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Samodurov A.S.,Marine Hydrophysical Institute | Scranton M.I.,State University of New York at Stony Brook | Astor Y.,Estacion de Investigaciones Marinas de Margarita | Ivanov L.I.,Woods Hole Group Inc. | And 3 more authors.
Deep-Sea Research Part I: Oceanographic Research Papers | Year: 2013

A simple 1.5-dimensional model of vertical exchange for heat, salt, and other dissolved substances has been developed for the Cariaco Basin. The model parameters are derived based on the temperature and salinity data collected monthly at a deepwater station in the eastern part of the basin from 1995 through 2007 during the CARIACO time series program. The model describes the processes of turbulent (eddy) diffusion, which includes the integrated effect of diffusive exchange mechanisms acting in the basin, and of vertical advection, which arises following injection of dense water into deep layers following an inflow from the Caribbean Sea. The model takes into account the changes in the horizontal cross-section area of the basin with respect to depth.Temporal variability is an important feature of the hydrography of the Cariaco Basin. To assess profiles of the vertical eddy diffusion coefficient and vertical advection velocity, we examined a time series of CTD profiles (potential temperature and salinity). Two distinct time intervals were identified as the result of this examination. During the first period, the thermohaline structure of the basin was apparently influenced by one or more inflows. The second period, in contrast, showed little or no influence of an inflow. The data from the second period, where no inflows were observed, were incorporated into corresponding transfer equations to assess the profile of the vertical eddy diffusion coefficient, k(z). Then, the result of this assessment was used with the data from the first period to estimate the profile of the vertical advection velocity, W(z), for a time when the effects of an inflow were evident. For that case, the transfer equations include the terms describing the effect of the inflow.Analysis of the vertical profile of the turbulent diffusion coefficient suggests that, in the upper stratified part of the water column, the diffusion mechanism is mostly associated with transient mixing events, which occur due to shear instability in the field of low frequency internal waves. We speculate that below 400. m bottom friction over the sloping bottom and geothermal heat flux play the decisive role in the vertical exchange. Analysis of the W(z) profiles reveals two layers dominated by the entrainment of the ambient fluid into the down flow of dense water from the Caribbean Sea, and two layers where this down flow breaks down through the formation of isopycnal intrusions. © 2012 Elsevier Ltd.

Hamilton Jr. R.P.,Woods Hole Group Inc.
Hydro International | Year: 2011

Woods Hole Group, headquartered in Falmouth, Massachusetts, is an international environmental scientific and engineering consultancy focused on water and sediment from the deep ocean through the coastal zone. Scientific and engineering expertise includes: Oceanography & Measurement Systems; Coastal Sciences, Engineering & Planning; and Environmental Assessment & Remediation.

Magnell B.A.,Woods Hole Group Inc. | Ivanov L.I.,Woods Hole Group Inc.
Proceedings of the Annual Offshore Technology Conference | Year: 2014

We discuss the results of a process-oriented analysis of current profile measurements collected from 2005 through 2010 in the Gulf of Mexico by oil industry operators, who are required to measure ocean current profiles and transmit these data in near-real-time. The individual data ensembles are sent to NDBC where they are processed, quality checked, archived and made available to the public through the NDBC website. WHG performed a thorough inspection of the data, including a review of the temporal and spatial continuity of the data, cross-check between neighboring stations and between current data and satellite altimetry charts, and verification of the metadata using independent sources of [1]. The cleaned and quality-controlled data were analyzed to identify and classify the observed cases of stronger currents. The analysis identified 140 cases of current events characterized by a subsurface 'jet' peaking at 30-50 cm/s that does not have a surface expression.. In most of the mid-water current events identified in the 2005-2010 NTL data, the current speed peak is located somewhere between 300m and 800m, most frequently around 500m, much deeper than similar patterns identified in earlier studies. Some of the events identified in our study lasted for less than one day, but many events were of a much longer duration. Most of these events were observed southeast of the Mississippi delta and had horizontal scales over 15 miles and lingered in the area for an extended period of time. Some of the identified events were caused by strong inertial oscillations with multiple speed peaks confined to a relatively narrow layer centered around 500m. Mid-water jets have been identified in previous work [2] but this new analysis provides far more cases and suggests that the jets have an upper limit of about 50 cm/s. Such magnitudes are unlikely to govern extreme loads on offshore risers or tendons but they could be a factor in fatigue. Copyright © 2014, Offshore Technology Conference.

