East Asia and Western Pacific METEOROLOGY AND CLIMATE

Lambert reflector, there is no need to measure the brightness of
targets and background with a photometer. At the same time, through
the investigation of the properties of quasi-horizontal sky brightness
and the reflective properties of airport's cement runways and white
marks on the runway, he suggested the concept of "effective
reflectivity"* According to this concept, low visibilitiesdess than
2 kilometers) can be probed^.
3* In the numerical research based on the double scattering
lidar equation*- 21 J, the empirical correction of multiple scattering
was made to the extinction coeficient*- *, so as to raise futher the
probing precision of low visibility.
4. By means of IAG frequency doubling technology^, we adopted
a laser beam with a wavelength of 530 nm; it is closer to the
chromolight that is most sensitive to the human eyes(550nm), so it is
quite favourable for the improvement of probing precision of
visibility.
5. The validating experiments made at airports showed'- 22 *' that
the correlation between the laser probed and human eye observed
visibilities is as good as 0.93Cbased on 65 pairs of horizontal
visibility samples). For various ranges of visibility, the errors are
small enough to meet the requirements of aviation. When the
visibility is less than 500 meters, average error is 44 meters. As to
slant visibility, the comparing results of 21 pairs of samples are:
the average error of laser probed visibility and human eye observed
slant visual range is 10 percent; the maximum error is 33 percent*
Only two pairs of samples exceed the limitation of aviation for
probing precision of visibility(20 percent).
173
2. Multi-Parameter Remote Sensing of Aerosol Optical Properties
Remote sensing of atmospheric aerosols is better than in-situ
measurements in many situations. It can maintain the natural state of
atmospheric aerosols, and produce timely and promptly the spatial and
temporal variation of aerosols. At present, the passive remote
sensing of aerosols is mainly with the solar extinction