Ceilometer CT25K
User’s Guide CT25K-U059en-2.1
14
2.4 Using the Tilt Feature
The Measurement Unit and Pedestal of Ceilometer CT25K are designed so
that the unit can operate in a tilted direction. The built-in tilt angle sensor
CT3675 detects the tilt angle, i.e. deviation from the vertical. The tilt angle
ranges from -15 to +90 degrees from vertical; the angle is positive when the
measurement unit door turns towards the ground. The cosine of the tilt angle
is used for automatic correction of the detected cloud base height, which
enables accurate cloud base measurements also in a tilted direction.
Several advantages can be realized with the aid of this feature:
• Heavy weather conditions
Using a slight tilt angle for instance 15 degrees, the measurement unit
window is kept better protected from precipitation, thus enhancing the
availability of correct measurements in heavy weather conditions.
• Aircraft approaches
The beam can be directed towards a direction, which better represents the
approach of an aircraft than the straight vertical. Useful e.g. for helicopter
approaches, and sites where the ceilometer cannot be located exactly at the
desired spot.
• Hard target and testing purposes
Tilting the unit down by 90 degrees permits verification of operation
against a hard target at a known distance. Useful in connection with
installation and maintenance. Enables real backscatter signal detection
when there are no clouds in the sky.
WARNING
Make sure that nobody is viewing the unit from the beam
direction with magnifying optics!
• Maintenance
By tilting the unit back -15 degrees, better access is gained to the interior
during maintenance.
• In the tropics
Between the latitudes of ± 25 degrees, where the sun can be straight above
the unit, a slight tilting prevents the laser from direct sun radiation, which
would otherwise destroy the laser. The other alternative is to use a tropics
window on the measurement unit instead of a standard window.
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