Measurements of aerosols are urgently required for understanding and modelling their role in the climate system and to investigate interactions between aerosols, clouds and radiation. Lidar is an excellent tool for aerosol observations, in particular, as it provides range resolved data. In this paper we briefly describe the different lidar configurations useful for aerosol observations and discuss in particular the limitations due to the unknown lidar ratio and strategies to overcome this problem. As a result, extinction coefficient as a function of height can be obtained. Recent approaches to derive microphysical parameters are introduced as well. The potential of lidars for aerosol remote sensing is illustrated by highlighting a few of the most important lidar activities of the last years and the upcoming spaceborne experiments.

It is of great interest to investigate the radiative features on the cloud optical, microphysical, and geometrical properties of clouds that play crucial role in the climate system. Here, top height, base height, and geometrical thickness of cloud layer are considered as cloud geometrical properties. Previous studies show that information of some spectral regions including oxygen A-band, enables us to retrieve cloud geometrical properties as well as optical thickness, effective particle radius of cloud. In this study, an algorithm was developed to retrieve simultaneously cloud optical thickness, effective particle radius, top height, and geometrical thickness of cloud layer with the spectral information of visible, near infrared, thermal infrared, and oxygen A-band channels. This algorithm was applied to the GLI dataset on board ADEOS-II satellite that has been launched recently. The preliminary results are not so strange and to be validated in future, comparing to the in-situ observations.

We discuss the relationship between instrument footprint size, field-of-regard sample density, and cloud clearing technique on measured top of the atmosphere radiance error under partly cloudy conditions. The cloud clearing technique (N*) uses the linear relationship between observed radiance and the amount of cloud in a field-of-view. We extrapolate radiance observed for two adjacent fields-of-view possessing differing cloud amounts to the cloud free value (i.e., zero cloud). Options include techniques to compensate for “black” or “gray” clouds, where a single channel N* may not provide adequate spectral correction. Spectrally dependent error statistics are developed from partly cloudy samples of varying footprint size and sample patterns. Data were collected by the NPOESS (National Polar-orbiting Operational Environmental Satellite System) Aircraft Sounding Testbed-Interferometer (NAST-I) flying on the NASA Proteus or ER-2 high altitude research aircraft, and include tropical, temporal and arctic flight sections. Analysis shows that larger sounder footprints contain more cloud contamination and higher cloud clearing errors; these errors can be significantly reduced by techniques that utilize high-spectral and -spatial resolution coincidently collected radiance measurements from sensors like MODIS. Data also indicates that full area sampling results in smaller cloud clearing errors than small footprint sampling on a wider spaced grid.

The micro- and macrophysical properties of clouds play a crucial role in Earth’s radiation budget. The NASA Clouds and Earth’s Radiant Energy System (CERES) is providing simultaneous measurements of the radiation and cloud fields on a global basis to improve the understanding and modeling of the interaction between clouds and radiation at the top of the atmosphere, at the surface, and within the atmosphere. Cloud properties derived for CERES from the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra and Aqua satellites are compared to ensure consistency between the products to ensure the reliability of the retrievals from multiple platforms at different times of day. Comparisons of cloud fraction, height, optical depth, phase, effective particle size, and ice and liquid water paths from the two satellites show excellent consistency. Initial calibration comparisons are also very favorable. Differences between the Aqua and Terra results are generally due to diurnally dependent changes in the clouds. Additional algorithm refinement is needed over the polar regions for Aqua and at night over those same areas for Terra. The results should be extremely valuable for model validation and improvement and for improving our understanding of the relationship between clouds and the radiation budget.

The Atmospheric Infrared Sounder (AIRS), launched in May 2002, is the first of a new generation of high-spectral resolution temperature and humidity sounders for numerical weather prediction and climate change studies. The accuracy of the AIRS radiances, and the validity of the clear sky AIRS Forward Model, have already been demonstrated. With daily global coverage by the instrument, the almost continuous wavelength coverage in the 10-12 micron and 3.7 micron atmospheric windows enables AIRS to excel at detecting cirrus clouds. This paper presents global retrievals of cloud top pressure, ice particle size and amount, using the AIRS radiances. Cloud optical depths lower than 0.1 (at 10 μm) have been detected. We also present comparisons between retrievals done using spherical particles to those done using nonspherical particles.

Cloud is an important factor for the radiation budget through reflection of solar radiation and absorption of terrestrial radiation. Climate change is dependent on these two effects and focusing on an aerosol-cloud interaction. In East Asian region, consumption of fossil fuels is increasing and emits many kinds of gas and particles in addition of natural sources. The indirect effect of aerosol depends on the aerosol characteristics and weather conditions. The particle size and chemical features of aerosols affect cloud formation and particle size. Therefore, it is interesting to understand cloud properties such as a liquid water path (LWP) and cloud effective radius (Reff). This study is to estimate these two parameters with ground-based observations. In the paper a method to estimate a cloud effective radius and optical thickness is proposed using a combination of corrected LWP and the downward solar radiation. It is useful for continuous observation, especially LWP can be estimated for all day.

Spatial remote sensing atmospheric correction algorithms validation remains a challenge particulary over land and coastal environment. To assess this type of algorithm in the case of MERIS scheme, we propose a methodology based on the use of in-situ extinction and sky measurements from the world-wide Sun radiometer network AERONET. The spectral dependency in the blue and red derived from the extinction measurements is used to parameterize an aerosol model defined by the Jung power law size distribution in a first step and a chemical composition represented by a refractive index. This model is used to compute the phase function, a main input to a radiative transfer code (successive order of diffusion based) that allows to simulate the atmospheric parameters (radiances, transmittances). A comparison between the diffuse transmittance from sky measurements and that simulated allow to check the validity of the proposed method. The context of the study is calibration and validation in remote sensing using only the radiative properties of the atmosphere. A sensitivity study of the method to various parameters and an error budget will be reported.

This work describes an iterative algorithm capable of determining the atmospheric parameters (temperature and water vapour profiles) by using NOAA ATOVS data and “in situ” observations currently collected at the Broglio Space Centre (BSC, located in Malindi-Kenya, 40 E, 3 S) of the Centro di Ricerca Progetto San Marco (CRPSM) of the University of Rome “La Sapienza” (Italy). The method is based on the usual approach to the problem of retrieving atmospheric characteristics: 1. a forward model (using the Modtran atmospheric code); 2. a numerical method for solving systems of non-linear equations (by means of a Broyden’s Quasi-Newton methods and a regularization method coupled with a preconditioning to computing stabilized solutions to the ill-posed problems). The retrieval method for the temperature and water vapour is discussed in detail; comparisons are also made with available co-located atmospheric information from balloon-based soundings. The aim of this paper is to evaluate the accuracy of the estimate of the tropical atmosphere parameters using a retrieval algorithm developed by authors, based on Broyden’s method for systems of non-linear equations.

The LIDPORT V2PLUS radiative transfer package is designed for simulation and retrieval applications for nadir viewing remote sensing instruments such as GOME, GOME-2, SCIAMACHY, OMI and MODIS. The package is based on the LIDORT family of linearized discrete ordinate models, and it will deliver earthshine radiances, analytic profile, total column and surface property Jacobians. LIDORT V2PLUS includes a quasi-exact single scatter computation for all solar beams and the line of sight direction in a curved spherical-shell refracting atmosphere, and a full treatment of the diffuse radiation field in the pseudo-spherical approximation at all points along the line-of-sight. We give examples of radiances and O₃ air mass factors at 325 nm, and Jacobians for O₃ total column and profiles and for surface albedos, with particular emphasis on the wide-angle spherically-corrected viewing mode. We also look at the effect of horizontal inhomogeneity caused by varying surface properties along the line of sight.

