Dale N. Chayes

Improved processing of Hydrosweep DS multibeam data on the R/V Maurice Ewing

We have developed a new software package, called MB-System, for processing and display of Hydrosweep DS multibeam data on the R/V Maurice Ewing. The new software includes tools for modeling water sound velocity profiles, calculating multibeam bathymetry from travel time values by raytracing through a water sound velocity profile, interactive and automatic editing of multibeam bathymetry, as well as a variety of tools for the manipulation and display of multibeam data. A modular input/output library allows MB-System programs to access and manipulate data in any of a number of supported swath-mapping sonar data formats, including data collected on Hydrosweep DS, Sea-Beam “Classic”, SeaBeam 2000, SeaBeam 2100, H-MR1, Simrad EM12, and other sonars. Examples are presented of the softwares application to Hydrosweep data recently collected on the R/V Maurice Ewing.

A new digital bathymetric model of the world's oceans

General Bathymetric Chart of the Oceans (GEBCO) has released the GEBCO_2014 grid, a new digital bathymetric model of the world ocean floor merged with land topography from publicly available digital elevation models. GEBCO_2014 has a grid spacing of 30 arc seconds, and updates the 2010 release (GEBCO_08) by incorporating new versions of regional bathymetric compilations from the International Bathymetric Chart of the Arctic Ocean (IBCAO), the International Bathymetric Chart of the Southern Ocean (IBCSO), the Baltic Sea Bathymetry Database (BSBD), and data from the European Marine Observation and Data network (EMODnet) bathymetry portal, among other data sources. Approximately 33% of ocean grid cells (not area) have been updated in GEBCO_2014 from the previous version, including both new interpolated depth values and added soundings. These updates include large amounts of multibeam data collected using modern equipment and navigation techniques, improving portrayed details of the world ocean floor. Of all non-land grid cells in GEBCO_2014, approximately 18% are based on bathymetric control data, i.e., primarily multibeam and single beam soundings, or pre-prepared grids which may contain some interpolated values. The GEBCO_2014 grid has a mean and median depth of 3897 m and 3441 m, respectively. Hypsometric analysis reveals that 50% of the Earths surface is comprised of seafloor located 3200 m below mean sea level, and that ~900 ship-years of surveying would be needed to obtain complete multibeam coverage of the worlds oceans.

New integrated data management system for Ridge2000 and MARGINS research

The initiation of dedicated databases for the U.S. National Science Foundation (NSF)-supported Ridge2000 and MARGINS programs provides the opportunity to develop a data management system capable of handling the primary data types of marine geoscience research. Ridge2000 and MARGINS are broad initiatives focused on fundamental problems of crustal creation, evolution, and destruction along the world’s tectonic plate boundaries.These programs involve the collection of a wide range of geophysical data types, as well as rock, fluid, and biological samples, and time series data. An effective data management scheme is essential for the success of the Ridge2000 and MARGINS programs, to facilitate integration of the broad suite of studies carried out within

New software for processing sidescan data from sidescan-capable multibeam sonars

The authors have developed new software tools for the processing and display of sidescan data obtained with the latest generation of multibeam sonars; these programs are distributed as part of the MB-System software package. The new utilities provide a straightforward means for several common processing tasks, including analyzing the drop in backscatter intensity with increasing grazing angle, correcting sidescan images for the amplitude vs. grazing angle variation, and filtering. The grazing angle correction is particularly effective when applied to multibeam sonar sidescan for which high-resolution co-registered bathymetry is available. Examples are provided using multibeam sidescan and bathymetry obtained using a 12 kHz, 120/spl deg/ SeaBeam 2112 sonar.

A Portable System For Ocean Bottom Imaging and Charting

The Sea Mapping and Remote Characterization (Sea MARC) system is a sophisticated means of data acquisition in support of geophysical, acoustic, oceanographic, and hydrographic activities in all water depths. Typical real-time Sea MARC outputs can include ocean floor bathymetry, slant range corrected side-scan images, and sub-bottom profiles; these can be made at survey rates up to 10 square miles per hour. In addition to real-time displays, the Sea MARC data (along with ships data and navigation information) are recorded on magnetic tape for later processing at on-shore computer facilities. Designed to be highly modular and flexible in configuration, the Sea MARC system comprises four primary sub-systems: an instrumented towfish, a telemetry and towing cable, a self-powered shipboard handling system and an on-deck data processing center. The system can be readily adapted to meet the data acquisition needs of a wide range of applications, from physical oceanography and marine geophysics to pipeline route surveys, drilling lease site investigations, and ocean mineral deposit characterization. During the past two years, while engaged by commercial, governmental, and academic agencies, one Sea MARC system has successfully imaged more than 10,000 square miles of ocean floor, including: the Mississippi and Laurentian fans, deepwater fracture zones, polymetallic sulfide deposits on the Juan de Fuca Ridge, and the continental margins of the U.S. and Canadian east coast. The use of a portable system for data acquisition as just described provides a cost effectiveness that cannot be matched by large, special purpose ships. As the outfitting and operating costs of these ships continues to escalate, systems such as the Sea MARC will perform an increasing portion of the offshore ocean survey activities that previously were the exclusive realm of large, dedicated oceanographic vessels.

