Tutorial: Introduction to Inverse Synthetic Aperture Radar

Presented by:
Marco Martorella
Department of Information Engineering
University of Pisa, Italy

Course Description:

Inverse Synthetic Aperture Radar (ISAR) is a technique used for reconstructing radar images of targets. Modern tracking radars implicitly offer the system requirements needed for implementing ISAR imaging. ISAR images are obtained by means of a signal processing that can be enabled both on and off-line. Automatic Target Recognition (ATR) systems are often based on the use of radar images because they provide a 2D e.m. map of the target reflectivity. Therefore, classification features that contain spatial information can be extracted and used to increase the performance of classifiers.
This tutorial aims at providing an introduction to ISAR. Specifically, the first part deals with the basic principles of ISAR whereas the second part concerns basic and advanced ISAR techniques. The ISAR system is introduced by defining the radar-target geometry and by considering simple radar concepts. The derivation of the ISAR processor is obtained by defining the signal model and by interpreting it in the Fourier domain. Differences between ISAR and SAR are also highighted in order to better understand ISAR concepts.
Basic and advanced techniques are presented in order to provide an overview of the current methods used for implementing ISAR and improving its performance. In particular, the problem of ISAR image autofocus is analysed in details and several solutions are presented. The time window selection and cross-range scaling problems are also addressed.
The last two topics of this tutorial deal with polarimetric and bistatic/multistatic ISAR, which represent two new frontiers in ISAR imaging. ISAR processors for such systems are defined and their performance are analysed and compared to monostatic and single polarisation ISAR systems.
Several examples with simulations and real data are provided throughout the tutorial in order to demonstrate the effectiveness and potentiality of ISAR imaging.

1. Introduction
1.1 Synthetic Aperture Radar (SAR)
1.2 Inverse Synthetic Aperture Radar (ISAR)
1.3 ISAR system
1.4 Examples of applications

2. Signal modelling
2.1. Radar-target geometry
2.2. Transmitted signal
2.3. Received signal (Time-Frequency representation)
2.4. Radial motion compensation
2.5. Interpretation of the received signal in the Fourier Domain

3. ISAR image reconstruction
3.1. Image formation
3.1.1. Range-Doppler
3.1.2. Polar Reformatting
3.1.3. Back-projection
3.2. Point Spread Function (PSF)
3.3. Image Resolution
3.4. Analogies and differences with SAR

4. ISAR image Autofocus
4.1. Hot Spot (HS) or Prominent Point Processing (PPP)
4.2. Phase Gradient Autofocus (PGA)
4.3. Image Contrast Based Autofocus (ICBA)
4.4. Image Entropy Based Autofocus (IEBA)

5. Cross-range scaling
5.1. Back-projection method
5.2. Chirp estimation method

6. Time window selection
6.1. Max Image Contrast (IC) method
6.2. Ad-hoc techniques for ISAR imaging of ships

7. Polarimetric ISAR
7.1. Concept of multi-polarisation image processing
7.2. Polarimetric ISAR Autofocus
7.2.1. Pol-PGA
7.2.2. Pol-PPP
7.2.3. Pol-ICBA
7.2.4. Pol-IEBA
7.3. Polarimetric decomposition and image interpretation

8. Bistatic/Multistatic ISAR
8.1. Geometry
8.2. Signal modelling
8.3. Image reconstruction
8.4. Analysis of the distortions introduced by time-varying bistatic angles and synchronisation errors

Requirements: Basics of Radar

 

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Instructor Biography:

Marco Martorella was born in Portoferraio (Italy) in June 1973. He received the Telecommunication Engineering Laurea (cum laude) and Ph.D. degrees from the University of Pisa (Italy) in 1999 and 2003, respectively. He became a Postdoctoral Researcher in 2003, a Researcher/Lecturer in 2005 and a permanent Senior Researcher/Lecturer in 2008 at the Department of Information Engineering of the University of Pisa. He has been a regular visitor of the Department of Electrical and Electronic Engineering (EEE) of the University of Melbourne, the Department of Electrical and Electronic Engineering (EEE) of the University of Adelaide and the Department of Information Technology and Electrical Engineering (ITEE) of the University of Queensland since 2001. He has co-authored more than 20 journal papers and 40 conference papers. He has given lectures and seminars in several research institutions in US, Australia, South Africa and Europe and presented a tutorial at the IEE/IEEE 2007 Radar Conference in Australia. His research interests are mainly in the field of radar imaging. He is an IEEE Senior Member.