The Defense Meteorological Satellite Program (DMSP) satellites currently in orbit are designated the Block SD-2 series. Characterized by on-board processing and near full redundancy, the Block 5D-2 design provides a stable, highly reliable platform for a sophisticated sensor suite. Under both solar and lunar illumination conditions, the payload instruments provide visual radiances with very high dynamic range, as well as calibrated radiances in the infrared and microwave spectral regimes. Additional space environmental sensors provide in-situ measurements of electrons and ions, energy distribution of charged particles, and changes in the local magnetic field. The DMSP mission sensor digital data is now available from the National Geophysical Data Center in Boulder, Colorado. The future 5D-3 spacecraft, currently in production, will be a larger structure with increased power and weight capability to accommodate a greater payload, including a combined microwave sensor providing imaging and temperature and moisture profiling in one instrument. New space environmental instruments observing in the ultraviolet spectrum will improve specification ofthe ionosphere. On 5 May 1994, the U.S. President directed convergence ofthe Department ofDefense (DOD) DMSP system and the Department of Commerce (DOC) National Oceanic and Atmospheric Administration's (NOAA) Polar-orbiting Operational Environmental Satellite (POES). The Integrated Program Office (IPO) was formed to implement the merger and develop a single system, the National Polar-orbiting Operational Environmental Satellite System (NPOESS), to provide data for U.S. civil and defense as well as international needs. Negotiations between NOAA and EUMETSAT are underway for an interim Joint Polar System (JPS). This is proposed to be a two-satellite constellation in which one satellite is POES and one is from EUMETSAT. In the timeframe ofNPOESS, it is anticipated that continued cooperation with EUMETSAT will lead to a three-satellite JPS constellation, in which two are NPOESS and one is from EUMETSAT.

The Support of Environmental Requirements for Cloud Analysis and Archives (SERCAA) program is a two phase basic research program to develop techniques for analysis of multi-source multi-spectral satellite sensor data for the purpose of estimating cloud fractional amount, location, height, and type. In the first phase, cloud analysis algorithms were developed for each imaging sensor. A major innovation was an analysis integration approach to combine the separate algorithm results from the temporally, spatially, and spectrally inconsistent sources into a single logically consistent analysis. In the second phase, work includes algorithms for retrieval and estimation of the cloud physical and optical properties such as phase, drop size distribution, optical thickness, and emissivity. Also under investigation are cloud environment parameters including vertical profiles of temperature and moisture available from sounding sensors.

This paper presents a quantitative comparison oftwo cloud detection techniques using satellite observations. The AVHRR (Advanced Very High Resolution Radiometer) Processing scheme Over cLouds Land and Ocean (APOLLO) makes use of five spectral channels with a spatial resolution of I .I km. The Collocated BIRS/2 and AVHRR ProductS (CHAPS) operates with more spectral channels but a lower spatial resolution. To reference the satellite derived cloud amounts, APOLLO results are compared with surface observations of cloud amount. The APOLLO cloud amount and surface observations of cloud cover are generally within over vegetated surfaces. Over oceans, the agreement in total cloud cover between the two satellite techniques is very good (r=O.92). Application of a dependent sample i-test to the two cloud amount data sets indicates that there is a greater than 99.9% probability that the two samples were drawn from the same population. This demonstrates that the subsampling of AVHRR pixels in the CHAPS processing is appropriate for deriving cloud amounts over a 2.5degree oceanic region. For such a region there is a tendency for CHAPS to derive higher cloud amounts than APOLLO. This is attributed to differences in clear-sky radiance thresholds derived from the CHAPS spatial variability test. Over land, the derived cloud amount products from the two methods are considerably different. The CHAPS product is an effective cloud amount defined for each HIRS field ofview which is the product of cloud fraction and cloud emissivity rather than a simple areal percentage. Also, the HIRS/2 footprint size (17 km at nadir) is much larger than that of the AVHRR. There is a good correlation of the two cloud products (r=O.82); however, a t-test indicates the two techniques are deriving fundamentally different parameters. This is consistent with the above differences. Recommendations for improving the two cloud retrieval techniques are suggested.

