Comments: To obtain more information, about topographic height and/or superimposed scatterer, the cylindric symmetry has to be broken. To do so, simply a second image is used, acquired from a slightly different position. To do so, there are two possibilities. First, the same sensor comes back after a while and take the second image. This is called repeat-pass interferometry. The other possibility is to mount a second antenna on the sensor platform and operate both in parallel. This is called single-pass interferometry.