The last step, correction of the estimation bias, is strictly related to the number of degrees of freedom n used in the estimation. Now the relation between measured and true coherence is known. An example with a given degree of freedom is shown in figure 5 . The correction for all ERS Tandem pairs was performed based on this relation. 8 shows corrected coherence values.
Coherence is almost stable for the whole time-series.
Coherence bias was removed. With a given estimator of coherence, we conclude that correction of the coherence estimation bias is significant only in low coherence areas. Figure  9 illustrates backscattering coefficients and their deviations for several ground cover types. Coherence provides a much better discriminator between different ground cover types. Meteorological data provided by the Swiss Meteorological Office for the BernLiebefeld station.