This paper reports on the status of SIRTF--the Space Infrared Telescope Facility. SIRTF will be a cryogenically- cooled space telescope instrumented with large-format, state of the art infrared detector arrays. SIRTF will complete NASA's family of Great Observatories and also serve as a cornerstone of the Origins program. SIRTF will be launched in 2001, carrying a complement of imaging and spectroscopic instrumentation, for a mission approximately 5 yr in duration. SIRTF will be placed in an earth-trailing heliocentric orbit; the very favorable thermal environment of this orbit has enabled a novel warm-launch architecture for the cryogenic system. More than 75% of the observing time on SIRTF will be available to the general scientific community. The community involvement in SIRTF began in June of 2000 with the formal release of the call for Legacy Science proposals.

SIRTF requires detector arrays with extremely high sensitivity, limited only by the background irradiance. Especially critical is the near infrared spectral region around 3 micrometers , where the detector current due to the zodiacal background is a minimum. IRAC has two near infrared detector channels centered at 3.6 and 4.5 micrometers . We have developed InSb arrays for these channels that operate with dark currents of < 0.2 e/s and multiply-sampled noise of approximately 7 e at 200 s exposure. With these specifications the zodiacal background limited requirements has been easily met. In addition, the detector quantum efficiency of the InSb devices exceeds 90% over the IRAC wavelength range, they are radiation hard, and they exhibit excellent photometric accuracy and stability. Residual images have been minimized. The Raytheon 256 X 256 InSb arrays incorporate a specially developed (for SIRTF) multiplexer and high-grade InSb material.

The Infrared Array Camera (IRAC) is one of three focal plane instruments in the Space Infrared Telescope Facility (SIRTF). IRAC is a four-channel camera that obtains simultaneous images at 3.6, 4.5, 5.8, and 8 microns. Two adjacent 5.12 X 5.12 arcmin fields of view in the SIRTF focal plane are viewed by the four channels in pairs (3.6 and 5.8 microns; 4.5 and 8 microns). All four detectors arrays in the camera are 256 X 256 pixels in size, with the two shorter wavelength channels using InSb and the two longer wavelength channels using Si:As IBC detectors. We describe here the results of the instrument functionality and calibration tests completed at Goddard Space Flight Center, and provide estimates of the in-flight sensitivity and performance of IRAC in SIRTF.

Traditional photoconductive detectors are used at 70 and 160 microns in the Multiband Imaging Photometer for SIRTF. These devices are highly sensitivity to cosmic rays and have complex response characteristics, all of which must be anticipated in the data reduction pipeline. The pipeline is being developed by a team at the SIRTF Science Center, where the detailed design and coding are carried out, and at Steward Observatory, where the high level algorithms are developed and detector tests are conducted to provide data for pipeline experiments. A number of innovations have been introduced. Burger's model is used to extrapolate to asymptotic values for the response of the detectors. This approach permits rapid fitting of the complexities in the detector response. Examples of successful and unsuccessful fits to the laboratory test data are shown.

We describe the test approaches and results for the Multiband Imaging Photometer for SIRTF. To verify the performance within a `faster, better, cheaper' budget required innovations in the test plan, such as heavy reliance on measurements with optical photons to determine instrument alignment, and use of an integrating sphere rather than a telescope to feed the completed instrument at its operating temperature. The tests of the completed instrument were conducted in a cryostat of unique design that allowed us to achieve the ultra-low background levels the instrument will encounter in space. We controlled the instrument through simulators of the mission operations control system and the SIRTF spacecraft electronics, and used cabling virtually identical to that which will be used in SIRTF. This realistic environment led to confidence in the ultimate operability of the instrument. The test philosophy allowed complete verification of the instrument performance and showed it to be similar to pre-integration predictions and to meet the instrument requirements.

The Infrared Array Camera (IRAC) is one of three science instruments that will fly aboard the Space Infrared Telescope Facility mission scheduled for launch in December, 2001. This paper summarizes the `as built' design of IRAC along with important integration and testing results.

