Background - Revision history

Meylan at 10:52, 10 September 2009

2009-09-10T10:52:50Z

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	In this chapter, we give a background on the topics covered in the thesis.		In this chapter, we give a background on the topics covered in the thesis.

Adi Kurniawan: /* Wave Attenuation */

2008-12-24T06:09:50Z

Wave Attenuation

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	According to [[shen_squire98]], other factors which may be relevant include: the absorption due to hysteresis as floes deform on the passing wave field, the absorption in the water column from processes such as wave breaking and the absorption due to collisions and other interactions between floes.		According to [[shen_squire98]], other factors which may be relevant include: the absorption due to hysteresis as floes deform on the passing wave field, the absorption in the water column from processes such as wave breaking and the absorption due to collisions and other interactions between floes.
	[[shen_etal87]] however find that collisional stresses are only small and [[mckenna_crocker90]] conclude that floe collisions cannot account for the observed decrease in wave energy.		[[shen_etal87]] however find that collisional stresses are only small and [[mckenna_crocker90]] conclude that floe collisions cannot account for the observed decrease in wave energy.


	==Wave Attenuation Models==		==Wave Attenuation Models==

Adi Kurniawan: /* Scattering Models */

2008-12-24T06:09:25Z

Scattering Models

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	The ice floe therefore scatters incoming ocean wave energy due to a mismatch between the mode of propagation beneath the raft as compared to that under an open water surface ([[Squire et. al. 1995]]).		The ice floe therefore scatters incoming ocean wave energy due to a mismatch between the mode of propagation beneath the raft as compared to that under an open water surface ([[Squire et. al. 1995]]).
	This scattering energy generates an energy reflection and transmission wave.		This scattering energy generates an energy reflection and transmission wave.


	===Solitary plates and two semi-infinite plates===		===Solitary plates and two semi-infinite plates===

Akohout: /* Methods */

2008-12-11T23:50:04Z

Methods

Akohout: /* Available Data Sets */

2008-12-11T23:49:34Z

Available Data Sets

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	Floe size distributions along the flight path into the ice were derived from overlapping vertical photographs taken from helicopter.		Floe size distributions along the flight path into the ice were derived from overlapping vertical photographs taken from helicopter.
	The main sources of experimental error were changes in the swell conditions during the experiment, difficulties in determining the ice floe size distribution and thickness, and difference in the swell direction for different periods or multi-directional swell.		The main sources of experimental error were changes in the swell conditions during the experiment, difficulties in determining the ice floe size distribution and thickness, and difference in the swell direction for different periods or multi-directional swell.

	The attenuation coefficients from the experiments in the Greenland Sea in September 1978, September 1979 and July 1983 are given in [[Wadhams et. al. 1988]] and are used in this study.		The attenuation coefficients from the experiments in the Greenland Sea in September 1978, September 1979 and July 1983 are given in [[Wadhams et. al. 1988]] and are used in this study.
	We also use the attenuation coefficients from the Bering Sea in March 1979 and February 1983.		We also use the attenuation coefficients from the Bering Sea in March 1979 and February 1983.

Akohout: /* Available Data Sets */

2008-12-11T23:49:08Z

Available Data Sets

Akohout: /* Available Data Sets */

2008-12-11T23:46:37Z

Available Data Sets

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	===Available Data Sets===		===Available Data Sets===
	''Early Data Sets''		''Early Data Sets''

	The wave decay measurements from the 60's and early 70's are available and have been summarised and compared against wave-attenuation theory in [[Wadhams 1986]].		The wave decay measurements from the 60's and early 70's are available and have been summarised and compared against wave-attenuation theory in [[Wadhams 1986]].

Akohout: /* Available Data Sets */

2008-12-11T23:46:10Z

Available Data Sets

Akohout: /* Wave Attenuation */

2008-12-11T23:45:21Z

Wave Attenuation

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	==Wave Attenuation Models==~~(7)~~		==Wave Attenuation Models==
	[[Wadhams 1986]] was a significant paper, as it showed how to estimate the transmitted energy through a set of floes in terms of the transmitted energy through a single floe, so that an attenuation coefficient could be estimated.		[[Wadhams 1986]] was a significant paper, as it showed how to estimate the transmitted energy through a set of floes in terms of the transmitted energy through a single floe, so that an attenuation coefficient could be estimated.
	The possible paths of each wave vector through the ice field are considered, and the final forward vector summed through all possible multiple reflections.		The possible paths of each wave vector through the ice field are considered, and the final forward vector summed through all possible multiple reflections.

