Amplitude-Aided 3-D Phase Unwrapping for Temporary Coherent Scatterers Interferometry

Spaceborne multitemporal interferometric synthetic aperture radar (MT-InSAR) technique is widely used in mapping large-scale deformation with high precision. As the time series lengthens, radar scatterers with a surface change will suffer from a loss of coherence, denoted as the temporary coherent scatterers (TCSs), which can be identified by analyzing the amplitude time series. However, current amplitude analysis is sensitive to noise, especially for short temporal subsets, which leads to a high probability of false detected candidates. In this article, an amplitude-aided 3-D phase unwrapping (PU) is proposed to achieve a reliable TCS detection. First, the pre-selection of TCS candidates is conducted using two hypothesis tests. Then, an adaptive thresholding approach is proposed to get the relative optimal thresholds for varying lengths of time series. Based on the initial step-times, a hybrid 3-D PU algorithm is developed to jointly separate the noise from the candidates and refine the moments of the step-times. Finally, three application-based taxonomies are given to fuse the TCS temporal subsets and show their different temporal patterns. Experimental results using real TerraSAR-X and COSMO-SkyMed images show that the proposed amplitude-aided 3-D PU has a low probability of false alarming and an increase in the ensemble coherence. The use of different types of TCS would be beneficial to both deformation monitoring and urban change detection.