Modeling and Processing of Radar Signals for Earth Observation (original) (raw)
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Introduction to Synthetic Aperture Radar (SAR
The synthetic aperture radar principle has been discovered in the early 50 th. Since then, a rapid development took place all over the world and a couple of air-and space-borne systems are operational today. Progress made in technology and digital signal processing lead to very flexible systems useful for military and civilian applications. Radar has proved to be valuable before, because of its day-and-night capability and the possibility to penetrate clouds and rain. Optical instruments however had great advantages in the interpretation of depicted objects. The great wavelength of radar signals limits the achievable resolution in cross range direction of real aperture radar systems. Thus, imaging cannot be realized using static radar systems 1. The idea of SAR was to transmit pulses and store the scene echoes along a synthetic aperture (i.e. the path of the SAR sensor) and to combine the echoes afterwards by the application of an appropriate focussing algorithm. The combination is carried out coherently. As we will see, it is quit easy to understand the basic idea of SAR. We will show also the hardware concept or a SAR system and give an idea for a processing algorithm. 1.0 GENERAL FACTS ABOUT SAR Today, synthetic aperture radar (SAR) plays an important role in military ground surveillance and earth observation. Since the late eighties a couple of SAR-systems have been developed for both space and airborne operation. The underlying radar principle offers advantages compared to competing sensors in infrared or visible spectral area. This chapter describes the field of applications where SAR can be used to gain valuable information. Physical conditions like propagation of electromagnetic waves and scene reflectivity affect the choice of several radar design parameters.
A Tutorial on Synthetic Aperture Radar
IEEE Geoscience and Remote Sensing Magazine, 2013
Synthetic Aperture Radar (SAR) has been widely used for Earth remote sensing for more than 30 years. It provides high-resolution, day-and-night and weather-independent images for a multitude of applications ranging from geoscience and climate change research, environmental and Earth system monitoring, 2-D and 3-D mapping, change detection, 4-D mapping (space and time), security-related applications up to planetary exploration. With the advances in radar technology and geo/bio-physical parameter inversion modeling in the 90s, using data from several airborne and spaceborne systems, a paradigm shift occurred from the development driven by the technology push to the user demand pull. Today, more than 15 spaceborne SAR systems are being operated for innumerous applications. This paper provides first a tutorial about the SAR principles and theory, followed by an overview of established techniques like polarimetry, interferometry and differential interferometry as well as of emerging techniques (e.g., polarimetric SAR interferometry, tomography and holographic tomography). Several application examples including the associated parameter inversion modeling are provided for each case. The paper also describes innovative technologies and concepts like digital beamforming, Multiple-Input Multiple-Output (MIMO) and bi-and multi-static configurations which are suitable means to fulfill the increasing user requirements. The paper concludes with a vision for SAR remote sensing.
Introduction - Background, Goal and Content of the Lecture Series on Polarimetric SAR Interferometry
2007
Scientists and engineers already engaged in the fields of radar surveillance, reconnaissance and scattering measurements, for instance, generally gain their specialist knowledge in Polarimetry by working through scientific papers and specialised literature available on the subject. Usually, this is a time consuming exercise, as it is difficult for a newcomer to collate material especially on Polarimetry but also on interferometry and related subjects. Presently, the treatment of basic Polarimetry concepts, in the currently available literature, lacks a coherent framework of theory, and, moreover, several basic definitions and conventions are not yet unified sufficiently under the light of physical principles. This Lecture Series is an attempt to readdress this problem. The aim of this Lecture Series is to provide a substantial and balanced introduction to the basic theory, scattering concepts, systems and applications typical to polarimetric and interferometric radar reconnaissance and surveillance and to introduce the cutting-edge technologies, new ideas and methodologies as well. The following topics will be addressed: Basics, advanced concepts and applications of both radar Polarimetry and SAR Interferometry, cross track and along track Interferometry, single and dual pass Interferometry, differential interferometry, Interferometry errors and accuracy, polarimetric SAR processing and image analysis, decomposition theorems, polarimetric interferometry and polarimetric-interferometric SAR image analysis, processing principles, calibration, Polarimetric SAR analysis and applications, Digital Elevation Models, realized and future airborne and space-borne systems as Examples E-SAR, SIR-C/X-SAR, SRTM, ERS-1/2, RadarSAT, ENVISAT/ASAR, and CARTWHEEL. 1. BACKGROUND The use of high resolution radar especially SAR is indispensable for surveillance, reconnaissance and remote sensing. Radar Polarimetry and Radar Interferometry are advancing rapidly. Each target is a specific polarization transformer and, therefore, these technologies are increasing the target identification and classification capability decisively. With multi polarization the target fine-structure, target orientation, symmetries and material constituents can be recovered with considerable improvement above that of standard 'amplitude-only' radar. With radar interferometry the target's spatial structure can be explored and differential interferometry, presently, is the most sensitive all weather technique for change detection. In 'Polarimetric Interferometric SAR' it is possible to recover co-registered textural and spatial information simultaneously, including the extraction of ground based stealth targets, the development of Digital Elevation Maps etc. as well. Among surveillance and reconnaissance techniques, the polarimetric & interferometric SAR attracts currently the most appreciable and outranking attention because of its capabilities for 3-D high resolution imaging with abundant additional information Then, by either designing 'Multiple Dual-Polarization Antenna POL-IN-SAR' systems or by applying advanced 'POL-IN-SAR image compression techniques' will result in 'Polarimetric Tomography' which is an important progress in Foliage Penetration Radar and Ground Penetration Radar as well.
