393 research outputs found
Constrained Minimization Algorithms. Linear Models
This book is a collection of 19 articles which reflect the courses given at the Collège de France/Summer school “Reconstruction d'images − Applications astrophysiques“ held in Nice and Fréjus, France, from June 18 to 22, 2012. The articles presented in this volume address emerging concepts and methods that are useful in the complex process of improving our knowledge of the celestial objects, including Earth
SGM to Solve NMF – Application to Hyperspectral Data
This book is a collection of 19 articles which reflect the courses given at the Collège de France/Summer school “Reconstruction d'images − Applications astrophysiques“ held in Nice and Fréjus, France, from June 18 to 22, 2012. The articles presented in this volume address emerging concepts and methods that are useful in the complex process of improving our knowledge of the celestial objects, including Earth
Supervised Nonlinear Unmixing of Hyperspectral Images Using a Pre-image Methods
This book is a collection of 19 articles which reflect the courses given at the Collège de France/Summer school “Reconstruction d'images − Applications astrophysiques“ held in Nice and Fréjus, France, from June 18 to 22, 2012. The articles presented in this volume address emerging concepts and methods that are useful in the complex process of improving our knowledge of the celestial objects, including Earth
Les enjeux de la conférence de Paris : penser autrement la question climatique
International audienc
Détection bayésienne de saut de fréquence par des méthodes MCMC
Le problème traité est celui de la détection et de l'estimation hors-ligne d'un saut de fréquence dans une sinusoïde complexe bruitée. Une approche bayésienne utilisant une méthode de Monte Carlo par chaînes de Markov (MCMC) nous permet d'estimer l'instant de rupture r et les pulsations avant et après le saut uniquement à partir des observations. Une version adaptative de l'algorithme de Metropolis-Hastings (M-H) à marche aléatoire est utilisée permettant de régler de façon optimale et automatique les paramètres de l'algorithme. Les performances de détection estimées en terme de distribution de l'erreur d'estimation de r et d'estimation de l'amplitude de la rupture sont présentées
New Developments in the SCIAMACHY Level 2 Ground Processor Towards Version 7
SCIAMACHY (SCanning Imaging Absorption spectroMeter for Atmospheric ChartographY) aboard ESA’s
environmental satellite ENVISAT observed the Earth’s atmosphere in limb, nadir, and solar/lunar occultation
geometries covering the UV-Visible to NIR spectral range. It is a joint project of Germany, the Netherlands and
Belgium and was launched in February 2002. SCIAMACHY doubled its originally planned in-orbit lifetime
of five years before the communication to ENVISAT was severed in April 2012, and the mission entered its
post-operational phase.
In order to preserve the best quality of the outstanding data recorded by SCIAMACHY, data processors are still
being updated. This presentation will highlight three new developments that are currently being incorporated into
the forthcoming Version 7 of ESA’s operational Level 2 processor:
1. Tropospheric BrO, a new retrieval based on the scientific algorithm of (Theys et al., 2011). This algorithm had originally been developed for the GOME-2 sensor and was later adapted for SCIAMACHY.
2. Improved cloud flagging using limb measurements (Liebing, 2015). Limb cloud flags are already part of
the SCIAMACHY L2 product. They are currently calculated employing the scientific algorithm developed by
(Eichmann et al., 2015). Clouds are categorized into four types: water, ice, polar stratospheric and noctilucent
clouds. High atmospheric aerosol loadings, however, often lead to spurious cloud flags, when aerosols had been
misidentified as clouds. The new algorithm will better discriminate between aerosol and clouds. It will also have a
higher sensitivity w.r.t. thin clouds.
3. A new, future-proof file format for the level 2 product based on NetCDF. The data format will be aligned and harmonized with other missions, particularly GOME and Sentinels. The final concept for the new format is still under discussion within the SCIAMACHY Quality Working Group
A global catalogue of large SO \u3c inf\u3e 2 sources and emissions derived from the Ozone Monitoring Instrument
Sulfur dioxide (SO2) measurements from the Ozone Monitoring Instrument (OMI) satellite sensor processed with the new principal component analysis (PCA) algorithm were used to detect large point emission sources or clusters of sources. The total of 491 continuously emitting point sources releasing from about 30 kt yr-1 to more than 4000 kt yr-1 of SO2 per year have been identified and grouped by country and by primary source origin: volcanoes (76 sources); power plants (297); smelters (53); and sources related to the oil and gas industry (65). The sources were identified using different methods, including through OMI measurements themselves applied to a new emission detection algorithm, and their evolution during the 2005-2014 period was traced by estimating annual emissions from each source. For volcanic sources, the study focused on continuous degassing, and emissions from explosive eruptions were excluded. Emissions from degassing volcanic sources were measured, many for the first time, and collectively they account for about 30 % of total SO2 emissions estimated from OMI measurements, but that fraction has increased in recent years given that cumulative global emissions from power plants and smelters are declining while emissions from oil and gas industry remained nearly constant. Anthropogenic emissions from the USA declined by 80 % over the 2005-2014 period as did emissions from western and central Europe, whereas emissions from India nearly doubled, and emissions from other large SO2-emitting regions (South Africa, Russia, Mexico, and the Middle East) remained fairly constant. In total, OMI-based estimates account for about a half of total reported anthropogenic SO2 emissions; the remaining half is likely related to sources emitting less than 30 kt yr-1 and not detected by OMI
Intercomparison of Metop-A SO2 measurements during the 2010- 2011 Icelandic eruptions
The European Space Agency project Satellite Monitoring of Ash and Sulphur Dioxide for the mitigation of Aviation
Hazards, was introduced after the eruption of the Icelandic volcano Eyjafjallajökull in the spring of 2010
to facilitate the development of an optimal EndtoEnd
System for Volcanic Ash Plume Monitoring and Prediction.
