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Digital archive of theses discussed at the University of Pisa


Thesis etd-03042013-124402

Thesis type
Tesi di dottorato di ricerca
Thesis title
Polarimetric Radar Signal Processing Techniques based on Decomposition Theorems for Detection and Classification of Natural and Man-made Targets
Academic discipline
Course of study
tutor Prof. Dalle Mese, Enzo
  • Classification
  • Data Processing
  • Polarimetry
  • Radar
  • SAR
  • Signal Processing
  • Weather Radar
Graduation session start date
The field of polarimetry has as its object to study the state of polarization of an electromagnetic (e.m.) wave and its changes of state. Radar polarimetry is based on the concept that the knowledge of the behavior of a wave interacting with a target, allows the radar to use not only the whole power re-radiated by the target, but also information not present in traditional radar. In other words, a wave which travels in free space brings with it a large number of information (amplitude, Doppler frequency, phase, direction), among which the polarization, that is, the trajectory described by the electric field vector.
When the wave comes into contact with a target, it is re-radiated and received by the radar with a state of polarization, which may be different from the one used in transmission. In fact, such a change or transformation is related not only to the polarization used in transmission, but also to the geometric and structural characteristics of the object. The main limitation of the radar used in the 70'-80' was due to the fact that they transmitted and received with the same polarization. This means that, using a mono-polarized radar, a change of state of polarization, due to the presence of a target, is not disclosed by the radar itself, causing a considerable loss of information. This suggests that full polarimetric survey and subsequent extraction of information are a valuable aid for the detection and classification of the target.
Indeed, it is thanks to the growth of the theory of radar polarimetry and the phenomenological theory of the target that the design technology of complex equipment has been able to grow up to the design of fully polarimetric radar that makes use of discriminant of polarization states.
The benefits of an e.m. wave polarimetric study are related not only to the detection, classification and recognition of targets, but also to a minimization of the effects of multipath in the radar mapping and tracking in the field of remote sensing and imaging applications.
In this thesis we focus mainly on the applications of radar polarimetry in various fields, and showing the feasibility of new methods of feature extraction, namely scattering matrix decomposition method in support of more traditional polarimetric feature extraction for improved classification for various types of target.
First part of thesis deals with volumetric target simulation and analysis, namely meteorological targets, both airborne and ground-based, and introduces the concept of Polarimetric Target Decomposition, showing how polarimetry, especially in the case of airborne operations, is able to help to detect and classify possible hazards encountered during the flight, or, in the case of ground-based operation, is able to give a enhanced awareness of the structure of the perturbation with a better understanding of the whole picture. In current avionic systems, for example, is impossible to distinguish the type of precipitation, water, snow, hail. Of course, assumptions can be done, i.e., high reflectivity in a zone where temperature is 15-20 degrees below zero is likely to indicate an hailstorm, but we can have no precise information on type of precipitation near and below the melting height (which also depends on season and geographic region). About 70% of the high-reflectivity echoes that pilots see on their radar are non-hazardous (other than causing a decrease in visibility and making runways wet). To determine whether or not a particular “red” echo is hazardous in terms of turbulence and hail and other dangers, the pilot must first know if the atmosphere in which he is flying is conducive to hail and high turbulence. It is worth noting to recall that heavy rain without turbulence is not an issue for the safety of the flight. But even with atmospheric knowledge, a pilot cannot say whether a particular high-reflectivity area is hazardous. Usually, the pilot evades that area, with an increase of costs, time and polluting emissions due to the detour.
In the latter part we describe also the work made in collaboration with TU Delft in the Netherlands using real polarimetric radar data.
The second part of the thesis deals with man-made target polarimetric analysis; we analyzed in particular a marine environment, studying a system of detection of ships responsible of illegal discharges in the sea. While first part of the system deals with the analysis of non-polarimetric data, spill and ship detection, the second part is oriented to the feasibility of polarimetric classification of different ships.