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The Ocean and Land Color Instrument (OLCI) onboard the Copernicus Sentinel-3A satellite is a medium-resolution and multi-spectral push-broom imager acquiring radiance in 21 spectral bands covering from the visible to the far near-infrared. These measurements are primary dedicated to land & ocean color applications, but actually include also reliable information for atmospheric aerosol and surface brightness characterization. In the framework of the EUMETSAT funded study to support the Copernicus Program, we describe the retrieval of aerosol and surface properties from OLCI single-viewing multi-spectral Top-Of-Atmosphere (TOA) radiances based on the Generalized Retrieval of Atmosphere and Surface Properties (GRASP) algorithm. The high potential of the OLCI/GRASP configuration stems from the attempt to retrieve both aerosol load and surface reflectance simultaneously using a globally consistent high-level approach. For example, both over land and ocean surfaces OLCI/GRASP uses 9 spectral channels (albeit with different weights), strictly the same prescribed aerosol models and globally the same a priori constraints (though with some differences for observations over land and ocean). Due to the lack of angular multi-viewing information, the directional properties of underlying surface are strongly constrained in the retrieval: over ocean the Fresnel reflection together with foam/whitecap albedo are exclusively computed using a priori wind speed; over land, the Bidirectional Reflectance Distribution Function (BRDF) is slightly adjusted from a priori values of climatological Ross-Li volumetric and geometric terms. Meanwhile, the isotropic reflectance is retrieved globally under mild spectral smoothness constraints. It should be noticed that OLCI/GRASP configuration employs innovative multi-pixel concept (Dubovik et al., 2011) that enhance retrieval by simultaneously inverting large group of pixels. The concept allows for benefiting from knowledge about natural variability of the retrieved parameters. The obtained OLCI/GRASP products were validated with the Aerosol Robotic Network (AERONET) and Maritime Aerosol Network (MAN) and intercompared with the Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol and surface products. The overall performance is quite comparable to the community-referenced MODIS. Over ocean the OLCI/GRASP results are encouraging with 67% of the AOD (550 nm) satisfying the Global Climate Observing System (GCOS) requirement using AERONET coastal sites and 74% using MAN deep ocean measurements, and an AOD (550 nm) bias 0.01 with AERONET and nearly zero bias with MAN. Over land, 48% of OLCI/GRASP AOD (550 nm) satisfy the GCOS requirement and a bias within ±0.01 for total and AOD < 0.2. Key challenges are identified and discussed: adequate screening of cloud contaminations, retrieval of aerosol over bright surfaces and in the regions containing complex mixtures of aerosol.

This work presents a study on the sensitivity of two satellite cloud height retrievals to cloud vertical distribution. The difference in sensitivity is exploited by relating the difference in the retrieved cloud heights to cloud vertical extent. The two cloud height retrievals, performed within the Freie Universität Berlin AATSR MERIS Cloud (FAME-C) algorithm, are based on independent measurements and different retrieval techniques. First, cloud-top temperature (CTT) is retrieved from Advanced Along Track Scanning Radiometer (AATSR) measurements in the thermal infrared. Second, cloud-top pressure (CTP) is retrieved from Medium Resolution Imaging Spectrometer (MERIS) measurements in the oxygen-A absorption band and a nearby window channel. Both CTT and CTP are converted to cloud-top height (CTH) using atmospheric profiles from a numerical weather prediction model. First, a sensitivity study using radiative transfer simulations in the near-infrared and thermal infrared was performed to demonstrate, in a quantitative manner, the larger impact of the assumed cloud vertical extinction profile, described in terms of shape and vertical extent, on MERIS than on AATSR top-of-atmosphere measurements. Consequently, cloud vertical extinction profiles will have a larger influence on the MERIS than on the AATSR cloud height retrievals for most cloud types. Second, the difference in retrieved CTH (ΔCTH) from AATSR and MERIS are related to cloud vertical extent (CVE), as observed by ground-based lidar and radar at three ARM sites. To increase the impact of the cloud vertical extinction profile on the MERIS-CTP retrievals, single-layer and geometrically thin clouds are assumed in the forward model. Similarly to previous findings, the MERIS-CTP retrievals appear to be close to pressure levels in the middle of the cloud. Assuming a linear relationship, the ΔCTH multiplied by 2.5 gives an estimate on the CVE for single-layer clouds. The relationship is stronger for single-layer clouds than for multi-layer clouds. Due to large variations of cloud vertical extinction profiles occurring in nature, a quantitative estimate of the cloud vertical extent is accompanied with large uncertainties. Yet, estimates of the CVE provide an additional parameter, next to CTH, that can be obtained from passive imager measurements and can be used to further describe cloud vertical distribution, thus contributing to the characterization of a cloudy scene. To further demonstrate the plausibility of the approach, an estimate of the CVE was applied to a case study. In light of the follow-up mission Sentinel-3 with AATSR and MERIS like instruments, Sea and Land Surface Temperature Radiometer (SLSTR) and (Ocean and Land Colour Instrument) OLCI, respectively, for which the FAME-C algorithm can be easily adapted, a more accurate estimate of the CVE can be expected. OLCI will have three channels in the oxygen-A absorption band, possibly providing enhanced information on cloud vertical distributions.

