A Surprise Occurrence in Acoustic Bottom Backscatter Measurements Conducted in the Eastern Bering Sea

Acoustic backscatter measurements at different frequencies were made in the eastern Bering Sea in August 2006 from the NOAA Ship Fairweather. The measurements consisted of approximately 2,250 nm of trackline acoustic backscatter data from a 100 kHz RESON model 8111; 2,250 nm of trackline acoustic backscatter data from a 40 kHz Reson model 8160; 750 nm of trackline acoustic backscatter data from a 455 kHz Klein model 5410; and 750 nm of trackline acoustic backscatter data from a 180 kHz pre-production Klein model 7180. The two Klein systems were each towed SW-NE once along the same specified 750 nm of tracklines. The two RESON systems were each operated twice SW-NE and once NE-SW along the same tracklines as the Klein systems. The acoustic backscatter was typically what might be expected from a flat, featureless expanse of fine grained sediments. However, there was a chance encounter with an embedded community of gastropods that was documented both with bottom grab samples and video footage of the seabed. The presence of the embedded community of gastropods drastically changed the level and angle dependence of the backscatter. This paper presents a comparative analysis of the backscatter properties of the gastropod community that were observed at 40 kHz, 100 kHz, 180 kHz and 455 kHz

Automatic Detection of Outliers in Multibeam Echo Sounding Data

The data volumes produced by new generation multibeam systems are very large, especially for shallow water systems. Results from recent multibeam surveys indicate that the ratio of the field survey time, to the time used in interactive editing through graphical editing tools, is about 1:1. An important reason for the large amount of processing time is that users subjectively decide which soundings are outliers. There is an apparent need for an automated approach for detecting outliers that would reduce the extensive labor and obtain consistent results from the multibeam data cleaning process, independent of the individual that has processed the data. The proposed automated algorithm for cleaning multibeam soundings was tested using the SAX-99 (Destin FL) multibeam survey data [2]. Eight days of survey data (6.9 Gigabyte) were cleaned in 2.5 hours on an SGI platform. A comparison of the automatically cleaned data with the subjective, interactively cleaned data indicates that the proposed method is, if not better, at least equivalent to interactive editing as used on the SAX-99 multibeam data. Furthermore, the ratio of acquisition to processing time is considerably improved since the time required for cleaning the data was decreased from 192 hours to 2.5 hours (an improvement by a factor of 77)

Sensor-Assisted Video Mosaicing for Seafloor Mapping

This paper discusses a proposed processing technique for combining video imagery with auxiliary sensor information. The latter greatly simplifies image processing by reducing complexity of the transformation model. The mosaics produced by this technique are adequate for many applications, in particular habitat mapping. The algorithm is demonstrated through simulations and hardware configuration is described

Seafloor Video Mapping: Modeling, Algorithms, Apparatus

This paper discusses a technique used for construction of high-resolution image mosaic from a videosequence and the synchronously logged camera attitude information. It allows one to infer geometric characteristics of the imaged terrain and hence improve the mosaic quality and reduce the computational burden. The technique is demonstrated using numerical modeling and is applied to videodata collected on Rainsford Island, Mass. Calculation of the transformation relating consecutive image frames is an essential operation affecting reliability of the whole mosaicing process. Improvements to the algorithm are suggested, which significantly decrease the possibility of convergence to an inappropriate solution

The Design of an Uncertainty Model For The Tidal Constituent and Residual Interpolation (TCARI) Method for Tidal Correction of Bathymetric Data