The goal of achieving background-limited performance in SIRTF's cryogenic telescope environment places stringent demands on focal plane sensitivity. SIRTF's prime imaging instrument, the InfraRed Array Camera (IRAC), employs 256 X 256 Si:As Impurity-Band Conduction (IBC) arrays for its two longest wavelength channels at 5.8 micrometers and 8.0 micrometers . Background-limited performance is achieved at very low levels of zodiacal background radiation with cryo-optimized readout and detector technology from Raytheon. Presented here are performance measurements of IRAC flight candidate IBC arrays. Operating at a temperature of 6 K, these devices meet all IRAC sensitivity requirements, with dark currents well below the 10 e-/s specification, Fowler-sampled noise levels of 16 e-, and excellent photometric stability.

The Infrared Spectrograph, IRS, for SIRTF is a set of four compact low and medium resolution infrared spectrographs designed to work in the wavelength range from 5.3 - 40 micrometers at resolutions, (lambda) /(Delta) (lambda) from 65 to 600. The design involves all reflecting optics with no moving parts. The basic design philosophy, the fabrication process, the test program, and the real-time pointing capabilities are discussed.

In this paper a flat-field micro-spectrometer is designed by using varied-pitch gratings. The geometrical parameters which affect the focal curve, i.e. the radius of curvature, pitch variation, incidence angle, and the position of the focal plane, are analyzed. Then a planar concave grating is optimized by the Simulated Annealing Algorithm. The spectral region covers 400 - 800 nm and the linear dispersion is about 6 micrometers /nm. The obtained linearity of the focal curve is better than 98%. Furthermore, to get better aberration, the concave grating with arbitrary grating profile is also discussed.

VIRTIS, the infrared imaging spectrometer of the ESA/ROSETTA mission, to be launched in January 2003, is devoted to the in-orbit remote sensing study of comet P/46 Wirtanen. Within the infrared imaging spectrometer VIRTIS, the high spectral resolution channel, VIRTIS-H, has for main scientific objectives to study the fine spectral details of the coma and cometary nucleus, with their composition and physical parameters, in parallel with the imaging spectrometer channel VIRTIS-M. The instrument is a cross-dispersor spectrometer, working in the range 2 - 5 micrometers , at about approximately 1200 spectral resolving power. Its design consists of a telescope, an entrance slit, followed by a collimator, and a prism separating 8 orders of a grating

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 like a notch filter. The second monochromator collects and recombines the transmitted radiation at its exit slit. Behind the exit slit and the beam forming elements can the sample be positioned. 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 spectrophotometric measurements the total transmitted power is measured at every stop of the lamella. From this array of measurement results the transmittance or the reflectance of the sample can be calculated as a function of the wavelength.

The Stratospheric Wind Interferometer for Transport Studies is a limb viewing satellite instrument which is intended to measure stratospheric wind velocities in the altitude range of 20 to 40 km. Tandem etalon filters made of Germanium and a field-widened Michelson interferometer operating in mid- infrared are major components of this instrument. A He-Ne laser and a CCD camera were used to observe Haidinger and Fizeau fringes in visible light and compare their characteristics with mid-infrared measurements. The Fizeau fringes in the visible can be used to observe the irregularities in the Michelson interferometer's path difference. In addition a CO₂ laser operating at 9.26 micrometers has been used to test the Michelson interferometer and the filters together. The filters are thermally tuned to the CO₂ laser line and the filter output was incident on a diffuse surface in front of the Michelson input aperture. The Michelson interferometer was then pressure scanned to observe its performance in combination with the filters.

