Tilman Dinter

Universität Bremen, Bremen, Bremen, Germany

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Publications (34)31.3 Total impact

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    ABSTRACT: Phycobiliproteins are a family of water-soluble pigment proteins that play an important role as accessory or antenna pigments and absorb in the green part of the light spectrum poorly used by chlorophyll a. The phycoerythrins (PEs) are one of four types of phycobiliproteins that are generally distinguished based on their absorption properties. As PEs are water-soluble, they are generally not captured with conventional pigment analysis. Here we present a statistical model based on in situ measurements of three transatlantic cruises which allows us to derive relative PE concentration from standardized hyperspectral underwater radiance measurements (Lu). The model relies on Empirical Orthogonal Function (EOF) analysis of Lu spectra and subsequent Generalized Linear Model with measured PE concentrations as the response variable and EOF loadings as predictor variables. The method is used to predict relative PE concentrations throughout the water column and to calculate integrated PE estimates based on those profiles.
    Journal of Geophysical Research 01/2013; 118(6):2948–2960. · 3.17 Impact Factor
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    ABSTRACT: The goal of this study was to improve PhytoDOAS, which is a new retrieval method for quantitative identification of major phytoplankton functional types (PFTs) using hyper-spectral satellite data. PhytoDOAS is an extension of the Differential Optical Absorption Spectroscopy (DOAS, a method for detection of atmospheric trace gases), developed for remote identification of oceanic phytoplankton groups. Thus far, PhytoDOAS has been successfully exploited to identify cyanobacteria and diatoms over the global ocean from SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) hyper-spectral data. This study aimed to improve PhytoDOAS for remote identification of coccolithophores, another functional group of phytoplankton. The main challenge for retrieving more PFTs by PhytoDOAS is to overcome the correlation effects between different PFT absorption spectra. Different PFTs are composed of different types and amounts of pigments, but also have pigments in common, e.g. chl a, causing correlation effects in the usual performance of the PhytoDOAS retrieval. Two ideas have been implemented to improve PhytoDOAS for the PFT retrieval of more phytoplankton groups. Firstly, using the fourth-derivative spectroscopy, the peak positions of the main pigment components in each absorption spectrum have been derived. After comparing the corresponding results of major PFTs, the optimized fit-window for the PhytoDOAS retrieval of each PFT was determined. Secondly, based on the results from derivative spectroscopy, a simultaneous fit of PhytoDOAS has been proposed and tested for a selected set of PFTs (coccolithophores, diatoms and dinoflagellates) within an optimized fit-window, proven by spectral orthogonality tests. The method was then applied to the processing of SCIAMACHY data over the year 2005. Comparisons of the PhytoDOAS coccolithophore retrievals in 2005 with other coccolithophore-related data showed similar patterns in their seasonal distributions, especially in the North Atlantic and the Arctic Sea. The seasonal patterns of the PhytoDOAS coccolithophores indicated very good agreement with the coccolithophore modeled data from the NASA Ocean Biochemical Model (NOBM), as well as with the global distributions of particulate inorganic carbon (PIC), provided by MODIS (MODerate resolution Imaging Spectroradiometer)-Aqua level-3 products. Moreover, regarding the fact that coccolithophores belong to the group of haptophytes, the PhytoDOAS seasonal coccolithophores showed good agreement with the global distribution of haptophytes, derived from synoptic pigment relationships applied to SeaWiFS chl a. As a case study, the simultaneous mode of PhytoDOAS has been applied to SCIAMACHY data for detecting a coccolithophore bloom which was consistent with the MODIS RGB image and the MODIS PIC map of the bloom, indicating the functionality of the method also in short-term retrievals.
    Ocean Science. 11/2012; 8(6):1055-1070.
