The results of model study for CO₂ retrievals from numerically synthesized GOSAT (Greenhouse gases Observing SATellite) observation data are presented. The GOSAT is scheduled to be launched in 2008 to monitor column amounts of CO₂ and CH₄. A nadir-looking Fourier-Transform Spectrometer (FTS) of Short Wavelength Infrared (SWIR, 1.6 μm and 2 μm) and 0.76 μm oxygen A-band regions will be mounted on GOSAT. To assess CO2 sources and sinks, the monthly averaged CO2 column amounts estimated by satellite-based measurements should have a precision of within 1% or better to provide an advantage over existing ground-based measurement networks. This study focuses on CO₂ retrievals in the presence of cirrus clouds. An important feature of this problem is to apply radiance data measured in several spectral channels. In particular, 1.58 μm spectral band was utilized for CO₂ total column amount retrievals. The cloud correction was performed using an original approach that is based on the application of the equivalence theorem with parameterization of photon path-length probability density function (PPDF). The PPDF parameters were estimated using nadir radiance in the oxygen A-band and in the H₂O-saturated area of the 2.0 μm spectral band.

The Ozone Mapping Detector (OMAD) on board FASat-Bravo micro-satellite observed backscattered UV radiation to retrieve atmospheric ozone with low-spatial-resolution (150 x 150 km). This relatively coarse resolution with continuous global coverage allowed the observation of the seasonal ozone layer depletion over Antarctica in the austral spring in 1998. Previous analysis of this instrument have shown agreement in the radiances observed by OMAD and NASA's Total Ozone Mapping Spectrometer (TOMS-EP); these have even indicated the detection of an apparently higher ozone content anomaly due to a volcanic cloud of Nyamuragira volcano during its eruption in October 1998 [1]. A new improved version of the simplified algorithm used in OMAD data has been applied to the austral region to determine the total Ozone content. The new data processing allowed the observation of the development of the ozone depletion in 1998 from September to early December when ozone depletion normally occurs. The OMAD results showed good agreement overall when compared with those obtained from TOMS-EP despite their intrinsic instrumental differences. Results indicate Ozone contents lower than 150 Dobson Units (DU) in the Antarctic region with absolute errors less than 10 % in the vertical column content and high cross-correlations when compared with TOMS-EP. The value of this low-cost earth observation approach is discussed on the potential of such missions to provide additional atmospheric observations of large-scale phenomena.

The wide range of products available from AIRS have made it invaluable as a tool for operational weather forecasting and climate modeling. AIRS has improved the 5 day forecast by 6 hours in the NCEP operational system and researchers have identified further improvement potential by assimilation of more channels and footprints. AIRS data have been used to validate the distribution and transport of water vapor and greenhouse gases in climate models, resulting in the identification of significant errors in the handling of these quantities. We present the AIRS Version 5 products and their accuracies and reference key papers involving their use. We also touch briefly on the limitations of AIRS due to its coarse spatial resolution, particularly in achieving boundary layer sensitivity.

The aim of this paper is to characterize the aerosol loadings, their optical and microphysical properties over Morocco, by use of the AERONET network and satellite data. Three AERONET stations in Morocco; Saada, Ras_El_Ain and Dakhla are considered in this work. The aerosol parameters studied are the aerosol optical thickness, the Angstrom parameter, the size distribution, the single scattering albedo and the refraction index. An inter-comparison with satellite data has been achieved. The most popular satellite products, TOMS (Earth Probe and OMI), MODIS and MISR have been considered. It comes out from this study that the mean aerosol optical thickness (550 nm) vary from 0.22 to 0.3, with a peak in summer time of 0.56 for Dakhla, 0.42 for Ras_El_Ain and 0.35 for Saada. The Angstrom parameter mean is 0.6 for Dakhla and 0.75 for Saada and Ras_El_Ain with a summer minimum of 0.32 for Dakhla and 0.55 for Saada and Ras_El_Ain. The size distribution is bimodal with a predominance of the coarse mode except for Saada in winter and autumn. This region depicts desert dust predominant environment with a single scattering albedo varying from 0.72 to 0.96. Saada and Ras_El_Ain being at 52 km apart, their coincident daily AOT correlate with a correlation coefficient; R=0.93. Concerning the correlation between satellite data and AERONET AOT, TOMS EP has a correlation coefficient of 0.53 for Saada (all data), 0.68 for Dakhla (all data). TOMS OMI correlation coefficient is 0.68 for Saada (all data) and 0.71 for Ras_El_Ain (year 2006). MISR (level 3 data) correlation coefficient is 0.77 for Saada (all data) and 0.85 for Dakhla (all data). MODIS (level 3) correlation coefficient is 0.86 for Saada (all data) and 0.92 for Dakhla (all data). Level 2 MODIS correlation coefficient is 0.69 for Saada (year 2006), 0.86 for Ras_El_Ain (year 2006) and 0.97 for Dakhla (year 2003).

Remotely sensed data can be of great interest for the site selection of astronomical observatories. In particular, candidate sites of the future European Extremely Large Telescope (E-ELT) of 30-60 m diameter from ESO need to be assessed and analytically compared in their observing characteristics. Parameters such as cloud cover and precipitable water vapor which are important for optical and infrared astronomical observations have been assessed with the MEdium Resolution Imaging Spectrometer (MERIS) instrument on the Envisat satellite with a resolution of 1km pixel. A validation of the data was made by comparing MERIS data and in situ measurement available from ESO observatories in Chile, La Silla and Paranal, combined with lower resolution values from the GOES weather satellite. A detailed analysis of daytime cloud cover from 2002 to 2006 at four sites under study both in the northern and in the southern hemisphere for the E-ELT is presented.

The main goal of this work is the analysis of new approaches in order to study the properties of astronomical sites. The objective is to calibrate the atmospheric extinction provided by in situ techniques through remote sensing data retrieved from satellite-platforms. We have explored the usefulness of data provided by different spectrographs onboard NASA and ESA satellites with better spatial and temporal resolutions than TOMS and centered on channels of astronomical interest as a possible tool for site characterization. In addition, from these satellite data is possible to go back at the cloud coverage, the climatic trend or the atmospheric turbulence from troposphere winds. The main problem to use these values is their interpretation and their quantitative calibration. Data analysis need to be complemented with those provided by in situ instruments (telescopes, airborne particles counters, ground meteorological stations, etc.).

Solar occultation observations made by the SAGE family of space instruments have provided a record of global stratospheric and upper tropospheric aerosols that extends over 25 years. Since the demise of SAGE II and SAGE III however, there are presently no space instruments devoted to continuing this aerosol data set. The paper aims to demonstrate that aerosol extinction profiles, together with a moment of the size distribution, can be accurately retrieved from Limb Scatter measurements. The methodology is described, and retrieval examples are presented using data from a Limb Scatter instrument, namely SAGE III. The retrieved extinction profiles are compared with SAGE II and SAGE III occultation aerosol products for a series of wavelengths. It is shown that the relative retrieval accuracy is good (less than 5%), with a relative precision on the order of 25%. Once operational, it is planned to apply the retrieval method to the data collected by the two still-operating Limb Scatter instruments (namely OSIRIS and SCIAMACHY) in order to extend the aerosol data record into the present time. In the future, the OMPS Limb Profiler instrument, which is presently manifested on NPP with a launch date of September 2009, will be used for additional stratospheric aerosol research.

