Spaceborne remote sensing observations ar used to obtain better understanding of cloud properties and cloud physics. To validate and supplement the satellite observations, continuous cloud measurements have been made by a groundbased network (CDS) located in the Netherlands. The spatial and temporal variability of cloud cover has been compared extensively with collocated synoptic observations. Frequency analysis of groundbased and spaceborne radiometer signals identify cloud layer temperatures within the area. CDS provides a powerful database that comprise tow years of different atmospheric conditions, from which a.o. cloud cover, cloud top, cloud base, optical thickness, IR emissivity and LWP can be obtained.

Abstract not available.

The Global Ozone Monitoring Experiment (GOME) on board the ERS-2 satellite is an across-track nadir-viewing spectrometer which measures solar light reflected from the Earth's atmosphere and surface in the UV visible. The cloud retrieval algorithm presented here combines spectral threshold test on GOME's broad-band radiances with the fitting of reflectances to GOME's moderately high resolution spectra in and around the O₂ A band to retrieve cloud- cover fraction, cloud-top height and cloud optical thickness. The algorithm utilizes the latest O₂ spectroscopic data and features dynamical updating procedures to provide global threshold sets of GOME reflectances. Auxiliary information is obtained from GOME measurements of the Ring effect and the degree of polarization of the Earth's radiation field.

A method is presented for inferring the microphysical and radiative properties of vertically inhomogeneous cloud layers from high spectral resolution measurements of emitted thermal radiation. The algorithm iteratively estimates vertical profiles of liquid water content and effective droplet radius by comparing spectral radiance observations with calculations from a multiple scattering IR radiative transfer model. Theoretically consistent spectral emissivity and effective temperature values are determined from the resulting cloud vertical structure. The influence of cloud vertical inhomogeneity on the retrieval is discussed.

In this work, a method to estimate the emissivity distribution is developed for stratocumulus clouds paying special attention to water vapor over these clouds. The main aim is to obtain an approximate distribution of effective radius for optically thick stratocumulus clouds. This method is based on night imagery obtained from the NOAA-AVHRR IR channels, and an atmospheric radiative transfer model that makes use of the discrete ordinate method called DISORT. We have solved the problem of the local estimation, for the Canary Islands, of the influence of the water vapor over the stratocumulus level. Finally we associate the emissivity distribution with the distribution of the droplet effective radius. This allows us to estimate a unique effective radius for the cloud taking advantage of statistic in the image in order to avoid the non-monotonous behavior of emissivity with the droplet effective radius in the 3.7 micrometers band. The results are compared with satellite data from NOAA-14.

In this work, a method for the retrieval of droplet radius, temperature and optical thickness of oceanic stratocumulus is developed.It is based on night imagery obtained from the NOAA-AVHRR IR channels and an atmospheric radiative transfer model that makes use of the discrete ordinate method called DISORT. Using this mode, we have simulated the theoretical radiance that reaches the satellite supposing a planar homogeneous cloud layer. The stratocumulus clouds are assumed to be composed by spherical water droplets with a gamma size distribution that provides a particular effective radius. The single scattering parameters are deduced from Mie's theory. Once evaluated the model behavior, we must invert a non lineal system of three equations to obtain the cloud parameters from the channels, 3,4 and 5 brightness temperatures. The main problem is the behavior of the radiative parameters when the effective radius is varied, because exist several values that provide the same temperatures. That implies that the systems have not a unique solution and, in order to avoid this problem we propose an optimal radii discretization on the basis of the above-mentioned microphysical features.