The Crosstalk Infrared Sounder (CrIS) is one of the key sensors now under developed for the National Polar-orbiting Operational Environmental Satellite System program, which is the follow-on to the current DMSP and POES meteorological satellite systems. CrIS is a interferometric sounding sensor which accurately measures upwelling earth radiances at very high spectral resolution, and uses this data to construct vertical profiles of atmospheric temperature, moisture and pressure. The purpose of this paper is to describe the CrIS system design, discuss key trade studies that led to selection of the design, discuss risk reduction demonstrations that were performed to confirm the readiness of the technologies used in the CrIS design, and summarize the key performance capabilities of the CrIS system.

A moving spot illuminated semiconductor panel is used to convert millimeter wave images to visible displays. The response of semiconductors to moving spot illumination is important in this method. In this paper the response of a semiconductor panel to a moving Gaussian (laser) spot is considered in detail. Initially, the profile of excess carrier in the bulk of the semiconductor panel for Gaussian illumination vs. position, scanning velocity, width of the semiconductor panel, etc., are studied. Using the expression for excess carrier, the single path attenuation of a millimeter wave through moving Gaussian spot illuminated semiconductor panel vs. standard deviation of Gaussian spot and scanning velocity is studied.

Hybrid sensors performance critically depends on the performance of the analog read-out electronics. The analog design methodologies are very well known and documented provided the operating temperature stays above temperatures where carrier freeze-out occurs. Even though the behavior of individual MOS transistors at low temperature, i.e. below 30 K, has been studied in detail, this has not yet led to design guidelines for the design of building blocks and/or complete systems that will operate satisfactorily at these low temperatures. The main challenges are the design of amplifiers with high open-loop gain, low electrical power consumption and low noise. By providing cryogenic design guidelines, this paper tries to bridge the gap that exists between the information available on the MOS transistors and the needs of design engineers confronted with practical problems. The issue of transistor dimensioning using simple models of the MOS transistor will be discussed.

Spatial distributions of hole trap sites on a quasipixel level in InSb arrays for SIRTF are examined. The dependence of flux, fluence, and applied bias on image latency is investigated, and experimental results are presented and discussed. Models of linearity and capacitance are compared with experimental results. We find increasing the depletion width in a light exposed pixel by larger reverse biasing decreases the trapped charge (or latency) in that pixel by factors of approximately 3. Assumed pixel geometries lead to an apparent spatial density of active trap sites that falls quickly with distance from the implants.

This paper describes the application of airborne remote sensing techniques for the detection of sub-surface archaeology in the Heslerton Parish Project area, Vale of Pickering, North Yorkshire, NERC vertical-color-air photographs and Airborne Thematic Mapper multispectral digital data have been evaluated for the detection of crop marks under different land use and soil moisture conditions. The value of thermal infrared imagery over visible imagery in relation to these variables is discussed. Thermal imagery represents the emitted, rather than the reflected radiation from the target. This technique therefore exploits variations in surface characteristics which may not be evident on visible imagery produced using reflected energy. The results suggest that thermal infrared imagery may be useful for the detection of crop marks in situations where traditional data (air photographs) give poor returns, for example over potatoes.

The Space Infrared Telescope Facility Infrared Array Camera (IRAC) uses two dichroic beamsplitters, four bandpass filters, and four detector arrays to acquire images in four channels at wavelengths between 3 and 10 micrometers . Accurate knowledge of the pass bands is necessary because, in order to meet the science objectives, IRAC is required to do 2% relative photometry in each band relative to the other bands. We report the in-band and out-of-band polarized transmittance and reflectance of these optical elements measured near the instrument operating temperature of 1.4 K. Details of the experimental apparatus, which include a continuous flow liquid helium optical cryostat and a Fourier transform infrared spectrometer are discussed.

