HomeChair: John Fay, Naval Undersea Warfare Center, USA
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Saman S Abeysekera, Curtin University of Technology (Australia)
Prabhakar S Naidu, Institute of Science, Bangalore (India)
Yee-Hong Leung, Curtin University of Technology (Australia)
Henry Lew, Defence Science and Technology Organisation (Australia)
By using the acoustic scattering form function, a method for classifying underwater spherical shell targets in an open ocean environment is proposed. The resulting backscatter signal from an incident wideband signal is used to illustrate some of the salient scattering features such as mid-frequency enhancement (MFE). A shell classification technique is then developed. An affine transformation of a template form function is used in the classification scheme. It is shown that the proposed scheme is robust against uncertainties in the material properties and noise.
ic981452.pdf (From Postscript)
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Mahmood R. Azimi-Sadjadi, Colorado State University (U.S.A.)
Chunhua Yuan, Colorado State University (U.S.A.)
JoEllen Wilbur, Coastal Systems Stations (U.S.A.)
Robert J. McDonald, Coastal Systems Stations (U.S.A.)
In processing of sonar data, beamforming process plays a central role in reducing the effects of the surface and bottom reverberation. In shallow water environments where the reverberation is dominant, target detection from the beamformed results is not effective and may lead to significantly high false alarm rate. This paper presents a novel approach for post-processing sonar beamformed imagery in order to improve the detectability of the targets while substantially reducing the occurrence of the false detection. This is done using the recursive high order correlation (RHOC) method which exploits the spatial-temporal correlation between consecutive pings of the beamformed images. Test results on several sets of sonar data show the great efficiency and power of the proposed method especially in very high cluttered environment.
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Gareth J Cook, University of Western Australia (Australia)
Anthony Zaknich, University of Western Australia (Australia)
Characterisation of the shallow water acoustic communications channel involves the analysis of sounding data. Chirp signals have many properties which make them an attractive choice for channel sounding. They are easily generated and channel responses can be processed in the time or frequency domain for channel estimation. In the rapidly varying shallow water environment time domain techniques are most appropriate. In this case weighting windows can be used to reduce clutter in the estimate. A channel sounding experiment is described which employs very simple hardware to generate and record chirp responses for offline processing.
ic981453.pdf (From Postscript) TOP
Ivars P Kirsteins, Naval Undersea Warfare Center (U.S.A.)
Sanjay K Mehta, Naval Undersea Warfare Center (U.S.A.)
John Fay, Naval Undersea Warfare Center (U.S.A.)
Motivated by Thomson's multiple taper spectral estimation technique, we derive a new, robust procedure for automatically separating time series data into its constituent narrowband and broadband components. The new procedure avoids the pitfalls of adaptive notch filters, PCI method, or other similar algorithms, of mistaking and filtering local spectral peaks of thebroadband component as narrowband components by decomposing the data vector into local subbands by a bank of matrix filters. Then in piecewise fashion, the narrowband components are estimated and filtered from each subband using the Principal Component Inverse method. Finally, the filtered components are coherently recombined to obtain the narrowband and broadband time series estimates. Computer simulation results show that the new procedure works well and can have performance close to the clairvoyant Wiener filter.
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Peter K Willett, University of Connecticut (U.S.A.)
Biao Chen, University of Connecticut (U.S.A.)
For quickest detection of a permanent change in distribution of otherwise iid observations, Page's test provides the optimal processor. Page's test has also been applied to the detection of transient (i.e. temporary) changes in distribution; it is easy to implement and has reliable performance, but as applied to the transient problem its optimality is questionable.In this paper we offer an alternative to the Page procedure which we call the iterated generalized sequential probability ratio test, or IGSPRT. While Page's test is itself an IGSPRT, its form and performance are constrained by its reliance on constant thresholds and biases. We demonstrate that with these time-varying, markedly increased detection probabilities are possible. The IGSPRT is easiest to understand and motivate in the Gaussian shift-in-mean problem, and we discuss this in detail; but since that problem is of limited practical interest, we also examine the effect of the IGSPRT in a more realistic situation.
ic981292.pdf (From Postscript) TOP
Michael Papazoglou, Duke University (U.S.A.)
Jeffrey L Krolik, Duke University (U.S.A.)
In previous work, electromagnetic matched-field processing was proposed for estimating aircraft altitude with over-the-horizon radar using a single radar dwell. Although this approach exploits the altitude dependence of unresolved multipath returns in complex delay-Doppler space, its performance suffers in situations where the coherent integration time (CIT) of the radar is short. To overcome this limitation, this paper presents a matched-field estimation approach which uses multiple consecutive dwells on the target. The technique exploits the altitude dependence of dwell-to-dwell shape changes in the complex delay-Doppler multipath return. Monte Carlo simulations results indicate that using short CIT's, moderate signal bandwidth, and a 30 second revisit rate, multi-dwell matched-field estimation can achieve better than 5,000 ft. accuracy after as few as four radar dwells. The results of processing actual radar data for a high flying commercial aircraft of known altitude are presented which serve to validate the technique.
ic981839.pdf (From Postscript) TOP
Matthew C. Bromberg, Radix Technologies (U.S.A.)
Brian G. Agee, Radix Technologies (U.S.A.)
This paper addresses the problem of direction finding for unstructured emitters in environments that contain interference signals with exploitable properties. The CA-JML algorithm, presented here, offers dramatic angle estimation improvement in environments that contain exploitable interference. The performance improvement is equivalent to the removal of the interferers from the environment. The complexity of the algorithm, however is comparable to MUSIC. Even when structured interferers are not present, the CA-JML algorithm can reduce the angle error bias exhibited in MUSIC in challenging environments. The CA-JML algorithm also admits a simple relaxation technique as each emitter is localized, which reduces the probability of angle estimation error due to the presence of ambiguous peaks in the angle objective function.
ic982415.pdf (From Postscript) TOP
Karim Abed-Meraim, University of Melbourne (Australia)
Yingbo Hua, University of Melbourne (Australia)
We address the problem of joint Schur decomposition (JSD) of several matrices. This problem is of great importance for many signal processing applications such as sonar, biomedicine, and mobile communications. We first present a least-squares (LS) approach for computing the JSD. The LS approach is shown to coincide with that proposed intuitively by Haardt et al, thus establishing the optimality of their criterion in the least-squares sense. Following the LS criterion, we then propose new Jacobi-like algorithms that extend and improve the existing JSD algorithms. An application of the new JSD algorithms to multidimensional harmonic retrieval is also presented.
ic981327.pdf (From Postscript) TOP