Using the principle of reciprocity, observations acquired by the SEVIRI radiometer on-board the Meteosat Second Generation satellites provide multi-angular and multi-spectral measurements that can be used for retrieving information on both the atmospheric aerosol load, and the Earth surface. The purpose of the presented new Land Daily Aerosol algorithm developed at EUMETSAT is to derive simultaneously the mean daily tropospheric aerosol load and the land surface properties from the SEVIRI observations. The algorithm is based on the Optimal Estimation theory. The aerosol load is calculated through the optical depth parameter, for various classes of aerosols over land surfaces, and is inferred from the inversion of a forward radiative transfer model against daily-accumulated observations in the 0.6, 0.8 and 1.6 SEVIRI bands. These daily time series provide the angular sampling used to discriminate the radiative effects that result from the surface anisotropy, from those caused by the aerosol scattering. Results of comparisons with AERONET data are presented to validate the modelling approach and the algorithm that resolves the inversion problem. The retrieval error is analysed, together with the effects on the retrieval quality of updating in time the prior information.

Dust aerosols have an impact in the thermal infrared wavelengths that we can use to detect aerosols over desert surfaces. To retrieve the aerosol properties over land, we have to account for the surface contribution. The surface radiation depends on the skin temperature, which is characterized by a strong diurnal variation. Therefore, it is better to use the surface emissivity, which we assume constant over a time span of 24 hours.¹ The surface emissivity is based on clear sky observations that are corrected for atmospheric extinction and emission. The clear sky image is a composite of pixels that is characterized by the highest brightness temperature of the SEVIRI channel at 10.8μm. Due to the lower temperatures of clouds and aerosols we can assume that the selected pixel values are obtained for a clear sky day. We use a forward model to simulate the thermal infrared radiation transfer in the dust layer. The apparent surface radiation in the presence of aerosols is calculated as a function of the geometric angles, the surface emissivity, and the aerosol optical depth (AOD). This is stored in lookup tables (LUT) that are inverted to retrieve the AOD from the observed apparent surface radiation. The retrieval algorithm consists of firstly, processing the clear sky image and computing the surface emissivity, secondly, processing of the instantaneous image and computing the apparent surface radiation, and thirdly, selecting the corresponding LUT and retrieving the AOD that matches to the observed apparent surface radiation.

Many applications require the elimination of atmospheric effects caused by molecular, particulate scattering and atmospheric water content factors, a process known as atmospheric correction, compensation, or removal. Retrieval of atmospheric water content from remote sensing data is very important for atmospheric correction. This paper introduces and derives the algorithm about retrieving water content of atmosphere from AISA+ (Airborne Imaging Spectrometer for Application) data based on Modtran code. AISA+ sensor is put on the aviation platform covering the East Sea in China on July 29, 2005. AISA+ is Hyperspectral Imaging sensor including 61 bands from visible to NIR, and band 56 and band 59 are in water absorbed region and band 51 is in atmospheric window. So the three bands were used to in following expressions. The authors utilized 2 near-IR "water vapor" channels in addition to existing "windows" channels, it will be possible to derive the water vapor amount from AISA+ data in Eastern Sea in China and analyze the retrieving result. Finally, the relationships between the transmittance and atmospheric water content of AISA+ data was computed and analyzed. The maximum atmospheric water content retrieved from AISA+ image is 1.43 cm and the minimum water content is 0.04 cm, and average atmospheric water content is 0.40 cm. The results are consistent with the real conditions, so the methods are feasible for retrieval of atmospheric water contents from AISA+ data.

The Spinning Enhanced Visible and Infra Red Imager (SEVIRI) radiometer, on board on Meteosat Second Generation (MSG) geostationary satellite, collects, each 15 minutes, images of the underneath part of the globe in 12 spectral bands with a spatial resolution of 3 km. In this work the Aerosol Optical Thickness (AOT) retrieval over land using SEVIRI data is presented. AOT at 0.55 μm is estimated minimizing the difference between measured and computed radiances in the visible channel centered at 0.6 μm by means Look-Up Tables (LUT) obtained using 6S radiative ransfer code. The 0.6 μm surface reflectance has been computed using different procedures based on SEVIRI channels 3 and 4 centered respectively around 1.6 and 3.9 µm. For the 0.6 μm surface reflectance retrieval using the 1.6 μm procedure, the measurements of five automatic sun-photometers of the Aerosols Robotic Network (AERONET) located in the Mediterranean area (Avignon, Laegeren, Modena, Rome and Lecce) has been used. The procedures show encouraging results in case of 1.6 μm procedure retrieval and the inadequacy of 3.9 μm procedure. An AOT map of the Po Valley (Italy), obtained from an MSG image taken during a typical winter polluted day, is shown in the paper and compared with MODIS retrieval.

The SPATRAM (Spectrometer for Atmospheric TRAcers Monitoring) instrument has been developed by the collaboration between CGE-UE, ISAC-CNR and ENEA. SPATRAM is a multi-purpose UV-Vis-NIR spectrometer (250-950 nm). It is installed at the Observatory of the CGE since April 2004 and actually it is utilized to carry-out measurements of the zenith scattered radiation, the so-called "Passive mode", in order to retrieve-by application of DOAS (Differential Optical Absorption Spectroscopy) methodology-the vertical content of some atmospheric tracers such as Ozone (O3) and Nitrogen Dioxide (NO2). For the continuous NO2 monitoring the 425-455 nm spectral region is investigated. For the Ozone retrieval the spectral interval 320-340 nm is chosen. In this study, after a brief description of the instrument, a short explanation of the DOAS methodology and of the inversion algorithms used for the determination of the vertical distribution of the some atmospheric compounds are provided. The obtained results in terms of diurnal and seasonal variation of O3 and NO2 total column are presented. The measurements are in good agreement with the photochemical theory of NO2 and O3, showing the maximum values during the summer season and the minimum during the winter. In addition the application, to the output of the DOAS program, of sophisticated inversion schemes, using the Air Mass Factor (AMF) matrix as the kernel of the inversion algorithm, allowed for the determination of vertical distribution of some atmospheric tracers. The results obtained for NO2 and O3 are presented and discussed.

The retrieval algorithm for aerosol remote sensing has still some problems to be solved. For example, miss-leading of aerosol type selection has often happened due to the difficulties to detect the absorbing aerosols, such as carbonaceous and dust aerosols, over land. The POLDER polarization data are useful to estimate the aerosol information even over land region. This work intends to modify the satellite retrieval procedure by combining the model simulations. The result of numerical simulations is used as a priori information of existence of absorbing aerosols in the atmosphere. Our procedure, in practice, is applied to the POLDER observation period in April, 1997. As results, aerosol optical thickness at three wavelengths are retrieved, and then they are applied to estimate the mass concentration of fine mode aerosols based on the relationship between AOT by ground based sun photometry and PM_2.5 sampling. It is found that in April of 1997 the bio-mass burning aerosols are heavily loaded over South East Asia.

