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Laboratorio mobile lidar atmosferico


Referente: Dr. Luca Fiorani
luca.fiorani@enea.it

Fig. 1. The mobile lidar ATLAS in the industrial zone of Brindisi, Italy (Cerano power plant). The laser has been aimed to the chimney, thus probing the atmosphere in a near-horizontal optical path.

The atmospheric lidar ATLAS (Agile Tuner Lidar for Atmospheric Sensing) has been developed and mounted on the mobile laboratory ENVILAB (ENVIronmental LABoratory), hosted in a small truck. ATLAS can be decomposed in four subsystems: transmitter, receiver, detector and ADC (Analog-to-Digital Converter). The main parts of the transmitter are a tunable TEA (Transverse Excited Atmospheric) CO2 laser and an off-axis reflective beam expander consisting of two OFHC (Oxygen-Free High Conductivity) copper mirrors manufactured in our laboratory. The laser is tunable thanks to the agile tuner consisting of a diffraction grating and a scanning mirror actuated by a computer-controlled galvo motor. The receiver is based on a Newton telescope. A liquid-nitrogen-cooled mercury-cadmium-telluride photodiode, coupled with a pre-amplifier designed to compliment it, has been chosen as detector. The ADC is embedded in a PCI (Peripheral Component Interconnect) card mounted in the personal computer that controls the experiment. ATLAS has been deployed in polluted zones and in volcanic areas. In particular, the Etna and Stromboli volcanic plumes have been characterized by the ATLAS. At Etna, the extinction coefficient inside the volcanic plume was retrieved, while at Stromboli also water vapor concentration in cross sections of the plume and wind speed at the crater were measured. Water vapor concentration and wind speed were retrieved by differential absorption lidar and correlation technique, respectively. Lidar returns were obtained up to a range of 5 km. The spatial resolution was 15 m and the temporal resolution was 20 s. By combining these measurements, the water vapor flux in the Stromboli volcano plume was found. To our knowledge, it is the first time that a CO2 laser-based lidar is used to profile a volcanic plume and a lidar retrieves water vapor concentrations in a volcanic plume.

TABLE 1: Main specifications of Atlas
Transmitter Pulse energy 850 mJ (at the 10R18 and 10R20 emission lines)
Pulse duration 60 ns (full width at half maximum)
Repetition rate 2 ÷ 20 Hz
Transmitted wavelength 9.2 ÷ 10.8 ?m
Laser linewidth 0.13 cm-1
Beam divergence 0.7 mrad
Receiver Mirror coating Au
Diameter 310 mm
Focal length 1.2 m
Range of overlap 150 m (partial), 300 m (full)
Detector Diameter 1 mm
Specific detectivity 4×1010 cm Hz1/2 W-1
Gain 200
Linear dynamic range 0.1 ÷ 1000 mV
Bandwidth 0 ÷ 10 MHz
Analog-to-digital converter Dynamic range 8 bit
Sampling rate 10 Ms s-1

Fig 2. Water vapor concentration retrieved by ATLAS during two scans at 237 (a) and 192 (b) azimuth angles.
The white points are the lidar measurements.
The black crosses are the points where the water vapor concentration maxima of the two scans occurred.


Fig 3. Extinction coefficient (a) and correlation versus wind speed (b) retrieved at 13:57 pm by ATLAS.


Fig. 4. ATLAS staff in front of ENVILAB in the petrochemical plant of Brindisi, Italy: D. Del Bugaro, A. Palucci, A. Scoditti and L. Fiorani (from the left).


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References:

  • L. Fiorani, "Environmental monitoring by laser radar," in Larkin S.B., ed., Lasers and Electro-Optics Research at the Cutting Edge, Nova, New York (2007);
  • L. Fiorani, F. Colao and A. Palucci, "Measurement of Mount Etna plume by CO2-laser-based lidar," Optics Letters 34, 800-802 (2009);
  • L. Fiorani, F. Colao, A. Palucci, D. Poreh, A. Aiuppa and G. Giudice, "First-time lidar measurement of water vapor flux in a volcanic plume," Optics Communications (in press).
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