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Polar stratospheric clouds (PSC) were observed with the multi-wavelength lidar of the MOANA project (Modelling and Observations of Aerosols in the Northern Atmosphere) during SESAME (Second European Stratospheric Arctic and Mid-latitude Experiment). The physical state, liquid or solid, of the cloud particles can be inferred from the lidar data. Using isentropic back-trajectories to obtain the thermal history of the sampled air masses, it is possible to reconcile most of the observations with current ideas on PSC formation and evolution. When the cloud particles were identified as liquid, changes in the size distribution of the droplets along the trajectory were calculated using a micro-physical box model. Backscatter ratios calculated from the size distributions are in broad agreement with the lidar data, giving confidence in current understanding of the evolution of ternary solution (H2SO4, HNO3 and H2O) droplets. Results from two soundings are shown which bear on the problem of the formation of solid particles. In the first, solid particles were detected. The air mass had cooled to the frost point 12 hours earlier. In the second no solid particles were detected although the air temperature was below the nitric acid trihydrate existence point, and had decreased by 12K in the previous 14 hours.

Measurements have been performed at eight laboratories on Raman-shifted radiation from frequency-quadrupled Nd:YAG and KrF lasers. Each of these sources is a possible candidate for making differential-absorption lidar measurements of ozone in the free troposphere. The spectral purity, efficiency and divergence of the different sources are compared and explained using a simplified model of the Raman interaction. Particular attention has been given to the use of buffer gases to optimize the Raman gain and divergence. The experimental results show that the operating conditions required to optimize the output energy of each of these types of laser source can be quite different. In the case of the KrF laser, it has been shown that high energies can be generated at low active gas pressures, and that increasing the pressure increases the beam quality, but decreases the energy. (Less)

A four wavelength backscattering depolarization LIDAR designed for polar stratospheric cloud and stratospheric aerosol measurement is described. The system uses the following wavelengths: 355 nm, 532 nm, 750 nm, and 850 nm. These wavelengths, obtained by means of the third- and second-harmonic of a Nd: YAG laser and by means of a tunable Ti: Sapphire laser, are chosen in a way to better characterize the particel size of such stratospheric aerosols. They are not emitted simultaneously as the LIDAR system is designed with only two detection channels permitting to detect, in the analog and in the photon counting mode, both the direct and the depolarized backscattered signal. The system has been operational in northern Finland since the end of November 1991.

In the present paper a Lidar (light detection and ranging) system is described. It allows high-speed data acquisition of Lidar signals and meteorological parameters by means of standard instrumentation. The Lidar, controlled by a computer, utilized two laser sources (Nd: Yag and ruby), a modified Ricthey-Chretien telescope and signal detection, storage and real-time monitoring equipment. The whole system was installed in a container for field experiments.

An elastic backscattering lidar and initial results are described. The lidar system has been designed to operate in Antarctica for the Italian National Programme for Antarctic Research. The first field trials were held during the period from 31 December 1987 to 10 February 1988. Data were collected for both tropospheric and stratospheric atmospheric parameters. Tropospheric measurements included the cloud base, optical depth, extinction and backscattering coefficients for clouds, whereas aerosols and the molecular atmosphere were monitored in the stratosphere. The lidar system was also tested for the determination of temperature and density in ranges up to 40 km. Preliminary results of the lidar measurements carried out at Terra Nova Bay are presented. The lidar system is composed of a Nd−YAG laser, a Newtonian telescope and two receiving channels with computer-controlled data acquisition and display equipment. The system is operated in a mobile container specifically designed for the Antarctic environment.

The ability of an infra-red scanner to detect oil spills over the sea surface is discussed on the basis of the first results of the Archimedes experiment 1983. During this experiment an infra-red scanner was flown over two oil spills and a real-time detection was achieved. The IR images were also recorded and processed in order to improve the film-thickness evaluation. An infra-red visible package was then developed which allows a real-time remote sensing of oil spills, eventually from small aircrafts.

Lidar stratospheric aerosol measurements have been carried out at IROE since April 1982, just after the eruption of the Mexican volcano El Chichon. Over two years evolution in stratospheric aerosol loading has been monitored and compared with data collected by other stations. Since the Lidar system can perform an average signature, every minute, also short-time fluctuations in Lidar signatures have been analysed in order to obtain information on stratospheric air turbulence and on the possible presence of gravity waves