Akohout: /* Solitary plates and two semi-infinite plates */

2008-12-11T23:35:14Z

Solitary plates and two semi-infinite plates

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	A more challenging problem involves solving for two semi-infinite plates with arbitrary properties.		A more challenging problem involves solving for two semi-infinite plates with arbitrary properties.
	The first significant work on this problem was done by [[Evans Davies 1968]], who presented a solution method for evaluating the transmission and reflection of waves, propagating from a semi-infinite region of open water into a semi-infinite region of a floating elastic plate.		The first significant work on this problem was done by [[Evans and Davies 1968]], who presented a solution method for evaluating the transmission and reflection of waves, propagating from a semi-infinite region of open water into a semi-infinite region of a floating elastic plate.
	The method of solution was based on the Wiener--Hopf technique.		The method of solution was based on the Wiener--Hopf technique.
	[[Evans and Davies 1968]], however, only solved explicitly for the case of shallow water.		[[Evans and Davies 1968]], however, only solved explicitly for the case of shallow water.
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	The three-dimensional floating circular ice floe is solved in [[Meylan and Squire 1996]] via an extension of [[Meylan and Squire 1994]] and [[Peter et. al 2004]] solve for the finite depth case using matched eigenfunctions.		The three-dimensional floating circular ice floe is solved in [[Meylan and Squire 1996]] via an extension of [[Meylan and Squire 1994]] and [[Peter et. al 2004]] solve for the finite depth case using matched eigenfunctions.
	[[Meylan 2002]] solves for arbitrary floe shapes where the dry modes are substituted into the integral equation for water to give a linear system of equations for the coefficients used to expand the ice floe motion.		[[Meylan 2002]] solves for arbitrary floe shapes where the dry modes are substituted into the integral equation for water to give a linear system of equations for the coefficients used to expand the ice floe motion.
	The modes are determined generally using a finite element approach.		The modes are determined generally using a finite element approach.

	===Multiple plates===		===Multiple plates===

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	A number of different methods are discussed below.		A number of different methods are discussed below.

	''Early measurements''		''Early measurements''<br/>
	The first measurements of wave decay in the zone of discrete ice floes near an unconfined ice margin were made by shipborne wave recorder ([[Robin 1963]]) and reported in [[Wadhams 1979]] and [[Wadhams 1986]].		The first measurements of wave decay in the zone of discrete ice floes near an unconfined ice margin were made by shipborne wave recorder ([[Robin 1963]]) and reported in [[Wadhams 1979]] and [[Wadhams 1986]].
	Later measurements were made by upward-looking echo sounder from a submerged hovering submarine ([[Wadhams 1972]] and [[Wadhams 1978]]) and by airborne laser profilometer ([[Wadhams 1975]]).		Later measurements were made by upward-looking echo sounder from a submerged hovering submarine ([[Wadhams 1972]] and [[Wadhams 1978]]) and by airborne laser profilometer ([[Wadhams 1975]]).

	''Wave buoys''		''Wave buoys''<br/>
	Wave buoys have been the standard instrument for measuring waves for many years.		Wave buoys have been the standard instrument for measuring waves for many years.
	The most recent buoys use ultra-sensitive tiltmeters and novel re-zeroing techniques to autonomously gather wave data.		The most recent buoys use ultra-sensitive tiltmeters and novel re-zeroing techniques to autonomously gather wave data.
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	It is difficult to obtain accurate wave-attenuation data using wave buoys, as it requires extensive logistical support to measure wave properties simultaneously (or near simultaneously), and results can be skewed by changes in the swell conditions during the experiment and difference in the swell direction for different periods or multi-directional swell.		It is difficult to obtain accurate wave-attenuation data using wave buoys, as it requires extensive logistical support to measure wave properties simultaneously (or near simultaneously), and results can be skewed by changes in the swell conditions during the experiment and difference in the swell direction for different periods or multi-directional swell.

