InSAR Principles by Alessandro Ferretti, Andrea Monti-Guarnieri, Claudio Prati,

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When the value of z is determined, it is easy to choose the multiple of 2π to be added to each interferogram: the correct value of the phase will correspond, in fact, to the height value nearest to the estimated one. In order to compute the conditional density we use the coherence maps associated with each interferogram. From the absolute value of the local coherence γ and the number of looks in the interferogram (the number of degrees of freedom in the estimate of Δφ ), it is possible to compute the expression of the PDF of the interferometric phase and thus of the elevation.

Since the locally optimised baseline values compensate not only for orbit indeterminations but for atmospheric distortions too, they are called effective baselines. The need for optimisation procedures would make the implementation of the algorithm cumbersome and very time consuming. For that reason the processing is carried out at two different resolution levels. 4 where the apex specifies one of the NI interferograms. As already mentioned, all these variations are defined with respect to a reference point chosen inside each block.

If now we consider a pair of targets not too far apart (distance less than, say, 1 km), it is usually possible to estimate Δv (relative mean velocity) and Δε z (relative elevation error) with a high degree of accuracy. 1 rad2 are common. Moreover, the motion of neighbouring pixels is usually correlated. If this hypothesis is verified, σ 2μ should be low as well. Estimation of (v, ε z) is then obtained by integrating the values of (Δv, Δε z) previously estimated from pairs of neighbouring pixels.