Along Track Scanning Radiometer-2 (ATSR-2) measurement made over tropical cirrus clouds are analyzed on the basis of radiative transfer calculations for clouds consisting of hexagonal ice crystals. Single scattering properties are calculated using the geometrical-optics approximation and ray-tracing techniques. The imperfect shape that is usually found in real atmospheric ice crystals in mimicked by applying a random variation in photon paths at air/ice interfaces. Multiple scattering is calculated on the basis of the doubling-adding method. The ATSR-2 measurements are analyzed at a non-absorbing and an absorbing wavelength and for nadir and forward viewing direction. The measurements reveal that for small optical thickness the relationship between the reflectivities at the two wavelengths considered is highly linear, whereas for increasing optical thickness the gradient decreases and eventually vanishes. This characteristic pattern can be well reproduced by the model using a stratiform cloud consisting of imperfect randomly oriented columnar ice crystals of type 'C2'. The variation in crystal size across the optically thick part of the cloud system is modest.

The inversion of TIROS-N Operational Vertical Sounder measurements by the Improved Initialization Inversion (3I) Algorithm provides cloud parameters as well as atmospheric temperature and water vapor profiles. By the use of a cirrus radiation scheme based on Anomalous Diffraction Theory, that includes analytical expressions for extinction and absorption coefficients as function of ice particle shapes, size distribution parameters and wavelength, we study the possibility to infer information on cirrus microphysics at global scale from 3I data.

Beginning of 1998, Aerospatiale, SOCATA, ONERA and LAMP made in situ microphysical and Infrared measurements on cirrus clouds from a TBM 700 aircraft able to fly up to 35,000 ft. The ice particles images and the cloud particles scattering phase function were measured to validate radiative transfer model. An airborne IR Cyogenic Spectrometer measured the IR spectral radiance from above cirrus in the wavelength band from 1.5 micrometers to 5.5 micrometers . The flight path of the airplane was computed and recorded to perform in situ microphysical measurements followed by IR measurements at different grazing angles.

The far-IR spectral region is very important in the Earth Radiation Budget for the considerable cooling of the atmosphere by the strong rotational band of the water vapor. This effect can be modulated by the presence of cirrus clouds. The heating rate in cloudy conditions have been examined using a two stream approximation with a new parameterization of ice and water optical properties, which accounts also for the scattering effects of the ice particles. In the spectral region from 100-1000 cm^-1 cirrus clouds act as a heating source which affect the layers in which they are located. The behavior changes when they are completely opaque. The largest signature in the Heating Rate is fond in 400-600 cm^-1 and in the atmospheric window. There is a moderate heating/cooling effect in layers close to the clouds: the general picture is a warming below the cloud and a cooling above.

The far IR spectral region is fundamental for the understanding of the earth's radiation balance, in particular because of a strong cooling to space due to the water vapor rotation band and continuum. Cirrus clouds play an important but poorly characterized role in this spectral region. Using a line-by-line code to model at high resolution the atmospheric transmittance, in association with a multiple scattering radiative transfer scheme, we simulate the impact of cirrus clouds on the atmospheric heating rates in the spectral region from 100 to 1000 cm^-1. Compared with clear sky conditions, we find that cirrus clouds induce a heating from the ground to the cloud base at all wave numbers. Within the cloud, a heating effect occurs in the window region, whereas a strong cooling occurs in the far-IR. The particles' shape are modeled with either a size distribution of spheres or randomly oriented spheroids. We show that, for a range of different ice water path and particles, size, for a same average volume of ice per particle, spheroids have a bigger impact than spheres at all wave numbers on the cooling/heating rates as well as for the top of the atmosphere radiances.

The effect of cirrus clouds in the IR has been simulated at high spectral resolution and the sensitivity to crystal, size, aspect ratio, size distribution and cloud ice water path, has been investigated. The single scattering parameters of the cloud particles were determined using Mie theory for distributions of spheres and the T-Matrix method for spheroids. Cloudy-sky radiances, fluxes and atmospheric heating rates were calculated using the discrete ordinates multiple scattering code, with clear sky atmospheric transmission determined using the GENLN2 line-by-line code. It can be seen from these results that both the volume and the cross section of the cirrus particles are important in determining the spectral variation of the radiance and fluxes and also affect their spectrally integrated values. This implies that particle aspect ratio is a radiatively important parameter in the IR. In order to further investigate these differences, singular value decomposition analysis was carried out on seventy spectra calculated for the 700-2500 cm^-1 spectral region using spheroids of different size and aspect ratio for a range of cloud ice water paths.

