The Long Wavelength Spectrometer is a focal plane instrument for the ESA Infrared Space Observatory, operating over the wavelength range 45 to 180 pm. To perform the alignment, testing and calibration of the spectrometer requires much of the telescope optics, instrument fixtures and temperature conditions to be replicated or simulated in the laboratory. In addition, facilities for achieving photometric and spectral calibration are required. A cost-effective solution to the problem is described here which involves a minimum size for the test cryostat.

The vacuum facility FOCAL 5 (Facilite d' Optique et de Calibration a Liege de 5 metres) is a test facility of the space research centre "IAL Space" of the University of Liege - Belgium. It has been tailored for thermal vacuum testing of medium size payloads and progressively upgraded for cryogenic payloads including 4.6 K (liquid helium temperature) experiments. The first part of this paper presents the current status of the facility with its potential capabilities. The second part will describe the experimental set-up and the results obtained in the case of the cryogenic testing of either the ESA Hipparcos astrometry payload or the ESA ISO infrared telescope subsystems. The various product assurance, quality control and cleanliness aspects are also reviewed.

In 1988, when the work reported in this paper was carried out, many studies had been conducted concerning the feasibility and design of free-space optical communications links between satellites but very little hardware work had been carried out, particularly concerning the tracking aspects.

Optical alignment is used extensively for alignment of weapon systems. Its speed, simplicity and very high accuracy are all eminently suitable for these demanding tasks. The various uses are so many that we will concentrate on the use for missiles, aircraft and gun barrels. I will also briefly show what is now possible with newer instruments with facilities for remote data logging.

Evaluation of instruments has been carried out at several independent laboratories in Europe over a period of many years, and this service has been provided at Sira for over 30 years.

This paper presents results of environmental tests performed on high frequency packaged, polarisation maintaining fibre-pigtailed Ti:LiNbO3 phase and Mach Zehnder intensity modulators. Most of the environmental tests carried out conform to the UK Defence Standard 07-55 and the test requirements specified by the European Space Agency (ESA) for components and equipment employed in space applications [1]. The modulators were subjected to vibration, shock and temperature cycling, to assess ruggedness of package and quality of fibre pigtailing technique. Stability of Ti:LiNbO3 devices in relation to pyroelectric and buffer layer drift is presented. Results of some preliminary work on the effect of moisture and outgassing of the epoxy used for fibre pigtailing are presented.

Pure diamond has excellent mechanical and infra red properties and would make an ideal window material were it readily available. Synthetic diamond films can be grown with good infra red transmission and used as protective coatings. Many coating requirements can already be met using diamond-like carbon films.

Infrared filters for use in space programs are discussed together with the problems relating to material choice and manufacturing methods needed to provide the components for space applications.

The exceptional properties of diamond have stimulated a considerable research effort into the low pressure synthesis of diamond thin films for a diverse range of applications including:- tribological coatings, semiconductor heat sinks and (as in this work) protective optical coatings. Numerous deposition techniques have been reported in the literature including Microwave Plasma Assisted CVD (MPACVD). This paper briefly describes the MPACVD deposition system used at Plessey Research Caswell Ltd and outlines the effects of important deposition parameters on the growth morphology of diamond crystallites and thin films. Techniques including SEM, TEM and X-ray diffraction have been used to study the growth mechanisms of MPACVD diamond. IR and Raman spectroscopy have been used to characterise the deposited films and an IR reflection technique is described for studying the infrared properties of the layers. The effect of deposition parameters on the properties of diamond thin films is discussed with regard to the use of these films for protecting IR windows and domes.

Layers of amorphous germanium/carbon with low absorption loss and good abrasion resistance have been deposited on infrared substrates by RF plasma deposition of germanium in carbon containing atmospheres (from feedstocks of CH4, C4H10 etc). The optical properties of the layers (up to 100 μm thick) have been assessed using a FTIR spectrometer and found to be strongly dependent on deposition parameters and layer composition. Layers can show high hydrogen content and absorptions caused by C-H and Ge-H bonding, but, by suitable choice of starting materials and deposition conditions, layers free of such absorption bands can be prepared with good transmission from 3pm to 12pm. Application of this novel material to the development of high durability antireflecting coatings for zinc sulphide and germanium is discussed.

This paper reviews recent liquid impact work in this laboratory. The research has included a theoretical study of the early stages of a liquid/solid collision where compressible effects in the liquid dominate the behaviour; experiments with two-dimensional gelatine shapes which combined with high-speed schlieren photography have allowed shock structures and jetting to be recorded; the development of techniques such as the single jet impact and multiple impact jet apparatus (MIJA) for producing controlled liquid/solid collisions in the laboratory, and studies of damage production in a wide range of aerospace materials. Quantitative studies of damage using post impact ("residual strength") measurement are described. Of particular interest are the "threshold velocities" for strength loss and the extent of strength loss following impact. Research on zinc sulphide has included a study of the effect of grain size on the hardness and Kic values of the material. Data are presented on a range of glasses, zinc sulphide, sapphire and germanium.