The Clouds and Earth’s Radiant Energy System (CERES) project is using multispectral imagers, the Visible Infrared Scanner (VIRS) on the tropical Rainfall Measuring Mission (TRMM) satellite and the Moderate Resolution Imaging Spectroradiometer (MODIS) on Terra, operating since spring 2000, and Aqua, operating since summer 2002, to provide cloud and clear-sky properties at various wavelengths. This paper presents the preliminary results of an analysis of the CERES clear-sky reflectances to derive a set top-of-atmosphere clear sky albedo for 0.65, 0.86, 1.6, 2.13 μm, for all major surface types using the combined MODIS and VIRS datasets. The variability of snow albedo with surface type is examined using MODIS data. Snow albedo was found to depend on the vertical structure of the vegetation. At visible wavelengths, it is least for forested areas and greatest for smooth desert and tundra surfaces. At 1.6 and 2.1-μm, the snow albedos are relatively insensitive to the underlying surface because snow decreases the reflectance. Additional analyses using all of the MODIS results will provide albedo models that should be valuable for many remote sensing, simulation and radiation budget studies.

Four earth-viewing nonscanning active cavity radiometers of the ERBS (Earth Radiation Budget Satellite) have been measuring the radiation arising from the earth-atmosphere system since its’ launch day, October 5, 1984. The ERBS spacecraft was placed in a non-sun-synchronous trajectory inclined at 57°. Two radiometers out of four, namely the wide field-of-view total (WFOV-T) radiometer which measures the radiation in the total spectral band of 0.2 - 100 μm, and the wide-field-of-view shortwave (WFOV-SW) radiometer measures the Earth’s reflected radiation in the wavelength region of 0.2 - 5 μm were used in this study. These sensors were calibrated continuously by observing the in-flight internal black bodies as well as the Sun every two weeks. The WFOV-T channel was found very stable within 0.1%. The monthly flux values of the ERBS nonscanning active cavity radiometers at satellite altitude and the corresponding NCDC (National Climatic Data Center) global surface temperature data for the period of fifteen years (1985-1999) were used in this paper. The effect of Mt. Pinatubo eruption is very clearly noticeable in the running trends of both WFOV-T and WFOV-SW radiometric measurements. Further the resulting twelve month running trends derived from the outgoing longwave radiation was found to follow the twelve month running trend determined from the global surface temperature data set. Both trends are real and increasing. The “global-cooling-like” event caused by the Mt. Pinatubo eruption was also found under both day and nighttime conditions.

A comparison of unfiltered radiances measured by CERES instruments (FM1 and FM4) operating on two different platforms, Terra and Aqua satellites, is presented. Data for the comparison were collected at orbital crossings in July and August 2002. Using a special scanning mode, viewing geometries of the instruments were matched to provide a large data set for comparing all three channels. In addition, the data collected over Greenland were used for a more stringent test of the consistency of the shortwave radiances. Statistics include different scene types and α tests on compiled averages.

The main objective of the SCALES Project is to exploit the unique opportunity offered by the recent launch of the first European METEOSAT Second Generation geostationary satellite (MSG-1) to generate and validate new radiation budget and cloud products provided by the GERB (Geostationary Earth Radiation Budget) instrument. SCALES’ specific objectives are: (i) definition and characterization of a large reasonably homogeneous area compatible to GERB pixel size (around 50 x 50 km²), (ii) validation of GERB TOA radiances and fluxes derived by means of angular distribution models, (iii) development of algorithms to estimate surface net radiation from GERB TOA measurements, and (iv) development of accurate methodologies to measure radiation flux divergence and analyze its influence on the thermal regime and dynamics of the atmosphere, also using GERB data. SCALES is highly innovative: it focuses on a new and unique space instrument and develops a new specific validation methodology for low resolution sensors that is based on the use of a robust reference meteorological station (Valencia Anchor Station) around which 3D high resolution meteorological fields are obtained from the MM5 Meteorological Model. During the 1st GERB Ground Validation Campaign (18th-24th June, 2003), CERES instruments on Aqua and Terra provided additional radiance measurements to support validation efforts. CERES instruments operated in the PAPS mode (Programmable Azimuth Plane Scanning) focusing the station. Ground measurements were taken by lidar, sun photometer, GPS precipitable water content, radiosounding ascents, Anchor Station operational meteorological measurements at 2m and 15m., 4 radiation components at 2m, and mobile stations to characterize a large area. In addition, measurements during LANDSAT overpasses on June 14th and 30th were also performed. These activities were carried out within the GIST (GERB International Science Team) framework, during GERB Commissioning Period.

A 'measure’ of the surface effect on downwelling radiance in the solar principal plane (SPP), K, is built by analysing simulations by a radiative transfer code. K describes the solar angle dependence of the radiance measured at a viewing angle θ_v=40° over radiance measured at θ_v=70°, both in SPP. The surface effect is described by a surface albedo value, used as an input parameter of the Successive Orders of Scattering code [Deuze et al., 1989]. K is mainly sensitive to the surface albedo but also to the Ångström exponent α and to the real part of the refractive index m_R. α is derived from independent measurements of spectral aerosol optical thickness and m_R is estimated in a first step of the method from radiance measurements made at θ_Sun=70°. The method is applied on data acquired at the AERONET site of Sede Boker, Israel, in 2000. Results give a high reflective surface with small spectral dependence. An event of increase of vegetation cover (which we suppose is caused by rain falls) is observed as the surface albedo at 675 nm decreases while it remains constant at 870 nm. Aerosol single scattering albedo derived at 675 nm from radiance measurements varies little around 0.90 only if surface albedo change is considered.

The Scanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) is a contribution to the ENVISAT-1 satellite, which has been launched in March 2002. The SCIAMACHY instrument measures sunlight transmitted, reflected and scattered by the Earth's atmosphere or surface simultaneously from the UV to the SWIR spectral region (214 - 2380 nm) in nadir, limb, and occultation viewing geometry. SCIAMACHY allows the characterisation of the composition of the Earth atmosphere from the ground to the mesosphere. This paper gives an overview of the SCIAMACHY instrument and its in-flight detector, spectral and radiometric performance. Furthermore first results on trace gas retrieval from limb and nadir measurement mode will be summarised.

There are large errors in satellite estimation of downward surface solar radiation (DSSR) at hourly time scales. This is due to several factors including mismatch in the spatial scale of the satellite vs. point measurements from surface pyranometers; and most importantly, structural variability in cloud properties. The authors examined the temporal and spatial variability of UV-B erythemal irradiance under cloudy stratocumulus conditions in Hobart Australia. Three radiometers were deployed at distances under 5 km. Short-term statistics were analysed and related to estimates from a three-dimensional radiation/cloud model with fractal properties in the horizontal. Results indicate that accuracy in satellite-derived hourly solar radiation may be improved with several satellite scans per hour, ideally every 10 minutes. However ground validation is a problem because an hourly measurement of irradiance in cloudy conditions is not likely to represent well the regional average as estimated from satellite.

The CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) experiment measured mid- and far-infrared limb spectra during two Shuttle missions in November 1994 and August 1997 from the upper troposphere to the lower thermosphere. From the CO₂ 15μm spectra temperatures in the mesosphere and lower thermosphere were derived using a non-LTE model coupled to a line-by-line radiative transfer code. CO₂ and atomic oxygen densities were calculated from the simultaneously recorded 4.3 μm (CO₂) and 9.6 μm (ozone) measurements. The retrieved temperatures reveal the very low high latitude summer mesopause temperatures. Zonal structures are found at all altitudes and in the summer hemisphere as well as in the winter hemisphere. The north polar temperature distribution near the mesopause is dominated by a wave 1 structure with some wave 2 contribution. The same pattern is observed in the distribution of polar mesospheric clouds (PMC) which were detected via their thermal emission near 12 μm. The appearance of the PMCs thus verifies the temperatures obtained from the non-LTE modeling. The wave structures extend well into the thermosphere.

