Lidar remote sensing and co-operative observations: Processing methods and aerosol radiative transfer

This Ph.D. thesis focuses on: (i) the design and integration of a polarimetric channel for the multi-spectral Raman lidar station of the Universitat Politècnica de Catalunya (UPC), Remote Sensing, Antennas, Microwaves and Superconductivity Group (CommSensLab), (ii) the study of the temporal and spatial evolution of atmospheric aerosol optical, microphysical and radiative properties by means of active and passive remote sensing in the context of ACTRIS and Spanish National projects, and (iii) rainfall rate retrieval by means of a vertically-pointed ceilometer in the context of the Verification of the Origins of Rotation in Tornadoes Experiment Southeast (VORTEX-SE). The first goal of this Ph.D., tested on the UPC multi-spectral Raman lidar station, consists of developing a secondary optical receiving chain, installed next to the laser source. The secondary telescope, mounted in the optical chain, allows retrieving the cross-polarized return signal separately from the total-power signal, avoiding the need of a very precise characterization of the crosstalk parameters of the beam-splitters. The first experimental results, corresponding to a collection of atmospheric conditions over the city of Barcelona, are also presented. The second goal of this Ph.D. deals first with the GAME (Global Atmospheric Model) code, necessary to retrieve the aerosol radiative properties. The radiative fluxes estimated in the short-wave and long-wave spectral ranges at the bottom and the top of the atmosphere by GAME are compared to the ones retrieved by a different radiative transfer model, namely Two-Stream, in order to know the importance of the spectral parameterization of a radiative transfer code. Then, GAME code, in both configurations, is fed by means of three different datasets to evaluate the parameterization of the vertically-resolved properties and to assess the uncertainty of GAME when is tuned with input parameters from different sources. Afterwards, an evaluation of the seasonal variability of the aerosol background optical and radiative properties in the Western Mediterranean Basin (WMB) is performed by means of AERONET (Aerosol Robotic Network) sun-photometers data from two background sites, Ersa (Corsica Island, France) and Palma de Mallorca (Mallorca Island, Spain). In addition, in order to detect possible northeast-southwest gradients in the aerosol properties, a third site located at Abolrán (Alborán Island, Spain) is considered. Finally, during 15-24 June 2013 a moderate Saharan dust multi-intrusion was detected by some EARLINET/ACTRIS (Granada, Barcelona, Naples, Potenza and Serra la Nave (Italy)) and ADRIMED/ChArMEx (Cap d’en Font, (Minorca Island, Spain) and Ersa) stations. This Ph.D. uses this event to study the spatio-temporal evolution of the mineral dust properties, since the lidar stations were supported during the multi-intrusion by collocated AERONET sun-photometers and the Falcon 20 aircraft. Also the GAME code is used to estimate the aerosol radiaite effect during the Saharan dust event. Besides, air- and space-borne lidar measurements, satellite images and back-trajectories are used to confirm the multi-intrusion aspect of the event. The last goal of this Ph.D. pursues estimation of the rain rate (RR) from ceilometer measurements. In VORTEX-SE, a Vaisala CL-31 ceilometer, a S-band radar, and a disdrometer were deployed in Alabama during March-April 2016. First, rain-extinction coefficients from ceilometer attenuated backscatter measurements are derived by means of a modified form of the well-known slope-method. These coefficients are compared with the RRs measured by a collocated S-band radar and a disdrometer in order to get the RR-to-extinction models. Advanced covariance-weighted techniques are used to best assess and validate the estimated models. These models can be used to estimate the RR from the ceilometer in similar situations without need to have a collocated