sum value has been chosen. 
Pulse 7 
  
  
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Figure 4: Pulse 7 Peak Enlargement 
The values of the distances obtained by the DIAL system are 
equal, respectively, to 339.3 and 1086.0 m; the relevant standard 
deviations are equal to 0.73 and 1.47 m. The values obtained 
with the total station are equal to 337.579 and 1085.231 m. 
The DIAL facility is generally used for the RS of atmospheric 
parameters, so, a test with gaseous targets has been made. 
The concentration of water vapour has been obtained with the 
DIAL system, along a straight line, connecting the system mirror 
and a building of the university. The laser beams crossed the 
atmosphere on the botanic garden, delimited by a road and a 
built zone (Figure 5). 
  
Figure 5: Layout of the University of Calabria 
Some variations of concentration have been detected, in 
corrispondence of the buildings and of the botanic garden; the 
DIAL signals are shown in the Figure 6. Figure 7 shows the H,O 
concentration variations along the laser beams path. 
  
  
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The difference between the ranges obtained by DIAL system and 
total station is about 10 meters. In this case, to obtain the water 
vapour concentration, it is necessary to consider a 20 m cell, to 
have a good evaluation of the gradients of the lj, and loft 
signals, as shown in the DIAL equation. 
Angle measurements 
The first problem to solve is the alignment of the laser beams 
with the telescope axis. For this aim, a HeNe laser beam, 
previously aligned with the telescope axis, has been projected at 
a distance of about 15 m and a red spot has been obtained on a 
wall of the laboratory. In this point, an IR target (thermal 
printing paper) has been positioned. The energy of the CO» laser 
pulses is sufficient to generate a black spot on the paper. Two 
mirrors, allowing micrometric movements, have been tilted to 
superimpose the black spot on the red one. In this way, the 
6 Intemational Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998 
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