Bathymetry of Molloy Deep: Fram Strait between Svalbard and Greenland

The sea floor of Fram Strait, the over 2500 m deep passage between the Arctic Ocean and the Norwegian-Greenland Sea, is part of a complex transform zone between the Knipovich mid-oceanic ridge of the Norwegian-Greenland Sea and the Nansen-Gakkel Ridge of the Arctic Ocean. Because linear magnetic anomalies formed by sea-floor spreading have not been found, the precise location of the boundary between the Eurasian and the North American plate is unknown in this region. Systematic surveying of Fram Strait with SEABEAM and high resolution seismic profiling began in 1984 and continued in 1985 and 1987, providing detailed morphology of the Fram Strait sea floor and permitting better definition of its morphotectonics. The 1984 survey presented in this paper provided a complete set of bathymetric data from the southernmost section of the Svalbard Transform, including the Molloy Fracture Zone, connecting the Knipovich Ridge to the Molloy Ridge; and the Molloy Deep, a nodal basin formed at the intersection of the Molloy Transform Fault and the Molloy Ridge. This nodal basin has a revised maximum depth of 5607 m water depth at 79°8.5N and 2°47E.     

Modern swathe sounding and sub-bottom profiling technology for research applications: The Atlas Hydrosweep and Parasound Systems

This chapter describes two separate but complementary research echosounder systems originally developed by Krupp Atlas Elektronik GmbH for the new German oceanographic research vessel Meteor.The Hydrosweep is a Hydrographic wide-swathe sweep survey echosounder for both shallow and deep water applications providing accurate bathymetric surveys and terrain-following navigation capabilities.The Parasound system is a hull-mounted dual channel parametric narrow-beam deep sea survey and sub-bottom profiling echosounder enabling particularly high vertical and horizontal resolution of seabed features.     

Three-dimensional visualization of mission planning and control forthe NPS autonomous underwater vehicle

The Naval Postgraduate School (NPS) is constructing a small autonomous underwater vehicle (AUV) with an onboard mission control computer. The mission controller software for this vehicle is a knowledge-based artificial intelligence (AI) system requiring thorough analysis and testing before the AUV is operational. The manner in which rapid prototyping of this software has been demonstrated by developing a controller code on a LISP machine and using an Ethernet link with a graphics workstation to simulate the controller's environment is discussed. The development of a testing simulator using a knowledge engineering environment (KEE) expert system shell that examines AUV controller subsystems and vehicle models before integrating them with the full AUV for its test environment missions is discussed. This AUV simulator utilizes an interactive mission planning control console and is fully autonomous once initial parameters are selected     

Evidence for slope instability and current-induced sediment transport,the RMSTitanic wreck search area,Newfoundland rise

The first map of the sea bed morphology and sedimentary features within the RMSTitanic search area is proposed from the interpretation of SAR side-scan sonar images. Downslope sedimentary features such as erosional furrows and crown scarps constitute a 7 km wide instability corridor. A large field (15 km²) of asymmetrical sediment waves indicating a downslope transport is identified. Current-induced features corresponding to associated sand ribbons and barchan dunes resulting from the Western Boundary Undercurrent action are mapped. The morphology of theTitanic Canyon is also precised from the SAR images. Finally, the origin of the sea bed features is discussed in an attempt to link each bed form to a sedimentary process.     

Proximate Constituents, Biomass, and Energy in Posidonia oceanica (Potamogetonaceae)

Abstract. The proximate composition of the various components of Posidonia oceanica is given in terms of gravimetric and energetic level and amount of plants from 2 depths at Port-Cros (Var. France). The level of proximate constituents differed little between the leaves (regardless of age) and the roots, but the rhizome contained much more soluble carbohydrate and less structural carbohydrate and ash. Because of this, the energy level in the leaves was more in terms of organic material and less in terms of total material than the energy level in the rhizome. The leaves of a P. oceanica shoot at 2 m depth in July contained 1.6 g organic material. 29.0 kJ. The weight and energy of the soluble carbohydrate in the rhizome from the base of the leaves to the 18th sheath scale decreased by ca. 40% from October to March and increased by ca. 100% from March to July.     

Design of a 3D Chirp Sub-bottom Imaging System

Chirp sub-bottom profilers are marine acoustic devices that use a known and repeatable source signature (1–24 kHz) to produce decimetre vertical resolution cross-sections of the sub-seabed. Here the design and development of the first true 3D Chirp system is described. When developing the design, critical factors that had to be considered included spatial aliasing, and precise positioning of sources and receivers. Full 3D numerical modelling of the combined source and receiver directivity was completed to determine optimal source and receiver geometries. The design incorporates four source transducers (1.5–13 kHz) that can be arranged into different configurations, including Maltese Cross, a square and two separated pairs. The receive array comprises 240 hydrophones in 60 groups whose group-centres are separated by 25 cm in both horizontal directions, with each hydrophone group containing four individual elements and a pre-amplifier. After careful consideration, it was concluded that the only way to determine with sufficient accuracy the source–receiver geometry, was to fix the sources and receivers within a rigid array. Positional information for the array is given by a Real Time Kinematic GPS and attitude system incorporating four antennas to give position, heading, pitch and roll. It is shown that this system offers vertical positioning accuracy with a root-mean-square (rms) error less than 2.6 cm, while the horizontal positioning rms error was less than 2.0 cm. The system is configured so that the Chirp source signature can be chosen by software aboard the acquisition vessel. The complete system is described and initial navigational and seismic data results are presented. These data demonstrate that the approach of using fixed source-receiver geometry combined with RTK navigation can provide complete 3D imaging of the sub-surface.     

Cross-Calibration and Long-Term Monitoring of the Microwave Radiometers of ERS, TOPEX, GFO, Jason, and Envisat

The radiometers on board the satellites ERS-1, TOPEX/Poseidon, ERS-2, GFO, Jason-1, and Envisat measure brightness temperatures at two or three different frequencies to determine the total columnal water vapor content and wet tropospheric path delay, a major correction to the altimeter range measurements. In order to asses the long-term stability of the path delay, the radiometers are calibrated against vicarious cold and hot references, against each other, and against several atmospheric models. Four of these radiometers exhibit significant drifts in at least one of the channels, resulting in yet unmodeled errors in path delay of up to 1 mm/year, thus limiting the accuracy at which global sea level rise can be inferred from the altimeter range measurements.