N.J.S. Stacy

Defence Science and Technology Organisation (DSTO), Canberra, Australian Capital Territory, Australia

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Publications (63)59.95 Total impact

  • A.S. Goh · M. Preiss · N.J.S. Stacy
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    ABSTRACT: The application of polarimetric techniques to bistatic SAR data is a topic of current research interest. The Australian Defence Science and Technology Organisation's Ingara multi-mode imaging radar system has previously collected a sizable set of X-band fine-resolution multi-polarimetric bistatic SAR data for research purposes. This paper presents results from a preliminary bistatic polarimetry investigation using the Ingara data which is based on an examination of the correlation between different polarisations: initial observations are presented of the scattering behaviour of a surface target over a wide range of bistatic geometries.
    No preview · Conference Paper · Jan 2013
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    ABSTRACT: PLIS is an airborne synthetic aperture radar designed to be used in conjunction with a passive radiometer to collect microwave data at L-band for the remote sensing of soil moisture. The objective is to collect data to carry out a pre-deployment validation of algorithms for the NASA Soil Moisture Active Passive (SMAP) satellite. Key features of the PLIS radar are described. The ground swath of PLIS is such that the incidence angle ranges from 15 degrees from nadir on the near side of the swath to 45 degrees on the far side, resulting in an almost 3:1 variation in ground range resolution across the swath. Initial investigations into the impact of this on the statistics of backscattered data are presented.
    Full-text · Article · Jan 2011
  • A.S. Goh · M. Preiss · N.J.S. Stacy · D.A. Gray
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    ABSTRACT: Synthetic aperture radar (SAR) operation in a bistatic configuration not only offers various advantages over its now well-established monostatic counterpart but also poses various challenges. As part of a research programme into the potential benefits and challenges of bistatic SAR, the Ingara fully polarimetric X-band airborne imaging radar system, developed and operated by the Australian Defence Science and Technology Organisation, was upgraded to conduct experimental SAR data collections in a bistatic geometry. Initial trials of the new bistatic SAR system were conducted between December 2007 and April 2008: these involved operation of the existing airborne radar in a fine-resolution (600 MHz bandwidth) circular spotlight-SAR mode, in conjunction with a newly developed fully polarimetric stationary ground-based bistatic receiver. These experimental trials produced a set of fully polarimetric simultaneously collected monostatic and bistatic SAR data, collected over a wide range of bistatic angles. Results from a preliminary analysis of the data have been encouraging: focussed fine-resolution imagery has been obtained, indicating the successful maintenance of synchronisation and phase stability between the independent airborne and ground-based systems. Furthermore, interferometric coherence has been demonstrated between single-pass simultaneously collected monostatic and bistatic images from the airborne and ground-based receivers, and between repeat-pass bistatic images from the ground-based receiver collected some 100 min apart. This study gives an overview of the Ingara bistatic SAR system, discusses the experiments and data processing and presents initial experimental results.
    No preview · Article · Jul 2010 · IET Radar Sonar ? Navigation
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    L. Rosenberg · D.J. Crisp · N.J. Stacy
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    ABSTRACT: Robust maritime surveillance with radar requires an accurate description of the backscatter from the sea. An estimated probability distribution of the backscatter is commonly used to determine the threshold for separating targets from clutter at a given false alarm rate. Data collected at medium to high grazing angles by the Defence Science Technology Organisation (DSTO) Ingara fully polarimetric X-band radar demonstrate that the commonly used K-distribution is not always adequate for modelling the probability distribution. This is especially the case for the horizontal polarisation and in regions of high backscatter where target detection can be a problem. An alternative proposed as a more accurate model in this region is known as the KK-distribution. The analysis presented in this study describes this model with the addition of multiple looks and a thermal noise component to produce greater accuracy in the mean and underlying shape. The threshold required to achieve a constant false alarm rate is then studied and compared with the K-distribution.
