The Short-Wavelength Spectrometer (SWS) is one of the four focal plane instruments of ESA's Infrared Space Observatory (ISO). The satellite was launched on November 15, 1995 with a super fluid Helium content of about 2300 liters to keep the telescope, the scientific payload and the optical baffles at operating temperatures between 2 and 8 K. On April 8, 1998 the liquid Helium depleted and the instruments were switched-off when the focal plane reached a temperature of 4.2 K. A satellite engineering test program was conducted between April 20 and May 10. Timeslots before and during the test program were used to operate the InSb detectors of the SWS instrument while the temperature of the focal plane slowly increased up to 40 K. The instrument was used to record spectra of 260 stars between 2.36 and 4.05 microns at a resolution of 2000 and with high S/N. Goal of the program was to observe a set of stars covering the entire MK spectral classification scheme to extend this classification scheme to the infrared. We discuss changes in the instrument relevant for operating and calibrating the instrument at temperatures above 4K: changes in the InSb detector behavior (dark levels, noise, response, ...), behavior of the JFETs and geometry changes in the grating scanner mechanism. We also show that the calibration of the data obtained after Helium loss is accurate, resulting in a data set of great scientific value.

The Photoconductor Array Camera and Spectrometer (PACS) is an imaging spectro-photometer which forms part of the science payload of the Far InfraRed and Submillimeter Telescope (FIRST), an ESA cornerstone mission (CS4) to be launched in 2007. This paper reports the preliminary developments of the motorized grating assembly for the PACS spectrometer. The PACS grating shall be capable of accurate positioning (4 arcsec) within a large angular throw (40 arcdeg) in cryogenic environment (4 K). Technologies and trade-offs of grating manufacturing, actuators, pivots, position sensors, and servo- control are presented.

The array camera and spectrometer PACS to be flown aboard the European 3.5 m infrared space telescope FIRST will apply a cold focal plane chopper. Its development has to meet ambitious goals, such as large chopper throws, high operational accuracy in several modes, very low heat dissipation in the cryogenic environment, sufficient rigidity to meet the ARIANE5 launch conditions and a long lifetime thereafter. The prototype development of such a chopper and test results under cryovacuum conditions are reported here.

For the Photoconductive Array Camera and Spectrometer (PACS) 2 sensor arrays consisting of each 16 X 25 pixels are foreseen. The sensors arranged in linear arrays with 16 detectors are tuned to the wavelength ranges 60 micrometer to 130 micrometer and 130 micrometer to 210 micrometer by applying different levels of stress to the Ge:Ga crystals utilizing a special leaf spring which is part of each of the 25 modules. The electronics of the sensors are mounted on the same module but thermally isolated from the sensor level which is linked to a 1.7 K stage. The sensors are read out by a new generation of the integrating and multiplexing cryogenic readout electronics (CRE). With the optical design a 100% filling factor is achieved and with a fore optics made of light cones in front of the detector cavities a high detection efficiency close to 1 is expected. In order to achieve extreme high stress uniformity among all detectors and therefore equal cutoff wavelengths, a high degree of the quality of the Ge:Ga detectors and of the assembling components used for this dedicated stress mechanism is required. The first two engineering modules have been successfully manufactured and tested afterwards. The relative responsivity of a set of pixels has been determined and a good performance demonstrated for the sensors which are very close to fulfill the requirements for PACS aboard the infrared telescope FIRST.

The Photoconductor Array Camera & Spectrometer (PACS) is one of the three science instruments for ESA's Far Infra-Red and Submillimeter Telescope (FIRST). It employs two 16 X 25 pixels Ge:Ga photoconductor arrays (stressed/unstressed) to perform imaging photometry and imaging line spectroscopy in the 60 - 210 micrometer wavelength band, with an optional extensions to approximately 300 micrometer. In photometry mode, it will simultaneously image two bands, 60 - 90 or 90 - 130 micrometer and 130 - 210 micrometer, over fields of view of approximately 1' X 1.5' and approximately 2' X 3', respectively, with full beam sampling in each band. In spectroscopy mode, it will image a field of approximately 50' X 50', resolved into 5 X 5 pixels, with an instantaneous spectral coverage of approximately 1500 km/s and a spectral resolution of approximately 175 km/s. In both modes background-noise limited performance is expected, with sensitivities (5(sigma) in 1h) of 4 - 6 mJy or 3 X 10^-18 W/m², respectively.

