Radar and lightning detection
The Royal Meteorological Institute operates a Lightning Location System (LLS) to detect and locate in real time the total electrical activity over Belgium and its adjacent neighboring countries.
The Belgian Lightning Location System (BELLS) is a network of lightning sensors that records the electromagnetic pulses emitted by lightning discharges. In the current network setup, BELLS consists of 14 sensors, 5 of which belong to RMI. The sensors detect both lightning strikes to the ground, as well as the more frequent discharges in the clouds. By combining the data sent by each sensor to the central computer in Uccle, the exact location, time, type and intensity of each lightning discharge is determined.
The estimated detection efficiency (DE) for cloud-to-ground (CG) flashes over Belgium is 95% or higher.
To determine the exact location of the lightning discharges, data from multiple lightning sensors are analyzed. Each of the antennas detects the discharge, but at a slightly different time depending on their respective distance from the lightning discharge. Using these very small differences in arrival time, also known as "time-of-arrival", the location of each lightning discharge is determined using a specific algorithm applied for this purpose. As such, BELLS detects lightning discharges with a geographical accuracy of several hundred meters.
RMI has been operating an LLS since 1992. The original network consisted of four sensors of type SAFIR. The central processor used an interferometric lightning location retrieval method in the very high frequency (VHF) band to retrieve the location of intracloud source points using triangulation. In addition, the SAFIR sensors were equipped with an electric field antenna detecting the low frequency (LF) return stroke signature, allowing the system to discriminate between CG and intracloud electrical signals.
RMI's lightning location system has undergone updates over the years in terms of both the type of sensors and the processing software. BELLS no longer makes use of the aforementioned SAFIR sensors, but nowadays utilizes low frequency LS7002 type sensors.