In this paper, we present a retrieval algorithm for nonlinear retrieval problems based on regularization theory. The proposed method is based on the Gauss-Newton method for nonlinear least square problems. In the proposed algorithm, Tikhonov and truncated singular value decomposition techniques are used to regularize the solution of the linearization problem used to compute the Gauss-Newton search direction. The dependency of the performance and behavior of the proposed algorithms on the initial guess, stopping criterion, and regularization parameter is studied by means of simulations. Results are presented for atmospheric temperature retrievals based on radiometry from the HIRS/2 and MSU instruments in NOAA TOVS.

Radiation transport modulates the spatial frequencies of atmospheric structures, acting as a low pass filter, which causes the power spectra of the accumulated radiance to have different power spectral slopes than the underlying atmospheric structure. Additional effects arise because of the non-stationarity of the atmosphere. The SHARC atmospheric radiance code is used to model both non- stationarity of the atmosphere. The SHARC atmospheric radiance code is used to model both equilibrium and non- equilibrium radiance and radiance fluctuation statistics. It predicts two dimensions. Radiance spatial covariance functions and power spectral densities, PSDs. Radiance power spectral slopes for paths through isotropic Kolmogorov turbulence are predicted to vary from -5/3 to -8/3 depending on the length of the path through the turbulence. The input gravity wave 3D covariances and PSDs of atmospheric temperature are consistent with current gravity wave theory, having vertical and horizontal power spectral indices of -3 and -5/3, respectively. Altitude profiles of variances and correlation lengths account of the non-stationary of the gravity wave structure in the atmosphere. The radiance covariance and PSD power spectral slopes differ from the atmospheric gravity wave temperature model values of -3 and -5/3. These modulations depend on LOS orientations, and scale lengths of the sampled altitudes along the LOS.

Knowledge of water cycle in the atmosphere is very useful for several climatological and meteorological applications. This work presents a forward model of atmospheric emission in clear sky conditions, over Mediterranean sea. Solving a polarized radiative transfer scheme, brightness temperatures at the top of atmosphere were calculated. By fitting such temperatures against those measured by he SSM/I microwave radiometer effective vertical profiles of atmospheric water vapor were retrieved. Eventually, total precipitable water values were estimated. These values were compared with those obtained through statistical well-known algorithms from SSM/I brightness temperatures. The reported procedure was applied on a dataset, made up of Mediterranean scenes acquired during summer. The present work showed the feasibility of obtaining total precipitable water estimates as accurate as statistical ones; moreover, this approach provides information about the effective vertical atmospheric temperature, pressure and water vapor profiles, that allows this procedure to be more flexible and reliable, both form a spatial and a temporal point of view. Therefore, we characterized the presented research, calibrating our procedure for the Mediterranean area: a relative poor region, as far as field observation are concerned.

An empirical technique to blend satellite imagery into a conventional meteorological analysis has been developed in order to enhance the 3D humidity field in a numerical weather prediction model. Temperatures retrieved from IR Meteosat images are used to locate and grossly characterize clouds, and this information further employed to dry and moisten individual atmospheric cells from a previous conventional analysis. To verify the improvements attained with this technique, we have compared a set of 260 forecasts obtained with a conventional initialization of the mesoscale model MASS, and those from the enhanced initialized. Standard indexes, such as mean error, k root mean squared error and S1, have been used to objectively evaluate the quality of the forecasts over the Southwestern European region. It turns out that the inclusion of satellite imagery in the initial analysis leads to improvements up to 30 percent in more than 200 out of the 260 days considered over the typical meteorological fields. Although for several reasons no attempt has been made to compare complex fields such as precipitations, it is obvious that an improved depiction of the driving fields might result in better weather forecasts.

