| DQR ID | Subject | Data Streams Affected |
|---|---|---|
| D000514.4 | SGP/SIROS/E13 - occasional spikes in readings | DsgpsirosE13.00, sgpsirosE13.a1 |
| D020620.50 | SGP/SIROS/E13 - wrong units for broadband irradiance | sgpsirosE13.a1 |
| D940822.2 | SIROS 10M Data Release | sgpsirosE13.a1 |
| D941227.3 | SIROS data corrupted when tower was down | sgpsirosE13.a1 |
| D950328.1 | Installation of new data logger PROM | sgpsirosE13.a1 |
| D960423.9 | SGP/SIROS/E13 - Wrong units for broadband irradiance | sgpsirosE13.a1 |
| D960501.2 | SGP/SIROS - wrong units for broadband irradiance | sgpsirosE1.a1, sgpsirosE10.a1, sgpsirosE11.a1, sgpsirosE12.a1, sgpsirosE13.a1, sgpsirosE15.a1, sgpsirosE16.a1, sgpsirosE18.a1, sgpsirosE20.a1, sgpsirosE22.a1, sgpsirosE24.a1, sgpsirosE3.a1, sgpsirosE4.a1, sgpsirosE7.a1, sgpsirosE8.a1, sgpsirosE9.a1 |
| D960602.3 | Level of pyranometer for global solar was slightly off | sgpsirosE13.a1 |
| D960914.7 | time stamp error | sgpsirosE13.a1 |
| D970317.1 | downwelling solar irradiance measurement adjustments | sgpbsrnC1.a1, sgpsirosE13.a1 |
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 11/11/1993 | 0000 | 09/10/1994 | 0000 |
| Subject: | SGP/SIROS/E13 - occasional spikes in readings |
| DataStreams: | DsgpsirosE13.00, sgpsirosE13.a1 |
| Description: | Since installation of this SIROS site to the dates specified, negative spikes occurred in the data streams indicated, especially up_short_hemisp, down_short_hemisp, down_long_diffuse_hemisp, and short_direct_normal. These spikes were induced by electrical interference from the fence that was used to keep out cattle. The spikes were eliminated by moving the fence further away from the SIROS sensors in September 1994. An assessment by Mike Split on the effects of the spikes indicated that the spikes superimposed on the readings ranged from -10 to -100 W m^-2. As many as 40 per day could occur. As a result of these spikes, the daily average reading of irradiance could be reduced by as much as 1 W m^-2, a half-hour average could be reduced by as much as 2 W m^-2, and a 5-min average could be affected by as much as 5 W m^-2. |
| Measurements: | sgpsirosE13.a1:
DsgpsirosE13.00:
|
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 01/06/1994 | 2042 | 01/23/1996 | 2359 |
| Subject: | SGP/SIROS/E13 - wrong units for broadband irradiance |
| DataStreams: | sgpsirosE13.a1 |
| Description: | Headers for SIROS, MFR25m and MFR10m give the units for broadband irradiance as 'watts per square meter' (W/M^2). However, the units are really 'counts'. The fields affected are SIROS: 'hemisp_broadband:units' 'diffuse_hemisp_broadband:units' 'direct_norm_broadband:units' MFR: 'mfr_up_hemisp_broadband:units' This problem has existed since the beginning of the data streams, and was corrected by Jeff Slater on 1/23/96 (see C960314.2 by Ken Yates that closed P960229.2) |
| Measurements: | sgpsirosE13.a1:
|
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 04/26/1994 | 0000 | 08/18/1994 | 1855 |
| Subject: | SIROS 10M Data Release |
| DataStreams: | sgpsirosE13.a1 |
| Description: | This DQR needs to accompany SIROS 10 meter tower data release
from the Central Facility. The SIROS 10 meter tower data release
is for the time period between August 18 and April 26, 1994.