MIPAS on ENVISAT measures vertical profiles of atmospheric temperature, ozone, and other species with nearly global coverage and high accuracy/precision. The standard observation mode covers the altitude region between 6 and 68 km. The atmospheric state parameters retrieved from MIPAS measurements using the IMK data analysis processor are compared with a number of other satellite observations. Our comparisons in this paper will focus on temperatures measured by MIPAS, HALOE, SABER, and UKMO Stratospheric Assimilated Data. Both individual profiles and zonal means measured by MIPAS and other instruments at different seasons and geolocations show reasonable agreement, though some differences exist due to characteristics of the individual instruments and observation scenarios. The MIPAS measurements during the stratospheric major sudden warming during the southern hemisphere winter of 2002 are also presented to show the features of this unusual event. The analysis indicates the reliability of MIPAS-IMK data products and their capability for providing valuable scientific information.

High-altitude limb infrared radiance spectra (CO₂ 15μm and O₃ 9.6μm bands) registered during CRISTA-1 experiment in November 1994 were interpreted using multiparameter inversion algorithm accounting for the nonlocal thermodynamic equilibrium conditions (non-LTE). Global distributions of temperature in the altitude range 40-120 km were obtained simultaneously with the distributions of CO₂ and O₃ (40-90 km) and vibrational temperatures of the lower vibrational states of CO₂ and O₃ molecules. Mean zonal values of temperature agree with CIRA-86 and SMLTM models. The root mean square variability of temperature reaches its maximum of 45 K at 105 km. Mesospheric temperature inversions were detected in 85% of cases during observations. The retrieved CO₂ profiles demonstrate that the altitude level, up to which CO₂ is well mixed, is considerably lower (70-75km) than predicted by models (85-90 km). Maximal diurnal variations of ozone were observed at 90 km altitude, where the mean value of volume mixing ratio is close to 2 ppmv for daytime and 7 ppmv for nighttime. The altitude levels of the LTE breakdown for the vibrational states of CO₂ and O₃ molecules and also the magnitude and vertical behavior of the non-LTE effect are in good agreement with numerical models.

The Solar Occultation for Ice Experiment (SOFIE) is one instrument proposed for the recently selected Aeronomy of Ice in the Mesosphere (AIM) satellite. SOFIE will characterize profiles of temperature, particle extinction, and gas concentration using differential solar occultation measurements with eight channel pairs covering wavelengths (λ) from 0.290 to 5.32 μm. Six of these broadband (~2% filter width) channels are designed to measure gaseous absorption (O₃, CO₂, H₂O, CH₄, and NO), and two are dedicated to particle absorption. Each channel uses two detectors, one that measures the target gas in a strongly absorbing spectral region and one that measures in an adjacent weakly absorbing spectral region. In addition to direct measurements, simultaneous difference signals measured for the eight channel pairs allow extraordinarily precision, resulting in a limb-path extinction of 10^-6 or less. Measurements in two CO₂ bands will be used to simultaneously retrieve profiles of temperature and CO₂ mixing ratio. In addition, temperature profiles will be retrieved in the lower stratosphere using measurements of the solar refraction angle versus height, an approach conceptually similar to that used in Global Positioning Satellite (GPS) refraction angle temperature retrievals. SOFIE measurements will accurately characterize temperature, gas mixing ratios, and particle extinction at altitudes from the tropopause into the lower thermosphere. Implementation and design issues, plus proof-of-concept are presented.

The Atmospheric Infrared Sounder (AIRS), launched in May 2002, is the first of a new generation of high-spectral resolution temperature and humidity sounders for numerical weather prediction and climate change studies. The accuracy of the AIRS radiances, and the validity of the clear sky AIRS Forward Model, have already been demonstrated. This paper presents global daytime measurements by the instrument, showing the effects of NLTE in the 4.3 μm CO2 band. Simulations using upper atmosphere NLTE temperatures are compared to actual AIRS measurements, for various solar angles.

The SABER instrument aboard the TIMED satellite is providing highly resolved and precise broadband limb emission measurements. Inverting these measurements to temperature profiles that extend into the lower thermosphere (90+ kilometers) is a complicated and often unstable process. Non-Local Thermodynamic Equilibrium models must be employed to model the upper atmosphere physics that thwarts the normal limb measurement advantages available to lower atmosphere retrievals. Maintaining hydrostatic pressure constraints while accurately modeling the effects of upwelling radiation can induce instabilities in attempts at iterative relaxation. We show that the limb geometry can be used to apply boundary conditions during “bottom-up” procedures that stabilize the process and allow rapid convergence by minimizing the required calculations of upwelling flux.

The SABER instrument on TIMED continuously measures certain infrared limb radiance profiles with unprecedented sensitivity. Among these are emissions of CO₂ ν₃ at 4.3 μm, routinely recorded to tangent heights of ~140-150 km, and NO at 5.3 μm, seen to above ~200 km and ~300 km, respectively. We use these infrared channels of SABER and coincident far ultraviolet (FUV) measurements from GUVI on TIMED, to study the geometric storm of April 2002. These all give a consistent measure of auroral energy input into the lower thermosphere at high latitudes. Emission in yet another SABER channel, near 2.0 μm, correlates well with enhanced electron energy deposition. We also have, in the 5.3-μm emissions from the long-lived population of aurorally produced NO, a tracer of how this energy is transported equator-ward and released over an extended period of time, a few days. In this paper, we discuss the global patterns of energy deposition into the expanded auroral oval, its transport to lower latitudes, and its loss as revealed by the NO 5.3-μm emissions.

The Institute of Applied Physics has developed a new ground-based radiometer for measurements of water vapour profiles in the stratosphere and mesosphere. The uncooled instrument, called MIAWARA, has a very good sensitivity and is calibrated using a combination of tipping curve and balancing calibration. Using this combination the instrument can operate as a self calibrating system without the need for routine maintenance. We present a validation technique for the tipping curve calibration and a new approach for the reference absorber design used in the balancing calibration. The uncommon design of the reference absorbers decreases standing wave artifacts and thus enhances the sensitivity of the instrument, leading to a very good altitude coverage in the range of 20 - 80 kilometres.

For altitudes above about 80 km, oxygen molecules are increasingly dissociated by solar vacuum ultraviolet absorption, and O atoms, together with N₂, become a principal constituent of the atmosphere. Through collisions with the ambient O atoms, the ground vibrational state of CO₂ is efficiently excited to its lowest excited vibrational state, with one quantum of energy in the ν₂ bending mode. In the near-space environment, a sizable fraction of this population relaxes via 15-μm spontaneous infrared emission, which effectively converts ambient kinetic energy into radiative energy that passes into space. This process is the principal upper atmospheric cooling mechanism in the 75-120 km altitude range. Despite the importance of this mechanism, current estimates of the CO₂(ν₂)-O vibrational relaxation rate constant k_O(ν₂) vary over a factor of six, with the laboratory measurements clustering in the 1-1.5 × 10^-12 cm³s^-1 range, and the aeronomical estimates in the 3-6 × 10^-12 cm³s^-1 range. We are currently pursuing vibrational relaxation measurements on the CO₂(ν₂)-O system in the laboratory, using the temperature jump method together with transient diode laser absorption spectroscopy detection of the CO₂ vibrational level populations. We will present the current state of progress of the experimental effort, as well as possible future directions.

