Ashok Kumar Gwal

Analysis of space-and ground-based parameters prior to an earthquake on 12 December 2009

The present study includes observations of anomalies at ionospheric and ground levels using data from global positioning system (GPS)-based total electron content (TEC), ionospheric electron density by Detection of Electromagnetic Emissions Transmitted from Earthquake Regions (DEMETER), and ground-based ultra-low-frequency (ULF) emission prior to an earthquake that occurred on 12 December 2009. The analysis of the data from these three different techniques show relations with preseismic activities. The GPS-based TEC showed enhancement three days prior to the day of the earthquake. On converting the satellite azimuth into latitude and longitude, a large number of passes giving anomalous TEC values were observed covering a zone 17–23° N and 70–74° E (i.e. around the epicentre). Electron density and temperature as measured by DEMETER also show enhancement of the tracks around the epicentre one day prior to the earthquake. For ground-based ULF emission, we used different analysis techniques for the detection of abnormal changes in ULF emission before the earthquake. We observed changes in different parameters such as polarization ratio and fractal dimension. Clear enhancement is observed for polarization parameters (Z/X, Z/Y) and fractal analysis (for the Z component). The results provide useful information in acquiring data prior to earthquakes.

Development of computerized ionospheric tomography technique and its application to study the Equatorial Ionization Anomaly over the Indian region

The paper explores the development and validation of latest ionospheric monitoring technique known as computer added ionospheric tomography (CAIT) for its application in understanding the dynamics of ionosphere. The Total Electron Content (TEC) is derived from the differential Doppler method by receiving the two coherent radio signals from beacon receivers aligned in the same meridian. The estimated TEC is then further used to generate the 2-dimensional (2D) tomographic image with the help of the conventional Algebraic Reconstruction Technique (ART). The results show that the technique can be successfully utilized to study the 2D structure of electron density and Equatorial Ionization Anomaly (EIA) which is one of the most crucial phenomenons of equatorial and low-latitude region.