The advent of the laser in 1960 substantially modified the use and teaching of optics. At one stage the laser was termed `a solution looking for an application'. Nowadays the applications have arrived and range from long haul telecommunications, metal working, medical diagnostics, surgery, optical metrology to battlefield use, Strategic Defence Initiative, SDI applications. Most of this change has been generated because a considerable amount of development has been put into reducing the laser down to an acceptable size for the application while increasing the efficiency and energy and power outputs. This has led to the problem of laser induced damage approaching from two mututally irreconcilable directions. Not only, because of its monochromaticity, low divergence and coherence the laser can be focused to diffraction limited spot sizes and therefore be used for fusion and defence applications as well as being a hazard to eyes and viewing optics, but the laser resonator itself provides one of the most hostile environments that an optical component can be subjected to. Not only are laser components called upon to handle ever greater power and energy densities but they also have to withstand adverse conditions in terms of u.v. irradiation, plasma arcs, and the presence of active species. This paper briefly summarises the factors affecting the laser induced damage thresholds of components and coatings used in optical systems and laser resonators and then goes on to discuss the changes and consequent component damage/system degradation that is induced in the characteristics of these components during the irradiation interval.

At Barr & Stroud, dedicated laser damage assessment facilities have been established for a number of years. These are based on a "Q"-switched Nd:YAG laser, a "Q"-switched pumped dye laser and a CO2 TEA laser. This paper describes the facilities, some of the methods used to assess optical damage and then gives practical examples of how the assessment may lead to improvements in the laser induced damage threshold (LIDT) of optical components.

Increase in international trade has highlighted a long-standing problem of specifying the levels of surface quality needed for the wide range of optical components employed in modern defence equipment. This paper will review the problems resulting from the use of existing national standards and the effectiveness of the various suggestions made to create objective methods of measurement. After extensive trials, it has been concluded that the most appropriate and convenient way of quantifying a flaw is by measuring the total amount of light it removes from a beam of light and the preferred way of measuring surface roughness is by some form of micro-interferometry. The paper concludes by describing the design and performance of a microscope image comparator, which is capable of quantifying flaws and roughness, has traceability to national standards, and which is expected to form the basis of a revision of BS 4301 and a new ISO standard.

The opto-mechanical design and manufacture of a Thermal Imaging Airborne Laser Designator (TIALD) Pod is reviewed. The design concept is that the equipment should be modular in form, allowing the pod to be reconfigured for a variety of applications. Possible advantages of incorporating a TV camera in such a system are discussed and the versatility of a modular system is illustrated by the ease with which such a TV sensor can be added to the original thermal imaging equipment.

For the dual waveband detector of the TICM II thermal imaging system which is sensitive over the wavelength range from 3gm to 5gm and from 8gm to 12gm an afocal with magnification change has been designed. The afocal is color corrected for both wavelength bands without focus shift and it has a reduced Petzval-sum.

The development of focal plane technology in the production of very large linear arrays for infra-red sensors must be matched with optical systems capable of resolving up to 3000 pixels. Such systems have application in earth observation from space or airborne platforms. Radiometric rigour and stray radiation rejection are aided by the provision of an intermediate focus. The suggested optics can provide a flat image field and relative apertures to F/2 with a compact system of co-axial spherical optical surfaces. Although the design is for current detectors operating in the 3-5 μm infra-red window, the design is appropriate for the 8-13 pm window or dual band with alternative optical materials and surface coatings.

"Tweaking" is a time-honored art in the production of lenses. In recent years it has taken on the more sophisticated name of "Computer-Aided-Alignment". The skilled interpretation of a star image has given way to a phase-modulated Interferometer communicating with an Optical Design Program which calculates "tweaks" of certain elements within the lens - the so-called compensators.

Most antireflection coatings in use today are derived from concepts based on the use of quarter-wave (Q) and half-wave (H) optical thickness layers. We show an alternative and more general way of viewing the concepts and how special cases reduce to the commonly used forms. The monotonically graded inhomogeneous index layer from the substrate to the medium has been extensively reported by Jacobsson and Martensson(1), Dobrowolski and Ho(2), and others. Various oscillating index profiles between the substrate and the medium show promise in producing superior broadband AR coatings. These concepts have evolved from observation of broadband designs using multiple homogeneous quarter- and half-wave optical thickness layers as described by DeBell(3). The viewpoint leads to some further understanding of the possibilities and limitations of AR coatings in general.

An f/1 objective lens for use in the infrared from 7 to 12 µm has been designed using axial gradients in zinc sulfide/zinc selenide. The resulting optical systems are color corrected and use fewer elements than comparable conventional designs. Lens blank material has been produced by chemical vapor deposition and a prototype lens assembly is being fabricated and tested.

Recent years have seen progression in the use of fibre optic aided remote condition monitoring techniques which was once reserved for medical application. The use of such systems provides important and useful information on the operational status of components and equipment in their normal remote operating condition and environment. Their application in a specific area usually requires some innovative design work, that utilises the basic fibre optic system for the required tasks. The remote condition monitoring technique requires the automated system of fibre optics probe and Charge Couple Device camera as means of visually monitoring the component insitu. This paper presents some of the difficulties and constraints encountered in the conceptualisation of an automated remote condition monitoring technique. It deals mainly with the optical aspects of the technique. This includes the results of some experimental work, and the problems that are inherent in the development of the concept of a computer controlled camera orbital scanning system.