The ATSR-1 is an infrared radiometer designed principally to measure sea surface temperature from space to an unprecedented accuracy (<0.3 K) to meet the needs of the climate research community. To achieve this, a conical scan is employed resulting in two views of the same surface scene; a 'nadir' view with a zenith angle at the surface of between 0 and 25°, and a 'forward' view with a zenith angle from 52 to 55°. Upwelling radiance at wavelengths centred around 1 .6, 3.7, 1 1 and 12 jim are measured at each view angle for a nominal surface pixel size of approximately 1 km (the forward view pixels are about twice as large because of the geometry). Thus the atmospheric effect on the radiances can be removed and the sea surface temperature measured by using both spectral and multi-path information. The 1.6 jim channel operates only during the daytime (at the expense of the 3.7 tm channel) and is included primarily to aid in the cloud-clearing process. ATSR-2, launched June 1995, carries additionally, three visible wavelength channels; 0.55,0.67 and 0.87 rim. These were added to meet the growing needs of the land resources research community. This paper explores some of the possibilities offered by ATSR-1 and -2 data for retrieval of cloud microphysical and bulk parameters.

In this paper, a fast and accurate method is proposed for two cloud detection tests on thermal infrared( IR) images over sea obtained from Along-Track Scanning Radiometer(ATSR); an JR gross cloud test and a spatial coherence test. The proposed method is based on a regional segmentation technique. After the segmentation of an JR image, small regions were regarded as cloudy due to their high spatial variability in temperature. This technique preserved the spatial resolution of the detected cloud image which would be degraded by the conventional spatial coherence test. It also reduced the computation dramatically compared to the conventional spatial coherence test. An accurate temperature threshold between clear sea and clouds was determined directly from the segmented image. This post-determined threshold was tested to be more accurate than pre-determined temperature thresholds. Since this algorithm does not require any human interaction, it can be combined with other tests in an automatic cloud detection algorithm.

While considerable effort has been expended on research into the analysis of optically-thin cirrus clouds, the global detection and accurate identification of these clouds remains inadequate, especially in daytime meteorological satellite imagery collected over land surfaces. Recently, 1.38 micron imagery was recommended for the improved detection of thin cirrus clouds. Since this channel is centered on a strong water vapor absorption band and watervapor is concentrated in the lower atmosphere, solar energy normally reflected by the Earth's surface is absorbed in the 1.38 micron spectral band. Thus, any energy measured by an airborne (or spaceborne) radiometer should originate from scattering off of mid-level water and high-level ice clouds, making even thin cirrus readily detectable. While initial results have been encouraging, quantitative analyses are needed to assess the value of 1.38 micron imagery as a candidate for the next generation of meteorological satellite sensors. Thus, this project investigates the potential for improved thin cirrus detection in daytime imagery using scenes of nearly coincident Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) sensor data, which collects 1.38 micron imagery, and imagery collected by the operational NOAA AVHRR sensors. Automated cloud analyses from these data are compared against manual (ground truth) cloud analyses for each data type. Initial results show that 1.38 micron imagery is valuable for improved thin cirrus detection over land surfaces.

Radiance fields provided by geostationnary satellites are fundamental for the knowledge of the spatial heterogeneity and life cycle of clouds and cloud systems. However, detection and analysis of the cloud cover properties from VIS and/or JR radiance field is not obvious 1,2 and numerous methods, giving sometimes quite different results, have been proposed 3. In the present paper, we introduce a new parameter in the classification scheme we developed before 45 : the slope of the regression line between visible and infrared radiances. Moreover, studying the time evolution of cloud classes requires to ensure the classification consistency from one hour to the other. A new way of initializing the classification process is proposed and tested on a time series of Meteosat radiance fields taken over North Atlantic and West Europe during the 1989 ICE experiment. The 10 day cloud classification built is compared with the Cl climatology cloud cover. The time persistence of high clouds is studied and maps of the frequency of occurence of different cloud classes are built from the previous analysis. After isolating high cloud cells on the classified images, a description of the shape and radiative properties of these individual cells is undertaken. Preliminary results on cloud cell size distribution are presented.

Subvisual cirrus is defined as optically thin cirrus with visible optical depth □ 0.05. This includes threshold subvisual cirrus as defined in the literature. Subvisual cirrus is associated with at least five different dynamical phenomenon in the atmosphere. These associations are: 1) equatorial, 2) frontal, 3) jet stream, 4) orographic and 5) other types. Characteristic properties of each cirrus association derived from observations reported in the literature are provided. Rough estimates of the effects of subvisual cirrus on vertical profiles of atmospheric radiances show that these clouds have the potential to significantly affect sensor performance.

