GPS World, August 2013

GOVERNMENT Remote Sensing FIGURE 2 The IGS global tracking network of 439 stations occur from geophysical events such as geomagnetic storms which can be indicated by global Kp indices while MSTIDs are genrally not related to any high score Kp indices An underground nuclear explosion can result in an MSTID TIDs are generated either by internal gravity wave IGW or by acoustic gravity wave AGW The collisional interaction between the neutral and charged components cause ionospheric responses The experimental results indicate IGWs can change the ozone concentration in the atmosphere In the ionosphere the motion of the neutral gas in the AGW sets the ionospheric plasma into motion The AGW changes the iso ionic contours resulting in a traveling ionospheric disturbance The past 10 15 years has resulted in a significant body of research and eventually a practical application with worldwide coverage of GPS based ionosphere monitoring A significant number of International GNSS Service IGS permanent GNSS tracking stations see FIGURE 2 form a powerful scientific tool capable of near real time monitoring and detection of various ionospheric anomalies such as those originating from the underground nuclear explosions UNEs The network is capable of continuously monitoring global ionospheric behavior based on ionospheric delays in the GNSS signals The GNSS signals are readily accessible anywhere on Earth at a temporal resolution ranging from about 30 seconds up to less than 1 second A powerful means to isolate and FIGURE 3A Pictorial representation of the scenario describing a GNSS station tracking a satellite and the ionospheric signal 3 point STEC derivative not to scale FIGURE 3B The scenario describing a GNSS station tracking a satellite and the ionospheric signal and a point source e g UNE that generates acoustic gravity waves not to scale FIGURE 3C The scenario describing a GNSS station tracking a satellite and the ionospheric signal and the propagation of the acoustic gravity waves generated by a point source e g UNE not to scale FIGURE 3D The scenario describing a GNSS station tracking a satellite and the ionospheric signal at the epoch when the GNSS signal is affected by the propagation of the acoustic gravity waves generated by a point source e g UNE not to scale FIGURE 3F Same as 3D after the TID wave passed the line of sight between the GNSS stations and the satellite not to scale FIGURE 3E Same as 3D indicating that the geometry between GNSS station the satellite and the IPP can be recovered and used for locating the point source multiple GNSS stations are needed to find the point source location and the the velocity components of TID and ionospheric winds not to scale GPS World August 2013 www gpsworld com 36