Aerosols – cirrus - contrails
The above-described protocol is taking into account both elastic and Raman
acquired signals and it is integrating complementary local meteorological and
regional radiosounding data
. Raman technique allows a preliminary estimation
of the absolute value of aerosol’s extinction coefficients. The obtained low-
resolution (i.e. highly smoothed data) extinction profile is then introduced,
instead of the a priori lidar ratio profile, in the Fernald inversion, in order to
obtain the high-resolution backscatter coefficient. By reapplying the Fernald
inversion using this newly determined high-resolution backscatter coefficient,
the extinction coefficient can be retrieved at the same resolution as the elastic
backscatter. Finally this allows a more precise determination of the lidar ratio,
which can then be used as a more realistic approximation in case of similar
considered atmospheric conditions.
3.1 Molecular upper troposphere
The backscatter coefficients based on Eq. (5) and Eq. (6) corrected for the
Rayleigh extinction allow simulation of the Rayleigh (i.e. pure molecular
atmosphere) correspondent lidar signals. These molecular simulated backscatter
signals were compared both to Raman (387 and 532 nm) and elastic (1064 nm)
signals for clear sky situations. Simulated pure molecular lidar shows very good
agreement with real lidar detected signals (elastic or inelastic) in the aerosol-free
upper troposphere situation for all relevant wavelengths as shown in the example
presented in Figure 2 (a).
The extremely good correlation validates the proposed semi-empirical approach
 to estimate the molecular upper troposphere above the Alps. In order to
verify the degree of molecular purity of an apparently perfectly clear blue-sky
day, measurements of the total optical depth (TOD) using a sun-photometer (i.e.
RSL 10 channels Reagan, specifications in annex A20) were also considered.
The related sun-photometer measurements are plotted in annex A21. In Figure 2
(b) only the TOD measured at midday on May 8, 2001 (e.g. an apparently clear
sky day) is plotted together with the calculated molecular extinction coefficients.
Fitting a power law in ~
one may easily observe that despite the high visibility
and the apparently clear sky the A exponent for the sun-photometer AOD is
~ 2.14, smaller than the simulated Rayleigh one ~ 4.09, suggesting the presence
of a certain amount of small size particles in the upper troposphere.
A quasi-complete set of MatLab, LabView and Delphi software routines were developed
within the present work for implementing the proposed procedure as depicted in Figure 1. The
main examples are illustrated in the annexes: A17 to A19.