Raytracing analysis of DME ranging error variation due to atmospheric change

GNSS (global navigation satellite systems) are widely used in aircraft navigation. However, a GNSS backup system is required due to GNSS vulnerability. Enhancement of DME (distance measuring equipment) is one of candidates for the GNSS backup system. Optimization of tropospheric propagation delay is suggested as one of technologies for the enhancement. In developing an optimization technology, first, the amount of variation in tropospheric propagation delay at very low elevation angles for aircraft application should be clarified quantitatively. Moreover, the cause of the variation should be detailed. This study analyzes these issues by using the raytracing method and upper-air observation data. The result provides data that can be utilized for the future development of the DME enhancement.