The irregular shape of mineral dust provides a strong signature on active and passive polarimetric remote sensing observations. Nowadays, advanced lidar systems operating in the framework of ACTRIS are capable of providing quality assured, calibrated multi-wavelength linear particle depolarization ratio measurements, while new developments will provide us more polarimetric measurements in the near future. Passive polarimeters are already part of ACTRIS and their integration in operational algorithms is expected in the near future. This wealth of new information combined with updated scattering databases and sophisticated inversion schemes provide the means towards an improved characterization of desert dust in the future.
We present here some examples from the ACTRIS journey on dust research during the last decade, aiming to demonstrate the progress on issues such as: (a) the discrimination of desert dust in external mixtures, (b) the separation and estimation of the fine and coarse particle modes, (c) the synergy of passive and active remote sensing for the derivation of dust concentration profiles, (d) the provision of dust-related CCN and IN particle concentrations for aerosol-cloud interaction studies, (e) the development of new scattering databases based on realistic particle shapes, (e) the application of these techniques on spaceborne lidar retrievals for the provision of global and regional climatological datasets. Future plans within ACTRIS for the evaluation and advancement of the methodologies and retrievals are also discussed, combined with new developments within the framework of the D-TECT ERC Grant.
In this paper the possible synergy between advanced lidars and ceilometers for the monitoring of atmospheric
aerosols is evaluated. The advanced measurement capabilities of the multi-wavelength Raman lidar are used
to investigate the capability of ceilometers to provide reliable information about the atmospheric aerosol content.
At the CNR-IMAA Atmospheric Observatory (CIAO), a ceilometer is operational since September 2009
providing vertical profiles of atmospheric backscatter at 1064nm up to 15km; at the same location, the Potenza
EArlinet Raman Lidar (PEARL), a quality-assured, multi-wavelength Raman lidar operates in the framework
of EARLINET and performs regular measurements plus measurements of special events (Sahara dust outbreaks,
volcanic eruptions etc.). Using the PEARL data products as a reference, the capability of ceilometers to detect
aerosol layers and provide quantitative information about the atmospheric aerosol load is investigated. The
variation of ceilometers' performance in different atmospheric conditions is analysed. A procedure for obtaining
backscatter coefficient profiles from ceilometer signals is proposed and its limitations are discussed.
At the Istituto di Metodologie per l'Analisi Ambientale of the Italian National Research Council (CNR-IMAA) an
advanced observatory for the ground-based remote sensing of the atmosphere is operative. This facility is equipped with
several instruments including two multi-wavelength Raman lidars, one of which mobile, a microwave profiler, a 36 GHz
Doppler polarimetric radar, two laser ceilometers, a sun photometer, a surface radiation station and three radiosounding
stations.
CNR-IMAA atmospheric observatory (CIAO) is located in Southern Italy on the Apennine mountains (40.60N, 15.72E,
760 m a.s.l.), less than 150 km from the West, South and East coasts. The site is in a valley surrounded by low mountains
(<1100 m a.s.l.) and this location offers an optimal opportunity to study different kinds of weather and climate regimes.
CIAO represents an optimal site where testing possible synergies between active and passive techniques for improving
the profiling capabilities of several atmospheric key variables, such as aerosol, water vapour and clouds, and for the
development of an integration strategy for their long-term monitoring.
CIAO strategy aims at the combination of observations provided by active and passive sensors for providing advanced
retrievals of atmospheric parameters exploiting both the high vertical resolution of active techniques and the typical
operational capabilities of passive sensors. This combination offers a high potential for profiling atmospheric parameters
in an enlarged vertical range nearly independently on the atmospheric conditions. In this work, we describe two different
integration approaches for the improvement of water vapour profiling during cloudy condition through the combination
of Raman lidar and microwave profiler measurements. These approaches are based on the use of Kalman filtering and
Tikhonov regularization methods for the solution of the radiative transfer equation in the microwave region. The
accuracy of the retrieved water vapour profiles during cloudy conditions is improved by the use of the water vapour
Raman lidar profiles, retrieved up to a maximum height level located around the cloud base region (depending on their
optical thickness), as a constraint to the obtained solution set. The presented integration approaches allow us to provide
physically consistent solution to the inverse problem in the microwave region retrieving water vapour vertical profiles
also in presence of thick clouds. The integration of Raman lidar and microwave measurements also provides a
continuous high-resolution estimation of the water vapour content in the full troposphere and, therefore, a useful tool for
the evaluation of model capability to capture mean aspects of the water vapour field in nearly all weather conditions as
well as for the identification of possible discrepancies between observations and models.
