An Efficient Polyphase Filter Based Resampling Method for Unifying the PRFs in SAR Data

Variable and higher pulse repetition frequencies (PRFs) are increasingly being used to meet the stricter requirements and complexities of current airborne and spaceborne synthetic aperture radar (SAR) systems associated with higher resolution and wider area products. POLYPHASE, the proposed resampling scheme, downsamples and unifies variable PRFs within a single look complex (SLC) SAR acquisition and across a repeat pass sequence of acquisitions down to an effective lower PRF. A sparsity condition of the received SAR data ensures that the uniformly resampled data approximates the spectral properties of a decimated densely sampled version of the received SAR data. While experiments conducted with both synthetically generated and real airborne SAR data show that POLYPHASE retains comparable performance to the state-of-the-art BLUI scheme in image quality, a polyphase filter-based implementation of POLYPHASE offers significant computational savings for arbitrary (not necessarily periodic) input PRF variations, thus allowing fully on-board, in-place, and real-time implementation

Comparison of super-resolution algorithms applied to retinal images

A critical challenge in biomedical imaging is to optimally balance the trade-off among image resolution, signal-to-noise ratio, and acquisition time. Acquiring a high-resolution image is possible; however, it is either expensive or time consuming or both. Resolution is also limited by the physical properties of the imaging device, such as the nature and size of the input source radiation and the optics of the device. Super-resolution (SR), which is an off-line approach for improving the resolution of an image, is free of these trade-offs. Several methodologies, such as interpolation, frequency domain, regularization, and learning-based approaches, have been developed over the past several years for SR of natural images. We review some of these methods and demonstrate the positive impact expected from SR of retinal images and investigate the performance of various SR techniques. We use a fundus image as an example for simulations

Innovative SAR & ISAR Signal Processing

This thesis reports on research into the eld of Synthetic Aperture Radar (SAR) and Inverse Synthetic Aperture Radar (ISAR) signal processing. The contributions of this thesis may be divided into two following parts: A new bistatic 3D near eld circular SAR imaging algorithm was devel- oped. High resolution radar imaging is typically obtained by combining wide bandwidth signals and synthetic aperture processing. High range resolution is obtained by using modulated signals whereas high cross range resolution is achieved by coherently processing the target echoes at dierent aspect angles of the target. Anyway, theoretical results have shown that when the aspect angle whereby the target is observed is suf- ciently wide, high resolution target images can be obtained by using continuous wave (CW) radars [2], therefore allowing to reduce hardware costs. In a similar way, three dimensional radar imaging can be per- formed by coherently processing the backscattered eld as a function of two rotation angles about two orthogonal axes [3].Three dimensional tar- get radar imaging can be eciently obtained by means of a 3D Fourier Transform, when the far-eld (planar wave) approximation holds. Oth- erwise, the wavefront curvature has to be accounted for. For this reason, a new algorithm based on a near eld spherical wave illumination that takes into account the wavefront curvature by adopting a planar piece- wise approximation was designed. This means that the wavefront is as- sumed to be locally planar around a given point on the target. The oper- ator that the algorithm uses for the focusing procedure is a space variant focusing function which aims at compensating the propagation losses and the wavefront curvature. The algorithm has been developed under the Microwave Electronic Imaging Security and Safety Access (MELISSA) project. The system MELISSA is a body scanner whose purpose is the detection of concealed objects. The added value of the system is the capability to provide an electromagnetic image of the concealed objects. The author would like to thank all people that worked at the project, all LabRass colleagues, all people who designed and acquired real data, all people that permitted the drafting of the rst part of this thesis. The developed algorithm was presented in the chapter 1. The goal of this work was the system design concerning the imaging point of view, by simulating and therefore predicting the system performance by means of the developed algorithm. In the chapter 2 was shown how the design was achieved. Finally, in the chapter 3, the results on real data measured in anechoic chamber with a system with characteristics very close to the nal system prototype MELISSA, was presented. A new way of ISAR processing has been dened, by applying the tradi- tional ISAR processing to data acquired from passive radars. Purpose of the ISAR processing is to extract an electromagnetic bi-dimensional im- age of the target in order to determine the main geometric features of the target, allowing (when possible) recognition and classication. Passive radars are able to detect and track targets by exploiting illuminators of opportunity (IOs). In this work of thesis, it will be proven that the same concept can be extended to allow for Passive Inverse Synthetic Aperture Radar (P-ISAR) imaging. A suitable signal processing is detailed that is able to form P-ISAR images starting from range-Doppler maps, which represent the output of a passive radar signal processing. Multiple chan- nels Digital Video Broadcasting - Terrestrial (DVB-T) signals are used to demonstrate the concept as they provide enough range resolution to form meaningful ISAR images. The problem of grating lobes, generated by DVB-T signal, is also addressed and solved by proposing an innovative P-ISAR technique. The second part of this thesis has been developed un- der the Array Passive ISAR adaptive processing (APIS) project. APIS is dened as a multichannel, bi-static single receiver for array passive radar, capable of detecting targets and generating ISAR images of the detected targets for classication purposes. The author would like to thank all people that worked at the project, all LabRass colleagues, all people who designed, built the prototype and acquired real data, all people that per- mitted the drafting of the second part of this thesis. In the chapter 4, the basics on Passive Bistatic Radar (PBR) was brie y recalled, the P-ISAR processor was detailed and the new algorithm per the Grating Lobes Cancellation was presented. In the chapter 5, some numerical results on simulated data was shown, in order to demonstrate the potentiality of the P-ISAR, for the imaging and classication purpose. In fact, by using more than three adjacent channels and by observing the signal for a long time, ner range and cross-range resolutions, respectively, could be achieved. Finally, the obtained results on real data was discussed in the chapter 6

