Measurement of Waves - Revision history

Meylan: /* Wave Gages */

2009-08-19T08:37:02Z

Wave Gages

← Older revision		Revision as of 08:37, 19 August 2009
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	Double integration of vertical acceleration gives displacement. The double integration, however, amplifies low-frequency noise, leading to the low frequency signals seen in Figures 4 and 5 of of [[Waves and the Concept of a Wave Spectrum]]. In addition, the buoy's heave is not sensitive to wavelengths less than the buoy's diameter, and buoys measure only waves having wavelengths greater than the diameter of the buoy. Overall, careful measurements are accurate to 10% or better.		Double integration of vertical acceleration gives displacement. The double integration, however, amplifies low-frequency noise, leading to the low frequency signals seen in Figures 4 and 5 of of [[Waves and the Concept of a Wave Spectrum]]. In addition, the buoy's heave is not sensitive to wavelengths less than the buoy's diameter, and buoys measure only waves having wavelengths greater than the diameter of the buoy. Overall, careful measurements are accurate to 10% or better.

	= Wave ~~Gages~~ =		= Wave Gauges =
	Gauges may be mounted on platforms or on the seafloor in shallow water. Many different types of sensors are used to measure the height of the wave or subsurface pressure which is related to wave-height. Sound, infrared beams, and radio waves can be used to determine the distance from the sensor to the sea surface provided the sensor can be mounted on a stable platform that does not interfere with the waves. Pressure gauges described in ?.8 can be used to measure the depth from the sea surface to the gauge. Arrays of bottom-mounted pressure gauges are useful for determining wave directions. Thus arrays are widely used just offshore of the surf zone to determine offshore wave directions.		Gauges may be mounted on platforms or on the seafloor in shallow water. Many different types of sensors are used to measure the height of the wave or subsurface pressure which is related to wave-height. Sound, infrared beams, and radio waves can be used to determine the distance from the sensor to the sea surface provided the sensor can be mounted on a stable platform that does not interfere with the waves. Pressure gauges described in ?.8 can be used to measure the depth from the sea surface to the gauge. Arrays of bottom-mounted pressure gauges are useful for determining wave directions. Thus arrays are widely used just offshore of the surf zone to determine offshore wave directions.

Adi Kurniawan at 03:53, 2 March 2009

2009-03-02T03:53:22Z

← Older revision		Revision as of 03:53, 2 March 2009
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	Because waves influence so many processes and operations at sea, many techniques have been invented for measuring waves. Here are a few of the more commonly used. [[Stewart 1980]] gives a more complete description of wave measurement techniques, including methods for measuring the directional distribution of waves.		Because waves influence so many processes and operations at sea, many techniques have been invented for measuring waves. Here are a few of the more commonly used. [[Stewart 1980]] gives a more complete description of wave measurement techniques, including methods for measuring the directional distribution of waves.


	= Sea State Estimated by Observers at Sea =		= Sea State Estimated by Observers at Sea =

Meylan: /* Synthetic Aperture Radars on Satellites */

2006-10-28T23:25:52Z

Synthetic Aperture Radars on Satellites

← Older revision		Revision as of 23:25, 28 October 2006
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	= Synthetic Aperture Radars on Satellites =		= Synthetic Aperture Radars on Satellites =

	[http://en.wikipedia.org/wiki/Synthetic_Aperture_Radar Synthetic Aperture Radars] map the radar reflectivity of the sea surface with spatial resolution of 6-25m. Maps of reflectivity often show wave-like features related to the real waves on the sea surface. I say "wave-like" because there is not an exact one-to-one relationship between wave-height and image density. Some waves are clearly mapped, others less so. The maps, however, can be used to obtain additional information about waves, especially the spatial distribution of wave directions in shallow water ([[Vesecky and Stewart 1982]]). Because the directional information can be calculated directly from the radar data without the need to calculate an image ([[Hasselmann 1991]]), data from radars and altimeters on ERS-1 & 2 are being used to determine if the radar and altimeter observations can be used directly in wave forecast programs.		[http://en.wikipedia.org/wiki/Synthetic_Aperture_Radar Synthetic Aperture Radars] map the radar reflectivity of the sea surface with spatial resolution of 6-25m. Maps of reflectivity often show wave-like features related to the real waves on the sea surface. I say "wave-like" because there is not an exact one-to-one relationship between wave-height and image density. Some waves are clearly mapped, others less so. The maps, however, can be used to obtain additional information about waves, especially the spatial distribution of wave directions in shallow water ([[Vesecky and Stewart 1982]]). Because the directional information can be calculated directly from the radar data without the need to calculate an image ([[Hasselmann 1991]]), data from radars and altimeters on [http://en.wikipedia.org/wiki/ERS-1 ERS-1 & 2] are being used to determine if the radar and altimeter observations can be used directly in wave forecast programs.

