The detection, classification, and localization of targets or features on the seafloor in acoustic data are critical to many disciplines. This is most important in cases where human safety is in jeopardy, such as hazards to navigation, mitigation of mine countermeasures, or unexploded ordnance. This study quantifies the absolute localization of targets, in the form of inert unexploded ordnance, in very shallow waters (2–3 m) on two intertidal bottom types in a meso-tidal environment (tide range = ~3.0 m). The two sites, a sandy intertidal flat and a mixed sand and gravel beach with abundant cobble-sized material, were seeded at low tide with targets (wax-filled 60-, 81-, 105- and 155-mm, projectile and mortar shells). An RTK-GPS was used to collect positional data for the targets and an unoccupied aerial system (UAS) survey was conducted on both sites. At the next high-tide, a vessel-based acoustic survey was performed, and at the subsequent low tide, the targets were re-surveyed with RTK-GPS. We focus here on the sidescan backscatter from a phase-measuring sidescan sonar (PMSS) and the sources of uncertainty for absolute localization. A total of 1426 calls of acoustic targets were made within the sidescan backscatter data, yielding an accuracy of 0.41 ± 0.26 m, with 98.9% of all calls <1 m from their absolute location. Distance from nadir was the most significant source of uncertainty, and targets between 3–7 m had the lowest uncertainty (0.32 ± 0.23 m) with increasing values toward and away from nadir. Bathymetry and bathymetry-mode backscatter were less useful for the detection and classification of targets compared to sidescan backscatter, but once detected, the accuracy of absolute localization were similar. This is likely due to target calls from these two datasets that were orders of magnitude less and that focused on the larger sized targets, thus more work is needed to better understand these differences. Lastly, the absolute localization of targets detected on sandy and cobble bottoms for all datasets were statistically similar. These acoustic instruments, their datasets, and methods presented herein can better document the absolute localization within acoustic data for many uses in very shallow waters.

This paper discusses the utility of using seismic-reflection profiling and sediment cores in addition to bottom grab samples and acoustic data to develop shallow-water benthic habitat maps. Currently, the classification system used herein does not provide for the incorporation of stratigraphic data, but we believe that the utility of these maps would improve if such data were included. We conducted vessel-based seafloor-mapping surveys using a phase-measuring sidescan sonar in very shallow waters (mean depth = 3.2 m) covering an area >6.7 km2 in Pleasant Bay in 2014. We collected a total of 192 bottom grab samples to document macro-invertebrates and sediment characteristics. We conducted seismic-reflection profiling surveys to document stratigraphy and determine optimal locations for multiple sediment cores during the 2014 field season; we collected both Kullenberg and Livingstone cores. The seismic-reflection data, though conducted at the reconnaissance scale, proved useful to place the seafloor acoustic data in context. The acoustic and benthic habitat data and mapping products become more valuable when an understanding of the underlying stratigraphy is used as context for the benthic habitat maps. Sediment coring and analysis can provide insights into past and current basin evolution, which can further aid marine natural resource managers. However, we believe that stratigraphic data should be incorporated into standard benthic habitat mapping protocols. These multi-modal datasets provide a better understanding of these habitats for the multidisciplinary teams that typically produce and use these maps as well as coastal managers.

A new conceptual model describes the inlet migration and inlet transition phases of development of the Nauset Beach–Pleasant Bay barrier beach system. The model uses historical cartographic resources to inform geomorphological analysis of sedimentary processes, inlet migration, and new inlet formation for the purpose of estimating future system configurations and conditions. Using this model, we place the natural evolution of the system in context and observe that an anthropogenic alteration of the mainland shore, a stone revetment, likely contributed to the system's transition to a single inlet system.

Detection, classification, and localization (DCL) techniques are being developed around the use of a phase-measuring sidescan sonar (PMSS) in very shallow waters. The instrument simultaneously collects co-located sidescan imagery and bathymetry in extreme shallow water environments (<1 m water depth). In addition to the bathymetry, an uncalibrated backscatter data set, referred to in this study as phase-measured, bathymetry-mode backscatter (BMB), is also collected. This BMB has been minimally addressed in the literature. This work aims to use the BMB to detect and differentiate between various objects on the seafloor, including unexploded ordnance (UXO), and placed marine debris, or ‘clutter’, such as lobster pots, boat propellers, and car tires. The differentiation from multiple seafloor types including mud, sand, and gravel and different types of objects occurred through various statistical analysis methods including binomial and multinomial logistic regression. These methods have been applied to create statistical regression models for several variables including phase-measured, bathymetry-mode backscatter amplitude, sounding distance from nadir, per-ping vessel roll, orientation offset between per-ping vessel heading and object orientation, and all combinations of these variables. These statistical tests produced maximum likelihood odds ratios of individual soundings being associated with the various seafloor and object types. Results from these analyses shows that DCL could be possible with phase-measured, bathymetry-mode backscatter from this PMSS system, though these results may not be representative for all bed types and phase-measuring systems.

Along the shoreline of a coastal lagoon with fringing salt marsh, we used the basinward edge of marsh vegetation, or marshline, as a shoreline indicator. We quantified uncertainties associated with the delineation of this indicator from aerial photographs. Where both could be delineated, we compared the marshline to the most widely used proxy-based shoreline indicator, the high water line (HWL). The marshline was shown to better represent change than the HWL along fringing marsh shorelines in this study. The visual cues used to delineate the marshline on aerial photographs were more objective, repeatable, and reliable than the visual cues associated with the HWL. In addition, several sources of uncertainty in calculating rates of shoreline change are eliminated, or significantly reduced, when using the marshline. Uncertainties associated with the timing of aerial photographs regarding tidal stage, seasonality, storm impact, as well as the misinterpretation of the shoreline indicator are all either negligible or of minimal influence when calculating uncertainty for the marshline. We calculated rates of shoreline change along a 40-km stretch of lagoon shoreline with fringing marsh. Less than 9.8 km of coast was outside the range of uncertainty using the HWL as compared to 22.5 km using the marshline for the same segments of shoreline for the same temporal period.