Earth resources, a continuing bibliography with indexes

This bibliography lists 541 reports, articles and other documents introduced into the NASA scientific and technical information system. Emphasis is placed on the use of remote sensing and geophysical instrumentation in spacecraft and aircraft to survey and inventory natural resources and urban areas. Subject matter is grouped according to agriculture and forestry, environmental changes and cultural resources, geodesy and cartography, geology and mineral resources, hydrology and water management, data processing and distribution systems, instrumentation and sensors, and economic analysis

Frequency Diversity for Improving Synthetic Aperture Radar Imaging

In this work, a novel theoretical framework is presented for using recent advances in frequency diversity arrays (FDAs). Unlike a conventional array, the FDA simultaneously transmits a unique frequency from each element in the array. As a result, special time and space properties of the radiation pattern are exploited to improve cross-range resolution. The idealized FDA radiation pattern is compared with and validated against a full-wave electromagnetic solver, and it is shown that the conventional array is a special case of the FDA. A new signal model, based on the FDA, is used to simulate SAR imagery of ideal point mass targets and the new model is used to derive the impulse response function of the SAR system, which is rarely achievable with other analytic methods. This work also presents an innovative solution for using the convolution back-projection algorithm, the gold standard in SAR image processing, and is a significant advantage of the proposed FDA model. The new FDA model and novel SAR system concept of operation are shown to reduce collection time by 33 percent while achieving a 4.5 dB improvement in cross-range resolution as compared to traditional imaging systems

Monostatic Airborne Synthetic Aperture Radar Using Commercial WiMAX Transceivers In the License-exempt Spectrum

The past half-century witnessed an evolution of synthetic aperture radar (SAR). Boosted by digital signal processing (DSP), a variety of SAR imaging algorithms have been developed, in which the wavenumber domain algorithm is mature for airborne SAR and independent of signal waveforms. Apart from the algorithm development, there is a growing interest in how to acquire the raw data of targets’ echoes before the DSP for SAR imaging in a cost-effective way. For the data acquisition, various studies over the past 15 years have shed light on utilizing the signal generated from the ubiquitous broadband wireless technology – orthogonal frequency division multiplexing (OFDM). However, the purpose of this thesis is to enable commercial OFDM-based wireless systems to work as an airborne SAR sensor. The unlicensed devices of Worldwide interoperability for Microwave Access (WiMAX) are the first option, owing to their accessibility, similarity and economy. This dissertation first demonstrates the feasibility of applying WiMAX to SAR by discussing their similar features. Despite the similarities they share, the compatibility of the two technologies is undermined by a series of problems resulted from WiMAX transceiver mechanisms and industrial rules for radiated power. In order to directly apply commercial WiMAX base station transceivers in unlicensed band to airborne SAR application, we propose a radio-frequency (RF) front design together with a signal processing means. To be specific, a double-pole, double-throw (DPDT) switch is inserted between an antenna and two WiMAX transceivers for generating pulsed signal. By simulations, the transmitted power of the SAR sensor is lower than 0dBm, while its imaging range can be over 10km for targets with relatively large radar cross section (RCS), such as a ship. Its range resolution is 9.6m whereas its cross-range resolution is finer than 1m. Equipped with the multi-mode, this SAR sensor is further enhanced to satisfy the requirements of diversified SAR applications. For example, the width of the scan-mode SAR’s range swath is 2.1km, over five times the width of other modes. Vital developed Matlab code is given in Appendix D, and its correctness is shown by comparing with the image of chirped SAR. To summarize, the significance of this dissertation is to propose, for the first time, a design of directly leveraging commercial OFDM-based systems for airborne SAR imaging. Compared with existing designs of airborne SAR, it is a promising low-cost solution

Earth Resources: A continuing bibliography with indexes, issue 40

This bibliography lists 423 reports, articles, and other documents introduced into the NASA scientific and technical information system between October 1 and December 31, 1983. Emphasis is placed on the use of remote sensing and geophysical instrumentation in spacecraft and aircraft to survey and inventory natural resources and urban areas. Subject matter is grouped according to agriculture and forestry, environmental changes and cultural resources, geodesy and cartography, geology and mineral resources, hydrology and water management, data processing and distribution systems, instrumentation and sensors, and economical analysis

Dynamic bandwidth allocation in ATM networks

Includes bibliographical references.This thesis investigates bandwidth allocation methodologies to transport new emerging bursty traffic types in ATM networks. However, existing ATM traffic management solutions are not readily able to handle the inevitable problem of congestion as result of the bursty traffic from the new emerging services. This research basically addresses bandwidth allocation issues for bursty traffic by proposing and exploring the concept of dynamic bandwidth allocation and comparing it to the traditional static bandwidth allocation schemes

The University Defence Research Collaboration In Signal Processing

This chapter describes the development of algorithms for automatic detection of anomalies from multi-dimensional, undersampled and incomplete datasets. The challenge in this work is to identify and classify behaviours as normal or abnormal, safe or threatening, from an irregular and often heterogeneous sensor network. Many defence and civilian applications can be modelled as complex networks of interconnected nodes with unknown or uncertain spatio-temporal relations. The behavior of such heterogeneous networks can exhibit dynamic properties, reflecting evolution in both network structure (new nodes appearing and existing nodes disappearing), as well as inter-node relations. The UDRC work has addressed not only the detection of anomalies, but also the identification of their nature and their statistical characteristics. Normal patterns and changes in behavior have been incorporated to provide an acceptable balance between true positive rate, false positive rate, performance and computational cost. Data quality measures have been used to ensure the models of normality are not corrupted by unreliable and ambiguous data. The context for the activity of each node in complex networks offers an even more efficient anomaly detection mechanism. This has allowed the development of efficient approaches which not only detect anomalies but which also go on to classify their behaviour