    Preview · Article · May 2010 · IET Radar Sonar ? Navigation
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    D.J. Crisp · L. Rosenberg · N.J. Stacy · Yunhan Dong
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    ABSTRACT: Performance modelling techniques for maritime radar target detection problems typically make use of a parametric probability distribution for the background ocean backscatter. In this paper, measured X-band sea clutter is analysed by fitting a K-distribution and the variation of its parameters with radar resolution, polarisation, viewing grazing and azimuth angles and ocean wind and wave conditions is examined. Grazing angles lie in the range 10° to 45°. Earlier work has already characterised the variation in the mean of the distribution. Here, the shape parameter ¿ is studied. Surprisingly, it is found that ¿ exhibits a sinusoidal like variation with azimuth angle which is aligned with the direction of the wind waves rather than the swell.
    Preview · Conference Paper · Nov 2009
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    L. Rosenberg · D.J. Crisp · N.J. Stacy
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    ABSTRACT: Robust maritime surveillance with radar requires an accurate description of the backscatter from the sea. An estimated probability distribution of the backscatter is commonly used to determine the threshold for separating targets from clutter at a given false alarm rate. Data collected at medium to high grazing angles by the Defence Science Technology Organisation (DSTO) Ingara fully polarimetric X-band radar demonstrates that the commonly used K-distribution is not always adequate for modelling the probability distribution. This is especially the case for the horizontal polarisation and in regions of high backscatter where target detection can be a problem. An alternative proposed as a more accurate model in this region is known as the KK-distribution. The analysis presented in this paper describes this model with the addition of multiple looks and a thermal noise component to produce greater accuracy in the mean and underlying shape. The threshold required to achieve a constant false alarm rate is then studied and compared with that derived from the K-distribution model.
    Preview · Conference Paper · Nov 2009
  • M.E. Nord · Thomas L. Ainsworth · Jong-Sen Lee · Nick J. S. Stacy
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    ABSTRACT: Compact polarimetry is a technique that allows construction of pseudo quad-pol information from dual-polarization synthetic aperture radar (SAR) systems. Compact polarimetry showed promise of being able to reduce the complexity, cost, mass, and data rate of a SAR system while attempting to maintain many capabilities of a fully polarimetric system. In this paper, we study different transmit/receive configurations to determine which polarimetric configurations allow for superior reconstruction of the fully polarimetric data. We discuss modifications of the original reconstruction algorithm proposed by Souyris , which show potential to better reconstruct fully polarimetric data.
    No preview · Article · Feb 2009 · IEEE Transactions on Geoscience and Remote Sensing
  • David J. Crisp · Ross Kyprianou · Luke Rosenberg · Nick J.S. Stacy
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    ABSTRACT: This document reports on work undertaken at DSTO towards modelling the mean ocean backscatter coefficient at low to medium grazing angles for X-band radar. The particular range of angles used lies within the so-called plateau region where Bragg scattering dominates. The motivation for the work is to consider future maritime radar surveillance from high altitude airborne platforms. The requirement is for a model which takes account of radar polarisation, imaging geometry and ocean surface conditions. In order to assess modelling performance, a comprehensive set of ocean backscatter data was collected using Ingara (DSTOpsilas airborne multi-mode radar system.) Several candidate backscatter models were assessed against this data set and found to be unsuitable. Consequently, a new empirical model was developed which provides a significantly better fit to the measured data than the existing models. This paper reports on the measured data, the creation of the new model and the comparison against the existing models.
    No preview · Conference Paper · Oct 2008
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    ABSTRACT: An upgrade programme to add a bistatic collection capability to the Ingara airborne X-band fully-polarimetric imaging radar has recently been completed, and the first field trials of the new bistatic SAR system were conducted in December 2007. This involved a set of experimental SAR data collections in a bistatic geometry, in which the airborne radar was operated in a fine-resolution (600 MHz bandwidth) circular spotlight-SAR mode, in conjunction with a newly-developed fully-polarimetric stationary ground-based bistatic receiver. These data collections were largely successful, and produced a set of fully-polarimetric bistatic SAR data, collected over a wide range of bistatic angles. In this paper, we give an overview of the Ingara bistatic SAR system, describe the recent bistatic SAR experiment, discuss the techniques employed for processing the data, and present preliminary experimental results.