Direct solar irradiance and IR atmospheric radiance have been measured during different measurements campaigns, conducted in three mountain sites in Italy, far from anthropogenic sources. Direct solar irradiance has been measured by a high resolution (1.5 nm) AVANTES radiometer, working in the spectral range 400 nm-900 nm, while down welling IR sky radiance measurements has been measured by an MR100 BOMEM Fourier Transform Spectrometer covering the spectral ranges 500 cm^-1-5000 cm^-1 and 1 cm^-1 of resolution. At least two Radiosonde launches per day furnished temperature and water vapour profiles. The instruments were located on a mobile laboratory, specifically projected to host them. The parameters obtained from direct solar irradiance are Aerosol Optical Depth, Angstrom parameters and Aerosol Size Distributions retrieval, while from IR data water vapour and temperature profiles have been retrieved. Different orographic characteristics and different air-masses circulation on the measurement sites influenced Aerosol Optical Depth values and variation. Infrared radiances inversion allows the water vapour content retrieval and a correlation between aerosol effective radii and water vapour content has been looked for.

Results from the latest of a series of joint U.S.-Russian programs investigating atmospheric effects on satellite remote sensing systems are reported. Recent efforts were directed at obtaining metrologically supported experimental data for validation, correction and verification of theoretical models describing scattering and polarization of IR radiation in clouds containing particles in the crystalline phase. On-going experimental investigations are being carried out in fullsize cloud chambers of the State Institution Research and Production Association (RPA) "Typhoon" under conditions comparable with actual atmospheric conditions. A unique instrument and experimental setup has been created at the Institute of Experimental Meteorology (IEM) of RPA "Typhoon". It includes the means to form clouds with prescribed characteristics, a system controlling thermodynamics and microstructure of the particles formed, and an instrumentation complex, spectrometer-polarimeter-indicatrix meter (SPIN), designed for the measurement of the polarization characteristics of radiation scattered by cloud ice particles. The data obtained can be used to develop all-weather observation systems and to define experiments for remote sounding and environmental monitoring of the Earth from space.

Atmospheric Motion Vectors (AMVs) are one of the most important products generally derived from geostationary satellites, and especially from Meteosat at EUMETSAT, because they constitute a very important part of the observational data fed to Numerical Weather Prediction. The height estimation or 'assignment' (HA) is still the most challenging task in the AMV extraction scheme. The advent of Meteosat Second Generation provides many new opportunities for improving the HA of AMVs. Indeed, the existence of a CO₂ absorption channel at 13.4 μm on the SEVIRI instrument enables the simultaneous use of the IR/CO2 ratioing methodology in addition to the 'WV-IRW intercept method' (also called STC), for semi-transparent cases. Due to the existence of several Water Vapour and Infrared channels on SEVIRI, each method is implemented in slightly different configuration, and several pressures are then calculated for each AMV. It was expected at first to use the agreement of these pressures as a quality check for the final AMV height. Unfortunately, the various methods (STC and CO₂ slicing) have clearly their own sensitivity and domain of application, which makes a quality check very challenging. It appeared then necessary to define these domains of application more precisely, in order that better use may be made of these methods operationally. This paper presents such results using simulated SEVIRI radiances calculated by the FASDOM radiative transfer code. FASDOM accounts for gaseous absorption as well as cloud scattering and absorption and can precisely consider various types of clouds with various microphysical properties. We then have the possibility to compare the outputs of the HA methods knowing precisely the input to the model, especially the pressure of the simulated cloud.

The Wide Field Camera (WFC) is one of three instruments in the CALIPSO science payload, with the other two being the Cloud-Aerosol LIdar with Orthogonal Polarization (CALIOP) and the Infrared Imaging Radiometer (IIR). The WFC is a narrow-band, push-broom imager that provides continuous high-spatial-resolution imagery during the daylight segments of the orbit over a swath centered on the CALIOP footprint. The instantaneous field of view of each WFC pixel is approximately 125 m × 125 m when projected on the Earth's surface from an orbit altitude of 705 km. The spectral band of the WFC, with a center wavelength of 645 nm and a FWHM bandwidth of 50 nm, is designed to match the Aqua MODIS instrument's channel 1. The primary WFC Level 1 products are radiance and reflectance registered to an Earth-based grid centered on the CALIOP ground track. "First light" WFC images were acquired on 18 May 2006 and routine data acquisition began in early June 2006. An initial science assessment of the WFC on-orbit performance was conducted based on analysis of the first twelve months of flight data. Comparisons of the WFC measurements with the well-calibrated Aqua MODIS channel 1 data were performed to evaluate the on-orbit radiometric performance of the WFC. Overall agreement is excellent, especially over bright deep convective clouds where the WFC measurements agree to within a few percent of MODIS. This paper provides a summary of our overall assessment of the on-orbit radiometric performance of the WFC.

For inferring cirrus optical and microphysical properties from satellite imagery, a common assumption is that the radiative properties of a cirrus cloud may be represented by those associated with a specific ice crystal habit, a single particle size distribution and Ice Water Content (IWC). Various algorithms have been developed to retrieve cirrus optical and microphysical properties in the past 20 years. They can be categorized into the techniques based on either thermal infrared or solar reflection measurements. However, in-situ measurements have shown that shapes, sizes and IWC of ice crystals may vary substantially with height within the clouds. Given the different sensitivity of thermal infrared and solar wavelength to cloud microphysics, it is unlikely that a single cloud layer with homogeneous cloud properties can be used to reproduce both type of measurements. Thus, it is necessary to assess the effect of vertical inhomogeneity within cirrus on the radiative transfer calculations and on the retrieval techniques. The purpose of this study is to investigate a microphysical cirrus model composed of different layers in terms of ice crystal habit, size and IWC. The vertical structure will be given by simple analytic formula derived from various prescribed physical constraints. The primary goal of this study is to determine a simple cloud model that can be used to retrieve consistent information from both solar and thermal measurements. For this purpose, we examine the sensitivity of cirrus reflectances and brightness temperature to its vertical description for a suite of MODIS (MODerate-resolution Imaging Spectroradiometer) bands spanning visible, near infrared and thermal infrared wavelengths. Results of this study are presented and potential application to remote sensing of cirrus clouds with MODIS are discussed.

Measurements performed with a backscatter and Raman lidar at Thessaloniki, Greece were used to characterize cirrus clouds and aerosol layers by determining their optical properties. This is achieved through the application of different post-processing algorithms. We retrieved the cirrus cloud's optical properties by using three independent mathematical methods. In the first method, an iterative procedure was used based on the criterion that forward and backward integration coincide to the desired degree of accuracy. In the second method, the optical depth of the cirrus cloud can be determined by comparing the backscattering signals just bellow and above the cloud if the lidar signals are correctly represent the scattering medium. The third method, the well known Raman method, is applicable to night time measurements and is capable for determining the vertical profile of lidar ratio. The results are considerably influenced by multiple scattering effects, that not taken into account and this leads to a significant underestimation of calculated cirrus optical depths and lidar ratios. To estimate and correct this effect we have applied a radiative transfer model that calculates the multiple scattering contributions for each cirrus case analyzed. We have compared the resulting optical depths and lidar ratios and found a good agreement between these methods. The comparison has been performed to the effective values of optical depth and lidar ratio.

Data of remote multiangle measurements of reflected radiance are used for retrieval of the optical thickness, single scattering albedo and phase function parameter of cloudy and clear atmosphere. The method of perceptron neural network has been tried for obtaining the surface albedo, optical thickness, single scattering albedo and phase function parameter from input values of multi-angle radiance and solar incident angle of clear pixels. All mentioned parameters were randomly varied on the base of statistical models of possible measured parameters variation. An analytical method of the retrieval is applied to remote observations of reflected radiance of cloudy pixels. The slight horizontal heterogeneity of cloud is approximately taken into account. The simultaneous retrieval of the optical thickness and single scattering albedo at every wavelength independently and without rough restrictions on parameters retrieved is the advantage comparing with earlier studies. The methodology of the asymmetry parameter retrieval is proposed.

