Previous: Introduction Next: Ozone vertical profiles Up: Ext. Abst.
II. Dial system
The DIAL system (figure 1) requires two different wavelengths, in this case provided by two lasers, one emitting pulses at l on = 308 nm (ozone absorption) and the other one at l off = 355 nm, providing the reference signal (practically without absorption). The election of these values is based on the commitment of minimizing the statistical and systematic errors in the lower stratosphere(2) .
Figure 1. Setup of the differential absorption lidar (DIAL) for the measurement of stratospheric ozone profiles installed at CEILAP, Villa Martelli, Great Buenos Aires.
The backscattering signals of the atmosphere are collected by a Newtonian telescope and detected by fotomultipliers. By means of an external optical synchronism, those signals are acquired alternatively in a photocounting system, and after a numerical treatment the concentration of ozone is determined. For this calculation, the data of temperature and pressure obtained by the radiosound of National Meteorological Service located at Ezeiza Airport (30 Km from CEILAP) and the CIRA for our latitude and the corresponding month are used. More details are given in reference (3).
The DIAL equation determining the concentration of ozone in function of height has two terms(4)
|
|
(1) |
where
|
|
(2) |
is the number of backscattering photons at l
i for an atmospheric layer D z located
at a distance z, during the time of integration D
t, and
is the effective cross section
of ozone for l i.
,
where: e diff(z), e m(z), e p(z) y e e(z) are the terms for the atmospheric diffusion, the attenuation by molecules, by particles and by others constituents of the atmosphere (excluding the ozone)(5).