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.
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.
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.
The synergistic use of the measurements carried out using active and passive techniques represent a powerful
solution to fully exploit the capabilities of each remote sensing techniques and to contemporarily overrun its main
limitations. The ground-based facility operational at the CNR-IMAA for the study of the atmosphere is an optimal site
where testing possible synergies between active and passive techniques for improving the profiling capabilities of
atmospheric key variables, such as aerosol, water vapor and clouds.
The combination of the measurements provided by a lidar and a passive sensor is a particularly promising
approach because it puts together the high-resolution measurements obtained using a lidar and the operational
capabilities typical of passive sensors. In particular, the combination of the Raman lidar and sunphotometry
measurements allows to describe the aerosol optical and microphysical properties, supporting the lidar retrievals during
daytime and in presence of thick clouds. Moreover, the use of Raman lidar and microwave measurements, integrated
using an approach based on the Kalman filter, is an optimal way to provide high-resolution measurements of the
tropospheric water vapor in nearly all weather conditions. A strong improvement in the supercooled liquid water
retrieval, obtained through the inversion of the microwave brightness temperature, is also achievable using the cloud
base height information retrieved using the lidar backscattering ratio profile to constrain the microwave retrieval.
At CNR-IMAA, an aerosol lidar system is operative since May 2000 in the framework of EARLINET (European Aerosol Research Lidar Network) ), the first lidar network for tropospheric aerosol study on continental scale. Since August 2005, PEARL (Potenza EARlinet Lidar) system provides backscatter coefficient profiles at 1064 nm, and independent measurements of extinction and backscatter coefficient profiles at 355 and 532 nm. In addition, measurements of the vertical profiles of aerosol and cloud depolarization ratio at 532 nm are obtained by means of the detection of components of backscattered light polarized perpendicular and parallel to the direction of the linearly polarized transmitted laser beam. High quality multi-wavelength measurements (3 backscatter + 2 extinction) plus depolarization measurements make PEARL a reference point for the validation of CALIPSO data products. A direct comparison with CALIPSO data can be carried out for depolarization ratio and aerosol backscatter at 532 and 1064 nm measurements. Furthermore PEARL aerosol extinction measurements at 532 nm and 355 nm and backscatter measurements at 355 nm can be used to improve the retrieval of aerosol backscatter coefficient from pure backscatter lidar. Since 14 June 2006, devoted measurements are performed at CNR-IMAA in coincidence of CALIPSO overpasses (maximum 80 km and 2 hours as spatial and temporal distance). First results of comparison between PEARL and CALIPSO observations are shown.
Lidar technique is the most suitable for high vertical and temporal resolution aerosol profiling. In particular the Raman/elastic lidar combined approach allows independent determination of aerosol extinction and backscatter coefficient without any assumption about their relationship. This technique allows the determination of vertical profiles of the lidar ratio, i.e. the ratio of aerosol extinction and backscatter coefficients. In elastic lidar technique an assumption on the lidar ratio profile is needed for the retrieval of aerosol backscatter coefficient. To improve aerosol backscatter coefficient accuracy in the case of pure elastic backscatter lidar, a climatology of lidar ratio values for specific aerosol types is necessary.
