| DQR ID | Subject | Data Streams Affected |
|---|---|---|
| D010423.14 | SGP/SIRS/E13 - Diffuse Pyranometer Thermal Offsets | sgpsirsE13.a0, sgpsirsE13.a1 |
| D970927.1 | SIRS NIPs affected by condensation at E8, E11, E13, & E15 | sgpsirsE11.a1, sgpsirsE13.a1, sgpsirsE15.a1, sgpsirsE8.a1 |
| D980224.1 | Reference Broadband Shortwave Data at SGP Central Cluster during Fall IOP '97 | sgpbsrnC1.00, sgpbsrnC1.a0, sgpbsrnC1.a1, sgpsirosE13.00, sgpsirosE13.a1, sgpsirsE13.a0, sgpsirsE13.a1 |
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 08/29/1997 | 0421 | 02/22/2001 | 2021 |
| Subject: | SGP/SIRS/E13 - Diffuse Pyranometer Thermal Offsets |
| DataStreams: | sgpsirsE13.a0, sgpsirsE13.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 Additionally, the Model PSP radiometer has been replaced by a Model 8-48 which uses a black and white thermopile detector known to reduce the thermal offset errors to less than 2 Watts per square meter [3].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: | sgpsirsE13.a0:
sgpsirsE13.a1:
|
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 09/26/1997 | 1230 | 09/26/1997 | 1415 |
| 09/26/1997 | 1230 | 09/26/1997 | 1330 |
| 09/26/1997 | 1230 | 09/26/1997 | 1345 |
| Subject: | SIRS NIPs affected by condensation at E8, E11, E13, & E15 |
| DataStreams: | sgpsirsE11.a1, sgpsirsE13.a1, sgpsirsE15.a1, sgpsirsE8.a1 |
| Description: | Comparison of data from the unshaded PSP to that derived from the 'direct + diffuse' (NIP + shaded PSP) indicated low values of the 'direct+diffuse' combination starting at sunrise and lasting for about an hour at E8, E11, E13 and E15. Futher examination revealed that the NIPs were reading low and were likely affected by condensation during this brief period. Weather conditions were foggy over the area early that morning, and fog quickly dissipated after sunrise. |
| Measurements: | sgpsirsE15.a1:
sgpsirsE11.a1:
sgpsirsE8.a1:
sgpsirsE13.a1:
|
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 09/17/1997 | 0000 | 10/03/1997 | 2359 |
| Subject: | Reference Broadband Shortwave Data at SGP Central Cluster during Fall IOP '97 |
| DataStreams: | sgpbsrnC1.00, sgpbsrnC1.a0, sgpbsrnC1.a1, sgpsirosE13.00, sgpsirosE13.a1, sgpsirsE13.a0, sgpsirsE13.a1 |
| Description: | This is a recommendation for the best available broadband shortwave data from the SGP Central Cluster (Lamont, OK) during the Combined Fall IOP, 15 Sept - 5 Oct 1997. Data available from the SGP Radiometer Calibration Facility (RCF) has lower measurement uncertainties than similar measurements from the C1, E-13, and BSRN/BRS platforms. The RCF data were collected using the same Broadband Outdoor Radiometer CALibration (BORCAL) system used for routine calibration of pyranometers and pyrheliometers at the RCF. The data are available for 30-second interval. Direct normal irradiance measurements from a windowed RCF Absolute Cavity Radiometer during the IOP is considered more accurate (+/- 0.5%) than the Normal Incidence Pyrheliometers (NIP) at the Central Cluster (+/- 2%). The Automated Hickey-Frieden cavity radiometer is electrically self-calibrating and provides reference standard data suitable for the calibration of the NIPs used at all the CART sites. Diffuse horizontal irradiance is available as the average of two Eppley Precision Spectral Pyranometers and is considered slightly more accurate than the downwelling diffuse (DD) data from the Central Cluster instruments. The RCF data will have periodic gaps during the electrical calibration intervals (about 6-10 minutes, 4 or 5 times per day). The reference global horizontal (or Downwelling Shortwave - DS) has been computed from the measured direct normal and diffuse components: DS = NIP x Cos(Z) + DD, where, Z = solar zenith angle. All RCF data collected during the IOP are on the ARM IOP Web page (iop.archive.arm.gov/arm-iop). with other data from the Fall97 shortwave IOP. Additional corrections to the diffuse data may be possible after researching PSP nighttime offsets. Data from C1, E-13, and BSRN/BRS platforms during the SW-IOP '97 are still being investigated. |
| Measurements: | sgpsirosE13.a1:
sgpbsrnC1.00:
sgpbsrnC1.a1:
sgpbsrnC1.a0:
sgpsirosE13.00:
sgpsirsE13.a0:
sgpsirsE13.a1:
|