Gravity wave variances in CLAES temperature data are isolated by a 0-6 zonal wavenumber Kalman filter. Resulting vertical profiles of temperature residuals are analyzed by a combination of Maximum Entropy Method (MEM) and harmonic analysis for gravity waves (GWs). This is the same method previously employed to study GWs in CRISTA data. We obtain nearly 1.5 years of continuous GW data between 34S and 34N and good coverage at higher latitudes depending on UARS yaw maneuvers. Results are compared to CRISTA data and interpreted for different wave sources. A time series of zonal mean GW variance shows the seasonal shift of the tropical maximum of GW variance around the equator. Maximum variances are reached 1-2 months after summer solstice, consistent with the shift of the inner tropical convergence zone. Quiet summer and enhanced winter values at mid and high latitudes are due to a combination of wind filtering and wind modulation. Wind filtering occurs when GWs propagate from tropospheric west winds into the lower stratosphere. There prevailing winds reverse from west wind in winter to east wind in summer, thus causing a critical layer for low phase speed GWs during summer. The term wind modulation is used for the Doppler shift of the GW spectrum by the wind at the observation altitude shifting parts of the GW spectrum in and out the vertical-wavelength visibility limits of the instrument. We find evidence for both processes in the data and indication that GW filtering might be the more important one.

The limb scattering radiances measured by SAGE III are analyzed. After accounting for instrument issues, ozone and nitrogen dioxide vertical density profiles are retrieved from the data and compared with results from other instruments. These initial results are very promising and show the potential of SAGE III to operate in this mode.

DARE (Dedicated Aerosol Retrieval Experiment) is a study to design an instrument for accurate remote sensing of aerosol properties from space. DARE combines useful properties of several existing instruments like TOMS, GOME, ATSR and POLDER. It has a large wavelength range, 330 to 1000 nm, to discriminate between aerosol types. The wide swath will enable daily global coverage of the earth at a pixel size of 5 x 5 km² (nadir). The instrument will have three viewing angles, looking forward, at nadir and backward. These angles will facilitate the separation of atmospheric and surface contributions to the satellite signal. Multiple views will also help to determine the height and thickness of aerosol layers. Full polarization information will be measured for at least one of the viewing angles and at many of the available wavelengths. Polarization helps to separate surface/atmosphere signals and it contains valuable information on the shape of aerosol particles. Cloud detection will be enhanced by adding thermal infrared detectors at the same spatial resolution. Simulations and tests were performed to optimize the current design of the instrument. The expected performance of DARE in comparison to other instruments will be discussed.

Atmospheric Infrared Sounder (AIRS) measurements of the sea surface temperature at 2616cm-1 show an unexpected cold bias compared to the NCEP Global Real Time SST. This cold bias, which is distributed in large scale patterns which are stable on the time scale of several months, has a satellite zenith angle (sza) dependent and a sza independent component. The sza independent component is strongly temperature dependent, and is most likely related to a larger than expected gradient between the bulk and the skin temperature, possibly due to not understood regional or seasonal weather patterns. The sza dependent component of about 0.4K is most likely due to some form of aerosol which is not included in the radiative transfer. AIRS was launched 4 May 2002 on the EOS Aqua into polar orbit.

The aim of this study is the retrieval of aerosol optical depth from the National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) sensor over land. The region of interest covers central Europe ranging from 50°N to 40.5°N and from 0°E to 17°E including the European Alps. On the temporal scale, we limit the data set to afternoon NOAA-16 passes of the entire year 2002. In this region, there are sixteen stations from the Aerosol Robotic Network (AERONET) at which we can compare the ground based versus the space borne measurements. The most crucial parameter in the retrieval procedure is the estimate of a correct surface reflectance since inaccuracies of 0.01 can result in AOD variations of ±0.1. Surface reflectance has been estimated by extracting the minimum reflectance within 10° intervals of the satellite zenith angle within two-month intervals. This method eliminates the varying reflectance with varying satellite zenith angle but the extracted surface reflectance still contains an aerosol signal. Most stations show a clear relationship between the AVHRR and the AERONET data. In case of a weak or non-existing relationship, we were able to identify reasons for this behavior. The standard error of estimate is about 0.18. The largest potential for increasing the accuracy of this product posses an improvement of the cloud mask. We can conclude that aerosol retrieval over land using AVHRR is a challenging task but it is possible to extract some valuable results.

A series of sensitivity studies is carried out to explore the feasibility of space-based global carbon dioxide (CO₂) measurements for global and regional carbon cycle studies. The detection method uses absorption of reflected sunlight in the CO₂ vibration-rotation band at 1.58 μm. The sensitivities of the detected radiances are calculated using a line-by-line model implemented with the DISORT model to include atmospheric scattering. The results indicate that (a) the small (~1%) changes in CO₂ near the Earth’s surface are detectable in this CO₂ band provided adequate sensor signal-to-noise ratio and spectral resolution are achievable; (b) the modification of sunlight path length by scattering of aerosols and cirrus clouds could lead to large systematic errors in the retrieval; therefore, ancillary aerosol/cirrus cloud data are important to reduce retrieval errors; (c) the atmospheric path length, over which the CO₂ absorption occurs, must be known in order to correctly interpret horizontal gradients of total column CO₂; thus an additional sensor for surface pressure measurement needs to be attached for a complete measurement package; (d) CO₂ retrieval requires good knowledge of the atmospheric temperature profile, e.g. approximately 1-K RMS error in layer temperature. Several candidate technologies are available to potentially meet these requirements.

Over land, the aerosol remote sensing is based on the observation of Dense Dark Vegetation (DDV) and this concept is applied on SeaWiFS with a spectral index (ARVI) to detect the DDV and the use of the bands at 412 nm, 443 nm and 670 nm to characterize the aerosols. We first extend the possibility to remote sense aerosol over less dark vegetation through a simple modeling of the vegetation reflectance ρ_DD.V versus the ARVI. A linear relationship exists between ρ_DD.V and ARVI, regardless of the geometrical conditions, but with a slight seasonal dependence. We then developed a level 3 aerosol product for global studies with 32 by 32 SeaWiFS pixels combined in a macro-pixel in order to include a significant number of DDV pixels Within these macro pixels, we documented the composition of the scene (sea, land and clouds), the mean aerosol products and the spatial dispersion of the aerosol product. This level 3 will be first used to investigate the sensitivity of the aerosol module to the inputs parameters: DDV models, assumptions on the aerosol model, accuracy of the radiometric calibration... Then, we will produce statistics on the aerosols over Europe over the SeaWiFS life time.

The paper is devoted to the application of the newly developed aerosol retrieval algorithm to a study of the aerosol optical thickness(AOT) spatial distributions for a number of hazard situations including fires and dust outbreaks. In particular we find that the spectral slope of the optical thickness decreases with the distance from a fire. This is owing to the aerosol aging mechanism. Also we discuss possible reasons for the spectral cloud optical thickness anomalous behaviour in the short-wave region.

