analysis tool for evaluating the radiometric sensitivity to various subsystem parameters and observational conditions in support of requirements analyses and conceptual design studies. Instrument characteristics are modeled using analytic expressions where appropriate. HIRAM incorporates the results of detailed design and performance analyses conducted elsewhere (e.g. APART straylight analyses) as input parameters to the model. Random effects, such as detector noise, are generally modeled as band-limited white Gaussian noise. Where spectral dependence is important, such as modeling random line-of-sight jitter, a power spectral density function is used to define the frequency content of a random error source.

Radiation temperature calibrations of IR radiometers and imaging systems, pre-launch characterization of spaceborne optical sensors require low and medium-background test facilities, equipped with reference blackbodies for full aperture calibration. Such extended area blackbodies have been recently developed and characterized by VNIIOFI and Vega International, Inc. Target technical specifications for the low temperature blackbody include 100 mm full aperture, plus or minus 12 degrees viewing angles, 0.999 effective spectral emissivity in 3 micrometer to 15 micrometer band, 100 K to 450 K temperature range, 50 mK temperature uniformity across aperture and, finally, 30 mK temperature setting/measurement accuracy. Monte Carlo technique and finite element method were employed for computer modeling of temperature distributions and effective emissivities of radiating cavities consisting of V-grooved flat bottom and particularly profiled reflector. The design features and technical specifications of blackbodies, developed for operation in high vacuum conditions in the temperature range from 100 K to 900 K, are presented. Results of investigation confirm applicability of the selected approach, though leaving space for improvement of blackbodies performance. Main directions of further research and development are discussed.

Integration of detector arrays and digital CMOS circuitry can confer significant performance improvements on an imaging system. In this paper we present an integrated sensor array based on (Figure 1), micro bolometer (MB) elements deposited on a CMOS substrate containing electronics for random access readout, amplification, gain and offset control and digitization. Such integrated MB arrays are effective components in a novel implementation of an earth-horizon attitude sensor for satellites. The bolometer elements are used to distinguish the earth's thermal IR from the space background. For this application, the reduced detectivity of MB arrays compared with cooled IR detectors can be tolerated. Low mass, enhanced reliability, and low power consumption are gained by using an uncooled IR detector, and by using an integrated circuit design. These considerations are especially important for microsatellites. The low cost per array facilitates the use of multiple arrays, which allows significant flexibility in the optical and systems designs. The integrated chip design allows for random-access readout, on-chip gain and offset compensation and local control of pixel geometry, which contribute to the overall system effectiveness and help to allay any performance reductions that come from reduced detectivity.

IASI is an Infrared Atmospheric Sounding Interferometer devoted to the operational metrology and to atmospheric studies and is to be installed on-board the second ESA Polar Platform METOP-1. This paper is devoted to an overview of the optical activities of the B phase of the project and presents the optimization of the spectral division. The last developments aiming to increase the optical transmission of the main optical parts are described, they are based on multidielectric coatings and the goal was to improve the transmission in the higher spectral zone, beyond 14 micrometer. The Cold Optical Unit is located at the focal plane of the Michelson Interferometer. This sub-assembly is designed to divide the IR input flux into 3 spectral bands and to focus it on the 3 detector arrays of detection. It includes a spectral separation using 2 beam splitters, consisting of two dichroic plates, dividing the incoming flux into 3 spectral bands which are 3.4 to 5.0 micrometer, 5.0 to 8.26 micrometer and 8.26 micrometer to 15.5 micrometer. 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. The principles of cold optics are presented. An overall design of the optics has been performed taking into account the space requirements. All critical items have been manufactured to check that they can meet the required performance (photoconductive and photovoltaic detectors, hybrid focal plane and packaging, microlenses, aspherical lenses, dichroic plates, field lens, antireflective coatings, cold links).

An atmospheric correction algorithm to include the effect of adjacent pixels on the emergent radiation from the top of the atmosphere is proposed. The surface is simulated by checkerboard type terrain composed of land or ocean pixels. The Look-Up-Table method is used for the atmospheric correction. To investigate the contribution of adjacent pixels, two additional parameters based on the diffuse transmission and reflection function of the atmosphere are introduced. These parameters are independent of the surface reflection properties. Thus the surface reflection property may be included, if it is given. At present, the ocean surface is in accordance with the Cox and Munk model surface, whereas that of land is assumed to be Lambertian. The upwelling radiation emerging from the top of the atmosphere is expressed by a sum of radiative interactions between the surface and the atmosphere, and it is simulated using these parameters and combinations until convergence. An example of numerical simulation is shown at a wavelength of 0.56 micrometer, which corresponds to the center wavelength of the shortest channel of ASTER on EOS-AM1. The dust-like model is used for the aerosols, and the land surface albedo is 0.2 or 0.4. The ocean wind is 5 m/sec, and the refractive index is 1.333. The effect of the land surface on the radiance over the ocean is stronger just off the coastal zone and decreases exponentially with increasing distance from the land. It depends upon the solar zenith angle and atmospheric condition as well. The present work is an improved version on the previous paper, in that the treatment of the multiple scattering differ. The present new version enables us to quantitatively discuss radiative transfer over the heterogeneous surface including the coastal zone.