Recent advances in processing multibeam sonar data brought about by the Combined Uncertainty and Bathymetric Estimator (CUBE) [1] have demonstrated the value of identifying and tracking survey uncertainties. Most of these uncertainties were outlined in Hare, Godin, and Mayer uncertainty model developed in 1995 [2]. That report identified the uncertainties in the various electronic systems used to acquire the bathymetric data. However, one of the largest contributors to the overall error budge t in a near coastal hydrographic survey is that contributed by water level uncertainty. As the ocean mapping industry pushes for ever finer spatial details in its data, the traditional method of discrete tide zoning [3] must be abandoned for a more robust method that can match the requirements of the data. The method currently under investigation by the National Oceanic and Atmospheric Administration is the Tidal Constituent And Residual Interpolation (TCARI) method [4]. TCARI has the ability to interpolate the water level at a vessel’s position for any location and instance in time. It can also produce a gridded water level surface of the entire survey area. While the potential of this method is encouraging, a rigorous investigation of the uncertainties associated with it has yet to be completed. This research seeks to close that gap by examining the uncertainties in this method, using both observed water level information from around the country as well as data acquired during the original 1995 NOS Kinematic GPS experiment in Galveston Bay, Texas [5]

Improvement of Image Alignment Using Camera Attitude Information

We discuss a proposed technique for incorporation of information from a variety of sensors in a video imagery processing pipeline. The auxiliary information allows one to simplify computations, effectively reducing the number of independent parameters in the transformation model. The mosaics produced by this technique are adequate for many applications, in particular habitat mapping. The algorithm, demonstrated through simulations and hardware configuration, is described in detai

Underwater Video Survey: Planning and Data Processing

The importance of underwater video surveys as an exploration tool has been steadily increasing over recent years [1]. Better photographic equipment, more effective sources of illumination, and improved processing techniques - all make video surveying a reliable tool for seafloor habitat mapping, sediment boundary delineation and groundtruthing, mapping and documentation of forensic and archaeological sites. There is a change in attitude towards video surveying that affects the way the data is collected, and hence its quality. Earlier video data processing algorithms had to cope with whatever was recorded (often simultaneously with acquisition of other data, considered to be more important). Now we have a chance to plan ahead and organize a survey in a way most suitable for the processing. The goal of this paper is to review available processing techniques and to discuss preferable survey patterns, associated errors and processing stability

Resolving the Ripples (and a Mine): High-Resolution Multibeam Survey of Martha\u27s Vineyard ONR Mine Burial Program Field Area

In an effort to better understand the coastal processes responsible for the burial and exposure of small objects on the seafloor, the Office of Naval Research is sponsoring the Mine Burial Program. Among the field areas chosen for this program is the site of the Martha\u27s Vineyard Coastal Observatory (MVCO), a permanent instrumented node in 12 m of water about 500 m off the southern shore of Martha?s Vineyard. In support of the ONR program, several site surveys of the MVCO area have been conducted (see Goff et al); here we report the result of the most recent of these surveys, a very high-resolution multibeam survey aimed at establishing a detailed base map for the region and providing a baseline from which subsequent surveys can measure seafloor change In late July we conducted a five day survey of an approximately 3 x 5 km area surrounding the MVCO node using a Reson 8125 focused multibeam sonar aboard the SAIC survey vessel Ocean Explorer. The 8125 is a newly developed multibeam sonar that operates at 455 kHz and uses dynamic focusing to compensate for the curvature of the wavefront in the near-field. By using a relatively long array, the system can achieve very high spatial resolution (0.5 degree beam width) and with the dynamic focusing, can operate in the near field. The real constraint on resolution using this system is the ability to position the soundings and thus three kinematic DGPS base stations were established on Martha?s Vineyard and three kinematic receivers were used on the survey vessel. The kinematic GPS positioning is also critical to the ability to do repeat surveys with an accuracy high enough to resolve small (less than 10 cm) seafloor changes. Also to aid in our ability to accurately position repeat surveys, divers jetted sonar reflectors into the seafloor to act as fiducials. A super high-resolution (4 m overlap) survey was conducted in a small area surrounding the MVCO node and mine burial sites, a slightly lower resolution survey (12 to 25 m overlap) in a box approximately 1 x 1 km surrounding the ?target box? and a lower resolution survey (25 to 40 m line overlap) in a 3 x 5 km region surrounding the 1 x 1 km box. The Reson 8125 produced approximately 1 gigabyte of data per hour. The bathymetric resolution we were able to achieve was beyond our expectations. The node site and all diver-emplaced reflectors were clearly identified Most amazingly, we are able to resolve fields of individual ripples that are less than 2 cm height. Of particular relevance to the mine burial program was our ability to resolve an instrumented mine that had been deployed earlier by NRL. This mine is buried in a scour depression and is only a few centimeters proud above the base of the depression

