Transition towards a new ceilometer network in the Netherlands: challenges and experiences

KNMI renews all cloud ceilometers in its national meteorological observing network in 2016 and 2017. At about 40 stations, the Vaisala-Impulsphysik LD40 is gradually being replaced by the Lufft CHM15k ceilometer. By taking this step, the Netherlands will have a future-proof network in place to continue the generation of operational cloud
information for synoptic and aeronautical purposes. This includes observing sites where meteorological reports are produced for the (AUTO)METAR system, such as civil airports and military airbases.

The new ceilometer network brings some great new opportunities. Benefits of the new instruments are primarily seen in the detection of high clouds and the sensitivity to aerosol layers, where the CHM15k clearly outperforms the LD40. Nevertheless, the
transition to the new sensor also introduces some significant differences. This mainly concerns cloud base observations relevant for aeronautical reports, typically in the lowest 5,000 ft. Hence, the generation of fully automated, validated cloud information with an acceptable performance level poses several challenges.