The observed depolarization of polarized lidar signals scattered from virga and a source cloud may be interpreted to show that the source cloud is largely glaciated, and the virga is composed of ice crystals not randomly oriented. The orientation of the ice crystals in the virga, generally possible only in a nonturbulent atmosphere, is demonstrated by depolarization ratios greater than 1. The cloud processes suggested by this observation are in agreement with other independent observations.

Clouds and their radiative effects strongly influence climate (Ramanathan et al., 1989). High priority has been assigned (CES, 1989) to research the role of clouds’ radiative properties in climate change, especially as feedback mechanisms, and on how to incorporate these effects properly in climate models. Measurements of climate-significant properties of clouds, such as height, optical density, and particle size distribution, are needed in intensive process studies and also in extended studies to observe the large variety of cloud conditions that occur.

During the summer of 1985, the Wave Propagation Laboratory of NOAA upgraded its pulsed CO2 Doppler lidar with a new transceiver. Previously, the system had operated with a hybrid TEA transmitter, producing approximately 100 mJ of energy per pulse at a 10 Hz pulse repetition frequency (prf). The upgraded transceiver, built by Spectra Technologies, Incorporated, of Bellevue, Washington, uses an injection-locked, unstable resonator configuration to produce frequency-stable pulses with 2 J of energy per pulse; maximum prf of the injection-locked system is 50 Hz. The larger pulse energy and higher pulse repetition frequency make the new lidar considerably more valuable for investigations of transient atmospheric phenomena and tropospheric backscatter climatology.

Observations were conducted over uniform, exceptionally flat farm land in Illinois during clear weather in July, 1983. Scintillation data were obtained at 116.30 and 172.91 GHz for a path 1.4 km long. Rigorous micrometeorological measurements, some of them path averaging, were made along the path. The results of these tests will be described.

Simultaneous measurements using several types of remote sensing techniques have been analyzed and combined to yield data sets on the optical properties of clouds and aerosols. The parameters observed include (1) extinction at nine wavelengths in the 0.3-to-10.0 μm wavelength range as measured by solar radiometers, (2) the backscatter coefficient and depolarization as a function of range as measured by a pulsed ruby lidar, (3) the angular scattering function out to 8° from the sun as measured by an aureole photometer, and (4) the visual characteristics and identification of sky conditions obtained through time-lapse sky photography. The data are sorted according to the type of cloud or aerosol present as determined by lidar backscatter information (height profile and depolarization characteristics) and visual identification. Some results on optical properties are presented including the wavelength dependence of aerosol extinction, and preliminary data on angular scattering in the near-forward direction and wavelength dependence of extinction due to several types of clouds. Practical applications of the data include their use in design of optical propa-gation links and solar energy systems, and as input to computer models of atmospheric transmission.

A parallel plate Stark cell has been used for measurements on millimeter wave transitions of the hydrogen sulfide molecule. With this cell and phase matched sources, high precision values for molecular dipole moments are achieved.

The Backus-Gilbert inversion technique was applied to scattering data and calculated examples were given to ascertain its ability to recover the aerosol properties with no a-priori assumptions. In order to cheque this inversion procedure as well as other techniques (such as Daves' and Herman's et al.), a controlled experiment was performed. The experiment dealt with spherical particles the Mie scattering curves of which was measured by use of a dye-laser. These curves were used to accurately determine the refractive index of the particles. Mixtures of three different known sizes were then prepared and the scattering intensity vs. wavelength was measured at 90 deg scattering angle. The mixtures contained also various known relative concentrations of the three sizes. The analysis of the measured results will be shown and discussed.

Measurements of atmospheric water vapor using the Raman backscatter from a pulsed laser were directly compared with measurements from meteorological instruments located on a tower. The experimental conditions and precautions required in making these observations in the atmosphere are discussed. The results indicate that water vapor profile measurement to a range of approximately 4 km is feasible with the lidar used in this experiment.