Maximum-likelihood retrieval of volcanic ash concentration and particle size from ground-based scanning lidar

An inversion methodology, named maximum-likelihood (ML) volcanic ash light detection and ranging (Lidar) retrieval (VALR-ML), has been developed and applied to estimate volcanic ash particle size and ash mass concentration within volcanic plumes. Both estimations are based on the ML approach, trained by a polarimetric backscattering forward model coupled with a Monte Carlo ash microphysical model. The VALR-ML approach is applied to Lidar backscattering and depolarization profiles, measured at visible wavelength during two eruptions of Mt. Etna, Catania, Italy, in 2010 and 2011. The results are compared with those of ash products derived from other parametric retrieval algorithms. A detailed comparison among these different retrieval techniques highlights the potential of VALR-ML to determine, on the basis of a physically consistent approach, the ash cloud area that must be interdicted to flight operations. Moreover, the results confirm the usefulness of operating scanning Lidars near active volcanic vents

Lidar-Radiometer Inversion Code (LIRIC) for the retrieval of vertical aerosol properties from combined lidar/radiometer data: development and distribution in EARLINET

The financial support by the European Union's Horizon 2020 research and innovation programme (ACTRIS-2, grant agreement no. 654109) is gratefully acknowledged. The background of LIRIC algorithm and software was developed under the ACTRIS Research Infrastructure project, grant agreement no. 262254, within the European Union Seventh Framework Programme, which financial support is gratefully acknowledged.r I. Binietoglou received funding from the European Union's Seventh Framework Programme for research, technological development and demonstration under the grant agreement no. 289923 - ITARS.This paper presents a detailed description of LIRIC (LIdar-Radiometer Inversion Code) algorithm for simultaneous processing of coincident lidar and radiometric (sun photometric) observations for the retrieval of the aerosol concentration vertical profiles. As the lidar/radiometric input data we use measurements from European Aerosol Research Lidar Network (EARLINET) lidars and collocated sun-photometers of Aerosol Robotic Network (AERONET). The LIRIC data processing provides sequential inversion of the combined lidar and radiometric data. The algorithm starts with the estimations of column-integrated aerosol parameters from radiometric measurements followed by the retrieval of height dependent concentrations of fine and coarse aerosols from lidar signals using integrated column characteristics of aerosol layer as a priori constraints. The use of polarized lidar observations allows us to discriminate between spherical and non-spherical particles of the coarse aerosol mode. The LIRIC software package was implemented and tested at a number of EARLINET stations. Intercomparison of the LIRIC-based aerosol retrievals was performed for the observations by seven EARLINET lidars in Leipzig, Germany on 25 May 2009. We found close agreement between the aerosol parameters derived from different lidars that supports high robustness of the LIRIC algorithm. The sensitivity of the retrieval results to the possible reduction of the available observation data is also discussed.European Union (EU) 654109ACTRIS Research Infrastructure project within the European Union 262254European Union (EU) 289923 - ITAR

Lidar-Radiometer Inversion Code (LIRIC) for the retrieval of vertical aerosol properties from combined lidar/radiometer data: Development and distribution in EARLINET

This paper presents a detailed description of LIRIC (LIdar-Radiometer Inversion Code) algorithm for simultaneous processing of coincident lidar and radiometric (sun photometric) observations for the retrieval of the aerosol concentration vertical profiles. As the lidar/radiometric input data we use measurements from European Aerosol Research Lidar Network (EARLINET) lidars and collocated sun-photometers of Aerosol Robotic Network (AERONET). The LIRIC data processing provides sequential inversion of the combined lidar and radiometric data. The algorithm starts with the estimations of column-integrated aerosol parameters from radiometric measurements followed by the retrieval of height dependent concentrations of fine and coarse aerosols from lidar signals using integrated column characteristics of aerosol layer as a priori constraints. The use of polarized lidar observations allows us to discriminate between spherical and non-spherical particles of the coarse aerosol mode. The LIRIC software package was implemented and tested at a number of EARLINET stations. Intercomparison of the LIRIC-based aerosol retrievals was performed for the observations by seven EARLINET lidars in Leipzig, Germany on 25 May 2009. We found close agreement between the aerosol parameters derived from different lidars that supports high robustness of the LIRIC algorithm. The sensitivity of the retrieval results to the possible reduction of the available observation data is also discussed

