DESCRIPTION OF SOLRAD (formerly ISIS) DAILY DATA FILES FILENAME INFORMATION: The files in these directories contain daily ASCII data from SOLRAD (formerly ISIS) stations organized in Universal Coordinated Time (UTC). The file naming convention is stayyjjj.dat, where sta is a three-letter station identifier, yy represents the last two digits of the year (i.e., 02 for 2002), and jjj is the day of the year (1-366). ys less than 100 are preceded by one or two zeros, e. g., day 75 would appear as 075, day 2 would appear as 002. The processing software is year 2000 compliant. The year within the data files is written unambiguously with 4 digits on each line. "abq" is the station identifier for Albuquerque, New Mexico "bis" is the station identifier for Bismarck, North Dakota "hnx" is the station identifier for Hanford, California "sea" is the station identifier for Seattle, Washington "tlh" is the station identifier for Tallahassee, Florida "slc" is the station identifier for Salt Lake City, Utah "ste" is the station identifier for Sterling, Virginia "msn" is the station identifier for Madison, Wisconsin "ort" is the station identifier for Oak Ridge, Tennessee For example, the file "abq02099.dat" contains data for Albuquerque on day 99 of 2002. DATA STRUCTURE: SOLRAD data are organized into daily files of one- or three-minute data, and are written in ASCII text. Before 1-jan. 2015 the data were reported as 3-min averages; on and after 1-Jan. 2015, SOLRAD data are reported as 1-min. averages of 1-sec. samples. The format was specified in such a way to ensure that all entries are separated by at least one space so that the files may be read with free format. SOLRAD follows the quality control (QC) philosophy of the BSRN. Bad data are deleted, but questionable data are only flagged. Integer QC flags follow each data point. The data files are written in ASCII. They may be read with the following FORTRAN code. The format was specified in such a way to ensure that all entries are separated by at least one space so that the files may be read with free format. Quality control parameters follow each measurement or calculated value. SOLRAD follows the quality control (QC) philosophy of the BSRN. Instead of deleting questionable data, they are flagged. A QC flag of zero indicates that the corresponding data point is good, having passed all QC checks. A value greater than 0 indicates that the data failed one level of QC. For example, a QC value of 1 means that the recorded value is beyond the physically possible range for that measurement. A value of 2 indicates that the data value failed the second level QC check, indicating that the data value may be physically possible, but should be used with scrutiny, and so on. Missing values are indicated by -9999.9 and should always have a QC flag of 1. It is not unusual that thermopile-based solar pyranometers register a small negative signal at night. Most of this error is attributed to the thermopile cooling to space. This generally affects the global and diffuse solar measurements, if thermopile- based instruments are used for those measurements. This error is also present in daytime data, but its magnitude is difficult to determine. Nighttime errors between 0 and -10 Wm^-2 are typical. Because this behavior is common, only nighttime signals that drop below the common range are flagged. Daytime diffuse measurements made by thermopile-based pyranometers are also adversely affected as much as the global measurements. Because they are shaded, the cosine error caused by the solar beam is precluded, and thus Eppley model 8-48 pyranometer (notorious for its cosine error) can be used for the diffuse measurement. The model 8-48 pyranometer has effectively no offset. The model 8-48 pyranometer relies on a differential signal between a black and a white surface on the detector. Since these two differently colored surfaces behave the same in the infrared, there is no error owing to radiative cooling of the sensor. Therefore, the offset error will now only be seen in the global solar measurement. These instruments were installed during the instrument exchanges of 2001. On June 18, 2009, a pgrgeometer was added to the Madison complement of instruments and the