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