Subject: SIROS 10M Data Release (April 26 thru August 18, 1994)
Name: Trevor Ley (SRRB\NOAA) Instrument Mentor Dr. John DeLuisi
Email address: trevor@srrb.noaa.gov
Telephone: (303) 497-7315
Institution: SRRB\NOAA
Platform/Measurement: 10 meter tower upwelling PIR
what level data: .a1 and .a0
period of time in question
start: April 26, 1994 at 00:00:00 (GMT)
end: August 18,1994 at 18:15:55 (GMT)
Data should be labeled:
- Incorrect
Discussion of Problem:
- The preamp on the upwelling PIR signal was bad.
During investigation of the raw data files, it was
found that the UPIR signal was reading too high
(2050-2200).
Other observations/measurements impacted by this problem:
Suggested Corrections of the Problem: None
REQUIRED ACTIONS:
This report is informational no further action required
Experiment Center action required as follows:
Supply with SIROS 10m data release (April 26 thru August 18, 1994)
-------------------------------------------------------
TO BE FILLED IN UPON COMPLETION OF ACTION ABOVE:
Action Taken:
Experiment Center:
Site Operations:
Archive:
EST:
-----------------------------------------------------------------
END |
| Measurements: | sgpsirosE13.a1:
|
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 08/18/1994 | 1530 | 08/18/1994 | 1630 |
| Subject: | SIROS data corrupted when tower was down |
| DataStreams: | sgpsirosE13.a1 |
| Description: | DQR No: Platform: sgpsiros13
Subject: SIROS data corrupted when tower was down
Date Submitted: 12/27/94
Submitted By: Marvin L. Wesely ___ Instrument Mentor
___ EST Member
___ Science Team Member
_x_ Other _Instrment Team 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 data levels for sgpsiros13
What location was the data collected at: SIROS CF
Period of time in question
Begin Date 18/AUG/94 Time 15:30 (GMT)
End Date 18/AUG/94 Time 16:30 (GMT)
Data should be labeled:
_x_ questionable _x_ All data fields affected
___ incorrect ___ Only some data fields affected
___ wrong calibration
___ others
Discussion of Problem:
The 10-m tower at the central facility central cluster was lowered
by site operations personnel and work was carried out on the SIROS
cabling and possibly the MFRSR-supplied data logger. Some data
might be missing, some might be out of range, and some might appear
reasonable but should not be trusted for the time interval and
location specified.
Other observations/measurements impacted by this problem:
SMOS sensors when tower was down between 1420 and 1520 GMT; see
DQR P940822.1
MFR10 sensor when tower was down between 1420 and 1520 GMT, as noted in
a separate DQR
Suggested Corrections of the Problem: (e.g. change calibration factor and
recompute, flag data with this comment, etc.)
Flat data with this comment.
Data Processing Notes Date |
| Measurements: | sgpsirosE13.a1:
|
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 03/08/1995 | 2033 | 03/08/1995 | 2302 |
| Subject: | Installation of new data logger PROM |
| DataStreams: | sgpsirosE13.a1 |
| Description: | DQR No: Platform: sgpsirosE13
Subject: Installation of new data logger PROM
Date Submitted: 95/03/27
Submitted By: Nels Larson _X_ Instrument Mentor
___ EST Member
___ Science Team Member
___ Other _____________________________
For questions or problems, please contact the ARM Experiment Center at
509-375-6898 or via email at dqr@arm.gov.
Platform/Measurement: All data
What level data: (raw,a0,a1,b1,c1 etc): All
What location was the data collected at: Central
Period of time in question
Begin Date 95/03/08 Time 20:33 (GMT)
End Date 95/03/08 Time 23:02 (GMT)
Data should be labeled:
___ questionable ___ All data fields affected
___ incorrect ___ Only some data fields affected
___ wrong calibration
___ others
Discussion of Problem:
The MFRSR head for sgpmsirosE13 was changed by the mentors. The old head, 917,
was removed for recalibration, and the new head, 921, was installed.
No data was acquired between 95/03/08 20:33-23:02.
The data logger PROM was upgraded from Version 12 to Version 13.
Other observations/measurements impacted by this problem:
The data logger clock lost 31 seconds per day after the PROM upgrade until
reset with a new clock constant at 95/03/16 05:33.
Suggested Corrections of the Problem: (e.g. change calibration factor and
recompute, flag data with this comment, etc.)
