Toward Developing an Algorithm for Separation of Transmitters of High Frequency Chirp Signals of Opportunity for the Purpose of Ionospheric Sounding

The ionosphere is a highly variable, ionized layer of the Earth's upper atmosphere. Extending from about 50-1000 km above the Earth's surface, the ionosphere consists of several regions each of varying altitudes and ionization. The ionosphere can be broken up into the D region, E region, and F region. One type of instrument utilized to make ground-based observations of the ionosphere are known as ionosondes, or ionospheric sounders. We focus primarily on chirp ionosondes, which are a type of ionospheric sounder that works by transmitting a high frequency (HF) signal that changes linearly in frequency with time from about 2 MHz to about 20 MHz. By using an HF Software Defined Radio (SDR) receiver and the GNU Chirpsounder2 software created by Juha Vierinen, it is possible to listen for chirp ionosonde signals of opportunity and decode these signals into oblique ionograms that can be used for scientific or operational purposes. Previous work developed an algorithm that can identify transmissions from the Relocatable-Over-The-Horizon-Radar in Chesapeake Virginia received near Scranton, Pennsylvania. However, there are ROTHRs transmitting from Vieques, Puerto Rico and Premont, Texas. We modify the existing algorithm identify these locations.