On absolute phase determinant ion techniques in SAR interferometry

Cross-track interferometric SAR can provide 3-dimensional radar images. The technique relies on determining the target elevation from the difference in slant range observed by two antennas having, across-track separation. The range differences estimated very precisely using the phase difference observed in an interferogram obtained from the two complex images. A key problem is that the range difference can only be determined to within a multiple of the wavelength, as the phase difference is measured modulo 27r. This paper discusses two different methods to determine the unknown multiple of 2z: l) the split-spectrum algorithm, and 2) the residual delay estimation algorithm. The Split-spectrum algorithm utilizes the carrier frequency dependence of the interferometric phase, as subdividing the available range bandwidth into two bands provides two slightly different interferograms. The phase difference of the interferograms corresponds to an interferogram obtained with a system having a carrier frequency which is the difference between the two band centers. The residual delay estimation method is based on the full bandwidth, onelook images used to formthei nterferogramand involves precision interpolation andcor-egistration steps. Principles are presented, along with possib]e implementations of the algorithms. Principal errcm sources, as well as advantages and disadvantages from a processor design and implernentatio npoint ofvieware also discussed.