| DQR ID | Subject | Data Streams Affected |
|---|---|---|
| D030312.10 | SGP/MWR/C1 - Intermittent Negative Sky Brightness Temperatures | sgp1mwravgC1.c1, sgp5mwravgC1.c1, sgpmwrlosC1.a1, sgpmwrlosC1.b1 |
| D050722.1 | SGP/MWR/C1 - REPROCESS - Revised Retrieval Coefficients | sgp1mwravgC1.c1, sgp5mwravgC1.c1, sgpmwrlosC1.a1, sgpmwrlosC1.b1, sgpmwrtipC1.a1, sgpqmemwrcolC1.c1 |
| D050915.1 | SGP/MWR/C1 - Instrument noise problem | sgp1mwravgC1.c1, sgp5mwravgC1.c1, sgpmwrlosC1.b1, sgpmwrtipC1.a1 |
| D960405.1 | SGP/MWR/C1 - Loss of thermal stabilization | sgp1mwravgC1.c1, sgp5mwravgC1.c1, sgpmwrlosC1.a1, sgpmwrlosC1.b1 |
| D961120.1 | SGP/MWR/B1/B4/B5/B6/C1 - Thermal Stabilization Adjustment | sgp1mwravgC1.c1, sgp5mwravgB1.c1, sgp5mwravgB4.c1, sgp5mwravgB5.c1, sgp5mwravgB6.c1, sgp5mwravgC1.c1, sgpmwrlosB1.a0, sgpmwrlosB1.a1, sgpmwrlosB4.a0, sgpmwrlosB4.a1, sgpmwrlosB5.a0, sgpmwrlosB5.a1, sgpmwrlosB6.a0, sgpmwrlosB6.a1, sgpmwrlosC1.a1, sgpmwrlosC1.b1 |
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 11/17/1999 | 1800 | 07/31/2002 | 2034 |
| Subject: | SGP/MWR/C1 - Intermittent Negative Sky Brightness Temperatures |
| DataStreams: | sgp1mwravgC1.c1, sgp5mwravgC1.c1, sgpmwrlosC1.a1, sgpmwrlosC1.b1 |
| Description: | Several related and recurring problems with the SGP MWRs have been reported dating back to 1999. These problems were due to the occurrence of blackbody signals (in counts) that were half of those expected. The symptoms included noisy data (especially at Purcell), spikes in the data (especially at Vici), negative brightness temperatures, and apparent loss of serial communication between the computer and the radiometer, which results in a self-termination of the MWR program (especially at the CF). Because these all initially appeared to be hardware-related problems, the instrument mentor and SGP site operations personnel (1) repeatedly cleaned and replaced the fiber optic comm. components, (2) swapped radiometers, (3) sent radiometers back to Radiometrics for evaluation (which has not revealed any instrument problems), and (4) reconfigured the computer's operating system. Despite several attempts to isolate and correct it, the problem persisted. It became apparent that some component of the Windows98 configuration conflicted with the DOS-based MWR program or affected the serial port or the contents of the serial port buffer. This problem was finally corrected by upgrading the MWR software with a new Windows-compatible program. |
| Measurements: | sgp5mwravgC1.c1:
sgpmwrlosC1.b1:
sgp1mwravgC1.c1:
sgpmwrlosC1.a1:
|
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 04/16/2002 | 2000 | 06/28/2005 | 2300 |
| Subject: | SGP/MWR/C1 - REPROCESS - Revised Retrieval Coefficients |
| DataStreams: | sgp1mwravgC1.c1, sgp5mwravgC1.c1, sgpmwrlosC1.a1, sgpmwrlosC1.b1, sgpmwrtipC1.a1, sgpqmemwrcolC1.c1 |
| Description: | IN THE BEGINNING (June 1992), the retrieval coefficients used to derive the precipitable water vapor (PWV) and liquid water path (LWP) from the MWR brightness temperatures were based on the Liebe and Layton (1987) water vapor and oxygen absorption model and the Grant (1957) liquid water absorption model. Following the SHEBA experience, revised retrievals based on the more recent Rosenkranz (1998) water vapor and oxygen absorption models and the Liebe (1991) liquid waer absorption model were developed. The Rosenkranz water vapor absorption model resulted a 2 percent increase in PWV relative to the earlier Liebe and Layton model. The Liebe liquid water absorption model decreased the LWP by 10% relative to the Grant model. However, the increased oxygen absorption caused a 0.02-0.03 mm (20-30 g/m2) reduction in LWP, which was particularly significant for low LWP conditions (i.e. thin clouds encountered at SHEBA). Recently, it has been shown (Liljegren, Boukabara, Cady-Pereira, and Clough, TGARS v. 43, pp 1102-1108, 2005) that the half-width of the 22 GHz water vapor line from the HITRAN compilation, which is 5 percent smaller than the Liebe and Dillon (1969) half-width used in Rosenkranz (1998), provided a better fit to the microwave brightness temperature measurements at 5 frequencies in the range 22-30 GHz, and yielded more accurate