We present our design for a field-imaging, far-infrared line spectrometer for the SOFIA airborne observatory. The instrument will employ two parallel, medium resolution (R approximately 1700) grating spectrometers for simultaneous observations in the wavelength bands 42 - 110 micrometer and 110 - 210 micrometer. The Littrov mounted gratings are operated in first and second order. Large stressed and unstressed 16 X 25 pixel Ge:Ga photoconductor arrays are operated in the spectrometer channel, providing good spectral coverage with high responsivity. Image slicers in each spectrometer branch redistribute the 5 X 5 pixel field of view along the 1 X 25 pixel entrance slits of the spectrographs, providing both, spatial and spectral multiplexing. Thus, for each of the 25 spatial pixels, we are able to cover a velocity range of approximately 1500 km/s around a selected far infrared line, with an estimated sensitivity of approximately 2 X 10^-15 W Hz^-1/2 per pixel.

A small Bi-spectral Infrared Detection (BIRD) push broom scanner for a small satellite mission is developed, which is dedicated to the detection and analysis of high temperature events (HTE) including the surrounding background scenario. To avoid the saturation of the detector at high temperatures keeping at the same time a reasonable radiometric resolution for the background a very large dynamic range is required, which will be realized by special adaptive sample techniques. These techniques were proved and verified during special airborne experiments. Using two cameras in different spectral regions (3.4 - 4.2 micrometer and 8.5 - 9.3 micrometer) with a well synchronized sampling mode, it is also possible to detect and analyze hot targets with an extension much less than the nominal ground pixel size. An excellent synchronization of the cameras is required to avoid time expensive matching procedures and therefore to enable a related real time processing. A pre-condition for these sub- pixel techniques is the recognition of the related areas distinguishing them from sun glints and similar false alarm candidates. Analyzing the data of the airborne experiments, the processing algorithms could be tested and improved.

A novel multispectral remote sensing instrument for microsatellites is described. By using 10² - 10³ 'chipxels,' a combination of high angular resolution, large coverage region, multispectral operation, and redundancy can be achieved. Each 'chipxel' has a detector array, optics, electronics, and an intelligent bus interface.

ATRAS (Atmospheric Radiation Spectrometer) is a nadir-looking Fourier Transform Spectrometer, which is a follow-on instrument of IMG onboard ADEOS satellite. ATRAS will have 0.05 (0.1 apodized) spectral resolution over 3 - 16 micron using 4 photo voltaic (InSb and/or PV-MCT) detectors. Objectives of ATRAS are to demonstrate the performance of high spectral resolution IR sounder using FTS technique on (1) monitoring of greenhouse gases, (2) operational temperature and water vapor sounding, and (3) monitoring of earth's radiation budget. ATRAS will have much better radiometric performance compared to the IMG. It was proposed to be launched onboard a Japanese small satellite, MDS-3 (Mission Demonstration Satellite). The mission strategy and results of conceptual design study of ATRAS will be discussed.

This study is stimulated by the finding that there is a decreasing trend of retrieved cloud droplet size during the lifetime of NOAA-9 and a sudden change of droplet size if different satellite data for the same period were used in the retrieval. This trend and sudden change in the retrieved results are apparently artifact rather than natural variations. Since channel 3 data of the AVHRR are used in the retrieval, the calibration method is examined to explore the possible explanation. Until now, no effort has been made for radiance calibrations of channel 3 although many investigations have been conducted for the visible and thermal infrared channels of AVHRR. There are two reasons for this lack of activity. First, detectors used for channel 3 of AVHRR are different from those for channels 4 and 5 and should not be subject to non-linearity. Second, the channel 3 of AVHRR has in-orbit calibration by looking at an internal calibration target (ICT) and space. This in-orbit calibration procedure is appropriate for earth temperature monitoring because the ICT radiates at around the earth surface temperature, and the intensity peaks at about 10 micrometer. There are evidences showing that the channel 3 brightness temperature does not change with satellites. However, in some other applications such as the retrievals of cloud particle sizes, the calculation of reflectance depends on the solar energy that radiates at much higher temperature (approximately 5800 K); the intensity of radiated solar energy peaks at about 0.50 micrometer. Therefore, the spectral response change of the instrument may lead to different values of in-band solar flux and thus cause errors in calculations of the reflection function of solar energy. For example, if the sensitivity of the response curve decrease is less in the short-wavelength end than at the long-wavelength end within the band after launch, then the in-band solar energy will be larger even if the channel 3 brightness temperature is calibrated against to the ICT. This will cause an overestimate of solar reflection function and an underestimation of droplet size because pre- launch value of in-band solar flux is used in the calculation. Several periods of satellite data have been used for this investigation: the overlapped AVHRR observations during January, 1985 for three weeks by NOAA-7 and NOAA-9; one month of NOAA-9 data of Oct. 1987 and Oct. 1989. The results of the study show that the ICT works well for calibration of thermal emission from the Earth's subjects. However, there are evidences showing that the in-band solar energy of channel 3 of AVHRR is underestimated for NOAA-7 comparing with NOAA-9 and this constant is increasingly underestimated during the satellite life-time of NOAA-9.

