Remote Sensing

Research focus

The Peer review has evaluated this group as Excellent

From the sixties, digital signal processing has been instrumental for great advances in oil prospecting using elastic sources. The group started in 1968 in a continuous cooperation with the Italian national oil company. After 1983, these methodologies have then been applied synergetically to Synthetic Aperture Radar (SAR). In essence, the targets are either insonified from the ground in one case or illuminated with microwaves from space, in the other. The reflected wave field (five dimensional in geophysics, i.e. four for surface source and receiver location plus time) is focused, using multidimensional frequency domain techniques and the physical characteristics of the propagation medium and of the scatterers are determined solving the Inverse Problem. In telecommunications, the medium is known and the message is not; in remote sensing the reciprocal is true. Hence, telecommunications and remote sensing share many concepts. The Communication Processing Group uses these technologies for channel equalization purposes. The Multimedia Processing Group uses tomographic techniques for non destructive controls and works on sequences of optical images from multiple cameras, synergizing many methodological instances. When applied to seismic prospecting, accurate digital signal processing yields methodologies for optimal reconstruction of medium velocity, equalization of target illumination, precise and efficient focusing techniques. Travel times are determined to a fraction of the wavelength. Reflection amplitudes are retrieved as a function of the bistatic angle for elastic impedance inversion, and of the azimuth angle to determine anisotropy and thus the direction of the medium fractures, to predict permeability. The same methodologies are extended to the vastly simpler case of electromagnetic wave propagation. Indeed, when applied to SAR, this synergy has yielded important results as optimal focusing techniques, new radars design, and technologies to identify stable target positions to a meter, and motion to a fraction of a millimeter per year. Nowadays SAR wave fields are only 3D, as bistatic studies are just beginning. The group has proposed important satellite experiments like the ESA-TANDEM, interferometry between two satellites SAR, carried out in 1995. The Permanent Scatterers concept, also invented here, allows removal of atmospheric and orbital disturbances. The results allow monitoring slow landslides, tectonic motion, subsidence, and are highly competitive with respect to millennia old optical leveling. This technology has allowed the discovery that those levees in New Orleans that broke down for the hurricane Katrina were in subsidence for more than one meter, prior to the disaster. In February 2007, following the lead of the patent and the paper published in Nature, the Canadian Space Agency has announced a research project for New Orleans SAR data analysis, in which 23 groups (among them the US Corps, USGS, NASA JPL) will try to emulate what has already been accomplished by our group in Milano. Further, highly detailed Digital Terrain Models can be determined, that in some cases could be competitive with laser scans, to predict which parts of towns are in danger of floods. More recently, as ever reusing past geophysical experience, bistatic SAR focusing has been studied and bistatic passive systems using TV satellites as illuminators. Recently, new radar techniques have been proposed for ESA satellites. Geophysical data processing is most likely to stay technologically ahead of SAR processing, grace to the high computational costs affordable for oil prospecting but prohibitive for SAR. Most research carried out for oil prospecting is proprietary and rarely published in full. SAR processing has led to 186 patents that spun Tele Rilevamento Europa and Aresys (totaling 35 researchers) off the Politecnico. Their principal committing agencies are ENI and the European Space Agency, but also end users, like Civil Protection Agencies, and regions. Regardless of the applications, the group has not been supported by the national Space Agency, Agenzia Spaziale Italiana. In another research subtopic, the estimation of the solar energy potential of building roofing has been the main issue together with its boundary conditions: photovoltaic technologies and costs issues. A critical research overview with national and international academic (INGF, Dresden Technical University) and professional (CGR, NET Nowak Energy & Technology Ltd, Cybercity) laboratories have suggested the investigation of high resolution 3D roofing and building estimation algorithms. The second focus is the monitoring of photovoltaic plants performance and environmental impact: it is based on the analysis of remote sensed images, transmission of in situ data with wireless communications equipments and generation of statistics.

Dipartimento di afferenza

Dipartimento di Elettronica e Informazione (DEI)

Docenti afferenti

Sergio Brofferio (full professor)
Claudio Prati (full professor)
Fabio Rocca (full professor)
Giancarlo Bernasconi (associate professor)
Giuseppe Drufuca (associate professor)
Andrea Monti Gurnieri (associate professor)