Cirrus cloud has an important effect on the radiation balance between the earth’s surface and the atmosphere. The vertical structures, optical depth and effective lidar ratio of cirrus cloud detected by Mie scattering-polarization-Raman lidar system in Beijing from April 11 to December 31, 2012 are analyzed. The results show that the cloud height in Beijing is lower in spring and higher in autumn, with a mean value of about 8km. The mean of cloud thickness is 0.74km. The mean of optical depth is 0.092, and most observed cirrus cloud is thin while optical depth is less than 0.3. The effective lidar ratio of cirrus is lower in summer and higher in winter, inversely related to local temperature, with a mean value of 32.29Sr.
Micro pulse lidar(MPL) is an effective tool for atmospheric aerosol and cloud detecting. In order to make the structure of the micro pulse lidar more compact, solve the problem that it always very difficult to adjust the transmitting and receiving optical paths to parallel in the traditional system, avoid the influence of the geometric overlap factor and reduce the complexity of the data processing, Anhui institute of optics and fine mechanics of the Chinese academy of sciences designs a new type of micro pulse lidar, particularly designs the followed up optical unit of the micro pulse lidar. A combination of emitting and receiving fibers in a signal bundle changes the structure of the subsequent optical unit in the traditional system to make the transmitting and receiving optical paths coaxial. The public end of the Y type optical fiber bundle is composed of a transmitting optical fiber in the center and eight receiving optical fibers in the periphery. After a brief introduction of the new system, the key parameters of the new micro pulse lidar system and the Y type optical fiber bundle were described in some detail. In order to verify the feasibility of the new structure of the micro pulse lidar system, a continuous observation experiment was carried out in Hefei area to detect the horizontal distribution of the atmospheric aerosol and pollutions. The data measured in the experiment in the November 2013 was processed with Fernald method and the profile of the atmospheric aerosol horizontal extinction coefficient distribution was inverted. The data inversion results showed that: the data acquired by the new lidar system and the extinction coefficient distribution inverted by Fernald algorithm are all very reasonable, and the time-space distribution of atmospheric aerosols extinction coefficient can reflect the distribution of the atmospheric aerosol and pollutions near the ground effectively. All of the experiment results indicate that the design of the new micro pulse lidar system is effective.
Proc. SPIE. 9142, Selected Papers from Conferences of the Photoelectronic Technology Committee of the Chinese Society of Astronautics: Optical Imaging, Remote Sensing, and Laser-Matter Interaction 2013
The cloud lidar, with the character of high precision and good stability, is an effective way to detect the cloud height. Pulse diode laser (PLD), as an essential part of the lidar system, needs the triggering pulse. In this paper, the emitting part of the lidar is studied，including the simulation of the backscatter SNR, the choose of the PLD and the design of trigging circuit to drive the 905nm PLD with the consideration of the optical system. A circuit for trigging the laser pulse with adjustable power and pulse width is contrived. Then the software Systemview is used to emulate the design and finally the making of PCB is finished. The results show whatever the parameters of the pulse, namely trigging pulse width, the rising edge, dithering , all these can be qualified to be in use in the practice and enjoys the merits of the low cost and convenience. The emitting module operates well.
Proc. SPIE. 7658, 5th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Optoelectronic Materials and Devices for Detector, Imager, Display, and Energy Conversion Technology
KEYWORDS: Mirrors, Photon counting, Backscatter, LIDAR, Signal attenuation, Aerosols, Clouds, Signal analyzers, Stray light, Signal detection
A co-axial transmission elastic-backscattered lidar aiming to detect the optical properties of the clouds is presented in
this paper. The modular co-axial design can guarantee the consistency of the transmitting part and the receiving part. In
practice a specific diaphragm is used to suppress the stray light of the primary mirror and background light to improve
SNR of the backscattered signal in the daytime. So the near ground signal must be corrected with the appropriate overlap
factor. A Licel transient recorder is used for data acquisition in analog and photon counting combined in one acquisition
system. With the 15 MHz sampling rate, the spatial resolution of 10 m can be attained. The control over the transient
recorder and the treatment of the data is performed on a PC. After getting the correctional backscattered signal, retrieving
and analyzing the extinction coefficient profile, the cloud base, cloud peak and related optical parameters of the clouds
can be confirmed. In order to testify the feasibility of our lidar, it was implemented with a Finland ceilometer Vaisala
simultaneously in May in 2008 in Hefei. Results show the lidar system is stable and the data is reliable.
In order to reach a green Olympics in 2008, an unprecedented environmental experiment jointly
launched by the Beijing municipal government and the Chinese Academy of Sciences (CAS) was
carried out. AIOFM (Anhui Institute of Optics and Fine Mechanics Experiment) took part in the
campaign with an elastic/non-elastic lidar to measure the aerosol distribution and the boundary layer in
summer in Beijing. With the combining solution of the Raman lidar and the elastic lidar equation, the
important optical parameters of the aerosols (extinction coefficient, backscatter coefficients thus the
lidar ratio) were attained. The lidar ratio on July 22 varied from 10sr to 30sr. Since the vertical
distribution of the lidar ratio demonstrate different microphysical characteristics in the lower and upper
parts of the cloud, so probably the cirrus with the mean lidar ratio of 25sr at the height of 6km can be
assumed. On the other hand, a well-mixed boundary layer was observed. Taking into account the
effects of the multiple scattering (5%-10%),we obtain a single-scattering optical depth of 0.15.The
boundary layer also offered the explanation of the steady ozone concentration measured by the DOAS
system at the same position of the observing site.