A new method is proposed to solve inverse problems with new types of a prior partial information about physical parameters to retrieve. The partial information are relative to integrals of the functions over an arbitrary range of a variable, and/or first and second derivatives of desired functions. They might be provided either form common features of desired solutions or from independent measurements. This inverse problem was solved in the framework of the iterative inversion method under the assumption of log-normal probability density function of measurements. As a typical example of the approach, we examined particle sizing of stratospheric aerosol from multi-wavelength extinction and angular aureole measurements in the visible.

The calculation of synthetic spectra in the absorption bands of molecules and aerosols and their iterative comparison with measurements is a fundamental background for many studies of planetary atmospheres. A radiative transfer simulation technique is described that will be applied to retrieve atmospheric and surface properties from IR radiation measurements recorded by a Planetary Fourier Spectrometer in an orbit around the planet Mars. A prestored set of temperature and pressure dependents absorption cross- sections which is based on quasi-monochromatic line-by-line calculations is used to predict the transmission functions of CO₂, H₂O and Co at 2.0 cm^-1 spectral resolution in a layered atmosphere. Aerosol absorption and scattering efficiencies for palagonite particles, which are considered as one of the most likely candidates to explain the observed Martian dust features, are determined from laboratory data on refractive indices by applying Mie subroutines. Synthetic IR spectra of the Martian radiance and brightness temperature have been valued in the 200-8000 cm^-1 wave number range for a variety of atmospheric models and surface reflectance features including aerosol multiple-scattering based on a successive order technique. The 15 and 2 (Mu) m CO₂ bands are used to retrieve temperature profiles and surface pressure simultaneously, while the 2.0 and 2.7 micrometers bands allow to separate radiance contributions from atmospheric dust emission and surface reflectance. Aerosol optical depths in the thermal IR are determined in the 8-13 micrometers window region. A first application of the radiative transfer and retrieval codes is shown for selected thermal emission spectra recorded by the IRIS instrument on-board the Mariner 9 orbiter.

GOMETRAN/SCIATRAN is a radiative transfer forward model developed for retrieval of atmospheric trace gas concentrations, aerosol and cloud parameters, and surface reflectance from the spectral radiance measurements of the SCIAMACHY/ENVISAT-1 and GOME/ERS-2 UV-Vis-NIR multichannel spectrometers. For radiative transfer modeling of the line absorptions of O₂, H₂O, CO₂, CH₄, N₂O, and CO, tow different schemes are under development: an accurate but rather slow line-by-line (LBL) implementation and a significantly faster correlated-k (c-k) distribution scheme. The c-k scheme has been matched to the resolution of the instruments, which is channel dependent. In spectral regions free of overlapping line-absorbers the multiply scattered radiance calculated with both, the LBL and the c-k scheme, agrees within 1-2 percent. Calculations in c-k mode are a factor of 25-800 faster depending on spectral interval. Good agreement has been found with the MODTRAN/DISORT radiative transfer model. First results concerning a new method are presented indicating that overlapping line-absorbers can be modeled with similar accuracy and speed as single line-absorbers.

The SAGE III is the fourth generation of solar occultation instruments designed to measure aerosols and trace gas species in the stratosphere and upper troposphere. It will be launched aboard a Meteor-3M platform in the summer of 1999 and the International Space Station Alpha in 2001. SAGE III preserves the robust characteristics of the SAGE series, including self-calibration and high vertical resolution, and adds new capabilities including a lunar occultation mode. This paper will describe the SAGE III instrument and outline its potential contribution to global change research.

We have determined the vertical integrated water vapor of the atmosphere based on the absorption features of the 940- nm band by means of ground-based measurements of direct solar spectral irradiances and modeled ones. The experimental irradiance data were performed under clear skies with a LIcor 1800 spectroradiometer, based on a monochromator system, of high to moderate spectral resolution in the 300-1100 nm range. The modeled data are based on the monochromatic approaches for atmospheric transmittance constituents, where for water vapor we used the band-model transmittance of LOWTRAN7 code. The method here used is a curve fitting procedure making use of the whole shape band absorption information and the contribution of molecular and aerosol constituents retrieving a unique water vapor value. The method were used to determine water vapor values for the period from March to November of 1995 at a rural station in Valladolid under different atmospheric conditions. The contribution of continuum absorption was also evaluated in the retrieval, obtaining lower values from 13 to 30 percent. This contribution appears as considerable greater than those expected.

