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Scientific Report 2007-2009
Geophysics
G3. Atmospheric acoustical and optical remote sensing at middle
latitudes
With climate and atmospheric pollution problems becoming
a critical political and decision making issue,
there is an increasing need for better monitoring the real
changes affecting the atmosphere.
In particular, how much atmospheric aerosol affects
the planetary radiative budget is acknowledged as being
one of the major uncertainties in assessing the climate
scenario.
In the Department of Physics there is a group involved
in remote sensing of the atmosphere with acoustical and
optical instruments.
The acoustical instrument is an active radar-like device
(SOund Detection and Ranging, SODAR) that
sends short sound bursts into the atmosphere and detects
the echoes produced by the turbulence induced variations
in the sound refraction index. The echo Doppler
shift is used to compute the wind velocity profile. Sodar
measurements can be carried out almost continuously
and produce a very good description of the thermodynamical
state of the atmospheric boundary layer displaying,
for example, the time evolution of the mixing layer
height above the instrument, the convective activity and
the possible propagation of gravity waves (Figure 1).
Figure 1: Facsimile output of the University of Rome sodar
during a typical clear day. Dark regions show intense smallscale
turbulence.
The optical instruments consist of active systems and
passive radiometers in different wave bands.
The lidar (LIDAR, LIght Detection And Ranging), a
radar-like instrument using a laser as radiation source
and an optical telescope as receiver, is able to detect
aerosol (by Mie scattering), minor constituents like water
vapor (by Raman scattering), and temperature (by
Rayleigh scattering) profiles through the troposphere
and the stratosphere [1].
Passive radiometers in the visible and UV use the sun
direct and/or diffuse radiation to measure the optical
depth and other important parameters (Ångstrom coefficient
and Single Scattering Albedo) of the atmospheric
aerosol; radiometers in the IR use the terrestrial radiation
to measure other atmospheric parameters (molecular
species, temperature, etc) [2]. A successful experiment
to measure aerosol optical depth was also carried
out using a digital camera and star light [3].
Figure 2: Example of sounding by lidar. Colors represent
different backscatter ratio values. Boundary layer pollution
is clearly visible while an aerosol layer probably produced by
the eruption of a volcano is detected above 15 km.
The Group of Atmospheric Physics runs a lidar
system (Stabile Rome Lidar, SRL) that performs
systematic measurements from the university campus
placed within the highly polluted city of Rome. SRL has
been operational in the last years and the measurements,
aimed at a wide range of scopes, cover the atmosphere
up to the lower stratosphere. At the same time another
somehow simpler lidar system (Mobile Rome Lidar,
MRL), installed inside a mobile van, can be deployed to
remote sites for special campaigns. MRL was recently
deployed to the Valle del Biferno (41 ◦ 56.8 ′ N, 014 ◦ 60.0E)
for studying the atmospheric boundary layer height
and performed two intensive campaigns coordinated
with other international atmospheric groups during
2009 (Figure 2). In cooperation with ENEA, another
lidar system is operated at the Station for Climate
Observations located in the island of Lampedusa, a
unique site for studying atmospheric aerosol (in particular
desert dust) far from highly populated regions [4].
References
1. I. Fiorucci, et al., J. Geophys. Res. 113, D14314 (2008).
2. A. di Sarra, et al., Appl. Opt. 47, 6142 (2008).
3. O. Lanciano, et al., Appl. Opt. 46, 5176 (2007).
4. Di Iorio, et al., J. Geophys. Res. 114, D02201, (2009).
Authors
G. Fiocco, D. Fuà, M. Cacciani, A. di Sarra 8 , T. Di Iorio, L.
Di Liberto, F. Angelini, O. Lanciano, V. Ciardini, C. Tirelli,
G. Casasanta.
http://g24ux.phys.uniroma1.it/
Sapienza Università di Roma 168 Dipartimento di Fisica