Data Processing Notes Date |
| Measurements: | sgpsirosE13.a1:
|
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 01/06/1994 | 2042 | 01/23/1996 | 2359 |
| Subject: | SGP/SIROS/E13 - Wrong units for broadband irradiance |
| DataStreams: | sgpsirosE13.a1 |
| Description: | Headers for SIROS, MFR25m and MFR10m give the units for broadband irradiance as 'watts per square meter' (W/m^2). However, the units are really 'counts'. The fields affected are SIROS: 'hemisp_broadband:units' 'diffuse_hemisp_broadband:units' 'direct_norm_broadband:units' MFR: 'mfr_up_hemisp_broadband:units' This problem has existed since the beginning of the data streams, and was corrected by Jeff Slater on 1/23/96 (see C960314.2 by Ken Yates that closed P960229.2) |
| Measurements: | sgpsirosE13.a1:
|
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 01/06/1994 | 0000 | 01/23/1996 | 2359 |
| Subject: | SGP/SIROS - wrong units for broadband irradiance |
| DataStreams: | sgpsirosE1.a1, sgpsirosE10.a1, sgpsirosE11.a1, sgpsirosE12.a1, sgpsirosE13.a1, sgpsirosE15.a1, sgpsirosE16.a1, sgpsirosE18.a1, sgpsirosE20.a1, sgpsirosE22.a1, sgpsirosE24.a1, sgpsirosE3.a1, sgpsirosE4.a1, sgpsirosE7.a1, sgpsirosE8.a1, sgpsirosE9.a1 |
| Description: | Headers for SIROS, give the units for broadband irradiance as 'watts per square meter' (w/m^2). However, the units are really 'counts'. The fields affected are: 'hemisp_broadband:units' 'diffuse_hemisp_broadband:units' 'direct_norm_broadband:units' This problem existed since the beginning of the data streams, and was corrected on 1/23/96. |
| Measurements: | sgpsirosE24.a1:
sgpsirosE13.a1:
sgpsirosE18.a1:
sgpsirosE4.a1:
sgpsirosE7.a1:
sgpsirosE16.a1:
sgpsirosE8.a1:
sgpsirosE12.a1:
sgpsirosE9.a1:
sgpsirosE15.a1:
sgpsirosE3.a1:
sgpsirosE22.a1:
sgpsirosE11.a1:
sgpsirosE10.a1:
sgpsirosE20.a1:
sgpsirosE1.a1:
|
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 01/06/1994 | 0000 | 12/06/1994 | 1313 |
| Subject: | Level of pyranometer for global solar was slightly off |
| DataStreams: | sgpsirosE13.a1 |
| 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. |
| Measurements: | sgpsirosE13.a1:
|
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 01/06/1994 | 0000 | 07/19/1996 | 2359 |
| Subject: | time stamp error |
| DataStreams: | sgpsirosE13.a1 |
| Description: | The internal code that runs the MFRSR data logger had a bug that occasionally caused the time stamp associated with the data to be slightly in error. This error is thought to be very small (say less than 30 seconds) and very infrequent. (Unfortunately, we cannot give firm estimates of the magnitude and frequency of the error). After 96/07/19 the problem was corrected. Those who use the data before this time should realize that the time stamp for each record of data might be slightly in error. |
| Measurements: | sgpsirosE13.a1:
|
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 10/13/1995 | 0000 | 08/20/1997 | 2359 |
| Subject: | downwelling solar irradiance measurement adjustments |
| DataStreams: | sgpbsrnC1.a1, sgpsirosE13.a1 |
| Description: | A comparison of BSRN and SIROS solar radiometers for measuring downwelling
irradiances at the SGP central facility was made with field standards and two
absolute cavity radiometers brought to the site or a two-week period in April
1996 by Mike Rubes (formerly of the National and Oceanic Atmospheric
Administration, Air Resources Laboratory, Surface Radiation Research Branch in
Boulder, CO). A description of this effort can currently be found on the
World Wide Web at http://www.srrb.noaa.gov/apr96iop/hagsie.html. Analyses of
the data from these comparisons have resulted in several observations on the
quality of data collected at the BSRN and SIROS platforms since October 13,
1995, which are probably valid to the present time, until these sensors are
replaced with more recently calibrated sensors. On Oct. 13, 1995, the two
BSRN pyranometers (PSPs) were replaced, so the observations do not apply to
the BSRN measurements of global and diffuse irradiation before that date.
