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This paper presents a technique by which a low-cost, minimally-equipped unmanned underwater vehicle (UUV) can localize itself while submerged using acoustic emissions of transiting sources of opportunity (SOOs). The technique provides a bounded estimate of the UUV position and is intended to supplement the on-board Inertial Navigation System (INS). The technique exploits two physical phenomena, the...
This paper presents a technique for extending the bandwidth of chirped active sonar signals. Bandwidth synthesis (BWS) results in improved range resolution, increased signal-to-noise ratio (SNR) and reduced fading due to delay-spread multipath. The approach demonstrated uses a low-order autoregressive (AR) process to model de-chirped segments of the received signal, which are then extrapolated using...
In this paper, we consider the use of synthetic aperture processing for developing completely virtual arrays designed for an operational wavelength other than that of a physical array. In towed array scenarios, we show it is possible to exploit existing array motion to mitigate the effects of main-lobe widening and spatial aliasing when source wavelengths are different from the operational wavelength...
Doppler-sensitive waveforms are often used in shallow water to mitigate high reverberation levels. This paper compares three Doppler sensitive sonar waveforms including coherently-processed pulse trains, uniform frequency combs, and nonuniform co-prime frequency combs in terms of their delay-Doppler responses. It is shown that the use of comb waveforms can reduce Doppler sidelobes without trading...
This paper presents an active sonar waveform that achieves range-Doppler performance similar to a uniform frequency comb, but uses far fewer tones to do so. The trade-off for this reduction in occupied bandwidth is a larger bandwidth extent. Co-prime comb signals consist of tones at non-uniformly spaced frequencies according to a 2-level nested co-prime array structure. Specialized non-matched filter...
The temporal coherence across a given spatial aperture of an HF array can vary over time depending on specific ionospheric conditions. Measurement of the temporal coherence, through measurement of the correlations of eigenvector beamformer wavefronts over time, can inform the coherent integration time (CIT) that should be used in the receiver processing. We show that when the temporal coherence is...
Passive geolocation of a skywave HF source requires accurate estimation of azimuth and elevation angles together with correct ionospheric modeling. Arrays of polarimetric vector sensors have been proposed to reduce the array aperture required for this purpose. However, several factors complicate their application including magneto-ionic raymode splitting resulting in closely-spaced arrivals in both...
This paper concerns estimating the partially coherent signal gain of a large, fully-populated planar HF phasedarray using simulated data from a few widely distributed receive elements. Our approach involves estimating magnitude-squared coherence between sensor elements in order to estimate parameters of a 2-D exponential model for signal decoherence, which, in turn, is used to predict array gain....
This paper presents a continuous active sonar (CAS) waveform which enables high revisit rates and wideband processing gains to be achieved with suppression of range-ambiguous returns. Non-recurrent wideband linear FM signals with circular Costas frequency-staggering across chirp repetition intervals is shown to provide ambiguity functions with good Doppler and range resolution, controllable Doppler...
This paper addresses the estimation of power versus azimuth and elevation using a sparse sensor array. In MIMO radar, clutter and noise field directionality can be measured both from the transmit array and to the receive array. In applications where sparse arrays must be used, however, often substantial ambiguities in the field directionality map occur due to spatial under-sampling and/or sidelobe...
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