The single lens (coaxial) optics has established its position as the leading technology applied in laser ceilometers. As compared to the traditional two lens (biaxial) optical design, the main advantage of the single lens optics is the strong and stable signal starting at virtually zero altitude. This means reliable detection of also the lowest clouds and ground based obscurations, the phenomena being most critical from the aviation safety point of view.

The new Vaisala ceilometer is based on enhanced single lens optics. The new technology practically removes the internal optical cross-talk between the laser transmitter and the receiver, a feature that requires separate compensation techniques in current single lens ceilometers. The enhanced optical design provides also improved robustness against contamination of the window by dirt or precipitation. This leads to a more reliable cloud detection under all weather conditions. The new ceilometer provides also better sensitivity for backscatter measurement, a usefull feature in other applications than just cloud base detection, like boundary layer profiling.

The paper will present the instrument design in detail, as well as measurement results in various weather conditions. Also comparison results against current ceilometers will be presented.