Examining the Links between Multi-Frequency Multibeam Backscatter Data and Sediment Grain Size

In the past, planning detailed visual investigations of deepwater archaeological sites has primarily been done with side scan sonar and subbottom profiler data. Advancements in multibeam bathymetry acquisition and processing, especially of backscatter data, now provide additional ways to view these sites. Deepwater archaeologists have begun to utilize bathymetry and backscatter data to develop better understandings of overall site conditions and attributes. As a result, they are able to develop more cost and time effective investigation plans to detail deepwater sites with increased accuracy. This paper will examine several deepwater shipwreck sites to demonstrate how use of the backscatter and bathymetry data has advanced the investigation methodologies used on deepwater archaeological sites. Introduction Underwater archaeology has long relied on technology to locate and initially document inundated archaeological sites or shipwrecks. For years, side scan sonars, subbottom profilers, and magnetometers have been the primary documentation tools for archaeologists studying sites in both shallow and deep water environs. Within the past decade, with access to new technologies, archaeologists added multibeam systems to their archaeological investigative tool kit. Multibeam bathymetry and backscatter provide high resolution, accurately positioned data that can be easily quantified, repeated, and integrated (Lawrence and Oxley, 2004). Using multibeam data with visualization software now allows three-dimensional (3D) views of archaeological sites from the shallowest lagoons to the deepest ocean reaches. Several innovative projects, including ScapaMap and RASSE, at the beginning of this century resulted in the increased use of multibeam data for archaeological investigations. These cutting edge studies proved the viability of multibeam bathymetry and backscatter for archaeology; they also influenced many areas of underwater archaeology, including deepwater archaeology. Deepwater archaeologists, many in oil and gas related fields, building upon these earlier studies have adopted multibeam data as part of a larger investigation methodology for deepwater shipwreck documentation and interpretation. This paper explores the role multibeam bathymetry and backscatter play within deepwater shipwreck investigation methodologies. Early Projects Using Multibeam on Shipwreck Sites At the beginning of the 21st century, several underwater archaeological projects employed multibeam systems for site documentation. Investigations on the Normandy Coast documented submerged features associated with the D-Day Landings. The project documented diverse submerged features including lost vehicles, vessels sunk as artificial breakwaters, and Mayberry Dock remnants originally used to hasten the supply flow to the beachheads (Mayer, et al., 2003). In Italy, high resolution multibeam surveys mapped the inundated Roman City at Baia and the Roman harbor at Porto Guilio (Wille, 2005). Two projects in the United Kingdom, ScapaMap and RASSE, were the most influential in illustrating the potential for multibeam in archaeology and the most pertinent to multibeams use for deepwater shipwreck studies.

Spatiotemporal variability on local-regional scale in subtidal meiofaunal assemblages along the southern coast of Korea

Macrofaunal biomass of the Lucero reef flat in the northwestern Philippines accounted for 9 to 52% of total sediment organic matter, and did not exhibit any significant temporal trend. The polychaetes and crustaceans consistently alternated as biomass dominants; the latter group showed monthly and seasonal variations along with the chaetognaths, molluscs, chordates, and chelicerates, among the major groups (p<0.05). Faunal abundance correlated significantly with biomass. Salinity, mean sediment grain size, sediment heterogeneity, and total organic matter were found to significantly influence faunal biomass. The sandy substrate community was characteristically heterotrophic throughout the monitoring period, i.e., P/R<1. Hourly rates of net primary production (p n ) did not exhibit any significant diurnal pattern. Monthly comparisons yielded significant differences for estimates of daily gross primary production, P, and respiration, R. Values of P were relatively low, and ranged from 2240 (± 1526 S.D.) to 4890 (± 1377) mg O2 m−2 d−1 while R ranged from 3744 (± 1504) to 6879 (± 903) mg O2 m−2 d−1. R was lower during the dry warm months than the wet months. Multiple regression analyses indicate that primary production was a positive function of light intensity and temperature, and a negative correlate of salinity (adjusted R 2 = 0.2444, p< 0.05). Respiration (r) did not appear to relate with any environmental variable, with total macroinfaunal abundance nor with biomass. Results of the study suggest that other heterotrophic components of the sand community were probably responsible for most of the energy consumption, and that these may be dependent on external sources of organic matter.

Expressions have been developed for bottom scattering strength as a function of frequency and four bottom parameters. These parameters are rms roughness. sound speed, mass density, and a volume scattering parameter. Procedures have been developed for assigning best values to these parameters for poorly characterized sites, e.g., for sites at which mean sediment grain size or porosity is the only known quantity. This model is based upon the composite roughness and Kirchhoff approximations, but empirical adjustments have been made to fit data that lie outside the region of applicability of these approximations. [Work supported by NAVSEA.]

