About the Vaisala Ceilometer

    The Vaisala Ceilometer CL51 measures cloud height and vertical visibility. The CL51 employs pulsed diode laser LIDAR technology where short, powerful laser pulses are sent out in a vertical or near-vertical direction. The reflection of light, backscatter – caused by haze, fog, mist, virga, precipitation, and clouds – is measured as the laser pulses traverse the sky. The resulting backscatter profile, that is, the signal strength versus the height, is stored and processed, and the cloud bases are detected. The time delay between the launch of the laser pulse and the detection of the backscatter signal indicates the cloud base height.

    The ceilometer CL51 is able to detect three cloud layers simultaneously. If the cloud base is obscured due to precipitation or ground-based fog, the CL51 reports Vertical Visibility. There is no need for adjustments in the field. The embedded software includes several service and maintenance functions and gives continuous status information from internal monitoring. The software is designed to give the full backscatter profile.