Proof of concept narrow-band etalon filters have been fabricated and characterized for the SWIFT instrument program. The Stratospheric Wind Interferometer For Transport studies is a limb viewing satellite instrument which is intended to measure stratospheric horizontal wind velocities in the altitude range of 20 to 40 km. In addition to providing the atmospheric research community with the first direct measurements of stratospheric dynamics on a global scale, continuous global SWIFT data is expected to improve long range weather forecasting in the troposphere. To isolate the single lines required for the Doppler measurement of the SWIFT instrument, two narrow-band germanium etalon filters centered near 9 micrometer and with 0.8 nm and 2.5 nm bandwidths were fabricated and tested. The SWIFT filter testbed consists of a cryogenic dewar and temperature controller for stabilizing and tuning the filters. The SWIFT filter requirements are discussed, as is the filter testbed design. The measured filter characteristics: transmittance as a function of wavelength, temperature and angle of incidence and tandem filter properties are discussed in the context of satellite instrument requirements.

The construction and testing of the detector system for the Geostationary Earth Radiation Budget (GERB) instrument has proved to be technically challenging in a number of areas. The detector system consists of an uncooled linear array of 256 thermoelectric pixels with 4 Application Specific Integrated Circuits (ASICs) to perform front end analogue signal processing, A/D conversion and multiplexing. The design of the detector and of the ASICs represents considerable development effort to meet, in particular, requirements of low noise and broad band spectral response and the designs have been presented in previous papers. The assembly and integration of the components into a suitably packaged flight focal plane assembly (FPA) has also been challenging, requiring a solution which would allow for individual testing of components before commitment to assembly into the focal plane package. Having assembled and qualified several detector systems, the characterization and performance of the flight detector system is presented in this paper.

The Geostationary Earth Radiation Budget (GERB) instrument employs a 256 element thermoelectric linear array. As part of the read-out electronics, a custom ASIC has been developed which provides parallel signal processing and digitization for 64 detector pixels. Four of these ASICs combine to provide complete detector read-out, culminating in a single serial digital interface for data output. We present details of the operation and performance of the ASIC achieved as part of the GERB focal plane assembly (FPA).

The detection of incipient wildfires from space is optimized by high spatial resolution, redundant coverage of a large swath, modest spectral resolution, and a high image frame rate. The desired information rate can exceed 10⁹ bytes/sec, which is difficult to achieve with conventional sensor designs. A design is described for a distributed sensor consisting of 10² - 10³ identical detection modules linked by a serial bus to a central controller. Each detection module or 'chipxel' contains an intelligent bus interface, a detector array, a multiplexer, amplifiers, digitizers, local data and program memory, a local controller, and modest image reprocessing. Clock, timing, and power control can also be present. The baseline detector element is an active CMOS image sensor, although a mix of detectors can share a common readout structure. The paper will describe the specifications for a two-chip implementation of a chipxel for space-based wildfire detection, with emphasis on the intelligent bus interface, power control, and on-chip preprocessing. Key analog and digital elements of the chip have been implemented in CMOS 0.35 micrometer technology, while ancillary functions and design augmentations can be evaluated in a gate array or similar hardware.

A very long photoresponse time and other drawbacks of extrinsic photoconductors used as low-background IR detectors are caused by their trap memory being uncontrolled at the operation under a fixed voltage. A proper pulsed voltage allows to control the memory. Below the principles of the control are set forth, and the brief theory of one of the operation modes with the controlled trap memory is given. This serves as the basis for further analysis of several detectors operated under such modes and for the notions applied to a drastic improvement of the performance of space IR detectors.

