There are a great many factors effecting the performance of ceilometers, but the key 2 issues for any given cloud volume backscatter coefficient are:
- The eye safe limit of the ceilometer . Infra Red Ceilometers must operate as Class 1M lasers which limits the energy density of the beam.
- The noise level. The inherent noise level of the ceilometer is the ultimate determinant of the signal to noise ratio which enables the ceilometer to discriminate cloud boundary.
The 8200-CHS has an extremely low level of inherent noise, which is tested for each ceilometer and is recorded as per the backscatter profile below.
The external source of noise is the shot noise of the scattered and or direct solar radiation within the spectral acceptance of the sensor . The laser operates around 910 nm and the filtering can only limit the “out of band” component of the solar noise spectrum. The ceilometer will thus t\detect cloud at higher altitudes at night.