Journal Articles

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http://hdl.handle.net/10204/11487

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Browsing Journal Articles by Author "Abdul Gaffar, MY"

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    Probability of helicopter blade flash interception in search radar
    (2021-12) Berndt, Robert J; Nel, Willem AJ; Abdul Gaffar, MY; O’Hagan, D
    Helicopter main rotor blade flashes in radar measurements are an oft-used feature for target classification. While focus is often placed on being able to detect them, little attention has been given to what is required to ensure that they are reliably and persistently intercepted. Using mathematical analysis and simulation, this paper explores the probability of helicopter blade flash interception in search radar. The effects of radar antenna azimuth beamwidth, scan rate, and waveform on the average probability of intercept for two-bladed helicopter blade flashes (a worst-case scenario) are examined. The results presented provide an upper bound on achievable flash detection performance and can be used to understand and optimize the performance of helicopter classification modes.
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    Quaternion-based transformation for extraction of image-generating Doppler for ISAR
    (2008-10) Abdul Gaffar, MY; Nel, Willem AJ; Inggs, MR
    Inverse synthetic aperture radar (ISAR) is an imaging technique that is dependent on an object’s rotational motion over a coherent processing interval. Maritime vessels and aircraft possess 3-D rotational motion, whereas it is only their ISAR contributing motion that is useful to the ISAR imaging process; the contributing motion consists of the Doppler generating axis and the effective angle of rotation. This letter presents a quaternion-based transformation that converts measured attitude and position data into an object’s Doppler generating axis and effective angular rotation rate. This transformation is significant since it isolates the component of the motion that directly influences the ISAR image. It provides an alternative approach that can be used to understand the causes of blurring of most ISAR images of sea vessels as well to identify good imaging intervals for applications such as cooperative ISAR for radar cross section measurement purposes
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    Selecting suitable coherent processing time window lengths for ground-based ISAR imaging of cooperative sea vessels
    (IEEE, 2009-09) Abdul Gaffar, MY; Nel, Willem AJ; Inggs, MR
    Inverse synthetic aperture radar (ISAR) imaging of sea vessels is a challenging task because their 3-D rotational motion over the coherent processing interval (CPI) often leads to blurred images. The selection of the duration of the CPI, also known as the coherent processing time window length (CPTWL), is critical because it should be short enough to limit the blurring caused by the 3-D rotational motion and long enough to ensure that the desired cross-range resolution is obtained. This paper proposes an algorithm, referred to as the motion-aided CPTWL selector (MACS) algorithm, which selects suitable CPTWLs for ISAR imaging of cooperative sea vessels. The suggested CPTWLs may be used to obtain motion-compensated ISAR images that have the desired medium cross-range resolution and limited blurring due to 3-D rotational motion. The proposed algorithm is applied to measured motion data of three different classes of sea vessels: a yacht, a fishing trawler, and a survey vessel. Results show that longer CPTWLs are needed for larger vessels in order to obtain ISAR images with the desired cross-range resolution. The effectiveness of the CPTWLs, suggested by the MACS algorithm, is shown using measured radar data. The suggested CPTWLs may also be used to select an effective initial CPTWL for Martorella/Berizzi’s optimum imaging selection algorithm when it is applied to measured radar data of small vessels. Lastly, the proposed technique offers significant computational savings for radar cross section measurement applications where a few high-quality ISAR images are desired from long radar recordings.