An introduction to the interim digital SAR processor and the characteristics of the associated Seasat SAR imagery

Basic engineering data regarding the Interim Digital SAR Processor (IDP) and the digitally correlated Seasat synthetic aperature radar (SAR) imagery are presented. The correlation function and IDP hardware/software configuration are described, and a preliminary performance assessment presented. The geometric and radiometric characteristics, with special emphasis on those peculiar to the IDP produced imagery, are described

Radar systems for the water resources mission, volume 2

The application of synthetic aperture radar (SAR) in monitoring and managing earth resources was examined. The function of spaceborne radar is to provide maps and map imagery to be used for earth resource and oceanographic applications. Spaceborne radar has the capability of mapping the entire United States regardless of inclement weather; however, the imagery must have a high degree of resolution to be meaningful. Attaining this resolution is possible with the SAR system. Imagery of the required quality must first meet mission parameters in the following areas: antenna patterns, azimuth and range ambiguities, coverage, and angle of incidence

Techniques for ground moving target detection and velocity estimation with multi-channel Synthetic Aperture Radars (SAR)

The main objective of this thesis is the study of a relatively new detection and velocity estimation technique for moving targets in sea scenarios. A Constant False Alarm (CFAR) detector based on fractional Fourier transform and on Displaced Phase Center Antenna (DPCA) has been implemented. For velocity estimation Along-Track interferometry (ATI) and, again, the fractional Fourier transform are used. Additional virtual channels are also studied in addition to standar 2 real channel receiving system. The aim of the thesis is to understand through simulations if such a technique provides improved velocity estimation combined with the detection based on the fractional Fourier transform. L'obiettivo principale di questa tesi è lo studio e l'implementazione nel simulatore della Università Politecnica della Catalogna di una tecnica relativamente nuova di identificazione di oggetti in movimento sulla superficie marina e la stima della velocità. E' stato implementato un identificatore a falso allarme costante basato nella trasformata frazionaria di Fourier. Per la stima della velocità si sono utilizzati l' ATI (Along Track Interferometry) e nuovamente la trasformata frazionaria di Fourier. Si sono anche implementati dei canali virtuali addizionali rispetto ai soli 2 standard canali reali in ricezione. Lo scopo della tesi è di capire attraverso le simulazioni se queste tecniche forniscono una migliore stima della velocità rispetto ad altre tecniche più classich

Waveform Design for MIMO Radar and SAR Application

Remote sensing applications using radar systems require specific signal processing to obtain high resolution for radar imagery. This high resolution is essential in detection and imaging processing and is provided by using synthetic aperture radar (SAR) processing. This chapter describes the application of the multiple-input multiple-output (MIMO) configuration and the orthogonal frequency-division multiplexing (OFDM) concept to overcome some existing limitations with conventional imaging systems as well as to assess the improvements achieved

Non-continuous piecewise nonlinear frequency modulation pulse with variable sub-pulse duration in a MIMO SAR radar system

This paper proposes an implementation of non-continuous piecewise nonlinear frequency modulation (N-PNLFM) signals in MIMO radar which are composed of a sequence of N-PNLFM subpulses. The N-PNLFM subpulse can be divided into three segments, the first and third segment are composed of linear frequency modulation (LFM) waveforms. The LFM waveforms in each N-PNLFM subpulse will be orthogonal in one sequence of our new N-PNLFM signal. A non-linear frequency modulation (NLFM) waveform is in the central component of each N-PNLFM subpulse, the bandwidths of each NLFM waveforms are distributed randomly. Each subpulse can be controlled by different variable parameters in both auto-correlation and cross-correlation functions. In order to suppress the high sidelobes in the new N-PNLFM signal and increase the diversity of signals, each subpulse duration is also distributed randomly. Our proposed PNLFM signals are optimized by applying a particle swarm optimization (PSO) algorithm. Comparing with other PNLFM signals, numerous simulations illustrate that our implementation achieves better performance

A Waveform-Encoded SAR Implementation Using a Limited Number of Cyclically Shifted Chirps