MODIS data have great potential in rice growth monitoring and yield estimation due to the low cost and high time resolution Unfortunately MODIS which is a kind of visible-infrared sensor cannot detect land surface through cloud and cloud-free image is quite rare during rice growth period due to cloudy weather Therefore, cloud contamination is one of the main obstacles in rice growth monitoring and yield estimation using MODIS data Based on spectral characteristics of cloud and MODIS channels taking it into account that MODIS data includes thirty-six bands, especially the infrared channels subdivided, it has realized cloud detection in MODIS images by multi-spectral synthesis method, infrared difference algorithm, index methods and cloud detection index in this paper. The result shows that infrared difference algorithm, index methods analysis are the simple and effective methods to detect cloud After geometric correction the cloud-free images are obtained through interpolating using time series MODIS data and ratio value using same date data of different year

In this work a threshold technique for cloud detection and classification is applied to 9 years NOAA-AVHRR imagery in order to obtain a cloud climatology of the Canary Islands region (Northeast Atlantic Ocean). Once the clouds are classified, a retrieval method is used to estimate cloud macro- and micro-physical parameters, such as, effective particle size, optical thickness and top temperature. This retrieval method is based on the inversion of the simulated radiances obtained by a numerical radiative transfer model, libRadtran, using artificial neural networks (ANNs). The ANNs, whose architecture was based on Multilayer Perceptron model, were trained with simulated theoretical radiances using backpropagation with momentum method, and their architectures were optimized through genetic algorithms. The global procedure was performed for both day and night overpasses and, from a set of more than 9000 images, maps of relative frequency were calculated. These results were compared with ISCCP data for the 21-year period 1984-2004. The relationships between the retrieved cloud properties and some climate and atmospheric variables were also considered.

Automatic monitoring of lower atmosphere layering was performed by continuous remote sensing measurements with ceilometer and sodar in Augsburg. The Vaisala ceilometers LD40 and CL31 were used which are eye-safe commercial lidar systems. Special software for these ceilometers provides routine retrievals of lower atmosphere layering from vertical profiles of laser backscatter data. A comparison was performed with parallel monitoring of the layering by acoustic remote sensing (sodar). From the acoustic and optical remote sensing data the following features are analysed. The sodar measurements provide the height of a turbulent layer characterized by high acoustic backscatter intensities due to thermal fluctuations and a high variance of the vertical velocity component. The ceilometer measurements add information about the range-dependent aerosol concentration; gradient minima within this profile mark the borders of mixed layers. Different examples of meteorological conditions will be discussed to demonstrate the possibilities of atmospheric layering retrieval.

During August-October 2005, several lidar measurements have been performed at many Italian lidar stations during the Launch (International Lindenberg campaign for Assessment of hUmidity aNd Cloud profiling systems and its impact on High-resolution modelling) campaign according with the IOP (Intensive Operational Period) schedule. IOP 4 episode (1-3 October 2005) has been selected and investigated with a special attention to the variability of water vapour mixing ratio vertical distribution to better understand the associated circulation in the coastal waters of the Gulf of Naples (Tyrrhenian Sea). A simulation is performed using the mesoscale model MM5 (version 3) model from PSU/NCAR^1,2 for this study. Water vapour mixing ratio observations have been detected in the Naples site (40°50'N, 14°11'E, 118 m asl) by a water vapour Raman lidar which is also able to measure the backscatter profile at 355 and 532 nm and the extinction profile at 355 nm. Water vapour mixing ratio vertical profiles retrieved by lidar have been compared with the MM5 water vapour mixing ratio vertical profiles. The agreement between the model and the lidar data is good; all the modelled and the lidar profiles are able to capture the cold air intrusion, that is the sharp decrease of the water vapour mixing ratio at about 2000 m. Also the water-layer between 3000 and 8000 m is well captured. Moreover, both the model and the observations are able to capture the land/sea breeze phenomena.

The present knowledge of the aerosol distribution is not sufficient to estimate the aerosol influence on global and regional environmental conditions and climate. This observational gap can be closed by using advanced laser remote sensing. EARLINET (European Aerosol Research Lidar Network) is the first aerosol lidar network, established in 2000, with the main goal to provide a comprehensive, quantitative, and statistically significant database for the aerosol distribution on a continental scale. EARLINET is a coordinated network of European stations (25 at present) using advanced lidar methods for the vertical profiling of aerosols. The network activity is based on simultaneous scheduled measurements, a rigorous quality assurance program addressing both instruments and evaluation algorithms, and a standardised data exchange format. Further observations are performed to monitor special events. EARLINET-ASOS (Advanced Sustainable Observation System) is a five year EC Project started in 2006, based on the EARLINET infrastructure. The main objectives are: to make EARLINET a world-leading instrument for the observation of the 4-D aerosol distribution on continental scale; to foster aerosol-related process studies, validation of satellite sensors, model development and validation, assimilation of aerosol data into operational models; and to build a comprehensive climatology of the aerosol distribution.

The ESA EarthCARE (Earth Clouds Aerosols and Radiation Explorer) mission includes the BBR (Broad-Band Radiometer), the instrument responsible to provide measurements of broadband radiances over the along-track satellite path. The BBR footprint will be geolocated in space and time with the passive sensor, MSI (Multi-Spectral Imager), and the active sensors, ATLID (ATmospheric LIDar) and CPR (Cloud Profiler Radar) onboard the same platform. The role of the BBR was defined to provide the boundary condition for top of atmosphere flux densities. Thus, the radiance to flux conversion is the main objective for the BBR retrieval algorithms. This conversion has been so far carried out by using specific angular distribution models (ADMs). In this process, every radiance is classified in a unique scene bin of observations characterized by a similar anisotropic behaviour. Each of these scene bins is defined by a range of values distinguishable by the MSI. But the MSI can only extract vertically integrated retrievals. Therefore, in multi-layer cloud configurations, scene identification (ID) by means of the MSI retrievals will not distinguish the 3-D structure of the real scenes. Thus, these scenes will most probably be wrongly identified. But, since active sensors are present on the same satellite platform, it would be possible to use their observations to contribute to the BBR scene ID. This work shows a preliminary simulation approach to demonstrate the advantages of this methodology by applying it to multi-layer clouds. The clouds have been built with a stochastic cloud generator model, and the radiative transfer simulations have been carried out with the EarthCARE Simulator, a Monte-Carlo code capable to reproduce the observations of the different mission instruments taking into account the specific characteristics of each sensor.

A mathematical model for statistical estimate of the bias and noise in satellite retrievals of atmospheric profiles and a case study are presented. The model allows accurate validation of actual performance of the remote sensing system while in orbit by comparing its measurements to correlative data sets, e. g. radiosonde network. The model accounts for the following factors: (i) The satellite and validating systems sample volumes of the atmosphere at times and locations that are not exactly co-located. (ii) The validated and validating systems have different characteristics, e. g. different vertical resolution and noise level. All the above factors cause apparent difference between the data to be compared. The presented model makes the comparison accurate by allowing for the differences. To demonstrate its practicability we present the case study that involves the radiosonde data from three stations: ARM Tropical Western Pacific (0.5° S, 167° E), ARM Southern Great Planes (37° N, 98° W), and Lindenberg (52° N, 14° E). For each station we considered temperature profile validation scenario and estimated associated errors. The model can be used for interpretation of the validation results when the above mentioned sources of discrepancies are significant, as well as for evaluation of validation data sources, e.g. GRUAN (GCOS Reference Upper-Air Network).

