In this paper various measurements of acoustic time series recorded in the Atlantic over source-to-receiver ranges of 600 to 12 900 m are analyzed. The transmitted source signature with a monitor hydrophone mounted on the source array was also recorded. The signature distortion introduced by propagation effects was treated by the use of single-channel deconvolution. In situations where the Green’s function structure is simple (e.g., direct arrival and surface reflection), single-channel deconvolution gave satisfactory results. When multipath effects (due to interaction with layered bottom sediments) were present, it was difficult to get a good source estimate. A way was developed of perturbing the Green’s functions such that the source estimates were guaranteed to improve. In most cases it was found that very small changes could produce significant improvement in the source estimates. This sensitivity was quantified by using the correlation coefficient. This sensitivity is not to be confused with the well-known fact that the single-channel deconvolution problem is ill-posed. That issue was treated separately.

It is well known that array deformations can distort beam patterns and introduce bearing errors if the beamformer assumes linearity. It is also known that deformed arrays can resolve left-right ambiguities, provided the shape is known. In this work, these two effects are studied for undamped and damped sinusoidally deformed arrays with small deformation amplitudes in the horizontal (x,y) plane only. By use of fixed arc-length separations along the array, the hydrophone (x,y) coordinates are determined numerically and the error in assuming equal x spacing is summarized for a sample array. Array-response patterns are analyzed for two conditions: ͑1͒ when the deformed array shape is assumed linear and ͑2͒ when the deformed array shape is known exactly. Degradations resulting from assuming linearity and the ability to resolve left-right ambiguities are discussed in terms of reduced gain, degraded angular resolution, and bearing errors. Shape-unknown signal-gain degradation ranges to 7 dB at broadside, but is less than 1 dB near endfire. For the shape-known case, signal gain for the true peak is greater than signal gain for the ambiguous peak by up to 9 dB for sources at broadside and to just over 2.5 dB for arrivals near endfire.

This paper investigates the estimation errors induced by noise in the quantification of damped sinusoids with the Pseudo-Wigner Distribution (PWD). A constant amplitude single frequency noise is first considered. This simple model shows how underestimation or overestimation errors depend on the relative phase between signal and noise for a fixed signal-to-noise ratio (SNR). In a second step, cross-terms and noise amplitude fluctuations are identified as the main sources of discrepancy between the theoretical model and a practical situation where wideband noise is linearly added to a synthetic free induction decay (FID) signal. Cross-terms can be attenuated by band-pass filtering noise or by using a weighting (or smoothing) window in the PWD. An original procedure is then derived to make an on-line and noise-specific estimation of the statistical error in the quantification step. This property of the Wigner distribution is a unique feature in quantitative MRS. Confidence intervals are evaluated for a single damped sinusoid corrupted by eight random noise sequences with three different SNR's, 20, 10 and 5 dB, respectively. They are shown to match the statistical ranges of quantification results obtained with linear regression, until the SNR drops below 10 dB. Estimation accuracy of amplitude and damping constant is finally evaluated from the comparison of the Cramér-Rao (CR) lower bounds with the variance of estimation errors. CR-bounds are shown to be nearly achieved at each SNR.

Ocean impulse response functions computed with the time-domain parabolic equation model are shown to be consistent with response functions measured in a bottom-limited ocean located off the east coast of the United States. The geoacoustics used in the model are developed from Deep Sea Drilling Project sites near the experimental area. Measured impulse responses are obtained by correlating the measured source signature of a 25- to 150-Hz linear, frequency-modulated signal with the signals received on a 15-element vertical line array. Correlation coefficients computed as a function of depth are used as a measure of comparison between measured and modeled responses. The capability of the time-domain parabolic equation to model wide-angle (68°–75°) multipaths and sub-bottom layers with high impedance contrasts is shown. Correlation loss between response functions measured from different transmissions at the same range is shown to be attributable to the degree to which spatial invariance of the ocean can be assumed.

Computer simulations are used to evaluate the performance of cross correlations, bicorrelations, and tricorrelations for time delay estimation of bandlimited deterministic transients in the presence of Gaussian noise for both known and unknown sources. Signals with and without multipath distortion are analyzed. Comparisons of performance are based on probabilities of correct correlation peak location as well as means, standard deviations, and maximum error values of incorrect correlation peak locations for a sequence of signal-to-noise ratios. The effects of rectification on these measures are investigated. For an unknown source, the higher-order correlations (with and without rectification) give higher probabilities of correct peak location than second order for some signals. For most signals with an unknown source, the standard deviations of incorrect peak locations are significantly lowered using rectification. Rectification does not produce this result when using a known source. For known source cases, the cross correlation usually shows higher probability of correct peak location than the higher-order correlations. [Work supported by NOARL.]