In this work, we present a methodology to obtain the daily net radiation flux from NOAA-AVHRR data. To get this objective we need firstly to obtain shortwave net radiation flux from the solar global radiation flux and the albedo map. Secondly, we need to obtain the upward longwave radiation flux from surface temperature and emissivity and the downward longwave radiation flux from air temperature. Like an example of application of this methodology a daily net radiation flux image of the Iberian Peninsula is presented, in which we show that daily net radiation flux can be obtained with a satisfactory precision lower than 1.0 mmday^-1.

Despite cloud recognition techniques that can routinely identify cloud classes form satellite images, observation of clouds from the ground is still needed to acquire a complete description of cloud climatology. Solar radiation in a given site is one of the meteorological magnitudes that are most affected by cloud cover. Presently, the number of stations where both global and diffuse total solar radiation is measured is growing, due basically to energetic applications of solar radiation. Global and diffuse hourly irradiation, along with some measure of the temporal variability of solar radiation, are used in this paper to describe the sky condition, and to classify it into several cloud types. A classical maximum likelihood method is applied for clustering data. One year of solar radiation data and cloud observations at a site in Catalonia, Spain is used to illustrate the ability of solar radiation measurements to describe cloud types. Preliminary results of the above methodology show that three clusters appear using global and diffuse hourly irradiation only. Fog, stratus, and stratocumulus from the first group. A second group includes altocumulus alone or mixed with other clouds, as well as scattered cumulus congestus. In a third group, we find clear skies, cirrus and scattered cumulus. Especially in this third group, variability of solar radiation within an hour helps to separate different situations.

The visible near IR and thermal channels of ATSR-2 on the ERS-2 satellite series provide a means for retrieving radiative and physical properties of tropical cirrus clouds. Utilizing the instruments multispectral and dual-look capabilities, retrievals of optical depth, particle size and ice water path are possible, as well as cloud temperature and IR optical depth. Results using ATSR-2 data are presented for five areas in the tropics, averaged over a one month period, subject to quality controls. The retrievals were made at a 12 by 12 pixel resolution, and the output result presented at a 1 by 1 degree grid size. Preliminary comparisons with ice water path model produces from the Hadley Centre, UK have been made.

Lidar equation has been derived for the case when the anisotropy of a scattering medium is assumed to be weak to introduce any essential distortions into the wave front of a sounding radiation. It is shown in the paper that this equation may successfully b used when interpreting data of lidar sensing of crystal clouds in the atmosphere.

A polarization backscattering phase matrix for oriented semitransparent plates is given in the present paper. The matrix elements have been numerically investigated. Regular dependences have been established of the matrix elements on the orientation angle of particles with respect to the sensing direction, the orientation angle of the polarization plane, and the refractive index of particles. An algorithm has been developed for determining the refractive index and the orientation angle of ice plates from the data of polarization lidar sensing for two-angle sensing geometry. A formula has been derived that relates the main parameters of the medium with the backscattering coefficient that can be used for interpretation of highly intense lidar return signal.

Two approaches are used to study the ratio r of radiative forcings at the top of the atmosphere (TOA) and at the underlying surface. According to regression approach to r determination, the cloud random geometry has little effect on the ratio of radiative forcings. The other approach assumes that r depends not only on absorption change due to occurrence of clouds in the clear atmosphere, but also no associated albedo alternations at TOA. For this reason, the r difference between cumulus and stratus clouds, while being small at low surface albedos A_s <EQ 0.2, may increase by tens of percent as A_s increases for optically thin clouds and small cloud fractions when solar zenith angle (xi) (direct sum) <EQ 30 degrees. After the ratio of radiative forcings is averaged over the entire set of cloud optical and geometrical characteristics, the dependence of r on cloud type becomes much weaker.