Long range transport and fate of a stratospheric volcanic cloud from Soufrière Hills volcano, Montserrat

International audienceVolcanic eruptions emit gases, ash particles and hydrometeors into the atmosphere, occasionally reaching heights of 20 km or more, to reside in the stratospheric overworld where they affect the radiative balance of the atmosphere and the Earth's climate. Here we use satellite measurements and a Lagrangian particle dispersion model to determine the mass loadings, vertical penetration, horizontal extent, dispersion and transport of volcanic gases and particles in the stratosphere from the volcanic cloud emitted during the 20 May 2006 eruption of Soufrière Hills volcano, Montserrat, West Indies. Infrared, ultraviolet and microwave radiation measurements from two polar orbiters are used to quantify the gases and particles, and track the movement of the cloud for 23 days, over a distance of ~18 000 km. Approximately, 0.1±0.01 Tg(S) was injected into the stratosphere in the form of SO2: the largest single sulphur input to the stratosphere in 2006. Microwave Limb Sounder measurements indicate an enhanced mass of HCl of ~0.003?0.01 Tg. Geosynchronous satellite data reveal the rapid nature of the stratospheric injection and indicate that the eruption cloud contained ~2 Tg of ice, with very little ash reaching the stratosphere. These new satellite measurements of volcanic gases and particles can be used to test the sensitivity of climate to volcanic forcing and assess the impact of stratospheric sulphates on climate cooling

Observability of Sudden Aerosol Injections by Ensemble-Based Four-Dimensional Assimilation of Remote Sensing Data

For sudden aerosol injections, uncertainties of emission source parameters impose the characterizing impediment for skillful numerical simulations. Large amounts of accidentally emitted aerosols can infer serious impacts on health, climate, environment, and economy. This highlights the societal need for reliable forecasts of released particles. Spatiotemporal assimilation techniques combine atmospheric dynamics as knowledge provided by the model with observations and induce constraints with potentially advantageous effects on the simulations. Ensemble-based analyses provide valuable information about the skill of forecast results. However, predictions remain uncertain in regions, where observational information is restricted. Observability investigates the impact of utilized observations, thus focusing on observation network optimization and information quantity specification. Taking volcanic eruptions as prototype for sudden aerosol injections, the research described in this thesis develops new methodologies to assess the impact of observations on the analysis. The emphasis is placed on assimilation-based analyses applying initial value and emission factor optimization for volcanic ash dispersion predictions of the Eyjafjallajökull eruption in April 2010. As observational input, two satellite-borne remote sensing principles are exploited: SEVIRI volcanic ash column mass loadings and CALIOP particle extinction coefficient profiles. For the assimilation within EURAD-IM, appropriate observation operators and their adjoints are constructed. The theoretical principles of observability in case of volcanic ash column mass loading observations are deduced from the viewpoint of the Kolmogorov-Sinai entropy. Ensemble versions of the 4D-var data assimilation technique and the particle smoother approach are implemented and processed, able to identify regions of high and low uncertainty in the dispersion simulation results. The analyses reveal a considerable constraining impact of SEVIRI retrievals to the ash dispersion, while CALIOP retrievals append information only on a very local scale. The variable degree of reliability is shown as a consequence of cloud cover dependent observability from space for both quasi-continuous SEVIRI data and sparse CALIOP overpasses

Sulfur Degassing From Volcanoes: Source Conditions, Surveillance, Plume Chemistry and Earth System Impacts