Adhesive bonded mounting of small optics for use at cryogenic temperatures provides improved heat transfer, low optical surface distortion, and reduced cost in comparison with conventional flexural mounts. A design methodology based on the thermo-elastic properties of the adhesive and its interaction with the mounted optic is presented. Key factors in the selection of the appropriate adhesive are high thermal conductivity, a low elastic modulus, a low glass-transition temperature, good adhesion characteristics to optic and substrate, and low outgassing. A design example of 17-mm diameter, 2-mm thick circular polycrystalline germanium window used at a temperature of below 100 K is discussed. During cooling at a rate of more than 3 K/sec the temperature at the center of the window mounted in this way lags behind the mount by no more than 20 K at any instant, and reaches equilibrium with the mount in about 50 sec. Maximum optical surface deformation of the mounted optic is less than 0.031 waves RMS differential (1 wave equals 633 nm) for a temperature change of 300 K to 102 K. Predicted peak tensile stress is less than 17 MPa. The adhesive bonded mount is also simple and economical in comparison with the complex flexural mounts often used for cryogenic optics.

Energen, Inc. has developed actuators based on cryogenic magnetostrictive materials. These actuators are designed to provide precision positioning and active control of adaptive optical surfaces such as those that are being considered for the Next Generation Space Telescope (NGST). The NGST is a large 8-mm diameter segmented reflecting telescope that uses a thin optical surface mounted on a rigid composite backstructure. The mounts consists of multiple actuators that are used to align the mirror segments and actively control the radius of curvature for optimum optical performance. Energen, Inc. has developed several types of actuators. A linear actuator consists of a rod of magnetostrictor surrounded by an electric coil that when energized causes the rod to elongate. These type of actuators are used for high speed active control. Energen also has developed a linear stepper motor that consists of an actuator mounted in two clamps. By operating the clamps and actuator in the proper sequence the actuator indexes forward and backward. Submicron positioning resolution along with strokes of 20 mm are possible. Furthermore, the stepper motor locks into position when powered off--ideal for applications where position must be held for long periods of time.

NASA Marshall Space Flight Center has maintained and operated a world-class x-ray optics and detector testing facility known as the X-ray Calibration Facility (XRCF) since the mid 1970's. The ground testing and calibration of the Chandra X-ray Observatory optics and detectors were successfully completed at the XRCF in 1997. In 1999, the facility was upgraded in preparation for cryogenic testing of lightweight telescope mirrors without compromising the existing x-ray testing capability. A gaseous Helium cooled enclosure or shroud capable of 20 degrees Kelvin and vibration isolated instrumentation mount were added to the existing facility. A precision remote-control five-axis motion mirror support was modified to operate under cryogenic conditions. Mirrors with diameters as large as two meters, and radii of curvature up to twenty meters can be accommodated in the He shroud.

NASA's Space Infrared Telescope Facility (SIRTF) is a 1- meter class cryogenically-cooled space observatory. The constituent sub-assemblies are currently in their assembly and verification phase. To facilitate the assembly and verification of the telescope, the Space Telescope Test Facility (STTF) has been built at the Jet Propulsion Laboratory. The STTF allows for the assembly, alignment, and optical characterization of individual components, as well as the telescope assembly with its cryogenic mechanism, at temperatures from 300 to 5 K in a chamber with interior diameter of 1.4 m, and a height of 2.3 m. The chamber is surrounded by a class 10,000 or better clean room. This paper reports on the functional and operational capabilities of this facility.

The Microwave Anisotropy Probe (MAP) Observatory, scheduled for a 2001 launch, is designed to measure temperature fluctuations (anisotropy) and produce a high sensitivity and high spatial resolution (< 0.3 degree(s) at 90 GHz) map of the cosmic microwave background radiation over the entire sky between 22 and 90 GHz. MAP utilizes back-to-back Gregorian telescopes to focus the microwave signals into 10 differential microwave receivers, via 20 feed horns. Proper alignment of the telescope reflectors and the feed horns at the operating temperature of 90 K is a critical element to ensure mission success. We describe the hardware and methods used to validate the displacement/deformation predictions of the reflectors and the microwave feed horns during thermal/vacuum testing of the reflectors and the microwave instrument. The smallest deformations to be resolved by the measurement system were on the order of +/- 0.030 inches (0.762 mm).