Space-based observations of tropospheric trace species have been identified as high-priority atmospheric science measurements to be included in Earth science missions of the 21st century. Critical to such measurements are tropospheric ozone (O₃) concentrations, which have been increasing and will continue to do so as levels of the precursor gases (oxides of nitrogen, methane and other hydrocarbons) necessary for the photochemical production of tropospheric O₃ remain rising; such a global monitoring capability is crucial to enhance scientific understanding as well as to potentially lessen the ill-health impacts associated with exposure to elevated concentrations in the lower atmosphere. An instrument concept to enable such a measurement capability for tropospheric (and total) O₃ utilizing Fabry-Perot interferometry has been developed and reported in earlier work. It involves a double-etalon series configuration Fabry- Perot interferometer (FPI) along with an ultra-narrow bandpass filter to achieve single-order operation with an overall spectral resolution of approximately .068 cm^-1, sampling a narrow spectral region within the strong 9.6 micrometer ozone infrared band from a nadir-viewing satellite configuration. Current research efforts are focusing on technology development and demonstration activities to address technology drivers and other design considerations associated with this measurement concept. Most importantly, we have developed a small-scale, modular, double-etalon prototype FPI for laboratory characterization and testing. This presentation will focus on advancements made pertaining to our laboratory prototype, specifically, toward the analysis and interpretation of measured solar absorption spectra. Topics will include processing of 'measured' spectra (i.e., spectral registration and drift correction) and simulation of 'true' spectra (i.e., atmospheric assumptions and instrument transfer function modeling), as well as subsequent comparisons and findings. Future developments will focus on incorporating other key elements into the prototype instrument, performing relevant laboratory and atmospheric testing, and developing methods for calibration. These activities along with concurrent scientific studies and atmospheric field testing will serve to demonstrate overall feasibility and provide technique validation for this instrumentation and may lead to a future space-based implementation.

The observation of high temperature events (HTE) is an important field of the remote sensing because of their influence on the global change of the environmental processes. Currently a small satellite BIRD (Bispectral Infrared Detection) dedicated to this task is under development in the German Aerospace Center. Considering the restrictions of an 80 kg satellite a bispectral infrared push broom scanner working in the Midwave and in the Thermal Infrared based on the latest technology of linear detector arrays was developed. The identical design for both infrared channels was realized to save resources and to guarantee the reliability. Because of the limited number of elements per line a subpixel detecting concept was chosen to estimate the parameters of the HTE with a reasonable ground resolution and swath wide. A special dual band optics and a compact sensor head design will ensure the required geometric stability. The subpixel measurement method for the hot spot detection requires a high detectivity and a large dynamic range. A special signal processing concept has been implemented at the sensor head controller. Recently the first airborne experiments were carried out together with a push broom scanner in the visible. During this experiments the sensor control, onboard signal processing and data transmission routines were tested.

The CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment is an infrared limb sounder designed to analyze the distribution of trace gases in the terrestrial middle and upper atmosphere with high spatial and temporal resolution. CRISTA was successfully flown aboard the CRISTA-SPAS freeflier together with ATLAS-3 during the Space Shuttle mission STS-66 in November 1994. A second and also very successful flight of CRISTA took place in August 1997 as part of the Space Shuttle mission STS-85. It was found that the measured trace gas distributions exhibited strong structures with scales from a few 100 km horizontally and from a few km vertically. Only under summer conditions trace gas concentrations were observed which followed latitudinal gradients alone. At other times pronounced longitudinal variations were found at all latitudes and at all altitudes. Streamers were seen in the distribution of several trace gases in both CRISTA missions. At high southern latitudes polar stratospheric clouds were detected which exhibited a significant spatial and temporal variability.