Five years of systematic lidar ratio measurements have been collected by means of a Raman/elastic lidar system operational at CNR-IMAA, since May 2000 in the framework of EARLINET, the first lidar network for tropospheric aerosol study on continental scale. The dependence of lidar ratio as a function of the altitude is analysed. A climatological analysis of the lidar ratio measurements in the Planetary Boundary Layer (PBL) and for Saharan dust intrusions is carried out. In addition, lidar ratio measurements concerning forest fires and volcanic eruptions are also analyzed.
The international experiment EAQUATE (European AQUA Thermodynamic Experiment) was held in September 2004 in Italy and in the United Kingdom. The Italian phase, performed in the period 6-10 September 2004, was mainly devoted to assessment and validation of performances of new IR hyperspectral sensors and benefits from data and results of measurements of AQUA and in particular of AIRS. It is also connected with the preparatory actions of MetOp mission with particular attention to calibration and validation of IASI products (as water vapour and temperature profiles), characterization of semitransparent clouds and study of radiative balance, demonstrating the role of ground-based and airborne systems in validation operations.
The Italian phase of the campaign was carried out within a cooperation between NASA Langley Research Center, University of Wisconsin, the Istituto di Metodologie per l'Analisi Ambientale (CNR-IMAA), the Mediterranean Agency for Remote Sensing (MARS) and the Universities of Basilicata, Bologna and Napoli. It involved the participation of the Scaled Composites Proteus aircraft (with NAST thermal infrared interferometer and microwave radiometer, the Scanning HIS infrared interferometer, the FIRSC far-IR interferometer), an Earth Observing System-Direct Readout Station and several ground based instruments: four lidar systems, a microwave radiometer, two infrared spectrometers, and a ceilometer. Radiosonde launches for measurements of PTU and wind velocity and direction were also performed as ancillary observations. Four flights were successfully completed with two different AQUA overpasses. The aircraft flew over the Napoli, Potenza and Tito Scalo ground stations several times allowing the collection of coincident aircraft and in- situ observations.
The European AQUA Thermodynamic Experiment was devoted to study atmosphere, ocean and land with high resolution measurements. It consisted of two phases: the first one took place in Italy in the 6-10 September period and the second one in England on 13-22 September. In the framework of the EAQUATE Italian phase, an intensive lidar measurement campaign was performed at CNR-IMAA, sited in Tito Scalo (40°36'N 15°44'E, 760 m a.s.l.). Independent measurements of aerosol extinction and backscatter coefficient at 355nm, and aerosol backscatter coefficient at 532 nm were obtained by means of an elastic\Raman lidar. Another Raman lidar allowed the vertical profiling of the water vapour mixing ratio. Both the lidar systems have high vertical and temporal resolution (15 m - 1 minute), allowing a characterization of the Planetary Boundary Layer as well as of the Free Troposphere also in terms of dynamical behaviour. Ancillary instruments were utilized contemporaneously with lidar measurements. In particular 17 Vaisala radiosondes for PTU measurements were launched during the campaign, 10 of these equipped with RS90 sensors, while 7 utilized RS92 sondes equipped with GSP sensors for wind velocity and direction measurement. Furthermore a 12 channels microwave radiometer providing all around the clock measurements of temperature, relative humidity and water vapour content, was used during the campaign together with a ceilometer for continuous indication of the cloud cover.
At CNR-IMAA located in Tito Scalo (40°36'N, 15°44'E, 760 m a.s.l.), two lidar systems are systematically operational: the first is devoted to tropospheric aerosol characterization, in the framework of EARLINET, and the second performs water vapour measurements. The aerosol lidar system provides independent measurements of aerosol extinction and backscatter coefficient at 355 nm and at 532 nm, aerosol backscatter profiles at 1064 nm and particles depolarization ratio at 532 nm. The Raman lidar for the water vapor allows the vertical profiling of the water vapour mixing ratio with high spatial and temporal resolution up to the tropopause. The system has been calibrated by means of intensive measurement campaign of simultaneous and co-located radiosonde launches. CNR-IMAA is also provided with a DIAL mobile system for pollutants 3-dimensional spatial distribution. Besides these lidar systems, the CNR-IMAA ground based facility for Earth Observation includes ancillary instruments: a radiosounding system for PTU, ozone and wind measurements; a Sun photometer operative since December 2004 in the framework of AERONET; a 12 channels microwave radiometer for continuous measurements of temperature, relative humidity and water vapor, operative since February 2004; a ceilometer for continuous cloud cover monitoring. Lidar systems together with these ancillary instruments make the CNR-IMAA a heavily instrumented experimental site for integrated observations of aerosols, clouds and water vapor to be used for climatological studies and for the validation of satellite data.
