The ESA-EVE Polarization Lidar for Assessing the Aeolus Aerosol Product Perfomance

We present the EVE lidar concept, a combined linear/circular polarization system, tailored to evaluate the spaceborne ALADIN Doppler lidar system aerosol retrievals. EVE, currently under development, aims to provide the ESA-Aeolus mission with a flexible, mobile reference ground-based lidar system capable of providing well-characterized fiducial reference measurements of aerosol optical properties. Since ALADIN detects only the co-polar component of the backscattered circularly polarized radiation, a portion of the received radiation gets lost, leading to an un-derestimation of the backscatter coefficient and the circular depolarization ratio in strongly depolarizing scenes with non-spherical particles. The main focus of the new EVE lidar is to quantify these uncertainties and to evaluate aerosol backscatter/extinction retrievals for Aeolus, and later also for EarthCARE product validation, quality assessment and improvement.

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The eVe reference polarisation lidar system for Cal/Val of Aeolus L2A product

10.5194/amt-2021-268 ◽

2021 ◽

Author(s):

Peristera Paschou ◽

Nikolaos Siomos ◽

Alexandra Tsekeri ◽

Alexandros Louridas ◽

George Georgoussis ◽

...

Keyword(s):

Direct Calculation ◽

Polar Component ◽

Atmospheric Conditions ◽

Backscatter Coefficient ◽

Lidar System ◽

Mechanical Parts ◽

Receiver Unit ◽

Reference Measurements ◽

Compact Design ◽

Calibration Techniques

Abstract. The eVe dual-laser/dual-telescope lidar system is briefly given here, focusing on the optical and mechanical parts of system’s emission and receiver units. The compact design of linear/circular emission unit along with the linear/circular analyser in the receiver unit, allows eVe to simultaneously reproduce the operation of the ALADIN lidar on board Aeolus as well as the operation of a traditional ground-based polarisation lidar system with linear emission. As such, eVe lidar aims to provide: (a) ground reference measurements for the validation of the Aeolus L2A aerosol products, and (b) the atmospheric conditions for which linear polarisation lidar systems can be considered for Aeolus L2A validation, by identifying any possible biases arisen from the different polarisation state in the emission between ALADIN and these systems, and the detection of only the co-polar component of the returned signal from ALADIN for the L2A products retrieval. In addition, a brief description is given concerning the polarisation calibration techniques that are applied in the system, as well as the developed software for the analysis of the collected signals and the retrieval of the optical products. More specifically, the system’s dual configuration enables the retrieval of the optical properties of particle backscatter and extinction coefficients originating from the two different polarisation states of the emission, the linear and circular depolarisation ratios, as well as the direct calculation of the Aeolus like backscatter coefficient, i.e., the backscatter coefficient that Aeolus would measure from ground. Two cases, one with slightly-depolarising particles and one with moderately-depolarising particles, were selected from the first conducted measurements of eVe in Athens, in order to give a glimpse of the system’s capabilities. In the slightly depolarising scene, the Aeolus like backscatter coefficient agrees well with the actual backscatter coefficient, which is also true when non-depolarising particles are present. The agreement however fades out for strongly depolarising scenes, where an underestimation of ~17 % of the Aeolus like backscatter coefficient is observed when moderately-depolarising particles are probed.

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Towards continuous monitoring of aerosol hygroscopicity by Raman lidar measurements at the EARLINET station of Payerne

10.5194/acp-2019-289 ◽

2019 ◽

Author(s):

Francisco Navas Guzmán ◽

Giovanni Martucci ◽

Martine Collaud Coen ◽

María José Granados Muñoz ◽

Maxime Hervo ◽

...

Keyword(s):

Continuous Monitoring ◽

Raman Lidar ◽

Backscatter Coefficient ◽

Lidar System ◽

Remote Sensing Technique ◽

Accuracy And Precision ◽

Lidar Measurements ◽

Constant Altitude ◽

Aerosol Backscatter ◽

Aerosol Hygroscopicity

Abstract. This study focuses on the analysis of aerosol hygroscopicity using remote sensing technique. Continuous observations of aerosol backscatter coefficient, temperature and water vapour mixing ratio are performed by means of a Raman lidar system at the aerological station of MeteoSwiss at Payerne (Switzerland) since 2008. These measurements allow us to monitor in a continuous way any change of aerosol properties as a function of the relative humidity (RH). These changes can be observed either in time at constant altitude or in altitude at a constant time. The accuracy and precision of RH measurements from the lidar have been evaluated using the radiosonde (RS) technique as reference. A total of 172 RSs were used in this intercomparison which revealed a small bias (

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EVE polarization lidar: ESA’s ground reference system for Aeolus L2A products Cal/Val

10.5194/egusphere-egu21-9570 ◽

2021 ◽

Author(s):

Peristera Paschou ◽

Nikolaos Siomos ◽

Vassilis Amiridis ◽

Volker Freudenthaler ◽

George Georgoussis ◽

...