cooperative instrument permanently deployed.Este Ph.D. se centra en: (i) en el diseño e integración de un canal polarimétrico para la estación lidar multi espectral del grupo de teledetección, antenas, microondas y superconductividad (CommSensLab) de la Universitat Politècnica de Catalunya (UPC), (ii) en el estudio de la evolución temporal y espacial de las propiedades ópticas, microfísicas y radiativas de los aerosoles por medio de teledetección activa y pasiva en el contexto de ACTRIS y proyectos estatales, y (iii) en la recuperación de intensidad de lluvia por medio de un ceilómetro en configuración vertical en el contexto del proyecto Verification of the Origins of Rotation in Tornadoes Experiment Southeast (VORTEX-SE). El primer objetivo, realizado en la estación lidar de UPC, consiste en el desarrollo de una cadena óptica secundaria instalada junto al láser. El telescopio secundario, montado en la cadena óptica, permite recuperar la componente cross-polarized de la señal total por separado, evitando la necesidad de conocer con precisión los parámetros de los beam-splitters. Se presentan también los primeros resultados obtenidos en Barcelona durante diferentes situaciones atmosféricas. El segundo objetivo de este Ph.D. se centra en el código GAME (Global Atmospheric Model), necesario para recuperar las propiedades radiativas de los aerosoles. Los flujos radiativos estimados tanto en onda larga como en onda corta en la base y en la parte superior de la atmósfera son comparados con los estimados por otro código de transferencia radiativa, Two-Stream, para conocer la importancia de la parametrización espectral. Después, el código GAME es alimentado con 3 bases de datos diferentes para evaluar la parametrización de las propiedades resueltas en altura y conocer la incertidumbre de GAME cuando es alimentado con parámetros con diferentes orígenes. Por otro lado, se presenta una evaluación de la variabilidad estacional de las propiedades ópticas y radiativas del aerosol de fondo en la cuenca oeste mediterránea (WMB) realizada con datos de fotómetros solares de la red AERONET (Aerosol Robotic Network) situados en dos puntos considerados libres de contaminación: Ersa (isla de Córcega, Francia) y Palma de Mallorca. Además, para detectar posibles gradientes noreste-suroeste en las propiedades delos aerosoles, se considera un tercer punto ubicado en la isla de Alborán. Por último, en este Ph.D. se aprovecha una multi intrusión moderada de polvo sahariano, detectada entre los días 15 y 24 de junio de 2013 por algunas estaciones EARLINET/ACTRIS (Granada, Barcelona, Nápoles, Potenza y Serra la Nave (Italia)) y ADRIMED/ChArMEx (Cap d'en Font (Menorca) y Ersa), para estudiar la evolución espacio-temporal de las propiedades del polvo mineral, ya que las estaciones lidar estaban apoyadas durante el evento por fotómetros solares pertenecientes a la red AERONET, situados junto a las estaciones lidar, y por vuelos del Falcon 20. GAME es usado para obtener también el efecto radiativo de los aerosoles durante el evento de polvo sahariano. Para confirmar el aspecto de multi intrusión se utilizan medidas lidar tomadas a bordo de aviones y satélites, imágenes satelitales y retro trayectorias. El último objetivo del Ph.D. persigue la estimación de la RR utilizando medidas de un ceilómetro. En VORTEX-SE, se desplegaron (Alabama, marzo-abril 2016) un ceilómetro Vaisala CL-31, un radar de banda S y un disdrómetro. Se han estimado los coeficientes de extinción debida a la lluvia a partir del retorno atenuado medido por el ceilómetro, utilizando una versión modificada del método de la pendiente. Estos coeficientes se comparan con las intensidades de lluvia (RR) estimadas con el radar y el disdrómetro para obtener modelos de RR-extinción. Para validarlos se utilizan técnicas avanzadas de covarianza ponderada. Dichos modelos pueden usarse para estimar la RR con un ceilómetro, en situaciones similares, sin necesidad de tener desplegado permanentemente un instrumento cooperativo.Postprint (published version