Ivanov L.I.,Woods Hole Group Inc. | Magnell B.A.,Woods Hole Group Inc.
OCEANS 2012 MTS/IEEE: Harnessing the Power of the Ocean | Year: 2012

Strong currents are a matter of great concern for the maritime industries in the Gulf of Mexico. Oil industry operators working in the gulf are required to measure ocean current profiles and transmit these data in near-real-time. The data are collected primarily using TRDI ADCPs mounted on the structures or nearby. The individual data ensembles are sent to NDBC where they are processed, quality checked, archived and made available to the public through the NDBC website. In 2011, Woods Hole Group Inc. (WHG) was contracted by DeepStar Technology Development for Deepwater Research to create a database of deep ocean currents for the Gulf of Mexico. One of the objectives of the project was to identify and make plots of strong current ('energetic') events. WHG performed a thorough inspection of the data, including a review of the temporal and spatial continuity of the data, cross-check between neighboring stations and between current data and satellite altimetry charts. Based on this extensive dataset, a total of 560 strong current events were identified and classified according to the candidate mechanisms that cause these current intensifications. © 2012 IEEE.

Lowell N.S.,Lowell Instruments LLC | Walsh D.R.,Woods Hole Group Inc. | Pohlman J.W.,U.S. Geological Survey
2015 IEEE/OES 11th Current, Waves and Turbulence Measurement, CWTM 2015 | Year: 2015

The relatively high cost of acoustic current meters has placed practical limits on the use of these meters in marine research projects. One approach to reducing the cost of current measurements has been the re-invention of the Tilt Current Meter (TCM). Recent developments in accelerometers, magnetometers and low-power non-volatile memory have made it possible to make small, accurate and inexpensive TCMs. Here we describe the design and calibration of the Lowell Instruments TCM and validate its performance in Vineyard Sound, Massachusetts. The performance of four TCMs was compared to an acoustic Doppler current profiler reference meter. The TCMs exhibited an R squared correlation of 0.97-0.98 as well as low slope and offset errors. Based on this demonstrated accuracy we believe the TCM would be useful for a variety of research projects especially where there is a risk of instrument loss or where increased spatial density of measurements is desired. © 2015 IEEE.

Magnell B.A.,Woods Hole Group Inc. | Gordon L.,Doppler Ltd. | Yamin H.,Tadiran Batteries Ltd.
2015 IEEE/OES 11th Current, Waves and Turbulence Measurement, CWTM 2015 | Year: 2015

Ocean deployments of battery-powered instruments often include lithium battery packs, which enable deployments to last three times as long as they would using alkaline battery packs. Lithium batteries are widely regarded as hazardous. When we discovered that one of our ADCPs, which had been deployed with lithium batteries, had flooded, we worried whether the result would pose a risk. What we found was that while the ADCP's electronics had irreparably corroded, the batteries had discharged but had not gotten particularly hot, and not much else had happened. This paper explains why things happen slowly in these lithium batteries, even when they are immersed in conductive sea water. The slow rate of discharge of these particular batteries prevents them from getting very hot in such circumstances. We conclude that these lithium batteries are probably not more dangerous than alkaline batteries, given appropriate venting of the pressure housing. © 2015 IEEE.

Magnell B.A.,Woods Hole Group Inc. | Ivanov L.I.,Woods Hole Group Inc. | Morrison A.T.,Woods Hole Group Inc. | Hasbrouck E.G.,Woods Hole Group Inc.
2015 IEEE/OES 11th Current, Waves and Turbulence Measurement, CWTM 2015 | Year: 2015