The Microwave Anisotropy Probe (MAP) Observatory, scheduled for a 2001 launch, is designed to measure temperature fluctuations (anisotropy) and produce a high sensitivity and high spatial resolution (< 0.3 degree(s) at 90 GHz) map of the cosmic microwave background radiation over the entire sky between 22 and 90 GHz. MAP utilizes back-to-back Gregorian telescopes to focus the microwave signals into 10 differential microwave receivers, via 20 feed horns. Proper alignment of the telescope reflectors and the feed horns at the operating temperature of 90 K is a critical element to ensure mission success. We describe the methods and analysis used to validate the in-flight position and shape predictions for the reflectors based on photogrammetric metrology data taken under vacuum with the reflectors at approximately 90 K. Contour maps showing reflector distortions were generated. The resulting reflector distortion data are shown to be crucial to the analytical assessment of the MAP instrument's microwave system in- flight performance.

The Engineering Model (EM) and Flight Model (FM) Focal Plane Assembly (FPA)/dewar assemblies have been fabricated, tested, and delivered for system integration, and the EM instrument has been assembled and tested. The key design features of the FPA and dewar have been presented in previous SPIE symposia and will only be briefly reviewed. The primary emphasis in this paper is on the performance results such as sensitivity, linearity and spectral response as well as environmental test results and a review of the assembly of the flight hardware.

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.

The Solar Occultation FTS for Inclined-orbit Satellite (SOFIS) is a solar occultation Fourier transform spectrometer developed by the Environmental Agency of Japan, and onboard the Global Change Observation Mission-AI (GCOM- A1) satellite. GCOM-AI will be placed in a 650 km non-sun- synchronous orbit in 2006, with an inclination angle of 69 deg. SOFIS is the successor of the Improved Limb Atmospheric Spectrometer-II, which is onboard the Advanced Earth Observing Satellite-II (ADEOS-II). SOFIS measures the vertical profile of the atmospheric constituents with 0.2 cm^-1 spectral resolution at 3 - 13 micrometers and 1 km vertical-resolutions. The target of SOFIS measurements is a global distribution of O₃, HNO₃, NO₂, N₂O, CH₄, H₂O, CO₂, CFC-11, CFC-12, ClONO₂, aerosol extinction, atmospheric pressure and temperature. SOFIS uses a double-pass flexible blade Fourier transform spectrometer (FTS) and a diode laser sampling system to reduce the size and weight of the apparatus. Two photovoltaic HgCdTe detectors and a pulse-tube cooler will provide high linearity and low-noise performance. SOFIS also has a visible (O₂ A-band) grating spectrometer for pressure and temperature retrieval and a sun-edge sensor for detecting the tangent height position. This paper describes the conceptual design of the instrument and examines the test results of laboratory models of the FTS and the detector.

The Crosstrack Infrared Sounder (CrIS) is one of the key sensors now under development for the National Polar- orbiting Operational Environmental Satellite system (NPOESS) program, which is the follow-on to the current DMSP and POES meteorological satellite systems. CrIS is a interferometric sounding sensor which accurately measures upwelling earth radiances at very high spectral resolution, and uses this data to construct vertical profiles of atmospheric temperature, moisture and pressure. The purpose of this paper is to examine small modifications to the CrIS design that enable it to be used for other applications where improved radiometric uncertainty is required. Modifications include changes to the onboard calibration target and onboard calibration systems, as well as enhancements to ground calibration algorithms that remove additional sources of radiometric error. An assessment is also made of the level of improvement in radiometric uncertainty that can be expected.

The Atmospheric Chemistry Experiment is the mission selected by the Canadian Space Agency for its new science satellite, SCISAT-1. Dr. Peter Bernatch of the University of Waterloo is the ACE Principal Investigator, and ABB Bomem is the prime contractor for the development of the ACE main instrument, a Fourier-Transform Spectrometer. The principal goal of the ACE mission is to measure and understand the chemical and dynamical processes that control the distribution of ozone in the upper troposphere and stratosphere. A comprehensive set of simultaneous measurements of trace gases, thin clouds, aerosols and temperature will be made by solar occultation from a satellite in a low Earth orbit.