	=Acknowledgement=		=Acknowledgement=

Meylan: /* Accelerometer Mounted on Meteorological or Other Buoy */

2006-10-28T23:19:26Z

Accelerometer Mounted on Meteorological or Other Buoy

← Older revision		Revision as of 23:19, 28 October 2006
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	This is a less common measurement, although it is often used for measuring waves during short experiments at sea. For example, accelerometers on weather ships measured wave-height used by Pierson & Moskowitz and the waves shown in Figure 2 of [[Waves and the Concept of a Wave Spectrum]]. The most accurate measurements are made using an accelerometer stabilized by a gyro so the axis of the accelerometer is always vertical.		This is a less common measurement, although it is often used for measuring waves during short experiments at sea. For example, accelerometers on weather ships measured wave-height used by Pierson & Moskowitz and the waves shown in Figure 2 of [[Waves and the Concept of a Wave Spectrum]]. The most accurate measurements are made using an accelerometer stabilized by a gyro so the axis of the accelerometer is always vertical.

	Double integration of vertical acceleration gives displacement. The double integration, however, amplifies low-frequency noise, leading to the low frequency signals seen in Figures ~~16.~~4 and ~~16.~~5. In addition, the buoy's heave is not sensitive to wavelengths less than the buoy's diameter, and buoys measure only waves having wavelengths greater than the diameter of the buoy. Overall, careful measurements are accurate to 10% or better.		Double integration of vertical acceleration gives displacement. The double integration, however, amplifies low-frequency noise, leading to the low frequency signals seen in Figures 4 and 5 of of [[Waves and the Concept of a Wave Spectrum]]. In addition, the buoy's heave is not sensitive to wavelengths less than the buoy's diameter, and buoys measure only waves having wavelengths greater than the diameter of the buoy. Overall, careful measurements are accurate to 10% or better.

	= Wave Gages =		= Wave Gages =

Meylan: /* Accelerometer Mounted on Meteorological or Other Buoy */

2006-10-28T23:19:03Z

Accelerometer Mounted on Meteorological or Other Buoy

← Older revision		Revision as of 23:19, 28 October 2006
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	= Accelerometer Mounted on Meteorological or Other Buoy =		= Accelerometer Mounted on Meteorological or Other Buoy =
	This is a less common measurement, although it is often used for measuring waves during short experiments at sea. For example, accelerometers on weather ships measured wave-height used by Pierson & Moskowitz and the waves shown in Figure ~~16.~~2. The most accurate measurements are made using an accelerometer stabilized by a gyro so the axis of the accelerometer is always vertical.		This is a less common measurement, although it is often used for measuring waves during short experiments at sea. For example, accelerometers on weather ships measured wave-height used by Pierson & Moskowitz and the waves shown in Figure 2 of [[Waves and the Concept of a Wave Spectrum]]. The most accurate measurements are made using an accelerometer stabilized by a gyro so the axis of the accelerometer is always vertical.

	Double integration of vertical acceleration gives displacement. The double integration, however, amplifies low-frequency noise, leading to the low frequency signals seen in Figures 16.4 and 16.5. In addition, the buoy's heave is not sensitive to wavelengths less than the buoy's diameter, and buoys measure only waves having wavelengths greater than the diameter of the buoy. Overall, careful measurements are accurate to 10% or better.		Double integration of vertical acceleration gives displacement. The double integration, however, amplifies low-frequency noise, leading to the low frequency signals seen in Figures 16.4 and 16.5. In addition, the buoy's heave is not sensitive to wavelengths less than the buoy's diameter, and buoys measure only waves having wavelengths greater than the diameter of the buoy. Overall, careful measurements are accurate to 10% or better.

Meylan: /* Synthetic Aperture Radars on Satellites */

2006-10-28T23:17:16Z

Synthetic Aperture Radars on Satellites

← Older revision		Revision as of 23:17, 28 October 2006
Line 28:		Line 28:

	[http://en.wikipedia.org/wiki/Synthetic_Aperture_Radar Synthetic Aperture Radars] map the radar reflectivity of the sea surface with spatial resolution of 6-25m. Maps of reflectivity often show wave-like features related to the real waves on the sea surface. I say "wave-like" because there is not an exact one-to-one relationship between wave-height and image density. Some waves are clearly mapped, others less so. The maps, however, can be used to obtain additional information about waves, especially the spatial distribution of wave directions in shallow water ([[Vesecky and Stewart 1982]]). Because the directional information can be calculated directly from the radar data without the need to calculate an image ([[Hasselmann 1991]]), data from radars and altimeters on ERS-1 & 2 are being used to determine if the radar and altimeter observations can be used directly in wave forecast programs.		[http://en.wikipedia.org/wiki/Synthetic_Aperture_Radar Synthetic Aperture Radars] map the radar reflectivity of the sea surface with spatial resolution of 6-25m. Maps of reflectivity often show wave-like features related to the real waves on the sea surface. I say "wave-like" because there is not an exact one-to-one relationship between wave-height and image density. Some waves are clearly mapped, others less so. The maps, however, can be used to obtain additional information about waves, especially the spatial distribution of wave directions in shallow water ([[Vesecky and Stewart 1982]]). Because the directional information can be calculated directly from the radar data without the need to calculate an image ([[Hasselmann 1991]]), data from radars and altimeters on ERS-1 & 2 are being used to determine if the radar and altimeter observations can be used directly in wave forecast programs.

