Description

A HMU (Height Monitoring Unit) is a ground based system consisting of two main components - HME (Height Monitoring Element) and TMU (Total vertical error Monitoring Unit).

The HME captures Transponder transponder signals from aircraft replying to interrogations from radar stations. The signals contain the information from modes S, C and A transmissions. The HME determines the geometric height and position of an aircraft by comparing the time of reception of the SSR transponder signals at different receiver locations. This information is transmitted to the TMU as one plot per second. The data is collated by the TMU to create a track history of the aircraft passing through the area of coverage. The track information is then combined with meteorological data to evaluate the overall value for Total Vertical Error (TVE).