Investigating Natural Hazards Using GNSS Measurements: The Chelyabinsk Meteor Ionospheric Impact

Abstract

Introduction. Natural hazards, including earthquakes, volcanic eruptions, and tsunamis, have been significant threats to humans throughout recorded history. The Global Positioning System satellites have become primary sensors to measure the effects of such natural hazards. Signatures in the GPS data include seismic deformation displacements, co-seismic vertical displacements, and real-time ocean buoy positioning estimates. Another way to use GPS observables is to measure and monitor ionospheric total electron content (TEC) variations generated by post-seismic atmospheric disturbances caused by earthquakes, volcanic eruptions, tsunamis, meteors and nuclear explosions [e.g., Artru et al., 2005]. Prior JPL Work. Advances in very high precision ionospheric GPS data processing at JPL have demonstrated that ground-based GPS receivers are capable of detecting TEC perturbations generated by atmospheric acoustic and gravity waves [Komjathy et al., 2012]. The 2011 Tohoku earthquake and tsunami data processing results have, for instance, demonstrated that the gravity-wave-derived TEC perturbations are visible 45 minutes after the earthquake [Galvan et al., 2012]. Applying JPL’s data processing techniques to multiple events, we have found that a 2004 volcanic eruption in Japan showed approximately 1-minute period waves in ionospheric TEC, whereas the September 2009 earthquake near Samoa produced signatures with an 8-minute period [Galvan et al., 2011]. There remains much to learn about the characteristics of these interactions between the Earth’s surface and ionosphere, including how and why they differ from one event to the next. Recent Natural Hazard Event of High Interest. The Chelyabinsk meteor provided a unique opportunity to observe TEC disturbances generated by a fireball in the atmosphere. The small asteroid entered the atmosphere at 3:20 UT on February 15, 2013 moving at a speed of about 20 km/s. The object, with an almost 20 meters in diameter, then burst into pieces at a height of 30-50 km above the ground. Large fragments moving at a high speed caused a powerful flash and a strong shockwave, with most of the meteor’s energy released at a height of 5 to 15 km above the earth. Technical Approach. We use JPL’s PyIono package (a bias-fixing algorithm) to generate high-precision calibrated TEC measurements. Calibrating TEC measurements serves multiple purposes for us including quality checking (QC) of processed data, leveling the phase measurements using pseudoranges and comparing modeled TEC perturbations with measured ones [Mannucci et al, 1998]. Obtaining absolute TEC values is useful to understand background conditions for the perturbations [e.g., Komjathy et al, 2005]. However, we are primarily interested in monitoring small-scale variations in ionospheric electron density, hence the changes in TEC are of interest, rather than absolute TEC values. Subsequently, JPL’s PyIono uses TEC observations to compute de-trended TEC data. A Butterworth band-pass filter (corresponding to waves with periods between 33 and 3.3 minutes ranging between 0.5 and 5 mHz) is applied to focus on acoustic and gravity wave generated TEC observations. This type of filtering allows us to more easily detect perturbations within an expected range of frequencies, which we can infer from previous observations of tsunami periods, for example [Galvan et al., 2012]. Summary and Anticipated Results. We have processed data from 23 GPS stations within a radius of 1500 km from the impact location in Russia for February 15 and the surrounding days. Initial results of monitoring TEC perturbations using the JPL technique suggest a strong impact of the individual explosions on the ionosphere. Furthermore, we observed a statistically significant correlation between the reported meteor trajectory and the ionospheric signatures measured by GPS. Preliminary modeling results of wave structures are presented and compared with the observed perturbations to investigate the po