Ceilometer CL51

for high-range cloud height detection

Model: CL51
Manufacturer: Vaisala – Finland


  • Cloud reporting range up to 13 km (43 000 ft)
  • Backscatter profiling over full range up to 15 km (49 200 feet)
  • Second-generation, advanced single-lens optics with excellent performance also at low altitudes
  • Field-proven, fully automatic 24/7 operation in all weather conditions
  • Modular design for easy installation and maintenance
  • Extensive self-diagnostics with fault analysis
  • Reliable operation in all weather: unsurpassed performance in precipitation
  • Based on robust and affordable laser diode technology
  • Detection of cirrus clouds
  • Latest technology from the world leading manufacturer – over 5000 ceilometer installations worldwide

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.


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.


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)

Measurement performance


Measurement range 0 … 13 km (0 … 43 000 ft)
Backscatter profiling range 0 … 15 km (0 … 49 200 ft)
Reporting resolution 10 m (30 ft), units selectable
Reporting cycle 6 … 120 s, or polling
Distance measurement accuracy against a hard target Greater of ±1 % or ±5 m (16 ft)


Inputs and outputs


Operating voltage 115/230 V AC 

100 – 127 V AC, 207 – 253 V AC

Power consumption (typical) 310 W
Backup battery 12 V internal, 2 Ah
Overvoltage category II
Data •  RS‑232 

• RS‑485, multidrop, 2‑wire 

• DXL421 modem module 

• LAN (Ethernet) interface option

Maintenance RS‑232 
Baud rate
RS‑232 / RS‑485 300 … 115 200 bps
Modem V.21, V.22 300 … 1200 bps


Operating environment


Operating temperature −55 … +60 °C (−67 … +140 °F)
Operating humidity 0 … 100 %RH
Wind tolerance Up to 55 m/s (123 mph)
Vibration Lloyds Register / IEC 60068‑2‑6 

5 … 13.2 Hz, ±1.0 mm 

13.2 … 100 Hz, ±0.7 g 

9.1 … 150 Hz, ±0.5 g

Pollution degree 2
Maximum operating altitude 3000 m (approx. 9800 ft)
IP rating IP65 (measurement unit)


Mechanical specifications


Measurement unit 834 × 266 × 264 mm 

(32.83 × 10.47 × 10.40 in)

Height with radiation shield 1531 mm (60.28 in)
Total  1531 × 335 × 324 mm 

(60.28 × 13.19 × 12.76 in)

Measurement unit  18.6 kg (41 lb)
Radiation shield and blower 27.4 kg (60.4 lb)
Total 46 kg (101.41 lb)
Plywood transport container
Container size 1650 × 540 × 480 mm 

(65 × 21.26 × 18.90 in)

Shipping weight Typically 75 kg (165.3 lb)


Spare parts and accessories


Cable termination box with extra transient protection Termbox-1200
PC maintenance cable QMZ101 
Shock absorbing mounting pad for ship installations CT35022
Modem DXL421
Attachment mechanics for radio modem antenna CL51RADIOKIT
Graphical User Interface for Ceilometers CL-VIEW
Boundary Layer View Software for Ceilometers BL-VIEW
Bird deterrent CL51BIRDKIT
Air Quality Plug and Play Package for Ceilometer with laptop and preinstalled BL‑View CLAQPACKAGE




EU directives and regulations LVD, EMC, RoHS
EMC immunity IEC/EN 61326‑1, industrial environment 
EMC emissions CISPR 32 / EN 55032, Class B 

EN 61000-3-2 

EN 61000-3-3

Electrical safety IEC/EN 60950
Environmental IEC/EN 63000
Eye safety IEC/EN 60825-1:2014
Compliance marks CE, RCM, China RoHS, UKCA

Ceilometer CL51


Product reviews

Review Ceilometer CL51

5 0% | 0 review
4 0% | 0 review
3 0% | 0 review
2 0% | 0 review
1 0% | 0 review
Review Ceilometer CL51
Choose a image
0 character ( Minimum of 10)

    There are no reviews yet.

    No comments yet

    Related products

    Cảm biến đo tầm nhìn khí quyển CS120A

    CS120A Atmospheric Visibility Sensor

    High-Performance Visibility Measurements
    Find out more
    Cảm biến dòng điện xoay chiều

    CS11-L AC Current Sensor

    Measure the ac Current along an Electrical Wire
    Find out more
    Cảm biến đo áp suất khí quyển CS106

    CS106 Barometer

    Wider Pressure Range, Resides inside weatherproof enclosure
    Find out more
    Cảm biến đo áp suất khí quyển CS100

    CS100 Barometric Pressure Sensor

    Standard Barometer, resides inside a weather-proof enclosure
    Find out more
    Cảm biến đo mực nước và nhiệt độ nước CRS456V 

    CRS456V Titanium Vented Stand-Alone Pressure Transducer

    Pressure Transducer Combined with a Recorder, High resolution and accuracy
    Find out more
    Cảm biến áp suất CRS456

    CRS456 Titanium Stand-Alone Pressure Transducer

    Self-Contained Memory, Easy to use software, reliable hardware
    Find out more
    Cảm biến áp suất

    CRS451 Stainless-Steel Stand-Alone Pressure Transducer

    Self-Contained Memory, Easy to use software, reliable hardware
    Find out more
    Hệ thống đo lường luồng khí theo phương pháp eddy-covariance

    CPEC310 Expandable Closed-Path Eddy-Covariance System with EC155, Pump Module, and Automatic Zero and Span

    Fully Expandable Design, Provides additional ports with automatic zero and span
    Find out more
    error: Content is protected !!