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    ABSTRACT: We are proposing the development of an algorithm, using the combination of data from OCLI (Sentinel-3) and Sentinel-5P sensors, which derives globally pyhtoplankton groups (phytoplankton functional types) biomass. The information of the total biomass will be achieved by standard processing of the Chlorophyll-a (chl-a) concentration using satellite data from multispectral imaging instruments (firstly SeaWiFS, MODIS and MERIS merged within the GlobColour data set, later OLCI data). The percentage of the main phytoplankton types on the total biomass will be retrieved by the analysis of characteristic absorption features in hyperspectral satellite measurements (firstly SCIAMACHY, later Sentinel-5-P) using the PhytoDOAS method by Bracher et al. (2009) and improved by Sadeghi et al. (2011). Thus, a synergistic product from information of multi- and hyperspectral satellite instruments which complements one another will be developed. The two instruments of the Sentinel mission will enable a data product of weekly to monthly temporal and 7 km by 7 km spatial resolution. On the the SCIAMACHY/Globcolour product (starting in 2002 until today) will be limited to a monthly and 0.5° degree resolution. The application of the algorithm is for assessing the spatial and temporal variability of specific phytoplankton types' biomass on longer time scale (10 to 20 and more years) with global coverage. This will engross the understanding of the role of different phytoplankton types in the world ocean's ecosystem and improve estimates on the contribution of different phytoplankton types to the global carbon cycle. The concept of the algorithm development, including its uncertainity determined via validaton with in-situ phytoplankton data and sensitivity studies using the coupled atmospheric-oceanic radiative transfer model SCIATRAN (Rozanov et al. 2002, Blum et al. in press) and examples for its application are given in the presentation.
    04/2012;
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    ABSTRACT: In this study temporal variations of coccolithophore blooms are investigated using satellite data. Eight years, from 2003 to 2010, of data of SCIAMACHY, a hyper-spectral satellite sensor on-board ENVISAT, were processed by the PhytoDOAS method to monitor the biomass of coccolithophores in three selected regions. These regions are characterized by frequent occurrence of large coccolithophore blooms. The retrieval results, shown as monthly mean time-series, were compared to related satellite products, including the total surface phytoplankton, i.e., total chlorophyll-a (from GlobColour merged data) and the particulate inorganic carbon (from MODIS-Aqua). The inter-annual variations of the phytoplankton bloom cycles and their maximum monthly mean values have been compared in the three selected regions to the variations of the geophysical parameters: sea-surface temperature (SST), mixed-layer depth (MLD) and surface wind speed, which are known to affect phytoplankton dynamics. For each region the anomalies and linear trends of the monitored parameters over the period of this study have been computed. The patterns of total phytoplankton biomass and specific dynamics of coccolithophores chlorophyll-a in the selected regions are discussed in relation to other studies. The PhytoDOAS results are consistent with the two other ocean color products and support the reported dependencies of coccolithophore biomass' dynamics to the compared geophysical variables. This suggests, that PhytoDOAS is a valid method for retrieving coccolithophore biomass and for monitoring its bloom developments in the global oceans. Future applications of time-series studies using the PhytoDOAS data set are proposed, also using the new upcoming generations of hyper-spectral satellite sensors with improved spatial resolution.
    Biogeosciences Discussions 12/2011; 8(6):11725-11765.
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    ABSTRACT: The goal of this study was to improve PhytoDOAS, which is a new retrieval method for quantitative identification of major Phytoplankton Functional Types (PFTs) using hyper-spectral satellite data. PhytoDOAS is an extension of the Differential Optical Absorption Spectroscopy (DOAS, a method for detection of atmospheric trace gases), developed for remote identification of oceanic phytoplankton groups. Thus far, PhytoDOAS has been successfully exploited to identify cyanobacteria and diatoms over the global ocean from SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CartograpHY) hyper-spectral data. The main challenge for retrieving more PFTs by PhytoDOAS is to overcome the correlation effects between different PFTs' absorption spectra. Different PFTs are composed of different types and amounts of pigments, but also have pigments in common, e.g., chl-a, causing correlation effects in the usual performance of the PhytoDOAS retrieval. Two ideas have been implemented to improve PhytoDOAS for the PFT retrieval of more phytoplankton groups. Firstly, using the fourth-derivative spectroscopy, the peak positions of the main pigment components in each absorption spectrum have been derived. After comparing the corresponding results of major PFTs, the optimized fit-window for the PhytoDOAS retrieval of each PFT was determined. Secondly, based on the results from derivative spectroscopy, simultaneous fit of PhytoDOAS has been proposed and tested for a selected set of PFTs (coccolithophores, diatoms and dinoflagllates) within an optimized fit-window. The method was then applied to the processing of SCIAMACHY data over the year 2005. Comparisons of the PhytoDOAS PFT retrievals in 2005 with the modeled PFT data from the NASA Ocean Biochemical Model (NOBM) showed similar patterns in their seasonal distributions for diatoms and coccolithophores, especially in the northern parts of the global ocean. The seasonal patterns of the PhytoDOAS coccolithophores indicated very good agreement with the global distributions of Particulate Inorganic Carbon (PIC) provided by MODIS (MODerate resolution Imaging Spectroradiometer)-Aqua level-3 products. Since PIC is known as a proxy for the abundance of coccolithophores (in open ocean), the latter agreement indicates the basic functionality of the method in retrieving coccolithophores. Moreover, as a case study, the simultaneous mode of PhytoDOAS has been applied to SCIAMACHY data for detecting a coccolithophore bloom around New Zealand (reported by NASA from MODIS imagery in December 2009); the result was quite consistent with the MODIS RGB image and the MODIS PIC map of the bloom, indicating the functionality of the method in short-term retrievals.
