Modern water-column-imaging multibeam sonars have been shown to be effective tools for a variety of ocean mapping applications but generate immense amounts of raw data when recording acoustic backscatter over the entire water column. High data acquisition rates can pose logistic, economic, and technical challenges for rapid processing, analysis, and archiving of these data. These limitations in multibeam water column imaging often provide unique challenges in commercial marine seep hunting surveys that routinely acquire large basin-scale high-resolution multibeam datasets that require rapid processing and interpretation required for selection of coring targets for geochemical sampling of seep sediments. Interpreting the seafloor position of gas emissions in multibeam water column data using common commercial software packages is hindered by slow processing due to these large file sizes, a manual “by eye” qualitative assessment of each sonar ping searching for acoustic anomalies, skill and experience of the interpreter, fatigue of the interpreter during field operations, and environmental or acquisition artifacts that can mask the location of gas emission on the seafloor. These restrictions over regional basin-scale surveys create a qualitative data set with varying inherent positional errors that can lead to missed or incorrect observations about seep-related seafloor features and processes. By vertically integrating midwater multibeam amplitude samples over a desired range of depths, a 2D integrated midwater backscatter raster can be generated and draped over bathymetric data, providing a quantitative synoptic overview of the spatial distribution of gas plume emission sites for enhanced seafloor interpretation. We reprocess a multibeam midwater data set from NOAA Cruise EX1402L2 in the northwestern Gulf of Mexico using a vertical amplitude stacking technique. Constructed midwater backscatter surfaces are compared with digitized plume positions interpreted during EX1402L2 for a comparison into assessing uncertainty in mapping approaches. Our results show that the accuracy of manually digitizing gas emission sites varies considerably when compared with the midwater backscatter amplitude maps. This quantitative plume mapping technique offers multiple advantages over traditional geopicking from cost effectiveness, offshore efficiency, mapping repeatability, and ultimately improving the detectability of gas plume emission on the seafloor. This study shows datasets generated from this method can be reliably be used as a geophysical proxy for locating chemosynthetic and related benthic habitats.

Over the past decade, Multibeam Echosounders (MBES) have become one of the most used techniques in sea exploration. Modern MBES are capable of acquiring both bathymetric information on the seafloor and the reflectivity of the seafloor and water column. Water column imaging MBES surveys acquire significant amounts of data with rates that can exceed several GB/h depending on the ping rate. These large file sizes obtained from recording the full water column backscatter make remote transmission difficult if not prohibitive with current technology and bandwidth limitations. In this paper, we propose an algorithm to decorrelate water column and bathymetry data, focusing on the KMALL format released by Kongsberg Maritime in 2019. The pre-processing stage is integrated into FAPEC, a data compressor originally designed for space missions. Here, we test the algorithm with three different datasets: two of them provided by Kongsberg Maritime and one dataset from the Gulf of Mexico provided by Fugro USA Marine. We show that FAPEC achieves good compression ratios at high speeds using the pre-processing stage proposed in this paper. We also show the advantages of FAPEC over other lossless compressors as well as the quality of the reconstructed water column image after lossy compression at different levels. Lastly, we test the performance of the pre-processing stage, without the constraint of an entropy encoder, by means of the histograms of the original samples and the prediction errors.