International audienceDespite its relatively minor abundance in magmas (compared with H2O and CO2), sulfur degassing from volcanoes is of tremendous significance. It can exert substantial influence on magmatic evolution (potentially capable of triggering eruptions); represents one of the most convenient opportunities for volcano monitoring and hazard assessment; and can result in major impacts on the atmosphere, climate and terrestrial ecosystems at a range of spatial and temporal scales. The complex behavior of sulfur in magmas owes much to its multiple valence states (-II, 0, IV, VI), speciation (e.g., S2, H2S, SO2, OCS and SO3 in the gas phase; S2-, SO42- and SO32- in the melt; and non-volatile solid phases such as pyrrhotite and anhydrite), and variation in stable isotopic composition (32S, 33S, 34S and 36S; e.g., Métrich and Mandeville 2010). Sulfur chemistry in the atmosphere is similarly rich involving gaseous and condensed phases and invoking complex homogeneous and heterogeneous chemical reactions. Sulfur degassing from volcanoes and geothermal areas is also important since a variety of microorganisms thrive based on the redox chemistry of sulfur: by reducing sulfur, thiosulfate, sulfite and sulfate to H2S, or oxidizing sulfur and H2S to sulfate (e.g., Takano et al. 1997; Amend and Shock 2001; Shock et al. 2010). Understanding volcanic sulfur degassing thus provides vital insights into magmatic, volcanic and hydrothermal processes; the impacts of volcanism on the Earth system; and biogeochemical cycles. Here, we review the causes of variability in sulfur abundance and speciation in different geodynamic contexts; the measurement of sulfur emissions from volcanoes; links between subsurface processes and surface observations; sulfur chemistry in volcanic plumes; and the consequences of sulfur degassing for climate and the environment

Quantitative comparison of the aerosol optical properties over Durban using ground and satellite based instrumentation.

Master of Science in Environmental Science. University of KwaZulu-Natal, Durban 2017.Aerosols are ubiquitous constituents in the atmosphere and are important for atmospheric processes. This is due to their ability to scatter and absorb solar radiation and influence cloud microphysics. This study will focus on discerning trends in aerosol optical properties in Durban (29.8587° S, 31.0218° E), a coastal city on the east coast of South Africa, using the preliminary results from the sun-photometer located at the University of KwaZulu-Natal. These results will also be compared to the well-established Skukuza sun-photometer. Skukuza is a rural agricultural area in the north eastern parts of South Africa. The Aerosol Optical Depth (AOD), Angstrom Exponent (α440–870), Columnar Water Vapour (CWV), Volume Size Distribution (VSD), Single Scattering Albedo (SSA), Asymmetry parameter (ASP), Real and Imaginary parts of the complex refractive index were studied for Durban and Skukuza. Analysis of the aerosol optical properties suggested that various sources of aerosols were identified for Durban, such as biomass burning, urban industrial aerosols and marine aerosols. Biomass burning aerosols impacted Skukuza during spring. There was a high extent of fine mode aerosols present throughout the year for Skukuza, indicating that urban industrial emissions from the South African Highveld region can also contribute to aerosol loads in the region. Preliminary results from the ground-based Durban sun-photometer was used to compare aerosol optical depth at 550 nm (AOD) to the satellite Moderate Resolution Imaging Spectroradiometer (MODIS) for the Aqua, Terra and Aqua and Terra combined (average of both) datasets for the dark target (DT) and deep blue (DB) retrieval algorithms to validate satellite retrievals. The results gave way to moderate correlations between MODIS Terra and the Durban sun-photometer for both DB (R2 = 0.70) and DT (R2 = 0.60), and between MODIS Aqua and the Durban sun-photometer for DB (0.68). Good correlations were observed for MODIS Terra and Aqua merged for both DB (0.79) and DT (0.74). The ability of MODIS to predict AOD was noted as dependent on the season and location. HYSPLIT 720 hour–backward trajectory analysis, AOD and α440–870 from the Durban sun-photometer, a Lidar profile and satellite imagery were used to determine if air mass from the Calbuco volcanic eruption in Chile in April 2015 reached Durban. Trajectory analysis found that only during May 2015, was air masses arriving from South America, within the 20 km altitude. This led to the assumption that stratospheric aerosols from the Calbuco volcano, travelled to Durban. Analysis of the AOD found that only during 2015 was a constant phenomenon driving AOD in Durban and this was attributed to the eruption. Lidar observations coupled with the backward trajectory analysis allowed for the identification of air masses in Durban arriving from the Calbuco volcano in Chile