A broad range of different of Bayesian cloud detection schemes is applied to measurements from the Medium Resolution Imaging Spectrometer (MERIS), the Advanced Along-Track Scanning Radiometer (AATSR), and their combination. The cloud detection schemes were designed to be numerically efficient and suited for the processing of large numbers of data. Results from the classical and naive approach to Bayesian cloud masking are discussed for MERIS and AATSR as well as for their combination. A sensitivity study on the resolution of multidimensional histograms, which were post-processed by Gaussian smoothing, shows how theoretically insufficient numbers of truth data can be used to set up accurate classical Bayesian cloud masks. Sets of exploited features from single and derived channels are numerically optimized and results for naive and classical Bayesian cloud masks are presented. The application of the Bayesian approach is discussed in terms of reproducing existing algorithms, enhancing existing algorithms, increasing the robustness of existing algorithms, and on setting up new classification schemes based on manually classified scenes.

Hyperspectral radiance measurements in the oxygen A band are sensitive to the vertical distribution of atmospheric scatterers, which in principle allows the retrieval of aerosol height from future instruments like TROPOMI, OCO2, FLEX, and CarbonSat. Discussed in this paper is a fast and flexible forward operator for the simulation of hyperspectral radiances in the oxygen A band and, based on this scheme, a sensitivity study about the inversion quality of aerosol optical thickness, aerosol mean height, and aerosol type. The forward operator is based on a lookup table with efficient data compression based on principal component analysis. Linear interpolation and computation of partial derivatives is performed in the much smaller space of expansion coefficients rather than wavelength. Thus, this approach is computationally fast and, at the same time, memory efficient. The sensitivity study explores the impact of instrument design on the retrieval of aerosol optical thickness and aerosol height. Considered are signal to noise ratio, spectral resolution, and spectral sampling. Also taken into account are surface inhomogeneities and variations of the aerosol type.

A newly developed daytime cloud property retrieval algorithm, FAME-C (Freie Universität Berlin AATSR MERIS Cloud), is presented. Synergistic observations from the Advanced Along-Track Scanning Radiometer (AATSR) and the Medium Resolution Imaging Spectrometer (MERIS), both mounted on the polar-orbiting Environmental Satellite (Envisat), are used for cloud screening. For cloudy pixels two main steps are carried out in a sequential form. First, a cloud optical and microphysical property retrieval is performed using an AATSR near-infrared and visible channel. Cloud phase, cloud optical thickness, and effective radius are retrieved, and subsequently cloud water path is computed. Second, two cloud top height products are retrieved based on independent techniques. For cloud top temperature, measurements in the AATSR infrared channels are used, while for cloud top pressure, measurements in the MERIS oxygen-A absorption channel are used. Results from the cloud optical and microphysical property retrieval serve as input for the two cloud top height retrievals. Introduced here are the AATSR and MERIS forward models and auxiliary data needed in FAME-C. Also, the optimal estimation method, which provides uncertainty estimates of the retrieved property on a pixel basis, is presented. Within the frame of the European Space Agency (ESA) Climate Change Initiative (CCI) project, the first global cloud property retrievals have been conducted for the years 2007–2009. For this time period, verification efforts are presented, comparing, for four selected regions around the globe, FAME-C cloud optical and microphysical properties to cloud optical and microphysical properties derived from measurements of the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra satellite. The results show a reasonable agreement between the cloud optical and microphysical property retrievals. Biases are generally smallest for marine stratocumulus clouds: −0.28, 0.41 μm and −0.18 g m−2 for cloud optical thickness, effective radius and cloud water path, respectively. This is also true for the root-mean-square deviation. Furthermore, both cloud top height products are compared to cloud top heights derived from ground-based cloud radars located at several Atmospheric Radiation Measurement (ARM) sites. FAME-C mostly shows an underestimation of cloud top heights when compared to radar observations. The lowest bias of −0.3 km is found for AATSR cloud top heights for single-layer clouds, while the highest bias of −3.0 km is found for AATSR cloud top heights for multilayer clouds. Variability is low for MERIS cloud top heights for low-level clouds, and high for MERIS cloud top heights for mid-level and high-level single-layer clouds, as well as for both AATSR and MERIS cloud top heights for multilayer clouds.

