A TEST TO DETERMINE THE GEOMETRIC ACCURACY OF THE
DIAL STATION OF THE UNIVERSITY OF CALABRIA
G.Artese (*,**), V.Achilli (*), C.Bellecci (***), A.Vettore (****)
. Osservatorio Vesuviano - Napoli - Italy
ve Dipartimento di Pianificazione Territoriale - Università della Calabria - Cosenza - Italy
... Dipartimento di Fisica -Università della Calabria - Cosenza - Italy
?9*9€9
Dipartimento di Costruzioni e Trasporti Sezione Rilevamento - Università di Padova - Italy
COMMISSION VII, Working Group 1
KEY WORDS: LIDAR, DIAL, ATMOSPHERE, REMOTE SENSING
ABSTRACT
At the University of Calabria (Cosenza, Italy) a DIAL station, based on two pulsed CO, laser transmitters, has been built and is
operating . The station is actually used for the RS of atmospheric parameters and of minor constituents of the atmosphere, and works
in a range of about 2 km. In the next months a mobile system will be realized, allowing a mapping of large zones and measurements
in peculiar sites (thermoelectrical power plants, factories, etc..). The results of the monitoring will be used to set up a GIS.
To check the geometric accuracy of the DIAL station, both range and angular measurements have been realized, and the results have
been compared with total station measurements. The geometric accuracy of the DIAL system is generally sufficient for the range
measurements, whilest the angular accuracy can be improved.
The DIAL facility, the tests and the obtained results are reported. A better kind of angular regulation, just built but not tested, is
described.
THE DIAL STATION AT THE UNIVERSITY OF
CALABRIA
The increasing availability of laser sources, operating from IR to
UV frequencies, offers interesting opportunities for the
developement of active remote sensing techniques. Several
systems have been set up, generally named LIDAR (Light
Detection And Ranging, based on a laser source) and DIAL
(DIfferential Absorbtion Lidar, based on two coupled laser
Sources).
At the University of Calabria (Cosenza, Italy) a DIAL station,
based on two pulsed CO, laser transmitters, has been built and
is operating (Bellecci et al., 1991, 1993), in the framework of a
national research (Barbini et al., 1991). The scheme of the
facility is shown in Figure 1.
The lasers are tunable on 64 lines on branches P and R between
9 and 10 um. The maximum output energy is equal to 3.8 J on
the 10P20 line, whilest the pulse lenght is around 80 ns.
The telescope used to send the pulses and to collect the
backscattered signal, is a Cassegrain type, with a 40 cm aperture
and an equivalent focal lenght of 250 cm. The detector is a
HgCdTe photosensor.
The station is actually used for the RS of atmospheric
parameters and of minor constituents of the atmosphere, and
works in a range of about 2 km.
For the purpose of remotely probing the atmospheric parameters,
the DIAL technique can be succesfully used. Two laser
wavelenghts, |... and lg, are selected such that |, corresponds
to the center wavelenght of some prominent absorption line of
the molecule of interest, while log lies on the wing of this line.
The used equation is (Measures, 1984):
1 Pon(R) PoffR + DR)
In [ l
Poe (B Pon(R + DR)
N(R) =
($08 ^ Soft) DR
where:
N(R) = average concentration of the element in the range cell DR
Son ^ Sofr ^ differential absorption cross sections for incident
radiation of wavelenghts ln and lofr
PQ = scatiered laser power received for the range R and
wavelenght lon
P,r(R) = scattered laser power received for the range R and
wavelenght lofr
P,g(R+ DR) = scattered laser power received for the range
R+DR and wavelenght loff
Pon(R + DR) = scattered laser power received for the range
R+DR and wavelenght |,
From the DIAL equation, the average concentration of the
monitored element is obtained in a range cell, having a depth
DR determined by the laser pulse lenght.
For the measurement of the atmospheric water vapour the CO,
laser transmitters can be tuned at the 10R20 (10.247 pum) and
Intemational Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998 3
