Geoscience Reference
In-Depth Information
Fig. 1. Block diagram of lidar system at Chung-Li, Taiwan. (PMT: photomultiplier
tube, Dis: discriminator, MCA: multi-channel analyzer, PC: personal computer).
of 24 m and a temporal resolution of 33 s. The schematic diagram of lidar
system is shown in Fig. 1. Details about our lidar studies/system can be
found in the studies of Nee
et al.
6
The lidar measures
height profile of backscattered signal from aerosols, which are converted
into backscattering ratio. The aerosols backscattering ratio,
et al.
5
and Chen
BR
, is defined
as follows:
)=
(
β
a
(
z
)+
β
m
(
z
))
BR
(
z
,
(1)
β
m
(
z
)
where
β
a
and
β
m
are the backscatter coecients of aerosols and molecules,
respectively. The backscattering coecient of molecule is derived from
the molecular concentration measured by radiosonde multiplied by total
Rayleigh scattering cross section. Calculation of aerosol backscattering ratio
involved Fernald solution.
7
For this study, the initial condition for the upper
height is set at 5 km, and the reference value of backscattering ratio is 1.05,
based on the earlier study.
8
The extinction-to-backscatter ratio or lidar
ratio for the aerosol and cloud cases was derived by Chiang
et al.
9
The polarization measurements were carried out by recording the
lidar returns for perpendicular and parallel polarizations. The aerosol
depolarization ratio (
δ
a
)iscalculatedas
)=
δ
(
z
)
∗
BR
(
z
)
− δ
m
δ
a
(
z
,
(2)
BR
(
z
)
−
1