The first Geostationary Earth Radiation Budget (GERB) instrument was launched during the 2002 summer together with the Spinning Enhanced Visible and InfraRed Imager (SEVIRI) on board of the Meteosat-8 satellite. This broadband radiometer aims to deliver near real-time estimates of the top of the atmosphere solar and thermal radiative fluxes at high temporal resolution thanks to the geostationary orbit. Such goal is achieved with the L20 GERB processing which generates these fluxes at several spatial resolutions from the directional filtered radiance measurements of the instrument. This processing consists of successive components, one of them being a radiance-to-flux conversion. Such conversion is carried out in the solar region by using the shortwave angular dependency models (ADMs) developed from the Tropical Rainfall Measuring Mission (TRMM) Clouds and the Earth's Radiant Energy System (CERES) experiment. As these ADMs are stratisfed according to specific scene properties, the GERB ground segment will have to rely on a scene identification of SEVIRI data which allows us to select the proper ADM. In this paper, we will briefly justify and describe the implementation of a specific GERB scene identification for the offcial Edition 1 release of the L2 products. Preliminary comparisons between GERB and CERES scene identifications both applied to SEVIRI data will follow. Finally, we will suggest possible improvements based on limitations which could be found.

This paper documents the development of the first integrated data set of global vertical profiles of clouds, aerosols, and radiation using the combined NASA A-Train data from the Aqua Clouds and Earth's Radiant Energy System (CERES) and Moderate Resolution Imaging Spectroradiometer (MODIS), Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), and CloudSat. As part of this effort, cloud data from the CALIPSO lidar and the CloudSat radar are merged with the integrated column cloud properties from the CERES-MODIS analyses. The active and passive datasets are compared to determine commonalities and differences in order to facilitate the development of a 3-dimensional cloud and aerosol dataset that will then be integrated into the CERES broadband radiance footprint. Preliminary results from the comparisons for April 2007 reveal that the CERES-MODIS global cloud amounts are, on average, 0.14 less and 0.15 greater than those from CALIPSO and CloudSat, respectively. These new data will provide unprecedented ability to test and improve global cloud and aerosol models, to investigate aerosol direct and indirect radiative forcing, and to validate the accuracy of global aerosol, cloud, and radiation data sets especially in polar regions and for multi-layered cloud conditions.

Clouds and the Earth's Radiant Energy System (CERES) instrument uses scanning radiometers on board the Terra and Aqua satellites use thermistor bolometers as detectors, with a sampling rate of 0.01s. During calibration testing a slow mode of detectors was found which had a magnitude of about three percent of the signal, and a characteristic time of 0.3 sec. To reduce the effect of this mode, a numerical filter was introduced. However, an analysis of the data from the CERES instruments aboard the Terra and Aqua satellites shows a difference of radiances in the forward scan compared to radiances from the backward scan. This difference is due to the slow mode not being characterized correctly. A focus of this work is to show results of setting slow mode filter parameters based on in-flight data. A gradient-based minimization strategy is employed to effectively find the filter parameters for each instrument to meet the performance goal of 0.15%. The newly designed numerical filters are to be used in processing the Edition 3 of CERES ERBE-like data products.

Interaction of light with atmospheric components is a major problem studied in the field of remote sensing and atmospheric propagation. Generally, mean atmospheric profiles are used to compute radiative transfer. But here, the sensitivity of radiances and transmittances to the climatic conditions is tested. The goal of this study is to evaluate and quantify atmospheric components variations that influence radiances and transmittances for airborne limb viewing observations. In particular, radiance variations are analyzed according to the variations of temperature and of different atmospheric molecules. This radiance variability is related to the water content and temperature modifications.

Increasing the radiometric accuracy and spectral resolution of aerospace optical imagers for Earth observation may allow enhanced results many remote sensing applications. This demand for accurate radiometric calibration and requests that atmospheric effects are carefully accounted for. Obtaining surface reflectance maps from the at-sensor radiance images requires improved atmospheric correction procedures. Based on the availability of data acquired at so high spectral resolution to allow the detection of different spectral features of some atmospheric constituents, an iterative estimation algorithm has been developed.. The default atmospheric profiles available in MODTRAN 4 have been firstly refined through at-ground level measurements of some parameters, like temperature, pressure, humidity. The algorithm uses the results of MODTRAN 4 simulations to calculate the apparent reflectance of several image pixels for various abundances of atmospheric constituents. The retrieved reflectance spectra are analysed in order to detect the presence of residual atmospheric absorption features, the amplitude of which is adopted as a score of sub-optimal atmospheric correction. A numerical minimization algorithm then finds the optima atmospheric parameters for the processed scene. Five parameters are estimated using this inversion procedure: visibility, H₂O vapour, CO₂, CO, and O₃. To test and validate the method some images acquired by the new airborne sensor HYPER / SIM-GA on 15^th December 2005 during a coastal zone remote sensing campaign have been utilized. Synthetic dataset simulating the above sensor have been employed too. First results are presented and discussed taking into account the feasibility of avoiding in-field measurements.

On June 30th, 2005 the REFIR-PAD (Radiation Explorer in the Far InfraRed-Prototype for Application and Development) Fourier transform spectroradiometer performed the first wide-band spectral characterization of the top-of-atmosphere emitted radiation in the far-infrared with an uncooled instrument. The nadir emitted radiance has been measured down to 100 cm^-1, thus covering a spectral interval that, until now, was nearly unexplored, and up to 1400 cm^-1, including the well characterized atmospheric window region, in which it is possible to perform comparison and intercalibration with operative instruments. The measurements were performed at an altitude of 34 km, from a stratospheric balloon launched in tropical region, near Teresina (Brazil). The acquired spectra have a spectral resolution of 0.5 cm^-1. It should be noted that despite the operating spectral range extending to the far-infrared region, REFIR-PAD does not require any cooled components, thanks to the use of pyroelectric detectors and an optical scheme that compensates for the instrument self-emission. This work shows the results of the analysis of the spectra, focusing on the far infrared portion of the atmospheric emitted radiance. The retrieval of the vertical profiles of water vapour and temperature during the flight is presented. The vertical resolution of the retrieval is 2 km in the upper troposphere-lower stratosphere (UTLS) region, and lower at higher altitudes. The comparison with ECMWF for validation is also shown. Besides the characterization of temperature and water vapour, from the analysis of the emitted radiance useful information can be gathered about cloud and aerosol contribution to radiation budget.

The classical Chandrasekhar's formula, which relates the surface albedo to the top of the atmosphere radiance, rigorously applies to a homogeneous Lambertian surface. For a non-homogeneous Lambertian surface in a plane parallel atmosphere, an extension of this formula proposed in the eighties has been implemented recently in the 6S algorithm. To analyze this extension, this paper derives the rigorous formula of the top of the atmosphere signal in a plane parallel atmosphere bounded by a non-homogeneous Lambertian surface. Then the 6S algorithm extension is compared to the exact formula and approximations and their validity are examined. The derivation of the exact formula is based on the separation of the radiation fields into direct and diffuse components, on the introduction of the Green's function of the problem and on integrations of boundary values of the radiation fields with the Green's function.

