## 3 Literature Review and Comparison of Interferometric Coherence and Intensity Correlation
### Combination of Interferometric Coherence and Intensity Correlation and Comparison of Both  
The application of both techniques coherence and intensity correlation at the same test site enables a comparison of both techniques. [PERSON] and [PERSON] [84] applied interferometric coherence and SAR intensity correlation to detect damaged areas after the 1995 Kobe Earthquake, Japan, using ERS imagery. The comparison of both techniques showed that the de-correlation of the intensity and of the interferometric coherence behave similar. For instance, generally urban areas show high correlation values, while water surfaces are characterized by very low values. Farmland is in-between both. Moreover, the authors emphasized the requirement of short spatial baselines (e.g., \(<\)139 m for ERS) to reduce spatial de-correlation effects (_cf._ also Section 2.1). Using C-band ERS SAR imagery, [PERSON] and [PERSON] [73] found that the coherence is more useful to distinguish slight to moderate damage levels, while the SAR intensity correlation is more sensitive to large surface changes, _i.e._, caused by stronger damage. These authors investigated the damage caused by the 1999 Kocaili Earthquake, Turkey, and compared it with information from field survey. For the 1999 Chi-Chi Earthquake (also named Great Taiwan Earthquake) [PERSON] _et al._[77] used ERS-2 SAR imagery to apply both SAR intensity and the interferometric coherence. They found out that the normalized coherence (see Equation (11), Section 2.3.) is much better suited for damage assessment than the normalized intensity correlation (see Equation (12)), as the former enables much better differentiation between damaged and still intact urban constructions. [PERSON] _et al._[92] also investigated the 1999 Chi-Chi Earthquake using ERS-2 SAR imagery. They confirmed the better usability of SAR interferometric coherence compared to the SAR intensity approach for damage assessment. Furthermore, the authors used the pre- and post-event SAR data to derive the land displacement caused by the earthquake using differential SAR interferometry (_cf._ Section 1.3). [PERSON] and [PERSON] [84] used coherence and intensity correlation for assessment of urban damage caused by the 1995 Hyogoken-Nanbu Earthquake, Japan. Damaged areas were detected by using the normalized differences approach explained in Equations (11) and (12). They found out that the similarity of the de-correlation of both aforementioned methods indicates that the major factor of the de-correlation is closely related to interferometric processes, _i.e._, the change of speckle patterns in the complex intensity images. [PERSON] _et al._[78] applied SAR intensity correlation and the coherence focusing on the 1999 Izmit Earthquake, Turkey, as well as on the 2003 Bam Earthquake, Iran. Their research was based on ERS-1/2 and ENVISAT ASAR data, respectively. They reported that the size of the averaging window to calculate coherence and intensity correlation affects the sensitivity of the change detection. The best-suited results were achieved by using a 5 (azimuth) \(\times\) 1 (range) pixel window for multi-looking and a 3 \(\times\) 3 window for the coherence calculation, which summarizes to a spatial resolution of _ca._ 140 m \(\times\) 140 m. Intensity correlation was found to be best suited at a 7 \(\times\) 7 window (_ca._ 140 m \(\times\) 140 m spatial resolution). [PERSON] _et al._[78] found out that the intensity correlation and the coherence detect different kinds of changes on the ground. While the intensity correlation is dominated by changes in the intensity (magnitude) of the SAR backscatter in the time between the two SAR acquisitions, the coherence influenced by differences of the phase between the SAR acquisitions is dominated by changes of the location of scatterers within a pixel, _i.e._, possible displacements due to an event (e.g., an earthquake).