Distribution and Sources of Polycyclic Aromatic Hydrocarbons in Sediments from Kyeonggi Bay, Korea

Seafloor characterization using multibeam echosounder (MBES) backscatter data is an active field of research. The observed backscatter curve (OBC) is used in an inversion algorithm with available physics-based models to determine the seafloor geoacoustic parameters. A complication is that the OBC cannot directly be coupled to the modeled backscatter curve (MBC) due to the correction of uncalibrated sonars. Grab samples at reference areas are usually required to estimate the angular calibration curve (ACC) prior to the inversion. We first attempt to estimate the MBES ACC without grab sampling by using the least squares cubic spline approximation method implemented in a differential evolution optimization algorithm. The geoacoustic parameters are then inverted over the entire area using the OBCs corrected for the estimated ACC. The results indicate that a search for at least three geoacoustic parameters is required, which includes the sediment mean grain size, roughness parameter, and volume scattering parameter. The inverted mean grain sizes are in agreement with grab samples, indicating reliability and stability of the proposed method. Furthermore, the interaction between the geoacoustic parameters and Bayesian acoustic classes is investigated. It is observed that higher backscatter values, and thereby higher acoustic classes, should not only be attributed to (slightly) coarser sediment, especially in a homogeneous sedimentary environment such as the Brown Bank, North Sea. Higher acoustic classes should also be attributed to larger seafloor roughness and volume scattering parameters, which are not likely intrinsic to only sediment characteristics but also to other contributing factors.

Increased human demand on the marine environment and associated biodiversity threatens sustainable delivery of ecosystem goods and services, particularly for shallow shelf-sea habitats. As a result, more attention is being paid to quantifying the geographical range and distribution of seabed habitats and keystone species vulnerable to human pressures. In this study, we develop a workflow based on unsupervised K-Means classification units and Generalized Linear Models built from multi-frequency backscatter analyses (95, 300 kHz), bathymetry and bathymetry derivatives (slope) to predict different levels of sandeel densities in Hempton's Turbot Bank Special Area of Conservation (SAC). For Hyperoplus lanceolatus densities, the performance of single frequency verses multi-frequency models is compared. Relatively high agreement between K-Means clustering outputs (from 95 kHz and multi-frequency models) and ground-truthed sandeel densities is noted. Moreover, Root Mean Squared Error (RMSE) values in this instance demonstrate that single-frequency models are favoured over the multi-frequency model in terms of predictive ability. This is mostly linked to the species strong affinity for sedimentary environments whose variability is better captured by the lower frequency system. Generally, these results provide important information about species-habitat relationships and pinpoint bedform features where sandeels are likely to be found and whose variability is potentially linked to the bathymetry domain. The workflow developed in this study also provides a proof of concept to support the design of a robust species-specific monitoring plan in marine protected areas. Most importantly, we highlight how decisions made during sampling, data handling, analysis could impact the final outputs and interpretation of Species Distribution Models and benthic habitat mapping.

The spatio-temporal texture characteristics are key parameters for understanding the dynamics of the sedimentary environment. This study was conducted to determine the sediment characteristics in swash zone of Lhoong Beach, Aceh Besar Regency. The analysis emphasizes the seasonal variation of sediment mean grain size (MGS) based on vertical stratification. Sediment samples were taken during November 2018, January 2019 and March 2019, from 3 stations. Samples from station 3 had the coarsest grain characteristics, where the highest MGS value at station 3 was recorded in the mid-layer (5-10 cm) in November. The grain size was found to vary with changing seasons and the depth of the sediment layer. Based on depth stratification, the highest standard deviation was obtained by the mid-layer (5-10 cm); while by period, the highest standard deviation of the MGS value was generated during November.

&amp;lt;p&amp;gt;Headwater streams are mainly responsible for providing sediments and nutrients to the downstream regions. In addition, the riparian vegetation of these streams is a source of large wood (LW) for the water channel. Sediments and LW play an ecologically-important role in maintaining aquatic habitat, meanwhile sometimes execute serious intensification of the impact of downstream large floods. The quantity and size distribution of sediments on the channel bed and LW certainly influence on channel hydraulics and stability as well as the quality of aquatic habitats. Hence, the characterization of sediments and LW supports the renaturalization and conservation of streams/rivers. Therefore, the objective of the present study was to evaluate the influence of the LW deposition and the channel morphology on the bed sediment grain size along a reach (700 m) inside a headwater catchment (15 km&amp;lt;sup&amp;gt;2&amp;lt;/sup&amp;gt;), southern Brazil. The mean slope of the reach channel is 0.33% which can be considered low. This catchment is characterized with the Mixed Ombrophilous Forest, the climate is the Cfb according to K&amp;amp;#246;ppen classification and the average annual rainfall is 1881 mm. Hydrological (rainfall and discharge) and LW dynamics monitoring has been carried out in this catchment since 2017. The step, pool and cascade are observed as channel morphologies along the study reach, which were divided into three parts (upstream, middle, and downstream). Furthermore, 26 cross-sections of the stream were established for field survey, such as measurement of the diameter (axis -a, -b, and -c) of the bed sediments (D&amp;lt;sub&amp;gt;90&amp;lt;/sub&amp;gt;, D&amp;lt;sub&amp;gt;84&amp;lt;/sub&amp;gt;, D&amp;lt;sub&amp;gt;50&amp;lt;/sub&amp;gt;, D&amp;lt;sub&amp;gt;16&amp;lt;/sub&amp;gt;, D&amp;lt;sub&amp;gt;10&amp;lt;/sub&amp;gt;, and D&amp;lt;sub&amp;gt;max&amp;lt;/sub&amp;gt;) and LW presence verification. The definition of the sampling points sought to ensure a correct representation of the fluvial geomorphology. The present study reported the results obtained through the field survey carried out on August 8th, 2020, using caliper, tree caliper, metric tape and GPS. The grain sizes varied from 324.64 mm to 2.76 mm (particles smaller than 2 mm were not computed). The results showed that the presence of LW in the section induced a smaller value of the sediment grain size. In the pool formation a greater variation in the sediment granulometry was found than in cascades and steps. Furthermore, within the pool, the sediment sizes tended to increase from upstream to downstream. It is concluded that the LW acts as natural barriers for sediment deposition, avoiding the sediments exhaustion and generating low-velocity zones, favoring the maintenance of aquatic habitat. Also, the difference in the granulometry of the sediments within the pool formation may be a function of the flow velocity. In Brazil, the importance of fieldwork involving the monitoring of LW and bed sediments should be highlighted as a tool for understanding the hydrogeomorphic processes and for conserving the riparian zone, because such fieldworks are still few.&amp;lt;/p&amp;gt;

