Advances in Multidimensional Synthetic Aperture Radar Signal Processing

Synthetic Aperture Radar can be considered nowadays as an established and mature technology to obtain high-resolution two-dimensional reflectivity images of the Earth surface in nearly all weather conditions and independently of the day-night cycle. During a first period, ranging from their conception in the 1950s to the beginning of the 1990s, SAR systems were characterized by a single acquisition channel, and it was proven that this technology allows the observation and characterization of the Earth surface in the microwave region of the electromagnetic spectra. At the beginning of the 1990s, SAR technology started to show its important potential with the availability of multichannel or multidimensional SAR system configurations. Among them, it is worth to mention: interferometric techniques (InSAR), using single-or multiple baselines configurations, polarimetric diversity (PolSAR), or the combination of these approaches called polarimetric SAR interferometry (PolInSAR). It is also important to note that in the recent years, the use of time diversity, in combination with any of the previously introduced multidimensional configurations, has emerged as a new and promising research field to improve the analysis of the areas being imaged, but also the observation and characterization of dynamic processes. The importance and interest on the different multidimensional SAR system configurations is partly due to the increase of the number of radar observables but primarily to the fact that the acquired multidimensional signals are sensitive to different biophysical and geophysical properties of the Earth surface and may then be used for quantitative retrieval purposes. Multidimensional SAR data have been shown to be very useful for the monitoring of the Earth surface in a wide range of applications. The spatial diversity exploited in InSAR configurations makes the exploration of the vertical structure of volumetric scenes possible. The complex correlation coefficient, constructed from two complex SAR images, represents here the most important radar observable. In the last 20 years, the sensitivity of the phase component to the terrain topography has been extensively exploited. The most relevant examples are the STRM mission, which provided, for the first time, the Earth topography at an almost global scale and the future Tandem-X mission, that pursues the same objective, but with an improved accuracy. InSAR has also demonstrated an enormous potential for the monitoring of terrain displacements using differential techniques. The amplitude of the complex correlation coefficient revealed to be very useful in diverse applications, like, for instance, volcano's pyroclastic flows monitoring, study and retrieval of …