The Intensive Field Observation of E1TCREX 94. (EUropean Cloud and Radiation EXperiment) held in April 1994 in Brest, France. was a three-aircraft and ground-based experiment dedicated to the development and the validation of algorithms to derive relations between cirrus radiative properties and cirrus microstructure from remote sensing measurements. A niultiangular visible radiometer with polarization capabilities called 1OLDER (POLarization and Directionality of Earth Reflectances) was installed doviiward. on-board the instrumented German Falcon of the DLR. This aircraft was also equipped with upwar(l and downward pyra.nometers and pyrgeometers and with PMS probe. The second instrumented aircraft was the ARAT (French Fokker 27 of INSU). It was equipped with the upward lidar LEANDRE (\ = O.53jtm), with a photometer POLDER looking downward, an(1 with upward and downward infrared radiometers (;\ E [9.5gm - 11.5um]) and upward and downward pyraliometers and pyrgeometers. During the upward and downward observations of the Fokker under cirrus, the Falcon performed optical measurements above and microphysical measurements i uside clouds. A ground-based station with Lidar, infrared radiometric and sunphol.omet.er measurenients w'as also operating during the same time. The third aircraft was specially devoted to the low level clouds and was equipped with a Fast FSSP, upward and downw'ard pyia noiieters and pvrgeometers and upward and downward infrared radiometers. During this intensive field of observations. four well documented cirrus cases were observed from aircraft and from the ground. Ana1ve of these observations is I)resented by comparison to a radiative transfer calculations. These calculations are performed taking into account the optical properties of hexagonal ice crystals obtained by a. ray-tracing method. All theses observations allow to determine a. bulk Properties of cirrus clouds in particular a. ra.dia.t.ively equivalent microstructure.

This article deals with a comparison between dust fluxes simulated with a physical emission scheme and satellite observations of desert dust emissions. This physical scheme allows to quantify the dust emissions as a function of the parameters describing the surface characteristics in the source-region: soil nature (size-distribution and mineralogy) and surface roughness. The surface properties of the western Sahara have been mapped on a grid (1°xl°), using a geomorphologic approach, in order to determine the soil parameters required to perform large-scale simulations of dust emissions. The surface wind velocities are supplied by the analyses of the European Centre for Medium Range Weather Forecast (ECMWF). The western Sahara proves to be strongly non-uniform as to the threshold velocities and the related dust emissions. The spatio-temporal distributions of the emitted dust simulated by the model and the Infrared Difference Dust Index (IDDI) derived from Meteosat observations reveal a close agreement, far from being reached when using the currently used single threshold source-functions. A quantitative relation is observed for the emission strength, in the form of a linear fit between the IDDI and the logarithm of the mass flux simulated by the dust production scheme.

The retrieval of cloud optical depth and particle radius is relatively straightforward for water clouds over low-albedo surfaces during the daylight hours. Under these conditions the nearly orthogonal relationship between optical depth and effective radius at one absorbing and one non-absorbing wavelength (e.g., the AVHRR 0.6 and 3.7 micron channels) can be exploited. However, high latitudes are characterized by highly-reflective surfaces and many months without solar radiation. The bright surfaces give rise to multiple solutions for thin clouds, and the long polar night precludes the use of shortwave channels. Thermal bands are therefore used to resolve the ambiguity when there are multiple solutions in the shortwave retrievals and to provide a solution when there is no solar radiation. But thermal methods must account for another unknown: the cloud height. Investigations using modeled radiances for a range of cloud heights show that two pairs of three thermal channels at 3.7, 11, and 12 microns can be used to obtain a unique solution. Unfortunately, validation data are not yet available so we assess the accuracy of these methods using estimates of surface radiative fluxes.

We present several case studies of thermal observations of cirrus using the Along Track Scanning Radiometer (ATSR) nadir and 55° forward view aboard ERS-1 (Earth Resources Satellite). We examine the potential of ATSR for retrieval of thermal optical depth at. 3.7, 10.8 and 11.9 tm and cloud temperature at 11.9 jm under absorption and scattering approximations. Ice crystal size is estimated by applying Mie theory under the assumption of spheres and Anomalous Diffraction theory (ADT), assuming hexagonal columns, plates, rosettes and planar polycrystals. The estimated particle sizes are compared using the two theories under assumed conditions of absorption and scattering. The potential use of the dual look capability of ATSR-2, with its additional visible channels at 0.55, 0.66, and 0.865 m, and advanced ATSR (AATSR) for crystal shape and size determination at 0.55 and 1.6 jm is demonstrated. For semi-transparent cirrus the difference in backscattered solar radiation at nadir and forward views is sensitive to ice crystal habit which is demonstrated using representative ice crystal phase functions (columns and polycrystals). The sensitivity to ice crystal size is examined using the forward view at 0.5 and 1.6 ,am for columns and polycrystals.

