On the Use of High Frequency Surface Wave Oceanographic Research Radars as Bistatic Single Frequency Oblique Ionospheric Sounders

We present an investigation demonstrating that passively collected high frequency coastal oceanographic radars, with suitable waveform characteristics, can be used as single frequency oblique ionospheric sounders. To our knowledge, this is one of the first demonstrations of dual purpose use of these HF coastal radars, in addition to their primary role as ocean current monitors. We present a technique for extracting the virtual height using the E-region as a time calibration; this technique is agnostic of the software defined radio used. The application of this investigation may be useful for expanding spatial coverage for traveling ionospheric disturbance studies, day-to-day variability studies, or within data-assimilation routines. Additionally, HF coastal radars may be used by the scientific community or radio amateur as an another suitable RF source. We performed an experiment in which we collected 10 days of data in March 2016 from a site in Maryland, USA (MSR) and 21 days of data collected in October 2020 from a site near Clemson, South Carolina, USA (CARL). For both experiments, we used a similar hardware setup utilizing an Ettus USRP N210 software defined radio, including the GPSDO unit. We performed radar signal processing to obtain the group delay time from the passively received signal of Coastal Ocean Dynamics Applications Radar (CODARs). Our observations for both intervals focused on one frequency band at 4.53718 MHz which included three CODAR transmitters located on the Coast of North Carolina and Virigina with callsigns: DUCK, CORE, and LISL. The digisonde located at Wallops Island, VA (WP937) was used as the diagnostic to compare and validate with the observations collected from oblique CODAR-MSR(CARL) paths.