Systematic lidar measurements of aerosol backscatter and extinction in the troposphere were performed since May 2000 with the aerosol lidar system operational at IMAA-CNR in Tito Scalo (Potenza) (Southern Italy, 40°36’N, 15°44’E, 820 m above sea level) in the framework of EARLINET. EARLINET is the first European network of 22 advanced lidar stations operating to provide a quantitative climatological database of the horizontal, vertical and temporal distribution of aerosols over Europe. Aerosol backscatter measurements were performed at both 355 nm and 532 nm, while aerosol extinction coefficient was retrieved from simultaneous N2 Raman backscatter signals at 386.6 nm. The lidar measurements at IMAA have been performed according to a regular schedule of two night time measurements per week (around sunset) and one daytime measurement per week (around 13:00 UT). Further measurements were devoted to observe special events such as Saharan dust, forest fires and volcanic eruptions. A statistical analysis on climatological aerosol extinction-to-backscatter ratio (lidar ratio) data, covering more than three years of systematic lidar observations, has been carried out. These lidar ratio data, in conjunction with an analysis on the air masses backtrajectories, provide information on microphysical properties of the aerosol on a wide range of meteorological conditions. Results obtained starting from both climatological data and special events (Saharan dust and volcanic eruptions) are presented and discussed.
The study of atmospheric aerosol is fundamental in order to get a best comprehension of the atmospheric system and to comprehend how they affect our environment at the local and global levels. Information about aerosol concentration and radiative properties in their ambient environment are indispensable and, in this respect, lidars represent the most powerful tool because their capability to provide information on atmospheric component and parameters with very high spatial and temporal resolutions. Two lidar systems are operational at Istituto di Metodologie per l’Analisi Ambientale of the National Council of Research (IMAA-CNR), Tito Scalo, Potenza, Italy; the first, used in the framework of EARLINET, is able to provide aerosol backscatter coefficient at two wavelengths (355 nm and 532 nm) and extinction coefficient in the UV in the troposphere, and the other, used in the framework of the validation program of ENVISAT, is devoted to measure both tropospheric and stratospheric aerosol in the UV and water vapor up to the tropopause. We present in this paper results obtained starting from three years of systematic aerosol lidar observations and more than one year of water vapor lidar measurements. Both local aerosol and dust transported from the Sahara regions have been characterized.
An intensive aerosol and water vapour measurement campaign, started on June 2002, is in progress at IMAA in Tito Scalo (PZ) (Southern Italy, 40°36'N, 15°44'E, 820 m above sea level) in the frame of the validation program of ENVISAT. Systematic measurements, using both active and passive ground based instruments, will be performed for a period of 12 months, in coincidence with ENVISAT overpasses. A Raman lidar system is used to perform both aerosol and water vapour measurements; aerosol backscatter and extinction coefficients are retrieved from simultaneous elastic signals at 355 nm and inelastic N2 Raman backscatter lidar signals at 386.6 nm, whereas, water vapour mixing ratio measurements are retrieved from simultaneous H2O and N2 Raman signals. A sun-photometer based on a Mechelle spectrometer is used to measure direct solar irradiance in the wavelength range 300 ÷ 1100 nm and a Fourier infrared spectrometer is used to measure vertical sky radiance in the range 500 ÷ 3000 cm-1. All the observations are complemented with radio-sonde launches. Two measurements per week are scheduled for the first six months of the validation campaign, while one measurement per week is scheduled for the last six months. First results of the measurement campaign are presented.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.