Geoscience Reference
In-Depth Information
The PAL system has been operated at Chiba Prefecture Environmental
Research Center (CERC), located in an industrial park, nearby an air
pollution monitoring station. The aerosol concentration data measured
by a beta-ray instrument at the pollution-monitoring station is compared
with the (optical) extinction data from PAL, yielding the value of mass
extinction eciency (MEE) of atmospheric aerosols in the boundary
layer.
4
,
5
In this chapter, as a further extension of the PAL data analysis, we
consider the relation between the PAL-observed features of aerosols/clouds
and meteorological conditions that bring about such behavior of the
atmosphere.
2. Monitoring System
The PAL is an eye-safe lidar with the laser energy of 20
J/pulse at 532 nm,
pulse width of 50 ns, and repetition frequency of 1.4 kHz. It is installed
on the second floor of the CERC (35.52N, 140.07E) building, and directed
toward the north sky with an elevation angle of 38
◦
. Detected in the photon
counting mode, the lidar signal gives a vertical profile of aerosol/cloud
concentration continuously every 20 s. The specification is given in Table 1.
In order to suppress the background due to sky radiation, the receiving field-
of-view (FOV) is limited to 0.2 mrad. Since this small FOV easily generates
off-alignment of the system due to temperature change, the direction of laser
beam is optimized every 15 min by adjusting the direction of the pointing
prism.
µ
Table 1.
Specification of PAL.
Laser
Diode (LD)-pumped Q-switched Nd:YAG laser
Wavelength
532 nm
Laser pulse width
50 ns
Laser pulse energy
15
µ
J/pulse
Pulse repetition rate
1.4 kHz
Telescope type
Schmidt-Cassegrainian
Telescope diameter
20 cm
Field of view
0.2 mrad
PMT detector
Hamamatsu:HPK-R1924P
Resolution
160 ns (∆
R
=24m)
Integration
20 s
Photon counting
SR430 (Stanford Research)
Remote control
Via Internet (ADSL modem)
Alignment interval
15 min
Pointing
Manual
