Demonstrating the use of a class of min-max smoothers for D-region event detection in narrowband VLF phase

This paper describes the use of a class of non‐linear smoothers for the identification of interesting phenomena in narrowband very low frequency (VLF) transmission phase caused by perturbation events in the D‐region of the ionosphere. The LULU smoothers, named for their smoothing of upward (L) and downward (U) peaks in a signal, usually used for image processing tasks, are described and examples are shown where these operators are used to automatically isolate and identify features in the phase of narrow band transmissions received at high and high‐middle latitudes (Antarctica and Marion Island, respectively). Identification of solar flare events, electromagnetic ion cyclotron wave precipitation and substorm injection events are demonstrated, showing the potential for this technique to be used for space weather monitoring.