The classical problem of one dimensional adjacency effects (so called coastal problem) is shown to be amenable to closed form error analysis when 1D adjacency correction schemes are used. In particular the error made when surface reflectance is retrieved using an infinite target (Lambertian) assumption is given in closed form. This allows deductions for the behavior of the error as a function of wavelength and optical thickness. Typical lengthscales of the adjacency effects are deduced and the range and magnitude of the error are also given in closed form.

The classical Chandrasekhar's formula relating the surface reflectance to the top of the atmosphere radiance rigorously applies to a Lambertian surface. For a homogeneous non Lambertian surface in a plane parallel atmosphere, an extension of this formula has been proposed in the work of Tanre and has been implemented in the 6S algorithm. To analyze this extension, this paper derives the rigorous formula of the top of the atmosphere signal in a plane parallel atmosphere bounded by an homogeneous non Lambertian surface. Then this formula is compared to the 6S algorithm extension and approximations used and their validity are pointed out. The methods used for this rigorous derivation are classical. They are based on the systematic separation of direct and diffuse components of the radiation fields, on the introduction of the Green's function of the problem and on convolutions of boundary values of the radiation fields with the Green's function.

Infrared hyperspectral imagery gives new opportunities for night observations for military, or security purposes, and for geological studies as rocks have specific infrared absorption bands. Generally, an optimized utilization of spectral information requires to retrieve spectral emissivity, which involves atmospheric compensation and surface temperature and emissivity separation (TES). This paper presents a new method dedicated to a future airborne hyperspectral sensor that will operate in the 3-5.5 and 8-12 µm spectral ranges, at 2.2 km height. It combines neural networks in order to characterize the required parameters for atmospheric compensation and a spectral smoothness approach for TES. The network training is performed with radiance spectra simulated with MODTRAN4, and using ASTER emissivities, and the TIGR atmospheric database. A sensitivity study based on experimental design is carried out in order to compare impacts of atmospheric and surface parameters on radiance at several wavelengths. Atmospheric compensation and TES methods are then presented and their accuracy is assessed. Sensitivity of the retrievals to instrumental characteristics such as signal to noise ratio and radiometric calibration, is also studied.

LIDAR (LIght Detection and Ranging) is an optical active remote sensing technology with many applications in atmospheric physics. Modelling of LIDAR measurements appears useful approach for evaluating the effects of various environmental variables and scenarios as well as of different measurement geometries and instrumental characteristics. In this regard a Monte Carlo simulation model can provide a reliable answer to these important requirements. A semianalytic Monte Carlo code for modelling LIDAR measurements has been developed at ISAC-CNR. The backscattered laser signal detected by the LIDAR system is calculated in the code taking into account the contributions due to the main atmospheric molecular constituents and aerosol particles through processes of single and multiple scattering. The contributions by molecular absorption, ground and clouds reflection are evaluated too. The code can perform simulations of both monostatic and bistatic LIDAR systems. To enhance the efficiency of the Monte Carlo simulation, analytical estimates and expected value calculations are performed. Artificial devices (such as forced collision, local forced collision, splitting and russian roulette) are moreover foreseen by the code, which can enable the user to drastically reduce the variance of the calculation.

This work is aimed to atmospherically correct remote sensing data in the solar spectral domain (Visible and Near Infrared) allowing the better assessment of the surface spectral material characteristics. This was obtained by the inversion of the radiative transfer equation for at-sensor signal. In order to detect targets with peculiar spectral characteristics, the atmospheric correction has to take into account the diffuse radiation that constitutes a significant component to the at sensor radiance. The effect of this component (namely adjacency effect), which tends to mask the pixel seen by the sensor, derives principally from the atmospheric scattering due to the aerosol loading in the scene. At this purpose an algorithm based on 6S calculation was defined to derive the direct and diffuse component of the radiation required to determine the contribution to the pixel reflectance related to the surrounding pixels. The developed algorithm allowed the assessment of this environmental contribution besides the pixel reflectance. Such application, on airborne hyperspectral sensor MIVIS (Multispectral Infrared and Visible Imaging Spectrometer) scenes, leads to obtain accurate pixel reflectance if compared with ground measurements acquired within testing areas. This work shows how adjacency effect has a significant role in the correction of remote sensing data, especially if acquired by an airborne hyperspectral sensor. The preliminary analysis of the results have highlighted that the adjacency effect is not negligible, mainly when pixels in the scene are spectrally heterogeneous.

The spectrally-resolved characterization of the atmospheric emission has a fundamental role in the study of the Earth radiation balance, and only a measurement performed in a wide spectral range enables us to separate the contributions to the radiative balance due to the different altitudes, constituents and physical phases. The REFIR-PAD (Radiation Explorer in the Far InfraRed-Prototype for Application and Development) Fourier transform spectroradiometer can perform a characterization of the broadband radiative signature of clouds and aerosols, with the only limitation of the need of low levels of water vapour like those that are obtainable in high altitude stations during winter. The capabilities of this kind of measurement have been assessed in a series of test campaign performed in Tuscany during the winter of 2006/2007 when atmospheric emission spectra have been acquired in various transparency conditions and the evidence of transparency in the far-infrared region below 600 cm^-1 has been demonstrated. REFIR-PAD operates in the spectral range extending from 100 to 1400 cm^-1 with a resolution of 0.5 cm^-1, using room-temperature detectors and optics and a compact, misalignment-compensated design. The instrument, developed at IFAC-CNR, Florence, has been successfully deployed in several campaigns, both in the ground based zenith-looking geometry and in the nadir-looking balloon borne configuration. The operating spectral range of the REFIR-PAD spectroradiometer encompasses great part of the atmospheric emission spectrum, from the relatively unexplored far-infrared region below 400 cm^-1, dominated by water vapour rotational band, to the atmospheric transparency window, where a number of atmospheric instruments are already operating and can provide intercomparison data.

Scintillation effects caused by the fluctuations of the refractive index of air are not negligible in the stratosphere. Recent experiments highlight the composite nature of optical turbulence in the stratosphere. We present an analytical model of scintillation based on a 3-D model of anisotropic and isotropic refractive index fluctuations spectrum that predicts scintillation rates inside the Rytov regime. This model uses a multi-layer decomposition of the turbulence profile. The effect of anisotropy leads to significant scintillation rates when a source is observed with a horizontal line of sight. Astronomical observations consisting in stellar scintillation made from balloon-borne spectrometer AMON-RA allow us to remotely probe statistical characteristics in the stratosphere, to validate the model of scintillation developed herein and to obtain refined values of its parameters. Data reduction from these observations brings out values of the inner scale of the anisotropic spectrum. We retrieve metric values of the inner scale that are compatible with space-based measurements. We find a major contribution of the anisotropic spectrum relatively to the isotropic contribution. This effect is particularly noticeable when the sight line plunges into the atmosphere, leading to strong scintillation as well as coupled chromatic refraction effects. This makes clear the presence of gravity waves in the stratosphere.

The response of the ionospheric E-region to solar-geomagnetic storms can be characterized using observations of infrared 4.3 um emission. In particular, we utilize nighttime TIMED/SABER measurements of broadband 4.3 um limb emission and derive a new data product, the NO+(v) volume emission rate, which is our primary observationbased quantity for developing an empirical storm-time correction the IRI E-region electron density. In this paper we describe our E-region proxy and outline our strategy for developing the empirical storm model. In our initial studies, we analyzed a six day storm period during the Halloween 2003 event. The results of this analysis are promising and suggest that the ap-index is a viable candidate to use as a magnetic driver for our model.