This paper discusses results from 12 months of a Round Robin exercise aimed at the inter-comparison of different cloud detection algorithms for Proba-V. Clouds detection is a critical issue for satellite optical remote sensing, since potential errors in cloud masking directly translates into significant uncertainty in the retrieved downstream geophysical products. Cloud detection is particularly challenging for Proba-V due to the presence of a limited number of spectral bands and the lack of thermal infrared bands. The main objective of the project was the inter-comparison of several cloud detection algorithms for Proba-V over a wide range of surface types and environmental conditions. Proba-V Level 2a products have been distributed to six different algorithm providers representing companies and research institutes in several European countries. The considered cloud detection approaches are based on different strategies: Neural Network, Discriminant Analysis, Multi-spectral and Multi-textural Thresholding, Self-Organizing Feature Maps, Dynamic Thresholding, and physically-based retrieval of Cloud Optical Thickness. The results from all algorithms were analysed and compared against a reference dataset, consisting of a large number (more than fifty thousands) of visually classified pixels. The quality assessment was performed according to a uniform methodology and the results provide clear indication on the potential best-suited approach for next Proba-V cloud detection algorithm.

New cloud property datasets based on measurements from the passive imaging satellite sensors AVHRR, MODIS, ATSR2, AATSR and MERIS are presented. Two retrieval systems were developed that include components for cloud detection and cloud typing followed by cloud property retrievals based on the optimal estimation (OE) technique. The OE-based retrievals are applied to simultaneously retrieve cloud-top pressure, cloud particle effective radius and cloud optical thickness using measurements at visible, near-infrared and thermal infrared wavelengths, which ensures spectral consistency. The retrieved cloud properties are further processed to derive cloud-top height, cloud-top temperature, cloud liquid water path, cloud ice water path and spectral cloud albedo. The Cloud_cci products are pixel-based retrievals, daily composites of those on a global equal-angle latitude–longitude grid, and monthly cloud properties such as averages, standard deviations and histograms, also on a global grid. All products include rigorous propagation of the retrieval and sampling uncertainties. Grouping the orbital properties of the sensor families, six datasets have been defined, which are named AVHRR-AM, AVHRR-PM, MODIS-Terra, MODIS-Aqua, ATSR2-AATSR and MERIS+AATSR, each comprising a specific subset of all available sensors. The individual characteristics of the datasets are presented together with a summary of the retrieval systems and measurement records on which the dataset generation were based. Example validation results are given, based on comparisons to well-established reference observations, which demonstrate the good quality of the data. In particular the ensured spectral consistency and the rigorous uncertainty propagation through all processing levels can be considered as new features of the Cloud_cci datasets compared to existing datasets. In addition, the consistency among the individual datasets allows for a potential combination of them as well as facilitates studies on the impact of temporal sampling and spatial resolution on cloud climatologies.For each dataset a digital object identifier has been issued:Cloud_cci AVHRR-AM: https://doi.org/10.5676/DWD/ESA_Cloud_cci/AVHRR-AM/V002Cloud_cci AVHRR-PM: https://doi.org/10.5676/DWD/ESA_Cloud_cci/AVHRR-PM/V002Cloud_cci MODIS-Terra: https://doi.org/10.5676/DWD/ESA_Cloud_cci/MODIS-Terra/V002Cloud_cci MODIS-Aqua: https://doi.org/10.5676/DWD/ESA_Cloud_cci/MODIS-Aqua/V002Cloud_cci ATSR2-AATSR: https://doi.org/10.5676/DWD/ESA_Cloud_cci/ATSR2-AATSR/V002Cloud_cci MERIS+AATSR: https://doi.org/10.5676/DWD/ESA_Cloud_cci/MERIS+AATSR/V002

For decades oceanographers have understood the Atlantic meridional overturning circulation (AMOC) to be primarily driven by changes in the production of deep-water formation in the subpolar and subarctic North Atlantic. Indeed, current Intergovernmental Panel on Climate Change (IPCC) projections of an AMOC slowdown in the twenty-first century based on climate models are attributed to the inhibition of deep convection in the North Atlantic. However, observational evidence for this linkage has been elusive: there has been no clear demonstration of AMOC variability in response to changes in deep-water formation. The motivation for understanding this linkage is compelling, since the overturning circulation has been shown to sequester heat and anthropogenic carbon in the deep ocean. Furthermore, AMOC variability is expected to impact this sequestration as well as have consequences for regional and global climates through its effect on the poleward transport of warm water. Motivated by the need for a mechanistic understanding of the AMOC, an international community has assembled an observing system, Overturning in the Subpolar North Atlantic Program (OSNAP), to provide a continuous record of the transbasin fluxes of heat, mass, and freshwater, and to link that record to convective activity and water mass transformation at high latitudes. OSNAP, in conjunction with the Rapid Climate Change–Meridional Overturning Circulation and Heatflux Array (RAPID–MOCHA) at 26°N and other observational elements, will provide a comprehensive measure of the three-dimensional AMOC and an understanding of what drives its variability. The OSNAP observing system was fully deployed in the summer of 2014, and the first OSNAP data products are expected in the fall of 2017.

The development of street lamps based on solid-state lighting technology is likely to introduce a major change in the colour of urban skyglow (one form of light pollution). We demonstrate the need for long-term monitoring of this trend by reviewing the influences it is likely to have on disparate fields. We describe a prototype detector which is able to monitor these changes, and could be produced at a cost low enough to allow extremely widespread use. Using the detector, we observed the differences in skyglow radiance in red, green and blue channels. We find that clouds increase the radiance of red light by a factor of 17.6, which is much larger than that for blue (7.1). We also find that the gradual decrease in sky radiance observed on clear nights in Berlin appears to be most pronounced at longer wavelengths.

