The migration of aerofauna is a seasonal phenomenon of global scale, engaging billions of individuals in long-distance movements every year. Multiband lidar systems are commonly employed for the monitoring of aerosols and atmospheric gases, and a number of systems are operated regularly across Europe in the framework of the European Aerosol Lidar Network (EARLINET). This work examines the feasibility of utilizing EARLINET for the monitoring and classification of migratory fauna based on their pigmentation. An EARLINET Raman lidar system in Athens transmits laser pulses in three bands. By installing a four-channel digital oscilloscope on the system, the backscattered light from single-laser shots is measured. Roughly 100 h of data were gathered in the summer of 2013. The data were examined for aerofauna observations, and a total of 1735 observations interpreted as airborne organisms intercepting the laser beam were found during the study period in July to August 2013. The properties of the observations were analyzed spectrally and intercompared. A spectral multimodality that could be related to different observed species is shown. The system used in this pilot study is located in Athens, Greece. It is concluded that monitoring aerial migration using it and other similar systems is feasible with minor modifications, and that in-flight species classification could be possible.
We present experimental results obtained in the frame of the QOMA project involving the design and development of a diode-pumped solid state (DPSS) Nd:YAG laser, operating at passively and actively Q-switched pulsed mode. Continuous wave (cw) and passively Q-switched operations are demonstrated obtaining 7.5 W and 2 mJ at 100 Hz, respectively with excellent beam quality using a multi-segmented (0.1%, 0.23%, 0.6% at Nd) Nd:YAG crystal. Comparisons with a uniform Nd:YAG rod reveals improvements of up to 64% in normalized optical conversion efficiency and 67% in output power for retaining the same beam quality. Active Q-switching operation was also obtained with the same multi-segmented crystal, demonstrating pulse energy of 1.20 mJ at 5 kHz repetition rate, preserving an almost Gaussian beam profile.
We present preliminary simulation and experimental results obtained in the frame of QOMA project funded by the European Space Agency (ESA), involving the design and development of a diode-pumped solid state (DPSS) Nd:YAG laser. The simulation results were obtained using the LASCAD software code, while the experimental results were obtained at the Laboratoire Charles Fabry (France) and the National Technical University of Athens (NTUA).
The arrival of the volcanic ash plume of the Eyjafjallajökull eruption was observed over Greece almost one week after its
major eruption (on April 14, 2010) with two multi-wavelength Raman lidar systems, members of the EARLINET
network. Intensive lidar measurements were performed throughout the event over Thessaloniki and Athens to derive the
optical properties of the ash aerosols in the troposphere. During April 21, 2010 two layers of volcanic ash were present
over Thessaloniki, one around 2.5 and one around 5 km height after circulating over central Europe. The first layer was
persistent but with variable thickness, while the thin layer observed at 5 km height disappeared after some hours. Later
on and at higher altitudes thin layers of ash were observed between 5 and 8 km, directly associated with the volcanic
eruption. The observed layer at around and 3 km was persistently observed till April 28. The volcanic ash was observed
over Athens, after passing over Southern Italy, during April and May 2010, in two height regions: between 6-10 km
height and between 4 km and the ground level. We found that this was directly linked to the maximum height of the
emitted volcanic ash. The most intensive period for ash presence over Athens was between April 21 and 23. In most
cases, ash layers were very well stratified in the form of filaments starting around 3-4 km down to 1.5 km height. Mixing
of ash with locally produced aerosols was frequently observed during the measuring period resulting to enhanced PM10
concentrations at ground level. Volcanic ash was also observed during May 10-11 and 17-19, 2010, after being
transported over Spain and Northern Italy. Both over Athens and Thessaloniki Saharan dust particles were mixed with
volcanic ones on certain days of May 2010, which resulted to more complicated structures of the aerosol layers observed
over Greece.
Routine lidar measurements of the aerosol vertical distribution have been performed over Athens, Greece using a multi-wavelength
(355-387-407-532-607-1064 nm) Raman lidar system, since 2006 in the frame of the EARLINET-ASOS
(2006-2011) project. Additionally, since June 2006, correlative measurements for CALIOP space-borne lidar are
performed. The aim of these measurements is to provide validation profiles for the CALIOP instrument in the lower and
middle troposphere (0.5-8 km) in terms of the aerosol backscatter coefficients at 532 nm and 1064 nm, the color ratio
(532/1064 nm) and the depolarization ratio at 532 nm, but mainly to provide information about the aerosol extinction
profiles and the corresponding lidar ratios at 532 nm. From the available correlative CALIOP level-2 and multi-wavelength
Raman lidar aerosol data over Athens, we selected to present cases that have been identified as Saharan dust
outbreaks and large biomass burning events, using air mass backward trajectories in order to characterize the source of
the aerosols. We found that the vertical profiles of the aerosol optical properties between CALIOP and NTUA lidars
were not always in a good agreement during the exact time of the satellite overpass, especially for daytime
measurements, when the distance between the two instruments was greater than 40 km. An improvement was noticed
when ground-based lidar measurements where performed previously or later than the CALIPSO overpass time. For the
nighttime intercomparison the agreement between the two instruments was better during the CALIPSO overpass time.
