Ceilometer CL51

Vaisala Ceilometer CL51 is designed to measure high‑range cirrus cloud heights without surpassing the low and middle layer clouds, or vertical visibility in harsh conditions.

CL51 employs a pulsed diode laser LIDAR (light detection and ranging) technology, where short, powerful laser pulses are sent out in a vertical or near-vertical direction. The reflection of light (backscatter) caused by clouds, precipitation or other obscuration is analyzed and used to determine the cloud base height.

Measurement from ground level

The enhanced single lens technology applied in CL51 ensures excellent performance starting at a height of virtually zero. The signal is strong and stable over the whole measurement range.

CL51 is able to detect 3 cloud layers simultaneously. If the cloud base is obscured due to precipitation or groundbased fog, CL51 reports vertical visibility. CL51 is able to provide the backscatter profile over the full measurement range. This information provides a possibility for an advanced boundary layer and atmospheric analysis. 

Designed for harsh weather 

CL51 has a shield with a blower and heater, which allows steady operation in precipitation and under extreme temperatures. Reliable solar protection is ensured by optical filters. A tiltable shield further protects the instrument from precipitation and specular reflection from ice crystals. The tilt angle measurement and correction is automatic.

Self-diagnostics

In addition to cloud height data, the fully automatic CL51 outputs messages with information on the instrument status.

The information is based on comprehensive self-diagnostic routines. In case of a malfunction the diagnostics help the user to identify the failed module.

Maintenance

Periodic maintenance of CL51 is normally limited to window cleaning. There is no need for adjustments in the field.

The automatic window blower with heater improves performance by keeping the window clean and dry. In cold conditions heating prevents frost generation on the window. Any

malfunction is automatically reported in the data and status messages.

Data messages

• Cloud hits and internal monitoring data
• Cloud hits, status, and backscatter profile
• Emulation of CL31 and LD-40
• Sky condition (optional)