A comparison study for the solar radiative flux above clouds is presented between the regional climate model system BALTEX integrated model system (BALTIMOS) and Moderate Resolution Imaging Spectroradiometer (MODIS) satellite observations. For MODIS, an algorithm has been developed to retrieve reflected shortwave fluxes over clouds. The study area is the Baltic Sea catchment area during an 11-month period from February to December 2002. The intercomparison focuses on the variations of the daily and seasonal cycle and the spatial distributions. We found good agreement between the observed and the simulated data with a bias of the temporal mean of 13.6 W/m2 and a bias of the spatial mean of 35.5 W/m2. For summer months, BALTIMOS overestimates the solar flux with up to 90 W/m2 (20%). This might be explained by the insufficient representation of cirrus clouds in the regional climate model.

In recent years, sleep medicine has evolved into a full-grown discipline, featuring a multidisciplinary approach to diagnosis and treatment of patients with sleep disorders. Sleep medicine cuts across the boundaries of different conventional disciplines and is therefore open to medical and non-medical professionals with different specialty backgrounds. The aim of the current paper is to introduce a qualification for those professionals whose main occupation is to practice sleep medicine in the setting of a sleep medicine centre. The drafting of guidelines dealing with requirements for such qualification was entrusted to a task force by the European Sleep Research Society. The guidelines are the result of a progressive consensus procedure in which standards were defined for education, training, and evaluation. The final step along this pathway is a theoretical and practical examination, providing proof of proficiency in the field of sleep medicine. This paper describes the object of specific competences, the scope of sleep medicine, and the qualification procedures that pertain to three professional categories: medical specialists, non-medical professionals with a university master degree (such as psychologists and biologists), and nurses and technologists. Indices of preceding practical experience and theoretical knowledge are presented in Appendices 1 and 2. These guidelines are a European standard. They may be adapted in the future according to new scientific insights. National certification programs that comply with these guidelines may be subject to homologation by the ESRS.

The Satellite Application Facility on Climate Monitoring (CM-SAF) is aiming to retrieve satellite-derived geophysical parameters suitable for climate monitoring. CM-SAF started routine operations in early 2007 and provides a climatology of parameters describing the global energy and water cycle on a regional scale and partially on a global scale. Here, the authors focus on the performance of cloud detection methods applied to measurements of the Spinning Enhanced Visible and Infrared Imager (SEVIRI) on the first Meteosat Second Generation geostationary spacecraft. The retrieved cloud mask is the basis for calculating the cloud fractional coverage (CFC) but is also mandatory for retrieving other geophysical parameters. Therefore, the quality of the cloud detection directly influences climate monitoring of many other parameters derived from spaceborne sensors. CM-SAF products and results of an alternative cloud coverage retrieval provided by the Institut für Weltraumwissenschaften of the Freie Universität in Berlin, Germany (FUB), were validated against synoptic measurements. Furthermore, and on the basis of case studies, an initial comparison was performed of CM-SAF results with results derived from the Moderate Resolution Imaging Spectrometer (MODIS) and from the Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP). Results show that the CFC from CM-SAF and FUB agrees well with synoptic data and MODIS data over midlatitudes but is underestimated over the tropics and overestimated toward the edges of the visible Earth disk.

The remote sensing of total column water vapour (TCWV) from polar orbiting, sun-synchronous satellite spectrometers such as the Medium Resolution Imaging Spectrometer (MERIS) on board of ENVISAT and the Moderate Imaging Spectroradiometer (MODIS) on board of Aqua and Terra enables observations on a high spatial resolution and a high accuracy over land surfaces. The observations serve studies about small-scale variations of water vapour as well as the detection of local and global trends. However, depending on the swath width of the sensor, the temporal sampling is low and the observations of TCWV are limited to cloud-free land scenes. This study quantifies the representativeness of a single TCWV observation at the time of the satellite overpass under cloud-free conditions by investigating the diurnal cycle of TCWV using 9 years of a 2-hourly TCWV data set from global GNSS (Global Navigation Satellite Systems) stations. It turns out that the TCWV observed at 10:30 local time (LT) is generally lower than the daily mean TCWV by 0.65 mm (4 %) on average for cloud-free cases. Averaging over all GNSS stations, the monthly mean TCWV at 10:30 LT, constrained to cases that are cloud-free, is 5 mm (25 %) lower than the monthly mean TCWV at 10:30 LT of all cases. Additionally, the diurnal variability of TCWV is assessed. For the majority of GNSS stations, the amplitude of the averaged diurnal cycle ranges between 1 and 5 % of the daily mean with a minimum between 06:00 and 10:00 LT and maximum between 16:00 and 20:00 LT. However, a high variability of TCWV on an individual day is detected. On average, the TCWV standard deviation is about 15 % regarding the daily mean.

