Tutorial HD-3: SAR Tomography: Basics and Applications

Presented by: Gianfranco Fornaro and Fabrizio Lombardini
1 CNR-IREA, Italy
2 University of Pisa, Italy

Thanks to the capability of providing direct physical measurements, synthetic aperture radar (SAR) Interferometry allowing generation of topographic maps, accurate localization of ground scatterers, and monitoring of possible displacements to a mm/year order, is one of the techniques that have most pushed the applications of SAR to a wide range of scientific areas, and it has provided significant returns to our society in terms of improvements in the risk monitoring.

SAR images relative to a same scene and suitable for interferometric processing are today acquired regularly, available for most of the Earth, and their number is exponentially growing. Archives associated to SAR spaceborne sensors are filled by data collected with time and observation angle diversity (multipass-multibaseline data); moreover, current system trends in the SAR field involve clusters of cooperative formation-flying satellites with capability of multiple simultaneous acquisitions (bistatic and multistatic SAR sensors), airborne systems with multibaseline acquisition capability in a single pass are also experimented, and unmanned air vehicles with capability of differential monitoring of rapid phenomena are incoming. In parallel, developments are underway of processing techniques, evolutions of the powerful SAR Interferometry, aimed at fully exploiting the information lying in such huge amount of multipass-multibaseline data, to produce new and/or more accurate measuring functionalities.

Focus of this tutorial is on processing methods that, by coherently combining multiple SAR images at the complex data level, differently from phase-only Interferometry, allow improved or extended imaging and differential monitoring capabilities, in terms of accuracy and unambiguous interpretation of the measurements.

The tutorial will cover interrelated techniques that have been shaping in the recent years an emerging branch of SAR interferometric remote sensing, that can be termed SAR Tomography, which is playing an important role in the development of next generation of SAR products and will enhance the application spectrum of SAR systems in Earth observation.

These techniques are: 1) Multibaseline Tomographic Separation of elevation layover scatterers, to locate different discrete scatterers interfering in the same pixel in complex surface geometries causing signal garbling; 2) Multibaseline Tomographic full 3D Imaging of volumetric scatterers, to provide a profiling of the scattering distribution also along the elevation direction for unambiguous extraction of physical and geometrical parameters in low frequency SARs; 3) Multipass Differential-Tomographic 4D (3D+velocity) Imaging of multiple layover scatterers with slow deformation motions, a very recent and promising multidimensional imaging mode crossing the bridge between Differential Interferometry and Multibaseline Tomography.

Basic concepts and processing techniques of coherent SAR data combination for SAR Tomography will be described in the array processing i.e. spatial spectral estimation framework, Fourier based, and of super-resolution kind (adaptive, a priori information-based, and model-based). A number of experimental results obtained with real data, multibaseline single-pass and multipass airborne, and multipass spaceborne, in X-, C-, L-, and P-band, over infrastructure, urban and forest areas, will be presented and discussed to show current and potential future achievements of these emerging techniques.

A general basic knowledge of standard SAR Interferometry is useful for fruitfully attending the tutorial.


Gianfranco Fornaro graduated, cum laude, in Electronic Engineering at the University of Napoli in 1992 and received the Ph.D. degree in Telecommunications in 1997. Since 1993 he has been with the "Istituto per il Rilevamento Elettromagnetico dell'Ambiente (IREA)" of the Italian National Research Council (CNR) where he currently holds the position of Senior Researcher. He has taught courses related to signal communication in several Universities located in south Italy. Dr Fornaro has been visiting scientist at the German Aerospace Center (DLR), at Politecnico of Milano and invited lecturer at the Istituto Tecnologico de Aeronautica (ITA) in Sao José dos Campos (Brazil), at RESTEC (Tokyo) and at the International radar/SAR Summer School in Bonn (Germany). His main research interests regard the signal processing field with applications to airborne and spaceborne Synthetic Aperture Radar (SAR) data processing, including motion compensation, SAR interferometry, differential SAR Interferometry and tomography. He has been chairman and tutorial lecturer in several conference sessions of the IEEE Geoscience and Remote Sensing Society and he has authored about sixty papers in ISI journals. In 2005 Dr. Fornaro served as guest editor of the "Advances in Interferometric SAR processing" special issue of the EURASIP Journal on Applied Signal Processing (JASP) and in 1997 was awarded the Mountbatten Premium by the Institution of Electrical Engineers (IEE).

Fabrizio Lombardini received the Italian Laurea degree, with honors, in electronic engineering and the PhD degree in telecommunication engineering from the University of Pisa, Italy, in 1993 and 1997, respectively. He was then granted by the EU a Marie Curie Fellowship of the Training and Mobility of Researchers (TMR) Program, which he spent as Postdoctoral Researcher at the Department of Electronic and Electrical Engineering of University College London, U.K., from 1998 to 1999. Then, he joined the Department of Information Engineering of University of Pisa, where he currently holds the position of Assistant Professor. He is IEEE Member since 1993 and Senior Member since January 2003. He has given lectures at universities and institutions in Italy and abroad, has chaired 12 special sessions on SAR multibaseline/multichannel interferometry/three-dimensional techniques at international conferences, has been guest editor of the EURASIP Journal of Applied Signal Processing special issue on Advances in Interferometric SAR Processing, and lecturer of 4 tutorials on SAR tomography and multidimensional SAR imaging at EUSAR'08, IEEE RadarCon09, IEEE IGARSS'10, and IEEE IGARSS'11. Dr. Lombardini's general interests are in the areas of statistical signal processing, estimation and detection, super-resolution spectral analysis, array processing, and performance bounds evaluation, with application to radar systems and SAR environmental remote sensing. In particular, his research interests include multisensor data fusion and radar detection in non-Gaussian clutter, multibaseline and multifrequency interferometric SAR algorithms and systems, both cross- and along-track, three-dimensional SAR tomography, and differential SAR interferometry. He recently originated the new interferometric mode of differential SAR tomography, and is engaging research on localization in RFID systems.