SCIAMACHY is a UV/visible/near-infrared grating spectrometer on board the European environmental satellite ENVISAT that observes the atmosphere in nadir, limb, and solar and lunar occultation viewing geometries with moderate spectral resolution (0.2-1.5 nm). At the University of Bremen a modified DOAS algorithm (WFM-DOAS) is being developed primarily for the retrieval of CH₄, CO, CO₂, H₂O, N₂O, and O₂ total columns from SCIAMACHY near-infrared and visible nadir spectra. A first version of this algorithm has been implemented based on a fast look-up table approach. The algorithm and the look-up table is described along with an initial error analysis. Weighting functions and averaging kernels indicate that the SCIAMACHY near-infrared nadir measurements are highly sensitive to trace gas concentration changes even in the lowest kilometer of the atmosphere. The results presented have been obtained by applying WFM-DOAS to small spectral fitting windows focusing on CH₄, CO₂, CO, and O₂ column retrieval and CH4 and CO2 to O2 column ratios (denoted XCH₄ and XCO₂, respectively). These type of data products are planned to be used within the EU research project EVERGREEN to constrain surface sources and sinks of CH₄ and CO₂ using inverse modeling techniques. This study discussed the first set of WFM-DOAS products generated for and to be further improved within EVERGREEN. Although no detailed validation has been performed yet we found that the retrieved columns have the right order of magnitude and show (at least qualitatively) the expected correlation of the well mixed gases CO₂ and CH₄ with O₂ and surface topography. The standard deviation of the dry air column averaged mixing ration XCO₂ within 10° latitude bands is ±10 ppmv or 2.7% (XCH₄: ±50 ppbv or ±2.8%) for measurements over land (over ocean the scatter is a factor of 2-4 larger). These values have been determined from ~25% of the ground pixels of one orbit which fulfill the following requirements: (nearly) cloud free, solar zenith angle <75°, XCO₂ error < 4% (XCH4 error < 6%). It has not been assessed how much of this variability can be attricuted to real column changes. The observed variability is about three times larger than expected from (single spectra) signal-to-noise considerations but might be affected by limitations of the current implementation of the retrieval algorithm (e.g., sensitivity to surface reflectivity) and calibrations issues (e.g., not yet considered ADC non-linearity correction). Especially the CO retrieval needs further study and improvement. The CO fit errors are 20-40% over land but typically significantly larger over the ocean. A clear identification of the weak CO lines is difficult as the CO fit residuals are dominated by relatively stable systematic artifacts (also observed in the CO₂ and CH₄ fitting windows) on the order of the weak CO absorption lines. This might be explained by the still preliminary calibration of the SCIAMACHY spectra and/or errors of the spectroscopic data.

The Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) is the first hyper-spectral remote sounding system to be orbited aboard a geosynchronous satellite. The GIFTS is designed to obtain revolutionary observations of the four dimensional atmospheric temperature, moisture, and wind structure as well as the distribution of the atmospheric trace gases, CO and O₃. Although GIFTS will not be orbited until 2006-2008, a glimpse at the its measurement capabilities has been obtained by analyzing data from the National Polar-orbiting Operational Environmental Satellite System (NPOESS) Airborne Sounder Test-bed- Interferometer (NAST-I) and Aqua satellite Atmospheric Infrared Sounder (AIRS). In this paper we review the GIFTS experiment and empirically assess measurement expectations based on meteorological profiles retrieved from the NAST aircraft and Aqua satellite AIRS spectral radiances.

Algorithms to simulate the statistical microphysical and optical models for aerosol and polar stratospheric cloud (PSC) are described. Examples of such models for stratospheric and tropospheric aerosols and PSC are given. Different ways of applying the statistical aerosol and cloud models are discussed: - optimal parameterization of spectral dependences of aerosol extinction coefficient using the natural orthogonal basis; - multiple regression for estimating the optical parameter from measured one (for example, estimation of scattering coefficients from SAGE III multiwavelength measurements of aerosol extinction coefficients); - retrieval of microphysical properties of stratospheric aerosol and PSC from SAGE III extinction measurements; - lidar sounding.

An algorithm for the combined retrieval of ozone, NO₂, spectral aerosol extinction profiles and different microphysical properties of stratospheric aerosol is described. Principal features of the algorithm are the use of simulated statistical aerosol models as a priori information and optimal parameterization of spectral dependence of aerosol extinction coefficients (by expanding in natural orthogonal basis). The statistical microphysical models of stratospheric aerosols are used for retrieving the aerosol size distribution function. Results of numerical experiments for the study of error budget of this algorithm are given. Data of slant path transmittance spectral measurements by SAGE III (Meteor-3M) have been processed and analyzed. Results of retrieving the different atmospheric parameters are compared with independent measurements.

The main engines exhaust of two Boeing 767-3ZR(ER) powered by Pratt & Whitney 4060 has been intensively studied using spectroscopic methods like Fourier Transform Infrared Spectroscopy (FTIR) and Differential Optical Absorption Spectroscopy (DOAS). All cockpit data was provided by the operating airline while the thrust level was varied between idle (25% N1) and 70 % N1 where N1 is the maximum number of revolutions of the fan. The investigated gaseous species were carbon dioxide, carbon monoxide, nitrogen oxides (NO and NO₂) and some hydrocarbons (C₂H₄, C₂H₂, HCOH and unburned kerosene). A comparison to the database of the International Civil Aviation Organization (ICAO) showed much higher emissions of CO and NOx-emissions in the same range. Although these two aircraft were of the same age and maintained by the same operator the emissions differed by a factor of two. Formaldehyde proved to be the most abundant hydrocarbon besides ethane and ethane.

The emission indices of aircraft engine exhausts were measured at airports non-intrusively by FTIR emission spectrometry at the engine nozzle exit as well as by FTIR absorption spectrometry and DOAS (Differential Optical Absorption Spectrometry) behind the aircraft. Two measurement campaigns were performed to compare these different measurement methods. A kerosene powered burner was operated in that way that the different methods were applied for the exhaust gas investigations during the same time and at nearly the same exhaust gas volume. The burner was built with a nozzle exit diameter of 37 cm and a power of about 150 kW. Fresh air was pumped into the burner tube by a fan. Calibration gases as pure CO and NO were added in different amounts to vary the concentration of these gases in the exhaust. The sampling probe of an intrusive measurement system was installed in the centre of the exhaust stream near the exhaust exit for measurements of these gases and CO₂ as well as NO₂, UHC, SO₂ and O₂. An APU (GTCP36-300) in a test bed was used in the same way. CO was mixed into the exhausts near the nozzle exit. The passive FTIR instrument was operated in the test bed using special noise and vibration isolation. The open-path instruments were installed at the chimney exit on the roof of the test bed building. The deviations between the different measurement methods were in the order of ±10 up to ±20 %.

The total length of natural gas pipelines in Germany exceeds 350,000 km. Currently, inspections are performed using hand-held sensors such as flame ionization detectors. Moreover, transmission pipelines are inspected visually from helicopters. In this work, remote detection of methane by passive Fourier-transform infrared (FTIR) spectrometry for pipeline surveillance is investigated. The study focuses on fast measurements in order to enable methane detection from a helicopter during regular inspection flights. Two remote sensing systems are used for the detection of methane: a scanning infrared gas imaging system (SIGIS), which was originally developed for the visualization of pollutant clouds, and a new compact passive scanning remote sensing system. In order to achieve a high spectral rate, which is required due to the movement of the helicopter, measurements are performed at low spectral resolutions. This results in overlapping signatures of methane and other constituents of the atmosphere in the measured spectrum. The spectra are analyzed by a detection algorithm, which includes simultaneous least squares fitting of reference spectra of methane and other atmospheric species. The results of field measurements show that passive remote sensing by FTIR spectrometry is a feasible method for the remote detection of methane.

