抄録
Two carrier frequencies, L1 and L2, used in Global Positioning System (GPS) can be used to isolate ionospheric total electron contents (TEC) by taking the phase differences between the two carriers (L4). Here we review technical aspects of geophysical applications of TEC measurements. Topics include conversion of standard format raw GPS data files into L4 and TEC, and numerical techniques to isolate disturbance signals with various time scales. We also introduce typical examples of TEC change signatures of variety of geophysical phenomena, e.g. volcanic eruptions, earthquakes, solar flares, ionospheric hole formation by rockets and missiles, solar eclipse, and elusive precursory TEC changes before earthquakes.