An automatic method is presented for extracting a microphysical index (related to the ratio of cloud absorption coefficients) of cirrus clouds from thermal infrared AVHRR data (11 jtm and 12 im). The processing scheme makes use of the optical properties of ice particles at the two wavelengths and of the relationship between emittance and transmittance of semitransparent cirrus clouds. The retrieved microphysical index is characteristic of the optical properties of ice particles and allows to explain the high Brightness Temperature Differences measured between AVHRR channel 4 and 5. Assuming that cirrus clouds are composed of ice spheres, the effective diameter of the particles can be deduced from this microphysical index. The retrieval scheme has obvious limitations. First, in order to perform the processing over a geographic zone, both (i) overcast semitransparent cimis cloud pixels, (ii) overcast opaque cirrus cloud pixels, and (iii) cirrus free pixels must be observed in this region. Such systems are frequently found on (50x50) - (200x200) Km2 regional scale. Secondly, for multilayered cloud systems, the processing is only able to derive the microphysical index related to the semi-transparent part of the coldest cirrus layer that contains the smallest particles. Finally, the determination of effective diameter beyond 60 .tm is no more accurate. The treatment is applied to 21 NOAA1 1-AVHRR images acquired during International Cirrus Experiment (ICE'89) on the North Atlantic and Europe region from 10 to 20 October 1989. This statistical approach shows that for cloud top temperature less than about 230 K, effective mean particle diameter is always greater than 20 jim, while warmer cirrus clouds contain, on an average, smaller particles.

Empirical relationships between cloud ice water path and their infrared absorption optical thickness are derived. These relationships are obtained using direct radiometric measurements of ice cloud optical thickness in the infrared atmospheric transparency "window" 10-1 1.4 jim and values of ice water path retrieved from the combined radar and radiometer measurements. Cloud particle bulk density and their characteristic size have a major influence on the correspondence between cloud optical thickness and ice water path. The relationships were obtained for several observational cases during the FIRE-il and ASTEX experiments and reflect vertical structure of cloud microphysical parameters. These results can be used for modeling longwave radiative impact of ice clouds.

The SAGE Ill and ILAS instruments are scheduled to be launched in 1998 and 1996, respectively. These instruments will provide unique information regarding the composition and size distribution of poiar stratosphere clouds. SAGE ffi, scheduled for a METEOR 3M launch, will provide aerosol extinction measurements at 7 wavelengths in the visible and near-infrared (385, 450, 525, 750, 940, 1020, and 1550 nm) from which the aerosol size distribution may be inferred. ILAS, which will be launched aboard ADEOS, will provide continuous spectral coverage between 6 and 12 tim. Extinction by aerosol at these wavelengths is strongly dependent on the composition of the aerosol. The combination of measurements from these instruments should provide substantially improved understanding of the microphysical character of PSCs and, ultimately, into ozone depletion.

The Polar Ozone and Aerosol Measurement [POAM II] instrument has been measuring the vertical distribution of aerosols, poiar stratospheric clouds [PSC], ozone, as well as several other atmospheric species since autumn 1993. The approach used to identify PSCs and polar mesospheric clouds [PMCs] from POAM II measurements will be described along a presentation of some of the early results of this high altitude cloud measurements. It is believed that the POAM II measurements of PMCs represent the first reported observations of PMCs directly by extinction; all previous observations utilized scattering.

Atmospheric spectra to be recorded in the infrared spectral range by a spaceborne Fourier transform spectrometer using a nadir view have been simulated. Relevant spectral domains have been selected for the retrieve of carbon monoxide, methane, ozone and nitrous oxide. A new inversion algorithm using neural networks techniques is proposed to retrieve integrated contents and low resolution vertical profiles.

The Measurements of Pollution in the Troposphere (MOPJTF) instrument is a spaceborne gas correlation radiometer designed to measure CO and CH4 in the troposphere. This instrument has been selected to be on board of the Earth Observing System's first platform, EOS-AM, which is scheduled for launch in 1998. A maximum likelihood retrieval algorithm has been selected for the MOPITT CO measurement in clear sky conditions. Performance of the algorithm has been evaluated. This paper describes the algorithm and presents the preliminary results of numerical retrieval experiments.