Methane (CH4) and carbon monoxide (CO) total column amounts (TCA) measured at the Research Institute of Physics of St. Petersburg State University (Russia) were used for: 1. study of temporal variability of CH₄ and CO; 2. identification of source regions of CO and CH₄ using trajectory analysis. CH₄ and CO showed distinct annual cycle with the amplitude of about 3% and 25% correspondingly. Period of 1999-2002 has a significant decline of CH₄ TCA for the St. Petersburg region. The suggested reason is hot and dry summers of 1998-2002. October 1998 - March 1999 is characterized by the strong irregular disturbances of CO TCA. Growth rates of CO TCA have changed at this period from (3.5±2.3)%/yr (for 1995-1998) up to (-2.1±1.5)%/yr (for 1999-2002). Enhanced CO and CH₄ TCA levels are observed for air masses originated from the sectors of the North Russia, continental Russia and the Eurasia. Europe can be classified as moderately polluted territory. Clean air comes from the Baltic Sea, Arctic Ocean and Scandinavia. Distribution of CO pollution levels over sectors repeats qualitatively situation for CH₄.

Knowledge of the global distribution of the vertical velocity of precipitation is important for estimating latent heat fluxes, and therefore in the general study of energy transportation in the atmosphere. Such knowledge can only be acquired with the use of spaceborne Doppler precipitation radars. Recent studies have shown that the average vertical velocity can be measured to acceptable accuracy levels by appropriate selection of radar parameters. Furthermore, methods to correct for specific errors arising from Non-Uniform Beam Filling effects and pointing uncertainties have recently been developed. As detailed in the Global Precipitation Mission (GPM) preparatory studies, the use of a dual-frequency precipitation radar allows improved estimation of the main parameters of the hydrometeor size distribution (bulk quantity and one shape parameter). Such parameters, in turn, lead to improved estimates of latent heat fluxes. In this paper we address the performance of a dual- frequency Doppler Precipitation Radar (DDPR) in estimating the latent heat fluxe from the measured rainfall vertical velocity and DSD parameters.

We present measurements of the vertical structure of the aerosol extinction coefficient in the lower troposphere, up to five kilometers. Lidar profiles were collected at Armilla (680 m asl) and Pitres (1252 m asl) during the VELETA-2002 campaign, organized to analyze the effect of altitude and aerosols on ground-level UV spectral irradiance. Single-wavelength lidar signals are inverted to derive vertically resolved aerosol extinction coefficient and integrated to provide aerosol optical depth (AOD) at 532 nm. These results are compared with measurements of the aerosol optical depth at the same wavelength provided by Licor LI-1800 spectroradiometers located at several altitudes. Lidar traces show that most of the aerosol loading is present in the first 2.5 km layer before a high-dust Saharan air mass overflew the site. On the 17th of July evening, an elevated aerosol layer was detected between 2.5 and 3.5 km and during the following three days the aerosol vertical profile of the lower atmosphere showed Sahara dust layers, producing relatively high values for the optical depth.

The Vaisala ceilometer CT25K is an eye-safe commercial lidar mainly used to report cloud base heights and vertical visibility for aviation safety purposes. Compared to ceilometers with biaxial optics, its single lens design provides a higher signal-to-noise ratio for lidar return signals from distances below about 600 m, thus increasing its abilities to examine the mixing layer. A CT25K ceilometer took part in the environmental research project VALIUM at the Lower Saxony State Agency for Ecology (NLO) in Hannover, Germany, investigating the air pollution in an urban surrounding with various sensors. Lidar return signals are reported every 15 s with a height resolution of 15 m. This paper covers two aspects of the interpretation of these signals. The aerosol backscatter of the atmosphere up to 30 m is compared to the PM10 concentration reported by an in situ sensor every 30 minutes, and the results are interpreted in respect of meteorological parameters such as humidity, temperature, wind, and global radiation. With relative humidity values below 62 % and no rain present the correlation between ceilometer backscatter and PM10 values is good enough to qualify standard ceilometers as instruments for a quantitative analysis of the atmospheric aerosol contents. Backscatter values up to 1000 m height are presented that allow an estimation of the convective boundary layer top in dry weather situations. The atmospheric boundary layer structures derived from ceilometer data are compared to those reported by a SODAR and a RASS that also took part in the VALIUM research project. Finally the backscatter data quality of a double lens ceilometer is compared to that of the single lens CT25K ceilometer to investigate to what extent these lidar systems are also able to report aerosol concentration.

A multi-wavelength lidar system that can measure simultaneously spectral extinction coefficient and depolarization ratio has been developed and tested. Some results from lidar measurements aerosol extinction coefficient, lidar ratio, and depolarization ratio of aerosols are presented. Lidar transmit system generates 20 Hz laser pulses at 355nm, 532nm, and 1064nm with an Nd:YAG laser. Backscattered light from atmospheric aerosol particles is collected with three Cassegrain type telescopes. Signal detection unit has 7-channels consisting of two 532nm channels and one 1064nm channel for measuring the stratospheric aerosols, two 532nm channels for the tropospheric aerosols, and 387nm channel for Raman scattering measurements. Aerosol observation has been conducted since December 2002 at Kwangju (35°10`N, 126°53`), Korea. Raman channel permitted better determination of optical properties of continental aerosols. The profile of the depolarization ratio is determined at 532 nm and used to investigate particle shape.

Regular aerosol backscatter measurements using an elastic-backscatter lidar were performed between May 2000 and November 2002 in Barcelona (Spain), in the frame of EARLINET (European Aerosol Research Lidar Network). The mixing layer height, required to understand the chemical and physical processes taking place in the low troposphere, was one of the major parameters to be retrieved. Three analytic definitions of the ML height have been tested using the range squared-corrected lidar signal: (1) the minimum of its first derivative, (2) the minimum of its second derivative, and (3) the minimum of the first derivative of its logarithm. The strong coastal and orographic influences and the climatological settling of Barcelona determine the complexity of its atmospheric boundary layer dynamics and the high heterogeneity of the lidar signals. Therefore, single lidar analyses do not allow an unambiguous determination of the mixing layer height in many cases and complementary data are needed, such as synoptic maps, backtrajectories, radiosoundings and solar irradiance profiles. The resulting mixing layer heights were compared to radiosoundings, and the second method was found to give statistically the best results. This definition was used to process the whole dataset. A number of 162 days and 660 profiles were examined. The mixing layer height was inferred in cases such as low clouds, Saharan dust events and sea breeze and mountain induced recirculation. Variations between 300 and 1450 m were observed over the three years.

We developed a cloud profiling radar transmitting frequency-modulated continuous wave (FM-CW) at 95 GHz for ground-based observations. Millimeter wave at 95 GHz is used to realize high sensitivity to small cloud particles. An FM-CW type radar would realize similar sensitivity with much smaller output to a pulse type radar. Two 1m-diameter parabolic antennas separated by 1.4m each other are used for transmitting and receiving the wave. The direction of the antennas is fixed at the zenith. The radar is designed to observe clouds between 0.3 and 15 km in height with a resolution of 15 m. Using the facility, test observations and long term campaign observations have been done. Results of observations show that the system is sensitive and stable enough to observe various clouds.

Two different lidar platforms were employed in the Pacific 2001 field study. A simultaneous upward/downward airborne lidar system called AERIAL (AERosol Imaging Airborne Lidar) was flown aboard the National Research Council of Canada Convair 580(CV580). The primary task of this platform was to establish a regional picture of particulate matter (PM) concentrations in the Lower Fraser Valley (LFV). The high temporal and spatial resolution of the lidar provided images of PM stratification and boundary layer structure along predetermined flight lines. The flight lines were divided into a series of north-south and east-west lines to provide a snapshot of the LFV as well as provide aerial support for four ground sites. The airborne lidar system also including a cross-polarization channel that is sensitive to particle shape (non-sphericity), for example smoke plumes from forest fires. There were 9 flights flown over a 3 week period including 2 night flights. The primary purpose of the night flights was to map PM transport in the lake valleys along the north range of the LFV. A scanning lidar facility called RASCAL (Rapid Acquisition SCanning Aerosol Lidar) was part of a suite of instruments making longer term measurements at the Langley Lochiel ground site. The lidar system was programmed to take three elevation scans (west, north and east) of the troposphere from the horizon to near zenith. Measurements were conducting for approximately 16 hours per day except longer during aircraft night flights. Results from both the airborne and scanning lidar facilities will be presented.