Another source of information is inspection of the SIROS and BSRN equipment by
Joe Michalsky (Atmospheric Science Research Center, State University of New
York at Albany) at various times. The results of the findings are summarized
as recommendations in the following several paragraphs. Some explanation and
further comments are provided in the parenthetical remarks.
ANALYSIS WHEN THE DIRECT BEAM WAS NOT OBSCURED BY CLOUDS
Direct-beam solar irradiance measured with the BSRN pyrheliometer (NIP) are
too large by approximately 0.5% compared to the two absolute cavity
radiometers. (This small underestimate is within the expected level of
uncertainty.)
Direct-beam solar irradiance measured with the SIROS pyrheliometer are too
small by approximately 2.1% compared to the two absolute cavity radiometers.
(This large discrepancy is unexplained and will be explored during future
calibration activities at the SGP Radiation Calibration Facility.)
Possibly the best estimate of downwelling total hemispherical solar (global)
irradiance can be made by summing the SIROS pyrheliometer irradiance reading
multiplied by 1.021 (and by the cosine of the solar zenith angle) and the
average of the readings for diffuse irradiance from the shaded BSRN and SIROS
pyranometers. The direct-beam part can alternatively be computed as 0.995
times the BSRN pyrheliometer reading. For data collected in October before
the 13th, when the BSRN shaded pyrheliometer was replaced, the diffuse
component is probably best computed directly from the SIROS shaded sensor
alone.
Downwelling total hemispherical solar (global) irradiance measured by the BSRN
unshaded pyranometer is approximately 2% too small (which is within the
expected level of uncertainty for unshaded pyranometer measurements) compared
to the values computed from the measured direct-beam and diffuse components.
(Downwelling total hemispherical solar irradiances measured by the SIROS
unshaded pyranometer systematically underestimates the global irradiances
by excessive amounts, i.e., by greater than 3%.)
The analyses leading to these recommendations are described in an extended
abstract presented in early February (J. Michalsky et al., "Optimal
Measurements of Surface Shortwave Irradiance Using Current Instrumentation--
The ARM Experience," in Preprint Volume, Ninth Conference on Atmospheric
Radiation, Feb. 2-7, Long Beach, California, pp. J5-J9, American
Meteorological Society, Boston, MA). Further relevant analyses were conducted
by Kato et al., (Seiji Kato, Pennsylvania State University) and are described
in a manuscript submitted for publication ("Uncertainties in Modelled and
Measured Clear Sky Surface Shortwave Irradiances")."
UNSHADED PYRANOMETER PERFORMANCE WHEN THE DIRECT BEAM WAS NOT OBSCURED
The above recommendations are based mostly on analyses conducted for
cloudless, midday conditions. Because the data reported from the unshaded
pyranometer were not corrected for cosine response, slight overestimates of
global irradiance from unshaded pyranometers tend to occur in cloudless
conditions at solar zenith angles less than 45 deg and slight underestimates
tend to occur for zenith angles greater than 55 deg. The maximum deviations
occur at extreme solar zenith angles and are about 2%.
TRACKER-SHADING PERFORMANCE
The data user should note, as has been noted in data release statements, that
analyses of the direct, diffuse, and/or direct beam irradiances should be
preceded by a check of sensor performances by summing the direct and diffuse
components and comparing the result to the directly measured global component.
When this is done, problems with solar tracking are usually apparent.
Because slight misalignments in the tracking and shading devices can be
difficult to detect, small deviations of the component sum from expected
behavior are sometimes difficult to explain. If such deviations tend to recur
for specific time intervals for several days, one might suspect a tracking or
shading problem. For the time period addressed here, the modern tracking-
shading assembly used with the SIROS sensors appeared to work well. For the
BSRN sensors until January 1996, an older tracking-shading system was used
that was not as reliable as the modern assembly used with the SIROS sensors;
problems with this BSRN tracking and shading system, were usually evident when
they occurred. A modern tracker-shader was installed for the BSRN sensors in
January 1996. The tracker was not aligned as well as it could be. Efforts are
underway to improve tracker alignment checks and procedures at all SIROS sites
and the BSRN site.