Seafloor Characterization from Spatial Variation of Multibeam Backscatter vs. Grazing Angle

Backscatter vs. grazing angle, which can be extracted from multibeam backscatter data, depend on characteristics of the multibeam system and the angular responses of backscatter that are characteristic of different seafloor properties, such as sediment hardness and roughness. Changes in backscatter vs. grazing angle that are contributed by the multibeam system normally remain fixed over both space and time. Therefore, they can readily be determined and removed from backscatter data. The variation of backscatter vs. grazing angle due to the properties of sediments will vary from location to location, as sediment type changes. The sediment component of variability can be inferred using the redundant observations from different grazing angles in several small pieces of seafloor where the sediment property is uniform in any given piece of seafloor yet vary from one piece of the seafloor to another. Thanks to the multibeam survey (Roger Flood, State University of New York) at SAX 99 Project sponsored by Office of Naval Research (ONR), which had 800\% coverage in most of the survey area; there is a data set, which is suitable for investigating seafloor characterization. The investigation analyzed the spatial variation of the backscatter vs. grazing angle and compared that with ground truth sediment data. In this research, the 6.9 gigabytes raw multibeam data were cleaned using an automated outlier detection algorithm (Tianhang Hou, Lloyd Huff and Larry Mayer. 2001). Then, the surveyed area was equally divided into 52X78 rectangle working cells (4056), the side of each cell was about 20 meters. The backscatter vs. grazing angle of backscatter data for each cell is computed by averaging backscatter data by the corresponding beam numbers using all data with the same beam number from different survey lines. Systematic effects on the backscatter vs. grazing angle, caused by multibeam system hardware or software as well as system installation, were corrected in order to remove the asymmetric and skew effects. In order to easily evaluate the spatial variation of the backscatter vs. grazing angle, a graphic interface was developed. With a mouse click, the images based on different subsets of the data can be compared throughout the survey area. The subsets were created using specific beam numbers. These images for different beams show significant variations between nadir and off-nadir beams. These variations allow an interesting interpretation to be made of the images in light of seafloor characteristics, which were derived from ground truth data, such as sediment grain size, density and velocity

Modern Under-Keel Clearance Management

This paper provides an overview of recent technological developments that have improved the ability to manage under-keel clearance (UKC) in ports. The inaccurate determination of the UKC of large-draft ships entering or leaving depthlimited ports can have serious safety, economic, and environmental consequences. A ship's master can manage his ship's UKC by: (1 ) taking actions that affect the ship's dynamic draft (such as changing the ship's speed) and (2) scheduling his ship's transit of the planned route to ensure that there will be sufficient water level for safe passage when the ship reaches locations with controlling depths. To do this, however, he must have accurate real-time and forecast environmental information along his route, as well as a validated method of predicting his ship's motion (and thus dynamic draft) for various situations. At a minimum, this information must include accurate charted depths and underwater hazards, water levels, and ship-specific channel-specific prediction formulas for dynamic draft (based on ship speed, static draft, and water depth). The dynamic draft calculation may also require information on currents, water density, and waves, swell, and/or seiching. Recently developed systems that can provide the necessary information for UKC management include: nowcast/forecast oceanographic model systems (a necessary step beyond real-time oceanographic systems); on-the-fly GPS systems to provide accurate ship motion data for calibrating dynamic-draft prediction systems; modern hydrographic measurement systems (such as shallowwater multibeam and side-scan sonar systems); and modern electronic nautical chart systems (and their supporting rapid update services). This paper includes discussion of what further improvements to these systems are needed to make effective UKC management a reality