921 Chichi Earthquake :
Preliminary Interferometric Interpretations
Results and interpretation (Fig.2A-B, 3, 4, 5)
On the amplitude image (Fig.2A), one may notice Taichung and surrounding city buildings (white pixels), fish ponds, rice fields and rivers (black pixels), Taiwan strait and vegetation onshore (grey pixels). From the processing of interferometrable image pairs, we have carried out calculation of several interferograms (e.g. Fig.3, 4 and 5) and coherence images (e.g., Fig. 2B). White pixels on the coherence image correspond to coherent points on the two radar images such as urbanized areas. The corresponding interferogram (Fig. ) and fringes on the western down-faulted block of the Chelungpu fault (Chichi earthquake). The rather low base line of the pair (100m in the specific area of Taichung) linked with low relief, logically suppresses fringes, due to topographic artefacts for example to DTM errors. Otherwise, with the aim of avoiding the hypothesis of parasitical fringes occurrence generated by atmospheric effects, we have to carried out other interferograms with independent pairs of images (work in progress).
So without parasitically effects, the interferograms (fig.4) shows particularly a serie of 10 complete fringes to the W of the Chelungpu fault. We interpret these fringes as corresponding to a present displacement witness.
Fig.2A : Amplitude image of the Taichung area (23/09/1999 - SAR-ERS) ; 2B : Coherence image of the Taichung area (02/25 ~ 09/23 pairs).
White pixels = coherent points (e.g. : urbanized areas), black and grey ones = not coherent (sea water, and vegetation).
Fig. 3 : Non ortho-referenced interferogram (02/25 ~ 09/23) of the Taichung area
Note the 10 fringes in the western down-faulted block of the Chelungpu active Fault
(location between white arrows)
Fig. 4: Ortho-referenced interferogram (05/06 ~ 09/23) of the Taichung area
(Intensity : Amplitude, Hue : Phase - interferogram, Saturation : Coherence)
Fig. 5: Ortho-referenced Interferogram (05/06 ~10/28) of the Taichung area
(Intensity : Amplitude, Hue : Phase - interferogram, Saturation : Coherence)