    Ocean Science Discussions. 11/2011; 8(6):2271-2311.
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    ABSTRACT: Since clouds play an essential role in the Earth's climate system, it is important to understand the cloud characteristics as well as their distribution on a global scale using satellite observations. The main scientific objective of SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) onboard the ENVISAT satellite is the retrieval of vertical columns of trace gases. On the one hand, SCIAMACHY has to be sensitive to low variations in trace gas concentrations which means the ground pixel size has to be large enough. On the other hand, such a large pixel size leads to the problem that SCIAMACHY spectra are often contaminated by clouds. SCIAMACHY spectral measurements are not well suitable to derive a reliable sub-pixel cloud fraction that can be used as input parameter for subsequent retrievals of cloud properties or vertical trace gas columns. Therefore, we use MERIS/ENVISAT spectral measurements with its high spatial resolution as sub-pixel information for the determination of MerIs Cloud fRation fOr Sciamachy (MICROS). Since MERIS covers an even broader swath width than SCIAMACHY, no problems in spatial and temporal collocation of measurements occur. This enables the derivation of a SCIAMACHY cloud fraction with an accuracy much higher as compared with other current cloud fractions that are based on SCIAMACHY's PMD (Polarization Measurement Device) data. We present our new developed MICROS algorithm, based on the threshold approach, as well as a qualitative validation of our results with MERIS satellite images for different locations, especially with respect to bright surfaces such as snow/ice and sands. In addition, the SCIAMACHY cloud fractions derived from MICROS are intercompared with other current SCIAMACHY cloud fractions based on different approaches demonstrating a considerable improvement regarding geometric cloud fraction determination using the MICROS algorithm.
    Atmospheric Measurement Techniques 01/2011; · 3.21 Impact Factor
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    ABSTRACT: Results of a new methodology for retrievals of surface particulate matter concentration (PM10) from satellite reflectance measurements over Germany are presented in this paper. The retrieval derives effective radii from Ångström-alpha exponents and benefits from the fitting of a smooth spectral slope from seven MERIS spectrometer channels. Comparisons with ground measurements from the air quality surveillance show standard deviations of 33.9% with -18.9% bias over Hamburg. Over rural sites a standard deviation of 17.9% (bias 12.9%) is reached. We discuss critically limitations and potential applications of the retrieval. Additionally, we talk about the aspects at comparing of retrieved particulate matter with ground station measurements.
    Atmospheric Measurement Techniques 01/2011; · 3.21 Impact Factor
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    ABSTRACT: For the determination of aerosol optical thickness (AOT) Bremen AErosol Retrieval (BAER) has been developed. Method and main features on the aerosol retrieval are described together with validation and results. The retrieval separates the spectral aerosol reflectance from surface and Rayleigh path reflectance for the shortwave range of the measured spectrum of top-of-atmosphere reflectance for wavelength less than 0.670 μm. The advantage of MERIS (Medium Resolution Imaging Spectrometer on the Environmental Satellite – ENVISAT – of the European Space Agency – ESA) and SeaWiFS (Sea viewing Wide Field Sensor on OrbView-2 spacecraft) observations is the availability of several spectral channels in the blue and visible range enabling the spectral determination of AOT in 7 (or 6) channels (0.412–0.670 μm) and additionally channels in the NIR, which can be used to characterize the surface properties. A dynamical spectral surface reflectance model for different surface types is used to obtain the spectral surface reflectance for this separation. The normalized differential vegetation index (NDVI), taken from the satellite observations, is the model input. Further surface bi-directional reflectance distribution function (BRDF) is considered by the Raman-Pinty-Verstraete (RPV) model. Spectral AOT is obtained from aerosol reflectance using look-up-tables, obtained from radiative transfer calculations with given aerosol phase functions and single scattering albedos either from aerosol models, given by model package "optical properties of aerosol components" (OPAC) or from experimental campaigns. Validations of the obtained AOT retrieval results with data of Aerosol Robotic Network (AERONET) over Europe gave a preference for experimental phase functions derived from almucantar measurements. Finally long-term observations of SeaWiFS have been investigated for 11 year trends in AOT. Western European regions have negative trends with decreasing AOT with time. For the investigated Asian region increasing AOT have been found.
