초록 ▼

In a method to resolve ambiguities in a phase measurement for application in radar interferometry, a frequency estimation method is used, starting from conjugate complex products of pairs of adjacent pixels in an interferogram. The resolution of these products is subsequently reduced through success

In a method to resolve ambiguities in a phase measurement for application in radar interferometry, a frequency estimation method is used, starting from conjugate complex products of pairs of adjacent pixels in an interferogram. The resolution of these products is subsequently reduced through successive addition or averaging, after which the differential phase of adjacent resolution levels is determined in each resolution level. The sum of the phase differences yields the estimated value for the phase gradient which is then used in a known method, such as the least-squares method, to reconstruct the absolute phase, thus resolving the phase ambiguities. The method according to the invention serves to resolve phase ambiguities in radar interferograms without producing the known distortions produced by the existing methods. The method is also robust at low coherence values as they occur in repeat-pass interferometry where the existing methods fail. The method allows for a simple adaptation to the common local variations in interferogram quality.

대표청구항 ▼

[ What is claimed is:] [1.] A method for resolving ambiguities in a phase measurement in radar interferometry, comprising the steps of:(a) providing radar data of a two-dimensional image matrix including pixels indexed by i and k;(b) forming an interferogram z(i,k) from the radar data;(c) providing

[ What is claimed is:] [1.] A method for resolving ambiguities in a phase measurement in radar interferometry, comprising the steps of:(a) providing radar data of a two-dimensional image matrix including pixels indexed by i and k;(b) forming an interferogram z(i,k) from the radar data;(c) providing a shifter and an adder;(d) forming from the interferogram in the shifter and the adder a first product EQU C.sub.0.sup.i (i,k)=z(i+1,k).multidot.z*(i,k)and a second product EQU C.sub.0.sup.k (i,k)=z(i,k+1).multidot.z*(i,k),wherein z* denotes a complex conjugate of z;(e) providing a multi-resolution unit (3);(f) subsequently reducing resolution of the first product and the second product by N increments in the multi-resolution unit, the step of reducing resolution including at least one ofa step of averaging adjacent pixels anda step of adding adjacent pixels;(g) providing a phase determination unit (4);(h) forming differential phases, between pairs of adjacent resolution levels in the phase determination unit, sequentially according to EQU .delta..sub.N.sup.i,k (i,k)=arg {C.sub.N.sup.i,k (i,k)}, EQU .delta..sub.N-1.sup.i,k (i,k)=arg {C.sub.N-1.sup.i,k (i,k).multidot.C.sub.N.sup.i,k* (i,k)},and in general EQU .delta..sub.n.sup.i,k (i,k)=arg {C.sub.n.sup.i,k (i,k).multidot.C.sub.n+1.sup.i,k* (i,k)},wherein superscript letters i, k indicate that an equation applies to both indices i, k,C.sub.n is a function produced by an nth step of the resolution reduction, and.delta..sub.n.sup.i,k is a differential phase of the function C.sub.n to C.sub.n+1, wheren=1, 2, 3 . . . N;(i) providing a summation unit (5);(j) determining estimated gradient values.gradient..psi.(i,k)of a phase gradient field by adding the differential phases in the summation unit from a lowest resolution level N to a predetermined resolution level n.sub.min ;(k) providing a reconstruction unit (6); and finally(l) reconstructing, in the reconstruction unit, an absolute phase .phi. from the estimated gradient values of the phase gradient field, whereby the ambiguities are resolved.