EARLINET, the European Aerosol Research Lidar NETwork, established in 2000, is the first coordinated lidar network
for tropospheric aerosol study on the continental scale. The network activity is based on scheduled measurements, a rigorous quality assurance program addressing both instruments and evaluation algorithms, and a standardised data
exchange format. At present, the network includes 27 lidar stations distributed over Europe.
EARLINET performed almost continuous measurements since 15 April 2010 in order to follow the evolution of the
volcanic plume generated from the eruption of the Eyjafjallajökull volcano, providing the 4-dimensional distribution of
the volcanic ash plume over Europe. During the 15-30 April period, volcanic particles were detected over Central Europe
over a wide range of altitudes, from 10 km down to the local planetary boundary layer (PBL). Until 19 April, the
volcanic plume transport toward South Europe was nearly completely blocked by the Alps. After 19 April volcanic
particles were transported to the south and the southeast of Europe. Descending aerosol layers were typically observed
all over Europe and intrusion of particles into the PBL was observed at almost each lidar site that was affected by the
volcanic plume. A second event was observed over Portugal and Spain (6 May) and then over Italy on 9 May 2010. The
volcanic plume was then observed again over Southern Germany on 11 May 2010.
Coordinated lidar observations of Saharan dust over Europe are performed in the frame of the EARLINET-ASOS
(2006-2011) project, which comprises 25 stations: 16 Raman lidar stations, including 8 multi-wavelength
(3+2 station) Raman lidar stations, are used to retrieve the aerosol microphysical properties. Since
the launch of CALIOP, the two-wavelength lidar on board the CALIPSO satellite (June 2006) our lidar
network has been performing correlative aerosol measurements during CALIPSO overpasses over the
individual stations. In our presentation, we report on the correlative measurements obtained during Saharan
dust intrusions in the period from June 2006 to June 2008. We found that the number of dust events is
generally greatest in late spring, summer and early autumn periods, mainly in southern and south-eastern
Europe. A measurement example is presented that was analyzed to show the potential of a ground based lidar
network to follow a dust event over a specific study area, in correlation with the CALIOP measurements. The
dust transport over the studied area was simulated by the DREAM forecast model. Cross-section analyses of
CALIOP over the study area were used to assess the model performance for describing and forecasting the
vertical and horizontal distribution of the dust field over the Mediterranean. Our preliminary results can be
used to reveal the importance of the synergy between the CALIOP measurement and the dust model, assisted
by ground-based lidars, for clarifying the overall transport of dust over the European continent.
CALIPSO is a satellite mission designed to measure the vertical structure and optical properties of aerosol and clouds
over the globe. The Science Team for the mission has organized an international program, named quid pro quo (QPQ), to
obtain correlative measurements to support validation of its retrieved products. EARLINET, a network of 25 European
lidar stations, joined the QPQ program and have been performing correlative measurements at all stations within 80 km
from the overpasses ("mandatory" measurements) and additionally at the lidar station which is closest to the actually
overpassed site ("suggested" measurements). In this work, we present the results obtained during the primary validation
phase for the #21 EARLINET station (CIEMAT-Madrid) correlative measurements. Two different data products have
been compared: The "Total Backscatter_Coefficient_532" from level 2 files (released on Jan/2008) and the version 2
(released on Dec/2007) Level 1 data product called "Total_Attenuated_Backscatter_532", that must be compared with a
simulated lidar profile calculated from the 532-nm extinction and backscattering coefficients profiles independently
measured by the unpolarized elastic channel and Raman channel of the ground system. Several cases with a reasonable
agreement in terms of backscattering coefficient magnitude have been found (7 cases, 26% of the total cases analyzed:
27 cases), while cases with bad agreement amounts to 38%. The rest correspond to cases with clouds (18%) and bad
assignment of aerosol layer as clouds (18%).
The European Aerosol Research Lidar Network (EARLINET) was established in 2000 to derive a comprehensive, quantitative, and statistically significant data base for the aerosol distribution on the European scale.
At present, EARLINET consists of 25 stations: 16 Raman lidar stations, including 8 multi-wavelength Raman lidar stations which are used to retrieve aerosol microphysical properties.
EARLINET performs a rigorous quality assurance program for instruments and evaluation algorithms. All stations measure simultaneously on a predefined schedule at three dates per week to obtain unbiased data for climatological studies.
Since June 2006 the first backscatter lidar is operational aboard the CALIPSO satellite. EARLINET represents an excellent tool to validate CALIPSO lidar data on a continental scale. Aerosol extinction and lidar ratio measurements provided by the network will be particularly important for that validation.
The measurement strategy of EARLINET is as follows: Measurements are performed at all stations within 80 km from the overpasses and additionally at the lidar station which is closest to the actually overpassed site. If a multi-wavelength Raman lidar station is overpassed then also the next closest 3+2 station performs a measurement.
Altogether we performed more than 1000 correlative observations for CALIPSO between June 2006 and June 2007.
Direct intercomparisons between CALIPSO profiles and attenuated backscatter profiles obtained by EARLINET lidars look very promising.
Two measurement examples are used to discuss the potential of multi-wavelength Raman lidar observations for the validation and optimization of the CALIOP Scene Classification Algorithm.