Lidar remote sensing and co-operative observations: Processing methods and aerosol radiative transfer

This Ph.D. thesis focuses on: (i) the design and integration of a polarimetric channel for the multi-spectral Raman lidar station of the Universitat Politècnica de Catalunya (UPC), Remote Sensing, Antennas, Microwaves and Superconductivity Group (CommSensLab), (ii) the study of the temporal and spatial evolution of atmospheric aerosol optical, microphysical and radiative properties by means of active and passive remote sensing in the context of ACTRIS and Spanish National projects, and (iii) rainfall rate retrieval by means of a vertically-pointed ceilometer in the context of the Verification of the Origins of Rotation in Tornadoes Experiment Southeast (VORTEX-SE). The first goal of this Ph.D., tested on the UPC multi-spectral Raman lidar station, consists of developing a secondary optical receiving chain, installed next to the laser source. The secondary telescope, mounted in the optical chain, allows retrieving the cross-polarized return signal separately from the total-power signal, avoiding the need of a very precise characterization of the crosstalk parameters of the beam-splitters. The first experimental results, corresponding to a collection of atmospheric conditions over the city of Barcelona, are also presented. The second goal of this Ph.D. deals first with the GAME (Global Atmospheric Model) code, necessary to retrieve the aerosol radiative properties. The radiative fluxes estimated in the short-wave and long-wave spectral ranges at the bottom and the top of the atmosphere by GAME are compared to the ones retrieved by a different radiative transfer model, namely Two-Stream, in order to know the importance of the spectral parameterization of a radiative transfer code. Then, GAME code, in both configurations, is fed by means of three different datasets to evaluate the parameterization of the vertically-resolved properties and to assess the uncertainty of GAME when is tuned with input parameters from different sources. Afterwards, an evaluation of the seasonal variability of the aerosol background optical and radiative properties in the Western Mediterranean Basin (WMB) is performed by means of AERONET (Aerosol Robotic Network) sun-photometers data from two background sites, Ersa (Corsica Island, France) and Palma de Mallorca (Mallorca Island, Spain). In addition, in order to detect possible northeast-southwest gradients in the aerosol properties, a third site located at Abolrán (Alborán Island, Spain) is considered. Finally, during 15-24 June 2013 a moderate Saharan dust multi-intrusion was detected by some EARLINET/ACTRIS (Granada, Barcelona, Naples, Potenza and Serra la Nave (Italy)) and ADRIMED/ChArMEx (Cap d’en Font, (Minorca Island, Spain) and Ersa) stations. This Ph.D. uses this event to study the spatio-temporal evolution of the mineral dust properties, since the lidar stations were supported during the multi-intrusion by collocated AERONET sun-photometers and the Falcon 20 aircraft. Also the GAME code is used to estimate the aerosol radiaite effect during the Saharan dust event. Besides, air- and space-borne lidar measurements, satellite images and back-trajectories are used to confirm the multi-intrusion aspect of the event. The last goal of this Ph.D. pursues estimation of the rain rate (RR) from ceilometer measurements. In VORTEX-SE, a Vaisala CL-31 ceilometer, a S-band radar, and a disdrometer were deployed in Alabama during March-April 2016. First, rain-extinction coefficients from ceilometer attenuated backscatter measurements are derived by means of a modified form of the well-known slope-method. These coefficients are compared with the RRs measured by a collocated S-band radar and a disdrometer in order to get the RR-to-extinction models. Advanced covariance-weighted techniques are used to best assess and validate the estimated models. These models can be used to estimate the RR from the ceilometer in similar situations without need to