UVB instrument was removed. After that date, Madison's file format changed. The following FORTRAN code may be used to read daily SOLRAD files EXCEPT for Madison after 18 June 2009: parameter (nlines=1440) character*80 station_name c integer year,month,day,jday,elevation,hr_to_LST,version integer min(nlines),hour(nlines) c real latitude,longitude,dt(nlines),zen(nlines) real direct(nlines) real dw_psp(nlines) real diffuse(nlines) real uvb(nlines),uvb_temp_v(nlines) c integer qc_direct(nlines) integer qc_dwpsp(nlines) integer qc_diffuse(nlines) integer qc_uvb(nlines) integer qc_uvb_temp(nlines) c c lun_in = 20 open(unit=lun_in,file=[filename.dat],status='old',readonly) c. c. c. read (lun_in,10) station_name 10 format(1x,a) read(lun_in,*) latitude, longitude, elevation, hr_to_LST c icount = 0 do i = 1,nlines c read(lun_in,30,end=40) year,jday,month,day,hour(i),min(i),dt(i), 1 zen(i),dw_psp(i),qc_dwpsp(i),direct(i),qc_direct(i), 2 diffuse(i),qc_diffuse(i),uvb(i),qc_uvb(i),uvb_temp(i), 3 qc_uvb_temp(i),std_dw_psp(j),std_direct(j),std_diffuse(j), 4 std_uvb(j) c icount = icount + 1 c 30 format(1x,i4,1x,i3,4(1x,i2),1x,f6.3,1x,f6.2,5(1x,f7.1,1x,i1), 1 4(1x,f9.3)) c enddo 40 type *,'end of file reached, ',icount,' records read' . . . c c c c c The following code can be used to read MADISON files AFTER 18 June 2009 c parameter (nlines=1440) character*80 station_name c integer year,month,day,jday,elevation,hr_to_LST,version integer min(nlines),hour(nlines) c real latitude,longitude,dt(nlines),zen(nlines) real direct(nlines) real dw_psp(nlines) real diffuse(nlines) real uvb(nlines) real uvb_temp_v(nlines) real dpir(nlines) !Downwelling IR in Wm^-2 real dpirc(nlines)!PIR case temperature (K) real dpird(nlines)!PIR dome temperature (K) c integer qc_direct(nlines) integer qc_dwpsp(nlines) integer qc_diffuse(nlines) integer qc_uvb(nlines) integer qc_uvb_temp(nlines) integer qc_dpir(nlines) integer qc_dpirc(nlines) integer qc_dpird(nlines) c c lun_in = 20 open(unit=lun_in,file=[filename.dat],status='old',readonly) c. c. c. read (lun_in,10) station_name 10 format(1x,a) read(lun_in,*) latitude, longitude, elevation, hr_to_LST c icount = 0 do i = 1,nlines c read(lun_in,30,end=40) year,jday,month,day,hour(i),min(i),dt(i), 1 zen(i),dw_psp(i),qc_dwpsp(i),direct(i),qc_direct(i), 2 diffuse(i),qc_diffuse(i),uvb(i),qc_uvb(i),uvb_temp(i), 3 qc_uvb_temp(i),dpir(i),qc_dpir(i),dpirc(i),qc_dpirc(i),dpird(i), 4 qc_dpird(i),std_dw_psp(i),std_direct(i),std_diffuse(i), 5 std_uvb(i),std_dpir(i),std_dpirc(i),std_dpird(i) c icount = icount + 1 c 30 format(1x,i4,1x,i3,4(1x,i2),1x,f6.3,1x,f6.2,8(1x,f7.1,1x,i1), 1 7(1x,f9.3)) c enddo 40 type *,'end of file reached, ',icount,' records read' . . . c The file structure includes two header records; the first has the name of the station, and the second gives the station's latitude, longitude, elevation above mean sea level in meters, and the displacement in hours from local standard time. The files are organized in Universal Coordinated Time (UTC). These are followed by at most, 480 lines of data for 3-min. data and 1440 lines for 1-min. data (from 2015 on). The date and timeparameters and solar zenith angle are given on every line. Data are reported as 1-minute or 3-minute averages of one-second samples. Reported times are the end times of the 3-min. averaging periods, i.e., the data given for 0000 UTC are averaged over the period from 2357 or 2359 (of the previous UTC day) to 0000. The solar zenith angle is reported in degrees on each line of data. It is computed for the central time of the averaging period of the sampled data, i. e., 1.5 minutes before the reported time on the line. Missing-data periods within the files are not filled in with missing values, therefore, a file with with missing periods will have fewer than 480 data records. Radiation values are reported to the tenths place. Although this is beyond the accuracy of the instruments, data are reported in this manner in order to maintain the capability of backing out the raw voltages at the accuracy that they were originally reported. Also, if the accuracies of the instruments improve to a fraction of a Wm^-2, the data format will not have to be changed. The variables, their data type, and description are