In 1973, Shepherd and Yang proposed silicide Schottky-barrier detector (SBD) arrays for infrared thermal imaging (11. Infrared image sensors with 25 x 50 and 256 x 1 SBDs with thick PtSi film (~ 1000 A) were demonstrated in 1978 [2, 3]. The major breakthrough in the improvement of the responsivity of PtSi SBDs by about two orders of magnitude came with the introduction of SBDs with optical cavity having a thin (20 to 50 A) PtSi film [4-7].

The design and fabrication of the P88000 series of large area scientific CCDs are described. Fabrication is carried out using a wafer stepper and a photolithographic 'stitching' technique. One member of this series, the P88200, was designed specifically for the ESA XMM X-ray spectroscopy space mission, and has been fabricated on high resistivity epitaxial silicon to provide improved detection efficiency for X-rays in the energy range 1 to 10 KeV. Enhanced imaging performance in the near infra-red is also achieved. Further work to improve performance for X-rays in the energy range 0.1 to 1.0 KeV is briefly described. Details are given of X-ray quantum efficiency, readout noise, charge transfer efficiency and energy resolution. Studies have shown that the major effect of radiation is a deterioration in charge transfer efficiency.

Recent thermal and radiation tests are described which give increased confidence in the use of direct contact Peltier Cooled CCDs in star trackers and other space instrumentation. Possibilities for improved performance, based on developments in CCD architectures, are also discussed.

For space applications, electronic devices have to be manufactured on an industrial basis and fully qualified through international procedures and standards. Charge coupled optical sensors (CCD) designed by THOMSON as TH 7805A linear array is, are produced in a very adapted environment through a qualified semiconductor n.MOS process. Then they exhibit both high reliability and really good electro optical performances.

Optical communication between satellites in orbit requires highly accurate tracking of an incoming laser beam, to allow the generation of necessary control signals for the pointing mechanisms. For the SILEX system planned by ESA the tracking sensor is required to determine the position of the centre of the focused laser spot with a la noise error within 0.1,um on the CCD detector (equivalent to a mispointing of 0.07μrad), for the nominal bandwidth of 8kHz and the minimum optical power of 110pw. This implies the determination of the centre position to small sub-pixel accuracies, achieved via mathematical interpolation from the fractions of the optical signal falling in the centre 4 pixels. This paper updates a previous paper'. It discusses the development of the tracking sensor breadboards by BAe and Sira. The detector unit, which uses the new 14x14 pixel CCD developed by Thomson-CSF, provides for fine adjustments of the CCD position. It also houses the electronics for CCD output buffering and amplification. The electronics unit carries out the processing of the video signal, to determine the coarse position of the spot over the 14x14 pixel area, and a very accurate position over the central 2x2 pixel area via an algorithm executed in a microprocessor. The paper presents some performance results including new results from the second breadboard, and routes to the design of flight sensors.

EEV has been in the business of uncooled thermal imaging for the last 20 years. The success of the pyroelectric vidicon, in particular in the Fire Service Camera, has highlighted the potential market for affordable thermal imaging systems. To exploit this market, EEV has in advanced development room temperature staring focal plane arrays of thermal detectors. This type of sensor will produce good quality thermal images at a fraction of the cost of current cooled systems, without the attendant logistic problem of cooling.

Current two dimensional staring arrays of CMT detectors have very good thermal resolution, but have limited numbers of elements with present fabrication techniques. This limited spatial resolution can be increased by scanning the detector over the scene. Several techniques can be used for this including macroscan and microscan, but the experimental imager described here uses continuous scan to increase the spatial resolution. Use is made of all the detector elements by employing the CCD readout registers of a fully staring 64 x 64 CMT detector to perform a time delay and integrate (TDI) function in the scan direction.

A continuous programme of development of the TICM II imager has allowed significant improvements in system performance to be realised. Some of these developments are described, concentrating in particular on modifications to the SPRITE detector and associated system components which have led to substantial increases in the thermal sensitivity and spatial resolution.

This review introduced the properties and generation methods for creating phase conjugate images in non-linear materials. Particular emphasis was made on phase conjugation in photorefractive materials but parallels were drawn with other mechanisms such as stimulated Brillouin scattering. The advantages of phase conjugation within optical systems, such as aberration correction, amplification and phase locking, were illustrated with particular optical systems. In conclusion, new methods of self-pumped phase conjugation in non-Brillouin active and non-photorefractive media were described. This will offer the prospect of high speed phase conjugation at moderate powers and over a wide range of wavelengths. Such advances would lead to the commercial viability of optical systems that embody the principle of phase conjugation.

A consideration of the effects of the transducer upon the performance of Acousto-Optic spectrum analysers indicates that significant improvements to current systems can be made by the use of large transducer (high Q) cells in conjunction with novel system configurations. These considerations have lead to extensive work over the last couple of years at the Admiralty Research Establishment on polychromatic r.f. spectrum analysers.

Accusto-optic (Bragg cell) devices are able to perform a wide range of signal processing functions including correlation and spectrum analysis. This paper discusses three Bragg cell architectures which have applications in electronic warfare, radar, lidar and spread spectrum communications. These are a 100 MHz bandwidth time-integrating correlator (TIC), a two-dimensional optical processor for generating the cross-ambiguity function (OAF) and an optical multi path analyser. This paper is illustrated by examples of hardware constructed by Marconi Defence Systems.