have a collocated cooperative instrument permanently deployed.Este Ph.D. se centra en: (i) en el diseño e integración de un canal polarimétrico para la estación lidar multi espectral del grupo de teledetección, antenas, microondas y superconductividad (CommSensLab) de la Universitat Politècnica de Catalunya (UPC), (ii) en el estudio de la evolución temporal y espacial de las propiedades ópticas, microfísicas y radiativas de los aerosoles por medio de teledetección activa y pasiva en el contexto de ACTRIS y proyectos estatales, y (iii) en la recuperación de intensidad de lluvia por medio de un ceilómetro en configuración vertical en el contexto del proyecto Verification of the Origins of Rotation in Tornadoes Experiment Southeast (VORTEX-SE). El primer objetivo, realizado en la estación lidar de UPC, consiste en el desarrollo de una cadena óptica secundaria instalada junto al láser. El telescopio secundario, montado en la cadena óptica, permite recuperar la componente cross-polarized de la señal total por separado, evitando la necesidad de conocer con precisión los parámetros de los beam-splitters. Se presentan también los primeros resultados obtenidos en Barcelona durante diferentes situaciones atmosféricas. El segundo objetivo de este Ph.D. se centra en el código GAME (Global Atmospheric Model), necesario para recuperar las propiedades radiativas de los aerosoles. Los flujos radiativos estimados tanto en onda larga como en onda corta en la base y en la parte superior de la atmósfera son comparados con los estimados por otro código de transferencia radiativa, Two-Stream, para conocer la importancia de la parametrización espectral. Después, el código GAME es alimentado con 3 bases de datos diferentes para evaluar la parametrización de las propiedades resueltas en altura y conocer la incertidumbre de GAME cuando es alimentado con parámetros con diferentes orígenes. Por otro lado, se presenta una evaluación de la variabilidad estacional de las propiedades ópticas y radiativas del aerosol de fondo en la cuenca oeste mediterránea (WMB) realizada con datos de fotómetros solares de la red AERONET (Aerosol Robotic Network) situados en dos puntos considerados libres de contaminación: Ersa (isla de Córcega, Francia) y Palma de Mallorca. Además, para detectar posibles gradientes noreste-suroeste en las propiedades delos aerosoles, se considera un tercer punto ubicado en la isla de Alborán. Por último, en este Ph.D. se aprovecha una multi intrusión moderada de polvo sahariano, detectada entre los días 15 y 24 de junio de 2013 por algunas estaciones EARLINET/ACTRIS (Granada, Barcelona, Nápoles, Potenza y Serra la Nave (Italia)) y ADRIMED/ChArMEx (Cap d'en Font (Menorca) y Ersa), para estudiar la evolución espacio-temporal de las propiedades del polvo mineral, ya que las estaciones lidar estaban apoyadas durante el evento por fotómetros solares pertenecientes a la red AERONET, situados junto a las estaciones lidar, y por vuelos del Falcon 20. GAME es usado para obtener también el efecto radiativo de los aerosoles durante el evento de polvo sahariano. Para confirmar el aspecto de multi intrusión se utilizan medidas lidar tomadas a bordo de aviones y satélites, imágenes satelitales y retro trayectorias. El último objetivo del Ph.D. persigue la estimación de la RR utilizando medidas de un ceilómetro. En VORTEX-SE, se desplegaron (Alabama, marzo-abril 2016) un ceilómetro Vaisala CL-31, un radar de banda S y un disdrómetro. Se han estimado los coeficientes de extinción debida a la lluvia a partir del retorno atenuado medido por el ceilómetro, utilizando una versión modificada del método de la pendiente. Estos coeficientes se comparan con las intensidades de lluvia (RR) estimadas con el radar y el disdrómetro para obtener modelos de RR-extinción. Para validarlos se utilizan técnicas avanzadas de covarianza ponderada. Dichos modelos pueden usarse para estimar la RR con un ceilómetro, en situaciones similares, sin necesidad de tener desplegado permanentemente un instrumento cooperativo