The Geostationary Earth radiation Budget (GERB) instrument will play an important role in Earth Observation Science, when it is launched on ESA's Meteosat Second Generation (MSG) satellite in 2000. The purpose of the instrument is to measure the reflected and emitted radiation of the Earth over at least a five year period, to an accuracy better than 1% within a 15 minute observation period. These scientific requirements have resulted in a detector system comprising several technological advances. The detector chosen for this instrument is a 256 pixel linear array of thermoelectric (TE) elements operating at room temperature. Based on an existing commercial design, the detector has pushed micromachined thermoelectric arrays to its limits to achieve the noise requirements. The spectral requirements of the instrument to give a flat spectral response over the 0.32 - 30 micrometer range has necessitated the blacking of the TE array. Blacking such small area arrays is a novel application and presented several problems during the course of the development. The signal conditioning electronics, consisting of 4 Application Specific Integrated Circuits, performs front end analogue signal processing, A/D conversion and multiplexing. The design of the detector system is presented in this paper, with the packaging, signal processing and blacking described in some detail.

Within the IASI (Infrared Atmospheric Sounding Interferometer) instrument, the principal function of the Interferometer and Hot Optics Subassembly (IHOS) is to create modulated interferograms which will be recorded by the Cold Box Subsystem. The IHOS is a spaceborne Fourier Transform Spectrometer (FTS) working in the 3.6 - 15.5 micrometer wavelength range. It is basically a Michelson interferometer where the flat mirrors are replaced with hollow corner-cubes retro-reflectors, one of which is moving along the optical axis in order to create a variable Optical Path Difference (OPD). The IHOS is mainly composed of the following components mounted on the same optical bench: (1) The Michelson interferometer, including the beamsplitter and the fixed and moving hollow cube-corners. (2) The cube-corner driving mechanism. (3) The entrance and exit optics. In addition, a reference interferogram is created by means of a reference laser source in order to generate a pulsed electrical signal defining the interferogram sampling times. The laser module consists in a highly stable laser source (10^-7) and its control loop electronics, and is deported from the optical bench by means of an optical fiber. The most critical requirements of the IASI interferometer are the lateral shifts of the moving cube-corner (seen through the beamsplitter), the misalignment of its scanning axis, and the reference laser alignment error. These contributions must not exceed 15 micrometer, 200 (mu) rad and 300 (mu) rad respectively during the five years mission in orbit.

The Spatial Infrared Imaging Telescope (SPIRIT III) is the primary sensor aboard the Midcourse Space Experiment (MSX), which was launched 24 April 1996. SPIRIT III included a Fourier transform spectrometer that collected terrestrial and celestial background phenomenology data for the Ballistic Missile Defense Organization (BMDO). This spectrometer used a helium-neon reference laser to measure the optical path difference (OPD) in the spectrometer and to command the analog-to-digital conversion of the infrared detector signals, thereby ensuring the data were sampled at precise increments of OPD. Spectrometer data must be sampled at accurate increments of OPD to optimize the spectral resolution and spectral position of the transformed spectra. Unfortunately, a failure in the power supply preregulator at the MSX spacecraft/SPIRIT III interface early in the mission forced the spectrometer to be operated without the reference laser until a failure investigation was completed. During this time data were collected in a backup mode that used an electronic clock to sample the data. These data were sampled evenly in time, and because the scan velocity varied, at nonuniform increments of OPD. The scan velocity profile depended on scan direction and scan length, and varied over time, greatly degrading the spectral resolution and spectral and radiometric accuracy of the measurements. The Convert software used to process the SPIRIT III data was modified to resample the clock-sampled data at even increments of OPD, using scan velocity profiles determined from ground and on-orbit data, greatly improving the quality of the clock-sampled data. This paper presents the resampling algorithm, the characterization of the scan velocity profiles, and the results of applying the resampling algorithm to on-orbit data.

ISIR (Infrared Spectral Imaging Radiometer) was designed and fabricated by Space Instruments, Inc. and flown by NASA/GSFC on the Discovery shuttle mission STS-85 in August 1997. ISIR collected over 60 hours of infrared data on a variety of cloud, land, and ocean scenes. Data was obtained in four spectral bands with a single, uncooled microbolometer detector array operating in the pushbroom mode. Data was collected with varying amounts of TDI (Time Delay & Integration) to enhance system sensitivity. The design of the ISIR instrument and selected mission results will be presented.

ClONO₂ is one of the most important species governing the chemistry of stratosphere, especially ozone depletion, particularly in the polar regions. A compact echelle grating spectrometer (f equals 200 mm) with 0.2 cm^-1 spectral resolution around the 780.2 cm^-1 chlorine nitrate (ClONO₂) absorption band has been designed and tested. This is a part of the flight model of the Improved Limb Atmospheric Spectrometer-II (ILAS-II) mission onboard Advanced Earth Observing Satellite II (ADEOS-II). Using an off axis parabolic collimator and two cylindrical off axis parabolic collecting mirrors, this spectrometer is a compact space-borne instrument optimized for solar occultation measurements. The solar absorption spectra measured with the array detector on the ground are consistent with the designed spectral resolution and the resolution simulated with the Code V optical performance simulator. Radiometric and spectrometric pre-launch calibration results of the spectrometer are discussed. The instrument slit function measurement with a tunable diode laser and integrating sphere is also discussed.

