	READ ME -- Example 1: USSA reference spectrum

This example shows how to generate a higher resolution version of the old 
terrestrial solar irradiance standards (ASTM E891-87, ASTM E892-87, ASTM G159-99; 
ISO 9845-1), now superseded by ASTM G173-03 (see Example 6). 

SMARTS will be run here from 300 to 4000 nm at 1 to 5 nm intervals, 
whereas these older standards are from 305 to 4045 nm at variable intervals. 
They have been generated by BRITE, a Monte-Carlo rigorous code that is not 
available anymore, so that SMARTS can be used as an alternative to reconstruct 
these reference spectra at finer resolution or simulate the effect of different 
atmospheric conditions.

These older standards specify an air mass of 1.5, a rural aerosol with 
optical thickness of 0.27 at 500 nm, a US Standard Atmosphere with 1.42 cm 
precipitable water and 0.34 atm-cm ozone, a fixed broadband albedo of 0.2, and 
circumsolar radiation within a cone of about 2.9 deg. half angle. 
The standards are for direct normal irradiance and for global irradiance 
received on a surface tilted 37 deg. toward the sun.

The Shettle & Fenn's rural aerosol model has been selected here because it is the 
closest approximation to the specific rural aerosol used in BRITE, which 
was a preliminary--but different--version of the Shettle & Fenn aerosol model 
used in SMARTS and MODTRAN. Almost identical results are obtained when using 
SRA's continental aerosol.

The illuminances corresponding to these irradiances are also calculated for 
demonstration purposes.