Both silicon and germanium are widely used as transmissive elements in the infrared region of the spectrum. Both materials are typically used in applications where significant temperature ranges exist. In this work we report transmission in the wavelength range of 1.39 to 22 micrometer and in the temperature range of room temperature (25 degrees Celsius) down to -100 degrees Celsius for silicon and germanium samples of various resistivities. The data presented indicate an orderly change in transmission with decreasing temperature for the various sample resistivities. Absorption coefficients are calculated from the transmission data.

The Atmospheric Infrared Sounder (AIRS) has been developed for the NASA Earth Observing System (EOS) program for a scheduled launch on the EOS PM-1 spacecraft in December 2000. AIRS, working in concert with complementary microwave instrumentation on EOS PM-1 is designed to provide both new and more accurate data about the atmosphere, land and oceans for application to NASA climate studies and NOAA and DOD 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, humidity profiles to 10% accuracy and surface temperatures with an average accuracy of 0.5 K. The AIRS measurement technique is based on passive IR remote sensing using a precisely calibrated, high spectral resolution grating spectrometer operating in the 3.7 - 15.4 micrometer region. The instrument concept uses a passively cooled multi- aperture 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. The AIRS instrument, which has been under development since 1991, has been fully integrated and has completed successfully a comprehensive performance verification program. Performance verification included thermal vacuum testing, environmental qualification and a full range of spatial, spectral and radiometric calibrations, which have demonstrated outstanding spectrometric performance. This paper provides a brief overview of the AIRS mission and instrument design along with key results from the test program.

A test system and set of procedures have been developed to fully test and calibrate the Atmospheric Infrared Sounder (AIRS), a facility instrument on NASA's EOS PM platform. The system has been used to test and calibrate, under simulated space conditions, the spatial, spectral, radiometric and polarization characteristics of AIRS for each of its 2378 spectral bands covering the IR range from 3.7 and 15.4 micrometer. Unique challenges included spectral line shape and out of band response characterizations over 3 decades of the response function, accurate radiometric response calibration for IR source brightness temperatures from 195 to 357 K, spectral channel center and width determinations to 3 ppm of wavelength, spatial co-registration determination of the 2378 bands to 0.002 degrees and polarization response determination over all bands. Measured sensitivity, spectral response and polarization response for the AIRS instrument met or bettered requirements. The test systems developed to meet these objectives are described and the procedures and summary results of testing are presented.

The Atmospheric Infrared Sounder (AIRS) has been developed for the NASA Earth Observing System (EOS) program with a scheduled launch on the first post meridian (PM-1) platform in December 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 predictions. 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 passive infrared remote sensing using a precisely calibrated, high spectral resolution grating spectrometer providing high sensitivity operation over the 3.7 micrometer - 15.4 micrometer region. To meet the challenge of high performance over this broad wavelength range, the spectrometer is cooled to 155 K using a passive two-stage radiative cooler and the HgCdTe focal plane is cooled to 58 K using a state-of-the-art long life, low vibration Stirling/pulse tube cryocooler. Electronics waste heat is removed through a spacecraft provided heat rejection system based on heat pipe technology. All of these functions combine to make AIRS thermal management a key aspect of the overall instrument design. Additionally, the thermal operating constraints place challenging requirements on the test program in terms of proper simulation of the space environment and the logistic issues attendant with testing cryogenic instruments. The AIRS instrument has been fully integrated and thermal vacuum performance testing is underway. This paper provides an overview of the AIRS thermal system design, the test methodologies and the key results from the thermal vacuum tests, which have been completed at the time of this publication.

A novel measurement methodology for determining the polarization response of optical instruments is described. The methodology was developed for testing the polarization response of the Atmospheric Infrared Sounder (AIRS), but has general applicability. The technique involves measuring the instrument's response to each of three distinct input polarization states, and computing from these signals a polarization transfer function using a special data processing algorithm. The equations that are the basis of the data processing algorithm are presented along with an outline of their derivation. The technique has been successfully used to test the polarization response of the AIRS IR Sensor Assembly as part of the Protoflight Model (PFM) Integration and Test program. The measured data shows excellent agreement with AIRS polarization response predictions, which were calculated using very complex numerical methods. A description of the test equipment are presented along with plots of the measured and predicted AIrS Spectrometer Polarization Ratio vs. wavelength.

