Study of structures of the sporadic E layer by using dense GNSS network observations

The sporadic E (Es) layer has been known to introduce long-range propagation of aeronautical very high frequency (VHF) navigation beyond the radio horizon and cause potential interference on the navigation system. This study utilizes a rate of total electron content (TEC) index (ROTI) map with dense Global Navigation Satellite System (GNSS) observations for effective Es layer detection. The daytime Es layer shows a well-defined frontal structure when ROTI values are mapped at the typical Es layer height (100 km). A methodology of detecting and characterizing the Es layer frontal structure without manual operation is developed by utilizing the Hough transform. The front direction and drift velocity are successfully derived. Sub-structures in the Es layer front are revealed by analysis using the characteristics of the frontal structure and TEC variation. The developed method is suitable for an automated real-time Es-layer monitoring system in a wide area.