Scattering-Based Model of the SAR Signatures of Complex Targets for Classification Applications
International Journal of Navigation and Observation, 2008
The modeling of complex target response in SAR imagery is the main subject of this paper. The analysis of a large database of SAR images with polarimetric and interferometric capabilities is used to accurately establish how the different structural parts of targets interact with the incident signal. This allows to relate the reflectivity information provided by SAR images with specific geometries and to fix variation reflectivity patterns in terms of different imaging parameters such as image resolution, incidence angle, or operating frequency. Most of the used images have been obtained from the SAR simulator of complex targets developed at UPC, which is able to generate realistic data for a wide range of observation and environmental conditions. The result is a precise scattering-based SAR model that opens the door, among others, to an alternative way for reliable geometry retrieval. Under this approach, a novel SAR classification method for ships has been proposed. The preliminary evaluation in simulated scenarios shows a notable classification capability even under strong clutter and ship motion conditions. Due to these promising results, the same methodology is intended to be applied to urban areas. Concerns about possible model limitations and required improvements are preliminarily treated.
2003
Polarimetric Interferometric Synthetic Aperture Radar (SAR) is a recent area of research that has had significant attention from the mid-1990s. This area of research has combined the utility of two SAR technologies: Polarimetric SAR (PolSAR) and Interferometric SAR (InSAR). Polarimetric SAR provides four channels which can be used to determine the polarimetric ellipse, and hence, structural information of the scatterer. Therefore PolSAR is suitable for target recognition and detection applications. InSAR data combines two SAR image data sets acquired from nearly the same perspective. The phase difference between these images provides information about the topography, or changes in the topography between the two image dates. InSAR methods have been used to map terrains, detect environmental changes and determine velocities of moving targets. By combining both technologies, polarimetric InSAR (Pol InSAR) permits distinction between different distributed targets at different elevations. In particular, most current research is investigating the use of this technology for measuring the height of forest, and to help estimate its biomass. Other applications under research include terrain moisture estimation, terrain roughness estimation, and (of more interest in mapping applications) vertical obstruction detection.
Special Issue “Synthetic Aperture Radar (SAR) Techniques and Applications”
Sensors
This editorial of the special issue titled “Synthetic Aperture Radar (SAR) Techniques and Applications”, reviews the nineteen papers selected for publication. The proposed studies investigate different aspects of SAR processing including signal modelling, simulation, image analysis, as well as some examples of applications. The papers are grouped according to homogeneous subjects, then objectives and methods are summarised, and the more relevant results are commented.
Modelling and analysis tools for interferometric SAR observations
2002
A quantitative deformation monitoring using the differential interferometric SAR (DInSAR) technique may be achieved when multiple DInSAR observations and suitable modelling and analysis tools are employed. The paper begins with a description of the main characteristics of the DInSAR data. Then, it discusses a new modelling and filtering strategy, which takes advantage of the specific properties of the DInSAR observations. The core of the procedure is the least squares collocation filtering and prediction, which exploits the correlation properties of the DInSAR data. The proposed procedure was tested on simulated DInSAR data that reproduce the characteristics of a small scale and slow deformation rate subsidence, and that include the main components of the interferometric data: the atmospheric contribution, the phase noise component, and the outliers due to the unwrapping related errors.