Analysis And Design Of A Synthetic Aperture Radar (SAR) System

CHAPTER ONE

1.0                                                        INTRODUCTION

1.1                                           BACKGROUND OF THE STUDY

The Synthetic Aperture Radar (SAR) is convenient for giving information about earth’s surface by using the respective motion between antenna and its target (Rajamani et al., 2014). In various applications like automatic target detection, surface surveillance, mine detection etc. the SAR images provide very important information. In SAR imagery, one of the main problems is that the image textures are usually contaminated with multiplicative speckle noise which is due to coherent radiation in the process of imaging (Deepika et al., 2015). The texture present in the images usually contains important information about the scene. The objective of despeckling method is to remove speckle noise and to protect all textural features in the SAR images (Murali et al., 2014).

Synthetic Aperture Radar (SAR) is a type of radar which is used for all-weather and all-time high resolution aerial and space based imaging of terrain. The term all-weather means that an image can be acquired in any weather conditions like clouds, fog or precipitation etc. and the term all- time means that an image can be acquired during day as well as night.

1.2      AIM AND OBJECTIVES OF THE STUDY

The Synthetic Aperture Radar (SAR) images are important application of optical satellite images because of its ability to operate in any weather conditions.  This work is aimed at studying the analysis and design of a synthetic aperture radar system (SAR).

The objectives of the study are:

1. To carry out System-Level Design and Analysis
2. Modeling and Simulation of a Synthetic Aperture Radar System along with the Implementation of the signal processor for SAR using a TI C6416 DSP.

• To study the workings of Synthetic Aperture Radar (SAR)

1.3      SCOPE OF THE STUDY

SAR is a radar imagery technique provides important data regarding to earth’s surface or subsurface. SAR is an active, day/night and all-weather remote sensing system. This study covers the analysis and design of a synthetic aperture radar system (SAR). The overall study consisted of basic understanding of radar concepts, various types of radar systems, radar principles, waveform design and analysis, signal processing techniques, SAR system level design considerations, SAR processing and image formation.

1.4      SIGNIFICANCE OF THE STUDY

Synthetic aperture radar is an extensive research area in the field of radar. Being used for imaging from air or from space, it has its applications in many important areas like defense, environmental monitoring and earth observations, etc. This importance of SAR was the motivation behind the selection of this project.

1.5        APPLICATIONS OF SAR

This section discusses a few of the applications for synthetic aperture radar. The applications increase rapidly as new technologies and innovative ideas are developed. While SAR  is often used because of its all-weather, day-or-night imaging capability, it also finds application because it renders a different view of a “target,” with synthetic aperture radar being at a much lower electromagnetic frequency than optical sensors.

Targeting , Reconnaissance, and Surveillance

Many applications for synthetic aperture radar are for targeting, reconnaissance, and surveillance. These applications are driven by the military’s need for all-weather, day-and-night imaging sensors. SAR can provide sufficiently high resolution to distinguish terrain features and to recognize and identify selected man made targets.

On the Oceans

Most of the man-made illegal or accidental spills are well visible on radar images. Ships can be detected and tracked from their wakes. Also natural seepage from oil deposits can be observed. They provide hints to the oil industries. Scientists are studying the radar backscatter from the ocean surface related to wind and current fronts, to eddies, and to internal waves. In shallow waters SAR imagery allows to infer the bottom topography. The topography of the ocean floor can be mapped using the very precise – ERS Altimeter, because the sea bottom relief is reflected on the surface by small variations of the sea surface height.

The ocean waves and their direction of displacement can be derived from the ERS SAR sensor operated in “Wave Mode”. This provides input for wave forecasting and for marine climatology. At high latitudes, SAR data is very useful for regional ice monitoring. Information such as ice type and ice concentration can be derived and open leads detected. This is essential for navigation in ice-infested waters.

Treaty Verification and Nonproliferation

The ability to monitor other nations for treaty observance and for the nonproliferation of nuclear, chemical, and biological weapons is increasingly critical. Often, monitoring is possible only at specific times, when overflights are allowed, or it is necessary to maintain a monitoring capability in inclement weather or at night, to ensure an adversary is not using these conditions to hide an activity. SAR provides the all-weather capability and complements information available from other airborne sensors, such as optical or thermal-infrared sensors.

Interferometry (3-D SAR)

Interferometric synthetic aperture radar (IFSAR) data can be acquired using two antennas on one aircraft or by flying two slightly offset passes of an aircraft with a single antenna. Interferometric SAR can be used to generate very accurate surface profile maps of the terrain. IFSAR is among the more recent options for determining digital elevation. It is a radar technology capable of producing products with vertical accuracies of 30 centimeters RMSE. Not only that, but IFSAR provides cloud penetration, day/night operation (both because of the inherent properties of radar), wide-area coverage, and full digital processing. The technology is quickly proving its worth.

On the Land

The ability of SAR to penetrate cloud cover makes it particularly valuable in frequently cloudy areas such as the tropics. Image data serve to map and monitor the use of the land, and are of gaining importance for forestry and agriculture.

1. Geological or geomorphological features are enhanced in radar images thanks to the oblique viewing of the sensor and to its ability to penetrate – to a certain extent – the vegetation
2. SAR data can be used to georefer other satellite imagery to high precision, and to update thematic maps more frequently and cost-effective, due to its availability independent from weather

• In the aftermath of a flood, the ability of SAR to penetrate clouds is extremely useful. Here SAR data can help to optimize response initiatives and to assess

Navigation, Guidance, and Moving Target Indication

Synthetic aperture radar provides the capability for all-weather, autonomous navigation and guidance. By forming SAR reflectivity images of the terrain and then by correlation of the SAR image with a stored reference (obtained from optical device or a previous SAR image), a navigation update can be obtained. Position accuracies of less than a SAR resolution cell can be obtained. SAR may also be used to guidance applications by pointing or “squinting” the antenna beam in the direction of motion of the airborne platform. In this manner, the SAR may image a target and guide a munition with high precision.

The motion of a ground-based moving target such as a car, truck, or military vehicle, causes the radar signature of the moving target to shift outside of the normal ground return of a radar image. New techniques have been developed to automatically detect ground-based moving targets and to extract other target information such as location, speed, size, and Radar Cross Section (RCS) from these target signatures.

1.6                                              BENEFIT OF USING  SAR

The primary reason of using SAR is that the quality of image does not depend on weather or light conditions and images can be taken at any part of the day and in any weather. An optical imaging device (e.g. a camera) cannot be used for aerial imaging of earth surface during night or when there is fog or clouds. Hence, synthetic aperture radars have an advantage over optical imaging devices.

1.7     DEFINITION OF TERMS

Radar: This is a system for detecting the presence, direction, distance, and speed of aircraft, ships, and other objects, by sending out pulses of radio waves which are reflected off the object back to the source.

Navigation: The process or activity of accurately ascertaining one’s position and planning and following a route.

weather condition: The atmospheric conditions that comprise the state of the atmosphere in terms of temperature and wind and clouds and precipitation.