5.0 Measurement Uncertainty
Filename Content FLA8705.DAT FSEC data 1987 May PGE8801.DAT PG&E data 1988 January SER8711.DAT SERI data 1987 NovemberData were not acquired in all months, so the months may not be contiguous.
Quality-control information has the same filenaming convention, with ".QC" extension (for example, FLA8705.QC). Daily notes are contained in the files FSEC.NOTES, PGE.NOTES, and SERI.NOTES, respectively. The measurement uncertainty is in the ".UNCERT" files.
The ".DAT" files contain two types of information: "D" for data, and "C" for instrument configuration. The first line of a data or configuration segment begins with a "D" or a "C", respectively, in the first column, followed by the site, year, day, and time stamp; the number of lines in the segment is in columns 76-80 so that the user can easily skip the desired number of lines. An example of the information in the configuration, or "C," segment is shown in Figure 6-1. It begins with a "C" followed by the site "FSEC," year "1987," day "122," and time "0830," latitude, longitude, and elevation. There are19 channels for measurements, zero spectra in the "C" segment, and 40 lines in the segment. The configuration information appears whenever the instrument set-up or calibration was changed, or the data acquisition system was restarted. If the configuration was not changed at the beginning of the month, the configuration segment will be in the previous month's ".DAT" file.
An example of a "D" segment is shown in Figure 6-2. This segment contains the measured meteorological data, broadband and spectral solar radiation data, and ancillary data. The data contained in each line and column, and its format, are as follows:
POSITION OF VARIABLES IN THE "D" SEGMENTS (ALL LINES ARE 80 CHARACTERS)
Line/Column Contents Format a = character i = integer f = floating point LINE 1: 1:1 D ( for data ) (a1) 3:15 Site, Year, Day Number, Time Stamp (a13) 3:6 FSEC, PG&E, or SERI (a4) 7:8 Year (a2 or i2) 9:11 Day Number (a3 or i3) 12:15 Standard Time (a4 or i4) 16:23 Latitude (°) (f8.4) 24:24 N (north) (a1) 25:33 Longitude (°) (f9.4) 34:34 W (west) (a1) 35:39 Elevation (m) (i5) 40:40 M (m) (a1) 41:52 Reference to Configuration Segment (a12) 54:69 Starting year, day, time for the spectral scan(s), if any, and number of attempts to acquire the scan (which indicates possible time delay from the starting time) 54:62 Year, Day Number, Time (a9 or i9) 63:63 "+" for plus number of attempts to acquire a spectrum (a1) 67:67 # of attempts to acquire a spectrum (i1) 70:73 Possible # of Measurements (19) (i4) 74:75 Number of Spectra in this Segment ( 0, 1, or 2 ) (i2) 76:80 Number of Lines in Segment (i5) LINE 2: Pointer to the quality-control, daily field notes, and measurement uncertainty information. Quality- control information is in the ".QC" file of the same month, with the same site, year, day, and time stamp. Daily field notes are in the ".NOTES" file for the same site, with the same site, year, and day stamp. Measurement uncertainty is in the files ".UNCERT" under the instrument serial number identified by PRS-xxx, and the columns in the uncertainty files for "+" and "-" uncertainty limits. (a80) LINE 3: Broadband measurements before the spectral scan. 1:3 Channel #1 (i3) 4:10 Direct Normal (thermopile) (W/m2) (f7.2) 11:13 Channel #5 (i3) 14:20 Direct Normal (silicon) (W/m2) (f7.2) 21:23 Channel #2 (i3) 24:30 Global Normal (W/m2) (f7.2) 31:40 Channel not used 41:43 Channel #3 (i3) 44:50 Global Horiz. (thermopile) (W/m2) (f7.2) 51:53 Channel #19 (i3) 54:60 Global Horiz. (silicon) (W/m2) (f7.2) 61:63 Channel #4 (i3) 64:70 Global Tilt (W/m2) (f7.2) 71:80 Channel not used LINE 4: Broadband measurements after the spectral scan; same format as before-scan (LINE 3). LINE 5: 1:6 Tilt of the fixed-tilt instruments from the horizontal (°) (f6.1) 7:12 Azimuth of the fixed-tilt instruments (°) (180° = south) (f6.1) 13:80 Description of any special instrument (for example, diffuse- horizontal measurements at SERI) (a88) LINE 6: 1:3 Channel #10 (i3) 4:10 Albedo (W/m2) (f7.1) 11:13 Channel #15 (i3) 14:20 Cloud Cover (tenths) (f7.1) 21:23 Channel #7 (i3) 24:30 Surface Pressure (mb) Measured at FSEC and PG&E; calculated from elevation at SERI [11, p. 100] (f7.1) 31:33 Channel #6 (i3) 34:40 Ambient Temperature (° C) (f7.1) 41:43 Channel #8 (i3) 44:50 Relative Humidity (%) (f7.1) 51:53 Channel #9 (i3) 54:60 Wind Speed (m/s) (f7.1) 61:63 Additional channel described in line 5 (i3) 64:70 Value (variable) 71:73 Additional channel described in line 5 (i3) 74:80 Value (variable) LINE 7: Sun Photometer readings (only recorded for SERI data; not used except for relative comparisons). LINE 8: 1:5 Earth-Sun distance correction (% deviation from 1.0) (f5.2) 6:12 Extraterrestrial Radiation (W/m2) (f7.1) 13:18 Zenith Angle (°) (f6.2) 19:24 Kt (ratio calc'd from thermopile instruments) (f6.1) 25:30 Kn (ratio calc'd from thermopile instruments) (f6.1) 31:36 D/GH (ratio calc'd from thermopile instruments) (f6.1) 37:42 Albedo (%) (f6.1) 43:48 Air Mass (f6.2) 49:68 Reserved for Turbidity, if calc'd 69:72 Precipitable Water Vapor, if calc'd from sun photometer 73:76 Precipitable Water Vapor from the National