Improvements to the limb scattering stratospheric aerosol record

In the last decade stratospheric aerosols have gained considerable attention due to the influence of a series of moderate volcanic eruptions. The eruptions have been explosive enough to inject aerosols and precursors into the stratosphere and cause minor but important radiative and chemical effects, impacting projections and modelling of the global climate. Improved understanding of these effects requires accurate measurements of aerosol levels at spatial and temporal scales that resolve the rapidly changing conditions after events such as volcanic eruptions while also providing global information. This has been enabled by the advent of satellite profiling observations beginning in the 1980s that are able to produce global, vertically resolved measurements of stratospheric aerosols. These records have helped improve estimates of radiative forcing but remain uncertain in key aspects, including the magnitude of the biases between different measurement systems, errors in records due to retrieval assumptions, and aerosol levels in the upper troposphere and lower stratosphere. This work quantifies and addresses these limitations using three studies. First, biases are explored between the two longest satellite-based stratospheric aerosol records: SAGE II from 1984-2005 and OSIRIS from 2001-present. Biases are found to be relatively small, approximately 10\%, in the majority of the stratosphere, and a merged aerosol record spanning 35 years is produced by adjusting for these measurement biases. This work produced an aerosol climatology suitable for use in climate models, but did not determine the reasons for the biases. The second study compares two instruments and their retrievals, OSIRIS and SCIAMACHY, to investigate the major sources of error. It is found that errors in the a priori assumptions including particle size and the aerosol profile at high altitudes cause the majority of biases, while differences in the retrieval techniques and the radiative transfer models have mostly negligible impacts. The final study uses these results to develop a new multi-wavelength retrieval for OSIRIS measurements that aims to minimize the errors from a priori assumptions and improve retrieval sensitivity in the upper troposphere and lower stratosphere. This is used to produce the publicly available version 7 OSIRIS aerosol product, and is validated using comparisons with SAGE measurements as well as satellite lidar observations. Significant reductions in particle size biases are found with this new algorithm, and an updated cloud filter allows for retrievals at lower altitudes than previously possible

Retrieval of microphysical properties of desert dust and volcanic ash aerosols from ground-based remote sensing

Aerosol particles are important constituents of the Earth's atmosphere. To quantify effects of aerosol particles, their distribution and properties need to be known. An important tool for the provision of such information is remote sensing. This thesis covers vertically-resolving remote sensing by lidar and vertically-integrating remote sensing by photometer, and thereby considers desert dust aerosols which cause a major uncertainty in climate forecasts, as well as volcanic ash aerosols which, in addition, are relevant for the flight safety of jet-driven aircrafts. Both aerosol types consist of ensembles of particles of varying size, shape, and chemical composition. This thesis aims to improve the retrieval of the physical properties of such mixtures from remote sensing observations, in particular by using Bayesian approaches and improved aerosol models. Three types of retrievals were developed. The first retrieval type applies to lidar observations, assumes spheroidal particle shapes, and is based on a Bayesian Monte-Carlo-approach. It was applied to observations of a pure volcanic ash plume from Iceland on 17 April 2010 over Maisach (Germany) for the retrieval of the mass concentration of the ash particles. The second retrieval type applies to photometer observations in the solar aureole, uses a pre-defined set of ensembles of irregularly-shaped particles, and was applied to observations of the same ash plume. Both methods consistently retrieved a maximum ash mass concentration of about 1.1 milligram per cubic meter over Maisach with an uncertainty range from 0.7 to 1.5 milligram per cubic meter. The third retrieval type searches for ensembles that agree with the observations from both remote sensing techniques; it uses a pre-defined set of ensembles derived from the aerosol database OPAC, but consisting of absorbing and non-absorbing irregularly-shaped particles. This approach was successfully applied to Saharan dust observations, which were performed during the SAMUM field campaigns in Morocco and on the Cape Verde islands. It turned out that, besides the particle shape, also the presence of non-absorbing components strongly influences the backscattering properties of the aerosols. In contrast, aureole radiances are hardly sensitive to particle shape and chemical composition, thus aureole radiances are well-suited for the retrieval of the size of ash and dust particles. It is expected that the accuracy of the retrievals further improves if all parameters observed by photometer are considered

