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# Using ArcGIS to map forest clearing needs to get full sunlight on a point

Question asked by pfreeman01 on Sep 27, 2014
Latest reply on Sep 29, 2014 by pfreeman01

I have ArcMap skills that are on the low end of "intermediate" and do volunteer work for a non-profit conservation organization.  I have what I think is a conceptually simple problem, but so far haven't found an automated practical solution:

Within a forested area with flat terrain, I have a point location where I want to provide full sunlight. Assume the surrounding forest is of uniform height.  NOAA  has a website which will calculate the position of the sun - both azimuth and height above the horizon - for any day and time given the latitude and longitude of the site.  The site provides spreadsheets that include the calculations.  I want the point to receive 100% of available sunlight from May 15-Sept 30, and I wish to calculate and map the extent of forest that must be cleared to provide this sunlight.  If the tree height is 65 feet and X is the distance from the point for which all the trees must be cut, then I believe (please correct me if I am in error) that X for a date and time can be simply calculated by dividing 65 by the tangent of the angle of the sun's elevation above the horizon at that moment.  The resulting solution will be the extent of clearing needed on that date at an azimuth from the point equal to the azimuth of the sun's location at that time on that date.  For this purpose I can ignore the small differences year-to-year in the sun's position on a given date.  So, conceptually, all I would need to do is apply the NOAA data to perform these calculations for each day between May 15 and Sept. 30 during the daylight hours at some time interval - maybe 5 or ten minutes.  For a given date and time, I could then use an ArcMap tool to create a point x distance from the point of interest at the calculated azimuth.  Starting at about due east and working clockwise to about due west, I would then determine the greatest plotted distance X by some rounded azimuth interval, connect the resulting points and have a map of the extent of clearing needed.  Conceptually simple but impractical due to time required.  Given that solar installers need to solve this problem routinely, I think somebody surely has created an ArcMap tool to do this, but I can't find it.  Can anybody help me with this?  I would greatly appreciate it.

Here's the link to the NOAA site:  http://http://www.esrl.noaa.gov/gmd/grad/solcalc/