Continuous monitoring of multiple layering by ceilometer in the Inn valley

Automatic mixing layer height monitoring was performed by continuous ceilometer measurements in the Inn valley near Innsbruck, Austria. The Vaisala ceilometer LD40 was used which is an eye-safe commercial lidar and designed originally to detect cloud base heights and vertical visibility for aviation safety purposes. Special software for this ceilometer provides routine retrievals of mixing layer height from ceilometer data. Particular emphasis is given to the detection of thermally stable layers and inversions within the lower troposphere and their temporal development. Such elevated layers influence the diurnal variations of air pollution. A comparison was performed with parallel mixing layer height retrievals from a SODAR. In clear and cold winter nights sometimes several layers, which strongly influenced the air quality in that valley, could be detected with both instruments. In the absence of low clouds and precipitation ceilometers can estimate the mixing-layer-height fairly well. Ceilometer and SODAR partly complement each other.