This plots displays the long-term tracking performance of a station, based on the daily percentage of each constellation tracked by the station. This percentage corresponds to the ratio of the number of complete observations (both the L1 and L2 frequencies are observed) with respect to the number of predicted observations. Input are the daily RINEX observation file and the RINEX navigation message, needed to compute the predicted observations.
The percentage, given in brown, is computed for a fixed elevation cut off angle of 15°. The percentage, given in red, is computed for a fixed elevation cut off angle of 0°. The EPN guidelines request that a station has a clear horizon above 5° which means that it is expected that the 15° value is close to 100%.
The black line on each plot is the elevation cut off angle as set in the station log file. The value in green is the elevation cut off angle as observed in the RINEX observation file, given by the lowest elevation at which satellite are seen.