    Atmospheric Measurement Techniques. 01/2011;
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    ABSTRACT: Natural, short-lived halocarbons play a role in the stratospheric ozone budget, besides the anthropogenic emitted long-lived chlorine- and bromine fluorocarbons. The tropical oceans are a known source of reactive iodine and bromine to the atmosphere in the form of iodinated and brominated methanes (VSLS), as methyl iodide (CH3I), dibromomethane (CH2Br2) and bromoform (CHBr3), which contributes to reactive bromine within the lower stratosphere. Elevated atmospheric concentrations above the oceans are related to oceanic super-saturations of the compounds, caused by photochemical and biological production. The tropical Western Pacific is of special interest since it is a largely uncharacterized region for the oceanic compounds and in certain regions a projected hot spot for their emissions and transport pathways into the stratosphere. Under the leadership of IFM-GEOMAR (Kiel, Germany) a cruise with RV Sonne was conducted from 9 to 25 October 2009 in the tropical western Pacific to investigate trace gas emissions on a 4030 nm (7,500 km) and 60 degrees latitude covering transit between Tomakomai (Japan, 42°35,4‘N/ 141°37,5‘E) and Townsville (Australia, 19°06,6’S/ 146°50,5‘E). The ships cruise crossed various biogeochemical regimes of the northern and southern western Pacific Ocean, which differ in seawater properties, currents, productivity and atmospheric dynamics (e.g. Kuroshio Front, Northern Pacific Gyre, Pacific warm pool and Coral Seas). We will present highlights of the oceanic and atmospheric halocarbon measurements during the ships campaign, halocarbon emissions from the western Pacific Ocean, sources and transport calculations, including contributions to stratospheric bromine.
    AGU Fall Meeting Abstracts. 11/2010; -1:0319.
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    ABSTRACT: Since clouds play an essential role in the Earth's climate system, it is important to understand the cloud characteristics as well as their distribution on a global scale using satellite observations. One of the main scientific objectives of SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) on ENVISAT is the retrieval of cloud parameters which are also relevant for the study of tropospheric constituents. On the one hand, SCIAMACHY has to be sensitive to low variations in trace gas concentrations which means the ground pixel size has to be large enough. On the other hand, such a large pixel size leads to the problem that SCIAMACHY spectra are not well suitable to derive a reliable cloud fraction that can be used as input parameter for subsequent retrievals of cloud properties or vertical trace gas columns. Therefore, we use MERIS/ENVISAT spectral measurements with its high spatial resolution as sub-pixel information for the determination of MerIs Cloud fRation fOr Sciamachy (MICROS). Since MERIS covers an even broader swath width than SCIAMACHY, no problems with spatial and temporal matches of measurements occur. This enables the derivation of a SCIAMACHY cloud fraction with an accuracy much higher as compared with other current cloud fractions that are based on SCIAMACHY's PMD (Polarization Measurement Device) data. We present our new developed MICROS algorithm based on the threshold approach as well as a qualitative validation of our results with MERIS satellite imageries for different locations, especially with respect to bright surfaces such as snow/ice and sands. In addition, the SCIAMACHY cloud fractions derived from MICROS are intercompared with other current SCIAMACHY cloud fractions based on different approaches demonstrating a considerable improvement regarding 'true' cloud fraction determination using the MICROS algorithm.