A laboratory model of the space borne compact FTS was manufactured and tested. This type of compact FTS with medium spectral resolution (approximately 0.8 cm^-1) and high spectral scan rate (approximately 10 Hz) is suitable for the observation of the vertical distribution of atmospheric constituents, especially for the observation of solar occultation. The rapid vertical velocity of tangent points requires a high spectral scan rate of the instrument. One of the candidates of platforms is the International Space Station (ISS). The results of a sensitivity study show that a moderate spectral resolution of approximately 1 cm^-1 is sufficient for measuring vertical distributions of the trace gases with a measurement error less than 10%. The laboratory model is based on the Bomem/MR series with balanced rotary scan action and a frictionless flex blade at the center of rotation. For data sampling, a diode laser is utilized instead of a He-Ne gas laser. This technique provides the compactness and longevity in FTS needed for the satellite borne system. For this instrument, a vibrational environment test was conducted and it was proved to be well-balanced and to be a stable structure with a high resonance frequency. This paper also proposes a space borne interferometer.

This paper presents the design and initial test results of the laboratory Wide Field-of-View Imaging Spectrometer (WFIS). The WFIS is a patented optical design intended for use in remote sensing of the Earth and the Earth's atmosphere in the hyperspectral imaging mode. It is meant to operate as a pushbroom imager to provide coverage of the Earth from low Earth orbit without scanning mechanisms. The optical system occupies a volume measuring less than 20 cm X 18 cm X 13 cm. The laboratory unit covers the 500 nm to 1000 nm wavelength range over a cross-track field of view of 70 degrees. The image is focused onto a CCD area array such that the spatial component falls along the horizontal direction and the spectral information is dispersed along the vertical direction. The system's focal length is 7.5 mm with an effective focal ratio of 3.7. A holographic grating produced on a unique convex substrate is the dispersing element. A key feature of the WFIS is an all-reflective optical path, allowing the basic design to be adapted to wavelength regions from the UV to the IR. Presented are the initial test results of the laboratory spectrometer that characterize its spatial and spectral performance over a 70 degree X 0.08 degree field of view.

Microbolometer array technology is making rapid progress in the commercial and tactical military world. An array was used for uncooled IR imaging in a very successful Shuttle flight and more is planned. Applications for long missions with microbolometers are on the drawing board. A recent study concluded that an uncooled staring array, when applied to Mid IR atmospheric ozone limb profile measurement could dramatically improve earth coverage, vertical precision and mixing ratio accuracy. Imaging by a staring array also alleviates some of the problems of non-imaging approach. This paper describes the technique and strategy of ozone profiling with an uncooled microbolometer array, the derived key instrument requirements and a brief discussion on the instrument implementation approach.

On focal plane analog to digital conversion, A/D has matured to such an extent that large low power arrays are now being built. Recently Amain developed a cooled MWIR 640 X 480 staring focal plane array with an A/D at each pixel. The technology, MOSAD$CPY, Multiplexed OverSample A/D, allowed the placement of over 300,000 converters on the focal plane on 27 micron centers with 12 bits dynamic range. A unique one bit digital data format, Stream Vision$CPY, was generated on focal plane and transmitted directly to a Ferroelectric LCD for real time viewing of the IR scene. This data stream produces apparent gray to the eye by rapidly modulating the on/off density of the display pixel in concert with the corresponding pixel on the focal plane array. To correct for detector nonuniformity (NUC), a systolic array of parallel processing elements was developed that provided offset and gain correction while preserving the dynamic range of the Stream Vision data. The benefits of this new digital format is that no transformation is required for processing and displaying the image data and there is no analog electronics in the system. Compared to present displays using either PCM to analog or PCM to pulse width modulation. Stream Vision uses less electronics and substantially lower switching bandwidth for the equivalent dynamic range. This development was sponsored by Naval Air Warfare Center under a Phase II SBIR program.

This paper presents a systematic new methodology for restoration of infrared images. The approaches described herein are applicable to single frame and multi-frame or hyper-spectra infrared images. The restoration problem is performed in two stages: (1) noise reduction and (2) linear blur and image estimation and restoration. The additive and multiplicative noise reduction is statistically optimal and improves the estimation of blurring function and restored image. For the restoration process we discuss alternate methods and provide the framework for error free restoration by eliminating the well known singularity problems that are often present in inverse solutions with singularities. Some initial results are presented.

