Results from UK Met Office investigations into new technology present weather sensors

Present Weather is defined as the type of weather observed at the reporting time. The Met Office in the United Kingdom uses Vaisala FD12P sensors to report the weather at some of its stations. Since 2001 it has been used with software known as the “Arbiter”, which modifies the Present Weather output when there is sufficient evidence from other sensors. However, even this modified system can sometimes have problems in accurately determining light and mixed precipitation events. Also, the Arbiter system does not always make direct measurements. A single Present Weather code output gives little information on uncertainty, and no raw data is output, which makes traceability, calibration and maintenance difficult.

This paper contains results from field trials conducted in 2007/8 of new laser disdrometers, in order to ascertain if Present Weather code output performance is improved over the existing system. An investigation is carried out to ascertain whether value is gained in letting the user interpret spectrum plots of drop size distribution data in uncertain events.