    05/2010;
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    ABSTRACT: Natural, short-lived halocarbons play a role in the stratospheric ozone budget, besides the anthropogenic emitted, long-lived chlorine- and brominefluorocarbons. The tropical oceans are a known source of reactive iodine and bromine to the atmosphere in the form of iodinated and brominated methanes (VSLS), as e.g.methyl iodide (CH3I), dibromomethane (CH2Br2) and bromoform (CHBr3), which contributes to reactive bromine within the lower stratosphere. Elevated atmospheric concentrations above the oceans are related to oceanic supersaturations of the compounds, caused by photochemical and biological production. The tropical Western Pacific is of special interest since it is a largely uncharacterized region for the oceanic compounds and in certain regions a projected hot spot for their emissions and transport pathways into the stratosphere. From 9 to 25 October 2009 the IFM-GEOMAR (Kiel, Germany) conducted a cruise with RV Sonne in the tropical western Pacific to investigate trace gas emissions on a 4030 nm (7,500 km) and 60 degrees latitude covering transit between Tomakomai (Japan, 42°35,4‘N/ 141°37,5‘E) and Townsville (Australia, 19°06,6'S/ 146°50,5‘E). The ships cruise crossed various biogeochemical regimes of the northern and southern western Pacific Ocean, which differ in seawater properties, currents, productivity and atmospheric dynamics (e.g. Kuroshio Front, Northern Pacific Gyre, Pacific warm pool and Coral Seas). We will present highlights of the oceanic and atmospheric halocarbon measurements during the ships campaign, halocarbon emissions from the western Pacific Ocean, sources and the relationship between VSLS emissions and various phytoplankton functional groups, as being derived from in situ and satellite measurements.
    04/2010; 12:8711.
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    ABSTRACT: A retrieval of particulate matter concentration (PM10) from satellite data is presented as well as improvements of the aerosol optical depth retrieval by the Bremen aerosol algorithm. The add-on retrieval of particulate matter uses the derivation of the effective radii from the Ångstroem exponents and an assumed log-normal size distribution function. The Ångstroem exponent is derived through the multi-channel approach using MERIS/Envisat data, and benefits from the fitting of a smooth spectral slope of aerosol optical depth and the surface reflectance. The advantage of the retrieval is that this retrieval of the aerosol mass, i.e., in particular the effective radius, is exclusively based on spectral information from satellite measurements, global aerosol models, and meteorological parameters. ECMWF Boundary layer height, humidity, temperature, and pressure data are used in the retrieval; a retrieval of PM inferred without meteorological information and a proper BRDF is shown to be not very promising. Over the city of Hamburg, the aerosol optical depths agree within a standard deviation of 0.03 and 0.068 for all thirteen wavelengths between 412 and 885 nm, compared with AERONET and ground based air quality measurements; the particulate matter concentrations show agreement with a correlation factor of 0.64. In addition to the urban site of Hamburg, comparisons of PM10 measurements over rural sites in Germany exhibit a correlation coefficient of 0.75.
    Atmospheric Measurement Techniques Discussions. 01/2010;
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    ABSTRACT: The goal of this study is to improve Phyto-DOAS, the retrieval method of identification of major Phytoplankton Functional Types (PFTs) using ocean-color data provided by a high spectrally-resolved satellite sensor, SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Cartography) on board ENVISAT. Phyto-DOAS is an extension of DOAS (Differential Optical Absorption Spectroscopy), originally developed to retrieve atmospheric trace gases, for remote identification of oceanic phytoplankton. So far Phyto-DOAS has been successfully exploited to identify Cyanobacteria and Diatom over global ocean (Bracher et al. 2009). The main challenge for retrieving more PFTs by Phyto-DOAS is to overcome the overlapping effects of different PFTs absorption spectra. Different PFTs are composed of different types and concentrations of pigments, but also have pigments in common, e.g. Chl-a, which cause correlation effects in the standard Phyto-DOAS retrieval. In this study two ideas have been implemented to overcome this limitation of Phyto-DOAS: Firstly, using the method of fourth-derivative spectroscopy (Aguirre-Gomez et al. 1995) the peak positions of the main pigment components in each absorption spectrum have been derived. After comparing the corresponding results of major PFTs, the optimized fit-window for DOAS-retrieval of each PFT is determined. Secondly, the simultaneous fitting of different PFTs has been implemented (over the year 2008) to include the real oceanic situation in the retrieval. Within this step the provided optimized fit-windows have been tested to produce higher fit quality. Validation of the global PFTs biomass distribution has been performed using in-situ data sets obtained during several transatlantic cruises in the year 2008.