Bragg cell spectrum analysers provide interception of simultaneous RF Si gnals over wide instantaneous bandwidths with 100% intercept probability. These properties make them attractive candidates for EW applications. Major issues currently being addressed by Marconi include dynamic range for single and multiple tones, miniaturisation and ruggedisation to meet stringent military specifications. This paper discusses these aspects with respect to both the power spectrum analyser (PSA) and the interferometric spectrum analyser (ISA). The discussion is illustrated by reference to Marconi 's range of Bragg cell receivers.

Electro-optical (EO) remote sensing is becoming more important for a growing range of civil and military applications. To-date the E0 band used spans the ultra-violet to the far infra-red (0.3μm to 14μm). In the military context E0 sensors form a major complementary element to the prime sensor-RADAR. The 2 key features which originally led to E0 being of high potential value are firstly the high spatial resolution possible and secondly passive (le non-radiating) operation. Consequently much research and development effort has been expended world-wide over recent years in producing automatic target-detection sensors with a very high probability of detection and low false alarm rate. Typical targets of interest include: - aircraft and missiles - AFVs - laser radiation - chemical and biological agents.

A method which allows the retention of the shape, size and positional properties of an image at the output of a temporal coherence processing sensor is described. Experimental results are presented which demonstrate the real-time image processing properties of the system for both laser and non-laser inputs.

The enhancement in detectivity of a pre-detector processing system through the maximum utilisation of the intrinsic optical properties of the incident flux is discussed. A number of examples of possible sensor configurations are then described which use both pre and post-detector processing.

The Size Invariant Processor is an optical technique which enhances the detectivity of narrow spectral bandwidth signals whilst simultaneously suppressing broadband background flux. The output format of the device is independent of both signal size and position. The principles of system operation are detailed in conjunction with theoretical and experimental assessments using real scene data. Finally, aspects of optical design are outlined which enhance sensor performance.

There have been many advances in thermal imaging systems and components in recent years such that an infrared capability is now readily available and accepted in a variety of military and civilian applications. Conventional thermal imagers such as the UK common module imager use a mechanical scanning system to sweep a small array of detectors across the thermal scene to generate a high definition TV compatible output. Although excellent imagery can be obtained from this type of system, there are some inherent disadvantages, amongst which are the need for a high speed line scan mechanism and the fundamental limit in thermal resolution due to the low stare efficiency of the system. With the advent of two dimensional focal plane array detectors, staring array imagers can now be designed and constructed in which the scanning mechanism is removed. Excellent thermal resolution can be obtained from such imagers due to the relatively long stare times. The recent progress in this technology will be discussed in this paper together with a description of the signal processing requirements of this type of imaging system.

A wide variety of techniques has been examined in the literature for the detection and segmentation of target objects in images. This paper is concerned with the comparison of a set of alternatives drawn from two generic approaches to the problem. Histogram-based techniques focus on the distribution of some descriptive attribute or set of attributes within the image. The use of several such algorithms is considered including a sampled peak-finding method, a sampled percentile-finding method, multivariate histogramming based on greylevel and edge information and the well-known superspike algorithm. Hierarchical target detection techniques, on the other hand, attempt to exploit links between multiple reduced resolution views of the image. A range of such methods is also described based on the use of both iterative and top-down traversal procedures. Each of the algorithms is discussed, and their performance on a database of synthetic and real infra-red images is compared in terms of segmentation quality and computational cost.

Interest has been rekindled in the potential utility of Ballistic Missile Defence (BMD) systems 1,2 and their ability to enhance the existing NATO strategic defence posture 3,4. Whereas in the past BMD systems have been thought to be vulnerable to relatively simple offence countermeasures, technological developments that have occurred over the past 20 years offer the potential to solve some of the main criticisms that have bedeviled BMD research since its inception in the early 1950s. One of the key areas where dramatic developments have taken place is in the field of electro-optic sensor technologies where developments in device sensitivity and packing density offer new solutions to threat detection, tracking and discrimination that complement data traditionally associated with radar based systems. Analysis has shown 5 that optical sensor systems can make a significant contribution to threat analysis in the boost and mid course phases of flight of ballistic missile systems. In the Boost phase the large amounts of energy contained within the plume of a ballistic missile system provides a signature that must be detected against cloud and earth backgrounds - necessitating viewing from space. The process of detection is complicated by reflected sunlight and other sources of false alarms. The optical sensor systems must therefore be adaptable and capable of reasoning about the location of the signatures, their persistence and temporal variations. Much of this processing is ideally carried out at the sensor system - in order to eliminate false alarms and reduce the communications bandwidths required to transfer the sensor data to centralised early warning and battle management facilities. In the mid course phase optical sensor systems can be used to detect warm objects against the background of deep space. These sensor systems can form tracks on these objects that can be merged into 3D tracks as data from individual sensor systems are combined. As closely spaced objects are resolved by sensor systems feature data can be extracted on individual objects that can be used by the defence system to attempt to discriminate between warheads, decoys and other penetration aids. This paper reviews work that has arisen from joint US SDIO and UK MOD research programmes into the feasibility of Theatre Missile Defence (TMD) systems that would be suitable for deploy ment and operation in a European theatre. The paper focuses on the problems of threat classification and discrimination in TtD systems and highlights the role of optical sensors. The paper discusses the integration of data derived from optical and radar sensors 6 and expands upon work previously reported into the use of an Artificial Intelligence (AI) approach to object classification and discrimination.