In this paper an introduction to the planned L2 retrieval algorithms for the Earth Clouds and Radiation Explorer (EarthCARE) lidar ATLID is given. The ATLID instrument is a high spectral resolution lidar which will provide independent retrievals of extinction and backscatter profiles and will be launched in 2018. A short description of the intended operational ESA products is given together with the logic behind the choices made.

A new method to retrieve cloud top heights stereoscopically using the dual-view facility of the Along Track Scanning Radiometer 2 (ATSR-2) instrument is assessed. This assessment is performed through a comparison of the cloud top heights obtained from ATSR-2 stereo and those derived from a 94-GHz radar, radiosonde profiles and independently from the Modular Optoelectronic Scanner (MOS) using the O2-A band. The data for this study were collected over the United Kingdom from September 1998-March 1999. The results show that the accuracy of the ATSR-2 stereo heights is generally as predicted on theoretical grounds, with the errors in the 1.6 µm and 0.65 µm stereo heights rarely exceeding 2 km. Case study periods with disagreements between the ATSR-2 heights and the ground-based retrievals are often due to the lack of precise match-ups between the ground-based and satellite scenes, while the MOS O2-A band is shown sometimes to miss the tops of high clouds. Evidence that the 11 µm channel is more sensitive to high clouds than originally thought is given and a future application of multi-spectral stereo cloud top heights is proposed.

Backscattered solar radiation as measured by MOS (Modular Optoelectronical Scanner) on the IRS3 (Indian Remote sensing Satellite 3) has been used in an algorithm to retrieve cloud top pressure. The algorithm uses a radiance ratio between absorbing channels in the Oxygen-A absorption band at 761 nm and a window channel at 750 nm. The ratios are directly related to the average photon path length, which is mainly determined by the cloud top pressure. This paper presents the principles of the retrieval scheme, results of a sensitivity study and a first validation using radiosondes.

Ground-based measurements of direct absorption of solar radiation between 9000 and 13,000 cm −1 (770– 1100 nm ) with a spectral resolution of 0.05 cm −1 are compared with line-by-line simulations of atmospheric absorption based on different molecular databases (HITRAN 2000, HITRAN 99, HITRAN 96 and ESA-WVR). Differences between measurements and simulations can be reduced to a great amount by scaling the individual line intensities with spectral and database dependent scaling factors. Scaling factors are calculated for the selected databases using a Marquardt non-linear least-squares fit together with a forward model for 100 cm −1 wide intervals between 10,150 and 11,250 cm −1 as well as for the water vapor absorption channels of the Medium Resolution Imaging Spectrometer (MERIS) onboard the European Space Agency's (ESA) ENVISAT platform and the Modular Optoelectronic Scanner (MOS) on the Indian IRSP-3 platform, developed by the German Aerospace Centre (DLR). For the latter, the scaling coefficients are converted into correction factors for retrieved total columnar water vapor content and used for a comparison of MOS-based retrievals of total columnar atmospheric water vapor above cloud-free land surfaces with radio soundings. The scaling factors determined for 100 cm −1 wide intervals range from 0.85 for the ESA-WVR molecular database to 1.15 for HITRAN 96. The best agreement between measurements and simulations is achieved with HITRAN 99 and HITRAN 2000, respectively, using scaling factors between 0.9 and 1. The effects on the satellite-based retrievals of columnar atmospheric water vapor range from 2% (HITRAN 2000) to 12% (ESA-WVR).

The detection of clouds in measurements taken by airborne and spaceborne remote sensing sensors in the visible and near-infrared is often difficult due to the high albedo of underlying surfaces such as snow- and ice-covered surfaces as well as sunglint regions of water surfaces. The authors show that the measured intensity of the reflected solar radiation together with texture information is effective in detecting clouds over water surfaces which are affected by sunglint. An automated cloud-masking technique for images measured by a compact airborne spectrographic imager ( casi ) during the ACE-2 CLOUDYCOLUMN experiment has been developed based on supervised learning of an artificial neural network. The neural network has been trained on radiances, texture features, and gradient-filtered radiances. The radiances were measured at a single wavelength but with high spatial resolution so that characteristic spatial features within an image can be used to discriminate clouds from sunglint, cloud shadow and oce...

True systems-of-systems are one of the toughest challenges for system engineers. They face the problem to balance complexity of design and project structure against the product's cost during its lifecycle. The main cost driver is undesired redundancy in the product and/or the development process. Here we present a method that enables system engineers to shape the architecture of the system to the needs of the users and the development organisation. First we will give our definition of a system-of-systems, show why they are so important, and what makes them so demanding for the system engineer. After a look at the conventional way to solve the complexity problem and a discussion of its disadvantages we will present our method. We will give an impression how we derived it, and of the variants in applying it.