Weather forecast-models need spatially high resolutioned vertical profiles of temperature and dewpoint for their initialisation. These profiles can be supplied by a combination of data from the Tiros-N Operational Vertical Sounder (TOVS) and the imaging Advanced Very High Resolution Radiometer (AVHRR) on board the NOAA polar orbiting sate!- lites. In cloudy cases the profiles derived from TOVS data only are of insufficient accuracy. The stanthrd deviations from radiosonde ascents or numerical weather analyses likely exceed 2 K in temperature and 5Kin dewpoint profiles. It will be shown that additional cloud information as retrieved from AVHIRR allows a significant improvement in theaccuracy of vertical profiles. The International TOVS Processing Package (ITPP) is coupled to an algorithm package called AVHRR Processing scheme Over cLouds, Land and Ocean (APOLLO) where parameters like cloud fraction and cloud-top temperature are determined with higher accuracy than obtained from TOVS retrieval alone. Furthermore, a split-window technique is applied to the cloud-free AVHRR imagery in order to derive more accurate surface temperatures than can be obtained from the pure TOVS retrieval. First results of the impact of AVHRR cloud detection on the quality of the profiles are presented. The temperature and humidity profiles of different retrieval approaches are validated against analyses of the European Centre for Medium-Range Weatherforecasts.

Regular, long-term, g1obalscale measurements of atmospheric minor gaseous and aerosol composition (MGAC) by means ofdifferent instruments (PHOENIX, OZONE-MIR, ISTOK-1, DOPI) are planned on board the SPECTR and PRIRODA modules of the Space Station MIR during 1995-1998. The main characteristics of these devices are given. The principal goals of the space experiments are: investigations of the spatial and temporal MGAC variations, comparisons of different space-borne atmospheric chemistry sensors and their intercalibration, validation of the space MGAC measurements using different ground-based station and aircraft data, and studies of the molecular absorption in the atmosphere aimed to enhance an accuracy of radiative transfer atmospheric models. Special attention is . devoted to radiative transfer model (line-mixing, line-shift, line-narrowing, Non-LTE effects). The numerical estimations of the errors of the MGAC vertical profile retrievals using different device data are carried out.

FASE is a line-by-line (LBL) atmospheric radiation code, grounded in the original USAF FASCODE (Fast Atmospheric Signature Code) line shape decomposition algorithm. The Department of Energy Atmospheric Radiation Measurement (ARM) Program and the AF/PL Geophysics Directorate jointly supported FASE which now envelops both agencies' important upgrades. ARM's LBLRTM (LBL Radiative Transfer Model authored by S.A. Clough and P.D. Brown of AER, Inc.) expanded the FASCODE algorithms to specifically address scientific and coding issues of particular concern to the climate community including: H20 and C02 continua, lineshape, radiance algorithms, sampling, vectorization, array parameterization, spectral ranges and inputloutput modes. These features have then been recombined with FASCODE non- LTE and laser options, plus shared common elements from MODTRAN (Moderate Resolution Transmittance Model, a 2 cm- band model) evolution. These include a new solar irradiance and UV cross sections. Examples of the feedback and validation between FASE and MODTRAN3 will be presented.

Retrieving of temperature profiles from radiance data obtained by interferograms is an important problem in remote sensing of atmosphere. The great amount of data to process and the ill-conditioning of the problem demand objective procedures able to reduce the error of the retrieval. In this paper we use Generalized Singular Value Decomposition (GSVD), which is able to deal with deficient-rank smoothing functionals in order to regularize the problem and the L-Curve criterion for choosing the optimal regularization parameter and then the proper amount of smoothing. Some test problems of temperature inversion are carried out to examine the effectiveness of the methods considered; to this purpose we use some indicators based on the bias and variance of the output temperature. We show that the objective L-Curve criterion does not perform fully satisfactory in estimating the optimal regularization parameter and then in reducing output error at best. In any case GSVD plus L-Curve criterion prove effective in reducing output error (with respect to the ordinary least squares method). In particular, reduction of variance over troposphere and stratosphere is high for all tested cases; reduction of bias depends on the first-guess profile. An important role in the latter is played by the choice of deficient-rank smoothing functional.