This was attributed mainly to the closer nighttime satellite track over the Athens lidar station.
The crystal field environment of the Ce+3 dopant in LiSrAlF6 (LiSAF) crystals has been studied by the Electron Spin Resonance (ESR) spectroscopic technique. Ce was found in a highly anisotropic trigonal environment which suggests that it substitutes for the Sr site. Na+ ions operate as charge compensators to Ce+3 possessing nearby to Ce, Sr sites. The ground state electronic wavefunction and the energy diagram of Ce are discussed in view of our ESR results.
In this paper we present the basic features of the laser remote sensing (lidar) system located at the National Technical University of Athens (NTUA), Greece. This compact and mobile lidar is in full operation since late 1999. This paper includes basic features of the lidar technique (technical description, temporal and spatial resolution, range etc.), a brief presentation of the instrumentation used and an outline of the algorithms applied to retrieve useful information from the backscattered lidar signals. We also present some examples of aerosol profiling measurements over Athens, which include monitoring of clouds and suspended aerosols (i.e. during Saharan dust and photochemical air pollution events), as well as the evolution of the Planetary Boundary Layer (PBL) over the Greater Athens Area (GAA).
Suspended aerosol particles play a significant role in the Global Change issue. Every year huge quantities of Saharan dust are transported to the European continent and North Atlantic Sea. Since May 1, 2000, an elastic backscatter lidar station is in operation in Athens, Greece, in the frame of the European LIDAR Network (EARLINET), aiming at the monitoring of extreme aerosol events over the Eastern Mediterranean Sea. During the first year of operation 20 cases of Saharan dust transport to the East Mediterranean Sea (EMS), were successfully observed. The lidar data are correlated with meteorological and satellite observations, including the aerosol index (AI data from the Total Ozone Mapping Spectrometer (TOMS) and the SeaWiFS satellite images. The analysis of the data collected so far, made possible a first statistical approach of the vertical and horizontal extent and of the seasonal variation of free tropospheric Saharan dust layers over the EMS area. The main results of this work are: (1) multiple dust layers of variable thickness (0.5 - 4 km) are systematically observed in the altitude region 2 - 6 km, (2) Saharan dust outbreaks take place all year round, with more pronounced frequencies during the summer period and can persist for a few days (1- 5), (3) 24 - 48 hours are usually needed for the Saharan air masses to reach the EMS area, and finally (4) the TOMS AI values can reach 1.5 - 3.5 over Greece. These lidar data gave the aerosol vertical structure over the Eastern Mediterranean Sea during Saharan dust outbreaks and can be a direct input for global radiative transfer models.
The Lidar technique is an efficient tool for continuous monitoring of clouds and aerosols, with high temporal and spatial resolution. Lidar systems can provide long-term accurate information on cloud top and base heights and their optical depth. The spatial distribution of clouds and the diurnal variation of cloud properties are important parameters in many operational and research applications (i.e. radiative transfer modeling, energy balance, meteorology, etc.). In this paper, we present the application of a compact mobile lidar system in monitoring of cloud properties, over Athens, Greece. Preliminary lidar measurements were performed during summer- autumn 1994, focusing on the study of short-time variability of spectral cloud properties at two wavelengths (355 nm and 532 nm), using a compact Nd:YAG laser. The Lidar dataset acquired is analyzed during selected cases and conclusions are drawn.
The LIDAR technique is an efficient tool for continuous monitoring of air pollution over urban areas, with high temporal and range resolution. The urban areas of Athens, Greece, exhibit high air pollution levels, especially those regarding suspended particulates, mainly linked with car traffic and industrial emissions. In this paper, we present the first mobile Greek LIDAR system, based on the LabVIEW code, now located at the Athens Technical University Campus, nearby the urban area of the city. The LIDAR dataset acquired, under various air pollution and meteorological conditions, gives specific indications of the diurnal variation of the backscattering coefficient and relative backscatter of the suspended particulates in the first 2500 - 3000 m ASL over the city of Athens. The LIDAR dataset acquired is analyzed in conjunction with meteorological data (temperature, humidity) and air pollution data (O3 CO, NOx), acquired at the same site, and conclusions are drawn.
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