High-Resolution Sporadic E Layer Observation Based on Ionosonde Using a Cross-Spectrum Analysis Imaging Technique

The appearance of the sporadic E (Es) layer is an occasional phenomenon in the ionosphere. Limited by range resolution, it is difficult to observe the fine structures and internal evolution processes using existing ionosonde detection techniques. In this study, by analyzing the cross-spectrum of the echo and the modulation sequence of the transmitted signal, the coherence between frequency components in the signal bandwidth is utilized. Using the Capon spectrum estimation method in the range dimension, the range resolution and use efficiency of the ionosonde are improved. This method does not rely on the joint processing of multifrequency detection data, unlike the frequency domain interferometry technique, maintaining the resulting time resolution. Using this imaging method, observations of the Es layer show that multiple peaks within an intrinsic range bin (3.84 km) can be resolved at a range that is 10-fold higher (384 m); the multilayer phenomenon inside the Es layer can be clearly imaged in a continuous echo. Semishading between the layers is present. In some cases, the mode of the echo traces can also be directly identified through high-resolution imaging. Concurrently, observations show that dramatic short-term evolution processes on the order of seconds inside the Es layer can be captured.