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Abstract
The sporadic E layer (EsL), characterized by enhanced ionospheric electron density at around 100 km altitude, has been recognized as one of the prominent phenomena in the E region ionosphere and is known to influence radio wave propagation, particularly in the HF and VHF frequency range. This study explores the spatial structure and dynamical characteristics of EsL using multiple radio observations, including Automatic Identification System (AIS) maritime signals, aeronautical navigation signals, GNSS-based ionospheric irregularity measurements and ionosondes. In particular, AIS signals at 162 MHz were utilized for the first time to show the two-dimensional structure of strong EsL (corresponding foEs is at least greater than 20 MHz) over maritime regions. The combined radio observations on May 30, 2023 revealed EsL structures extending east–west, showing dynamic behavior such as northward and southwestward movements. In particular, it was demonstrated that AIS signals can be used to track the motion of intense EsL events, and their integration with aeronautical radio and GNSS data allows for detailed visualization of EsL characteristics over a wide area. This result highlights the potential of combining multiple radio techniques to advance the understanding of EsL characteristics and its impact on radio propagation.