The Study Of The Algorithm Of Phase Unwrapping In Interferometry Synthetic Aperture Radar

InSAR (Interferometric Synthetic Aperture Radar) and D-InSAR (Differential In-SAR) are rapidly developing technologies of space geodesy during the late 20th century, and now are obviously becoming hot research topics in the field of microwave remote sensing. Compared to the other sensors, InSAR possesses many incomparable advantages such as the capability to work all-time under any weather condition, very high spatial resolution and strong penetrability through the ground surface etc. And there are more and more data can be used for us when there are many SAR sensors have been launched by the NASA, ESA, and JAXA etc. It will make a big progress for the InSAR study and application.Two-dimensional phase unwrapping is considered as one of the most important procedures in the data processing and analysis of InSAR. Phase unwrapping is indispensable for the purpose of either creating digital elevation model(DEM) or extracting surface deformation information with the InSAR approach. The achieved accuracy level of DEM or deformation measurements is highly dependent on the accuracy in the unwrapped phases.Although phase unwrapping has been studied for over 20 years in a number of disciplines, unwrapping of noisy interferogram still presents a challenge. Phase unwrapping of InSAR is particularly difficult because of the side-looking configuration that causes shadow, foreshortening, and layover. A number of phase unwrapping algorithms for InSAR have been proposed in recent years, however, none of the existing phase unwrapping algorithms are very satisfactory when the phase is noisy or dense fringes occur.While phase unwrapping algorithms have proliferated over the past twenty years, two main approaches are currently in use. Each is useful only for certain restricted applications. All these algorithms begin with the measured gradient of the phase field, which is subsequently integrated to recover the unwrapped phases. The first category reconstructs the continuous phase surface by a path-based integrating operation, and its typical representatives are the branch-cut, mask-cut and Flynn algorithm. This approaches in interferometric applications incorporated residue identification and cuts to limit the possible integration paths, while a second class using least-squares techniques was developed in the early 1990's. And its typical representatives are the DCT/FFT and PCG algorithm. This approaches conduct phase unwrapping by minimizing the sum of the square of gradient difference between the unwrapped and wrapped phase field. We compare the approaches and find that the residue-cut algorithms are quite accurate but do not produce estimates in regions of moderate phase noise. The least-squares methods yield complete coverage but at the cost of distortion in the recovered phase field.In this thesis we will introduce the two category approaches. For the branch-cut algorithm we will prove that existence of residues is a sufficient but unnecessary condition for the original phase discontinuity, and the true placement of the branch cut is unique. Then a modified method of placing branch cuts which is guided by improved quality map is proposed. The simulation test results will be given.