This paper will describe a 270 X 436 HgCdTe FPA/module that was developed for the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) H and M instruments. Raytheon Infrared Operations was selected by Officine Galileo and the Observatorie de Paris, Meudon to design, fabricate and deliver 4 flight modules for the VIRTIS H and M spectrometers.

A large format prototype infrared camera based on the MOSAD (Multiplexed OverSample A/D converter) concept was developed and demonstrated. Each pixel readout buffer is composed of a two integrator one bit modulator that converts the accumulating photon induced charge to a digital value. This camera is designed around a 640 X 480 pixel focal plane array with an A/D converter at each pixel. The focal plane is a CMOS design readout hybridized to a MWIR (3 - 5 micron) N on P Mercury Cadmium Telluride detector array with pixels placed on 27 micron centers. Amain developed and tested the readout, camera and electronics. Rockwell Science Center provided the detectors which they hybridized to the Amain readout.

With BIRD mission a new approach in the design of infrared sensors has been made. Starting with the requirements for a fire recognition sensor the technical solution and the problems of signal processing of this sensor will be described. BIRD is a small satellite mission with its restrictions in mass and power consumption. The state of art of the IR Technology does not allow to realize high resolution systems with large swath width. One of the main ideas of this project is the use of sub-pixel ability of the IR-sensor. This technique requires a conception for pixel coregistration of the different channels. The paper describes the problems of the technical solution, the implemented signal processing and the equipment for calibration and validation.

Overall, this work investigated the relationship between vegetation variables and reflectance of water stressed vegetation and showed that biophysical variables that affect canopy reflectance should be considered carefully in any attempt to implement remote sensing techniques.

The imaging photometer and spectroscopic camera PACS, one of the three scientific instruments aboard the European 3.5 m infrared space telescope FIRST, will apply a tilting mirror mechanism for optical beam switching. The development of this focal plane chopper, capable of operation under cryovacuum conditions, is reported here. In order to meet the stringent requirements with respect to power dissipation and positional accuracy, special drive coils and a new position sensor had to be developed. A simulation model including electromagnetic analysis by the 3D code MAFIA, verified by extensive cold testing of the prototype hardware, was used for the optimization of the system and led to the advanced prototype of the chopper. Closed loop control of the mirror deflection allows square wave modulation in the frequency range 0 - 15 Hz (80% duty cycle) with amplitudes of +/- 9 degree(s) with high positional accuracy of less than 30'. The power dissipation at operating temperature of 4 K is below 500 (mu) W.

In this paper we discuss operational considerations for the free-flying occulter. Operations consist of maneuvering the Solar-Powered Ion-Driven Eclipsing Rover (SPIDER) between targets, alignment with the space-based telescope line of sight to the target, and stationkeeping target-to-target maneuvers need to be optimized to conserve propellant. A reasonable balance needs to be determined between target observation rate and the number of targets that are observable during mission lifetime. Velocity matching of the SPIDER with the telescope is essential to mission performance. An appropriate combination of solar electric and cold-gas thrusters provides the ability to match velocities using positional information derived from comminution and ranging between telescope, occulter and any metrology stations. Desirable features of using an external coronagraphic vehicle include the ability to obtain coronagraphic data with any instrument on the telescope-- imaging, spectroscopic, or interferometric.

For the instrument PACS (Photoconductor Array Camera and Spectrometer) aboard FIRST two photoconductor arrays dedicated for different wavelengths bands are foreseen in the spectrometer section. Each camera consists of 25 linear arrays of 16 stressed Ge:Ga crystals. The arrays with 2 X 400 pixels will be used for imaging line spectroscopy in the wavelengths ranges 60 micrometers to 110 micrometers and 110 micrometers to 210 micrometers . The detectors are read out by a new generation of integrating and multiplexing cryogenic read-out electronics, which is currently under redesign and further development. The development of the arrays has passed the engineering phase and entered the qualification status. We summarize the results obtained with the engineering arrays and the first 6 qualification models with respect to their performance such as uniformity of current sensitivity and cutoff wavelength. The impacts of the result of the first 6 linear arrays on the qualification model are described together with the final design which is supposed to fulfill the specifications and requirements of the instrument PACS.