AIRS is a key facility instrument in the NASA Earth Observing System (EOS) program, a spaceborne, global observation system being implemented to obtain comprehensive long-term measurements of earth processes affecting global change. Designed to provide new and more accurate data about the atmosphere, land, and oceans for application in climate studies and weather prediction, AIRS performs passive IR remote sensing using a high resolution grating spectrometer with a wide spectral coverage focal plane assembly (FPA) operating at 58 K in a unique vacuum dewar package cooled to 155 K. The hybrid HgCdTe focal plane consists of 12 modules, 10 photovoltaic (PV) utilizing silicon readout integrated circuits (ROICs) in both direct and indirect hybrid configurations, and 2 photoconductive (PC) led out to warm electronics. This complex focal plane has a large optical footprint, 53 mm X 66 mm, and receives energy dispersed from the grating through a precision filter assembly containing 17 narrowband filters. Designed to prevent any interaction between the PV and PC devices, the FPA incorporates extensive shielding and lead routing in the multilayer carriers and flex cables, as well as features in the ROIC design. The 526 lines necessary to operate the FPA are led out of the vacuum dewar, which is cooled via the spectrometer. The focal plane is cooled to 58 K through a sapphire rod interfaced to a pulse tube cooler. The Engineering Model (EM) and Protoflight Model (PFM) detector/dewar assemblies have been fabricated, assembled, tested, and delivered for system integration, and the EM instrument has been assembled and tested. The key design features of the FPA and dewar assembly have been presented in previous SPIE symposiums and will be briefly reviewed. In this paper the emphasis will be on performance results such as sensitivity, linearity, assembly tolerances, environmental test results, and other parameters of interest, as well as a detailed review of the actual flight hardware assembly.

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-1) platform in the year 2000. AIRS is designed to provide both new and more accurate data about the atmosphere, land and oceans for application 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 1 K 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 infrared remote sensing using a precisely calibrated, high spectral resolution grating spectrometer operating in the 3.7 micrometer - 15.4 micrometer region. The instrument utilizes a cryogenically cooled infrared spectrometer that uses a pair of pulse tube cryocoolers operating at 55 K to cool the HgCdTe focal plane detectors to 58 K. The instrument also has a two- stage radiator operating at 190 K and 150 K to cool the spectrometer's optical bench and separate spacecraft supplied cooling plate system for removal of waste heat at 300 K. The cryocooler system is a highly integrated part of the AIRS Instrument development whose design is focused to maximize the overall performance of the instrument. The breadth of this paper provides a brief description of the AIRS Instrument design and centralizes on the recent results of the cryocoolers integration with the instrument focal plane assembly and spectrometer. The principal emphasis of this paper will be the current cryocooler system level performance achieved, to-date. Furthermore, this paper shall provide the 'to-date' preliminary acceptance test performance data on the recently received AIRS flight model cryocooler.

We describe the top level design of the High Resolution Dynamics Limb Sounder (HIRDLS) instrument including the optical and scanning subsystems which have been developed to meet 0.7 arcsec pointing and the 1% radiometric accuracy requirements. The HIRDLS instrument is an infrared limb- sounding radiometer designed to sound the upper troposphere, stratosphere, and mesosphere. The instrument performs high resolution limb scans at multiple azimuth angles, measuring infrared emissions in 21 spectral channels ranging from 6 to 18 microns. The instrument design includes an off-axis Gregorian telescope with high resolution optical shaft encoders, a silicon carbide scanning mirror, and a vibration isolation system incorporating accelerometers in a feed- forward scanning control system. The detector subsystem includes 21 HgCdTe detector elements cooled by a mechanical Stirling cycle cooler.

The HIRDLS instrument is an infrared limb-scanning radiometer designed to sound the upper troposphere, stratosphere, and the mesosphere as part of the Chemistry Platform for NASA's Earth Observing System (EOS) Program. The instrument performs limb scans at multiple azimuth angles, measuring CO₂, O₃, H₂O, aerosols and other significant greenhouse trace gases in 21 channels ranging from 6.12 to 17.76 micrometer. The Detector Subsystem (DSS) focal plane assembly (FPA) contains the 21 detectors for the science measurements and a set of alignment detectors to be used for instrument integration. All detector elements are Photoconductive HgCdTe operating in the 60 - 65 K range and each channel has a separate cold filter. The FPA is mounted in a customized vacuum dewar which couples to a Stirling-cycle mechanical cryocooler via a sapphire rod. Lockheed Martin has designed, fabricated and tested detectors covering the entire HIRDLS spectral range. All the n-type HgCdTe starting material was grown at Lockheed Martin. The vacuum dewar and the preamplifier designs were done at Lockheed Martin. In this paper, we will discuss the key features of and design drivers for the DSS design and the design validation activities. The details of the DSS to instrument interfaces will be discussed. We will consider the solutions found for design and packaging issues with the DSS, and the design trades made at the subsystem level to optimize the instrument performance and increase the ease of assembly and instrument integration.