			=Acknowledgement=

			The material in this page has come from [http://oceanworld.tamu.edu/resources/ocng_textbook/contents.html Introduction to Physical Oceanography] by [[Robert Stewart]].

	[[Category:Geophysics]]		[[Category:Geophysics]]

Meylan: /* Satellite Altimeters */

2006-10-24T07:15:29Z

Satellite Altimeters

← Older revision		Revision as of 07:15, 24 October 2006
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	= Satellite Altimeters =		= Satellite Altimeters =
	The satellite altimeters used to measure surface geostrophic currents also measure wave-height. Altimeters were flown on [http://en.wikipedia.org/wiki/Seasat Seasat] in 1978, [http://en.wikipedia.org/wiki/Geosat Geosat] from 1985 to 1988, [http://en.wikipedia.org/wiki/ERS-1 ERS-1 & 2]] from 1991, [http://en.wikipedia.org/wiki/Topex/Poseidon Topex/Poseidon] from 1992, and [http://en.wikipedia.org/wiki/Jason-1 Jason] from 2001. Altimeter data have been used to produce monthly mean maps of wave-heights and the variability of wave energy density in time and space. The next step, just begun, is to use altimeter observation with wave forecasting programs, to increase the accuracy of wave forecasts.		The satellite altimeters used to measure surface geostrophic currents also measure wave-height. Altimeters were flown on [http://en.wikipedia.org/wiki/Seasat Seasat] in 1978, [http://en.wikipedia.org/wiki/Geosat Geosat] from 1985 to 1988, [http://en.wikipedia.org/wiki/ERS-1 ERS-1 & 2] from 1991, [http://en.wikipedia.org/wiki/Topex/Poseidon Topex/Poseidon] from 1992, and [http://en.wikipedia.org/wiki/Jason-1 Jason] from 2001. Altimeter data have been used to produce monthly mean maps of wave-heights and the variability of wave energy density in time and space. The next step, just begun, is to use altimeter observation with wave forecasting programs, to increase the accuracy of wave forecasts.

	The altimeter technique works as follows. Radio pulse from a satellite altimeter reflect first from the wave crests, later from the wave troughs. The reflection stretches the altimeter pulse in time, and the stretching is measured and used to calculate wave-height (Figure 1). Accuracy is 10%.		The altimeter technique works as follows. Radio pulse from a satellite altimeter reflect first from the wave crests, later from the wave troughs. The reflection stretches the altimeter pulse in time, and the stretching is measured and used to calculate wave-height (Figure 1). Accuracy is 10%.
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	[[image:Fig16-11s.jpg]]		[[image:Fig16-11s.jpg]]
	</center>		</center>
	Figure 1 Shape of radio pulse received by the Seasat altimeter, showing the influence of ocean waves. The shape of the pulse is used to calculate significant wave-height. From [[Stewart 1985]].		Figure 1 Shape of radio pulse received by the Seasat altimeter, showing the influence of ocean waves. The shape of the pulse is used to calculate significant wave-height. From [[Stewart 1985]].

	= Synthetic Aperture Radars on Satellites =		= Synthetic Aperture Radars on Satellites =

Meylan: /* Accelerometer Mounted on Meteorological or Other Buoy */

2006-10-24T07:15:10Z

Accelerometer Mounted on Meteorological or Other Buoy

← Older revision		Revision as of 07:15, 24 October 2006
Line 9:		Line 9:
	This is a less common measurement, although it is often used for measuring waves during short experiments at sea. For example, accelerometers on weather ships measured wave-height used by Pierson & Moskowitz and the waves shown in Figure 16.2. The most accurate measurements are made using an accelerometer stabilized by a gyro so the axis of the accelerometer is always vertical.		This is a less common measurement, although it is often used for measuring waves during short experiments at sea. For example, accelerometers on weather ships measured wave-height used by Pierson & Moskowitz and the waves shown in Figure 16.2. The most accurate measurements are made using an accelerometer stabilized by a gyro so the axis of the accelerometer is always vertical.