    No preview · Conference Paper · Oct 2008
  • Luke Rosenberg · David Crisp · Nick Stacy
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    ABSTRACT: Understanding the characteristics of the sea is critical in forming a picture of the sea-clutter as seen by a radar. Current research at the DSTO is interested in the properties of sea-clutter at medium grazing angles, over all azimuth directions, with full polarisation and differing weather conditions. This paper builds on previous work which studied the Doppler spectrum over all azimuth directions using the three component Walker scattering model. An improved model is presented here which includes the aliasing present in low pulse repetition frequency (PRF) data collected using Ingara - the DSTOpsilas X-band synthetic aperture radar (SAR). This enables a large number of data sets to be analysed with differing grazing angles and weather conditions. The goal of this work is to characterise the sea-clutter and improve the fidelity of future analysis into the performance of medium grazing angle target detection algorithms in the maritime environment.
    No preview · Article · Sep 2008
  • Alvin S. Goh · Mark Preiss · Nick J. S. Stacy · Douglas A. Gray
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    ABSTRACT: The Ingara fully-polarimetric X-band airborne imaging radar system has recently been upgraded to conduct experimental SAR data collections in a bistatic geometry. Initial trials of the new bistatic SAR system were conducted in late 2007: these involved operation of the airborne radar in a fine-resolution (600 MHz bandwidth) circular spotlight-SAR mode, in conjunction with a newly-developed fully-polarimetric stationary ground-based bistatic receiver. This paper gives an overview of the Ingara bistatic SAR system, discusses the experiments and data processing, and presents initial experimental results.
    No preview · Conference Paper · Jul 2008
  • Mark Preiss · Nick J. S. Stacy
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    ABSTRACT: In repeat pass interferometric SAR man-made scene changes may be detected by identifying regions of low coherence. The ability to detect such changes however, depends on other sources of decorrelation such as environment effects and baseline decorrelation. Recently a Log Likelihood Change Statistic (LLCS) has been derived by formulating the problem in a Bayesian hypothesis testing framework. In this paper the LLCS is extended to exploit the additional information available in polarimetric SAR imagery. It is shown through simulation and application to experimental data that the fully polarimetric LLCS significantly improves the ability to detect scene changes.
    No preview · Conference Paper · Jul 2008
  • Luke Rosenberg · Nick Stacy
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    ABSTRACT: The performance of Moving Target Indication (MTI) algorithms is an important area of research formaritime surveillance. This paper presents a sea-clutter simulator that incorporates models for the first and second order statistics including the the Doppler spectrum of the sea as measured by the DSTO Ingara airborne radar. By synthesising a number of channels, the sea-clutter model can then be combined with moving targets, thereby allowing modelling of MTI algorithms. For this work, along track interferometry is used to detect simulated moving targets with different polarisations and varying strength sea-clutter. Detection performance is measured using a non-parametric constant false alarm rate detector.
    No preview · Conference Paper · Jul 2008
  • Nick Stacy · Mark Preiss
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    ABSTRACT: The detection of slow moving targets for surveillance applications can be achieved using the phase discrimination properties of Along Track Interferometry (ATI). This paper evaluates ATI in a log likelihood framework to generate receiver operator curves for different scenarios. The results enable the assessment of detection performance as a function of target speed, signal-to-noise ratio, coherency and radar multi-port antenna configurations. The results show the application of the log likelihood approach offers more than an order of magnitude reduction in false alarm rate compared to ATI phase detection and is robust to parameter changes explored in the scenarios used in this analysis.
    No preview · Conference Paper · Jul 2008
  • Luke Rosenberg · Nick J. Stacy
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    ABSTRACT: Doppler analysis of radar sea-clutter is typically performed from a static cliff top location looking out to sea. This constrains the grazing angle to low values and the radar look direction with respect to the wind. Current research at the DSTO is interested in the properties of sea-clutter at medium to high grazing angles, over all azimuth directions, full polarisation and different spatial resolutions. The sea clutter Doppler spectrum investigated in this paper was collected by an airborne platform and analysed using the three component Walker scattering model modified to include Doppler shifts from the moving platform. The modelling results enable the underlying Doppler spectrum and autocorrelation of the sea clutter to be estimated. This will enable future analysis into the performance of medium to high grazing angle target detection algorithms in the maritime environment.