Estimation of mineral dust direct radiative forcing at the European Aerosol Research Lidar NETwork site of Lecce, Italy, during the ChArMEx/ADRIMED summer 2013 campaign: Impact of radiative transfer model spectral resolutions

© 2016. American Geophysical UnionA field campaign took place in the western and central Mediterranean basin on June–July 2013 in the framework of the ChArMEx (Chemistry-Aerosol Mediterranean Experiment, http://charmex.lsce.ipsl.fr/)/ADRIMED (Aerosol Direct Radiative Impact on the regional climate in the MEDiterranean region, http://adrimed.sedoo.fr/) project to characterize the aerosol direct radiative forcing (DRF) over the Mediterranean. This work focuses on the aerosol DRF estimations at Lecce (40.33°N; 18.11°E; 30¿m above sea level) during the Saharan dust outbreak that affected southern Italy from 20 to 24 June 2013. The Global Atmospheric Model (GAME) and the Two-Stream (TS) model were used to calculate the instantaneous aerosol DRF in the short-wave (SW) and long-wave (LW) spectral ranges, at the surface and at the top of the atmosphere (TOA). The main differences between the two models were due to the different numerical methods to solve the radiative transfer (RT) equations and to the more detailed spectral resolution of GAME compared to that of TS. 167 and 115 subbands were used by GAME in the 0.3–4 and 4–37¿µm spectral ranges, respectively. Conversely, the TS model used 8 and 11 subbands in the same spectral ranges, respectively. We found on 22 June that the SW-DRFs from the two models were in good agreement, both at the TOA and at the surface. The instantaneous SW-DRFs at the surface and at the TOA varied from -50 to -34¿W¿m-2 and from -6 to +8¿W¿m-2, respectively, while the surface and TOA LW-DRFs ranged between +3.5 and +8.0¿W¿m-2 and between +1.7 and +6.9¿W¿m-2, respectively. In particular, both models provided positive TOA SW-DRFs at solar zenith angles smaller than 25° because of the mixing of the desert dust with anthropogenic pollution during its transport to the study site. In contrast, the TS model overestimated the GAME LW-DRF up to about 5 and 7.5 times at the surface and at the TOA, respectively, when the dust particle contribution was largest. The low spectral resolution of the real (n) and imaginary (k) refractive index values was mainly responsible for the LW-DRF overestimates of the TS model. However, we found that the “optimization” of the n and k values at 8.75 and 11.5¿µm was sufficient in this study to obtain a satisfactory agreement between the LW-DRFs from the two models, both at the TOA and at the surface. The impact of the spectral dependence of the water vapor absorption coefficients on the estimation of the flux without aerosol has also been addressed. Paper results did not reveal any significant impact due to the different numerical methods used by the two models to solve the RT equations.Peer ReviewedPostprint (published version

Depolarization channel for barcelona lidar. Implementation and preliminary measurements

A new depolarization channel has beenimplemented in the BarcelonaTech University(UPC) multi-wavelength lidar system. The opticaland mechanical designs are presented. The specialconfiguration of the total power channel is alsodetailed, with the relevant aspects in measurement inversion. Some preliminary measurements arepresented for Saharan dust intrusion events.Peer ReviewedPostprint (published version

Two-dimensional mineral dust radiative effect calculations from CALIPSO observations over Europe

A demonstration study to examine the feasibility of retrieving dust radiative effects based on combined satellite data from MODIS (Moderate Resolution Imaging Spectroradiometer), CERES (Clouds and the Earth's Radiant Energy System) and CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) lidar vertical profiles along their orbit is presented. The GAME (Global Atmospheric Model) radiative transfer model is used to estimate the shortwave and longwave dust radiative effects below the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite) orbit assuming an aerosol parameterization based on the CALIOP vertical distribution at a horizontal resolution of 5¿km and additional AERONET (Aerosol Robotic Network) data. Two study cases are analyzed: a strong long-range transport mineral dust event (aerosol optical depth, AOD, of 0.52) that originated in the Sahara Desert and reached the United Kingdom and a weaker event (AOD¿=¿0.16) that affected eastern Europe. The radiative fluxes obtained are first validated in terms of radiative efficiency at a single point with space–time colocated lidar ground-based measurements from EARLINET (European Aerosol Research Lidar Network) stations below the orbit. The methodology is then applied to the full orbit. The strong dependence of the radiative effects on the aerosol load (and to a lesser extent on the surface albedo) highlights the need for accurate AOD measurements for radiative studies. The calculated dust radiative effects and heating rates below the orbits are in good agreement with previous studies of mineral dust, with the radiative efficiency obtained at the surface ranging between -80.3 and -63.0¿W¿m-2 for lower dust concentration event and -119.1 and -79.3¿W¿m-2 for the strong event. Thus, results demonstrate the validity of the method presented here to retrieve 2-D accurate radiative properties with large spatial and temporal coverage.Peer ReviewedPostprint (published version

Diffuse sunlight based calibration of the water vapor channel in the UPC Raman lidar

