Research On The Technique Of Interferometric Synthetic Aperture Radar Elevation Mapping

Synthetic aperture radar interferometry (InSAR) was developed since late 1960's. It can provide the information about the digital terrain, the landform distortion and the slow-moving target indication, by employing the phase information of the interferometric data from synthetic aperture radar. The wide and latent applications of InSAR have been achieved in many areas of military and civil researches. For the all-weather, day and night capability, InSAR can create high resolution digital elevation model (DEM) to help people to deal with many terrain mapping difficulties which can't be solved by general means. In this dissertation, the signal processing of elevation measure is systematically studied.Chapter 1 is the introduction of the dissertation. The history of SAR and InSAR technology is outlined. And then based on the mode of radar data acquirement and the placement of radars, three kinds of InSAR systems are discussed. With different InSAR systems, the applications and the developments of InSAR technology are introduced in detail. After the summarization of the current state, the aim and contents of this work are addressed.Chapter 2 deals with the InSAR mechanism in elevation measure. We deduce the formula that denotes the connection of interferometric phase and the terrain elevation. The complex coherence coefficient is used to analysis the statistical characteristic of interferometric phase. The complex phase noise model is discussed. And a new variable is imported to describe the quality of interferometric phase instead of the complex coherence coefficient. At last, the procedure of InSAR elevation measure is briefly presented.Chapter 3 includes two problems:image registration and interferogram generation. Three rules in image registration are given and discussed. The fulfillings of those two problems are studied respectively. With raw date, we obtain the interferogram.Chapter 4 studies the interferogram filtering algorithms based on the wavelet transform. The characteristics of the interferometric phase and the stripes are analyzed to support the necessity that the interferogram filtering should be processed in complex number field. Based on the principle of wavelet transform, we establish the complex wavelet interferometric phase noise model. By the analysis of the wavelet coefficients, we educe the distributing law of the interferometric phase signal and the noise signal. Then a noise reduction algorithm based on discrete wavelet transform (DWT) is introduced. By using the static wavelet transform (SWT), we make an amelioration of this algorithm. The raw data simulations of those two algorithms help us to distinguish the performance of each algorithm with different noise intensity. Based on the analysis of simulation results, a new scheme, which has good performance both in reducing the phase noise and maintaining the continuity of the interferometric strips, is addressed. In addition, a SAR interferogram noise reduction algorithm based on the SNR threshold is proposed to decrease the amount of calculation when deal with the large-scale interferogram. Finally, compared to other niose-filtering algorithms, we make a detailed analysis with raw data simulation.Chapter 5 focuses on the phase unwrapping. The principle of phase unwrapping and the mechanism of the residues generation are introduced. Five pieces of interferogram are selected to exemplify different distribution of residues and help us to analyze their influence to the strips. Among the path-following algorithms, we investigate the Goldstein algorithm and the quality-guided path following algorithm. Aiming at the poor performance of those two algorithms in noisy region, we propose the residue-pairing (RP) algorithm, which can effectively decrease the length of brunch cuts and contract the isolated region especially in noisy region. Among the minimum-norm algorithms, a weighting process which can efficiently weaken the smoothing effect is discussed. However, the weight design of this method neglects the effects caused by residues.A method to quantization the reliability of the interferometric phase by wavelet transform is proposed, and we make an amelioration of the weight design.Chapter 6 deals with the topographic scale of facor, and the orthorecticfication.The DEM of Atna Mountain is given in the end.Chapter 7 summarizes the whole work of this thesis and points out the problems to be solved in the future.