Application for correction of point cloud data under water
A green laser beam can be used to visualize the topography under water. However, the laser beam must be corrected for the effect of the refractive index of water to accurately reproduce the topography. Laser light is characterized by its strong linearity, but since its speed is slower in water than in air, the laser light is refracted by the water surface and its direction of motion is changed. Have you ever experienced that the bottom of a river appears shallower than it actually is? Without taking into account this effect of water refraction, it is impossible to obtain accurate coordinates of the topography under water. Unfortunately, it is not possible to know the value of the refractive index of the water at the point of survey, and users usually do not have the knowledge of how to compensate for this. UNDERWATER CORRECT solves this problem. Simply specify the water surface location from the cross-section displayed on the screen, and UNDERWATER CORRECT automatically produces data that corrects for the effects of refractive index. This is a feature of TDOT 3 GREEN, produced by the concept of “drone surveying that anyone can use.
Image : Refraction
1.Noise removal
Laser point cloud data including the topography under water is displayed on the screen, and noise data is removed.
2.Specification of main and branch rivers
Draw a line connecting the center of the river’s flow (river center) to determine the main river and its tributaries.
Image : Specification of main and branch rivers
3.Specification of water surface
The cross-section data is automatically created by setting a measuring line perpendicular to the stream centerline. The water surface is then specified from the cross-section data on the screen.
Image : Specification of water surface
4.Calculation of correction of coordinate values for laser point cloud data below the water surface
The laser point cloud under water is corrected for refraction of the water surface and the speed of light, and converted into laser point cloud data with accurate three-dimensional coordinates.
Image : Results