Passive over-the-horizon radar with WWV and the first station of the Long Wavelength Array

We present a new passive, over-the-horizon (OTH) radar system consisting of the transmitters for the HF radio station WWV and the dipole-antenna array that comprises the first station of the Long Wavelength Array (LWA), or “LWA1.” We demonstrate that these two existing facilities, which are operated for separate purposes, can be used together as a relatively powerful bistatic, HF radar, capable of monitoring the entire visible sky. In this paper, we describe in detail the techniques used to develop all-sky, OTH radar capability at 10, 15, and 20 MHz. We show that this radar system can be a powerful tool for probing ionospheric structure by quantifying the degree of “tilt” effected by ionospheric density gradients along the ray paths, including the effect this has on OTH geolocation. The LWA1+WWV radar system appears to be especially adept at detecting and characterizing structures associated with sporadic-E. In addition, we also demonstrate how this system may be used for long-distance, OTH mapping of terrain/ocean HF reflectivity.