Measurements of the Eyjafjallajokull-plume were - from the beginning - continuously conducted at Munich,
Germany, with two EARLINET Raman- and depolarization-lidars. By means of range corrected signals the
temporal development of the ash-plume could be documented in real-time. The optical characterization includes
the backscatter coefficient at three wavelengths (1064 nm, 532 nm, 355 nm), and the extinction coefficient and
particle linear depolarization ratio at two (532 nm, 355 nm). The maximum extinction coefficient was as high as
0.75km-1 and wavelength independent - a strong indication for large particles. The particle linear depolarization
ratio was 0.35-0.37, indicating non-spherical particles. An inversion of the optical data considering the nonspherical
shape of ash particles led to a maximum mass concentration in the order of 1.1 mg/m3 over Munich,
however, relative uncertainties of more than 30% must be expected.
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.
Lidar techniques represent the most suitable tool to obtain information on the aerosol vertical distribution and therefore
to close this kind of observational gap. Lidar networks are fundamental to study aerosol on large spatial scale and to
investigate transport and modification phenomena. These are the motivations why EARLINET, the European Aerosol
Research Lidar Network, was established in 2000. At present, EARLINET consists of 25 lidar stations: 7 single
backscatter lidar stations, 9 Raman lidar stations with the UV Raman channel for independent measurements of aerosol
extinction and backscatter, and 9 multiwavelength Raman lidar stations (elastic channel at 1064 nm, 532 nm, 355 nm,
Raman channels at 532 nm and 355 nm, plus depolarization channel at 532 nm) for the retrieval of aerosol microphysical
properties.
EARLINET data can significantly contribute to the quantification of aerosol concentrations, radiative properties, long-range
transport and budget, and prediction of future trends on European and global scale. It can also contribute to
improve model treatment on a wide range of scales and to a better exploitation of present and future satellite data.
EARLINET is playing an important role in the validation and in the full exploitation of the CALIPSO mission.
EARLINET started correlative measurements for CALIPSO since June 2006. A strategy for correlative measurements
has been defined on the base of the analysis of the high resolution ground track data provided by NASA. Results in terms
of comparisons between EARLINET and available CALIPSO products, both level 1 and level 2 data, are presented.
The present knowledge of the aerosol distribution is not sufficient to estimate the aerosol influence on global and
regional environmental conditions and climate. This observational gap can be closed by using advanced laser remote
sensing. EARLINET (European Aerosol Research Lidar Network) is the first aerosol lidar network, established in 2000,
with the main goal to provide a comprehensive, quantitative, and statistically significant database for the aerosol
distribution on a continental scale. EARLINET is a coordinated network of European stations (25 at present) using advanced lidar methods for the vertical profiling of aerosols. The network activity is based on simultaneous scheduled
measurements, a rigorous quality assurance program addressing both instruments and evaluation algorithms, and a
standardised data exchange format. Further observations are performed to monitor special events.
EARLINET-ASOS (Advanced Sustainable Observation System) is a five year EC Project started in 2006, based on the
EARLINET infrastructure. The main objectives are: to make EARLINET a world-leading instrument for the observation
of the 4-D aerosol distribution on continental scale; to foster aerosol-related process studies, validation of satellite
sensors, model development and validation, assimilation of aerosol data into operational models; and to build a
comprehensive climatology of the aerosol distribution.
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.
EARLINET-ASOS (European Aerosol Research Lidar Network - Advanced Sustainable Observation System) is a 5-year EC Project started in 2006. Based on the EARLINET infrastructure, it will provide appropriate tools to improve the quality and availability of the continuous observations. The EARLINET multi-year continental scale data set is an excellent instrument to assess the impact of aerosols on the European and global environment and to support future satellite missions. The project is addressed in optimizing instruments and algorithms existing within EARLINET-ASOS, exchanging expertise, with the main goal to build a database with high quality aerosol data. In particular, the optimization of the algorithms for the retrieval of the aerosol optical and microphysical properties is a crucial activity. The main objective is to provide all partners with the possibility to use a common processing chain for the evaluation of their data, from raw signals to final products. Raw signals may come from different types of systems, and final products are profiles of optical properties, like backscatter and extinction, and, if the instrument properties permit, of microphysical properties. This will have a strong impact on the scientific community because data with homogeneous well characterized quality will be made available in nearly real time.