Commercial success of marine seep hunting exploration campaigns involves acquisition of high-quality bathymetry and backscatter along with targeted coring of shallow geochemical sampling of seep sediments. The sharp lateral chemical gradient encompassing seafloor seeps requires accurate identification of seep sites from high-resolution acoustic data. Active seafloor seeps featuring plumes of gas bubbles and oil droplets rising into the water column can be imaged with modern multibeam echosounders providing an effective approach to remotely characterizing seafloor seeps. Interpreting the seafloor position of gas plume emissions in multibeam data using existing mapping methodology is hindered by slow processing due to large files sizes, a manual “by eye” qualitative assessment of each sonar ping searching for plume anomalies, skill and fatigue of the geoscientist, and environmental or acquisition artifacts that can mask the precise location of gas emission on the seafloor. These limitations of midwater backscatter mapping create a qualitative data set with varying inherent positional errors that can lead to missed or incorrect observations about seep-related seafloor features and processes. By vertically integrating midwater multibeam amplitude samples, a 2D midwater backscatter raster can be generated and draped over seafloor morphology, providing a quantitative synoptic overview of the spatial distribution of gas plume emission sites for more refined seafloor interpretation. We reprocess multibeam midwater data set from NOAA Cruise EX1402L2 in the northwestern Gulf of Mexico using a vertical amplitude stacking technique. Constructed midwater backscatter surfaces are compared with digitized plume positions collected during the survey for a comparison into assessing uncertainty in mapping approaches. Our results show that the accuracy of manually digitizing gas emission sites varies considerably when compared with the midwater backscatter amplitude maps. This quantitative plume mapping technique offers multiple advantages over traditional geopicking from cost effectiveness, offshore efficiency, repeatability, and higher accuracy, ultimately improving the detectability and sampling of active seafloor seeps through precisely located cores.

Multibeam echosounder (MBES) technology has been constantly evolving since its commercial introduction in the late 1970s. The early systems were large and designed to efficiently acquire bathymetric data in deep water. As the underlying sonar technologies improved and computing power increased, systems became smaller and capable of operating on a wider range of vessels over a broader range of depths. Modern deep seafloor exploration, and our present understanding of the geomorphological and biophysical processes that shape it, are closely linked to advances in multibeam echosounder technology. Low to mid-frequency (12-30 kHz) acoustic waves generated by MBES sonars can penetrate kilometers of water column and remotely measure the deep seafloor and shallow subsurface. Reflectivity measurements of the seafloor and water column can also be extracted from MBES datasets, but until the last decade of the 20th century, only the bathymetric swath data was being utilized. In the 1990s, scientists began taking advantage of the multibeam acoustic wave's reflected energy, or backscatter, to interpret information on seafloor geometry (slope), physical characteristics (hardness and roughness), and intrinsic properties, such as composition, surficial and volumetric scattering. Analyzing the geophysical signature of reflected acoustic beams has proven an effective quantitative and qualitative tool to remotely characterize the lithologic composition and geologic nature of the seafloor. Analyzing seafloor backscatter and most recently, backscatter intensities in the water column, has been used for a wide range of applications, including fisheries research, marine biomass assessment, benthic habitat mapping, geological classification, subsea engineering and geohazard mitigation, and hydrocarbon seep studies. This presentation will briefly look at the evolution of MBES technology before focusing on how modern MBES surveys, using the latest generation technology, can deliver a comprehensive characterization of the seafloor and the waters above, as opposed to bathymetry data alone. With The Nippon Foundation-GEBCO Seabed 2030 Project now underway, and planning for the United Nations (UN) Decade of Ocean Science for Sustainable Development having recently commenced, modern MBES technology will play a critical role in bridging ocean bathymetry and ocean observation to improve our understanding of the ocean, its seafloor and its processes. One of the key R&D priorities of the Decade is a comprehensive map (digital atlas) of the ocean. Modern multibeam surveys will support not only bathymetric mapping, but also physical, biological, chemical, geologic, ecosystem, cultural and resource mapping of the world's oceans. Such an approach can feed both Seabed 2030 and the Decade to deliver, as the UN has so eloquently stated, “the ocean we want for the future we need.” Keywords- multibeam; sonar; mbes; echosounder; bathymetry; hydrography; marine geology; mapping; ocean mapping; seeps; seabed seeps; hydrocarbon seeps; exploration; ocean exploration; geophysical; survey; geophysical survey; ocean; seafloor; characterization; seafloor characterization; backscatter; multibeam backscatter; water column; observation; ocean observation; Seabed 2030, United Nations Decade of Ocean Science for Sustainable Development; Ocean Decade.

