With the DEM data in your area of interest, the following are some of the experiments I did in order to see the source of the contouring effects.
1. With the original DEM at 2m resolution, I ran the Visibility tool and I can reproduce the contouring effects in the output (rendered using Orange color in below). The contouring effect in the Visibility output is due to the presence of terraces in the data, which is visible in the hillshade/elevation background.
2. After the DEM is resampled to 5m resolution using the Nearest Neighbor method, I ran the Visibility tool again and the new output based on the 5m resolution still has some contouring effects, as shown below:
3. After the DEM is resampled to 10m resolution using the Bilinear method, I ran the Visibility tool again and the new output based on the 10m resolution is free of contouring effects, as shown below:
4. With the original 2m DEM, I changed the observer height to 10 meters, and re-ran the Visibility tool. The new Visibility output (purple) is overlayed underneath the original Visibility output (orange) as follows. The new output (purple) contains less contouring effects:
5. With the original 2m DEM, I changed the observer height to 20 meters, and re-ran the Visibility tool. The new Visibility output (purple) is overlayed underneath the original Visibility output (orange) as follows. The new output (purple) contains even less contouring effects:
In summary,
(1) For the given DEM (2m with terrace like landform), the tool is producing correct results. Only the edges of the terrace is visible, not the top, which is producing contouring effect.
(2) You can change the observer height (if applicable) to see the top of the terrace.
(3) Or, you can change the resolution of the DEM with the bilinear resampling method to remove the terraces from the DEM and make it smoother, which will remove the contouring effect. However, by doing so, you will be changing your DEM, which may or may not be appropriate for your analysis.
Please let me know if you have additional questions.
Thanks
Xuguang Wang