MeteorWatch is a concept for the observation of small meteor events from a microsatellite in low earth orbit. To achieve high spatial resolution (about 1 km), fast update rate (up to 50 Hz), and large instantaneous coverage (10⁷ km²), a distributed sensor is appropriate. The MeteorWatch sensor design has about 300 independent detection modules linked by a data bus to a central controller and image processor. Each detection module has a camera, digitizer, controller, image preprocessor, and bus interface. In operation, each detection module decides on the probability that a particular image has a meteor. Meteor event rates are expected to be low compared to the data rate, so that preprocessing at the detector modules reduces traffic on the data bus to the central controller. Image sequences with probable meteors are sent to the central controller for further processing and extraction of the meteor parameters. This paper gives an overview of MeteorWatch and describes the image processing approach, including partitioning of the tasks between the detection modules and the central image processor, the selection of clutter-rejection algorithms and the limits of detection for small meteors.

We examined three different methods, namely, Method-I, -II, and -III for retrieving local aerosol's optical parameters over the Japan Sea using the ADEOS/POLDER data by comparing with the validation data. Method-I, and Method-II use parameterized directional reflectance and polarization diagrams in two infrared bands, respectively. On the other hand, Method-III uses parameterized directional polarization- reflectance diagrams in a single infrared band. We found that Method-III gives the best agreement with the measured sky validation data. We also presented retrieved distribution maps for the aerosol optical thickness, and Angstrom exponent by Method-III and some discussions on further improvement for Method-III were given.

The main application of remote sensing is to evaluate the output of the crops. Cotton directly correlative to our life, the evaluation of cotton is obviously important. The extraction of cotton from satellite image is an economical and effective method. In the growth period of cotton, wheat and other crops also grow with it. So, some difficulties are existed in the extraction of cotton area. In this paper, we discussed the some methods of the cotton area extraction. Then, GSA algorithm and Competition algorithm (both based on Markov Random Field), FCM algorithm based on Fuzzy set and the algorithm based on the Renyi threshold are introduced in this paper. The experiment indicates that these methods are effective.

Direct imaging of terrestrial and Jupiter-size planets about other stars is a major goal of NASA's Origins Program and should be as well for the next generation of spaceborne telescopes. In this paper, we discuss a free-flying occulter to augment the design and imaging capability of space-based telescopes. The Umbral Mission Blocking Radiating Astronomical Sources (UMBRAS) space mission would consist of a Solar- Powered Ion-Driven Eclipsing Rover (SPIDER) and possibly one or two metrology platforms. The UMBRAS spacecraft would be semi-autonomous, with their own propulsion systems, internal power (solar cells), communications, and navigation capability. The spacecraft (the telescope, SPIDER, and any metrology platform) would define a reference frame for aligning the telescope and the SPIDER with the observed target. When stationed at distances of 1,000 to 15,000 km from a telescope, the occulter will enable an 8 m telescope to image very faint sources as close as 0.15' from the target stars. Three of the Doppler-detected planets about nearby stars are at this separation and could be directly imaged with this observing technique. It would be possible to image giant planets as close as 5 Au from parent stars at distances from the Sun as great as 30 pc. With this technique, terrestrial- size planets could be detected around nearby stars within the next decade. We briefly discuss the diffraction effects caused by the occulter and a preliminary proof-of-concept design for the UMBRAS spacecraft. Finally, we suggest types of observations other than planet finding that could be performed with UMBRAS.

Algorithm deriving the upwelling radiation from the top of the spherical atmosphere-ocean system is proposed. The method was developed using a technique similar to that of the plane parallel atmosphere bounded by a heterogenous surface. Numerical result indicated an effect of spherical atmosphere if the incident solar zenith angle is over 80 degrees.

According to the characteristics of the remote sensing image, the problem of segmentation can be converted to the problem of symbolizing, and finally converted to the solution of Maximum A Posterior (MAP). The global optimum can be found by the algorithm of Simulated Annealing (SA), but it requires a large amount of computations. So sub-optimal algorithm is often used. In this paper we provide a decisive algorithm which is based on 'Game Theory' and prove that it can converge to a local optimum. Because the image we got has too many fragments, we use a grid-algorithm to improve the segmented image and the good result has been got in the experiment.