Over the last few decades, multibeam echosounders (MBES) have become the dominant technique to efficiently and accurately map the seafloor. They now allow to collect water column acoustic images along with the bathymetry, which is providing a wealth of new possibilities in oceans exploration. However, water column imagery generates vast amounts of data that poses obvious logistic, economic, and technical challenges. Surprisingly, very few studies have addressed this problem by providing efficient lossless or lossy data compression solutions. Currently, the available options are only lossless, providing low compression ratios at low speeds. In this paper, we adapt a data compression algorithm, the Fully Adaptive Prediction Error Coder (FAPEC), which was created to offer outstanding performance under the strong requirements of space data transmission. We have added to this entropy coder a specific pre-processing stage tailored to the Kongsberg Maritime water column file formats. Here, we test it on data acquired with Kongsberg MBES models EM302, EM710, and EM2040. With this bespoke pre-processing, FAPEC provides good lossless compression ratios at high speeds, whereas lossy ratios reach water column file sizes even smaller than bathymetry raw files still with good image quality. We show the advantages over other lossless compression solutions, both in terms of compression ratios and speed. We illustrate the quality of water column images after lossy FAPEC compression, as well as its resilience to datagram errors and its potential for automatic detection of water column targets. We also show the successful integration in ARM microprocessors (like those used by smartphones and also by autonomous underwater vehicles), which provides a real-time solution for MBES water column data compression.

Marine seep hunting surveys are a current focus of hydrocarbon exploration surveys due to recent advances in offshore geophysical surveying, geochemical sampling, and analytical technologies. Hydrocarbon seeps are ephemeral, small, discrete, and therefore difficult to sample on the deep seafloor. Multibeam echosounders are an efficient seafloor exploration tool to remotely locate and map seep features. Geophysical signatures from hydrocarbon seeps are acoustically-evident in bathymetric, seafloor backscatter, midwater backscatter datasets. Interpretation of these signatures in backscatter datasets is a fundamental component of commercial seep hunting campaigns. Degradation of backscatter datasets resulting from environmental, geometric, and system noise can interfere with the detection and delineation of seeps. We present a relative backscatter intensity normalization method and an oversampling acquisition technique that can improve the geological resolvability of hydrocarbon seeps. We use Green Canyon (GC) Block 600 in the Northern Gulf of Mexico as a seep calibration site for a Kongsberg EM302 30 kHz MBES prior to the start of the Gigante seep hunting program to analyze these techniques. At GC600, we evaluate the results of a backscatter intensity normalization, assess the effectiveness of 2X seafloor coverage in resolving seep-related features in backscatter data, and determine the off-nadir detection limits of bubble plumes using the EM302. Incorporating these techniques into seep hunting surveys can improve the detectability and sampling of seafloor seeps.

Multibeam echo sounder (MBES) bathymetry and backscatter data from the 2013 R/V Falkor survey are used to define the Cretaceous–Paleogene (K-Pg) boundary deposit outcropping on the Campeche Escarpment and to characterize large-scale erosional processes on the Campeche shelf. We delineate the escarpment into four geomorphic provinces based on submarine canyon density and morphology, as well as pronounced geomorphological differences formed in response to erosional processes along strike of the Campeche Escarpment. Large-scale, retrogressive-appearing mass wasting has left high-angle scarps where large slabs of sediment have eroded the escarpment edge, giving the slope a terraced appearance. This erosion reveals higher backscatter intensity material overlain with remnants of lower backscatter intensity sediments within the slide scar. We infer this high-intensity backscatter material to be predominantly carbonate layers on which erosion occurred. The most prominent high-intensity backscatter layer is interpreted to identify the K-Pg boundary deposit (KPBD) that was reported previously based on a steep bathymetric change and constrained by cores from Deep Sea Drilling Project (DSDP) Sites 86 and 94. Given its proximity to the impact crater, the KPBD is likely to be composed of a massive impact breccia. Upslope, high-intensity backscatter layers are inferred to represent postimpact carbonates that progressively infilled the basin flank after the Chicxulub bolide impact. Lower intensity backscatter material is inferred to be fine-grained Cenozoic sediment drape. The stark contrast observed in MBES backscatter data between high-intensity carbonate material and lower-intensity sediments refines and constrains the location of the K-Pg boundary deposit exposed along the Campeche escarpment and provides new insights into the carbonate platform's postbolide impact evolution as observed in the erosional styles of the Campeche escarpment.