This study presents the first analysis of small-scale convective structures observed in a total column water vapor (TCWV) field obtained from full-resolution Medium Resolution Imaging Spectrometer (MERIS) near-infrared measurements. The high-resolution MERIS TCWV field for a high-pressure event occurring in May over central Europe allows the detection of horizontal convective rolls, due to the observation of parallel bands of alternating low- and high-TCWV values. The bands are aligned parallel to the boundary layer winds obtained from a numerical weather prediction model and radiosonde data. Closer examination further reveals that cloud streets observed in the east extend along bands of maximum TCWV. From a quantitative analysis of the TCWV data, combined with auxiliary data, it is shown that the roll wavelength and aspect ratio can be determined, which are found to be 6.5 km and 4.2, respectively, for this case study.

A number of aircraft flights have been performed with the airborne Optical Visible and near Infrared Detector during the European Cloud and Radiation Experiment in April 94. The OVID-Spectrometer consists of two similar detector systems (600 – 1100nm = VIS and 900 – 1700nm = IR). We have developed a data processing algorithm for the new instrument which includes an unprecedented high resolution wavelength- and radiance calibration, a requisite for analysing absorption processes within the atmosphere. The resulting spectral resolution is ∼ 1.7nm for the VIS-system and ∼ 6nm for the IR-system. A series of spectra was recorded over the Atlantic ocean under fair weather conditions. These spectra are analysed with special emphasis on the water vapour absorption bands. A precise knowledge of all these bands is necessary to predict the absorption of radiation within clouds. Together with model calculations such investigations will help us to develop new remote sensing techniques, such as for the retrieval of water vapour and cloud properties.

The global distribution of the atmospheric water vapour content plays an important role in the weather forecast and climate research. Nowadays there exist various methods dealing with remote sensing of the atmospheric water vapour content. Unfortunately, most of them are restricted to ocean areas, since, in general, the emission of land surfaces is not known well enough. Therefore, a new method is developed which allows the detection of the atmospheric total water vapour content from aircraft or satellite with the aid of backscattered solar radiation in the near infrared above land surfaces. The Matrix-Operator-Method has been used to simulate backscattered solar radiances, including various atmospheric profiles of temperature, pressure, water vapour, and aerosols of various types, several sun zenith angles, and different types of land surfaces. From these calculations it can be concluded, that the detection of water vapour content in cloudless atmospheres is possible with an error of In addition to the theoretical results first comparisons with aircraft measurements of the backscattered solar radiances are shown. These measurements have been carried out with the aid of OVID (Optical Visible and near Infrared Detector), a new multichannel array spectrometer, in 1993.

Strong radiative forcing is induced by absorbing aerosol overlying low level clouds, as it leads to a local change of the earth albedo due to the radiative interactions of the aerosol and clouds layers and to an extremely important but local warming effect in the aerosol layer (Frazer and Kaufman, 1980). There are few regions where this impact may be significant at regional scale. It is the case of biomass burning particles transported over the Atlantic West of central Africa above bright stratocumulus clouds. Although the general physical process of this interaction is well understood in terms of direct forcing, it is largely uncertain because of the lack of accurate global scale observations of the aerosol optical parameters above the clouds [Yu et al. 2006], but also because of the need to account for time and space variations of the aerosols and cloud properties in the analysis. Only limited regional in-situ measurements [Keil and Haywood 2003] and satellite data analysis [Chand et al. 2009] have been performed. Moreover, the retrieval of cloud properties is biased by the presence of aerosol above the clouds. The new developments combining polarized active (CALIPSO [Hu et al. 2007]) and passive (PARASOL [Waquet et al. 2009]) observations offer the opportunity to retrieve the properties of aerosol above the clouds with an accuracy difficult to achieve by a standard inversion of the lidar data or an analysis of the unpolarized radiance. Those polarized products used in combination of the recently developed CALIPSO/CloudSat synergies [Josset et al. 2010] offer a guidance to better estimate the potential bias in liquid water cloud properties retrieval in standard passive retrievals.

The influence of aerosols in the visible and near infrared part of the electromagnetic spectrum was studied by simulations of Landsat 5 Thematic Mapper measurements. The radiative transfer model used is based on the matrix-operator-method and was applied to different surface types, represented by specific spectral albedo values. On the basis of a single scattering approach for atmospheric correction, an algorithm was developed to correct for the influences of aerosols, air molecules and athmospheric trace gases on Thematic Mapper measurements above land surfaces using additional measurements above nearby located ocean surfaces to estimate the optical properties. The optical thickness of a cloud-free atmosphere has therefore been varied in the model for different aerosol types and surface reflectances.