A new correlated-k algorithm has recently been incorporated into SAMM-2, the Air Force Research Laboratory background radiance and transmission code. SAMM-2 incorporates all of the major components necessary for background scene generation at all altitudes: atmospheric characterization, solar irradiance, molecular chemical kinetics and molecular spectroscopic data. The underlying physical models are applicable for both low-altitude local thermodynamic equilibrium (LTE) conditions as well as high-altitude non-LTE (NLTE) conditions. Comprehensive coverage in the .4 to 40 micron (250 to 25,000 wavenumber) wavelength region for arbitrary lines-of-sight (LOS) in the 0 to 300 kilometer altitude regime is provided. A novel 1 cm-1 resolution correlated-k algorithm has been developed in order to provide the orders-of-magnitude increase in computational efficiency when compared to the existing SAMM-2 line-by-line (LBL) algorithm and applicable to both LTE and NLTE atmospheric conditions. The SAMM-2 correlated-k algorithm processes molecular lines at runtime by reading line center information from the HITRAN 2000 database and computing statistical cumulative probability distributions within a spectral interval under the presumption of a Voigt line shape profile. This algorithm is useful for treating atmospheric phenomena at all altitudes requiring a spectrally monochromatic treatment of the atmospheric transmission and/or radiance, including multiple scattering or atmospheric structure.

We investigated the contributions of the hydroxyl (OH) airglow to the illumination of resident space objects. During nighttime, in a moonless sky, the airglow is the largest contributor to the sky brightness in the visible (vis), the near-infrared (NIR) and short-wave infrared (SWIR) spectral region. The dominant contributors to the airglow are vibrationally excited hydroxyl radicals, OH(ν). The radicals are formed in vibrational states up to υ=9 by the reaction of hydrogen atoms with ozone. The strong emissions, known as Meinel emissions, are sequences with σν= 1-6. Emissions with υ = 3, 4, 5 and 6 occur in the visible and NIR between .4 and 1.0 µm. From 1.0 to 2.5 µm there are very strong emissions from the δν= 2 sequences. The σν= 1 emissions extend into the thermal infrared to 4.5 μm. In this work, we considered four band passes, a vis-NIR band pass, two SABER band passes centered at 1.6 and 2.0 μm, respectively, and a broad band pass around 2.7 µm. SAMM2 was utilized to compute spectra and line of sight radiances. We used line of sight (LOS) radiances to compute the irradiance on a space object that was taken as a flat plate with a Lambertian surface reflectance. Profiles of irradiance versus orientation were calculated. The OH airglow will illuminate a facet even if it is pointing somewhat upward. However, the irradiance in the 2.7 μm band pass comes almost entirely from the atmosphere in the low altitude and the earth emission.

Airport air quality is influenced by traffic mainly. Near runway the aircrafts are the main source. The quantification of these emission sources requires remote sensing methods because the airport operations should not be disturbed. DOAS is used in open-path mode to detect continuously NO₂ cross the runway during nearly one year. Those runway emission studies were performed for the first time. During the measurement campaign these findings were compared with corresponding aircraft taxiway emission measurements. The concentration measurements of CO₂ which are necessary to calculate emission indices are provided by open-path FTIR spectrometry. Aircraft emission indices of CO, NO and NO₂ could be determined at taxiway only. Open questions and required further developments will be discussed.

The scanning infrared gas imaging system (SIGIS-HR) and the quantitative gas analysis software MAPS (Multicomponent Air Pollution Software) are applied to investigate the spatial distribution of the temperature and gas concentrations (CO, NO) within the plume of aircraft engines at airports. The system integrates an infrared camera also. It is used for the localisation of the hot source that additionally suggests the best measurement position of the SIGIS-HR. The application of emission FTIR spectrometry for the measurement of temperature and gas emission index of CO and NO is presented for the exhaust of a small turbojet based on a helicopter turbine. In these measurements the emitted infrared radiation from the exhaust gas stream was collected by the SIGIS-HR at different spectral resolution (56 cm^-1 and 0.2 cm^-1). The software MAPS includes the Instrumental Line Shape (ILS) of the OPAG- 22 FTIR spectrometer obtained by active gas cell measurements and ILS modelling. The rough concept of the system will be presented and operational applications will be discussed. The results of the investigation of the temperature and gas concentrations (CO, NO) within the aircraft engine plumes will be shown. The limitations and of the systems will be discussed.

The optical properties and the spatial distribution of the tropospheric aerosols over Naples under Saharan dust outbreaks conditions have been studied by means of lidar measurements performed between May 2000 and August 2003 in the frame of the EARLINET project. Climatological analysis of sand plume has been done by comparing normal and dust affected conditions. Results in terms of backscattering and extinction coefficient as well as their integrated quantities show that the aerosol load from the ground level up to 2 Km during Saharan dust transport events is almost the same of normal conditions. This is probably due to the relevant widespread of local aerosol sources, such as vehicular traffic, industrial activities, etc. Nevertheless, when sand outbreaks occur, the extinction to backscattering ratio, i.e. the lidar ratio, clearly shows that the aerosol type in the lowest atmospheric layer changes. Moreover, Saharan dust transport events strong increase both integrated backscatter and optical dept above 2 km.

Detection of smoke from forest fire is one of the practical applications of lidar. As it is well known, smoke contains a large number of small particles of ash or soot, leading to a large backscattering efficiency and consequently favourable conditions for lidar application. We have developed a compact mobile lidar system based on Nd:YAG Q-Switched laser source, operating at three wavelengths: 1064 nm, 532 nm and 355 nm, with emission rate of 10 Hz and pulse duration equal to 5 ns when the laser operate at the fundamental harmonic and 4 ns for the second and the third ones. The system has been tested by experimental measurements of the smoke backscattering coefficients carried out in an ad hoc cell. Since the spatial resolution of laser pulse is smaller than the cell length it has been possible to evaluate the profile of the smoke backscattering coefficients inside the cell itself. Moreover it has been developed a computational model for simulating the temporal and spatial evolution of smoke within the cell. These experimental and theoretical data have been used to optimize the theoretical already developed to study the smoke evolution into the atmosphere. In this paper measurements of smoke backscattering coefficients into a cell and simulations of smoke evolution will be presented.

Properties of forest and peat-bog fires smoke are presented. Aerosol optical and microphysical properties were measured at spring 2007. Measurements were taken by lidar groups from B.I. Stepanov Institute of Physics, Minsk, Belarus and Institute of Geophysics PAS, Warsaw, Poland. Results of synergic lidar and sun-photometric observations were compared to NAAPS model results and back trajectories as well as ground measurements taken by local environmental services.

The synergy between the Geostationary Earth Radiation Budget (GERB) broadband radiometer and the Spinning Enhanced Visible and Infra Red Imager (SEVIRI) on board the European meteorological satellite Meteosat-8 is exploited to estimate the diurnal variation of the direct short wave aerosols radiative forcing (DSWARF) from biomass burning over Africa at sub-GERB footprint scale. Biomass burning are first identified at the SEVIRI resolution (3 km at nadir) by applying a multispectral thresholding algorithm to the SEVIRI spectral measurements. Reflected SW fluxes at the top-of-atmosphere for smoke aerosols are obtained by converting the measured GERB radiances at the 3×3 SEVIRI pixel window in term of flux using a theoretically derived smoke angular distribution model (ADM) based on the average scene identification (SI) from the 3×3 SEVIRI pixel box. The calculated smoke ADM is a function of aerosol optical depth, surface type and solar and viewing geometry. The TOA DSWARF for smoke aerosols is then estimated as the difference between radiative fluxes in the absence and presence of biomass burning aerosols.