The HIRDLS instrument contains 21 spectral channels spanning a wavelength range from 6 to 18 micrometer. For each of these channels the spectral bandwidth and position are isolated by an interference bandpass filter at 301 K placed at an intermediate focal plane of the instrument. A second filter cooled to 65 K positioned at the same wavelength but designed with a wider bandwidth is placed directly in front of each cooled detector element to reduce stray radiation from internally reflected in-band signals, and to improve the out- of band blocking. This paper describes the process of determining the spectral requirements for the two bandpass filters and the antireflection coatings used on the lenses and dewar window of the instrument. This process uses a system throughput performance approach taking the instrument spectral specification as a target. It takes into account the spectral characteristics of the transmissive optical materials, the relative spectral response of the detectors, thermal emission from the instrument, and the predicted atmospheric signal to determine the radiance profile for each channel. Using this design approach an optimal design for the filters can be achieved, minimizing the number of layers to improve the in- and transmission and to aid manufacture. The use of this design method also permits the instrument spectral performance to be verified using the measured response from manufactured components. The spectral calculations for an example channel are discussed, together with the spreadsheet calculation method. All the contributions made by the spectrally active components to the resulting instrument channel throughput are identified and presented.

This paper describes the design and manufacture of the filters and antireflection coatings used in the HIRDLS instrument. The multilayer design of the filters and coatings, choice of layer materials, and the deposition techniques adopted to ensure adequate layer thickness control is discussed. The spectral assessment of the filters and coatings is carried out using a FTIR spectrometer; some measurement results are presented together with discussion of measurement accuracy and the identification and avoidance of measurement artifacts. The post-deposition processing of the filters by sawing to size, writing of an identification code onto the coatings and the environmental testing of the finished filters are also described.

HIRDLS is a space-borne instrument that will measure the concentration of certain trace gases in the Earth's atmosphere. This requires accurate spectro-radiometric infra red measurements of weak sources of small angular size in the presence of strong adjacent sources of unwanted radiation. The design of the principal optical system is described and the constraints are explained. In particular, the important stray- light problems will be described, including incoherent scatter, ghost reflections and diffraction effects.

Test chipper performance, as well as mechanical design and electronic control concepts, are presented for the optical chopper developed for the High-Resolution Dynamics Limb Sounder (HIRDLS) to be flown on the CHEM-1 satellite of the NASA Earth Observing System (EOS). Optical chopping is essential in order to achieve the required sensitivity and accuracy in measurement of infrared emission from various chemical species in the earth's atmosphere. Chopping of the optical input as far forward in the telescope as practical minimizes calibration errors arising from variations in emission from warm optics and due to electronic drifts in the infrared detecting system. At 500 Hz, the reflective chopper blade switches between the atmospheric limb view and reference radiation from cold space. The HIRDLS chopper is a six- toothed, mirrored wheel driven by a three-phase, permanent- magnet, brushless DC motor with trapezoidal excitation synchronized to motor back-emf. Chopper design was driven by requirements of (1) continuous operation at 5000 RPM for 50,000 hours in space vacuum, (2) chopping amplitude stability of one part in 100,000, (3) lubricant loss control for both bearing reliability and prevention of optics contamination, (4) compact size to fit in the folded telescope, and (5) survival in the launch environment.

The High Resolution Dynamics Limb Sounder (HIRDLS) instrument is being built jointly by the UK and USA, and is scheduled for launch on the NASA EOS Chem satellite in 2002. HIRDLS will measure the concentration of trace species and aerosol, and temperature and pressure variations in the Earth's atmosphere between about 8 and 100 km altitude. It is an infrared limb emission sounder, and a primary aim is that it should measure to much finder spatial resolution than has previously been achieved, with simultaneous 1 km vertical and 500 km horizontal resolutions, globally, every 12 hours. Achieving these objectives will depend upon very precise pre-launch calibration. This will be undertaken at Oxford University in a test laboratory that is currently being constructed specifically for the task. The instrument will be surrounded by cryogenically cooled walls, and mounted together with the test equipment on an optical table contained in a vacuum chamber. The table will be mounted independently of the chamber, on an inertial mass supported on pneumatic isolators. Test equipment is being manufactured to measure (1) the radiometric response (with an absolute accuracy equivalent to 70 mK) using full aperture black body targets, (2) the spectral response of each of the filter channels using a grating monochromator, (3) the spatial response of the instrument field of view, including low level out-of-field contributions, to 10 (mu) rad accuracy using a monochromator. The methods and equipment used are described together with the principal requirements.