The NPL maintains and disseminates a spectral responsivity scale from the VUV to the infrared and has many years' experience of the calibration of optical radiation detectors. The measurement of spectral responsivity of a detector in any part of the spectrum is best divided into two processes: - measuring the relative spectral responsivity over the wavelength region of interest - measuring the absolute responsivity at one wavelength. This makes possible the use of different transfer standards and techniques for the different scales and minimises the uncertainties.

A technique for the high-speed capture of infrared spectral information of radiation emission is described. The development of the technique has led to instrumentation which has been used in the laboratory and field for the analysis of such events as gun flashes and rocket motor exhaust emission. Design features allow the system to measure full spectral characteristics up to 1000 times per second from targets at short or long observation ranges.

An earlier paper (Ref 1) described a scanning radiometer working broadband in the 8 to 12pm wavelength range. The main application envisaged for this instrument was the testing and radiometric calibration of thermal imager test facilities (eg. IR collimator systems for measuring MRTD etc). The present paper describes a recent development of this radiometer which is intended for a much wider range of applications.

This paper discusses the current status of Passive Millimetre Wave Radiometry as an imaging technique. The major problems are poor spatial resolution and lack of thermal sensitivity. Techniques for overcoming these difficulties are identified, including the use of aperture synthesis, multichannel receivers, correlation and inverse transform techniques.

A new measurement facility uses a TICM II thermal imager specially modified by NPL to determine the distribution of emissivity of non-uniform materials and artefacts at near ambient temperature. A dual-reference image processing algorithm is used to provide both image restoration and calibration. Systematic variations of responsivity across the image (fixed pattern errors) such as banding and narcissus effect, which arise from various optical, scanning, detector and electronic defects are completely removed, to the limits imposed by random noise and stability. The algorithm is applicable to greyscale images from any image processing transducer with near-linear response.

Since its launch on February 22nd, 1986, the French earth observation satellite SPOT-1, revolving around the Globe on a heliosynchronous orbit at an altitude of 832 km, has returned over a million 60 X 60 km images with 10 m ground resolution in the Panchromatic mode and 20 m in the Multispectral mode. Among the numerous applications of these observations in such diverse fields as cartography, agriculture, environmental studies, oil and mineral exploration, the use of SPOT imagery for National Defence requirements is increasing, both in France and in many other countries. The capacity to acquire data from all over the globe, and the precision of SPOT panchromatic images, superior to that of other civil observation satellites, are fully exploited for this use. Furthermore, the capacity to obtain stereopairs gives access to terrain relief, and introduces the possibility of producing particularly interesting flight simulations. These different applications in the Defence field are well-adapted to strategic needs and will be illustrated in the presentation by a number of examples. Beyond SPOT-1, the satellites SPOT-2, 3 and 4 will ensure service continuity for the international user community until at least 1998, a service continuity unequalled by any other observation satellite programme.

SPOT 1, the first of a series of high resolution imaging remote sensing satellites, has been successfully launched from KOUROU Space Center, CNES, by ARIANE vehicle on February 22, 1986. After 3 years and a half of in orbit life, the SPOT 1 operational behaviour is quite satisfactory, and no major evolution of image quality has been noticed. After reviewing the SPOT mission objectives and its most crucial parameters, this paper gives a description of the SPOT 1 satellite, the payload instruments and the supporting ground system. Then, the image quality performances are briefly overviewed, both in terms of radiometry and geometry. The continuity of the mission is illustrated through the SPOT 2 and 3 follow-on models, and the SPOT 4 improved version. The SPOT 4 system is presented, with a special emphasis on the major improvements provided.

The Optical Mapping Instrument (OMI) is intended to operate from a low earth orbit spacecraft, such as the Columbus Polar platform, and produce very high spatial resolution images of the ground, suitable for the manufacture of both conventional maps and digital elevation models. The instrument concept is based on the use of two fixed telescopes viewing in different directions along the sub-satellite track. The same area ground is viewed by each telescope within about a minute and a stereo pair of images thus produced. Processing of the images on the ground produces the appropriate cartographic product. OMI operates primarily in the near-infrared part of the spectrum and will produce a spatial resolution of approximately 5m over a swath of 60km. Secondary functions being considered for the instrument are an even better resolution over a reduced field of view, additional spectral bands in the visible and near-infrared, and a high spectral resolution mode.

