Use of Terrestrial HF Signals in Riometer Data to Investigate the Size of the Absorbing Region

In this study, we present the first results from the new prototype Hyper-Spectral Riometers (HSRs) developed by the University of Calgary and several U.S. institutions. HSRs measure signal power in frequencies ranging from 0-50 MHz. The nature of the system filtering conspires to allow for weak cosmic signals to be observed above ~20MHz at the same time as terrestrial HF signals are observed below 20MHz. We present event studies from three prototypes (Gillam MB, Meanook AB, and Rabbit Lake SK) where the instruments observed auroral absorption coincident with terrestrial HF drop-outs. Leveraging the Natural Resources Canada (NRCan) transmitter network (whose signals are observed in the HSR) and simulations of HF ray paths, we show that the terrestrial signals can be used to remote sense the size of the absorption region under certain conditions. In this paper, we present our preliminary results and discuss the capacity of the new measurements, and future plans for deployments.