The effect of global change in the past century, which led to increased levels of pollution and augmented values of cloud coverage, on the time of the apparent Sunrise and Sunset, is suggested to have shortened the day by 1 - 1.5 minutes in the past 4 decades in northern and mid-latitudes. This is supported by photographs of the setting Sun taken in Jerusalem during the months of July and August 2001, which reveal that in over 95% of the cases the Sun completely disappear to the naked eye below marked atmospheric layers at an average elevation angle of 0.5 - 2.5° above the solid earth horizon. Based on trends in past Sunshine Duration measurements, the day shortening effect is expected to increase in the future.
An analytical solution for calculation of double Raman-Mie scattering in the presence of a cloud is suggested. The model includes the Raman-Mie and Mie-Raman scattering processes occurring in the cloud volume as well as integrated Raman scattering signal from air molecules along the laser pulse from lidar to the cloud base. The developed algorithm allows for the comparison of relative contribution of these processes to the total Raman-shifted lidar signal. For typical lidar and cloud parameters, double scattering is not negligible and its contribution to the Raman signal is around 20%.
We consider here the electromagnetic wave scattering by a long and thin-wire helical particle. In contrast to several previous theoretical works, we adopt here the Mie theory to this case. In the present work a long helical particle is considered as a hollow cylinder with a thin non-homogeneous membrane for which the periodical boundary conditions are imposed.
The operation of laser radar in an automotive collision avoidance system under poor visibility conditions is analyzed. The equations were formulated to calculate (1) the signals returned to a laser radar system by a reflecting target positioned at a given range and (2) signals caused by the scattering of laser radiation by atmospheric particles only. The dependence of calculated signals on the density and the scattering properties of the atmospheric medium on one hand and on the geometry of the system on the other hand was studied. The multiple scattering processes were included in these calculations, and the polarization properties of the calculated signals were analyzed. An experimental verification of the theoretical results in a clear atmosphere and in a dense atmospheric environment has been performed. Good agreement was achieved only when multiple scattering was included in the theory. It is shown that multiple scattering is the main contributor to the signals received from the medium. Utilization of the results of this work can reduce significantly the very high false alarm rate typical for dense atmospheric conditions where successful anti- collision system performance is most crucial.
A lidar facility has been established at the Jet Propulsion Laboratory- Table Mountain Facility located at an altitude of 2300 m in the San Gabriel Mountains in Southern California. This facility is using the technique of differential absorption lidar to measure atmospheric ozone concentration profiles. Two separate systems are needed to obtain the profile from the ground up to an altitude of 45 to 50 km. A Nd:YAG-based system is described for measurements from the ground up to 1 5 to 20 km altitude, and an excimer-laser-based system for measurements from 15 km
to 45 to 50 km altitude. The systems were designed to make high-precision, long-term measurements to aid in the detection of changes in the atmospheric ozone abundance through participation in the Network of Detection of Stratospheric Change.