We report the results of our long-term monitoring study of cirrus clouds using our locally developed lidar sytem located in Hanoi, Vietnam (21.03°N, 105.85°E). Our data, spanning the period from 2011 to 2017, show that the cirrus clouds above Hanoi are generally found between 6.7 and 18.0 km with a mean height of 14.0 km. The cloud thickness is estimated to vary between 0.2 and 7.0 km with an average thickness of 2.3 ± 1.2 km. We also derive an average optical depth of 0.32 ± 0.22 and an average lidar ratio 30 ± 18. We also compare the geometrical and optical properties of cirrus clouds above Hanoi, where until now lidar study is still lacking, with that obtained for other locations in Asia and around the world.
In order to increase the detected range and reduce the effect of signal-induced noise in light detection and ranging (LIDAR) measurements of the high atmospheric layers, we have developed a normally off-gated photomultiplier tube module for use in the photon-counting mode. The module allows the detection of the weak backscattering signal, while at the same time rejecting the intense backscattering signal from the near range with an adjustable rejection range. The gating of our module is based on the application of positive voltage pulses on all the even dynodes of a photomultiplier head. We describe the electronic circuit design and discuss the implementation of the module. The capability of the module in rejecting intense backscattering signal from the near range was tested on our LIDAR system. The agreement between the range-corrected LIDAR signals and the standard atmospheric molecular number density up to a height of 60 km indicates a good performance by the module. Comparison between Raman and elastic backscattering signals under cloudy sky conditions indicates that the intense backscattering from near range is sufficiently suppressed and has a negligible effect on the performance of our module.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.