An obvious minimum was observed in the reflectance spectrum of ion implanted Hg_1-xCd_xTe. The anodic oxidation method and beveling technique were used to learn the spectrum changing with the depth. This minimum even can be observed when a layer with thickness thicker than the ion range was removed from the implanted surface. Considering the high electron concentration of the implanted layer, this phenomenon was explained by using the model of reflection of layered media in which the refractive index changes with the depth. By numerical fitting, the depth profile of the carrier density and refractive the index of the ion implanted layer were obtained.

Asymmetric dark current and photocurrent versus voltage characteristic in the Double Barrier Quantum Wells (DBQWs) photovoltaic infrared photodetector has been studied. A model based on asymmetric potential barriers was proposed. The asymmetric potential thick barrier, which due to the Si dopant segregation during growth makes a major contribution to the asymmetrical I-V characteristic, calculations based on our model agree well with experimental results. This work also confirms the potential use of this DBQWs for infrared photodetector with large responsivity and little dark current under negative bias.

A passive cryocooler has been developed for the cooling of small payloads to temperatures as low as 145 K. Although designed for a specific electronics experiment on the STRV-1d microsatellite, the device is suitable for a wide range of applications. The cryocooler uses coated surfaces for tailored radiative cooling. Mechanical support between components is provided by fiberglass struts. The measured end temperature reached is 151 K in a liquid nitrogen dewar which extrapolates to an end temperature of lower than 145 K in space. Thermal vacuum testing and random vibration testing at levels consistent with an Ariane 5 launch have been performed as part of formal qualification for the STRV mission. In this paper, details of the design, analysis, fabrication and testing of the passive cryocooler are presented.

The investigation of MBE CdHgTe photodiode characteristics after pressure applying to n-type of junction has been carried out. The diodes parameters have been studied in the temperature range of 5 divided by 120 K. It was found that the mechanical stress causes the increase of traps amount with E_t approximately equals E_v plus 0.043 eV and E_t approximately equals E_v plus 0.032 eV. The energies of these traps have some temperature dependence. The diodes generation-recombination and trap-assisted tunneling currents significantly increase at forward and reverse biases. The value of RoA decreases in an order at T less than 60 K because of trap assisted tunneling via the dislocation levels. At high temperatures T greater than 60 K the value of RoA does not change and determined by the diffusion mechanism.

We analyze the optical performance of a number of diluted- aperture configurations using the modulation transfer function. We select a single figure of merit, the practical resolution limit, over the traditional one, the cut-off frequency, as the most useful one for the detection of small sources. We compare the performance of a number of published configurations, using the practical resolution limit. A new design of a POST configuration is proposed on the basis of this analysis.

A novel method of phase reconstruction from high-spatial- frequency intensity patterns incorporates the technique of line integration of phase gradient to find the first approximation to the phase and the algorithm of successive approximations to find exactly the unknown phase. The error function is constructed to incorporate the measured intensity to assure rapid convergence.

A pair of thin prisms produces a controlled vectorial displacement of a wavefront with a high precision. We present ray-trace equations modeling a three-dimensional wavefront propagation. We propagate an array of rays through a pair of prisms for different angles of rotation between the prisms to obtain the exact performance of thin prisms. The high control of the wavefront position is required in a vectorial shearing interferometer.

We evaluate the error that arises when approximating the Planck's equation with a truncated series of t terms. We improve the accuracy of the truncated series representation by approximating the resulting error, obtaining integrable and differentiable approximations to the Planck's equation. We obtain the absolute error of less than 0.01 maximum, and relative error of 0.6% with just three terms in the Planck's equation for frequency. Approximately 0.03 absolute error maximum is obtained with only two terms, with 2.4% relative error.