The ATSR instrument is an advanced imaging radiometer designed to measure global sea surface temperature to an accuracy of the order of 0.3C from the ESA's ERS-1 satellite, due to be launched in late 1990. The instrument is designed to achieve a very precise correction for atmospheric effects through the use of carefully selected spectral bands, and a new "along-track" scanning technique. This involves viewing the same geophysical scene at two different angles, hence using two different atmospheric paths, so that the difference in radiative signal from the two scenes is due only to atmospheric effects, which can then be quantitatively estimated. ATSR is also a high performance radiometer, and embodies two important technological features; the first of these is the use of closed-cycle coolers, especially developed for space applications, and which were used to cool the sensitive infrared detectors. The radiometer also incorporates two purpose-designed on-board blackbody calibration targets which will also be described in detail. These two features enable the instrument to meet the stringent requirements of sensitivity and absolute radiometric accuracy demanded by this application. ATSR also incorporates a passive nadir-viewing two-channel microwave sounder. Measurements from this instrument will enable total atmospheric water vapour to be inferred, which will not only lead to improved SST retrievals, but will also considerably improve the atmospheric range correction required by the ERS-1 radar altimeter. ATSR is provided by a consortium of research institutes including the University of Oxford, Department of Atmospheric Oceanic and Planetary Physics, who are primarily responsible for scientific calibration of the instrument; University College London's Mullard Space Science Laboratory, who are responsible for the development of the blackbodies; the UK Meteorological Office, whose contributions include the focal plane assembly; the French laboratory CRPE, who are responsible for providing the microwave part of ATSR. Some of the industrial development work has been funded by the Department of Trade and Industry. There is also a significant contribution from Australia in the area of digital electronics. The ATSR consortium is co-ordinated and led by the Rutherford Appleton Laboratory.

The current METEOSAT Operational Program will continue its service until 1995, possibly till 1997. Subsequently, the METEOSAT Second Generation (MSG) is planned to replace the current system (similar to the "compatible" US " GOES-Next" and the Japanese GMS follow--on generation as major elements of the global geostationary meteorological satellite systems). The emphasis for this paper is on a 3-axis stabilised platform for MSG, though chances are that the current spin-stabilised concept may be maintained for cost reasons. The instrument described in this paper represents the " core" payload element in either satel-lite version; the total payload is expected to consist of: a Visible/Infrared Imaging Radiometer: an IR Vertical Sounder (IRS) - see subsequent paper. The technical concept for the first instrument, the VIRI, is presented as a result of a study performed on behalf of and supported by ESA/ESTEC (/1/). The Imaging radiometer shall have 2 visible and 6 IR channels for cloud tracking and sea surface / cloud top temperature measurements (compared to currently 3), partly split channels at reduced bandwidth and 2 km IFOV. The paper will present the proposed solution of a " hybrid" scan system, involving 2-axis mechanical scan combined with a North/South fine scan by means of short detector arrays. It should be noted that during the preparation of this paper a revised set of requirements for an imager designated EVIRI (Enhanced VIRI) has been issued in a proposal invitation which can not yet fully be covered within this paper; an outlook to the technical options to incorporate these requirements in § 4.

An IR sounder instrument for the Second Generation Meteosat satellite will be required to measure Earth radiance in a large number of narrow wavebands in the thermal IR region. A design concept for the sounder is described, based on use of a spectrometer to define the wavebands. With significant developments outlined, a spectrometer system appears preferable to the more conventional configurations based only on use of filters.

nulNASA's Hubble Space Telescope is an astronomical observatory to be placed in a nominally circular orbit at approximately 610 km (330nm) altitude, well above the obscuring layers of the atmosphere, by the Space Shuttle in March next year. The Optical Telescope Assembly (OTA) is the core of the Space Telescope and includes the 2.4 metre, f/24, Ritchey-Chretien Cassegrain-type telescope. The Faint Object Camera (FOC) is a long focal ratio, photon counting instrument designed to take high resolution two dimensional images of areas of the sky up to 44 by "44 arcseconds square in size with pixel dimensions as small as 0.0075 arcseconds squared in the 115nm to 650nm wavelength range. Its performance approaches that of an ideal imaging system at low light levels and it will be the only camera on board the HST to utilise fully the unprecedented spatial resolution capabilities of the Optical Telescope Assembly. The FOC is one of the European Space Agency's contributions to the HST programme.

The capabilities of satellite imaging spectrometers, such as ESA's proposed MERIS instrument, are reviewed in the context of how they may be applied in marine science. The increased information content of the spectrally dense measurements promises to be able to discriminate between water constituents having distinct spectral signatures. Evidence of the spectral variability occurring in coastal waters is provided by field spectrometry from Southampton Water. An approach to the analysis of sea-viewing spectral radiance data is outlined. It proposes a function optimisation routine to match the observed spectra with model predicted spectra in order to recover an estimate of the concentration of the optically active water constituents.

In the past Philips USFA has developed different high performance thermal imaging systems. These systems all use the 8-12 micron window, SPRITE detectors and a 2-dimensional scanning system based on the starrotor. Due to the emphasis on high performance this resulted in high cost for these types of systems. A general relative cost breakdown of these high performance thermal imaging systems will be given: optics, detector and cooling, scanning mechanism, electronics, mechanical housing and display. For all these modules the cost decrease using the 3-5 micron instead of the 8-12 micron window was discussed. A cost/performance analysis will be given comparing the high performance systems with the design of the low cost system. The various design features were discussed, such as: - field of view change with changing F-number: in both fields of view full pupil is used - one scanning mechanism using a drum with 10 tilted facets - electronic correction of scanner distortion - modular design - flexibility. Using this design approach models for different applications can easily be realised. At the exhibition a model developed for use in a light armoured vehicle was shown together with a handheld version for various applications.