    No preview · Conference Paper · Jun 2008
  • Alvin S. Goh · Mark Preiss · Douglas A. Gray · Nick J. S. Stacy
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    ABSTRACT: The accuracy with which distributed-target polarimetric calibration algorithms estimate crosstalk and the ratio of Tx-to-Rx channel imbalance is compared. The algorithms investigated are minor variants of previously-published algorithms but rederived for notational and definitional consistency. Numerical simulations were used to assess the algorithms' performance in the absence of noise. Results indicate that the imbalance parameter is generally accurately-estimated but that crosstalk estimation accuracy varies greatly.
    No preview · Conference Paper · Aug 2007
  • T.L. Ainsworth · M. Preiss · N. Stacy · J.-S. Lee
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    ABSTRACT: New space-borne polarimetric SAR systems employ, or will employ, dual-pol imaging modes as well as full quad-pol imaging, e.g. PALSAR, RADARSAT-2, TERRASAR-X. Therefore questions arise as to the capabilities (and limitations) of these various dual-pol SAR imaging modes. One novel offshoot of our work on dual-pol SAR image analysis and polarimetric decompositions of dual-pol data was the idea to collect two dual-pol images employing geometry appropriate for parallel repeat-pass interferometry. The polarizations of the dual-pol collections differ, e.g. one is (HH, HV) and the other (VV, VH). Using the example of transmitting either horizontal (H) or vertical (V) polarizations, one collects all four polarimetric channels, but only two per pass. Except for the interferometric repeat-pass nature of the SAR image collections the polarimetric information should be identical to standard quad-pol SAR imagery. The relevant open questions concern the interferometric baseline and temporal decorrelations between the repeat-pass dual-pol images.
    No preview · Conference Paper · Aug 2007
  • D.J. Crisp · N.J.S. Stacy · D.A. Hudson · P.B. Pincus · A.S. Goh
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    ABSTRACT: Fine resolution spotlight synthetic aperture radar (SAR) imagery collected on a circular flight path is used to investigate the variation in ship detection performance with respect to three fundamental radar parameters: the transmit/receive polarisation combination, the incidence angle and the azimuth angle. The polarisation combinations examined are HH, HV, VV, RR and cross-slant 45deg. Three different incidence angles are considered - 50deg, 60deg and 70deg - corresponding to collection geometries for high altitude maritime surveillance systems. Performance is assessed using a simple target-to-background contrast measure. Results are compared with preliminary results from a four component decomposition of the Mueller matrix. While the latter and cross-slant 45deg show promise, in general HH is shown to have the best performance.
    No preview · Conference Paper · Aug 2007
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    ABSTRACT: The overall objective of this paper is to assess SAR compact polarimetry (CP) architectures based on mixed polarization basis measurements allowing for an implementation on satellite at reduced cost. The potential applications include Earth observation or planetary Science. The performance assessment both concerns the level of information preserved in comparison with full polarimetry (FP), and the concurrent space segment complexity. The CP architectures considered here address a mixed basis measurement where the transmitter polarization is either circular or orientated at 45°, and the receivers are at horizontal and vertical polarizations. After a general overview of this CP concept, the paper focuses on a P band option, including FP information reconstruction from CP and assessment of Faraday effects. The FP information reconstruction is shown to perform well at P band (especially regarding the P band HV term which is a key parameter for biomass estimation), although calibration and Faraday corrections remain subjects for further studies.
    No preview · Article · Mar 2007
  • N. J. S. Stacy · M. Preiss · D. Crisp
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    ABSTRACT: The polarimetric characteristics of X-Band sea clutter are investigated using data from the DSTO Ingara airborne radar operating in a circular spotlight geometry. An analysis of the Doppler spectrum as a function of azimuth geometry with respect to the wind direction shows the difference in the surface velocity between the HH and VV scattering components reaches maxima in the upwind and down wind directions and the cross polarized HV channel has very similar Doppler characteristics to the VV channel. The Cloude-Pottier polarimetric decomposition parameters are in agreement with predominantly Bragg signal surface scattering with an additional HH sea spike component in the upwind direction.
    No preview · Conference Paper · Sep 2006