    01/2010;
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    ABSTRACT: The SAMUM field campaign in southern Morocco in May/June 2006 provides valuable data to study the emission, and the horizontal and vertical transports of mineral dust in the Northern Sahara. Radiosonde and lidar observations show differential advection of air masses with different characteristics during stable nighttime conditions and up to 5-km deep vertical mixing in the strongly convective boundary layer during the day. Lagrangian and synoptic analyses of selected dust periods point to a topographic channel from western Tunisia to central Algeria as a dust source region. Significant emission events are related to cold surges from the Mediterranean in association with eastward passing upper-level waves and lee cyclogeneses south of the Atlas Mountains. Other relevant events are local emissions under a distinct cut-off low over northwestern Africa and gust fronts associated with dry thunderstorms over the Malian and Algerian Sahara. The latter are badly represented in analyses from the European Centre for Medium–Range Weather Forecasts and in a regional dust model, most likely due to problems with moist convective dynamics and a lack of observations in this region. This aspect needs further study. The meteorological source identification is consistent with estimates of optical and mineralogical properties of dust samples.
    Tellus B 02/2009; 61B(2009):12-31. · 3.20 Impact Factor
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    ABSTRACT: Coincident observations made over the Moroccan desert during the Sahara mineral dust experiment (SAMUM) 2006 field campaign are used both to validate aerosol amount and type retrieved from multi-angle imaging spectroradiometer (MISR) observations, and to place the suborbital aerosol measurements into the satellite’s larger regional context. On three moderately dusty days during which coincident observations were made, MISR mid-visible aerosol optical thickness (AOT) agrees with field measurements point-by-point to within 0.05–0.1. This is about as well as can be expected given spatial sampling differences; the space-based observations capture AOT trends and variability over an extended region. The field data also validate MISR’s ability to distinguish and to map aerosol air masses, from the combination of retrieved constraints on particle size, shape and single-scattering albedo. For the three study days, the satellite observations (1) highlight regional gradients in the mix of dust and background spherical particles, (2) identify a dust plume most likely part of a density flow and (3) show an aerosol air mass containing a higher proportion of small, spherical particles than the surroundings, that appears to be aerosol pollution transported from several thousand kilometres away.
    Tellus B - Chemical and Physical Meteorology. 02/2009; 61B:239-251.
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    ABSTRACT: Main optical characteristics of desert dust, such as phase function and single scattering albedo, have been derived from combinations of sun-/sky-radiometer and satellite measurements during the SAMUM experiment (10 May–10 June 2006) at the site Porte au Sahara (30.237°N, 5.607°W) in South Morocco. Scattering phase functions have been retrieved using combined data of spectral aerosol optical thickness (AOT) and spectral sky brightness in the almucantar, considering non-spherical light scattering. Intercomparisons of modelled top-of-atmosphere (TOA) reflectance with satellite observations of the Medium Resolution Imaging Spectrometer (MERIS) and Scanning Imaging Absorption Spectrometer for Atmospheric Chartography () instrument have been used for the estimation of spectral single scattering albedo. For the radiative transfer calculations scattering phase functions and AOT from ground-based observations have been used. The spectral single scattering albedo ranges from 0.93 in the blue to 0.98 at 753 nm.
    Tellus B 01/2009; 61(1):206 - 215. · 3.20 Impact Factor
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    ABSTRACT: Approximately 30% of the land surface is arid, having desert or semi-desert conditions. Aerosol originating from these regions plays a significant role in climate and atmospheric chemistry of the atmosphere. Retrieving aerosol properties from space-borne platforms above desert conditions, where the surface reflectance is usually very bright, is a challenging task. The proportion of the surface to top of atmosphere (TOA) reflectance can reach values over 90%, especially for wavelength above 500 nm. For these reasons detailed knowledge of aerosol and surface optical properties from these regions is required to separate atmosphere from intrinsically bright surfaces.An approach to retrieve aerosol properties over arid and semi-arid regions based on the Bremen Aerosol Retrieval (BAER) has been developed and validated within the Dust Aerosol Retrievals from Space-Born Instruments (DREAMS) Project, which is part of the Saharan Mineral Dust Experiment (SAMUM, 2006). Combining measurements of the backscattered radiation from the Medium Resolution Imaging Spectrometer (MERIS) instrument aboard Environmental Satellite (ENVISAT) and ground-based measurements in Morocco in radiation closure experiments yields the aerosol optical properties of mineral dust at selected locations.