A new model of radiative transfer in a cloudy atmosphere NUALUM has been developed at ONERA. NUALUM uses the Discrete Ordinates Method. This code includes multiple scattering in clouds and takes into account the azimuthal distribution of radiation. NUALUM allows geometry and microphysics of the cloud to be varied (particle size, concentration, top and bottom altitude). The parameterization of a cumulus cloud with NUALUM is compared with airborne measurements performed by ONERA and CELAR: circularvariable filter cryogenic spectrometer SICAP (1.5-5.5 j.tm) and airborne infrared camera CIRAP (3-5 pm and 8-12 tm) aim at the same point of the cloud top. The observation azimuthal angle is variable. SICAP spectral measurements show great variations of the radiation with the azimuthal angle which are in agreement with NUALUM simulations. The correlation between the infrared radiation images CIRAP and mean calculated radiation is satisfactory.

The radiative properties of cirrus clouds are of wide interest because of the visually striking effects they produce, the significant global coverage of cirrus and thin cirrus, and their intrinsic complexity. Within a limited class of crystal shape and size, hydrodynamic forces tend to orient the crystals with their long axis nearly horizontal, which can produce a narrow, intense specular reflection. First-principles scattering calculations are especially difficult because the scatterers are diverse in shape, size and tilt distributions. However, a geometric optics approximation to the single-crystal BRDF combined with plausible distributions of flutter-angle can be used to both simulate the appearance of the specular radiance feature, and extract microphysical cloud information from imagery of the specular point. This paper will review an empirical approach to radiative-transfer in the specular layer and integrate two different models for the specular BRDF into a cloud radiance simulation code. This will then be used to illustrate the appearance of the subsun and Bottlinger's ring for various spectral bands. The extraction of microphysical information on the specular layer from vis - near-ir cloud imagery will then be discussed.

The Earth radiation budget experiment (ERBE) was developed to provide a complete temporal and spatial coverage of the solar reflected and Earth emitted radiation. ERB measurements were resumed in 1994 by the Scanner for Radiation Budget (ScaRaB) mission on a single sateffite. Due to sparse temporal sampling, diurnal variations must be accounted for in order to establish accurate unbiased daily and monthly mean radiant exitance. When the ERBE diurnal interpolation algorithm is used alone, large discrepancies are shown between monthly mean radiative flux of single and multi-sateffite measurements. We extend the algorithm by accounting for diurnally varying cloud cover and thickness using ISCCP data. Significant improvements are found in regions where clouds have a pronounced diurnal cycle.

Statistics of brightness temperatures from the water vapor (WV) band channel of Meteosat 2 (5.7- 7. 1pm) from July 1983 through July 1987 are analyzed. All measurements (clearor not) are used to produce monthly and lOday averages. The ISCCP cloudiness retrieval is used to assess the cloud influence on the monthly WV brightness temperatures. The regional repartition and the interannual variations of different cloud types are compared with the global WV brightness temperatures. The main problem is the scattered presence of very thin clouds. But generally speaking, the warmest spots in monthly WV images are related with clear or low cloudy skies while the coldest areas correspond to clouds whose top is above 440 hPa. To confirm these results, a clear sky image has been synthetised using a cloud clearing algorithm. The WV statistics are then used to characterize seasonal and interannual variations of both the ITCZ (coldest spots) and the subtropical subsidence areas (warmest spots). Because the seasonal variations of both phenomena are generally larger than their interannual changes, the seasonal cycle of WV radiances is used to study relationships between the intensity and the extension of the ITCZ compared to the dry subtropical areas. It is shown that, for the Meteosat sector, a wetter subtropical high troposphere is associated with an enhanced activity of the JTCZ, and vive-versa. This result seems to indicate a positive water vapor feedback in this particular region.

In satellite remote sensing ofclouds andthe atmosphere, theknowledge ofthe scattering behaviour of different irregularly shaped particles is of particular interest. Though there are various methods for describing nonspherical scattering, we want to present a formalism which is applicable to a variety of particles with non-separable geometries. This formalism uses the Method of Lines to solve the Helmholtz equation and results in a numerical generalization of the Mie theory for separable boundaries. In our contribution, we focus on nonspherical, axisymmetric scatterers and infmitely extended cylinders with non-circular cross sections. Separable geometries are included as borderline cases.