	''Remote Sensing''		''Remote Sensing''<br/>
	Remote sensing can be used to obtain sea-ice information on a continuous basis.		Remote sensing can be used to obtain sea-ice information on a continuous basis.
	Due to their all weather capability, microwave sensors like synthetic aperture radar (SAR) or the radiometer play an important role in this context.		Due to their all weather capability, microwave sensors like synthetic aperture radar (SAR) or the radiometer play an important role in this context.
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	Unfortunately, however, the use of SAR has not been found to be practical in measuring wave-attenuation through discrete floes.		Unfortunately, however, the use of SAR has not been found to be practical in measuring wave-attenuation through discrete floes.

	''Autonomous Underwater Vehicle (AUV)''		''Autonomous Underwater Vehicle (AUV)''<br/>
	In these experiments, an upward looking Acoustic Doppler Current Profiler (ADCP) is mounted on an autonomous underwater vehicle (AUV).		In these experiments, an upward looking Acoustic Doppler Current Profiler (ADCP) is mounted on an autonomous underwater vehicle (AUV).
	The AUV is a promising device which can sample at high resolution and can sample a large portion of the MIZ over short time scales ([[Hayes 2007]]).		The AUV is a promising device which can sample at high resolution and can sample a large portion of the MIZ over short time scales ([[Hayes 2007]]).

	===Available Data Sets===		===Available Data Sets===

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	===Available Data Sets===		===Available Data Sets===
	''Early Data Sets''		''Early Data Sets''<br/>
	The wave decay measurements from the 60's and early 70's are available and have been summarised and compared against wave-attenuation theory in [[Wadhams 1986]].		The wave decay measurements from the 60's and early 70's are available and have been summarised and compared against wave-attenuation theory in [[Wadhams 1986]].

	''The Scott Polar Research Institution (SPRI) Experiments''		''The Scott Polar Research Institution (SPRI) Experiments''<br/>

	The most substantial set of experiments to measure wave-attenuation in the MIZ were carried out by the SPRI in the late 1970's and early 1980's ([[Squire and Moore 1980]], [[Wadhams et. al. 1986]] and [[Wadhams et. al. 1988]]).		The most substantial set of experiments to measure wave-attenuation in the MIZ were carried out by the SPRI in the late 1970's and early 1980's ([[Squire and Moore 1980]], [[Wadhams et. al. 1986]] and [[Wadhams et. al. 1988]]).
	During these experiments, a helicopter was used to visit floes at intervals within the ice fields along the major axis of the incoming wave spectrum. At each site a wave buoy was inserted between floes to measure the local wave spectrum. The flexural, heave and surge responses of the experimental floe were measured with accelerometers and strain-meters.		During these experiments, a helicopter was used to visit floes at intervals within the ice fields along the major axis of the incoming wave spectrum. At each site a wave buoy was inserted between floes to measure the local wave spectrum. The flexural, heave and surge responses of the experimental floe were measured with accelerometers and strain-meters.
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	Unfortunately, due to possible reflection or absorption of waves from the fjords, accurate attenuation coefficients could not be calculated from the 1978 Greenland Sea experiments.		Unfortunately, due to possible reflection or absorption of waves from the fjords, accurate attenuation coefficients could not be calculated from the 1978 Greenland Sea experiments.

	''The Labrador Ice Margin Experiment (LIMEX)''		''The Labrador Ice Margin Experiment (LIMEX)''<br/>

	Another set of experiments took place off the east coast of Newfoundland, Canada, in 1987 and 1989.		Another set of experiments took place off the east coast of Newfoundland, Canada, in 1987 and 1989.
	These experiments provided synthetic aperture radar (SAR) imagery, wave buoy and ice property data.		These experiments provided synthetic aperture radar (SAR) imagery, wave buoy and ice property data.
	We attempted to obtain the results of this experiment, but unfortunately were not successful.		We attempted to obtain the results of this experiment, but unfortunately were not successful.

	''The Antarctic Peninsula Experiments''		''The Antarctic Peninsula Experiments''<br/>

	Most recently an experiment took place in the MIZ of Antarctica.		Most recently an experiment took place in the MIZ of Antarctica.
	Autosub, an Autonomous Underwater Vehicle (AUV), was used to complete four missions west of the Antarctic Peninsula in the Bellinghausen Sea during 22 -- 25 March 2003.		Autosub, an Autonomous Underwater Vehicle (AUV), was used to complete four missions west of the Antarctic Peninsula in the Bellinghausen Sea during 22 -- 25 March 2003.