We present the physical and empirical models that are actually developed for the Infrared Space Observatory (ISO) detectors together with dedicated inversion techniques. The problems encountered with ISO detectors are obviously extremely useful in order to test and improve the Si and Ge detectors used in the future.

Distributed optical fiber sensor systems are prospective candidates for the environmental pollution monitoring over large industrial sites. Among particular optical probes that are attractive for this application are the refractometric ones. However, despite all previous work on this subject, the performance limit of these probes, especially in case of the micro-optical of fiber-optical design, is not yet established. To clarify this point, computer simulations dealing with the response of the novel paraboloidal-shaped micro-optical probe to small changes in the refractive index of the surrounding media are presented. The relative sensitivity concept, which is the ratio of the probe output in two different media, is introduced. The relative sensitivity is proposed as an objective basis for the comparison of refractometric probes.

Our detectors are superconducting Transition-Edge Sensors that have been designed for photon counting in the energy (wavelength) range of 0.5 eV (2.5 micrometers ) to 10 eV (124 nm). Our design consists of a 6 X 6 array of 20 micrometers by 20 micrometers pixels, of which four were operated simultaneously at count rates exceeding 30 K-counts/pixel. Each photon is time-tagged to 0.4 microsecond(s) using a GPS signal processor, and the energy is determined to approximately 0.15 eV FWHM. These results are the best achieved for an energy dispersive spectrometer in the optical range. We discuss the detector design and operation, optical coupling, and high-rate data acquisition system. In addition, we discuss the next step towards detectors with improved light collection and higher energy resolution. We also present recent results from latest application of our fast spectrophotometers to the study of highly time-variable sources using the 2.7 m telescope at the McDonald Observatory.

In 1993 a network of differential optical absorption instruments was deployed in Argentina and Chile to study the evolution of the ozone layer in the mid latitudes of South America. The data obtained by this network were compared with the data provided by TOMS (NASA) and TOVS (NOAA) satellite instruments and a good correlation was found. NCAR meteorological data were also used to study in detail the ozone transport in the stratosphere under ozone hole conditions. The data provided by both, the ground based and the spaceborne instruments, revealed that sudden and transient decreases of total ozone column values took place in the mid-latitudes of South America each spring in the period 1993 - 1998. These low ozone events occurred quasi- simultaneously at quite different latitudes. The analysis of potential vorticity maps showed that the lower stratosphere polar vortex penetrated up to approximately latitude 50S in South America every spring since 1993. In addition it was found that the low ozone events were accompanied by sudden air temperature decreases in the lower stratosphere. The computation of the 3D back-trajectories of air parcels showed that air from the surroundings of the ozone hole were transported to the mid latitudes regions. An anti- correlation between air parcels height and total ozone along the trajectory was found suggesting that vertical displacement of air also contributed to the observed ozone and temperature decreases.

It is shown that the retrieval of temperature and pressure profiles can be obtained from vertically resolved limb emission measurements without requiring absolute radiance calibration. Only relative spectral and spatial response functions are required. The retrieved temperature and pressure profiles define the thermal IR source function, allowing absolute calibration of the flux input to channels sensing gases with known spectral parameters and mixing ratio. These calibration concepts have now been demonstrated using data from the Limb Infrared Monitor of the Stratosphere instrument on Nimbus 7.

We analyze the possibility of achieving increased sensitivity for the infrared remote sensing for civilian applications. We explicitly incorporate the effects of emissivity and introduce a new figure-of-merit, detected thermal contrast.