Spectral Solar Radiation Data Base Documentation, Vol. I

Table 3-1. Measurements and Documentation for Each File in the Spectral Solar Radiation Data Base

* Site identifier^a					* Global-tilt pyranometer value
  - Four-letter code					  - Tilt angle of pyranometer from horizontal, 
  - Longitude (decimal)					      and azimuth
  - Latitude (decimal)					   - Irradiance value (W/m²)
  - Site elevation (m)					* Irradiance-stability check (silicon	
* Date^a							    pyrheliometer)^b
  - Day number						* Irradiance-stability check (silicon
  - Year						    pyranometer)^b	 
* Local standard time^a					* Spectroradiometer scan(s) (2-nm step size)
  - Hour						    (W/m²-nm)
  - Minutes						* Repeat of broadband irradiance measurements^b
* Collection mode for spectral irradiance scan(s)	* Ambient temperature (°C)
  - Two-letter code:					* Surface pressure (mb)
    Global horizontal - GH				* Relative humidity (%)
    Global normal - GN					* Average wind speed (mph)
    Global tilt - GT, use tilt angle from 		* Ground albedo (measured or estimated)^c (%)
      horizontal (e.g., 30 deg) and azimuth		* Multiwavelength sunphotometer measurements 
    Direct normal - DN					    (four-channel maximum)^d
* Direct-normal irradiance value (W/m²)			* Opaque cloud cover (tenths)
* Global-normal irradiance value (W/m²)			* National Weather Service water vapor value (cm)
* Global-horizontal irradiance value (W/m²)		* Comment field (15 characters)

^a Location, date, and time are used to calculate air mass.

^b The silicon pyrheliometer, silicon pyranometer, and repeated broadband solar radiation values are included to allow evaluation of irradiance stability during the spectral irradiance scan.

^c Values should be representative of the dominant land-cover type or mixture in the vicinity of the spectroradiometer.

^d Spectral measurements at several wavelengths are made using sunphotometers with narrow-band filters to calculate atmospheric turbidity and water vapor.

http://www.nrel.gov/rredc