EARLINET, the European Aerosol Research Lidar Network, is the first aerosol lidar network, established in 2000, with the main goal to provide a comprehensive, quantitative, and statistically significant data base for the aerosol distribution on a continental scale. At present, 23 stations distributed over Europe are part of the network. The EARLINET-ASOS (Advanced Sustainable Observation System) EC Project, starting on the EARLINET infrastructure, will contribute to the improvement of continuing observations and methodological developments that are urgently needed to provide the multi-year continental scale data set necessary to assess the impact of aerosols on the European and global environment and to support future satellite missions. The main objective of EARLINET-ASOS 5-year project, started on 1 March 2006, is to improve the EARLINET infrastructure resulting in a better spatial and temporal coverage of the observations, continuous quality control for the complete observation system, and fast availability of standardized data products. This will be reached by defining and using common standards for instruments, operation procedures, observation schemes, data processing including advanced retrieval algorithms, and dissemination of data. The expected outcome is the most comprehensive data source for the 4-D spatio-temporal distribution of aerosols on a continental scale.
Measurements of aerosols are urgently required for understanding
and modelling their role in the climate system and to investigate
interactions between aerosols, clouds and radiation. Lidar is an
excellent tool for aerosol observations, in particular, as it
provides range resolved data. In this paper we briefly describe
the different lidar configurations useful for aerosol observations
and discuss in particular the limitations due to the unknown lidar
ratio and strategies to overcome this problem. As a result,
extinction coefficient as a function of height can be obtained.
Recent approaches to derive microphysical parameters are
introduced as well. The potential of lidars for aerosol remote
sensing is illustrated by highlighting a few of the most important
lidar activities of the last years and the upcoming spaceborne
experiments.
KEYWORDS: Clouds, LIDAR, Multiple scattering, Scattering, Mass attenuation coefficient, Signal attenuation, Monte Carlo methods, Backscatter, Chlorine, Photons
The contribution of multiply scattered photons to signals from a spaceborne backscatter signal is investigated. Monte Carlo calculations are performed for different atmospheric conditions and for different lidar configurations. It is found out that multiple scattering signals in most cases can accurately be described by a very simple approximation. It is concluded that the process of multiple scattering will be no drawback for the application of spaceborne lidars. In contrary, the transparency of clouds is enhanced so that lidar signals can fully penetrate cirrus clouds, even cirrostratus layers. As a consequence, clouds below a cirrus can be observed which would be obscured if only single scattering would occur.
The benefit of a spaceborne backscatter lidar for studies on clouds and aerosols is discussed. Based on the technical and orbital parameters as planned for the European atmospheric lidar ('ATLID') the potential to detect optically thin clouds and aerosol layers, to contribute to cloud climatologies and to derive optical properties, e.g. the extinction coefficient, was investigated. It was found out that under favorable conditions even very thin cirrus clouds (extinction coefficient alphap approximately equal to 0.05 km -1) can be identified by ATLID. Radiatively relevant ice clouds can be detected in any case. Caused by multiple scattering the detection of clouds below a cirrus layer is also possible. As a consequence, and according to the good spatial sampling, it is expected that ATLID will provide useful data for cloud climatologies. The determination of optical depths however seems to be difficult. Improvements of the present aerosol database can be anticipated at least in case of stratospheric layers and medium turbid planetary boundary layers. It is recommended to further investigate the benefit gained from the joint exploitation of different sensors such as a backscatter lidar, a cloud radar and imagers.
A mobile multi-channel backscatter lidar for aerosol remote sensing is established at the Meteorological Institute of the University of Munich. The scientific objectives, the instrument concept, and the present state of the data evaluation schemes are briefly described. The potential of the lidar will be demonstrated by several experiments planned for the near future.
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