LiDAR - Revision history

Bendikhansen: /* Application */

2020-10-01T14:27:49Z

Application

Kordula NTNU at 08:25, 30 September 2020

2020-09-30T08:25:16Z

Kordula NTNU at 08:23, 30 September 2020

2020-09-30T08:23:40Z

Laurent: /* Quick summary */

2020-06-01T12:44:19Z

Quick summary

Laurent: /* Quick summary */

2020-05-30T17:35:20Z

Quick summary

Laurent: /* Quick summary */

2020-05-30T17:34:50Z

Quick summary

Bendikhansen at 13:18, 5 April 2020

2020-04-05T13:18:20Z

Bendikhansen: Text replacement - "=Mitigation measures where MTD might be applied=" to "=Relevant mitigation measures and test cases="

2020-01-22T08:33:22Z

Text replacement - "=Mitigation measures where MTD might be applied=" to "=Relevant mitigation measures and test cases="

Bendikhansen at 12:59, 20 January 2020

2020-01-20T12:59:13Z

Bendikhansen at 11:26, 20 January 2020

2020-01-20T11:26:34Z

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 In Norway, most of the rivers are currently measured with a red laser (hence no underwater registrations). These are relatively easily available for research institutions through the public website hoydedata.no. Also available on this website are green laser derived bathymetry data of a selection of river reaches.
-The penetration depth of the green laser through water depends highly on turbidity, flow velocity, reflections on the surface / waves and water depth. It also depends most probably on the type of suspended load. Thus, green laser measurements are in many cases supplied with echosounding data.
+The penetration depth of the green laser through water depends highly on turbidity, flow velocity, reflections on the surface / waves and water depth. It also depends most probably on the type of suspended load. Thus, green laser measurements are in many cases supplemented with echosounding data.
 Problems can also be caused by any other overlap of objects such as trees above ground or submerged vegetation above river bottoms (Figure 3). This can lead to blurred areas and various z-data (height marker) for the same x/y coordinates.
 The measurements generate a point cloud. Post-processing is usually done in a specific software (commercial software, but also freeware) as is the case many other applications (such as [[Structure_from_motion_(SfM)|SfM]]). However, as it is a usual output format, it is not a specific part of the Lidar system.
 =Relevant mitigation measures and test cases=

← Older revision		Revision as of 08:25, 30 September 2020
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	Problems can also be caused by any other overlap of objects such as trees above ground or submerged vegetation above river bottoms (Figure 3). This can lead to blurred areas and various z-data (height marker) for the same x/y coordinates.		Problems can also be caused by any other overlap of objects such as trees above ground or submerged vegetation above river bottoms (Figure 3). This can lead to blurred areas and various z-data (height marker) for the same x/y coordinates.
−	The measurements generate a point cloud. Post-processing is usually done in a specific software (commercial software, but also freeware) as is the case many other applications (such as [[~~Structure for Motion~~\|SfM]]). However, as it is a usual output format, it is not a specific part of the Lidar system.	+	The measurements generate a point cloud. Post-processing is usually done in a specific software (commercial software, but also freeware) as is the case many other applications (such as [[Structure_from_motion_(SfM)\|SfM]]). However, as it is a usual output format, it is not a specific part of the Lidar system.

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 =Introduction=
-Lidar is a measurement technique that measures the distance from a georeferenced laser sensor to a ground target by illuminating the target with the pulsed light (Figure 1). The sensor detects the reflected pulses. The time shifts in laser return and wavelengths can then be used to make digital 3-D representations of the target areas, e.g. a river section. The laser pulses can have different wavelengths, most commonly red and green.
+Lidar is a measurement technique that measures the distance from a georeferenced laser sensor to a ground target by illuminating the target with pulsed light (Figure 1). The sensor detects the reflected pulses. The time shifts in laser return and wavelengths can then be used to create digital 3-D representations of the target areas, e.g. a river section. The laser pulses can have different wavelengths, most commonly red and green.
-The red laser is more common and therefore cheaper. However, other than the NeoDyn Yag laser it can not penetrate the water surface. Therefore the green laser (wavelength 532nm) is most preferred in scientific and especially river related measurements (Figure 2). However, a certain distance from the source of the light to the eye of any person passing accidentally the measurement must be guaranteed due to safety reasons. This is usually not a problem, as this application is used for large scale approached, mainly with so called Airborne Laser Scanning (ALS) where the laser is mounted to a small plane, a helicopter or even a large (more than 15 kg load) drone.
+The red laser is more common and therefore cheaper. However, other than the green NeoDyn Yag laser it cannot penetrate the water surface. Therefor the green laser (wavelength 532nm) is most preferred in scientific and especially river related measurements (Figure 2). However, a certain distance from the source of the light to the eye of any person, passing accidentally the measurement, must be guaranteed due to safety reasons. This is usually not a problem, as this application is used for large scale approaches, mainly with so called Airborne Laser Scanning (ALS) where the laser is mounted to a small plane, a helicopter or even a large (more than 15 kg load) drone.
 =Application=
 As the laser and also the plane or helicopter are a quite expensive set of devices, the measurements are usually taken by private contractors. Most of the time the client is a municipality, the government or a hydropower operator interested in the geometry of floodplains and the bathymetry of rivers.
-In Norway, most of the rivers are currently measured with a red laser (hence no underwater registrations). These are relatively easily available for research institutions through public website hoydedata.no. Also available at the website are green laser derived bathymetry of a selection of river reaches.
+Problems can also be caused by any other overlap of objects such as trees above ground or submerged vegetation above river bottoms (Figure 3). This can lead to blurred areas and various z-data (height marker) for the same x/y coordinates.
 =Relevant mitigation measures and test cases=

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 Developed by:
-Date: 2006
+Date: 1998
 Type: [[:Category:Devices|Device]], [[:Category:Tools|Tool]]

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 Developed by:
-Date: 2010
+Date: 2006
 Type: [[:Category:Devices|Device]], [[:Category:Tools|Tool]]

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 =Quick summary=
-[[file:lidar_setup.png|thumb|500px|Figure 1: Basic set up of a Lidar measurement (Mallet 2010).]]
+[[file:lidar_setup.png|thumb|250px|Figure 1: Basic set up of a Lidar measurement (Mallet 2010).]]
 [[file:lidar_red_green.png|thumb|250px|Figure 2: Comparison red vs green laser (Mallet 2010).]]
 [[file:lidar_als.png|thumb|250px|Figure 3: Discrete Echo and waveform signal comparison for Airborne Laser Scanning (https://commons.wikimedia.org/wiki/File:Airborne_Laser_Scanning_Discrete_Echo_and_Full_Waveform_signal_comparison.svg).]]

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 The measurements generate a point cloud. Post-processing is usually done in a specific software (also freeware) as is the case many other applications (such as SfM). However, as it is a usual output format, it is not a specific part of the Lidar system.
-=Mitigation measures where MTD might be applied=
+=Relevant mitigation measures and test cases=
 {{Suitable measures for LiDAR}}