Correlative observations with multi-wavelength Raman lidars provide also the data base for a harmonization of the CALIPSO aerosol data and the data collected in future ESA lidar-in-space missions.
Francisco Molero, Lucas Alados-Arboledas, Manuel Pujadas, Antonio Alcantara, Victoria Cachorro, Victor Estellés, Francisco Olmo, José Martinez-Lozano, Jerónimo Lorente, Juan Diaz, Antonio Labajo, Benito De La Morena, Helmut Horvath, Ana Silva
Ground-based sunphotometry measurements can be used to investigate atmospheric aerosol optical properties, such as the volume size distribution, an important parameter in the study of the effect of aerosol on atmospheric processes. Most inversion algorithms assume constant aerosol optical characteristics over the whole air column. In this work we present observational evidence of the limitations of this simplifying assumption in cases where the aerosol vertical
structure is highly inhomogeneous. During the field campaign VELETA 2002, carried out in Granada (Spain), a quite complete characterization of the atmospheric aerosol was obtained by simultaneously measuring the columnar aerosol characteristics, by means of CIMEL C318 sun-tracking photometers, the size-segregated near-surface aerosol mass concentration by a GRIMM 1108 dust monitor and the aerosol vertical profiles by a lidar system. During the last days of the campaign, a dust-rich air mass from the Sahara reached the site, producing a multilayered structure on the aerosol vertical profile. The ground level size distributions can be compared with the columnar ones using retrieved scale height values from a lidar extinction coefficient profiles, corresponding to the altitude where the integrated extinction is equal to 1-e-1 of the AOD. Comparisons of the column-integrated and the modified ground-level aerosol size distributions show a good agreement in the days previous to the arrival of the Saharan intrusion, when the aerosols are homogeneously distributed in a well-mixed boundary layer. But, when the vertical homogeneity is reduced due to elevated layers containing desert dust, the column properties clearly deviates from the surface properties. This indicates the importance of verifying the vertical distribution of aerosol in order to correctly relate column and ground-level optical properties.
Francisco Molero, Manuel Pujadas, Jose Fernandez, Maria Utrillas, Jose Martinez-Lozano, Roberto Pedros, Lucas Alados-Arboledas, Jeronimo Lorente, Victoria Cachorro, Ana Diaz Rodriguez, Antonio Labajo, Benito De la Morena, Jose Antonio Rodrigues, Ana Maria Silva, Helmuth Horvath
KEYWORDS: LIDAR, Aerosols, Mass attenuation coefficient, Signal attenuation, Atmospheric particles, Meteorology, Signal to noise ratio, Atmospheric sensing, Backscatter, Signal processing
We present measurements of the vertical structure of the aerosol extinction coefficient in the lower troposphere, up to five kilometers. Lidar profiles were collected at Armilla (680 m asl) and Pitres (1252 m asl) during the VELETA-2002 campaign, organized to analyze the effect of altitude and aerosols on ground-level UV spectral irradiance. Single-wavelength lidar signals are inverted to derive vertically resolved aerosol extinction coefficient and integrated to provide aerosol optical depth (AOD) at 532 nm. These results are compared with measurements of the aerosol optical depth at the same wavelength provided by Licor LI-1800 spectroradiometers located at several altitudes. Lidar traces show that most of the aerosol loading is present in the first 2.5 km layer before a high-dust Saharan air mass overflew the site. On the 17th of July evening, an elevated aerosol layer was detected between 2.5 and 3.5 km and during the following three days the aerosol vertical profile of the lower atmosphere showed Sahara dust layers, producing relatively high values for the optical depth.
KEYWORDS: Aerosols, LIDAR, Atmospheric particles, Mass attenuation coefficient, Refractive index, Backscatter, Satellites, Optical properties, Neodymium, Signal to noise ratio
This work presents the aerosol vertical profiles obtained by means of an elastic backscatter ground-based LIDAR, using the 532-nm radiation from a Nd:YAG laser. Simultaneously, the aerosol size distribution in the ambient air was continuously monitored at ground level using an aerosol spectrometer that performs particulate measurements by laser light scattering. Additional information about aerosol index was obtained from TOMS data. The vertical profiles have been useful to relate satellite observations with ground level measurements. In our experiment, deployed on the Iberian Peninsula, an estimation of the provenance of aerosols was made by analyzing the results provided by these instruments, jointly with synoptic meteorological information available.
In this work, experimental results obtained with the first Spanish LIDAR-DIAL prototype are presented. This DIAL consists of the well-known configuration of a dye laser as the tuning element, pumped by a Nd:YAG laser. In order to evaluate the performance of this DIAL, parallel measurements of SO2 from industrial point sources with a passive remote technique were carried out. The spectrometer used as reference instrument was a COSPEC V, widely used for SO2 concentration measurements from natural and anthropogenic plumes. Due to the different nature of these remote techniques, it has been necessary to design several field experiments and to homogenize all data before comparison. In this sense, the SO2 traceability, because of its high chemical stability in the atmosphere, has been important to assess the performance of the DIAL system by using this experimental strategy. Also, the data obtained from the continuous monitoring of the emissions in the stacks are in good agreement with those provided by the remote sensors. It can be concluded that the new DIAL system works properly in a 4 Km range. Quality control of industrial emission inventories can be considered as a promising line of application of this DIAL system.
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