Keyword(s):

Polarized Light ◽

Backscatter Coefficient ◽

Lidar System ◽

Circularly Polarized Light ◽

Circularly Polarized ◽

Polarized Emission ◽

Linearly Polarized ◽

Reference Measurements ◽

Backscattered Signals ◽

Aerosol Types

<p>The EVE (Enhancement and Validation of ESA products) lidar is a mobile, ground-based, polarization lidar system, developed to provide ground reference measurements for the validation of the Aeolus L2A products. The system utilizes a dual-laser/dual-telescope configuration that emits linearly and circularly polarized light at 355 nm&#160; interleaved and detects the linear and circular depolarization on the backscattered signals as well as the Raman backscattering at 387 nm. Consequently, the particle optical properties of backscatter coefficient, extinction coefficient, linear and circular depolarization ratios can be measured by the lidar. Moreover, the system&#8217;s dual configuration enables to mimic both the operation of ALADIN on board Aeolus that relies on the circularly polarized emission and the operation of a polarization lidar system with linearly polarized emission. Besides EVE&#8217;s main goal of the Aeolus L2A products performance evaluation under a wide variety of aerosol types, EVE can also validate the linear to circular depolarization conversions, which have to be used for the harmonization of the linearly polarized lidar systems with Aeolus, and as such, to evaluate any possible biases of the efforts of these systems on Aeolus L2A validation.</p>

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Investigating the performance of AEOLUS L2A products over Europe with EARLINET ground-based lidars

10.5194/egusphere-egu21-12460 ◽

2021 ◽

Author(s):

Nikolaos Siomos ◽

Antonis Gkikas ◽

Holger Baars ◽

Ulla Wandinger ◽

Vasilis Amiridis ◽

...

Keyword(s):

Light Emission ◽

Polarized Light ◽

Polar Component ◽

Time Interval ◽

Random Errors ◽

Backscatter Coefficient ◽

Direct Evaluation ◽

Circularly Polarized Light ◽

Ground Based Lidar ◽

Satellite Product

<p>In this study, we present a comparison of the AEOLUS satellite L2A product with the retrievals of the ground-based lidar systems of EARLINET (European Aerosol Research Lidar Network), part the European Research Infrastructure for the observation of Aerosol, Clouds and Trace Gases (ACTRIS). Dedicated ground&#8208;based measurements during AEOLUS overpasses have been performed among the 29 member stations since the beginning of the mission, however, we have included only the stations that have gathered a significant number of collocations in the analysis. The satellite timeseries we deployed covers the period 2019-2020 that correspond to the best available version of the satellite processing algorithms. We harvest the collocations using the following spacio-temporal criteria. Only overpasses that fall within a radius less than 100km around the station are included. Using this criterion, the AEOLUS L2A climatology is generated per station independently of the ground-based measurements. To isolate collocated data we reject all AEOLUS data with a time interval between the overpass and the central time of the ground-based measurement that is greater than 3 hours. The ground based lidar climatology is also computed per station. AEOLUS L2A products include aerosol extinction coefficient profiles and aerosol co-polar backscatter coefficient profiles from circularly polarized light emission. While the extinction profiles are directly comparable with the ground-based lidars, this is not the case for the backscatter profiles since AEOLUS cannot measure the cross polar component of the aerosol backscatter. The co-polar backscatter is close to the total backscatter only in the absence of depolarizing scatterers such as dust, pollen, volcanic ash, and cirrus ice crystals. Ground-based measurements are divided in two categories for the evaluation depending on whether aerosol depolarization measurements have been performed. If the particle linear depolarization ratio (PLDR) is available, it can be applied to convert the lidar total backscatter to an AOLUS-like co-polar backscatter coefficient. This category is applied for the direct evaluation of the satellite product. Cases that lack PLDR information assist to quantify the uncertainties introduced by using the AEOLUS co-polar backscatter as a substitute for the total backscatter. The analysis includes both an indirect climatological comparison and a direct collocation comparison between the ground based and satellite datasets. Via the collocation comparison, random and systematic uncertainties in the satellite product are identified and quantified. A climatological comparison can show the potential of AEOLUS to capture annual cycles despite its intrinsic random errors. In the future, the analysis will be further supported with auxiliary data such as sunphotometer measurements, aerosol classification flags, modeled backward trajectories, and satellite cloud fraction data.</p>

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Evaluation of a Method for Converting SAGE Extinction Coefficients to Backscatter Coefficient for Intercomparison with LIDAR Observations

10.5194/amt-2020-60 ◽

2020 ◽

Author(s):

Travis N. Knepp ◽

Larry Thomason ◽

Marilee Roell ◽

Robert Damadeo ◽

Kevin Leavor ◽

...

Keyword(s):

Aerosol Extinction ◽

Backscatter Coefficient ◽

Extinction Coefficients ◽

Mauna Loa ◽

Table Mountain ◽

Multi Wavelength ◽

Ground Based Lidar ◽

Aerosol Backscatter ◽

Lidar Observations ◽

Major Eruption

Abstract. Aerosol backscatter coefficients were calculated using multi-wavelength aerosol extinction products from the SAGE II and SAGE III/ISS instruments. The conversion methodology is presented followed by an evaluation of the conversion algorithm's robustness. The SAGE-based backscatter products were compared to backscatter coefficients derived from ground-based lidar at three sites (Table Mountain Facility, Mauna Loa, and Observatoire de Haute-Provence). This evaluation includes the major eruption of Mt. Pinatubo in 1991 followed by the atmospherically quiescent period beginning in the late nineties. Recommendations are made regarding the use of this method for evaluation of aerosol extinction profiles collected using the occultation method.

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