This study describes the atmospheric aerosol load encountered over a number of sites from the Southern Balkan region with a relatively well-known air quality factor. Using the aerosol optical depth AOD, retrieved from the two Moderate Resolution Imaging Spectroradiometers, MODIS, on board the Terra and Aqua NASA satellites, the aerosol content of numerous sites is investigated under the scope of local pollution sources, inter-regional transport and large scale dust and/or biomass burning events. The wide time range of seven full years of MODIS/Terra measurements permits the discussion of possible climatological aspects as well. The MODIS AOD is further validated using ground-based Brewer spectrophotometer measurements over a metropolis of Northern Greece, Thessaloniki. Thessaloniki is situated in a unique sea-side location which inflicts it with high humidity and sea-salt particles, and is furthermore frequently affected by biomass burning and desert dust aerosols arriving from surrounding sources. Local and regional pollution further influences the quality of the local air and the observed tropospheric optical depth. The air masses responsible for either transporting polluted air into the free troposphere or circulating boundary layer aerosol load around the region of Norther Greece have been identified and discussed in detail.

The relationship between concentration of suspended particulate matter (PM2.5) and column aerosol optical thickness (AOT) is examined based on the simultaneous measurements at a NASA/AERONET station at Kinki University Campus, Higashi-Osaka, Japan since March in 2004. We drew the following results: 1. A strong linear correlation exists between PM2.5 and AOT, 2. The correlation is better within each type of aerosols as anthropogenic type and dust type than overall, 3. The correlation coefficients take the highest value in such a case that PM2.5 values are measured in 30-minutes behind after AOT data. These facts are explained with the model simulations. Our results highlight the possibility that the PM2.5 concentration can be estimated from the AOT, and vice versa. Moreover, combining radiometric aerosol information with surfacelevel particulate mass data appears to be a promising approach for gaining a better understanding of air quality and the atmospheric environment.

In this paper we present a methodology for the retrieval of the vertical profile of atmospheric gas pollutants in the boundary layer from ground based remote sensing measurements. Nitrogen dioxide (NO₂) and ozone (O₃) slant column amounts have been obtained with the Differential Optical Absorption Spectroscopy (DOAS) technique used in the multiple axis configuration (the so called MAX-DOAS). The measurements have been carried out in the Presidential Estate at Castel Porziano (Rome) in the period from September to November 2006 in the frame of a programme started in 1994 for studying and monitoring the Estate's environment. The retrieval of information on the vertical profile of trace gases from their slant column amounts requires: (1) the simulation of the radiative transfer in the atmosphere for Air Mass Factor (AMF) calculation; (2) the application of inversion schemes. In this paper the vertical profiles of NO₂ and O₃ obtained from multiple axis DOAS measurements and their daily evolution are presented and discussed. The day under study is the 29th of October, 2006.

Shipboard hand-held sun photometers measurements which were collected over the East China Sea from December 15, 2006 to February 11, 2007, were used to discuss temporal and spacial distributions of aerosol optical thickness(AOT), and the type and source of aerosol particles over the East China Sea. The results of this study suggest that AOT was normally large in the coastal areas and became small gradually with the distance away from the coastal areas. The value of AOT also was larger in the coastal areas with industry than those without industry. AOT was closely related to the development of human activity and wind transportation. The analysis of many cases showed that the minimum AOT value over sea appeared at noon during a day and its reason could be found in weather data. The calculated Ångstrom wavelength exponent showed that the radius of aerosol particles was small in the coastal areas and large in the central area of the East China Sea. It can provide the basic data for marine regional climate and remote sensing.

The open-path technique is a widely use method for air pollution monitoring, being capable of detecting trace gases down to ppb concentrations. Using this technique, the DOAS system can measure simultaneously several types of atmospheric molecular compounds having UV absorption spectra, by averaging on a long optical path (hundreds of meters). In this paper, two kinds of comparative measurements by DOAS and in situ detectors (using the point monitoring technique), in high polluted areas from Bucharest and the surroundings, are presented and analyzed. Only point monitoring is a standardized technique and therefore by comparing the two methods, several strengths and weaknesses of the open path technique will be evidentiated. This study is intended to mark out main environmental conditions (e.g. atmospheric fluctuations, topography) responsible for important differences that appear between experimental data acquired with the two techniques.

Daily PM10 concentrations of samples collected at two sites, urban and rural from Romania have been used to estimate the aerosol direct radiative forcing. Using OPAC (Optical Properties of Aerosols and Cloud) model we determined the single scattering albedo, the aerosol optical depth and aerosol up-scatter fraction, aerosol's properties needed to estimate the magnitude and sign of direct aerosol radiative forcing. The surface albedo was assumed 0.2 for the urban site and 0.06 for the rural site for all wavelengths. For aerosol scale height we used 1km in winter and 2 km in the summer to calculate the optical depth of the boundary layer. Statistical analysis of the PM10 concentration for both sites show clear seasonal cycle with maxima in the winter. As a consequence of urban atmospheric pollution the radiative forcing for urban site appears strongly modified in comparison with rural site.

The present work aims to investigate the effects of Saharan desert dust storms on cloud properties and respective radiative forcing over the South of Portugal and nearby Atlantic Ocean, for a case study that occurred between 26 and 29 May 2006, using the MODerate Resolution Imaging Spectroradiometer (MODIS) satellite data. The determination of cloud properties in different regions subject to the presence of dust aerosols provides information on the possible alterations that these clouds may suffer due to the presence of an aerosol layer. Cloud effective radius, optical depth and water path retrieved values are considerably smaller for clouds developing in a dusty atmosphere than for clouds in a dust-free atmosphere. Due to these changes it was also possible to observe that the instantaneous cloud radiative forcing (ICRF) values at the top of the atmosphere (TOA) and at the surface are lower when dust aerosols are not present.

A VAISALA Ceilometer CL31 is operating continuously in the Observatory of the Évora Geophysics Centre (CGE) since May 2006. The CL31 ceilometer provides measurements of the cloud base height up to three simultaneous layers and of the profile of the backscatter coefficient, which in the absence of clouds gives a good approximation of the qualitative aerosol boundary layer profile. The ceilometer backscatter measurements are used here to study special aerosol events that reach Évora (38°34'N, 7°54'W, 300m a.m.s.l.) such as forest fires, desert dust transports originating from the Sahara desert, which often occur in the south of Portugal and European pollution. The aerosol backscatter coefficient corresponding to the lowest layers of the atmosphere is also correlated with mass concentration measurements obtained from a TEOM (Tapered Element Oscillating Microbalance) installed in the same place (CGE observatory). The TEOM measures the in situ mass concentration of aerosols near the ground, with aerodynamic diameter lower than 10μm (PM-10), with temporal sampling of 10min. Furthermore, ceilometer measurements and derived mixing height are also compared with measurements taken with a Lidar during an intensive campaign that took place at the CGE observatory in Évora, during the first half of June 2006.