Performance improvement of long-range scanning Mie lidar
for the retrieval of atmospheric extinction
F. Gao
a,b,
n
, D. Veberic
ˇ
b
, S. Stanic
ˇ
b
, K. Bergant
b
, D.-X. Hua
a
a
Xi’an University of Technology, China
b
University of Nova Gorica, Slovenia
article info
Article history:
Received 2 July 2012
Received in revised form
13 September 2012
Accepted 26 November 2012
Available online 11 January 2013
Keywords:
Long-range scanning Mie lidar
Data gluing
Offset of laser beam direction
Atmospheric extinction
abstract
To improve the detection range and signal to noise ratio in the remote sensing of atmos-
pheric processes using long-range scanning Mie lidar, simultaneously obtained analog
(A) and photon-counting (P) data traces were merged using a novel gluing method based
on the modification of the A trace so that it follows Poisson statistics. In comparison with
the traditional method based on the minimization of the distance between A and P, the
advantage of this new approach is an improved uniformity of the merged data trace
as well as a reduced influence of atmospheric conditions on the obtained transfer
coefficients. The atmospheric extinction was subsequently retrieved using the two- and
multi-angle method. The offset of the laser beam direction was calibrated against a self-
leveling laser, as an offset in elevation angle was found to produce considerable error in
the atmospheric extinction profiles obtained under the assumption of horizontal atmo-
spheric homogeneity.
& 2012 Elsevier Ltd. All rights reserved.
1. Introduction
A long range vertical scanning Mie lidar with the
wavelength of 355 nm at Otlica observatory (45.931N,
13.911E, 945 m above sea level) is being routinely used
for the investigation of atmospheric processes within the
atmospheric boundary layer (ABL) [1,2]. The system can
simultaneously record data traces in both analog and
photon-counting (PC) detection modes at elevation angles
ranging from 0 to 90 degrees. The front-view atmosphere
is then presented in the form of two-dimensional (2D)
spatial diagrams. Atmospheric optical variables (optical
depth and atmospheric extinction) are retrieved using the
two- and multi-angle method [3] with the assumption of
horizontal atmospheric homogeneity in the detectable
range, which was assessed by extracting horizontal pixel
data from the 2D diagram and investigating its linearity as
a function of distance from the lidar site.
In order to cover the entire range of interest, extending
2–30 km from the lidar site, analog data and PC data are
merged, as the analog detection mode gives better per-
formance in the near range (less than 10 km) while the
PC detection mode performs better in the case of weak
backscattering signals obtained from far-field (from
7.5 km to more than 30 km). Of the two, trace points in
the PC data are distributed according to Poisson statistics
(variance equals mean), while trace points in the analog
data trace are not [4,5]. Traditionally, a linear relationship
between the analog signal A and PC signal P was deter-
mined within an arbitrarily selected ‘‘valid’’ region
of ranges and the analog data was transformed into
‘‘PC-like’’ data by minimizing the distance between A
and P [6–8]. The accuracy in the reconstruction of lidar
data traces was further improved using modified regres-
sion and maximum-likelihood techniques [8,9]. However,
the lower and upper count rates that define the valid
region still had to be set manually, which resulted in
Contents lists available at SciVerse ScienceDirect
journal homepage: www.elsevier.com/locate/jqsrt
Journal of Quantitative Spectroscopy &
Radiative Transfer
0022-4073/$ - see front matter & 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.jqsrt.2012.11.027
n
Corresponding author at: Xi’an University of Technology, China.
Tel.: þ86 2982312441.
E-mail address: gaofei_xaut@163.com (F. Gao).
Journal of Quantitative Spectroscopy & Radiative Transfer 122 (2013) 72–78