Search

Knowledge of the velocity measurement distribution is useful for designing new coherent Doppler systems, for resolving velocity ambiguity, and for optimally combining measurements from multiple receivers and multiple carrier frequencies. In this paper, the effects of pulse-pair averaging and pulse-to-pulse autocorrelation are analyzed for ensembles consisting of up to ten pulse pairs. A formula is presented for the probability distribution of velocity measurements from a single pulse pair. This distribution is nonnormal for all values of the autocorrelation coefficient. In the limit of perfect pulse-to-pulse correlation, single pulse-pair measurements obey a Pearson Type VII distribution which has a higher peak and broader tails than a normal distribution. Second and fourth moments of the multiple pulse-pair measurement distributions are evaluated using a Monte Carlo method. The applicability of perturbation analysis for predicting velocity standard deviation is investigated. In the analysis of Zrnić (1977), it is assumed that perturbations in autocorrelation phase are small compared to the mean phase. Three prediction failure mechanisms are demonstrated through changes in the distribution of the complex autocorrelation coefficient; these occur for both high and low autocorrelation magnitude, and for short ensemble lengths. Measurement distributions from the Monte Carlo method are also used to determine the autocorrelation magnitude necessary to resolve velocity ambiguity using a dual-frequency coherent Doppler sonar. Simulations with a high-fidelity coherent Doppler sonar model show how the distribution of velocity measurements is affected by finite particle concentrations. While velocity standard deviation is insensitive to concentration above a threshold of approximately 1 particle per sample volume, kurtosis exhibits a strong dependence on concentration in the range of 0.1–5 particles per sample volume. [ABSTRACT FROM AUTHOR]

In previous work, we discussed an efficient form of predetection fusion for use as a preprocessing step before tracking on data sets with large sensor networks of low-quality sensors, with particular eye to application in multistatic sonar. This 2-D version (position measurements only) was compared against an optimal (slow) technique. In this work, we present the 4-D (using position and Doppler measurements) and 5-D versions [using position, Doppler, and also aspect-dependent signal-to-noise ratio (SNR) measurements] of predetection fusion. We demonstrate that improved results, in the sense of root mean square error (RMSE) and number of declared targets—and consequently better tracking results—are possible when Doppler measurements and SNR information are incorporated into our algorithm. [ABSTRACT FROM PUBLISHER]

Costas waveforms are a class of waveforms having the form of frequency-hopped pulse trains. When used as a transmit waveform in an active sonar system they may provide superior performance to conventional waveforms such as continuous-wave (CW) and frequency-modulated (FM) pulses, as each Costas waveform provides both range and speed information for a target echo. Matched-filtering identifies individual Costas waveforms from among a set of Costas waveforms that are received. This characteristic allows for more frequent ensonification of a water mass for targets at moderate ranges, giving a higher rate of return echoes for improved target tracking. Alternatively, it offers the potential for overlapping bandwidths and waveform types to be used in a multisonar environment. In this work, the Costas wideband ambiguity, cross- and autocorrelation functions are derived. The range and speed resolutions of Costas waveforms are compared to CW and FM pulse resolutions both via a broadband pulse propagation model and using data obtained during the Defence Research and Development Canada--Atlantic (DRDC Atlantic) Towed Integrated Active-Passive Sonar (TIAPS) deep sea trials in September 2003. Costas waveforms are shown to provide simultaneous range and speed resolution in deep- and shallow-water environments, and Costas waveforms are shown to be individually identifiable at the receiver. The performance of Costas waveforms in reverberation is also briefly examined, and found to be similar to that of FM pulses. [ABSTRACT FROM AUTHOR]