Ionospheric Effects on VHF Signals Transmitted from a LEO Satellite

Abstract We investigated the effects of the ionosphere on a very-high-frequency (VHF) signal transmitted from a polar orbiting National Oceanic and Atmospheric Administration (NOAA) weather satellite, NOAA-19, at an altitude of 861 km. NOAA-19 gathers cloud images and transmits reduced resolution images in the Automatic Picture Transmission format at 137.1 MHz. A software-defined VHF data collection system sampled the signal at Gakona, Alaska, during a high-frequency ionospheric heating experiment. A software algorithm was developed to extract the signal amplitude, frequency, and carrier phase, and the results were used to compute amplitude and phase scintillation indices as the signal traversed the artificially disturbed ionosphere. A strong response was observed in signal amplitude and phase due to the disturbances, in clear contrast to the mild disturbances experienced by global navigation satellite system signals traversing the ionosphere under similar conditions. The results demonstrate the frequency dependence of ionospheric effects on radio waves transmitted from low-Earth-orbit satellites. The study also reveals the deficiency in current ionospheric scintillation modeling in the VHF regime.