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The seafloor in the mouth of the Piscataqua River Estuary, near Portsmouth, New Hampshire, contains several geomorphological regions that are evident in bathymetric data from multibeam sonar soundings. Those morphological regions generally are associated with surficial sediment type classes previously identified from sediment samples. We demonstrate that the morphologies are distinguishable using parameters from models of spatial variation for gridded depth soundings and backscatter values. Ground‐truth seafloor‐video transects data suggest that apparent facies and morphological regions are associated with different surficial sediment classes and rates of facies transitions. We show that the spatial variability of depth and backscatter is associated with the substrate transition rate, the number of microhabitats (microfacies), and distribution of certain epifauna identified using video. We show that, in some cases, a single region defined based upon spatial morphological attributes from depth data and apparent sedimentological attributes from backscatter data represented several benthic habitats. The results suggest that although we can use spatial variability of depth or backscatter to segment the seafloor into apparent facies or habitat class regions, some of the regions will have unpredicted associated microhabitats and organisms. The results have implications for habitat‐specific assessment of organisms.

A recently‐developed statistical‐spectral approach to acoustic‐target identification (SSID) incorporates information contained in the frequency‐dependent signal amplitudes and their variances. In addition to identifying biological targets, the SSID has demonstrated utility for estimating fish aggregation densities, abundances, and behaviors, and detecting and classifying the seabed (e.g., accurate depth, within‐beam slope, hardness and roughness, and the height of the unresolved boundary region, and the so‐called dead zone). Further, the related multi‐frequency, bi‐planar, interferometric technique (MBI) allows much higher‐resolution measurements of the seabed and sub‐beam measures of slope, hardness, and roughness. Here we extend the utilities of the SSID and MBI methods, with explicit consideration of the single‐frequency signal phases and their variances, and frequency‐dependent split‐aperture phases and their variances, for improved estimations of pelagic‐target sizes, and their aggregation densities,...

Acoustic classifications of fish and estimations of their orientation distributions are possible using multi‐frequency or broad bandwidth measurements of their acoustic target strengths (TSs) with knowledge of their scattering directivity pattern and size distributions. To measure TS of in situ fish, single‐frequency interferometric methods provide information to detect resolvable single targets and estimate their location within the acoustic beam. This technique is compromised by multiple targets that are unresolvable because of their spacing, but this situation can be mitigated with the use of multi‐frequency interferometry. The ambiguity caused by coincident echoes can also be substantially reduced using single‐frequency, multiple‐aperture interferometry. This method uses phase differences from multiple sub‐arrays of a single‐frequency (200‐kHz) multibeam echosounder to estimate robustly when echoes originate from a resolvable single target and its position within the acoustic beams. Results provide accurate measures of beam‐compensated TS and, in cases of low‐density scatterers, estimates of their volume density. Multiple‐aperture interferometry can significantly improve the utility of single‐frequency multibeam echosounders for quantitative measures of fish and zooplankton, and seabed‐range detections.

Acoustic backscatter measurements from aggregations of Antarctic krill were collected over two field seasons (2006 and 2007) in the waters north of Livingston Island using two 5.5‐m inflatable vessels. One was equipped with a dual‐frequency (38‐ and 200‐kHz) single‐beam echosounder, while the other used a 200‐kHz multi‐beam system. In addition to independent survey operations, both vessels participated in joint survey operations where the two boats followed the same trackline separated by a small distance (10–40 m). These data allow us to compare how the two echosounder systems “see” the same (or very similar) krill aggregations. During 2006, some tracklines were also occupied by a large (300‐ft) vessel although vessel separation distances were larger during these operations. The combination of measurements from single‐ and multi‐beam echosounders (and nearby net tows) provides the opportunity to characterize krill aggregation size, shape, numerical density, and overall biomass. Observations of krill pred...

Fish dispersion and abundance are commonly estimated from volume backscattering coefficients (sv) of animals located directly beneath the survey vessel, inside a narrow transducer beamwidth. Fish density (♯/m2) is estimated from a ratio of integrated sv and a representative backscattering cross‐sectional area. Fish biomass is estimated from the product of fish density and the area sampled. Uncertainty in biomass estimates can arise from small sampling volumes, and the scattering directivities of the fish coupled with their orientations relative to the acoustic beam. Multibeam sonars can be used to increase the observational volumes, but add the complexity of a wider range of incident angles. If fish size and packing density are constant throughout a school, then the variation in sv versus aspect angle can be attributed to fish orientation. With modeling and multibeam sonar measurements, the following null hypotheses are explored: (1) The variability of sv versus roll angle is nearly uniform; (2) For measurements made with beams at or near vertical, sv variability is primarily due to the pitch angle; (3) For measurements with nonvertical beams, such as the outer beams of multibeam echosounders, sv variability is primarily due to the yaw angle.