given below: station_name character station name, e. g., Goodwin Creek latitude real latitude in decimal degrees (e. g., 40.80) longitude real longitude in decimal degrees (e. g., 105.12) elevation integer elevation above sea level in meters h_to_lst integer hours displaced from local standard time year integer year, i.e., 2002 jday integer Julian day (1 through 365 [or 366]) month integer number of the month (1-12) day integer day of the month(1-31) hour integer hour of the day (0-23) min integer minute of the hour (0-59) dt real decimal time (hour.decimalminutes),e. g., 23.5 = 2330 zen real solar zenith angle (degrees) dw_psp real downwelling global solar (Watts m^-2) direct real direct solar (Watts m^-2) diffuse real downwelling diffuse solar (Watts m^-2) uvb real global UVB (milliWatts m^-2) uvb_temp real UVB temperature (C) -- 25 deg. C is normal qc_dwpsp integer quality control parameter for downwelling global solar (0=good) qc_direct integer quality control parameter for direct solar (0=good) qc_diffuse integer quality control parameter for diffuse solar (0=good) qc_uvb integer quality control parameter for UVB irradiance (0=good) qc_uvb_temp integer quality control parameter for the UVB instrument temperature (0=good) std_dw_psp real standard deviation of the 1-sec. samples for global solar (dw_psp) std_direct real standard deviation of the 1-sec. samples for direct solar std_diffuse real standard deviation of the 1-sec. samples for diffuse solar std_uvb real standard deviation of the 1-sec. samples for uvb for MADISON AFTER 18 June 2009: dpir real downwelling thermal IR (Watts m^-2) dpirc real downwelling PIR case temperature (K) dpird real downwelling PIR dome temperature (K) std_dpir real standard deviation of the 1-sec. samples for downwelling IR std_dpirc real standard deviation of the 1-sec. samples for PIR case temp std_dpird real standard deviation of the 1-sec. samples for PIR dome temp All radiation parameters, except UVB, are reported in units of Watts m^-2; UVB is reported in milliWatts m^-2. The UVB flux is given as the total measured surface UVB flux convoluted with the Diffey erythemal action spectrum, i.e., that part of the UVB spectrum responsible for sun burns on human skin (erythema) and DNA damage. It is reported in this way because the response function of the UVB instrument approximates the erythemal action spectrum; thus the reported value is most representative of what the instrument is actually measuring. The temperature of the UVB instrument's filter is also reported in deg. C. 25 deg. C is normal. UVB irradiance values reported for instrument temperatures +/- 3 deg. C of the nominal value are not flagged. If the instrument temperature is outside that range, the UVB measurement is given a QC value of 2, and the QC value for the instrument temperature is assigned a bad value (1). The erythemal UVB irradiance reported in SOLRAD data files is computed for 298 Dobson units of ozone. This is done because the ozone value over the stations is unknown during the real-time processing. If the ozone for a particular day is less than 300 Dobson units, then the reported UVB irradiance is less than it should be. Tables to correct the reported values to the proper ozone may be obtained from SRRB. The field UVB instruments are calibrated against a triad of "standard" instruments that are maintained by SRRB's UV calibration facility. The standard instruments are periodically calibrated in the sun by comparing their broadband measurements to the integrated output of UV spectroradiometers. These calibrations are transferred to the field instruments just before they are deployed in the network by operating them side-by-side for a few days. A scale factor is computed for each day, which is simply a ratio of the test instrument's daily integral to that of the mean of the standards. The mean of the daily scale factors is used to transfer the standards' well maintained calibrations to the test instruments when they are deployed in the field. The standards' calibration factors are computed as a function of solar zenith angle, and are applied to the field instrument as such in the daily processing. For example, to compute the UVB irradiance, the output voltage, is