COHERENCE

In this step the following is computed. The (complex) coherence image
is computed, with or without subtraction of the reference phase and
the radarcoded DEM phase. The reference phase is subtracted if there
is a 2d-polynomial in the **products result file** (result of step FLATEARTH). It is
not subtracted if this is not in the **result file** or if the number of
coefficients is set to 0. For a proper estimation of the coherence
map, especially over mountainous areas, the radarcoded DEM phase
should also be subtracted. In this case, the result of step COMPREFDEM
is required in the products result file. This is the default procedure
since v4.01.

The complex coherence image between two images is defined as:

(1) |

Where:

is the expectation;

is the complex conjugated;

is the complex coherence;

The coherence is defined by and its estimator as:

(2) |

Multilooking can be performed to reduce noise. Usually a ratio of (line:pixel) = 5:1 between the factors is chosen to obtain more or less square pixels (20x20 for factors 5 and 1). (The resolution decreases of course if multilooking is applied.)

Data buffering is applied for the memory considerations.