[1] The Earth Clouds, Aerosols and Radiation Explorer (EarthCARE) mission developed by the European Space Agency and the Japan Aerospace Exploration Agency addresses the need to improve the understanding of the interactions between cloud, aerosol, and radiation processes. The broadband radiometer (BBR) instrument on board the EarthCARE spacecraft provides measurements of broadband reflected solar and emitted thermal radiances at the top of atmosphere (TOA) over the along-track satellite path at three fixed viewing zenith angles. The multiangular information provided by the BBR, combined with the spectral information from the EarthCARE's multispectral imager (MSI) can be exploited to construct accurate thermal radiance-to-flux conversion algorithms on the basis of radiative transfer modeling. In this study, the methodology to derive longwave (LW) fluxes from BBR and MSI data is described, and the performance of the LW BBR angular models is compared with the Clouds and the Earth's Radiant Energy System (CERES) Terra flux retrievals in order to evaluate the reliability of the BBR synthetic models when applied to satellite-based radiances. For this purpose, the BBR methodology proposed in this work is adapted to the CERES and the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument specifications, and new LW angular models for CERES are developed. According to plane-parallel simulations, the BBR LW flux uncertainty caused by flux inversion could be reduced up to 0.4 W m−2. The intercomparison between CERES BBR-like adapted and CERES original angular models is performed over a BBR-like database of CERES true along track, and the averaged instantaneous retrievals agree to within 2 W m−2.

Solar-induced chlorophyll fluorescence is a weak electromagnetic signal emitted in the red and far-red spectral regions by vegetation chlorophyll under excitation by solar radiation. Chlorophyll fluorescence has been demonstrated to be a close proxy to vegetation physiological functioning. The basis for fluorescence retrieval from passive space measurements is the exploitation of the O2-A and O2-B atmospheric absorption features to isolate the fluorescence signal from the solar radiation reflected by the surface and the atmosphere. High spectral resolution measurements and a precise modeling of the atmospheric radiative transfer in the visible and near-infrared regions are mandatory. Recent developments for fluorescence retrieval from passive high spectral resolution spaceborne measurements are presented in this work, which has been performed in preparation of the FLuorescence EXplorer (FLEX) mission, which is currently under development by the European Space Agency. A large data set of FLEX-like measurements has been simulated for the purpose of methodology development and testing. Issues related to vegetation chlorophyll fluorescence retrieval from space, a description of the proposed methodology, initial results from simulated test cases, and general guidelines for the specification of fluorescence retrieval instruments are presented and discussed in this work. Copyright 2010 by the American Geophysical Union.

MERIS Level 1 and Level 2 water products will be improved in the 3rd MERIS reprocessing which is planned to take place before the end of 2009. The instrument radiometric degradation model will be updated. Improvements to the atmospheric correction in both case 1 and case 2 waters will be implemented. A vicarious adjustment strategy to remove residual biases in the Level 2 marine signals will be put in place. In addition, a cloud screening scheme with improved detection capabilities will improve the cirrus detection capability. In parallel, long term algorithmic improvements are being pursued and are partially covered by three exploratory ongoing studies. The first study addresses the limitation of the current MERIS atmospheric correction scheme in sun glint conditions. The second aims at defining an operational adjacency effect correction. The third study makes use of the ability of MERIS to measure transmission in the O 2 -A oxygen band to better identify and characterize clouds and aerosols.

Motivated by several observations of the degree of linear polarization of skylight in the oxygen A (O(2)A) band that do not yet have a quantitative explanation, we analyze the influence of aerosol altitude, microphysics, and optical thickness on the degree of linear polarization of the zenith skylight in the spectral region of the O(2)A band, between 755 to 775 nm. It is shown that the degree of linear polarization inside the O(2)A band is particularly sensitive to aerosol altitude. The sensitivity is strongest for aerosols within the troposphere and depends also on their microphysical properties and optical thickness. The polarization of the O(2)A band can be larger than the polarization of the continuum, which typically occurs for strongly polarizing aerosols in an elevated layer, or smaller, which typically occurs for depolarizing aerosols or cirrus clouds in an elevated layer. We show that in the case of a single aerosol layer in the atmosphere a determination of the aerosol layer altitude may be obtained. Furthermore, we show limitations of the aerosol layer altitude determination in case of multiple aerosol layers. To perform these simulations we developed a fast method for multiple scattering radiative transfer calculations in gaseous absorption bands including polarization. The method is a combination of doubling-adding and k-binning methods. We present an error estimation of this method by comparing with accurate line-by-line radiative transfer simulations. For the Motivated by several observations of the degree of linear polarization of skylight in the oxygen A (O(2)A) band that do not yet have a quantitative explanation, we analyze the influence of aerosol altitude, microphysics, and optical thickness on the degree of linear polarization of the zenith skylight in the spectral region of the O(2)A band, between 755 to 775 nm. It is shown that the degree of linear polarization inside the O(2)A band is particularly sensitive to aerosol altitude. The sensitivity is strongest for aerosols within the troposphere and depends also on their microphysical properties and optical thickness. The polarization of the O(2)A band can be larger than the polarization of the continuum, which typically occurs for strongly polarizing aerosols in an elevated layer, or smaller, which typically occurs for depolarizing aerosols or cirrus clouds in an elevated layer. We show that in the case of a single aerosol layer in the atmosphere a determination of the aerosol layer altitude may be obtained. Furthermore, we show limitations of the aerosol layer altitude determination in case of multiple aerosol layers. To perform these simulations we developed a fast method for multiple scattering radiative transfer calculations in gaseous absorption bands including polarization. The method is a combination of doubling-adding and k-binning methods. We present an error estimation of this method by comparing with accurate line-by-line radiative transfer simulations. For the O(2)A band, the errors in the degree of linear polarization are less than 0.11% for transmitted light, and less than 0.31% for reflected light. band, the errors in the degree of linear polarization are less than 0.11% for transmitted light, and less than 0.31% for reflected light.

