Use this function to compute solar elevation and solar azimuth angles for a given time, latitude, and longitude. This function returns a two-element array of double-precision values representing solar elevation and azimuth, respectively, for the selected input values.
Syntax
Result = ENVI_COMPUTE_SUN_ANGLES (Day, Month, Year, GMTtime, Lat, Lon)
Arguments
Day
Use this keyword to specify the day of year for the desired solar angles. Day is an integer value, 1 through 31.
Month
Use this keyword to specify the month for the desired solar angles. Month is an integer value, 1 through 12.
Year
Use this keyword to specify the year for the desired solar angles. Year is an integer value of the form yyyy.
GMTtime
Use this keyword to specify the Greenwich Mean Time (GMT) for the desired solar angles. GMTtime is a floating-point value, 0 through 2400. For example, a value of 1430.0 represents a GMT time of 14:30.
Lat
Use this keyword to specify the latitude for the desired solar angles. Lat is a floating-point number in degrees. North is positive and South is negative.
Lon
Use this keyword to specify the longitude for the desired solar angles. Lon is a floating-point number in degrees. East is positive and West is negative.
Example
The following code computes solar elevation and azimuth angles for 34 degrees north, 117 degrees west on July 4, 1984, 22:45 GMT.
angles = envi_compute_sun_angles(4, 7, 1984, 2245., $
34., -117.)
print, 'Sun elevation= ', angles[0]
print, 'Sun azimuth= ', angles[1]
API Version
4.2