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Heidelberg, Germany

Sanghavi S.,SRON Netherlands Institute for Space Research | Platt U.,Institute For Umweltphysik | Landgraf J.,SRON Netherlands Institute for Space Research
Applied Optics | Year: 2010

We propose a method for identifying clear-sky scenarios from a measurement time series over satelliteobserved ground pixels of unknown surface albedo and aerosol type. The lack of a general monotonic relationship between aerosol loading and observed reflectance encumbers the ordering of the observation time series according to aerosol loading. This problem is ameliorated by using two wavelengths at which the surface albedos are known to differ. Treating an observation as being cloud/aerosol free allows for the determination of the corresponding Lambertian equivalent albedo, the relative contrast of which at the two wavelengths varies monotonically with respect to aerosol-loading, clear-sky and completely clouded scenarios representing the extreme cases. Applying this method to the Scanning Imaging Absorption Spectrometer for Atmospheric Chartography measurements over a nondark surface, we validate it by comparing measured against modeled O2 A- and B-band absorption at the retrieved albedo in an aerosol-free atmosphere. © 2010 Optical Society of America. Source

Christl M.,ETH Zurich | Casacuberta N.,ETH Zurich | Vockenhuber C.,ETH Zurich | Elsasser C.,Institute For Umweltphysik | And 2 more authors.
Journal of Geophysical Research: Oceans | Year: 2015

A reconstruction of historical discharges of 236U into the Northeast Atlantic Ocean by nuclear installations is presented. The nuclear reprocessing facilities Sellafield (SF), Great Britain (GB) and La Hague (LH), France and potentially also the nuclear fuel processing installation Springfields (SP), GB represent the main contributors of 236U in the Northeast Atlantic Ocean. Because data on 236U releases is lacking, 236U discharges from SP and SF are estimated based on the U-isotopic systematics found in the discharges from LH. The resulting reconstruction of 236U releases indicates that, until 2013, a total of (95±32) kg of 236U was discharged from SF, SP, and LH. In a second step, the reconstructed 236U releases are combined with 129I data from literature and oceanic and atmospheric box models are used to derive the 129I/236U and 236U/238U input functions that, for example, can be used to calculate tracer ages of Atlantic Waters in the Arctic Ocean. Our conceptual results show that the combination of 129I/236U and 236U/238U generally allows the estimation of tracer ages over the past approximately 25 years if contributions of 236U from global fallout are considered. Finally, as a proof of concept, the new method is applied to calculate tracer ages of Arctic Ocean surface samples (collected in 2011/2012) and the results are in good agreement with literature data. We conclude that the combination of 129I/236U with 236U/238U in a dual tracer approach provides a sensitive tool for the calculation of tracer ages and ventilation rates in the North Atlantic region. © 2015. American Geophysical Union. All Rights Reserved. Source

Bergamaschi P.,European Commission - Joint Research Center Ispra | Corazza M.,European Commission - Joint Research Center Ispra | Karstens U.,Max Planck Institute for Biogeochemistry | Athanassiadou M.,UK Met Office | And 26 more authors.
Atmospheric Chemistry and Physics | Year: 2015

European CH4 and N2O emissions are estimated for 2006 and 2007 using four inverse modelling systems, based on different global and regional Eulerian and Lagrangian transport models. This ensemble approach is designed to provide more realistic estimates of the overall uncertainties in the derived emissions, which is particularly important for verifying bottom-up emission inventories. We use continuous observations from 10 European stations (including 5 tall towers) for CH4 and 9 continuous stations for N2O, complemented by additional European and global discrete air sampling sites. The available observations mainly constrain CH4 and N2O emissions from north-western and eastern Europe. The inversions are strongly driven by the observations and the derived total emissions of larger countries show little dependence on the emission inventories used a priori. Three inverse models yield 26-56% higher total CH4 emissions from north-western and eastern Europe compared to bottom-up emissions reported to the UNFCCC, while one model is close to the UNFCCC values. In contrast, the inverse modelling estimates of European N2O emissions are in general close to the UNFCCC values, with the overall range from all models being much smaller than the UNFCCC uncertainty range for most countries. Our analysis suggests that the reported uncertainties for CH4 emissions might be underestimated, while those for N2O emissions are likely overestimated. © 2015 Author(s). Source

Lubcke P.,Institute For Umweltphysik | Lubcke P.,Max Planck Institute for Chemistry | Bobrowski N.,Institute For Umweltphysik | Illing S.,Institute For Umweltphysik | And 6 more authors.
Atmospheric Measurement Techniques | Year: 2013

Sulphur dioxide emission rate measurements are an important tool for volcanic monitoring and eruption risk assessment. The SO2 camera technique remotely measures volcanic emissions by analysing the ultraviolet absorption of SO2 in a narrow spectral window between 300 and 320 nm using solar radiation scattered in the atmosphere. The SO2 absorption is selectively detected by mounting band-pass interference filters in front of a two-dimensional, UV-sensitive CCD detector. One important step for correct SO2 emission rate measurements that can be compared with other measurement techniques is a correct calibration. This requires conversion from the measured optical density to the desired SO2 column density (CD). The conversion factor is most commonly determined by inserting quartz cells (cuvettes) with known amounts of SO2 into the light path. Another calibration method uses an additional narrow field-of-view Differential Optical Absorption Spectroscopy system (NFOVDOAS), which measures the column density simultaneously in a small area of the camera?s field-of-view. This procedure combines the very good spatial and temporal resolution of the SO2 camera technique with the more accurate column densities obtainable from DOAS measurements. This work investigates the uncertainty of results gained through the two commonly used, but quite different, calibration methods (DOAS and calibration cells). Measurements with three different instruments, an SO 2 camera, a NFOVDOAS system and an Imaging DOAS (I-DOAS), are presented. We compare the calibration-cell approach with the calibration from the NFOV-DOAS system. The respective results are compared with measurements from an I-DOAS to verify the calibration curve over the spatial extent of the image. The results show that calibration cells, while working fine in some cases, can lead to an overestimation of the SO2 CD by up to 60% compared with CDs from the DOAS measurements. Besides these errors of calibration, radiative transfer effects (e.g. light dilution, multiple scattering) can significantly influence the results of both instrument types. The measurements presented in this work were taken at Popocatépetl, Mexico, between 1 March 2011 and 4 March 2011. Average SO2 emission rates between 4.00 and 14.34 kg s -1 were observed. © Author(s) 2013. Source

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