Background Noise Modelling for Noise Reduction in GPS TEC

Disturbances in the ionosphere can be induced from space weather phenomena and seismic events which create acoustic waves at the surface of the Earth, coupling to acoustic-gravity waves in the ionosphere. These disturbances can be observed as perturbations in Total Electron Content (TEC) obtained as a byproduct of dual frequency GPS measurements. Travelling Ionospheric Disturbances (TIDs) from several events including earthquakes, tsunamis, volcanic explosions and underground nuclear tests have been observed using GPS-derived TEC. However, smaller signatures, such as ones from small surface explosions and underground nuclear tests, may be difficult to detect in the presence of noise in the TEC time series. While it may be easier to identify these signatures using time-frequency analysis, detection using time-frequency response still benefits from a prior model of the noise. Global measurements of line of sight TEC can be made using dual frequency GPS measurements made by ground-based GPS receivers from existing networks such as the USGS CORS and GEONET in Japan. Global GPS-derived TEC data from the USGS CORS and Japanese GEONET receiver networks have been analyzed to develop an empirical noise spectrum model for relative TEC. A basic spectral subtraction method using the 95% confidence interval of generated noise spectrum is then applied to GPS TEC to observe TIDs generated by acoustic-gravity waves from small surface explosions in Socorro, NM.