DQR ID | Subject | Data Streams Affected |
---|---|---|
D010423.1 | SGP/SIRS/C1 - Diffuse Pyranometer Thermal Offsets | sgpsirsC1.a0, sgpsirsC1.a1 |
D040322.1 | SGP/SIRS/C1 - Discrepancy between measured and derived downwelling shortwave hemispheric | sgpsirs20sC1.a0, sgpsirsC1.b1 |
D050420.3 | SGP/SIRS/C1 - Reprocess: Adjust Direct Normal Irradiance | sgp15swfanalsirs1longC1.c1, sgp1swfanalsirs1longC1.c1, sgpsirsC1.00, sgpsirsC1.01 |
D060630.8 | SGP/SIRS/C1 - Reprocessed: Longwave Calibration error | sgpsirsC1.b1 |
D990716.2 |
Start Date | Start Time | End Date | End Time |
---|---|---|---|
03/21/1997 | 1648 | 02/22/2001 | 2050 |
Subject: | SGP/SIRS/C1 - Diffuse Pyranometer Thermal Offsets |
DataStreams: | sgpsirsC1.a0, sgpsirsC1.a1 |
Description: | Broadband downwelling shortwave diffuse (sky) irradiance measurements available from SIRS during the period of this Data Quality Report (DQR), require adjustment for thermal offsets. These thermal, or ?zero? offsets refer to the generally reduced output signals from a shaded pyranometer due to the exchange of longwave (infrared) irradiance between the single black thermopile detector, the protective glass domes surrounding the detector, and the atmosphere. Originally considered an acceptable nighttime response of thermopile-type pyranometers, the generally negative bias is now recognized to significantly effect the accuracy of SIRS diffuse irradiance data during daylight periods. Studies of the Eppley Laboratory, Inc. Model PSP (Precision Spectral Pyranometer), used for the SIRS measurements of diffuse irradiance, suggest the thermal offset correction can range from near 0 to as much as 30 Watts per square meter, depending on the coincident net longwave, or infrared irradiance [1, 2]. Under very clear-sky conditions, the diffuse irradiance from a shaded PSP can be less than the minimum physical limit defined by radiative transfer model estimates based only on Rayleigh scattering effects. A correction method has been developed for adjusting SIRS diffuse irradiance data [3]. The resulting Value Added Product (VAP) will be applied to SIRS data for the period of this DQR. The VAP will not be applied to SIROS data collected before the instrument platform was converted to SIRS. Additionally, the Model PSP radiometer has been replaced by a Model 8-48 which uses a black and white thermopile detector known to reduce the thermal offset errors to less than 2 Watts per square meter [3]. The radiometer replacement at this SIRS location was completed on the ending date of this DQR. References: 1. Gulbrandsen, A., 1978: On the use of pyranometers in the study of spectral solar radiation and atmospheric aerosols. J. Appl. Meteorol., 17, 899-904. 2. Cess, R. D., X. Jing, T. Qian, and M. Sun, 1999: Validation strategies applied to the measurement of total, direct and diffuse shortwave radiation at the surface. J. Geophys. Res. 3. Dutton, E.G., J. Michalsky, T. Stoffel, B. Forgan, J. Hickey, D. Nelson, T. Alberta, and I. Reda, 2001: Measurement of Broadband Diffuse Solar Irradiance Using Current Commercial Instrumentation With a Correction for Thermal Offset Errors. J. Atmos. Oceanic Tech. Vol 18, No. 3, 297-314. (March 2001) |
Measurements: | sgpsirsC1.a0:
sgpsirsC1.a1:
|
Start Date | Start Time | End Date | End Time |
---|---|---|---|
03/18/2004 | 1500 | 06/10/2004 | 2000 |
Subject: | SGP/SIRS/C1 - Discrepancy between measured and derived downwelling shortwave hemispheric |
DataStreams: | sgpsirs20sC1.a0, sgpsirsC1.b1 |
Description: | Measured values of downwelling hemispheric shortwave radiation were up to 40 W/m^2 higher than derived values during the afternoon hours. Analysis reveals that this is likely an artifact of the cosine response of the particular installed PSP coupled with typical uncertainties of this set of installed radiometers. That is, this particular instrument cluster seems to be producing cumulative errors on the high side of accepted values. The PSP contains the most uncertainty in measurement at this station. Users should use a derived value for the downwelling shortwave hemispheric irradiance (DS). Where DS = diffuse component + direct normal * cos(SZA) component described in the SIRS handbook Sec 7.2 available at: http://www.arm.gov/publications/tech_reports/handbooks/sirs_handbook.pdf |
Measurements: | sgpsirsC1.b1:
sgpsirs20sC1.a0:
|
Start Date | Start Time | End Date | End Time |
---|---|---|---|
08/03/2000 | 1300 | 08/15/2001 | 1350 |
Subject: | SGP/SIRS/C1 - Reprocess: Adjust Direct Normal Irradiance |
DataStreams: | sgp15swfanalsirs1longC1.c1, sgp1swfanalsirs1longC1.c1, sgpsirsC1.00, sgpsirsC1.01 |
Description: | Direct normal broadband shortwave irradiance measured by NIP s/n 30722E6 was found to have a 0.62%% negative bias when compared in-situ with absolute cavity radiometer measurements taken on August 21, 2000. The estimated measurement uncertainty of the calibration of NIP s/n 30722E6 on July 18, 2000 was -2.6% to +4.8%. Data from NIP s/n 30722E6 can be adjusted according to the in-situ comparisons to reduce the apparent measurement bias. |
Measurements: | sgpsirsC1.01:
sgp1swfanalsirs1longC1.c1:
sgpsirsC1.00:
sgp15swfanalsirs1longC1.c1:
|
Start Date | Start Time | End Date | End Time |
---|---|---|---|
12/11/2003 | 1950 | 02/16/2006 | 1901 |
Subject: | SGP/SIRS/C1 - Reprocessed: Longwave Calibration error |
DataStreams: | sgpsirsC1.b1 |
Description: | Modified pyrgeometer calibration procedures were implemented beginning in December 2003. These modified procedures introduced a calibration bias in the longwave data. The previous procedures were re-implemented at all sites between December 2005 and February 2006 to restore proper calibrations. The data collected while the incorrect procedures were in place have been reprocessed to remove the calibration bias. The reprocessed 60 second averaged data are based on 3 instantaneous 20 second data records rather than on 60 1 second instantaneous data records. Still, these data are considered far superior to the originally processed data. The reprocessed data were archived in October 2006. |
Measurements: | sgpsirsC1.b1:
|
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