Spectral Solar Radiation Data Base Documentation, Vol. I


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References


APPENDIX

QUALITY-CONTROL PROCESSING

Limited quality-control processing was applied to the data base as described below. The results are in the ".QC" files on the data-base tape by site, year, and month. For example:

	FLA8705.QC is FSEC, 1987, May
	PGE8801.QC is PG&E, 1988, January
	SER8711.QC is SERI, 1987, November.
These files correspond to the ".DAT" files for the same site, year, and month. Each data segment that includes a spectrum was processed through this quality-control procedure. If the atmospheric conditions were unstable, and a spectrum was not acquired, the broadband and meteorological data were included on the data-base tape, but no quality-control processing was applied.

An example of a segment of a ".QC" file is shown in Figure 6-3. The first line begins with a "Q" followed by the site, year, day, and time stamp. The last columns give the number of lines in the segment so the user can skip to the next segment. Following the first line are messages that were printed whenever the quality-control processing flagged a suspect or poor value.

Following the messages in an 80-character QC line listing the variables that were examined are one of three quality-control codes: 1, good; 2, marginal or suspect; and 3, missing or poor. The QC line was prepared using an automatic (computerized) check of the variables, and manual editing to include information from correspondence, log sheets, and visual inspection. Additional messages were added above the QC line if appropriate.

The two-character descriptors in the QC line are:

  DN	Direct-normal (thermopile) solar radiation, before the spectral scan
  DN	Direct-normal (thermopile) solar radiation, after the spectral scan
  SN	Direct-normal (silicon), before
  SN	Direct-normal (silicon), after
  GN	Global-normal, before
  GN	Global-normal, after
  GH	Global-horizontal (thermopile), before
  GH	Global-horizontal (thermopile), after
  SH	Global-horizontal (silicon), before
  SH	Global-horizontal (silicon), after
  GT	Global-tilt, before
  GT	Global-tilt, after
  AL	Albedo (W/m2)
  AP	Albedo (%)
  PR	Surface Pressure
  TC	Temperature (°C)
  RH	Relative Humidity
  WV	Water Vapor (calculated from relative humidity)
  WS	Wind Speed
  KT	Kt
  KN	Kn
  DG	D/GH
  SP	First Spectrum
  IT	Integral of the First Spectrum
  SP	Second Spectrum
  IT	Integral of the Second Spectrum
The automatic tests that were performed to determine the QC code following each variable were:

  (a)  Check for missing or negative values for the broadband, solar radiation, 
       meteorological, or atmospheric data, or the spectral integrals:

         <0 = Code 2
         Missing (-9 or -99) = Code 3

  (b)  Check for atmospheric or broadband instrument instability using the 
       difference and ratio of the before- and after-scan values and redundant 
       measurements, if neither values are negative or missing:

       DN before/DN after      if the absolute difference
       SN before/SN after      is >10 W/m2 (e.g.,
       DN before/SN before     5% of 200 W/m2)
       DN before/SN after		    and
       GH before/GH after
       SH before/SH after      the ratio is <0.95 or >1.05, each of the
       GH before/SH before     two variables = Code 2
       GH after/SH after		   or
       GN before/GN after      the ratio is <0.90 or >1.10, each of the
       GT before/GT after      two variables = Code 3

  (c)  Check for DN > GN, or GH > ETR (extraterrestrial solar radiation) using 
       ratios of the variables:

       DN before/GN before      >0.95, each variable = Code 2
       DN after/GN after        >1.0, each variable = Code 3
       GN before/ETR
       GN after/ETR

  (d)  Check for values of Kt, Kn, and D/GH that are too high:

       KT (involves GH before and after and KT)
       KN (involves DN before and after and KN)
       DG (involves DN and GH, before and after, and DG)
					        >0.95, each variable = Code 2
					        >1.0, each variable = Code 3

  (e)  Check the spectral integrals for unusual ratios to the corresponding 
       broadband solar radiation value.

       IT/(Broadband value before and after)

       For direct spectra:  <0.6 or >0.85, IT = Code 2
       For global spectra:  <0.7 or >0.95, IT = Code 2
     
       For direct and global spectra:  <0.5 or >1.0, IT = Code 3
     
     

We suggest that users of the data base develop a computer program to access fields in the QC line and to print the messages. This limited quality control will not flag all possible errors and additional tests should be applied depending on the users' requirements and applications.


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