The development of a compact, low cost, high performance thermal imager is described. This imager is based on a novel coaxial scanning technique designed at RSRE. The paper reviews the essential design requirements for thermal imagers. These include the avoidance of Vignetting and pupil wander in the scanning elements and objective lenses, and the maximising of detector cold shielding. These aims are met by (a) choice of array technology, as exemplified in the UK development of SPRITE IR detectors, (b) use of either the pupil relay optics (as in the UK TICM II Scanner) or the alternative coincident pupils (as in the coaxial scanner). The optical design of the scanner and its implementation in hardware are given along with details of the telescopes, detectors and electronic modules used in the coaxial imager. Direct View and TV compatible outputs are discussed. The paper concludes with examples of the imager in various military applications including RPV's, airborne pods, helicopters and land based sights. Examples of the imagery obtained and the thermal performance of the imager are also described.

The philosophy of the U.K. Thermal Imaging Common Module programme, TICM, envisaged from the outset that future requirements that could not be met by using the basic module suite would be met by developing "stretched" or enhanced versions of the modules. The design of the system took that into account. The philosophy has been completely justified by the success of the many stretch programmes. In the ten years since the first class II imager was produced, the inventory of enhanced, "stretched" modules has grown to include higher sensitivity, improved spatial resolution, alternative line standards, reduced size, multi spectral variants and latterly an all digital version of the imager. This paper reviews those and other related stretch programmes.

Mission Management Department of the Royal Aerospace Establishment has won a Queen's Award for Technology, jointly with GEC Sensors, in recognition of innovation and success in the development and application of night vision technology for fixed wing aircraft. This work has been carried out to satisfy the operational needs of the Royal Air Force. These are seen to be: - Operations in the NATO Central Region - To have a night as well as a day capability - To carry out low level, high speed penetration - To attack battlefield targets, especially groups of tanks - To meet these objectives at minimum cost The most effective way to penetrate enemy defences is at low level and survivability would be greatly enhanced with a first pass attack. It is therefore most important that not only must the pilot be able to fly at low level to the target but also he must be able to detect it in sufficient time to complete a successful attack. An analysis of the average operating conditions in Central Europe during winter clearly shows that high speed low level attacks can only be made for about 20 per cent of the 24 hours. Extending this into good night conditions raises the figure to 60 per cent. Whilst it is true that this is for winter conditions and in summer the situation is better, the overall advantage to be gained is clear. If our aircraft do not have this capability the potential for the enemy to advance his troops and armour without hinderance for considerable periods is all too obvious. There are several solutions to providing such a capability. The one chosen for Tornado GR1 is to use Terrain Following Radar (TFR). This system is a complete 24 hour capability. However it has two main disadvantages, it is an active system which means it can be jammed or homed into, and is useful in attacking pre-planned targets. Second it is an expensive system which precludes fitting to other than a small number of aircraft.

This paper is a synopsis of a feasibility study to determine the potential of staring array infrared detectors for satellite detection with ground or space based systems. It discusses atmospheric irradiance data, and stellar clutter modelling. Irradiance figures for an 8 to 12 um CdHgTe staring array imager system were obtained by imaging planets.

The Air Defence Alerting Device, otherwise known as ADAD, is a passive infra-red system which detects the presence of a potentially hostile airborne threat and relays its bearings to a Close Air Defence Weapon System (CADWS). The equipment is therefore a cueing device which directs a weapon system operator (or his sight) to the bearing of the threat. From an overall weapon system point of view, use of ADAD realises a very significant increase in weapon effectiveness which is greatly welcomed in these times of constrained defence budgets. The ADAD system is believed to be the first of its kind in the world to be procured in production quantities - it will go into service with the UK Army in the early 1990's.

Hydrogen fires emit near zero radiation in the visible waveband : in daylight they are virtually invisible. This is a major safety hazard particularly in the aerospace industry where hydrogen is used as a rocket propellant. A practical imaging system has been constructed to detect non-visible radiation that these fires give off. The emission spectra, atmospheric transmission, background emission and reflection have been quantified under many conditions. This shows thermal wavelengths are well suited for this application. A low cost, uncooled, staring array TV compatible thermal imager has been optimised for this. The resultant image is 'punched through' to superimpose the flame on a bore-sighted visual TV picture. The theory and operation of the imager are explained.

Fibre Optic pressure sensors are playing an increasingly large role in intrusion detection systems. Their inherent characteristics also make them ideal for the battle field environment : small size, difficulty of detection and freedom from environmental noise. Distributed micro bend sensors are already providing the first volume application of optical sensors in the industrial safety field.

Semiconductor laser based optical intersatellite links are attractive for use in both DRS type applications, and as links in the existing satellite-based telecommunications networks (for example between EUTELSAT SMS and INTELSAT IBS business services satellites). Initial ISL experiments will demonstrate direct detection systems using intensity modulation. Coherent systems offer significant improvements over these: the use of frequency shift keying modulation and heterodyne receivers provide significantly improved system sensitivities, which will allow practical systems with reliable laser sources (50 mW CW), and small optical telescopes (20 cm diameter). The SILEX ADD-ON CHANNEL is intended to demonstrate the potential of such systems within the framework of the ESA SILEX program.

