Repairing cloud interference in a DEM

A digital elevation model (DEM) extracted from optical satellite imagery can often have large voids due, typically, to cloud interference. These voids can be challenging to correct. When a digital surface model (DSM) is extracted from optical imagery, clouds often create failed areas and false elevation values. This occurs because the image correlation could not match the clouds. Therefore, the elevation value that is extracted is much higher than the true ground level.

With the Smart GeoFill and DEM Editing features in Focus, you can fill voids in a DEM by using another DEM. If the alternate DEM is of a different resolution or projection, its elevation values will be resampled and reprojected on-the-fly to fit the DEM you are repairing.

To repair cloud interference in a DEM

Open the DEM that has the cloud voids you want to fill.
Typically, the DEM channel will be displayed on the Maps tab. If you do not see the DEM in which you want to fill cloud voids, on the Files tab, expand Rasters, right-click the DEM, point to View, and then click As Grayscale.
On the Layer menu, click DEM Editing.
The DEM is displayed as color-shaded relief, and the DEM Editing window appears
On the Tools menu, click Smart GeoFill.
In the Source list, select Custom File Set, and then in File Selector, select a DEM that overlaps the voids you want to fill.
That is, you copy pixels from this DEM to fill the voids.
Draw a polygon around the first cloud void and any shadow cast by the cloud.
Notice that when you close the polygon, the pixels inside the polygon are updated to show the cloud-free pixels in the overlapping DEM.

Tip: If you have associated imagery available, you may want to switch between viewing it and the DEM to more readily discern the area to repair. That is, in the DEM Editing window, click Display DEM to switch between displaying the DEM and not.
After you are satisfied with the repair to the cloud void, including the blend width, on the toolbar, click Paste.
Repeat steps 5 and 6 for each additional void you want to fill.