The main goal of the project is to determine a methodology to distinguish between the various types of Polar Stratospheric Clouds (PSCs) and, in the case of heavy volcanic aerosol loading, as at present after the Mt. Pinatubo eruption, also to discriminate between volcanic aerosols and Polar Stratospheric Clouds. After the EASOE campaign in the Arctic it was evident that the usual lidar procedure to identify PSCs were no more valid, as volcanic aerosols presented scattering ratios of the same amplitude and in the same altitude region as normally do PSCs.
Traditionally polar Stratospheric Clouds are identified by their lidar signatures and the atmospheric temperature. Two main types of PSCs are known: Nitric Acid Trihydrate (NAT) clouds, identified as Type I, and ice water clouds, identified as Type II. Type I clouds are subdivided into 2 subgroups, depending on their scattering and depolarisation properties. The following distinction is generally accepted:
Type la Type lb
scattering ration < 2 > 2
depolarisation ration > 10% < 10%
particle size > 1m < 1m
particles /CN <<1 = 1
The project intends to investigate the influence of various parameter (wavelength, polarization, scanning, multiple scattering) on the lidar data and derive improved calibration methods and measurement strategies to optimize the monitoring of such types of scattering media. This will help to better qualify and validate lidar data both from tropospheric and stratospheric measurements.
The work programme comprises the following tasks :
1. The possibility of classification of Polar Stratospheric Clouds by lidar measurements.
2. The influence of depolarization and multiple scattering on a lidar signal from PSC's.
3. Scanning mode and depolarization / multi-wavelengths and depolarization.
4. Improvement of lidar measurement techniques for discrimination of various types of particles.
5. Summary. Identification of parameters which have to be measured.
Funding SchemeCSC - Cost-sharing contracts