Difference between revisions of "Template:This weeks featured article"

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(→‎Use of Lidar for coastal habitat mapping)
(→‎Waves)
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==Use of Lidar for coastal habitat mapping==
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==Waves==
  
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[[image:lidar_fig_02.jpg|thumb|250px|left|Figure 1: Sketch of airborne lidar remote sensing and ground GPS]]
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[[Image:irregular storm a.jpg|thumb|200px|Fig. 1a. Irregular directional storm waves (including white capping)]]
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[[Image:irregular storm b.jpg|thumb|200px|Fig. 1b. Regular unidirectional swell.]]
  
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This article describes how Lidar (Laser or Light Detection and Ranging) can be used to collect data about coastal habitats. The article gives an introduction of the measurement principle and also explains how to plan for a Lidar-survey. More information about the conversion of collected [[data]] and the output of Lidar can be found in the article [[Data processing and output of Lidar]].  
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There is typically a distinction between short waves, which are waves with periods less than approximately 20 s, and long waves or long period oscillations, which are oscillations with periods between 20-30 s and 40 min. Water-level oscillations with periods or recurrence intervals larger than around 1 hour, such as [[tide|astronomical tide]] and [[storm surge]], are referred to as water-level variations. The short waves are wind waves and swell, whereas long waves are divided into [[surf beat]]s, harbour resonance, [[seiche]] and [[tsunami]]s. Natural waves can be viewed as a wave field consisting of a large number of single wave components each characterised by a [[wave height]], a [[wave period]] and a propagation direction. Wave fields with many different [[wave period]]s and heights are called irregular.
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Lidar (Laser Induced Detection And Ranging ou LIght Detection And Ranging) is an active [[remote sensing]] technique using light emission. Part of the light is diffused or absorbed by the environment and the other part is backscattered in the direction of the source of radiation. The time difference between signal emission and signal reception makes it possible to determine the distance covered since the speed of light is known. Knowing the precise altitude of the aircraft, it is then possible to determine altimetry (or [[bathymetry]]) in each point having received the radiation.
 
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The [[remote sensing]] components of Lidar include:
 
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*a Laser (Light Amplification by Stimulated Emission of Radiation) telemeter also called Laser Scanner,
 
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*a telescope allowing the measurement of backscattered light intensity, and
 
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*acquisition electronics and electro-optical components.
 

Revision as of 13:16, 6 October 2008

Waves

Fig. 1a. Irregular directional storm waves (including white capping)
Fig. 1b. Regular unidirectional swell.

There is typically a distinction between short waves, which are waves with periods less than approximately 20 s, and long waves or long period oscillations, which are oscillations with periods between 20-30 s and 40 min. Water-level oscillations with periods or recurrence intervals larger than around 1 hour, such as astronomical tide and storm surge, are referred to as water-level variations. The short waves are wind waves and swell, whereas long waves are divided into surf beats, harbour resonance, seiche and tsunamis. Natural waves can be viewed as a wave field consisting of a large number of single wave components each characterised by a wave height, a wave period and a propagation direction. Wave fields with many different wave periods and heights are called irregular.

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