Elements of spectroscopic continuous-wave, frequency-modulated ladar (CW-FM-ladar) concept based on principles of both CW-FM-range-finding and modulation spectroscopy, and also on modern techniques of optical signal transmission, reception and processing are presented. Features of heterodyning methods for ladar echo-signal reception are considered. The comparison of CW-FM-ladar with CW-FM-range-finder and incoherent pulse lidar is carried out. Estimations of the achievable signal-to-noise ratio, the operation range and the range resolution are performed using frequency-dependent parameters of the transmitting and receiving subsystems. Preliminary experimental results on the range-finding subsystem characteristics of the CW-FM-laser diode (LD)-ladar are discussed.

Lidar probing of dense water clouds gives rise to significant multiple scattering contributions. Instead of trying to mitigate the effect, we have developed methods to collect and angularly resolve the multiple scattering returns. The proposed retrieval method combines these measurements with a rapid semi-empirical computation method of the lidar multiple scattering contributions. Solutions are calculated for the extinction coefficient, the effective droplet diameter, the liquid water content and the rain rate. The paper reviews the main measurement methods, discusses briefly the concept and implementation of the retrieval technique, presents validation results obtained from Monte Carlo simulations, and compares lidar solutions for liquid water content and effective droplet diameter with in-cloud aircraft measurements. Good correlation is demonstrated for both simulation and field data. We conclude that multiple-scattering lidar is a practical option for the remote sensing of water cloud microphysical parameters up to the lidar penetration depths of typically 200 m.

Improved retrieval algorithms for aerosols, clouds and water vapor content from satellite data are described. A POLDER sensor, mounted on the Earth observation satellite ADEOS in 1996, is a unique sensor, which can gather multi-directional (up to 14) polarization measurements of one target. The POLDER sensor has been mounted on the satellite ADEOS-II launched on 14 December in 2002. Aerosol and cloud properties are derived from the POLDER polarization data over the land and the ocean. In addition POLDER data in the near infrared wavelengths are available to estimate the total column content of atmospheric water vapor. It is well known that the thermal data are useful for retrieval of cloud properties and water vapor contents over the ocean. Therefore combination use of ADEOS/POLDER and OCTS is considered for retrieval of atmospheric hydrologic substances in this study. The satellite derived results are validated with the ground-based data as AERONET. The obtained global maps of aerosol and cloud properties, and water vapor content are compared with one another. It is shown that column number density of aerosols has a negative correlation with the effective radius of cloud particles and proportionally correlates with the optical thickness and the column number density of cloud particles. These results confirm the indirect effect of aerosols, namely aerosols play sufficient role as cloud condensation nuclei.

Results will focus on cirrus events which occurred during the ARM FIRE Water Vapor Experiment (AFWEX 2000) and Texas 2002 (TX2002) field campaigns over the Southern Great Plains Cloud and Radiation Testbed site (Oklahoma, USA) on 8 December 2000 and 29 November 2002, respectively. Aircraft measurements were taken from the NPOESS Airborne Sounder Testbed-Interferometer (NAST-I) during AFWEX 2000 and the Scanning-High resolution Infrared Sounder (S-HIS) during TX2002. Surface measurements were acquired by the Atmospheric Emitted Radiance Interferometer (AERI), located at the Central Facility. A second AERI, operating in rapid-scan mode within the University of Wisconsin mobile AERIbago, was available during the Texas 2002 case. Spectral absorption optical depths were retrieved using the high spectral resolution infrared measurements combined with lidar measured cloud boundaries. The spectral variation in each optical depth measurement were used to infer cloud particle effective radius from a database of hexagonal column extinction calculations. Results will compare cloud optical properties from simultaneous below- and above-cloud measurements.

Cloud cover influences the distribution of the solar radiation reaching the ground. Resulting fluxes of sensible and latent heat are critical to the accurate characterization of boundary layer behavior and mesoscale circulation that often lead to convective developments. Therefore the spatial and temporal variation in cloud cover can greatly affect regional and localized weather processes. This work describes an algorithm aimed at identifying cloudy and clear pixels in MODIS images. The algorithm is a real time procedure which, from geolocated and calibrated data, allows obtaining cloud masks with four clear sky confidence levels.

Multi-angle multi-spectral scans of upward total and polarized radiance were measured by the Research Scanning Polarimeter onboard a Cessna 210 aircraft during the Chesapeake Lighthouse and Aircraft Measurements for Satellites experiment. The surface contribution to the polarized radiance (PR) was evaluated for its effect on the retrieval of aerosol properties from PR over land surfaces. The atmospheric contribution to PR was negligible at 2250 nm for an aerosol having an aerosol optical thickness (AOT) at 440 nm of 0.72 and AOT at 865 nm of 0.17. The atmospheric and surface contribution to PR at 865 nm were found to be similar for this aerosol load. Thus, although the 2250 nm measurements can be used to characterize the surface on this very turbid day, this is not the case for the 865 nm measurements. The polarized and total radiances at 1590 and 2250 nm were found to be strongly correlated, suggesting that a common physical process affects reflection and polarization since this correlation was present even within a given surface type. Near the backscattering direction a simple front facet Fresnel reflection model of surface polarization breaks down and the surface polarized reflectance shows considerable spectral variability and angular structure that may be of use in evaluating the structural parameters of vegetated and soil surfaces.

This paper studies ionospheric clutter conditions and compares ionosonde measurements in the mid-latitude and arctic regions to determine the most favourable conditions for HFSWR surveillance for surface vessels and low-altitude air targets. The best time to perform HFSWR surveillance is between approximately 06:00-15:00 UT and 20:00-00:00 UT. During these hours, the number of days that sporadic-E interference occurs in a month and the range of frequencies reflected is minimized compared to other times of the day. Of the sites considered, Resolute Bay is the most favourable site for HFSWR surveillance in the summer since sporadic-E interference occurs least often, resulting in reduced signal interference. Similarly, Eureka is the preferred site during the winter months. In addition, the ionosphere at Eureka generally reflects the lowest range of maximum frequencies (~4 - 8 MHz), again resulting in less clutter interference. In all the observations, polar cap sites Eureka and Resolute Bay yield results that are less prone to sporadic-E interference than the mid-latitude site Cambridge Bay.

Over land, the Dense Dark Vegetation is used to derive in a first stage the aerosol path radiance and in a second stage to propose an aerosol product which consists of the aerosol type and of the aerosol optical thickness. Air quality monitoring of the particles is based on measurements of PM₁₀ and PM_2.5 which are respectively the density of particles of diameter lesser than 10μm, lesser than 2.5 μm, at the surface. The satellite aerosol product can be converted into PM₁₀ and PM_2.5, based on different assumptions: particle density and vertical distribution mainly. This first attempt to monitor PM from space can be validated with in-situ data. An other approach will simply consist in using the in-situ PM measurements to calibrate the satellite imagery. With the frame of an European project, we generated, over an area centred on Lille (50'36° N, 3'08 E, North of France), a data base with the SeaWiFS archive, and the PM data collected by the regional air quality network. The above technique will be applied and validate using this data base.