Shallow seismic experiments using shear waves

During the summer of 1986, a series of seismo‐acoustic experiments was carried out in shallow water off the New Jersey shore. The purpose of these experiments was to measure the geoacoustic properties of the ocean sediments that comprise the upper few hundred meters of the sediment column. Seismic sources and receivers were deployed at or very near the bottom in order to excite shear waves in the sediment and minimize the effects of interference from waterborne propagation. The experiments were performed at several sites where prior field work had established physical properties and a detailed profile of the sediments. By using conventional air guns deployed in an unconventional way, strong interface and diving shear waves were generated; these data were inverted to obtain shear wave velocity as a function of depth. The inversion results were then compared with the predictions of a geoacoustic model that accounts for the effects of voids ratio, overburden pressure, and other physical parameters. The in si...

Navigation For Surveys Of Trans-Pacific Fiber-Optic Cables

Cable route surveys were carried out between Oahu and Luzon using the NECOR multi-narrow beam echosounding system on R/V Robert D. Conrad for AT&T Communications, Inc. Navigation systems included CA-code GPS (Magnavox T-set), 2-chain Range-Range LORAN C (Internav LC-408), Transit satellite (Magnavox 1107), 2-axis doppler speed log (Furuno CI-30) and gyro heading (Sperry MK-27 gyro). GPS positions include clock-aided (HP-5065A Rubidium standard) 2-satellite fixes in addition to fixes derived from 3, 4 and 5 satellites.

Ice profiling sonars: a comparison of error budgets

An accurate understanding of the volume of ice in the Arctic is a critical component of understanding the Earths heat budget. Estimation of this volume is a complex problem involving both spatial coverage issues as well as accuracy of the ice thickness measurements themselves. Much of the data from which such estimations are made has been taken from 637-class US Navy submarines. Unfortunately, there will be little or no data from this class of submarine in the future as they are all being decommissioned. New observations will be made with new sonars and the ability to accurately and robustly compare observations between the new and old measurement systems is necessary to minimize the confusion due to differences between them. This paper describes the sonar system used to collect the existing data sets from the 637-class submarines, a new sonar for making similar observations from autonomous underwater vehicles (AUVs) in the future and establishes a reference framework for evaluating error budgets in this type of sonar system. A careful intercomparison between the old and the new sonars to establish a robust basis for extending the observational time series should be done.

Seafloor Characterization and Mapping Pods (SCAMP): submarine-mounted geophysical mapping

Summary form only given. In 1998 the Seafloor Characterization and Mapping Pods (SCAMP) were deployed on the US Navy nuclear attack submarine USS HAWKIBILL for unclassified swath mapping and subbottom profiling under the Arctic ice canopy. Data was collected under the SCICEX program. SCAMP consists of a Sidescan Swath Bathymetric Sonar (SSBS) and a High-Resolution Subbottom Profiler (HRSP), and a marine gravity meter that are integrated with a physically compact Data Acquisition and Quality Control System (DAQCS). The transducers for each of the sonars are mounted in purpose built hydrodynamic pods that are temporarily fastened to special purpose threaded weldments along the boats keel. The inboard electronics for the system are packaged for submarine installation and mounted in the torpedo room. The SSBS is a 12 kiloHertz SeaMARC design adapted for under-ice mapping by adding transmit and receive beam forming and shading to suppress spurious returns from the ice canopy. Transducers are housed in a keel-mounted pod with electronics mounted outside the pressure hull but above the water line when surfaced. Swath image data is produced over a 135 to 140 degree swath centered at nadir while high quality bathymetry covers a 120 degree swath. The HRSP is a Bathy-2000P FM modulated subbottom profiler adapted for submarine installation and operation. It produces high quality subbottom data using an array of 9 DT-109 transducers driven by a 2 kilowatt transmitter. Seafloor penetration in excess of 100 meters with a resolution of 10s of centimeters is common in sediment filled areas of the Arctic basins. Initial at-sea tests on the submarine were conducted out of Pearl Harbor, Hawaii. The first deployment in the Arctic took place during SCICEX-98 during which more than 30 days of data were collected in the data release area.

Objectives for a cabled observatory in Alaska's Beaufort Sea

Study of the Arctic Ocean is limited by the sea ice and harsh weather that prevent access through much of the year. These constraints have restricted data acquisition in the past and obscured understanding of events, processes, and variability of the environment of the Arctic Ocean. Breaching this isolation can be achieved through the use of new technologies and the adaptation of existing instrumentation to monitor the shelf and basin independent of surface conditions. Through much of its history, Arctic oceanography has been dedicated to the study of large-scale seafloor structure, ocean circulation, and hydrographic structure. Recently, expedition-based observations have been augmented by moored or ice-tethered instruments that provide year-round observations during the span of their deployment. With increased knowledge collected over an extended period, variability has become apparent but is not well understood. Permanent seafloor instrumentation is the only way to understand this variability (seasonal and annual) in the context of what may be rapid climate change (annual to decadal).