HF Software Receiver Arrays (HFSRA)

Accurate real-time knowledge of the bottomside ionosphere is necessary for covert HF communications, near vertical incidence sounding, and geolocation of HF transmitters. Sky-wave TDOA geolocation is the "holy grail" of HF geolocation techniques due to its passive nature, low cost, and easy deployment. To achieve sky-wave TDOA it is necessary to know the dominant mode of propagation, which requires accurate knowledge of the bottomside ionosphere over a wide geographical region. The bottomside ionosphere is not well characterized, because existing instrumentation is expensive, sparse, and usually views only a local region. Thus, a requirement exists for low-cost sensors that can provide information over an extended region. To address this problem we propose a feasibility/design study involving two types of HF instrument: (1) a receive-only sensor, that collects data from all known HF "transmitters of opportunity"; (2) a transmit/receive sensor that cycles over a range of frequencies. We will also study the feasibility of combining multiple instruments into a network, whose data can be ingested into appropriate ionospheric specification algorithms. This system will provide the capability to determine the dominant propagation mode for HF geolocation, a solution to the long-standing problem of HF geolocation, and improved security for the USA.