	Double integration of vertical acceleration gives displacement. The double integration, however, amplifies low-frequency noise, leading to the low frequency signals seen in Figures 16.4 and 16.5. In addition, the buoy's heave is not sensitive to wavelengths less than the buoy's diameter, and buoys measure only waves having wavelengths greater than the diameter of the buoy. Overall, careful measurements are accurate to ?10% or better.		Double integration of vertical acceleration gives displacement. The double integration, however, amplifies low-frequency noise, leading to the low frequency signals seen in Figures 16.4 and 16.5. In addition, the buoy's heave is not sensitive to wavelengths less than the buoy's diameter, and buoys measure only waves having wavelengths greater than the diameter of the buoy. Overall, careful measurements are accurate to 10% or better.

	= Wave Gages =		= Wave Gages =

Meylan: /* Satellite Altimeters */

2006-10-19T03:34:50Z

Satellite Altimeters

← Older revision		Revision as of 03:34, 19 October 2006
Line 25:		Line 25:
	Figure 1 Shape of radio pulse received by the Seasat altimeter, showing the influence of ocean waves. The shape of the pulse is used to calculate significant wave-height. From [[Stewart 1985]].		Figure 1 Shape of radio pulse received by the Seasat altimeter, showing the influence of ocean waves. The shape of the pulse is used to calculate significant wave-height. From [[Stewart 1985]].

	Synthetic Aperture Radars on Satellites ~~These radars~~ map the radar reflectivity of the sea surface with spatial resolution of 6-25m. Maps of reflectivity often show wave-like features related to the real waves on the sea surface. I say "wave-like" because there is not an exact one-to-one relationship between wave-height and image density. Some waves are clearly mapped, others less so. The maps, however, can be used to obtain additional information about waves, especially the spatial distribution of wave directions in shallow water ([[Vesecky and Stewart 1982]]). Because the directional information can be calculated directly from the radar data without the need to calculate an image ([[Hasselmann 1991]]), data from radars and altimeters on ERS-1 & 2 are being used to determine if the radar and altimeter observations can be used directly in wave forecast programs.		= Synthetic Aperture Radars on Satellites =

			[http://en.wikipedia.org/wiki/Synthetic_Aperture_Radar Synthetic Aperture Radars] map the radar reflectivity of the sea surface with spatial resolution of 6-25m. Maps of reflectivity often show wave-like features related to the real waves on the sea surface. I say "wave-like" because there is not an exact one-to-one relationship between wave-height and image density. Some waves are clearly mapped, others less so. The maps, however, can be used to obtain additional information about waves, especially the spatial distribution of wave directions in shallow water ([[Vesecky and Stewart 1982]]). Because the directional information can be calculated directly from the radar data without the need to calculate an image ([[Hasselmann 1991]]), data from radars and altimeters on ERS-1 & 2 are being used to determine if the radar and altimeter observations can be used directly in wave forecast programs.

	[[Category:Geophysics]]		[[Category:Geophysics]]

Meylan: /* Satellite Altimeters */

2006-10-19T03:33:37Z

Satellite Altimeters

← Older revision		Revision as of 03:33, 19 October 2006
Line 17:		Line 17:

	= Satellite Altimeters =		= Satellite Altimeters =
	The satellite altimeters used to measure surface geostrophic currents also measure wave-height. Altimeters were flown on Seasat in 1978, Geosat from 1985 to 1988, ERS-1 & 2 from 1991, Topex/Poseidon from 1992, and Jason from 2001. Altimeter data have been used to produce monthly mean maps of wave-heights and the variability of wave energy density in time and space. The next step, just begun, is to use altimeter observation with wave forecasting programs, to increase the accuracy of wave forecasts.		The satellite altimeters used to measure surface geostrophic currents also measure wave-height. Altimeters were flown on [http://en.wikipedia.org/wiki/Seasat Seasat] in 1978, [http://en.wikipedia.org/wiki/Geosat Geosat] from 1985 to 1988, [http://en.wikipedia.org/wiki/ERS-1 ERS-1 & 2]] from 1991, [http://en.wikipedia.org/wiki/Topex/Poseidon Topex/Poseidon] from 1992, and [http://en.wikipedia.org/wiki/Jason-1 Jason] from 2001. Altimeter data have been used to produce monthly mean maps of wave-heights and the variability of wave energy density in time and space. The next step, just begun, is to use altimeter observation with wave forecasting programs, to increase the accuracy of wave forecasts.

	The altimeter technique works as follows. Radio pulse from a satellite altimeter reflect first from the wave crests, later from the wave troughs. The reflection stretches the altimeter pulse in time, and the stretching is measured and used to calculate wave-height (Figure 1). Accuracy is 10%.		The altimeter technique works as follows. Radio pulse from a satellite altimeter reflect first from the wave crests, later from the wave troughs. The reflection stretches the altimeter pulse in time, and the stretching is measured and used to calculate wave-height (Figure 1). Accuracy is 10%.