Processing of Synthetic Aperture Radar (SAR) Images

Henri Maître

• Publisher: Wiley-ISTE
• Year: 2013
• Print ISBN: 9781848210240
• eBook ISBN: 9781118623909
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

Synthetic aperture radar provides broad-area imaging at high resolutions, which is used in applications such as environmental monitoring, earth-resource mapping, and military systems.
This book presents the tools required for the digital processing of synthetic aperture radar images. They are of three types: (a) the elements of physics, (b) mathematical models and (c) image processing methods adapted to particular applications.

Chapter 1

The Physical Basis of Synthetic Aperture Radar Imagery ¹

1.1. Electromagnetic propagation

The physics behind radar image formation is complex and involves several different topics. Some deal with electronic components devoted to transmission and reception of the wave, but they will not be discussed here. Other aspects, namely wave propagation and the interaction between microwave frequency waves and materials, are more important for our purposes. These two topics are the subject of this chapter. Electromagnetism obviously underlies both these phenomena and we begin with a review of useful results in this area.

1.1.1. The laws of propagation in homogenous media

1.1.1.1. Basic equations

An electromagnetic wave such as that emitted by radars is characterized at any point in space and at every moment by four vector values:

(electric field),

(electric displacement),

(magnetic induction) and

(magnetic field).

These quantities verify Maxwell’s equations, which in the absence of free charges and current densities are written as [JAC 75]:

In the linear stationary case, the fields, the electric displacement and the magnetic induction are ruled by the following relations:

where

is the permittivity and µ is the permeability. We will consider them as scalar values in this book (they are tensors in the general case of anisotropic dielectrics).

The electric field

and magnetic field

vectors are sufficient to characterize this electromagnetic wave for an unbounded, homogenous, isotropic medium which is free of charges and currents. We will use Maxwell’s equations to show that every component of these fields verifies the wave equation:

[1.1]

We thus observe the electromagnetic energy transmission; v is the propagation velocity of the electromagnetic wave.

By denoting

₀ the vacuum permittivity and μ₀ the vacuum permeability, we deduce c, i.e. the speed of light, as being:

In the general case and in the absence of any charge or current, the relative permittivity

and relative permeability

of the propagation medium are normally used, which makes it possible to express the propagation velocity according to c:

The refractive index n for a propagation medium is defined as:

Note that in non-magnetic media we will deal with µ_r = 1, which leads to

Since the medium is unbounded,

and

are perpendicular to each other at any

and both are perpendicular to the propagation direction

that represents the energy path, which is also called a ray.

If a preferred direction can be specified by convention in the plan (

,

), we will then be able to characterize

(and therefore

) in terms of its polarization, i.e., its orientation with respect to the defined direction.

1.1.1.2. Propagation equation solution

In the presence of an isotropic radiation source

located at

the solution of propagation equation [1.1] at any

point in space is written:

[1.2]

The wave then propagates from the source (homogenous medium) in such a way that the wavefront, i.e., the normal ray surface everywhere in space, is a sphere centered on the source: the propagation between the source and any observer is carried out in a straight line.

In the specific case of satellite systems, the objects impinged by the ...

Table of contents

• Cover
• Title Page
• Copyright
• Introduction
• Chapter 1: The Physical Basis of Synthetic Aperture Radar Imagery
• Chapter 2: The Principles of Synthetic Aperture Radar
• Chapter 3: Existing Satellite SAR Systems
• Chapter 4: Synthetic Aperture Radar Images
• Chapter 5: Speckle Models
• Chapter 6: Reflectivity Estimation and SAR Image Filtering
• Chapter 7: Classification of SAR Images
• Chapter 8: Detection of Points, Contours and Lines
• Chapter 9: Geometry and Relief
• Chapter 10: Radargrammetry
• Chapter 11: Radarclinometry
• Chapter 12: Interferometry
• Chapter 13: Phase Unwrapping
• Chapter 14: Radar Oceanography
• Bibliography
• List of Authors
• Index