Woods Hole Group, Inc. (WHG), configured, assembled and deployed a Mooring Systems Inc. Trawl Resistant Bottom Mount (TRBM) platform equipped with current, wave, and water quality instrumentation at a site called NJORD, located approximately 17 miles southeast of Ocean City, NJ. On March 6-7, 2013, the area offshore New Jersey experienced severe storm conditions due to an extratropical cyclone passing approximately 100 miles south of the measurement site. NOAA's National Data Buoy Center has been collecting wave data at a nearby location since 1985. According to this record, the storm of March 6-7, 2013, in terms of wave height (Hm0=7.8m), ranks as the second most severe storm in nearly 30 years. The maximum significant wave height (Hm0 = 8.1m) was recorded by the NOAA Buoy on November 13, 2009. This most severe storm event was also associated with an extratropical cyclone that passed south of the site as it translated towards east-northeast. That fact makes the data collected at the NJORD site during typical severe storm conditions valuable. The measurements collected by WHG during the storm are of interest from an acoustic measurement perspective because significant wave height was a large fraction of the water depth, producing actively breaking waves in 28m of water. The performance of the bottom-mounted AWAC in this high energy environment is evaluated. © 2015 IEEE.

Llort-Pujol G.,Telecom Bretagne | Sintes C.,Telecom Bretagne | Chonavel T.,Telecom Bretagne | Morrison III A.T.,Woods Hole Group Inc. | Daniel S.,Laval University
Marine Technology Society Journal | Year: 2012

Current high-resolution sidescan and multibeam sonars produce very large data sets. However, conventional interferometry-based bathymetry algorithms underestimate the potential information of such soundings, generally because they use small baselines to avoid phase ambiguity. Moreover, these algorithms limit the triangulation capabilities of multibeam echosounders (MBES) to the detection of one sample per beam, i.e., the zero-phase instant. In this paper, we argue that the correlation between signals plays a very important role in the exploration of a remotely observed scene. In the case of multibeam sonars, capabilities can be improved by using the interferometric signal as a continuous quantity. This allows consideration of many more useful soundings per beam and enriches understanding of the environment. To this end, continuous interferometry detection is compared here, from a statistical perspective, first with conventional interferometry-based algorithms and then with high-resolution methods such as the Multiple Signal Classification (MUSIC) algorithm. We demonstrate that a well-designed interferometry algorithm based on a coherence error model and an optimal array configuration permits a reduction in the number of beam formings (and therefore the computational cost) and an improvement in target detection (such as ship mooring cables or masts). A possible interferometry processing algorithm based on the complex correlation between received signals is tested on both sidescan sonars and MBESs and shows promising results for detection of small in-water targets.

Dill N.L.,Woods Hole Group Inc.
Proceedings of the International Conference on Estuarine and Coastal Modeling | Year: 2012

Numerical modeling provides an efficient tool for simulating hydrodynamics in estuarine environments. It is particularly useful when extensive field data collection is impractical, or when impacts of proposed restoration or engineering alternatives must be evaluated. Often surface water flow within an estuarine system is controlled by hydraulic structures such as culverts, flap gates, weirs, and/or sluice gates. These types of structures typically require special treatment within hydrodynamic model codes due to spatial scale limitations and/or physical assumptions (e.g., free surface flow). The Environmental Fluid Dynamics Code (EFDC) provides a means to model hydraulic structures using withdrawal-return pairs of model grid cells. However, the application of withdrawal-return cells in an EFDC model requires a priori knowledge of the relationship between water level and flow rate for the particular structure (e.g. a head-discharge relationship, rating curve, look-up table). In many cases it is difficult or impractical to obtain this information. The flow regime (e.g., outlet control, inlet control, pressure flow) may change as well. To remedy this, additional subroutines have been implemented within the EFDC code to compute discharge through various types of flow control structures (e.g., pipe culverts, box culverts, sluice gates, flap gates). Flow rate is determined at each model time step based on the computed water surface elevation using standard engineering equations for the particular structure. The modeler is required to input the geometry of the structure (e.g., pipe length and diameter) and discharge coefficients or friction factors. There is no need to determine a head-discharge relationship for the structure a priori. Flux between the assigned withdrawal-return cells is accounted for using the original code, which maintains the conservation of mass and other scalar variables. Application of the additional subroutines is demonstrated using EFDC models of actual estuarine systems and validated using field observations. © 2013 American Society of Civil Engineers.

Woods Hole Group Inc. | Date: 2013-04-01

Real-time buoy-based deep-water meteorology and ocean monitoring system comprised of surface and sub-surface buoys, oceanographic sensors, meterological instruments and communication devices.

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