Five intertidal sites along the coast of the Yangtze Estuary, China were examined for concentrations of heavy metals including Cu, Zn, Pb, Ni, Mn and Fe in bulk surficial and core sediments. Differences in heavy metal concentrations are apparent between the sites, which are dependent on site-specific metal inputs and sediment grain size. With the exception of site A (Shidongkou), where the highest concentrations of Cu, Zn, Pb occur due to direct pollutant input from the nearby sewage outlet, heavy metal concentrations at other sites are largely determined by particle size characteristics. Clay-rich sediments, together with a downstream location relative to the sewage outlets, result in elevated concentrations of heavy metals at site C (Donghai). Within the intertidal zone at site C, the vegetated, upper marsh zone exhibits higher heavy metal concentrations in comparison with the bare mudflat. Monthly sampling (May to September) in the Scirpus marsh at site C records a temporal variation in heavy metal concentrations. Both of them can be related to the spatial and temporal variability of sediment grain size. A geomorphic understanding of the heterogeneity of sediment grain size is, therefore, vital to the assessment of sediment pollution in intertidal sediments. The present study reveals that the levels of heavy metals found in the Yangtze Estuary are relatively moderate compared with other estuaries in Asia and Europe. This is related to both the diluting effects of the huge volume of water and sediment in the estuary and a shorter period of industrialisation.

Microplastics: A potential proxy for tracing extreme flood events in estuarine environments

The element geochemical behavior and provenance of marine sediments are of significance to understanding the oceanic material cycle. Here, we tested the grain size and major and trace elements of 35 surface sediments in the offshore area of Sierra Leone, analyzed the content characteristics and controlling factors of the elements, discussed the material source of the sediments, and made a comparative study with the sediments in the offshore area of China. The results show that sandy silt is the main sediment type in the research area, and the average sediment mean grain size (Mz) is 4.15Φ. The content of Ca in the samples is the highest among the major elements (except Si), with an average of 5.1%. The content of Sr is the highest among the trace elements (except Ti, P, and Mn), with an average of 378.2 μg/g. The results of correlation analysis and factor analysis show that there are three main sources of sediments in the research area, namely, terrigenous weathering products, ilmenite-dominated ore, and oceanic biochemical substances. Compared with the sediments in China offshore, the sediments in the study area are more affected by marine biochemistry and have special ore input characteristics.

A one-layer, two-dimensional computer model for the time-dependent, lakewide advective and diffusive transports as well as physical regeneration of total phosphorus in Lake Erie has been developed. It has 60 × 16 square grid cells of 6.67-km mesh size and uses a time step of 12 h. The model has been verified and found to be in reasonably good agreement with the Canada Centre for Inland Waters (CCIW) monitor cruise data for October, November, and December during which period there were high winds with high phosphorus concentrations being observed. Computed, daily averaged currents from a hydrodynamic model developed at CCIW are used for the transport terms and actual data for the lake boundary conditions. The physical regeneration is attributed to wave motions induced by wind. A formula is proposed which expresses the regenerated amount of total phosphorus in terms of wave orbital velocity and sediment mean grain size. A discussion is presented on the choice of the settling rate and the regeneration coefficient which produce satisfactory model results.

A study is made of the effects of a distribution of grain size, a large absorption coefficient and overlapping diffraction lines on the values of grain size obtained from the number of spots on X-ray back reflextion photographs from polycrystalline material. It is shown that accurate values of the mean grain size can be obtained by extrapolation to high exposure ratios and that the general volume formula relating the number of spots to the penetration of the beam into the specimen is applicable also in cases in which the average penetration of the beam is small compared with the grain diameter.

High- and low- latitude forcing on hydroclimate variability in southern China over the last two millennia