In the frame of technological preparation for scientific Earth observation programs, the European Space Agency (ESA) has undertaken breadboarding activities dedicated to high resolution thermal radiometer to be implemented on a Low Earth Orbit satellite. Based on the lessons learned during the previous breadboarding phase and taken into account the modification of instrument concept, a LWIR linear focal plane breadboard has been studied and developed for the 11.3 to 12.3 micrometer range. The breadboard is made of two 256 pixels 30 micrometer pitch HgCdTe modules mechanically butted and indirectly hybridized to four multiplexers. Due to image rotation at focal plane level, a linear topology has been selected for pixel arrangement. To achieve the required 0.1 K NEdT, the detector is operated at 55 K. The detector breadboard manufactured and pre characterized by LETI/LIR and SOFRADIR has been integrated in a dedicated test set-up at MMS. First results of the characterization will be presented, with particular emphasis about the dark current and its dispersion as a function of temperature, and the low frequency noise measurements.

In the frame of technological preparation for scientific Earth observation programs, the European Space Agency (ESA) has undertaken breadboarding activities dedicated to hyperspectral imager to be implemented on a Low Earth Orbit satellite. Based on the lessons learned during the previous breadboarding phase, a SWIR focal plane breadboard has been studied and developed in the 1 to 2.35 micrometer range and was extensively characterized for demonstration of both performances and mechanical buttability. The hybrid technology is based on photovoltaic, HgCdTe diodes arrays coupled to full custom, CMOS, silicon, multiplexing circuitry dedicated to the hyperspectral imager requirements. Due to system constraint, the focal plane is operated at 150 K, and read-out at 3.3 Mpixels/s. Results of the characterization will be presented, with particular emphasis about the read-out noise, the dark current and its non uniformity, plus the linearity as a function of flux.

The Office of Naval Research (ONR) and the Naval Research Laboratory (NRL) are currently in the design phase of a program called the Hyperspectral Remote Sensing Technology (HRST) program. HRST will demonstrate the utility of a hyperspectral earth-imaging system to support Naval needs for characterization of the littoral regions of the world. One key component of the HRST program is the development of the Naval EarthMap Observer (NEMO) satellite system to provide a large hyperspectral data base. NEMO will carry the Coastal Ocean Imaging Spectrometer (COIS) which will provide images of littoral regions with 210 spectral channels over a bandpass of 0.4 to 2.5 micrometer. Since ocean environments have reflectances typically less than 5%, this system requires a very high signal-to-noise ratio (SNR). COIS will sample over a 30 km swath width with a 60 m Ground Sample Distance (GSD) with the ability to go to a 30 m GSD by utilizing the systems attitude control system to 'nod' (i.e., use ground motion compensation to slow down the ground track of the field of view). Also included in the payload is a co-registered 5m Panchromatic Imager (PIC) to provide simultaneous high spatial resolution imagery. A sun-synchronous circular orbit of 605 km allows continuous repeat coverage of the whole earth. One unique aspect of NEMO is an on board processing system, a feature extraction and data compression software package developed by NRL called the Optical Real-Time Spectral Identification System (ORASIS). ORASIS employs a parallel, adaptive hyperspectral method for real time scene characterization, data reduction, background suppression, and target recognition. The use of ORASIS is essential for management of the massive amounts of data expected from the NEMO HSI system, and for developing Naval products under HRST. The combined HSI and panchromatic images will provide critical phenomenology to aid in the operation of Naval systems in the littoral environment. The imagery can also satisfy a number of commercial and science community requirements for moderate spatial and high spectral resolution remote sensing data over land and water. Specific areas of interest for the Navy include bathymetry, water clarity, bottom type, atmospheric visibility, bioluminescence potential, beach characterization, underwater hazards, total column atmospheric water vapor, and detection and mapping of subvisible cirrus. These data support requirements for Joint Strike and Joint Littoral warfare, particularly for environmental characterization of the littoral ocean. Demonstrations of timely downlinks of near real-time data to the warfighter are also being formulated. The NEMO satellite is planned to launch in mid-2000 followed by an operational period of 3 to 5 years.

A wide variety of applications of imaging spectrometry have been demonstrated using data from aircraft systems. Based on this experience the Navy is pursuing the Hyperspectral Remote Sensing Technology (HRST) Program to use hyperspectral imagery to characterize the littoral environment, for scientific and environmental studies and to meet Naval needs. To obtain the required space based hyperspectral imagery the Navy has joined in a partnership with industry to build and fly the Naval EarthMap Observer (NEMO). The NEMO spacecraft has the Coastal Ocean Imaging Spectrometer (COIS) a hyperspectral imager with adequate spectral and spatial resolution and a high signal-to- noise ratio to provide long term monitoring and real-time characterization of the coastal environment. It includes on- board processing for rapid data analysis and data compression, a large volume recorder, and high speed downlink to handle the required large volumes of data. This paper describes the algorithms for processing the COIS data to provide at-launch ocean data products and the research and modeling that are planned to use COIS data to advance our understanding of the dynamics of the coastal ocean.