multiplied times the Standards' calibration factor for the solar zenith angle that the measurement was made, then that result is divided by the scale factor for that field instrument. The following table lists the UVB Standards' calibration information computed from UV Spectroradiometer intercomparison data. These, along with the scale factors computed for particular instruments are used to compute UVB erythemal(Diffey)-weighted irradiance for the SOLRAD field instruments. erythemal solar conversion zenith factor angle (W m^-2 / V) 0.230 0.0 0.231 5.0 0.232 10.0 0.233 15.0 0.234 20.0 0.233 25.0 0.232 30.0 0.231 35.0 0.229 40.0 0.229 45.0 0.230 50.0 0.233 55.0 0.240 60.0 0.251 65.0 0.270 70.0 0.300 75.0 0.343 80.0 0.405 85.0 0.344 90.0 QUALITY CONTROL AND QUALITY ASSURANCE These data are provisional. SRRB has attempted to produce the best data set possible, however the data quality is constrained by measurement accuracies of the instruments and the quality of the calibrations. Regardless, SRRB attempts to ensure the best quality possible through quality assurance and data quality control. The data are subjected to automatic procedures as the daily files are processed. At present, they are subjected only to this first-level check, and a daily "eye" check before being released, however, as quality control procedures become more refined, they will be applied, and new versions of the data files will be generated. Quality assurance methods are in place to ensure against premature equipment failure in the field and post deployment data problems. For example, all instruments at each station are exchanged for newly calibrated instruments on an annual basis. Calibrations are performed by world- recognized organizations. For example, pyranometers and pyrheliometers are calibrated at the National Renewable Energy Laboratory (NREL). Calibration factors for the UVB instrument are transferred from three standards maintained by SRRB's National UV Calibration Facility in Boulder. In general all of the standards the SRRB and NREL are traceable to NIST or its equivalent. THE INSTRUMENTS: 1. The Solar Light UVB Broadband Radiometer The conversion factor applied to the UVB data is valid for the solar spectral band from 280 to 320 nm and has a response function that approximates the erythemal (Diffey) action spectrum. The conversion factor applied varies as a function of the solar zenith angle. 2. The Normal Incidence Pryheliometer (NIP) The NIP measures direct solar radiation in the broadband spectral range from 280 to 3000 nm. Those used at SOLRAD stations are calibrated nominally on a biennial basis at the NOAA calibration facility in Boulder, CO 3. Precision Spectral Pyranometer (PSP) A PSP measures downwelling global irradiance at SOLRAD stations. These instruments are sensitive to the same broadband spectral range as the NIP, 280 to 3000 nm. They are calibrated on a biennial basis at the NOAA calibration facility in Boulder, CO An inherent problem with the PSP is that its sensor cools to space (if it is directed upward) and this causes a negative signal. This is apparent at night where it shows up as an erroneous negative irradiance that can be as high as -30 Wm^-2. Daytime data also contain this error but it is masked by the large solar signal. This error especially affects the diffuse measurement made by a PSP because the sensor is shaded. Therefore, the PSP is not used for the diffuse measurement. 4. Eppley 8-48 "black and white" pyranometer This pyranometer is used for the diffuse solar measurement. It has been found to have desirable properties for this measurement because it does not use a thermopile for the detector and thus does not have the "nighttime" offset problem. These instruments are sensitive to the same broadband spectral range as the NIP and PSP, 280 to 3000 nm. They are also calibrated on a biennial basis at the NOAA calibration facility in Boulder, CO 5. Precision Infrared Radiometer (PIR) The PIR measures and downwelling thermal infrared irradiance at Madison only. It is sensitive to the spectral range from 3000 to 50,000 nm. NOAA maintains three standard PIRs that are calibrated annually by a world-reputable organization. These standards are used to calibrate field PIRs.