Abstract The Campeche Escarpment is a prominent feature extending over 600 km along the northern flank of the Yucatan Peninsula with steep cliff faces of up to 80° and a relief of over 4000 m. Analysis of Multibeam Echo Sounder (MBES) backscatter and bathymetry data reveal new insights into the cliff-forming geologic units as well as largescale erosional processes on the Campeche shelf. In 2013, the R/V Falkor collected MBES bathymetry and backscatter data sonars in the area of the Campeche Escarpment using Kongsberg EM302 30 kHz and EM710 70 kHz MBES systems. We use Fledermaus GeoCoder to process backscatter data, and ArcGIS to create mosaic of all survey lines. Fledermaus is then used to create a 3D representation of the dataset. We delineate the escarpment into four geomorphic provinces based on submarine canyon density and morphology, as well as pronounced geomorphological differences formed in response to erosional processes along-strike of the Campeche Escarpment. Analysis of backscatter data reveals a high backscatter intensity unit comprising the steep cliff faces of the Campeche Escarpment. Due to the high backscatter intensity of the unit, we infer this to be a carbonate unit, which is also associated with the K-Pg boundary layer as previously reported by Paull et al. (2014) based on a steep bathymetric change and constrained by cores from DSDP Sites 86 and 94. Large-scale retrogressive-appearing erosion has left high-angle breaks where slabs of sediment have eroded the escarpment edge, thus giving the slope a terraced appearance. This erosion reveals higher backscatter intensity material overlain with remnants of lower backscatter intensity sediments within the slide scar. We infer the high backscatter intensity material to be carbonate layers on which erosion occurred. The stark contrast observed in MBES backscatter data between high intensity carbonate material and lower intensity sediments, refines and constrains the location of the K-Pg boundary layer exposed along the Campeche escarpment and provides new insights into the erosional styles of the Campeche escarpment. MBES backscatter analysis is a low cost method that yields a more detailed assessment of surface material than bathymetry alone. This proves to be a powerful tool; enabling further inferences about geomorphic features and geologic characteristics of a study area, and as an efficient means of locating seafloor hydrocarbon seeps.

Despite recent declines in oil and gas market expenditures, demand for marine hydrocarbon seep surveys continues to grow. Geochemical analysis of seafloor seep sediments is an effective hydrocarbon exploration tool. Identifying and sampling sites where thermogenic hydrocarbon fluids have migrated to the seafloor provides information on reservoir characteristics and commercial viability. Hydrocarbon seep features are ephemeral, small, discrete, and often difficult to precisely sample on the deep seafloor. Low to mid-frequency multibeam echosounders are an efficient exploration tool to remotely locate and map seafloor features associated with seepage. Geophysical signatures from hydrocarbon seeps are evident in bathymetric datasets (fluid expulsion features), seafloor backscatter datasets (carbonate outcrops, gassy sediments, methane hydrate deposits), and midwater backscatter datasets (gas bubble and oil droplet plumes). Interpretation of these geophysical seep signatures in backscatter datasets is a fundamental component of seep hunting. Degradation of backscatter datasets resulting from environmental, geometric, and system noise can interfere with the detection and delineation of seeps. We present a relative backscatter intensity normalization method and a 2X acquisition technique that can enhance the geologic resolution within seafloor backscatter datasets and ultimately assist in the interpretation and characterization of seafloor hydrocarbon seeps. As frontier exploration surveys migrate into deeper waters in search of oil and gas reserves, it is necessary to evaluate and develop tools and techniques that improve both data quality and the interpretation of multibeam datasets. Fugro has conducted over fifty seep hunting campaigns globally since 2001 and include single exploration blocks to multi-client “mega surveys” in Indonesia, Brazil, and most recently an industry-funded multi-client seep survey – the Otos multibeam survey (353,700 km) in the northern Gulf of Mexico and the Gigante multibeam seep survey (625,000 km) in the Southern Gulf of Mexico and Caribbean Sea. In total, over two million square kilometers of seafloor have been mapped with modern multibeam systems optimized to detect hydrocarbon seeps. This paper will provide an overview of seep detection methodologies applied during our marine seep hunting surveys.