Synthetic aperture radar (SAR) provides high-resolution images of the Earth’s surfaceirrespective of sunlight and weather conditions. In conventional spaceborne SAR, nadir echoescaused by the pulsed operation of SAR may significantly affect the SAR image quality. Therefore,the pulse repetition frequency (PRF) is constrained within the SAR system design to avoid theappearance of nadir echoes in the SAR image. As an alternative, the waveform-encoded SAR conceptusing a pulse-to-pulse variation of the transmitted waveform and dual-focus postprocessing canbe exploited for nadir echo removal and to alleviate the PRF constraints. In particular, cyclicallyshifted chirps have been proposed as a possible waveform variation scheme. However, a largenumber of distinct waveforms is required to enable the simple implementation of the concept.This work proposes a technique based on the Eulerian circuit for generating a waveform sequencestarting from a reduced number of distinct cyclically shifted chirps that can be effectively exploitedfor waveform-encoded SAR. The nadir echo suppression performance of the proposed scheme isanalyzed through simulations using real TerraSAR-X data and a realistic nadir echo model thatshows how the number of distinct waveforms and therefore the system complexity can be reducedwithout significant performance loss. These developments reduce the calibration burden and makethe concept viable for implementation in future SAR systems

Radar Imaging in Challenging Scenarios from Smart and Flexible Platforms

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Opportunistic radar imaging using a multichannel receiver

Bistatic Synthetic Aperture Radars have a physically separated transmitter and receiver where one or both are moving. Besides the advantages of reduced procurement and maintenance costs, the receiving system can sense passively while remaining covert which offers obvious tactical advantages. In this work, spaceborne monostatic SARs are used as emitters of opportunity with a stationary ground-based receiver. The imaging mode of SAR systems over land is usually a wide-swath mode such as ScanSAR or TOPSAR in which the antenna scans the area of interest in range to image a larger swath at the expense of degraded cross-range resolution compared to the conventional stripmap mode. In the bistatic geometry considered here, the signals from the sidelobes of the scanning beams illuminating the adjacent sub-swath are exploited to produce images with high cross-range resolution from data obtained from a SAR system operating in wide-swath mode. To achieve this, the SAR inverse problem is rigorously formulated and solved using a Maximum A Posteriori estimation method providing enhanced cross-range resolution compared to that obtained by classical burst-mode SAR processing. This dramatically increases the number of useful images that can be produced using emitters of opportunity. Signals from any radar satellite in the receiving band of the receiver can be used, thus further decreasing the revisit time of the area of interest. As a comparison, a compressive sensing-based method is critically analysed and proves more sensitive to off-grid targets and only suited to sparse scene. The novel SAR imaging method is demonstrated using simulated data and real measurements from C-band satellites such as RADARSAT-2 and ESA’s satellites ERS-2, ENVISAT and Sentinel-1A. In addition, this thesis analyses the main technological issues in bistatic SAR such as the azimuth-variant characteristic of bistatic data and the effect of imperfect synchronisation between the non-cooperative transmitter and the receiver

Arrayed synthetic aperture radar

In this thesis, the use of array processing techniques applied to Single Input Multiple Output (SIMO) SAR systems with enhanced capabilities is investigated. In Single Input Single Output (SISO) SAR systems there is a high resolution, wide swath contradiction, whereby it is not possible to increase both cross-range resolution and the imaged swath width simultaneously. To overcome this, a novel beamformer for SAR systems in the cross-range direction is proposed. In particular, this beamformer is a superresolution beamformer capable of forming wide nulls using subspace based approaches. SIMO SAR systems also give rise to additional sets of received data, which includes geometrical information about the SAR and target environment, and can be used for enhanced target parameter estimation. In particular, this thesis looks at round trip delay, joint azimuth and elevation angle, and relative target power estimation. For round trip delay estimation, the use of the traditional matched filter with subspace partitioning is proposed. Then by using a joint 2D Multiple Signal Classification (MUSIC) algorithm, joint Direction of Arrival (DOA) estimation can be achieved. Both the use of range lines of raw SAR data and the use of a Region of Interest (ROI) of a SAR image are investigated. However in terms of imaging, MUSIC is not well-suited for SAR, due to its target response not corresponding to the target's true power return. Therefore a joint DOA and target power estimation algorithm is proposed to overcome this limitation. These algorithms provide the framework for the development of three processing techniques. These allow sidelobe suppression in the slant range direction, along with the reconstruction of undersampled data and region enhancement using MUSIC with power preservation.Open Acces