The Eyjafjallajökull plume drifted towards Europe and caused major disruptions of European air traffic for
several weeks affecting the everyday life of millions of people. The limitations in volcanic plume monitoring and
prediction capabilities gave birth to this observational system which is based on comprehensive satellitederived
ash plume and sulphur dioxide [SO2] level estimates, as well as a widespread validation using supplementary
satellite, aircraft and groundbased
measurements. Intercomparison
of the volcanic total SO2 column and
plume height observed by GOME2/
MetopA
and IASI/MetopA
are shown before, during and after the Eyjafjallajökull
2010 eruptions as well as for the 2011 Grímsvötn eruption. Colocated
groundbased
Brewer Spectrophotometer
data extracted from the World Ozone and Ultraviolet Radiation Data Centre for de Bilt, the Netherlands,
are also compared to the different satellite estimates. Promising agreement is found for the two different
types of instrument for the SO2 columns with linear regression coefficients ranging around from 0.64 when
comparing the different instruments and 0.85 when comparing the two different IASI algorithms. The agreement
for the plume height is lower, possibly due to the major differences between the height retrieval part of the
GOME2 and IASI algorithms. The comparisons with the Brewer groundbased
station in de Bilt, The Netherlands
show good qualitative agreement for the peak of the event however stronger eruptive signals are required
for a longer quantitative comparison
Retrieval of stratospheric and tropospheric BrO profiles and columns using ground-based zenith-sky DOAS observations at Harestua, 60° N
A profiling algorithm based on the optimal estimation method is applied to ground-based zenith-sky UV-visible measurements from Harestua, Southern Norway (60° N, 11° E) in order to retrieve BrO vertical profiles. The sensitivity of the zenith-sky observations to the tropospheric BrO detection is increased by using for the spectral analysis a fixed reference spectrum corresponding to clear-sky noon summer conditions. The information content and retrieval errors are characterized and it is shown that the retrieved stratospheric profiles and total columns are consistent with correlative balloon and satellite observations, respectively. Tropospheric BrO columns are derived from profiles retrieved at 80° solar zenith angle during sunrise and sunset for the 2000–2006 period. They show a marked seasonality with mean column value ranging from 1.52±0.62×10<sup>13</sup> molec/cm² in late winter/early spring to 0.92±0.38×10<sup>13</sup> molec/cm² in summer, which corresponds to 1.0±0.4 and 0.6±0.2 pptv, respectively, if we assume that BrO is uniformly mixed in the troposphere. These column values are also consistent with previous estimates made from balloon, satellite, and other ground-based observations. Daytime (10:30 LT) tropospheric BrO columns are compared to the <i>p</i>-TOMCAT 3-D tropospheric chemical transport model (CTM) for the 2002–2003 period. <i>p</i>-TOMCAT shows a good agreement with the retrieved columns except in late winter/early spring where an underestimation by the model is obtained. This finding could be explained by the non-inclusion of sea-ice bromine sources in the current version of <i>p</i>-TOMCAT. Therefore the model cannot reproduce the possible transport of air-masses with enhanced BrO concentration due to bromine explosion events from the polar region to Harestua. The daytime stratospheric BrO columns are compared to the SLIMCAT stratospheric 3-D-CTM. The model run used in this study, which assumes 21.2 pptv for the Br<sub>y</sub> loading (15 pptv for long-lived bromine species and additional 6 pptv for very short-lived species (VSLS) added by a scaling of CH<sub>3</sub>Br), significantly underestimates the retrieved BrO columns. A sensitivity study shows that a good agreement can only be obtained if 6 to 8 pptv accounting for VSLS are added directly (and not by a scaling of CH<sub>3</sub>Br) to the SLIMCAT long-lived bromine species profile. This contribution of the VSLS to the total bromine loading is also consistent with recently published studies
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