A Controlled Experiment of Ionospheric Effects on VHF Signals Transmitted from A NOAA Weather Satellite

We investigate the ionospheric effects using a real VHF signal transmitted from a polar orbiting NOAA weather satellite, NOAA-19, at 861 km altitude. NOAA-19 gathers weather satellite image data and transmits reduced resolution images in the Automatic Picture Transmission (APT) format at 137.1 MHz. A software-defined VHF data collection system was tuned to the transmission signal center frequency to sample the signal at Gakona, Alaska, during an HF ionosphere heating experiment. Software algorithm has been developed to extract the signal amplitude and carrier phase and the results are used to compute amplitude and phase scintillation indices as the signal traverses the artificially disturbed ionosphere. The strong response in signal amplitude and phase disturbances is a clear contrast to the mild disturbances experienced by GNSS signals traversing ionosphere under similar conditions. The results from this study demonstrated the strong frequency dependence of radio waves transmitted from LEO satellites on ionospheric disturbances. The study also revealed the deficiency in current ionospheric scintillation modeling at VHF.