Figure 9: TIPs induced by 26th December 2004 Indian ocean Tsunami derived using differential (dTEC), residual (rTEC) and SPLA (gROT) methods are plotted as a function of time vs. inter-IPP distance. Size and color of the circles represent amplitudes of the normalized TIPs. For better visual clarity dTEC is shifted in distance with 7km and 4hrs in time, gROT is shifted in distance with 14km and 8hrs in time.Red and blue boxes represent the artifacts and aliasing.
In contrast, the residual method has another shortcoming in the form of artifacts. The artifacts in rTEC arise due to the limitation in characterizing the trend of normal TEC variation, particularly, when the observation is discontinuous, for example, IISC26 (Fig. 7) and HYDE29 (Fig. 8). Similarly, multiple breaks between 11 and 14 UTC create a severe signal aliasing in rTEC of COCO17 (Fig. 6a) and such a strong signal is neither present in dTEC nor in gROT. Similar aliasing and artifacts in dTEC and rTEC at various satellite-PRN pairs are shown in Fig. 9.