The Global Ozone Monitoring Experiment (GOME) aboard ESA's ERS-2 satellite measures the reflected and backscattered radiation from the Earth in the UV/visible spectral range at moderate spectral resolution. Vertical ozone profile distributions can be derived form top-of-atmosphere nadir observations using the Full Retrieval Method FURM, which is based upon an advanced Optimal Estimation inversion scheme. During the Arctic spring seasons 1997 and 1998 hemispheric ozone profile distributions have been derived from GOME observations. In 1997 the polar vortex formed late in winter and record low temperatures were reached in late March. In the lower stratosphere depleted levels of ozone were observed by GOME. From vertical ozone distributions inside the polar vortex obtained on 24 days between 9 March and 16 May 1997, chemical ozone loss rates in the lower stratosphere are estimated. The lower stratospheric temperatures in spring 1998 were comparable to the longterm mean and the polar vortex was relatively weak. Preliminary results from this period are also presented. In both spring seasons ozone mini-hole events, which are characterized by intrusion of ozone poor subtropical air into mid and polar latitudes, were observed. From transects of GOME orbits the 2D structure of the zone mini-hole can be studied in detail.

Ozone profiles on a global scale can be derived form GOME satellite data by minimzing the difference between the measured and the corresponding simulated spectra as a function of the vertical distribution of O₃. For this purpose the FUll Retrieval Method was developed, which is based on the optimal estimation approach and contains the radiative transfer code GOMETRAN as an essential component. The quality of the Gome ozone profiles is assessed by comparing them with coincident ozonesonde, lidar, and SAGE II measurements. The comparison results show good agreement at mid-latitudes in winter and spring. For measurements performed at low solar zenith angles GOME tends to overestimate the ozone content at the altitude of the ozone maximum and above. This systematic effect is most probably due to errors in the radiometric calibration of the GOME spectra.

Estimation of Sea Surface Temperature (SST) from split- window algorithms for NOAA-AVHRR data can be determined with rms values of 0.7 K on a global basis. However, this figure is not compatible with the stringent accuracy of 0.3 K required by climate studies. Among the different sources of errors, the presence of tropospheric aerosols in the satellite field of view prevents the retrieval of accurate satellite SSTs. Still, the effect of aerosols on temperature measurements derived from remote sensing techniques has been traditionally overlooked. Very few studies have addressed the problem of giving split-window algorithms which incorporate aerosol correction, although retrieving algorithms of the aerosol loading from the images do exist. The aim of this study is the evaluation of the effect of the aerosols on the SST MODTRAN code. Such code was used to compute the upwelling radiances and, subsequently k, the brightness temperatures under cloud-free conditions. The filter response functions for the NOAA14 instrument are used to produce theoretical brightness temperatures for the zenith angles: 0 degrees, 30 degrees and 55 degrees. The results show that for most of all the atmospheres that we have considered, deviations as far as 0.8 K are reached compared with the case in which the aerosols are not considered. It is important to point up that deviations higher than 0.4K are able to mask the improvement introduced by a diminution of the Noise Equivalent Temperature in the new sensors as a consequence of error propagation.

We present a preliminary study of the urban effects on the aerosol optical thickness. Since Valencia is close to the sea, the measurement campaigns were carefully planned in order to separate urban effects and the sea's influence. Measurements of spectral direct irradiance were taken simultaneously at rural continental, rural coastal and urban coastal sites. The distance between these locations was 50 km. The measurements were obtained using three Li-cor 1800 spectroradiometers provided with a radiance limiting tube with afield of view of 4.7 degrees. All the measurements were made under clear sky conditions. In order to avoid the uncertainties associated with the determination of the water vapor content and the other atmospheric constituents, the analysis of the optical thickness values was limited to the 400-670 nm band. The result corresponding to the aerosol optical thickness at wavelengths of 400 and 550 nm are presented. An analysis of their evolution with the optical air mass and of their relation with the characteristics of the wind and the relative humidity at ground level is also made.

