Coherence

The coherence is a measure for the correlation of the phase information of two corresponding signals and varies in the range of 0 to 1. The degree of coherence can be used as a quality measure because it significantly influences the accuracy of phase differences and height measurements. Bright areas indicate regions of high coherence, whereas dark areas represent low coherence regions.

There are several factors decreasing the coherence. In approximate order:

• Local slope (steep slopes lead to low coherence)
• Properties of the surface being imaged (vegetated or moving surfaces have low coherence).
• Time difference between the passes in an interferogram (long time difference lead to low coherence)
• The baseline (large baselines lead to low coherence)
• Technical details of the generation of the interferogram (poor co-registration or resampling leads to low coherence)