Vertically resolved monitoring of atmospheric aerosols over Portugal with a multi-wavelength Raman Lidar

Foram realizadas pela primeira vez em Portugal medições regulares com Lidar. As medições com alta resolução da distribuição vertical dos aerossóis foram efetuadas com um Lidar Raman multiespectral instalado no Centro de Geofísica de _Évora (38.57_ N, 7.91_ W, 290 m acima do nível do mar) em _Évora, desde Setembro de 2009. Neste trabalho é apresentada uma climatologia de dois anos de tipos diferentes de aerossóis. Foram caracterizadas camadas de aerossóis na troposfera livre do ponto de vista das suas propriedades ópticas. Além das medições regulares efetuadas em datas pré estabelecidas, foram também realizados estudos intensivos durante eventos específicos: aerossóis de erupções vulcânicas na troposfera e estratosfera, de incêndios florestais e poeiras minerais do Sahara foram estudados detalhadamente. Nestes casos, os dados de Lidar foram combinados com dados de outros instrumentos de detecção remota activa e passiva e também in-situ instalados na superfície, para obter uma caracterização mais completa dos aerossóis; ABSTRACT: For the rst time, lidar measurements were performed in Portugal on a regular basis. Highly resolved measurements of the vertical distribution of aerosols were done with a multi-wavelength Raman lidar at the Evora Geophysics Center (Centro de Geof sica de Evora) (CGE) (38.57 N, 7.91 W, 290 m above sea level (asl)) in Evora since September 2009. A two-year climatology of di erent types of aerosols is presented within this work. Free tropospheric aerosol layers were characterised regarding their optical properties. Besides regular measurements performed on xed dates, intensive studies of special events were realised. Aerosol from volcanic eruptions in the free troposphere and stratosphere, forest re smoke as well as mineral dust from the Sahara were transported towards the southern Iberian peninsula and were investigated thoroughly. For such studies, the data of the ground based lidar were combined with other active and passive remote sensing and ground based in-situ instruments to allow a comprehensive aerosol characterisation; Zusammenfassung: Erstmalig wurden regelm a ige Lidarmessungen in Portugal durchgef uhrt. Mit einem Mehrwellenl angen-Raman-Lidar wird seit September 2009 am Centro de Geof sica de Evora (38.57 N, 7.91 W, 290 m uber dem Meeresspiegel) in Evora die vertikale Aerosolverteilung gemessen. Anhand von Daten eines Zeitraumes von zwei Jahren wurde eine Charakterisierung verschiedener Aerosoltypen erstellt. Daf ur wurden die optischen Eigenschaften von Aerosolschichten in der freien Troposph are bestimmt. Neben regelm a igen Messungen zu festen Zeiten wurden intensive Langzeitmessungen durchgef uhrt, z. B. von Vulkanaerosol in der Troposph are und Stratosph are, Waldbrandaerosol und W ustenstaub aus der Sahara. F ur eine umfassende Untersuchung der Aerosoleigenschaften wurden f ur diese Studien die Lidardaten mit Daten aus anderen aktiven und passiven Fernerkundungsmessungen sowie bodengebundenen in-situ Messungen kombiniert