We develop a PIM-based functional for stochastic tomography with a Kalman filter, which aids in the regularization of the inversion problem associated with 4D ionospheric stochastic tomography. We let the GPS data select dynamically the best PIM parameters, in a 3DVAR fashion. We collect GPS data from GPS/MET and IGS for one of the World Space Days and we ingest them in a Parameterized Ionospheric Model (PIM). The process selects the ionospheric parameters that best fit the PIM model. We then compare our deduced ionospheric parameters with the values provided by the US National Geophysical Data Center. The resulting PIM-fitted model is compared to direct 3D voxel tomography. We demonstrate the value of this method analyzing IGS and GPS/MET GPS data.

Through this paper the authors propose a new approach for volcanic aerosols detection by satellite. By using only NOAA/AVHRR data at hands the proposed method seems able to detect eruptive volcanic clouds as well as long-period trends in stratospheric aerosol loading related to major eruptive events. Several examples of application to different events of volcanic emission are presented; some cases of Etna and Stromboli volcanoes have been investigated and an historical analysis has been performed in order to recognize stratospheric aerosols produced by Mount Pinatubo's eruption. In all cases the technique was able to detect anomalous particle loading in atmosphere, in an automatic way, without need of any specific transmittance model for the atmosphere or ancillary ground-based measurements. The main merit of this new approach is its effectiveness in recognizing field anomalies also in the presence of a highly variable background as well as its intrinsic exportability ensured by the use of thresholds which are local but automatically generate by using only satellite data at hands. By this way the proposed technique can be numbered among the others environmental applications of RAT approach in which it finds its origin.

Direct solar irradiance spectra under clear skies have been carefully measured in a rural station in the region of 'Castilla y Leon' of typical continental climate during 1995 in order to determine the physical and radiative characteristics of atmospheric aerosols in this area. About 300 spectra have been performed with a LI-1800 spectroradiometer with a spectral resolution of 6 nm from 300 nm to 1100 nm and a wavelength sampling of 1 nm. This high-moderate spectral resolution allowed us to retrieve the experimental spectral aerosol optical depth (AOD) using spectral windows of non-absorption modeling it by the Angstrom formula. These modeled AOD spectra was taken, instead of the experimental one, in order to determine the columnar particle size distribution of atmospheric aerosols using the Mie theory and a pseudo-inversion method. We have assumed a monomodal lognormal function with a fixed standard deviation of (sigma) equals 2.5 and two particle refractive indices based on climate characteristics of our continental are of study.

Satellite remote sensing of atmospheric properties is important for investigation of atmospheric pollution and also for remote sensing of the underlying surface, where an atmospheric correction is needed. For the proof of new methodological concepts the multispectral imaging spectrometer MOS was developed in the DLR Institute of Space Sensor Technology and launched on the Indian satellite IRS- P3. It has 13 bands in the VIS/NIR region with 10nm bandwidth. MOS successfully provides data for more than 2 years over European and Northern African coasts. The paper will introduce a standard atmospheric correction scheme for MOS data over water regions using measurements in the near IR form 685 nm to 1000 nm. This method is based on a 2- channel correction, estimating the aerosol optical depth and the Angstrom coefficient for the spectral behavior of the optical thickness. After extrapolation of the visible region the atmospheric correction is applied. Examples will be shown from the Baltic and North Sea regions. The obtained result will be compared and discussed with available in situ measurements taken simultaneously with MOS overflights. Lastly, this algorithm is applied to an observation of forest fire smoke over Malaysia.

GOME is the first satellite instrument with the possibility to retrieve height-resolved ozone densities in both stratosphere and troposphere. The high accuracy and spectral resolution of the GOME spectrometer in the range of 240-790 nm combined with sophisticated retrieval algorithms enables the derivation of accurate ozone profiles. This paper discusses in detail the retrieval procedure of ozone profiles from the GOME observations. The resulting profiles and their calculated errors are discussed and compared to local ozone profiles form ozone sonde measurements.