MSTI-III is the third in the Miniature Sensor Iechno1o' Integration series of satellites originally conceived of and developed by BMDO and now being conducted by the US Air Force1. As the name implies, the MSTI . satellites are members of the class of satellites which have come to be known as "smalisats" or, alternatively, as "lightsats". The satellite is tentatively planned for launch in early 1996 into a sun-synchronous orbit which will allow the satellite to revisit a given region at the same solar time, that is, at the same solar illumination conditions. Among the objectives ofthe MSTI-III mission is the characterization of the optical properties of clouds in the mid-wavelength infrared (MWIR), short-wavelength-infrared (SWIR), and visible spectral regions as a function of spectral band, latitude, season, cloud type, cloud altitude, and solar scattering geometry. MSTI-III is planned to be operational for a minimum of one year to ensure the collection of a statistically significant data base. MSTI-III will also image the EartWs limb and surface. Radiometric characterization and calibration completed in Aug 1995 indicate that MSTI-III will provide high-spatial-resolution infrared images with high signal-to-noise ratios, based upon the scene radiances predicted for the planned measurement modes from existing models or estimated from empirical data. The data-collection experiments planned for MSTI-III and the utility of the MSTI-III data base for the validation and development of cloud, atmospheric, and surface radiance models are discussed.

The radiometer CLIMAT is a highly sensitive field instrument designed for multispectral thermal infrared measurements. Ground-based measurements can be performed. but the instrument has capabilities for operating from aircraft or balloon. The optics consist of an objective lens and a condenser mounted according to the Koehler principle to provide uniform irradiation over the detector surface. The radiometric signal is treated by a fast thermopile detector characterized by a low noise and a very weak temperature dependence of its responsivity. The managing system allows either manual or automated measurements. The energy consumption of the instrument is optimized for a maximum autonomy. The optical and electrical units of the instrument are described. Different experimental studies for measuring the sensitivity accuracy, spectral characteristics, thermal behavior and, field of view of the instrument are described. The instrument is dedicated to ground and vegetation on the one hand. and on the other hand, clouds and atmospheric soundings. The radiometer is also designed for calibrations or analyses of satellite radiometry data. Some atmospheric measurements obtained with a prototype are presented. Prospects are the development and the qualification of a narrow field-of-view instrument adapted to inhomogeneous targets such as cirrus clouds. A 3.7-tim channel and an internal blackbody are under study.

A review of the development status of high-Ta transition edge thermometer bolometers is given with emphasis on the excess HTS film noise. It is shown that Si3N4 membrane technology should enable the production of 1 x 1 mm2 size bolometers with a Noise Equivalent Power (NEP) smaller than 3 x 1O_12 w/4f.

In this contribution we shortly review the current Fabry-Perot concept for remote sensing of stratospheric OH and in more detail a number of sensitivity aspects. In this context the following topics will be addressed: imaging aspects, instrument throughput and signal to noise optimisation, diffraction and the application of small detector arrays instead of an image slicer. A separate paper is given on the review and optimisation of bolometric detectors.

This paper describes an all-sky photometric complex being developed at the Institute of Atmospheric Optics, Siberian Branch of the Russian Academy of Sciences, Tomsk. The complex is intended for the observation of distribution of scattered solar radiation over the sky. Also given in this paper are description of an operating model of such an all-sky photometer and some preliminary results of observations. The solar radiation scattered in the atmosphere is one of the important sources of information about the optical and physical state of the atmosphere.1 The development of means for observation of the atmospheric state based on recording of the solar radiation scattered in the atmosphere remains urgent now. Means for diagnostics of the optical and physical states of the atmosphere in real time on the basis of angular brightness distribution with allowance for the parameter variations as functions of elevation angle and time are of special interest not only for scientific research, but also for meteorological and ecological applications.2 T1i is the objective to be pursued by the development of the all-sky photometric complex.

The database application system is developed to improve the selection of aerosol parameters for radiation transport calculations. The user has to choose location and time for his simulation calculations. The system presents proposals for the height dependence of optical properties of aerosols as graphics. Depending on the user requirements ofthe simulation calculations the user may manipulate the data content (e. g. variation of the mixing ratio, number of aerosol components, humidity, height distribution, wavelength range). As one option the output of the database system can be immediately used for MODTRAN calculations.

The results of floodlight sounding of atmospheric layers with spatio-oriented nonspherical particles are represented in this paper. It is shown that components obeying the regularities of diffuse scattering and specular reflection occur in the scattered radiation as a result of interaction of the directional optical radiation with such a layer. Depending on observational conditions the intensity of specularly reflected component may be several times higher than the intensity of radiation diffusely scattered in the same direction.

The generalization of classic Lorentz -Lorenz formula (LLF) is obtained for effective perrnittivity of a medium with non -point correlated particles. It follows from the regular procedure developed, and takes into account particle correlations. Instead of polarizability of point dipole it contains the T -operator of scattering on non -point scatterer. When this operator is taken in dipole approximation and all correlation are neglected, it reduces to LLF. In the case of rarefied media it gives known results, described by van de Hulst formula.