PARTLY CLOUD CONDITIONS
An analysis by Chuck Long (formerly at the Pennsylvania State University and
now with the University of Colorado and the National Oceanic and Atmospheric
Administration) indicated that data users who are investigating partly cloudy
sky conditions will usually find that the BSRN outputs are more reliable for
short periods of time, say less than 30 min, than are the SIROS outputs. This
tends to occur because the SIROS data are recorded only every 20 s while the
BSRN data represent one-minute averages computed on the basis of sampling once
per second. Under partly cloudy conditions, sampling only once every 20 s
tends to provide inadequate statistical representation of downwelling
irradiances.
ESTIMATES FOR CLOUDY CONDITIONS
The component sum technique is not applicable for overcast conditions. For
the time period addressed here, the SIROS shaded sensor appears most reliable
before October 13, 1995. Thereafter, an average of data from the SIROS shaded
pyranometer, the shaded BSRN sensor, and the shaded BSRN sensor multiplied by
1.02 might be the best estimate of global irradiance for cloudy conditions.
However, a rigorous analysis on the results of this procedure has not been
carried out, so the data user should approach this technique with caution.
SOME ADDITIONAL INFORMATION
The excessively large deviations noted above for the pyranometers result in
part from a mixture of different sources of calibration procedures. The
following table lists the sources of calibration:
Sensor Coefficient used Calibration Installation
to process data date date
BSRN PSP DS BORCAL Sept. 1995 Oct. 13, 1995
BSRN PSP DD Eppley June 1995 Oct. 13, 1995
BSRN NIP BORCAL July 1993 March 17, 1994
SIROS PSP DS Eppley June 1995 July 25, 1995
SIROS PSP DD Eppley June 1995 July 25, 1995
SIROS NIP BORCAL Sept. 1994 July 25, 1995
DS = downwelling solar or global
DD = downwelling diffuse
PSP = precision spectral pyranometer
NIP = normal incidence pyrheliometer for direct-beam solar
BORCAL = broadband outdoor radiometer calibration, conducted by the National
Renewable Energy Laboratory (NREL)
Eppley = denotes calibrations in an integrating sphere by the manufacturer,
Eppley Laboratory, Inc.
The BORCAL calibrations result in estimates of solar irradiances that are
typically 1.5% larger than Eppley calibrations, a situation which is under
investigation by Tom Stoffel at NREL and John Hickey at Eppley. They are
working together to document this difference. This difference helps to
explain the larger estimates of global irradiance measurement with the BSRN
sensor than with the SIROS sensor.
A greater source of concern than over differences between the NREL versus the
Eppley calibrations at this time is the insufficiently frequent recalibrations
of sensors in operation at the SGP site. Although the NIPs are expected to
hold their calibrations for rather long periods of time, the pyranometers
typically should be recalibrated at least once every 12 months. Change out
with freshly calibrated pyranometers and pyrheliometers at the SGP site will
begin in 1997, with the goal of routinely replacing every pyranometer and
pyrheliometer with freshly calibrated sensors once every year.
Data users can inspect metrics provided on the World Wide Web by the SGP site
scientist team on data quality at the following address:
http://manatee.gcn.uoknor.edu/metrics/METRICS.html
Other observations/measurements impacted by this problem:
Any derived estimates of downwelling solar radiation components using data
from central facility SIROS or BSRN sensors (for downwelling solar radiation)
for the time period indicated.
Suggested Corrections of the Problem: (e.g. change calibration factor and
recompute, flag data with this comment, etc.)
Use of these recommendations by data users. Ideally, the component sum
technique would be applied in a value-added product (VAP) implemented at the
Experiment Center, but this has not been done yet. In the meantime, users of
recent data can inspect plots of component sum technique on the World Wide Web
site noted above. |
| Measurements: | sgpsirosE13.a1:
sgpbsrnC1.a1:
|