The GOME was launched on the European Space Agency's ERS-2 satellite on April 20, 1995. GOME measures the Earth's atmosphere in the nadir geometry, using four spectrometers that cover the UV and visible at moderate resolution, employing silicon diode array detectors. GOME takes some 30,000 spectra per day, obtaining full global coverage at 40 X 320 km² resolution in three days. It provides measurements of ozone, NO₂, SO₂, H₂CO, H₂O, BrO, ClO, and OClO. We directly fit GOME radiance spectra using nonlinear least-squares analysis to obtain column amounts of several trace species, including ClO, BrO, SO₂, and H₂CO. The use of recent improvements in the underlying physical and spectroscopy permits the fitting of radiances to very high precision, approaching 2 X 10^-4 in favorable case, for standard 1.5s integration time GOME measurements. Examples of the fitting of BrO and SO₂ are presented here.

The Earth Explorer Earth Radiation Mission proposed by the scientific community for the ESA Earth Explorer line of missions will provide for the first time a multi-year set of cloud profiling and aerosols observations to progress in understanding the transport of energy and water between the Earth's surface and the top of the atmosphere. A backscatter lidar and a cloud profiling radar will be used separately, in complement and synergy to provide these profiles that will be extended across track by a visible-IR cloud imager and a two-channel broadband radiometer, from a satellite at around 400 km altitude. The mission is unique for the combination and capability of its sensors and for its utilization.

The first CERES instrument has been placed in orbit on the TRMM Spacecraft. This instrument is designed to measure the Earth's radiation budget and also the anisotropy of reflected solar radiation and outgoing longwave radiation. The TRMM orbit and the combination of CERES with other instruments aboard the spacecraft provide a unique opportunity for a number of scientific studies. Results from the on-board calibration system compared well with ground calibrations. Data products include radiant fluxes at the top of the atmosphere', surface reflected solar and longwave radiant fluxes and cloud-radiative interactions.

REFIR is a Fourier Transform Spectrometer designed to measure the upwelling IR Earth's emission from space in the spectral range 100 to 1000 cm^-1 with an unapodized spectral resolution of about 0.5 cm^-1. One of the main scientific objectives of REFIR is to monitor the far IR planetary emission and the principal drivers of this emission, with particular attention being paid to the poorly understood mid and upper troposphere. The expected retrieval performance for temperature and water vapor profiles, from a subset of REFIR measurements, is evaluated and presented in this paper.

We have analyzed international GPS Service for Geodynamics (IGS) data and GPS/MET occultation data with the GIPSY-OASIS II package and our tomographic software to study the ionospheric electronic content. During the period of February 20, 21 and 23, 1997, when AS was off, IGS permanent network data as well as GPS/MET used to extract sub- TOPEX/POSEIDON Total Electron Content (TEC) fields. The resulting global maps of the ionosphere were compared against TOPEX/POSEIDON ionospheric correction data showing good agreement. We emphasize that delays produced in the GPS signal above TOPEX/POSEIDON's orbit can be a source of bias in TEC estimates, and that techniques which are able to discriminate vertically the ionospheric electron content, such as the one described here, are required. We show that tomography improves TEC estimation below the radar altimeter on board TOPEX/POSEIDON by accounting correctly for the protonospheric contribution of the GPS delays. Other approaches which exist for estimating TEC are discussed and compared. Our results suggest the feasibility of absolute ionospheric calibration of Radar Altimeters using the tomographic technique described here.

A cloud radar detection algorithm has been developed to assess the optimum methodology for determining cloud coverage. The radar model was used with cloud data obtained from satellites and within cloud measurements. Form this it was found that the value of returned cloud cover for example is critically dependent on the detection threshold and radar pixel size used. Detection thresholds that minimize the difference between this returned cloud cover and true cloud cover were then found. These were discovered to be strongly dependent on the pixel size but not greatly dependent on the true cloud cover.