A method for determining the calibration factor of the water vapor channel of a Raman lidar, based on zenith measurements of diffuse sunlight and on assumptions regarding some system parameters and Raman scattering models, has been applied to the lidar system of Universitat Politècnica de Catalunya (UPC; Technical University of Catalonia, Spain). Results will be analyzed in terms of stability and comparison with typical methods relying on simultaneous radiosonde measurements.Peer ReviewedPostprint (published version

Considerations about the determination of the depolarization calibration profile of a two-telescope lidar and its implications for volume depolarization ratio retrieval

We propose a new method for calculating the volume depolarization ratio of light backscattered by the atmosphere and a lidar system that employs an auxiliary telescope to detect the depolarized component. It takes into account the possible error in the positioning of the polarizer used in the auxiliary telescope. The theory of operation is presented and then applied to a few cases for which the actual position of the polarizer is estimated, and the improvement of the volume depolarization ratio in the molecular region is quantified. In comparison to the method used before, i.e., without correction, the agreement between the volume depolarization ratio with correction and the theoretical value in the molecular region is improved by a factor of 2–2.5.Peer ReviewedPostprint (published version

Calibration of Raman lidar water vapor mixing ratio measurements using zenithal measurements of diffuse sunlight and a radiative transfer model

This is a postprint (author final draft) version of article that has been accepted for publication. A fully version can be found at: https://doi.org/10.1109/TGRS.2018.2851064 © 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Among the different techniques available for measuring the atmospheric water vapor content, Raman lidars stand out as accurate instruments providing detailed profiles with high temporal and altitude resolution. Their principle is based on obtaining the range-resolved ratio of the lidar signals corresponding to Raman returns from water vapor and nitrogen molecules, which is proportional to the water vapor mixing ratio. To do this, it is necessary to determine a calibration factor, specific of each lidar instrument. A method for obtaining this parameter, based on zenith measurements of diffuse sunlight, on Raman scattering models and on simulations, using a radiative transfer model, to estimate sky radiances at the wavelengths of interest, has been applied to the lidar system of Universitat Politècnica de Catalunya (UPC; Technical University of Catalonia, Barcelona, Spain). A set of calibrations, performed between 2016 and 2017, has permitted assessing the calibration procedure and analyzing the stability of the calibration factor in the UPC instrument. Results show that although the calibration factor can remain stable for long periods of time, it can suffer sudden variations that make indispensable to implement a convenient and reliable procedure to perform regular calibrations. We show that the method, which can be applied to any lidar with water vapor and nitrogen Raman channels, can completely dispense with radiosonde data. The calibration method is validated by comparison with simultaneous radiosonde water vapor measurements. Limitations of radiosondes for validating--and eventually calibrating--water vapor Raman lidars have been revealed.Peer ReviewedPostprint (author's final draft

Vertically resolved precipitation intensity retrieved through a synergy between the ground-based NASA MPLNET lidar network measurements, surface disdrometer datasets and an analytical model solution

In this paper, we illustrate a new, simple and complementary ground-based methodology to retrieve the vertically resolved atmospheric precipitation intensity through a synergy between measurements from the National Aeronautics and Space Administration (NASA) Micropulse Lidar network (MPLNET), an analytical model solution and ground-based disdrometer measurements. The presented results are obtained at two mid-latitude MPLNET permanent observational sites, located respectively at NASA Goddard Space Flight Center, USA, and at the Universitat Politècnica de Catalunya, Barcelona, Spain. The methodology is suitable to be applied to existing and/or future lidar/ceilometer networks with the main objective of either providing near real-time (3 h latency) rainfall intensity measurements and/or to validate satellite missions, especially for critical light precipitation (< 3 mm h-1).Peer ReviewedPostprint (published version

An architecture providing depolarization ratio capability for a multi-wavelength Raman lidar: implementation and first measurements

A new architecture for the measurement of depolarization produced by atmospheric aerosols with a Raman lidar is presented. The system uses two different telescopes: one for depolarization measurements and another for total-power measurements. The system architecture and principle of operation are described. The first experimental results are also presented, corresponding to a collection of atmospheric conditions over the city of Barcelona.Peer ReviewedPostprint (published version