N.J.S. Stacy

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

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Publications (49)49.51 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.
    Radar (Radar), 2013 International Conference on; 01/2013
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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.
    01/2011;
  • 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.
    IET Radar Sonar ? Navigation 07/2010; · 0.92 Impact Factor
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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.
    IET Radar Sonar ? Navigation 05/2010; · 0.92 Impact Factor
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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.
    Radar Conference - Surveillance for a Safer World, 2009. RADAR. International; 11/2009
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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.
    Radar Conference - Surveillance for a Safer World, 2009. RADAR. International; 11/2009
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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.
    Radar, 2008 International Conference on; 10/2008
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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.
    Synthetic Aperture Radar (EUSAR), 2008 7th European Conference on; 07/2008
  • 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.
    Synthetic Aperture Radar (EUSAR), 2008 7th European Conference on; 07/2008
  • 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.
    Synthetic Aperture Radar (EUSAR), 2008 7th European Conference on; 07/2008
  • 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.
    Synthetic Aperture Radar (EUSAR), 2008 7th European Conference on; 07/2008
  • L. Rosenberg, N.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.
    Radar Conference, 2008. RADAR '08. IEEE; 06/2008
  • A.S. Goh, M. Preiss, D.A. Gray, N.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.
    Geoscience and Remote Sensing Symposium, 2007. IGARSS 2007. IEEE International; 08/2007
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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.
    Geoscience and Remote Sensing Symposium, 2007. IGARSS 2007. IEEE International; 08/2007
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    M. Preiss, D.A. Gray, N.J.S. Stacy
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    ABSTRACT: In repeat-pass interferometric synthetic aperture radar (SAR), man-made scene disturbances are commonly detected by identifying changes in the mean backscatter power of the scene or by identifying regions of low coherence. Change statistics such as the sample mean backscatter-power ratio and the sample coherence, however, are susceptible to high false-alarm rates unless the change in the mean backscatter power is large or there is sufficient contrast in scene coherence between the changed and unchanged regions of the image pair. Furthermore, as the sample mean backscatter-power ratio and sample coherence measure different properties of a SAR image pair, both change statistics need to be considered to properly characterize scene changes. In this paper, models describing the changed and unchanged regions of a scene are postulated, and the detection problem is expressed in a Bayesian hypothesis-testing framework. Forming the log-likelihood ratio gives a single sufficient statistic, encoding changes in both the coherence and the mean backscatter power, for discriminating between the unchanged- and changed-scene models. The theoretical detection performance of the change statistic is derived and shows a significant improvement over both the sample mean backscatter-power ratio and sample coherence change statistics. Finally, the superior detection performance of the log-likelihood change statistic is demonstrated using experimental data collected using the Defence Science and Technology Organisation's Ingara X-band airborne SAR
    IEEE Transactions on Geoscience and Remote Sensing 09/2006; · 3.47 Impact Factor
  • M. Preiss, N.J.S. Stacy
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    ABSTRACT: Not Available
    Geoscience and Remote Sensing Symposium, 2005. IGARSS '05. Proceedings. 2005 IEEE International; 08/2005
  • N.J.S. Stacy, D. Crisp, A. Goh, D. Badger, M. Preiss
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    ABSTRACT: Not Available
    Geoscience and Remote Sensing Symposium, 2005. IGARSS '05. Proceedings. 2005 IEEE International; 08/2005
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    ABSTRACT: The Ingara airborne multi-mode X-Band imaging radar system developed by DSTO has been upgraded to a fully polarimetric collection capability with a 600 MHz bandwidth. The initial trial of the upgraded system in December 2002 included the collection of synthetic aperture radar data sets of a calibration scene including interferometric repeat passes. The application of calibration techniques to the data yields a measured channel cross talk less than -30 dB.
    Geoscience and Remote Sensing Symposium, 2003. IGARSS '03. Proceedings. 2003 IEEE International; 08/2003
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    ABSTRACT: The Global Hawk high altitude endurance unmanned aerial vehicle was deployed to Australia in April 2001 for six weeks. The system conducted eleven missions with the focus on maritime surveillance. This was the culmination of two years collaboration between the United States and Australia which included development of three new sensor modes, sensor control and exploitation techniques to efficiently perform surveillance with a system primarily developed for the reconnaissance role. The paper describes the Australian contribution to the Global Hawk deployment. It describes the sensor, system integration, system control, mission management and ground element challenges presented by shifting the operational focus from reconnaissance to surveillance.
    Information, Decision and Control, 2002. Final Program and Abstracts; 03/2002
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    ABSTRACT: The Global Hawk system is a high altitude endurance unmanned aerial vehicle developed under the United States Air Force Advanced Concept Demonstrator program primarily as a reconnaissance system for use against fixed and mobile targets. The Global Hawk system deployed to Australia in April 2001 for six weeks and in this period conducted 11 missions with the focus on maritime surveillance. The Australian deployment was the culmination of two years collaboration between the United States and Australia that included modifications to the radar sensor, system control and exploitation to support a surveillance focus. This paper presents aspects of the Australian contribution to the Global Hawk deployment including the rationale behind the sensor modifications and employment that achieved a surveillance capability with a system primarily designed for land reconnaissance.
    Geoscience and Remote Sensing Symposium, 2002. IGARSS '02. 2002 IEEE International; 02/2002

Publication Stats

287 Citations
49.51 Total Impact Points

Institutions

  • 2008
    • Defence Science and Technology Organisation (DSTO)
      Canberra, Australian Capital Territory, Australia
  • 1998
    • University of Illinois, Urbana-Champaign
      • Department of Electrical and Computer Engineering
      Urbana, IL, United States
  • 1991–1993
    • Cornell University
      • Department of Astronomy
      Ithaca, New York, United States
    • Brown University
      • Department of Geological Sciences
      Providence, RI, United States
  • 1990
    • National Astronomy and Ionosphere Center
      • The Arecibo Observatory
      Arecibo, Arecibo, Puerto Rico