Hello ArcViewers,

This is the original query:

"I need to calculate the theoretical insolation in some seasons of the year
for a DEM that I have. The purpose is to determine fire risk. Can anyone
help me?"


Thanks to Stephane Morel and Justin Quirouette, both suggest to use use
Solar Analyst. It's an Arcview's extension, but it has a cost associated.
You can have a look at:

http://www.hemisoft.com/products/solar_analyst.html


Thanks to Paul Hughes, he suggest a methodology that he used in several
projects:

APPLICATION of direct solar radiation to a surface

The shading and strike angle factors are used by the Hillshade function in
both ARC/INFO and ArcView Spatial Analyst software applications developed by
Environmental Systems Research Institute (ESRI). All that is required is to
input the azimuth and elevation of the sun.

Hillshade values are produced in the range 0-254, where 0 is shaded and 254
is perpendicular to the solar radiation direction. There is a presumption
that the values produced by Hillshade are the sine of the Strike Angle X.
The azimuth and elevation for each hour are applied to the Digital Elevation
Model (DEM) using Hillshade, then the results for each hour are summed.

When the direct solar radiation values are reduced in proportion to the
hillshade value, the surface direct solar radiation value can be found.

The following parameters were used:

*       IR = Incoming direct solar radiation (MJ/m2/hr) at hourly intervals
*       HS = Hillshade value (range 0-254) at hourly intervals
*       SRH = Surface Radiation/Hour (MJ/m2/hr) at hourly intervals
*       SRD = Surface Radiation/Day (MJ/m2/day)
*       ·

The following equations were used:

        <<...OLE_Obj...>>
(1)
        The hourly value of direct solar radiation (SRH) for a surface is
the product of the Hillshade factor and the Incoming Radiation.

        <<...OLE_Obj...>>
(2)
        Total direct solar radiation (SRD) for a surface is the sum of the
hourly direct solar radiation (SRH) for all hours when direct solar
radiation occurs.



I found, in ESRI Site, an ArcScript to 3d Analyst named 3dsunpos.avx. Thanks
to John Platts too, the author, he explain that this extension sets the sun
position in a 3D Scene. You can find out the sun azimuth and sun altitude by
selecting Properties from the 3D Scene Menu after setting it using the
extension.


Thanks for all the help.


Paulo Cabral
Parque Natural de Montesinho
Instituto da Conservação da Natureza
Portugal
paulocabral@icn.pt