Surface Displacement Measurement from Remote Sensing Images

6The Interferometric Phase: Unwrapping and Closure Phase

Béatrice PINEL-PUYSSÉGUR¹ , Francesco DE ZAN² and Johann CHAMPENOIS¹

¹CEA, DAM, DIF, Arpajon, France

²Remote Sensing Technology Institute, German Aerospace Center (DLR), Oberpfaffenhofen, Germany

6.1. Introduction

This chapter describes some properties of interferometric phase and the associated processing. Interferometric phase is naturally given as a wrapped number and needs to be unwrapped to obtain a valuable measurement. Besides its use in InSAR, phase unwrapping is a mathematical problem arising in several fields of optics, such as laser interferometry, sonar and nuclear magnetic resonance. In this chapter, only methods derived from the literature on InSAR are described. Historically, phase unwrapping algorithms were applied to single interferograms, as satellite acquisition rates were low. A fundamental property of the unwrapped phase in the spatial domain is that the closure of the phase around a spatial loop is null. This property, called irrotationality, is used by all unwrapping algorithms. The last 20 years have exhibited an unprecedented increase in the amount of data, which has led to the development of 3D phase unwrapping algorithms, the third dimension being time: instead of unwrapping each interferogram separately, the whole time series of interferograms is unwrapped at once. Naturally, the principles used in 2D algorithms were extended in 3D, especially irrotationality. However, in the last 10 years, ...