Discussion about the DCT/FFT phase-unwrapping algorithm for interferometric applications

After discussing Schofield's fast Fourier transform (FFT) algorithm, a (weighted) discrete-cosine-transform-based (DCT-based) phase-unwrapping (PU) algorithm is described. The algorithm could unwrap some high-phase-variation map which the FFT algorithm could not solve. Although the DCT algorithm is derived from Schofield's FFT PU algorithm, unlike FFT, it avoids the mirroring operation in implementing the boundary conditions so that it has higher efficiency in PU. Furthermore, in order to improve the reliability and noise robustness, we introduce the phase derivative variance (PDV) quality weight extracted from quality map into the DCT algorithm. The unwrapped results of both the computer-simulated and interferometric synthetic aperture radar (IFSAR) data demonstrate that the (weighted) DCT PU algorithm is generally effective, especially in dealing with the high-phase-variation and/or irregular-phase-distribution maps.