This work describes the optical properties of aerosols derived by sun/sky radiometry over Japan during APEX-E3 from March to May in 2003. Two Cimel Sun/sky radiometer (CE-318-2 and CE-318-1) and a Prede Sky radiometer (POM-100P) were set up at Noto, Shirahama, and Fukue-jima site. These radiometers are available for direct- or diffuse-solar radiation measurements in order to derive the aerosol optical thickness, size distribution, and so on. Four large aerosol events [a) March 14, b) March 25-27, c) April 12-13, and d) May 20-24] were observed from March to May in 2003. Event-a and -b are described by anthropogenic particles. The event-c is the typical Asian dust event which is indicated by small Angstrom values and peek of particle radius ~ 1-2 μm. The event-d results in the Siberian large bio-mass burning plume. It is of interest to mention that both events b and c are confirmed by the NOAA’s HYSPLIT backward trajectory simulations in order to investigate the aerosol origins.

The calibration of integrated water vapor amount retrieved from Cimel Sun radiometer, the main instrument of the worldwide Sun radiometer network AERONET (http://aeronet.gsfc.nasa.gov) is analyzed. The assessment procedure is based on the using of independent measurements derived from Global Positioning System (GPS) meteorology and parametric solar transmittance methods in solar 940 nm band. The results highlight the importance and the necessity of a continuous and flexible monitoring system for Sun radiometric retrieved water vapor. The established improved calibration procedure is useful in the framework of both water vapor spatial remote sensing calibration and validation activities, and climate applications for which this parameter remains a source of uncertainty.

Based on the evidence of the correlation between certain differential spectral parameters that can be estimated through attenuation measurements in the 18-22 GHz spectral range and the columnar content of atmospheric water vapor (IWV: Integrated Water Vapor), recently we pointed out that such correlation can be profitably exploited to provide direct estimates of the IWV along vertical Earth-satellite links, showing in particular that at 19 GHz a practically deterministic relationships holds between the IWV and such differential spectral parameters. In this paper we present some new simulation results to show that the parameters can be estimated by means of a 19 GHz CW-FM nadir pointing radar, providing in this way a continuous monitoring of the IWV along vertical atmospheric sections. Differential attenuation measurements are made by exploiting the backscatter from the Earth surface. Simulations, that are based on real vertical profiles of temperature, pressure and water vapor concentration as provided by a large radiosonde dataset, refer to a LEO satellite and to an airborne configuration, indicate the possibility to retrieve the IWV in both cases.

Systematic Lidar measurements of tropospheric aerosols optical properties have been carried out in the urban area of Napoli (Southern Italy, 40°50’18”N, 14°10’59”E, 118 m above sea level), in the framework of EARLINET project. Lidar systematic measurements of aerosol backscattering and extinction profiles have been performed at laser wavelength of 351nm and were obtained from simultaneously measurements of elastic and N₂ Raman signals. Following the EARLINET protocol, regular measurements have been performed three times a week in two days and they provide information on aerosol optical properties, with a final spatial resolution of 60m and a temporal resolution between 1 and 30 min. A statistical analysis in terms of integrated backscattering (BI), optical depth (OD), extinction to backscattering ratio (LR), and Dust Layer height (DL), obtained from measurements carried out in clear sky conditions over 30 months, has been realized. Further measurements have been performed during Saharan Dust transport events and some detailed observation of complete diurnal cycle has been carried out, in order to know the dynamic and the evolution of the Planetary Boundary Layer

Recent studies worldwide have revealed the relation between urban air pollution, particularly fine aerosols, and human health. The current state of the art in air quality assessment, monitoring and management comprises analytical measurements and atmospheric transport modeling. Earth observation from satellites provides an additional information layer through the calculation of synoptic air pollution indicators, such as atmospheric turbidity. Fusion of these data sources with ancillary data, including classification of population vulnerability to the adverse health effects of fine particulate and, especially, PM₁₀ pollution, in the ambient air, integrates them into an optimally managed environmental information processing tool. Several algorithms pertaining to urban air pollution assessment using HSR satellite imagery have been developed and applied to urban sites in Europe such as Athens, Greece, the Po valley in Northern Italy, and Munich, Germany. Implementing these computational procedures on moderate spatial resolution (MSR) satellite data and coupling the result with the output of HSR data processing provides comprehensive and dynamic information on the spatial distribution of PM₁₀ concentration. The result of EO data processing is corrected to account for the relative importance of the signal due to anthropogenic fine particles, concentrated in the lower troposphere. Fusing the corrected maps of PM₁₀ concentration with data on vulnerable population distribution and implementation of epidemiology-derived exposure-response relationships results in the calculation of indices of the public health risk from PM₁₀ concentration in the ambient air. Results from the pilot application of this technique for integrated environmental and health assessment in the urban environment are given.

Backscatter lidar measurements were performed in the atmospheric boundary layer and the troposphere above Neuchatel, Switzerland (47.00°N, 6.95°S, 485m asl). The backscatter lidar is based on Nd:YAG laser. The lidar measurements are done in the period from June 2000 till February 2002 as part of the EU project EARLINET (http://lidarb.dkrz.de/earlinet/). From the lidar measurements, we determine the following values vertical profile of the aerosol backscatter coefficients, the gradient of the range-corrected lidar signal and the variance of the range-corrected lidar signal. These values are used to determine the aerosol mixed layer (AML) height in the atmospheric boundary layer (ABL). In this work, we present a comparison of these different lidar methods to determine the AML height. The lidar-obtained values are also compared with the values for ABL top, as determined from upper air weather parameters. This comparison is performed and presented for various seasons and time in the diurnal cycle.

In a number of measurement scenarios it is necessary to operate a lidar in remote sites with a minimum personnel attendance on the spot. This requires a stability of operation, automatic functioning and remote control of the instrument status, and data downloading. Such backscatter/depolarisation lidar is realised by Observatory of Neuchatel and was operated for one year in Basel, Switzerland as part of Urban Boundary Layer study (BUBBLE project). The lidar is optimal for measurements at altitudes of planetary boundary layer (PBL) and troposphere. The operation was remotely controlled via internet from the premises of Observatory of Neuchatel. The lidar measurements covered a large number of the diurnal cycles of PBL development. We present a brief description of the lidar and its operation. We also present a preliminary results for PBL diurnal cycle measurements. These results include: determination of the aerosol mixed layer height using the altitude derivative of the lidar backscatter range-corrected signal and determination of the aerosol backscatter coefficient with a lidar signal inversion procedure.

We introduce a low cost, lightweight and compact polarisation sensitive radiometer for the measurement of Cirrus clouds in the submilimeter and far-infrared region (10-50 cm^-1). It is widely recognised that enhanced global measurements of cirrus properties are essential to the development of General Circulation and Climate Prediction Models (GCMs) since cirrus clouds have a strong effect on the Earths Global Radiation Budget. We introduce a project currently under development in Cardiff, to design and build a novel instrument suitable for aircraft deployment in order to measure Ice Water Path (IWP) along with cirrus particle size and shape. The radiometer will capitalise on the on going measurements of the NASA led, Fourier Transform interferometer based, Far-Infrared Sensor for Cirrus (FIRSC) instrument for which Cardiff has been closely associated. Data from FIRSC campaigns is being used to select optimum radiometer channels that exhibit good sensitivity to specific cirrus. This new multi-channel radiometer will however have some key advantages over similar spectroscopic instruments for example: portability, increased optical efficiency, a multi-angle field of view and a reduced integration period leading to an improved spatial resolution. The radiometer will benefit from the application of state-of-the-art submm/FIR polariser and solid filter technology currently being developed in Cardiff.