Synthetic aperture radar interferometry(8)

Synthetic aperture radar interferometry is an imaging technique for measuring the topography of a surface, its changes over time, and other changes in the detailed characteristics of the surface. By exploiting the phase of the coherent radar signal, interf

during LS unwrapping.For example,unweighted LS squares solutions have been shown to be biased estimators of slope [44].Whether slope biases are introduced for weighted LS depends on the particular implementation of the weighting scheme and on whether steps are taken to compensate,as by iteration or initial slope removal with a low-resolution DEM [45].

Phase unwrapping using branch cuts is a well established and mature method for interferometric phase unwrapping.It has been applied to a large volume of interferometric data and will be used as the algorithm for the shuttle radar topog-raphy mission data processor(see below).Unweighted LS algorithms are not sufficiently robust for most practical ap-plications[30],[41].While weighted LS can yield improved results,the results are highly dependent on the selection of weighting coefficients.The selection of these weights is a problem of similar complexity to that of selecting branch cuts.

d)Other methods:Recently,other promising methods have been developed that cannot be classified as either branch cut or least-squares methods.Costantini[38],[39] developed a method that minimizes the weighted absolute value of the gradient differences

(

,

then

(52)

The noise in the differential interferogram is comparable to

that of the“standard”interferogram,but typically larger by

a factor of two.After scaling the differential absolute phase

value,the noise at the actual RF carrier phase is typically

much larger

than