Weather Service (f4.1) 77:80 Precipitable Water Vapor Calc'd from Relative Humidity (f4.1) LINE 9: 1:2 Channel #17 (i2) 3:6 Number of Wavelengths Recorded by Spectroradiometer #1 (i4) 7:11 Beginning Wavelength (nm) (i5) 12:16 Ending Wavelength (nm) (i5) 17:20 Wavelength Step Size (nm) (f4.1) 21:25 Spectroradiometer #1 Tilt from the Horizontal (°) (f5.1) 26:31 Spectroradiometer #1 Azimuth (°) (f6.1) 32:36 Angle of Incidence of the Direct Beam on Spectroradiometer #1 (°) (f5.1) 38:39 Measurement Type (DN, GN, GH, GT, DF) (a2) 40:40 Attachment (Teflon Dome D, Integrating Sphere S, View-limiting Tube T) (a1) 41:42 Channel #18 (i2) 43:46 Number of Wavelengths Recorded by Spectroradiometer #2 (i4) 47:51 Beginning Wavelength (nm) (i5) 52:56 Ending Wavelength (nm) (i5) 57:60 Wavelength Step Size (nm) (f4.1) 61:65 Spectroradiometer #1 Tilt from the Horizontal (°) (f5.1) 66:71 Spectroradiometer #2 Azimuth (°) (f6.1) 72:76 Angle of Incidence of the Direct Beam on Spectroradiometer #2 (°) (f5.1) 78:79 Measurement Type (DN, GN, GH, GT, DF) (a2) 80:80 Attachment (Teflon Dome D, Integrating Sphere S, View-limiting Tube T) (a1) LINE 10: Saved for extra spectroradiometers if needed.If no spectral data were recorded, the number of lines in the "D" segment is 10, the number of spectra is 0, and there is no corresponding quality-control information for this date/time in the ".QC" files. No quality control was performed because the atmosphere was unstable. If the number of spectra is 1, there are 60 lines in the "D" segment; if there are two spectra, the number of lines is 100.
If the number of spectra is 1 or 2, the spectral data follow after the first 10 lines of the "D" segment. There are 10 spectral measurements per line, with the number in the left-most column indicating the first or second spectroradiometer (1 or 2), followed by the starting wavelength (in nanometers) and the 10 spectral measurements (in W/m2-nm). The 10 measurements are at wavelength increments of 2 nm. There are 401 spectral measurements from 300 to 1100 nm in 2-nm steps, with 10 measurements per line for 40 lines, and one measurement in the 41st line. The last number in the 41st line is the spectral integral. If a second spectroradiometer was used, the next 41 lines follow the same format. Blank lines follow the spectral data to fill the "D" segment to 60 or 100 lines.
An example of a ".QC" file is shown in Figure 6-3. The first line of each segment begins with a "Q" followed by the site, year, day number, and time stamp, with the number of lines in the segment given in the last columns of the line. Following the identifier are messages about variables that were flagged by the automatic quality-control processing (see appendix), noted by an operator at the measurement site, or noted during inspection at SERI. The last line of the segment shows the QC code for variables such as DN (direct normal, thermopile detector), SN (direct normal, silicon detector), AL (albedo), and SP (spectrum), as described in the appendix. Three quality-control codes are used: 1 = good; 2 = suspect, see messages and daily notes; and 3 = poor or missing, see messages and daily notes. The broadband codes (DN, SN, GN, GH, SH, and GT) have two values; the first is the before-scan measurement and the second is the after-scan measurement.
Figure 6-4 shows an example of a segment of the daily notes from the FSEC.NOTES file. Each segment of the file begins with an "N" followed by the site, year, and day number stamp, with the number of lines in the segment given in the last columns of the line. The next line contains the site operator log sheet number, month, day, year, day number, spectroradiometer serial number(s), and measurement mode(s). The PG&E and SERI notes do not include the daily log sheet number. The first two lines are followed by field notes. Notes that were added after inspection at SERI are separated from the operator notes with "-------". The existence of slides or photographs is indicated as well as their quality, i.e., good (G), marginal (M), or poor (P). In the example in this figure, there were two log sheets for this day (number 116 and 117) because the measurement mode changed from global horizontal (GH) to global tilt (GT).
An example of a segment of the measurement uncertainty file "UNCERT.CAL" is shown in Figure 6-5. The first line begins with a "U" followed by the serial number of the spectroradiometer. The upper and lower measurement uncertainty limits are given in the columns following wavelength, with the appropriate measurement mode, dates, and description at the top of the column. The second line in each segment of the ".DAT" files is a pointer to the correct uncertainty information in "UNCERT.CAL". The broadband solar radiation and meteorological instrument measurement uncertainty follows each spectral measurement uncertainty segment in "UNCERT.CAL".
The format of this data base was established at SERI to accommodate expanded, multiyear, long-term data collection. Users can reformat the data to suit their particular needs. We recommend the following steps for accessing and documenting particular data sets:
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