FLEX (FLuorescence EXperiment) is a candidate mission for the European Space Agency (ESA) Earth Explorer program. The main objective of the mission is the measurement the chlorophyll fluorescence signal emitted by vegetation at the red and far-red spectral regions (roughly 630-770 nm). The current FLEX mission design includes different instruments intended to provide the appropriate characterization of those atmospheric and surface parameters necessary for the retrieval and interpretation of the fluorescence signal. The complete processing chain for the derivation of fluorescence and reflectance products from the radiance data acquired by the different instruments included in the FLEX payload is described in this paper. Six processing modules have been implemented: cloud screening, aerosol optical thickness (AOT) retrieval, automatic spectral characterisation, columnar water vapor (CWV) retrieval, fluorescence retrieval and reflectance retrieval. The processing chain has been tested against a scene-based simulated data set which reproduces FLEX instruments and realistic atmospheric conditions. © 2008 IEEE.

A representative albedo is required by ESA for the improved retrieval of atmospheric products, such as water vapour, from the ENVISAT-MERIS instrument. This albedo is required at 13 of the 15 spectral channels of MERIS. An algorithm is described which has been applied to the generation of a global albedo for these 13 spectral bands of MERIS over 16-day time periods at a resolution of 0.05deg for the time period from June 2002 to December 2006. Inputs to this algorithm include improved cloud and snow detection, aerosol correction using the MERIS data itself and derived Spectral surface Directional Reflectances, SDRs (Schroder et ah, Preusker et al, see, http://envisat.esa. int/workshops/meris_aatsr2005/). Owing to the lack of sufficient directional samples for most of the Earth's land surface, even for a monthly compositing time period, direct inversion of BRDF parameters for MERIS are not possible worldwide. Instead the 16-day Collection 4 MODIS BRDFs at 0.05deg resolution (derived using either full inversions or magnitude inversions from the MOD43 values) were employed in a magnitude inversion scheme for the 4 common MERIS (490plusmn5 [b3], 560plusmn5 [b5], 665plusmn5 [b7], 865plusmn10 [bl3]) bands with MODIS (459-479 {b3}, 545-565 {b4}, 620-670 {bl}, 841-8766 {b2}). The impact of applying Terra-only compared to Terra+Aqua-combined are here compared and presented. In keeping with previously reported results, there are larger numbers of full MODIS inversions (and consequently better MERIS albedos) for the combined BRDF but the total number of MODIS BRDF retrievals remains stubbornly similar. Spectral interpolation to the remaining 9 MERIS bands and to 3 broadband regions (0.4-0.7 mum, 0.7-3 mum, 0.4-3 mum) is then performed using polynomial look-up tables derived by Dr Shunlin Liang (University of Maryland). As spectral albedo data is required on monthly time-steps for most applications, a simple- minded weighting function based on the fractional time-period of each 16-day time period within a month was adopted for creating monthly products from 16-day products at 10km and 0.1deg. Global products on a 16-day time-step are being generated for the whole time period using both Terra-only and, where available, Terra+Aqua-combined Collection 4 MODlS-BRDFs. These EO products have been compared against contemporaneous MODIS spectral albedos (over 16-days) which have been gap-filled (Moody et al., 2005) as well as Collection 5 products, where available. Satellite intercomparisons have also been performed for monthly products of the monthly MERIS spectral albedo products for common bands against M1SR level-3 and POLDER level-3 products as well as for a subset of M1SR level-2 instantaneous products and the results will be shown here. Finally, inter-comparisons are shown of these EO products against ground-based albedometer measurements for a site in Finland will be presented as representative of one of several worldwide sites available through the CA VE taking into account, where necessary, issues associated with land cover heterogeneity.

Atmospheric water vapour is a major limitation for high precision Interferometric Synthetic Aperture Radar (InSAR) applications due to its significant impact on microwave signals. We propose a statistical criterion to test whether an independent water vapour product can reduce water vapour effects on InSAR interferograms, and assess the potential of the Medium Resolution Imaging Spectrometer (MERIS) near-infrared water vapour products for correcting Advanced SAR (ASAR) data. Spatio-temporal comparisons show c. 1.1mm\ud agreement between MERIS and GPS/radiosonde water vapour products in terms of standard deviations. One major limitation with the use of MERIS water vapour products is the frequency of cloud free conditions. Our analysis indicates that in spite of the low global cloud free conditions (~25%), the frequency can be much higher for certain areas such as Eastern Tibet (~38%) and Southern\ud California (~48%). This suggests that MERIS water vapour products show potential for correcting ASAR interferometric measurements in certain regions.