Just as an image is the output of a camera, a point cloud is the output of a Lidar sensor. A LIDAR sensor captures attributes such as the location in the xyz coordinates, the intensity of the laser light and the normal surface at each point in a point cloud. The typical output products of a Lidar topographic survey are listed in table 2 below. In reality, the system provides the position (X, Y, Z) of the bottom with reference to the WGS 84 ellipsoid, but also the height of the water, which in turn indicates the level of the water surface.
In reality, the surface level is obtained from a large window of averages that guarantees greater reliability and also provides the height of the waves. Each point is marked with an indication of whether land or water was found and, in the latter case, if the background was detected. A timestamp allows you to evaluate data by comparing it with tidal data. The signal amplitude is also available, however, if the returning photons pass through a photomultiplier, the resulting signal is in volts, making it difficult to budget energy.
Some systems provide software to visualize the waveforms at each point, which could provide an indication of the type of background (see the Lidar backscatter intensity below). What I mean by that is that it sends more than 160,000 pulses per second. For every second, every 1-meter pixel receives about 15 pulses. This is why LiDAR point clouds create millions of points.
Since then, Lidar technology has greatly expanded its capacity and LIDAR systems are used to perform a series of measurements that include the development of cloud profiles, the measurement of winds, the study of aerosols and the quantification of various atmospheric components. The ground reflection of an aerial LIDAR provides a measure of surface reflectivity (assuming that atmospheric transmittance is well known) at the wavelength of the LIDAR; however, ground reflection is commonly used to perform atmospheric absorption measurements. For example, LIDAR altimeters look down, an atmospheric LIDAR looks up, and LIDAR-based collision avoidance systems look sideways.
Lidar
systems also collect a georeferenced video directly downwards simultaneously with the Lidar measurements.There is a wide variety of LIDAR applications, in addition to the applications listed below, as is often mentioned in national LIDAR data set programs. Therese Reinsch: When the LiDAR system collects the data, point cloud, all the LiDAR data points are not ranked as to what they are affecting.
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