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I have received tif Laserscan images interpolated from Ascii data. I did not process the data so cannot say which processes or tools were used to interpolate the data. There are strange distortions on water surfaces which I cannot understand and seek an explanation.

Image 1 shows the Surface model. There are smooth elevations around vegetation. (Maybe due to the Spline interpolation technique?)

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Image 2 shows the same areas but in the Terrain model. Here it seems the interpolation technique was different as the smoothing is missing.

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Image 3 shows the las data.

enter image description here

Are the raised areas due to reflections of the trees on the water?

If so, why are reflections registered and not somehow eliminated?

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In some cases, water will reflect the LIDAR beam away from the sensor (specular effect at some incidence angle) or absorb all its energy (water has a low reflectance in near Infrared.)

As a results, there are often missing data above water. I confirm that what you observe is the result of the interpolation, probably spline on top and TIN at the bottom, as you said. However this is due to gaps, not to the reflection of the trees in water. If you start from the raw point cloud, you could create a point density layer that tells your where you should be careful.

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