    Tellus B 01/2009; 61(1):229 - 238. · 3.20 Impact Factor
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    ABSTRACT: A simple scheme has been developed to discriminate surface, sun glint and cloud properties in satellite based spectrometer data utilizing visible and near infrared information. It has been designed for the use with data measured by SCIAMACHY's (SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY) Polarization Measurement Devices (PMD) but the applicability is not strictly limited to this instrument. The scheme is governed by a set of constraints and thresholds developed by using satellite imagery and meteorological data. Classification targets are ice, water and generic clouds, sun glint and surface parameters, such as water, land, snow/ice, desert and vegetation. The validation has been done using MERIS (MEdium Resolution Imaging Spectrometer) and meteorological data from METAR (MÉTéorologique Aviation Régulière – a network for the provision of meteorological data for aviation). Qualitative validation using MERIS satellite imagery shows good agreement. However, the quantitative agreement is hampered by the heterogeneity of MERIS classifications within each SCIAMACHY PMD ground pixel. The comparison with METAR data shows good agreement. The comparison for sun glint classifications and MERIS results exhibits excellent agreement.
    Atmospheric Chemistry and Physics 01/2009; · 4.88 Impact Factor
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    ABSTRACT: In this study the technique of Differential Optical Absorption Spectroscopy (DOAS) has been adapted for the retrieval of the absorption and biomass of two major phy-toplankton groups (PhytoDOAS) from data of the Scanning Imaging Absorption Spectrometer for Atmospheric Chartog-raphy (SCIAMACHY) satellite sensor. SCIAMACHY mea-sures back scattered solar radiation in the UV-Vis-NIR spec-tral regions with a high spectral resolution (0.2 to 1.5 nm). In order to identify phytoplankton absorption characteristics in the SCIAMACHY data in the range of 430 to 500 nm, phytoplankton absorption spectra measured in-situ during two different RV "Polarstern" expeditions were used. The two spectra have been measured in different ocean regions where different phytoplankton groups (cyanobacteria and di-atoms) dominated the phytoplankton composition. Results clearly show distinct absorption characteristics of the two phytoplankton groups in the SCIAMACHY spectra. Using these results in addition to calculations of the light pene-tration depth derived from DOAS retrievals of the inelas-tic scattering (developed by Vountas et al., 2007), globally distributed pigment concentrations for these characteristic phytoplankton groups for two monthly periods (February– March 2004 and October–November 2005) were determined. This satellite information on cyanobacteria and diatoms dis-tribution clearly matches the concentrations based on high pressure liquid chromatography (HPLC) pigment analysis of collocated water samples and concentrations derived from a Correspondence to: A. Bracher (astrid.bracher@awi.de) global model analysis with the NASA Ocean Biogeochemi-cal Model (Gregg et al., 2003; Gregg and Casey 2007). The quantitative assessment of the distribution of key phytoplank-ton groups from space enables various biogeochemical re-gions to be distinguished and will be of great importance for the global modeling of marine ecosystems and biogeochem-ical cycles which enables the impact of climate change in the oceanic biosphere to be estimated.
    Biogeosciences 01/2009; 6:751-764. · 3.75 Impact Factor
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    ABSTRACT: We observed a long-range transport event of mineral dust from North Africa to South Europe during the Saharan Mineral Dust Experiment (SAMUM) 2006. Geometrical and optical properties of that dust plume were determined with Sun photometer of the Aerosol Robotic Network (AERONET) and Raman lidar near the North African source region, and with Sun photometers of AERONET and lidars of the European Aerosol Research Lidar Network (EARLINET) in the far field in Europe. Extinction-to-backscatter ratios of the dust plume over Morocco and Southern Europe do not differ. Ångstr¨om exponents increase with distance from Morocco. We simulated the transport, and geometrical and optical properties of the dust plume with a dust transport model. The model results and the experimental data show similar times regarding the appearance of the dust plume over each EARLINET site. Dust optical depth from the model agrees in most cases to particle optical depth measured with the Sun photometers. The vertical distribution of the mineral dust could be satisfactorily reproduced, if we use as benchmark the extinction profiles measured with lidar. In some cases we find differences. We assume that insufficient vertical resolution of the dust plume in the model calculations is one reason for these deviations.
    Tellus B - Chemical and Physical Meteorology. 01/2009; 61B(2009):325-339.