In this paper, we examine the role of polarimetry in synthetic aperture radar (SAR) interferometry. We first propose a general formulation for vector wave interferometry that includes conventional scalar interferometry as a special case. Then, we show how polarimetric basis transformations can be introduced into SAR interferometry and applied to form interferograms between all possible linear combinations of polarization states. This allows us to reveal the strong polarization dependency of the interferometric coherence. We then solve the coherence optimization problem involving maximization of interferometric coherence and formulate a new coherent decomposition for polarimetric SAR interferometry that allows the separation of the effective phase centers of different scattering mechanisms. A simplified stochastic scattering model for an elevated forest canopy is introduced to demonstrate the effectiveness of the proposed algorithms. In this way, we demonstrate the importance of wave polarization for the physical interpretation of SAR interferograms. We investigate the potential of polarimetric SAR interferometry using results from the evaluation of fully polarimetric interferometric shuttle imaging radar (SIR)-C/X-SAR data collected during October 8-9, 1994, over the SE Baikal Lake Selenga delta region of Buriatia, Southeast Siberia, Russia.

Polarimetric SAR interferometry

We propose a theoretically and practically improved density-based, hierarchical clustering method, providing a clustering hierarchy from which a simplified tree of significant clusters can be constructed. For obtaining a “flat” partition consisting of only the most significant clusters (possibly corresponding to different density thresholds), we propose a novel cluster stability measure, formalize the problem of maximizing the overall stability of selected clusters, and formulate an algorithm that computes an optimal solution to this problem. We demonstrate that our approach outperforms the current, state-of-the-art, density-based clustering methods on a wide variety of real world data.

Density-based clustering based on hierarchical density estimates

본 논문에서는 인공 신경망의 일종인 Extreme Learning Machine의 학습 알고리즘을 기반으로 하여 노이즈에 강한 특성을 보이는 퍼지 집합 이론을 이용한 새로운 패턴 분류기를 제안 한다. 기존 인공 신경망에 비해 학습속도가 매우 빠르며, 모델의 일반화 성능이 우수하다고 알려진 Extreme Learning Machine의 학습 알고리즘을 퍼지 패턴 분류기에 적용하여 퍼지 패턴 분류기의 학습 속도와 패턴 분류 일반화 성능을 개선 한다. 제안된 퍼지 패턴 분류기의 학습 속도와 일반화 성능을 평가하기 위하여, 다양한 머신 러닝 데이터 집합을 사용한다.

Extreme Learning Machine 기반 퍼지 패턴 분류기 설계

This is a book review of 'The Micro-Doppler Effect in Radar' by V. C. Chen. Artech House, 16 Sussex Street, London, SW1V 4RW, UK. 2011. 290pp + diskette. Illustrated. £90. ISBN 978-1-60807-057-2.

'The Micro-Doppler Effect in Radar' by V.C. Chen

The Self-Organizing Map (SOM) algorithm has attracted a great deal of interest among researches and practitioners in a wide variety of fields. The SOM has been analyzed extensively, a number of variants have been developed and, perhaps most notably, it has been applied extensively within fields ranging from engineering sciences to medicine, biology, and economics. We have collected a comprehensive list of 5384 scientific papers that use the algorithms, have benefited from them, or contain analyses of them. The list is intended to serve as a source for literature surveys. The present addendum contains 2092 new articles, mainly from the years 1998-2002. We have provided a keyword index to help finding articles of interest, and additionally a modern automatically constructed variant of a thematic index: a WEBSOM interface to the whole article collection of years 1981-2000. The SOM of SOMs is available at http://websom.hut.fi/websom/somref/search.cgi for browsing and searching the collection.

Bibliography of Self-Organizing Map SOM) Papers: 1998-2001 Addendum

This paper describes a processing technique for combining stepped-frequency waveforms efficiently to obtain higher range resolution. Essentially this method involves the reconstruction of a wider portion of the target's reflectivity spectrum by combining the individual spectra of the transmitted narrow-bandwidth pulses in the frequency domain. This paper describes the signal processing steps involved, and shows simulation results which validate and illustrate the method.

Stepped-frequency processing by reconstruction of target reflectivity spectrum

This paper demonstrates a method to produce high resolution SAR images using stepped-frequencies. An advantage of the stepped-frequency approach is the reduction of the instantaneous bandwidth and sampling rate requirements of the radar system, as well as the possibility of skipping frequencies that might be corrupted due to external interfering frequency sources. The technique described involves the construction of a wide-bandwidth chirp pulse produced from a burst of narrow-bandwidth chirp pulses transmitted at stepped-frequency intervals. A description of this technique is given and simulation results are shown.

High resolution SAR processing using stepped-frequencies

Radio frequency interference (RFI) suppression in SAR images often requires a great amount of computation. The authors describe how significant computational savings can be achieved by integrating the RFI suppression stage, implemented with a least-mean-squared (LMS) adaptive filter, with the range compression stage of the range/Doppler SAR processing algorithm.

Efficient RFI suppression in SAR using LMS adaptive filter integrated with range/Doppler algorithm

Recent developments involving the orthogonal frequency division multiplexing (OFDM) structure call for new potentials in radar. In this paper, a novel wideband OFDM based waveform is presented and the high range resolution (HRR) processing is derived.We show by means of comparisons with standard wideband waveforms the benefits of this concept. Radial velocities can be retrieved unambiguously and high velocities can be handled at no extra computational effort since the range migration constraint is related to the small pulse bandwidth as opposed to the large synthetic bandwidth. In our analysis, we inspect the impact of Doppler modulation on the processing and give recommendations for improvement in terms of the OFDM parameters. We address the problem caused by a correlation artefact and discuss the risk of intersymbol interference (ISI) typical with OFDM. Lastly, we show that our concept has inherent low probability of detection (LPD) characteristics.

Stepped OFDM radar technique to resolve range and doppler simultaneously

The merit of evolutionary algorithms (EA) to solve convex optimization problems is widely acknowledged. In this paper, a genetic algorithm (GA) optimization based waveform design framework is used to improve the features of radar pulses relying on the orthogonal frequency division multiplexing (OFDM) structure. Our optimization techniques focus on finding optimal phase code sequences for the OFDM signal. Several optimality criteria are used since we consider two different radar processing solutions which call either for single- or multiple-objective optimizations (MOO). When minimization of the so-called peak-to-mean envelope power ratio (PMEPR) single-objective is tackled, we compare our findings with existing methods and emphasize on the merit of our approach. In the scope of the two-objective optimization, we first address PMEPR and peak-to-sidelobe level ratio (PSLR) and show that our approach based on the nondominated sorting genetic algorithm-II (NSGA-II) provides design solutions with noticeable improvements as opposed to random sets of phase codes. We then look at another case of interest where the objective functions are two measures of the sidelobe level, namely PSLR and the integrated-sidelobe level ratio (ISLR) and propose to modify the NSGA-II to include a constraint on the PMEPR instead. In the last part, we illustrate via a case study how our encoding solution makes it possible to minimize the single objective PMEPR while enabling a target detection enhancement strategy, when the signal-to-noise ratio (SNR) metric would be chosen for the detection framework.

Michael Inggs

Papers

Stepped-frequency processing by reconstruction of target reflectivity spectrum

High resolution SAR processing using stepped-frequencies

Efficient RFI suppression in SAR using LMS adaptive filter integrated with range/Doppler algorithm

Stepped OFDM radar technique to resolve range and doppler simultaneously

Design of OFDM radar pulses using genetic algorithm based techniques