The primary mission of the Naval EarthMap Observer (NEMO) is to demonstrate the importance of hyperspectral imagery in characterizing the littoral battlespace environment and littoral model development. NEMO will demonstrate real time on-board processing and compression of hyperspectral data with real-time tactical downlink of ocean and surveillance products directly from the spacecraft to the field. The NRL's Optical Real-time Adaptive Spectral Identification System (ORASIS) will be deployed on a 3.8 Gflop multiprocessing computer, the Imagery On-Board Processor (IOBP), for automated data analysis, feature extraction and compression. NEMO's wide area coverage (10⁶ km² imaged per day), as well as power and cost constraints require data compression between 10:1 and 20:1. The NEMO Sensor Imaging Payload (SIP) consists of two primary sensors: first, the Coastal Ocean Imaging Spectrograph (COIS) is a hyperspectral imager which records 60 spectral bands in the VNIR (400 to 1000 nm) and 150 bands in the SWIR (1000 to 2500 nm), with a GSD of either 30 or 60 meters; and second, the 5 m GSD Panchromatic Imaging Camera (PIC). This paper describes the design and implementation of the data processing hardware and software for the NEMO satellite.

The Sensor Imaging Payload for the Navy EarthMap Observer (NEMO) satellite consists of a hyperspectral imager and a coaligned panchromatic imager. The sensors have a ground swath width of 30 km, with a ground sample distance of 30 m (or 60 m with pixel binning) for the hyperspectral imager, and 5 m for the panchromatic imager. The hyperspectral imager has a spectral resolution of 10 nm over the 0.4 - 2.5 micrometer region, and the panchromatic imager has a 0.49 - 0.69 micrometer bandpass. The payload weighs less than 61 kg, uses less than 90 watts power on average, and is designed for a five-year mission lifetime.

The Space Dynamics Laboratory at Utah State University is building an infrared Hyperspectral Imaging Polarimeter (HIP). Designed for high spatial and spectral resolution polarimetry of backscattered sunlight from cloud tops in the 2.7 micrometer water band, it will fly aboard the Flying Infrared Signatures Technology Aircraft (FISTA), an Air Force KC-135. It is a proof-of-concept sensor, combining hyperspectral pushbroom imaging with high speed, solid state polarimetry, using as many off-the-shelf components as possible, and utilizing an optical breadboard design for rapid prototyping. It is based around a 256 X 320 window selectable InSb camera, a solid-state Ferro-electric Liquid Crystal (FLC) polarimeter, and a transmissive diffraction grating.

The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument is a 10-channel earth limb- viewing sensor that is to measure atmospheric emissions in the spectral range of 1.27 micrometer to 16.9 micrometer. Presented in this paper is the stray light design and analysis of SABER. Unwanted radiation from the earth and atmosphere are suppressed by the use of stray light features that are critical to mission success. These include the use of an intermediate field stop, an inner and outer Lyot stop, and super-polished mirrors. The point source normalized irradiance transmission (PSNIT) curve, which characterizes the sensor's off-axis response, was computed using the stray light analysis program APART. An initial calculation of the non-rejected radiance (NRR) due to emissions and scatter from the earth and atmosphere was made using the PSNIT data. The results indicate that stray light will not impede the mission objectives.

The Wide-Field Infrared Explorer (WIRE) is a small cryogenic spaceborne infrared telescope being readied for launch in September 1998 as the fifth of NASA's Small Explorers. WIRE utilizes two 128 X 128 Si:As Focal Plane Arrays (FPAs) produced by Boeing North American with a 30 cm diameter Ritchey Cretien diamond turned mirror system. This mission takes advantage of recent advances in infrared array detector technology to provide a large sensitivity gain over previously flown missions. Two broad pass bands are defined for a deep pointed survey to search for protogalaxies and to study the evolution of starburst galaxies. The Space Dynamics Laboratory at Utah State University (SDL/USU) used the multifunction infrared calibrator and other special purpose cryogenic equipment to perform a ground characterization of the WIRE instrument. The focus was verified cold with two independent measurements. Both in-band and out-of-band Relative Spectral Response measurements were made; some sensitivity to temperature, bias voltage, and location on the long wavelength focal plane array were found. Dark current and dark noise measurements are also reported.

We evaluate the thermal contrast detected by a quantum detector in a focal plane of an infrared instrument. The detected thermal contrast is shown to consist of two terms. The term corresponding to the temperature dependence of emissivity, previously neglected, is evaluated and shown to be a significant contributing factor. For the case of a metal mirror as a source of stray light, ghost images, and narcissus, the error is estimated to be about 20%. The term in the detected contrast associated with radiative emission is shown to be proportional to temperature to the power of 2, rather than 3, published previously.