The retrieval ofthe non-LTE ro-vibrational populations ofthe CO2 molecules and line source functions has been performed from numerically simulated high resolution limb spectra in the 15 m and 4.3 p.m spectral region, which imitate the limb radiance measurements to be obtained by the MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) experiment on board the European Space Agency's ENVISAT- 1. The possibility of retrieving kinetic and vibrational temperatures in the middle and upper atmosphere from the values of populations and source functions is studied.

The French-Russian-German 4-channel ScaRaB (Scanner for Radiation Budget) instrument operated on board the Russian Meteor-3/7 satellite from February 1994 to March 1995. Earth Radiation Budget (ERB) detenninations depend on the two broad-band channels -an unfiltered total (TW) channel sensitive from 0.2 to at least 50 gm, and a short-wave (SW) channel in which a fused silica filter cuts off sensitivity at about 4 jim. In-flight SW calibration depends on lamp sources which may drift or fluctuate. Because daytime LW determinations depend on a weighted subtraction of SW from LW measurements, SW calibration errors will affect the results and can induce a spurious diurnal cycle in the LW. The relative SW sensitivity of the TW and SW channels can be checked, independently of on-board SW lamp sources, by using the ScaRaB JR window (IRW : 1O.5-12.5jim) channel and insisting on diurnal/nocturnal LW consistency. Both the IRW channel and the LW portion of the TW channel are calibrated by reliable on-board black bodies. Results for the first several months of ScaRaB operation are presented, considering also the difficulties arising from the thermal radiation in the near-IR portion of the SW channel. These results are compared with those obtained using the on-board lamp sources. They show that these two methods are complementary: iamps allow accurate monitoring of short-term gain fluctuations while the geophysical method ensures reliability oflamp calibration over the monthly time scale.

Using spectral imaging data acquired with the Airborne Visible Infrared Imaging Spectrometer (AVIRIS) from an ER-2 aircraft at 20 km altitude during various field programs, it was found that narrow channels near the center of the strong 1 .38-jim water vapor band arevery effective in detecting thin cirrus clouds. Based on this observation from AVIRIS data, a channel centered at 1 .375im with a width of 30 nm was selected for the Moderate Resolution Imaging Spectrometer (MODIS) for remote sensing of cirrus clouds from space. The sensitivity of the 1 .375-jim MODIS channel to detect thin cirrus clouds during the day time is expected to be one to two orders of magnitude better than the current infrared emission techniques. As a result, much larger fraction of the satellite data is expected to be identified as being covered by cirrus clouds. In order to make better studies of surface reflectance properties, thin cirrus effects must be removed from satellite images. We have developed an empirical approach for removing/correcting thin cirrus effects in the 0.4 - 1.0 j.tm region using channels near 1 .375 tim. This represents a step beyond the detection of cirrus clouds using water vapor absorption channels.

Although polar stratospheric clouds (PSCs) are a critical component in the ozone depletion process, their timing, duration, geographic extent, and annual variability are not well understood. The goal of this study is the development of an automated classification scheme for detecting PSCs using NOAA AVHRR data. Visual interpretation, density slicing, and standard multispectral classification detect most optically thick PSCs, but only some thin PSCs. Two types of automated techniques for detecting thin PSCs are being investigated: namely, multispectral classification methods, including the use of texture and other imagederived features, and back-propagation neural networks, including the use of hyperspatial and hypertemporal data. UARS CLAES temperature and aerosol extinction coefficient data are being used as a verification dataset. If successful, this classification scheme will be used to process the entire record of AVHRR data in order to assemble a long-term PSC climatology.

Highly accurate absorption cross-sections, k (cm1atm1), have been measured in the 7.8 ,m band of CFC- 14 (CF4) at temperatures between 180 and 296 K using a high-resolution Fourier-transform spectrometer. The measured absorption cross-sections are free from instrumental distortion, since the spectra were recorded at spectral resolution that was sufficiently high at broadening pressures corresponding to tropospheric and stratospheric layers. Our data were obtained at pressures and temperatures which characterize commonly adapted model atmospheres and represent tangent heights in solar occultation type remote sensing observations of the atmosphere, have also been extended to conditions to be encountered in the atmosphere at Arctic and Antarctic latitudes. The combined absolute intensity of the bands contributing to the absorption around 7.8 m is 1.926 0.012 x 1016 cm molecule .