In this paper we present an IR-radiometer circuit that allows to carry out measurements of week photoelectric signals on considerably lower level of the inherent noise than known IR- detector systems for (delta) equals 4.5 - 5; 8 - 13 micrometers ((mu) ) atmospheric windows. Contrary to similar developments, here additional circuit solutions suggested to decrease preamplifier noise, for the amplitude stabilization of photosensitive bridge feeding pulses to correct basic and useful signals phases as well as to improve characteristics of the synchronous detector.

We analyze the imaging performance of synthetic-aperture optical systems (diluted-aperture, and segmented-aperture) using the modulation transfer function. We select a single figure-of-merit, the functional cutoff frequency, over the traditional cutoff frequency, as the most useful one for assessing the optical performance of an instrument for detection of small details. On the basis of this analysis, a simplified layout of the Keck telescope is proposed with an equivalent performance, but employing a smaller number of segments.

The vectorial shearing interferometer is based on the Mach- Zehnder configuration, by incorporating the displacement shearing system, composed of a pair of wedge prisms that modify the optical path difference and the tilt of the sheared wave front with respect to that of the reference wave front. When the shearing direction is chosen along the CCD pixels rows and columns, a two-dimensional derivative of the phase function is obtained, allowing its complete recovery in two- dimensions. The variable shear and tilt may be implemented along any direction, by choosing the displacements (Delta) x and (Delta) y. The number of fringes and their orientation may be controlled with the shear direction and its magnitude.

We analyze the problem of recording and detection of high density fringe patterns with finite pixel size. Two detrimental consequences of the pixalation are identified, both increasing the difficulty of phase reconstruction. First, the intensity information is undersampled for the large pixel center-to-center separation. Second, the intensity distribution, averaged over a pixel of about the same size or larger than the fringe width, significantly decreases the detected fringe visibility. In the limiting case that the pixel width is equal to that of a fringe and with a proper registration, no phase information is recorded: a condition we call the moire limit. Neither the intensity, nor contrast, nor phase reversal effects are seen in the simulations. We show that the high-density fringe detection may not be characterized with the modulation transfer function.

On December 5, 1998, the Submillimeter Wave Astronomy Satellite has been launched with a PEGASUS carrier after more than 3 years delay. SWAS is observing molecular line signals (H₂O, ¹³CO, Cl, O₂ and H₂ ¹⁸O) from astronomical sources at frequencies between 487 and 557 GHz. SWAS is the first sub-millimeter heterodyne space mission, and, for the spectral analysis of the received signals, it carries the first acousto-optical spectrometer (AOS) in space. The AOS has been built at University of Cologne, and it covers 1.4 GHz bandwidth with approximately 1400 frequency channels. The total weight is 7.5 kg and the power consumption is 5.5 Watts only. The very stable temperature conditions on SWAS allow longtime integrations at total observing times far above 100 hours still with radiometric performance. So far, the AOS- spectra have not been degraded by particle hits, particularly the CCD detector of the AOS does not exhibit any visible effect due to cosmic rays. SWAS has already observed many interstellar sources in our galaxy. Emission of water is seen to be very abundant, while signals of molecular oxygen seem to be too weak to be observable.

We compare the detected contrast measured with a quantum and a modern, uncooled, thermal detectors, including the previously neglected term due to the change in the scene emissivity. For earth-based remote monitoring of room- temperature processes, the contrast detection using the quantum detector is better than that using the thermal one, even in the case that the contrast arises solely due to the emissivity changes.

We analyze the performance of a remote temperature sensor incorporating erbium-doped silica fiber as a sensing element. Its physical principle of operation is based on the thermalization between two energy levels responsible for the emission in green (²H_11/2 and ⁴S_3/2), using the fluorescence intensity-ratio technique. We evaluate the sensor performance for different spectral lines in the wavelength interval (510 nm - 570 nm), with the radiometric figures-of-merit, such as the responsivity, the detectivity star, and the noise equivalent power, starting from the signal-to-noise analysis. We find an improved signal-to-noise ratio for this sensor of about 38.3 dB for the spectral line at 520 nm. The sensitivity of this sensor is anticipated to be less than 0.01 K^-1 at room temperature. The usable temperature interval of its operation is from 300 K to about 850 K.