A Laser Diode Transmitter Package [LDTP] has been designed to collimate,align and shape the beam from a semi-conductor laser with the following optical beam characteristics: a far-field beam divergence [to the 1/e2 intensity points] of ± 30°, a beam aspect ratio of 3:1, astigmatism varying from 6-10um and wavelength range of 1500-1550nm. The optical package consists of a collimator, null lens, beam anamorphosers and alignment wedges. The optical collimator is based upon a simple Kingslake-type configuration. A detailed study of the collimator has been undertaken analysing the variation of RMS WFE performance with field angle, focal shift, and astigmatism.In addition the manufacturing tolerances have been predicted based upon a maximum allowed RMS wavefront error of X/20. Finally a package integration study has been undertaken which is largely concerned with the integration of the Laser diode block and the collimating lens. This includes an analysis of assembly technique with regard to achieving the extremely tight positioning tolerances required to achieve a X/20 RMS WFE performance.Considerations are also given to the problems of thermal stability, hermeticity, and the effect of ambient to vacuum pressure changes.

The requirements on sources for optical communication links in space are extremely demanding and only two laser types can address these requirements. The first is to use single spatial mode semiconductor lasers as the transmitter itself. The second is to use semiconductor lasers to pump another type of laser such as Nd:YAG or Nd:glass which is then used as the transmitter.

A tunable Wavelength Division Multiplexing [WDM] scheme, suitable for Optical Inter-Satellite Link [OISL] communications, has been designed. The scheme can combine [and separate] four or more beams from laser diode devices in the 800-900nm wavebands and incorporates a number of tunable narrow-band holographic reflection filters. By choosing the correct point source construction geometry the 'tuning' along one direction of the filter can be made to vary approximately linearly with position on the substrate. The advantages of such filters with regard to achieving the tight tuning tolerances [typically <± 0.5nm] required for space communications is discussed. In the DEMUX arrangement a 'double bounce' method is employed to minimise the effect of holographic sidebands on the received noise levels. The overall transmission for the scheme has been predicted for each channel.

This paper discusses the use of long wavelength (1300-1600 nm) semiconductor sources in a single channel digital coherent system operating at 140 Mbit/s and presents the results obtained on experimental systems.

Properties of different CO2-waveguide lasers with output power from 0.1 to 10 Watt are presented. Results of lifetime tests, performance at low and high temperature and measurement techniques to specify the spectral performance will be discussed.

The design and performance of a compact, sealed, high power CO2 waveguide laser in which the basic gain cell can support several different output formats is described. The laser can be operated in continuous wave (cw) mode or with frequency or amplitude modulation (FM or AM) depending on the cut of the CdTe intra-cavity crystal employed. Particular attention is given here to the FM performance of the device where the crystal is subjected to high intra-cavity powers.

Technological limitations have so far restricted the applications of laser light scattering techniques to terrestrial applications, because of size, cost and fragility. Following our recent experimental advances* (based on the use of a new set of solid-state technologies in this field), we will discuss proposed experimental uses of miniaturised laser light scattering systems in the microgravity environment. Non-invasive particle-size capability can be applied to new experiments where the absence of sedimentation and convection is crucial. Precision non-invasive velocity measurement has many potential uses, from flame studies to fluid-flow inventories.

The sizes, costs and fragility of gas lasers and photomultipliers have limited the applications of laser anemometry. Following our recent work with miniature all-solid-state laser anemometers*, we will describe a system for use in confined spaces in hostile environments. In particular we have been concerned with pressures to 25 Bar and high vibration. Operation range is up to 0.5m and with flow velocities up to 20ms-1, useful in many hydrodynamic studies. The velocimeter is packaged in a stainless steel cylindrical canister with an end-face optical port. Particular care is needed in the coupling of these two components. Problems of traversing the measurement volume, aberration-correction and calibration are central to its successful operation.

The design of a laser rangefinder based on a frequency doubled Co laser is described. An AgGaS2 crystal is used to double the output of a Co2 laser from the 9.4 micron band to 4.7 microns. A monostatic approach is adopted in the design of the rangefinder and a cooled CMT detector is used to detect the return radiation.

This paper describes the evaluation of diode-pumped Nd:YAG lasers as sources in multiplexed interferometer systems.

A space-qualifiable electrooptic phase modulator for broadband CO2 laser communications (wavelength 10.6 μm) was developed under ESA-contract in cooperation with the Institut fur Nachrichtentechnik and Hochfrequenztechnik / Technische Universitat Wien. The concept of a traveling wave modulator with an oversized optical waveguide -3 constituted by eight Cadmium-Telluride crystals in a row with 30x0.6x0.6 mm each - was employed to achieve the following performance data: electrical bandwidth 2 GHz, maximum VSWR 1.75: 1, optical transmittance > 80%, optical power handling 6 W cw, modulation efficiency 12.5% for 20 W RF drive power, modulation frequency response : ±1 dB up to 1GHz. In a follow-on ESA contract, Schrack Aerospace and the Institut fur Nach-richtentechnik and Hochfrequenztechnik cooperate to develop an intensity modulator for Nd: YAG laser radiation at 1.06 pm with the following specifications: maximum data rate 1 Gbit/s, optical transmittance > 76 %, optical power handling 1 W cw, 100% intensity modulation with 8 W RF power and 13 dB dynamic extinction ratio.