Refractivity coefficient: The input is not within the defined domain

Hi,

I've followed the steps in "Setting up the viewshed geoprocessing service (ArcGIS Pro).pdf".

But when I excute "ElevationTools.pyt" I get these errors:

```
Start Time: lunes, 18 de julio de 2022 19:56:07
Maximum distance: 15000 meters, DEM resolution: 90 meters, Mosaic Layer: C:\ElevationPro\Data\Elevation.gdb\dem90m, Observer offset: 1.75, Surface offset: 0.0.
Failed to execute. Parameters are not valid.
[ERROR 000864:](javascript:void(0);) Refractivity coefficient: The input is not within the defined domain.
[ERROR 000892:](javascript:void(0);) The numeric value is outside of the valid range.
Failed to execute (Visibility).
File "", line 729, in execute
File "", line 319, in executeVisibility
File "D:\Program Files\ArcGIS\Pro\Resources\ArcPy\arcpy\geoprocessing\_base.py", line 512, in
return lambda *args: val(*gp_fixargs(args, True))
arcgisscripting.ExecuteError: Failed to execute. Parameters are not valid.
ERROR 000864: Refractivity coefficient: The input is not within the defined domain.
ERROR 000892: The numeric value is outside of the valid range.
Failed to execute (Visibility).
Failed to execute (Viewshed).
Failed at lunes, 18 de julio de 2022 19:56:13 (Elapsed Time: 5,48 seconds)
```


In addition to the previous error. I have this questions, Is it necessary an ArcGIS Image Server license to publish the viewshed script tool?

Start with “Setting up the viewshed geoprocessing service (ArcGIS Pro).pdf” and reproduce the failure by running ElevationTools.pyt with the reported parameters. Trace the Visibility/Viewshed execution, especially executeVisibility, to identify why the refractivity coefficient is rejected, then verify the corrected behavior and determine whether publishing requires an ArcGIS Image Server license.

Written by the indexing model from the issue text.