Description: | DQR No: Platform: sgpsiros13
Subject: Level of pyranometer for global solar was slightly off
Date Submitted: 6/1/96
Submitted By: Marv Wesely ___ Instrument Mentor
___ EST Member
___ Science Team Member
_x_ Other __IT leader__
For questions or problems, please contact the ARM Experiment Center at
509-375-6898 or via email at dqr@arm.gov.
Platform/Measurement:
What level data: (raw,a0,a1,b1,c1 etc):
All levels of sgpsiros13, but only for down_short_hemisp.
What location was the data collected at:
Period of time in question
Begin Date 01/06/94
End Date 12/06/94 Time 06:00 (GMT)
Data should be labeled:
___ questionable ___ All data fields affected
___ incorrect _x_ Only some data fields affected
___ wrong calibration
_x_ others
Discussion of Problem:
Analysis of SIROS data from the central facility has indicated
that the pyranometer (or PSP) used for global (solar) irradiance
observations appeared to be slightly off level until site operations
personnel re-leveled the sensor on Dec. 6, 1994. Calculations suggest
that the sensor was leaning roughly toward the east by about 1.2 degrees.
Comparisons to the nearby BSRN pyranometer ("psp2") show that the
SIROS sensor was reading to high in the morning by as much as 5% and
too small in the late afternoon by about the same percentage.
Little, if any, effect was seen between 1700 and 2100 UTC (in
November), and the effect was be practically zero under cloudy
skies.
Users of the data could conceivable adjust the data (down_short_hemisp
for sgpsiros13) with the direct-beam SIROS or BSRN observation and
values of the solar zenith and azimuth angles, which would need to
be computed, and some fairly straighforward geometry calculations.
Possibly an easier course of action is to rely on the BSRN observation
of global solar radiation for small solar elevation angles.
(This analysis was conducted by John DeLuisi and colleagues
in 1994 but was not documented with a DQR. Some recent
discussions I have had with Science Team members have indicated
that they have seen this problem also.)
Other observations/measurements impacted by this problem:
None.
Suggested Corrections of the Problem: (e.g. change calibration factor and
recompute, flag data with this comment, etc.)
Ideally, this note would be sent Send to people who received SIROS13
data for dates before Dec. 6, 1994, and the appropriate data in the
archive would be flagged with this comment. |