Applied Ocean Physics and Engineering (AOP&E)
http://hdl.handle.net/1912/10
Thu, 25 Aug 2016 06:12:47 GMT
20160825T06:12:47Z

Diffuse venting at the ASHES hydrothermal field : heat flux and tidally modulated flow variability derived from in situ timeseries measurements
http://hdl.handle.net/1912/8236
Diffuse venting at the ASHES hydrothermal field : heat flux and tidally modulated flow variability derived from in situ timeseries measurements
Mittelstaedt, Eric; Fornari, Daniel J.; Crone, Timothy J.; Kinsey, James C.; Kelley, Deborah S.; Elend, Mitch
Timeseries measurements of diffuse exitfluid temperature and velocity collected with a new, deepsea camera, and temperature measurement system, the Diffuse Effluent Measurement System (DEMS), were examined from a fracture network within the ASHES hydrothermal field located in the caldera of Axial Seamount, Juan de Fuca Ridge. The DEMS was installed using the HOV Alvin above a fracture near the Phoenix vent. The system collected 20 s of 20 Hz video imagery and 24 s of 1 Hz temperature measurements each hour between 22 July and 2 August 2014. Fluid velocities were calculated using the Diffuse Fluid Velocimetry (DFV) technique. Over the ∼12 day deployment, median upwelling rates and mean fluid temperature anomalies ranged from 0.5 to 6 cm/s and 0°C to ∼6.5°C above ambient, yielding a heat flux of 0.29 ± 0.22 MW m−2 and heat output of 3.1± 2.5 kW. Using a photo mosaic to measure fracture dimensions, the total diffuse heat output from cracks across ASHES field is estimated to be 2.05 ± 1.95 MW. Variability in temperatures and velocities are strongest at semidiurnal periods and show significant coherence with tidal height variations. These data indicate that periodic variability near Phoenix vent is modulated both by tidally controlled bottom currents and seafloor pressure, with seafloor pressures being the dominant influence. These results emphasize the importance of local permeability on diffuse hydrothermal venting at midocean ridges and the need to better quantify heat flux associated with young oceanic crust.
Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 17 (2016): 1435–1453, doi:10.1002/2015GC006144.
Wed, 27 Apr 2016 00:00:00 GMT
http://hdl.handle.net/1912/8236
20160427T00:00:00Z

Evidence of energy and momentum flux from swell to wind
http://hdl.handle.net/1912/8234
Evidence of energy and momentum flux from swell to wind
Kahma, Kimmo; Donelan, Mark; Drennan, William M.; Terray, Eugene
Measurements of pressure near the surface in conditions of wind sea and swell are reported. Swell, or waves that overrun the wind, produces an upward flux of energy and momentum from waves to the wind and corresponding attenuation of the swell waves. The estimates of growth of wind sea are consistent with existing parameterizations. The attenuation of swell in the field is considerably smaller than existing measurements in the laboratory.
Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 46 (2016): 21432156, doi:10.1175/JPOD150213.1.
Thu, 23 Jun 2016 00:00:00 GMT
http://hdl.handle.net/1912/8234
20160623T00:00:00Z

Graphical model driven methods in adaptive system identification
http://hdl.handle.net/1912/8230
Graphical model driven methods in adaptive system identification
Yellepeddi, Atulya
Identifying and tracking an unknown linear system from observations of its inputs and outputs
is a problem at the heart of many different applications. Due to the complexity and
rapid variability of modern systems, there is extensive interest in solving the problem with
as little data and computation as possible.
This thesis introduces the novel approach of reducing problem dimension by exploiting
statistical structure on the input. By modeling the input to the system of interest as a
graphstructured random process, it is shown that a large parameter identification problem
can be reduced into several smaller pieces, making the overall problem considerably simpler.
Algorithms that can leverage this property in order to either improve the performance
or reduce the computational complexity of the estimation problem are developed. The first
of these, termed the graphical expectationmaximization least squares (GEMLS) algorithm,
can utilize the reduced dimensional problems induced by the structure to improve the accuracy
of the system identification problem in the low sample regime over conventional methods
for linear learning with limited data, including regularized least squares methods.
Next, a relaxation of the GEMLS algorithm termed the relaxed approximate graph
structured least squares (RAGSLS) algorithm is obtained that exploits structure to perform
highly efficient estimation. The RAGSLS algorithm is then recast into a recursive
framework termed the relaxed approximate graph structured recursive least squares (RAGSRLS)
algorithm, which can be used to track timevarying linear systems with low complexity
while achieving tracking performance comparable to much more computationally intensive
methods.
The performance of the algorithms developed in the thesis in applications such as channel
identification, echo cancellation and adaptive equalization demonstrate that the gains admitted
by the graph framework are realizable in practice. The methods have wide applicability,
and in particular show promise as the estimation and adaptation algorithms for a new breed
of fast, accurate underwater acoustic modems.
The contributions of the thesis illustrate the power of graphical model structure in simplifying
difficult learning problems, even when the target system is not directly structured.
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2016
Thu, 01 Sep 2016 00:00:00 GMT
http://hdl.handle.net/1912/8230
20160901T00:00:00Z

Approximate formulas and physical interpretations for horizontal acoustic modes in a shelfslope front model
http://hdl.handle.net/1912/8227
Approximate formulas and physical interpretations for horizontal acoustic modes in a shelfslope front model
DeCourcy, Brendan; Lin, YingTsong; Siegmann, William
The structure and behavior of horizontal acoustic modes for a threedimensional idealized model of a shelfslope front are examined analytically. The Wentzel–Kramers–Brillouin–Jeffreys (WKBJ) method is used to obtain convenient simple expressions and to provide physical insight into the structure and behavior of horizontal modes as trapped, leaky, or transition types. Validity regions for WKBJ expressions in terms of slope and frontal parameters are found, and outside the regions the asymptotic formulas for large order and large argument Hankel functions are used. These combined approximations have very good accuracy as shown by comparisons with numerical solutions for modal shapes and horizontal wavenumbers.
Author Posting. © Acoustical Society of America, 2016. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 140 (2016): EL20, doi:10.1121/1.4954881.
Thu, 07 Jul 2016 00:00:00 GMT
http://hdl.handle.net/1912/8227
20160707T00:00:00Z