retrievals. Accordingly, revised MWR retrieval coefficients have been developed using MONORTM, which utilizes the HITRAN compilation for its spectroscopic parameters. These new retrievals provide 3 percent less PWV and 2.6 percent greater LWP than the previous retrievals based on Rosenkranz (1998). Although the MWR data will be reprocessed to apply the new monortm-based retrievals, for most purposes it will be sufficient to correct the data using the following factors: PWV_MONORTM = 0.9695 * PWV_ROSENKRANZ LWP_MONORTM = 1.026 * LWP_ROSENKRANZ The Rosenkranz-based retrieval coefficients became active as follows (BCR 456): SGP/C1 (Lamont) 4/16/2002, 2000 SGP/B1 (Hillsboro) 4/12/2002, 1600 SGP/B4 (Vici) 4/15/2002, 2300 SGP/B5 (Morris) 4/15/2002, 2300 SGP/B6 (Purcell) 4/16/2002, 2200 SGP/E14(Lamont) 4/16/2002, 0000 NSA/C1 (Barrow) 4/25/2002, 1900 NSA/C2 (Atqasuk) 4/18/2002, 1700 TWP/C1 (Manus) 5/04/2002, 0200 TWP/C2 (Nauru) 4/27/2002, 0600 TWP/C3 (Darwin) inception The MONORTM-based retrieval coefficients became active as follows (BCR 984): SGP/C1 (Lamont) 6/28/2005, 2300 SGP/B1 (Hillsboro) 6/24/2005, 2100 SGP/B4 (Vici) 6/24/2005, 2100 SGP/B5 (Morris) 6/24/2005, 2100 SGP/B6 (Purcell) 6/24/2005, 1942 SGP/E14(Lamont) 6/28/2005, 2300 NSA/C1 (Barrow) 6/29/2005, 0000 NSA/C2 (Atqasuk) 6/29/2005, 0000 TWP/C1 (Manus) 6/30/2005, 2100 TWP/C2 (Nauru) 6/30/2005, 2100 TWP/C3 (Darwin) 6/30/2005, 2100 PYE/M1 (Pt. Reyes) 4/08/2005, 1900** ** At Pt. Reyes, the original retrieval coefficients implemented in March 2005 were based on a version of the Rosenkranz model that had been modified to use the HITRAN half-width at 22 GHz and to be consistent with the water vapor continuum in MONORTM. These retrievals yield nearly identical results to the MONORTM retrievals. Therefore the Pt. Reyes data prior to 4/08/2005 may not require reprocessing. |
| Measurements: | sgpmwrtipC1.a1:
sgp5mwravgC1.c1:
sgpmwrlosC1.b1:
sgp1mwravgC1.c1:
sgpqmemwrcolC1.c1:
sgpmwrlosC1.a1:
|
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 07/28/2005 | 1400 | 08/05/2005 | 1700 |
| Subject: | SGP/MWR/C1 - Instrument noise problem |
| DataStreams: | sgp1mwravgC1.c1, sgp5mwravgC1.c1, sgpmwrlosC1.b1, sgpmwrtipC1.a1 |
| Description: | Various variables including the mixer temperatures were very noisy. After several attempts to fix the problem, the instrument was taken off line and returned to the manufacturer for repair. |
| Measurements: | sgpmwrtipC1.a1:
sgp5mwravgC1.c1:
sgpmwrlosC1.b1:
sgp1mwravgC1.c1:
|
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 08/19/1995 | 0000 | 08/20/1995 | 2359 |
| 08/26/1995 | 0000 | 09/04/1995 | 2359 |
| 07/01/1996 | 1825 | 07/23/1996 | 2300 |
| Subject: | SGP/MWR/C1 - Loss of thermal stabilization |
| DataStreams: | sgp1mwravgC1.c1, sgp5mwravgC1.c1, sgpmwrlosC1.a1, sgpmwrlosC1.b1 |
| Description: | Periodically during August and September 1995 all microwave radiometers at the SGP CART generated error messages in the Site Operations Log like: Time: Sat Aug 19 18:41:20 1995 MWRLOS.C1, tkxc: Value above Maximum. This indicates that the temperature of the microwave hardware (specifically, the cross-coupler or "xc") exceeded its controlled temperature (47-52 deg C) at which point it was no longer thermally stabilized and the gain was uncontrolled. During these periods which typically last about 8 hours from about local noon until about sunset the data behave anomalously and should be considered invalid. Specifically the precipitable water vapor increases and the liquid water path decreases (and becomes SIGNIFICANTLY NEGATIVE (-0.1 mm) on clear sky days). The RMS noise level in the data also increases sharply. The 'Tkxc' field appears ONLY in the a0-level data and does NOT appear in either the a1 (mwrlos) or c1 (mwr5avg) files. Therefore THESE ANOMALOUS VALUES HAVE BEEN INCLUDED IN THE 5-MINUTE AVERAGES. The microwave hardware is thermally stabilized to about +/- 0.1 deg C by resistive heating. When the internal temperature rises above the set point the thermal stabilization of the instrument gain is lost. >From an examination of the component temperature data it appears that increasing the set point temperature to about 55 deg C (328 K) would prevent a re-ocurrance of this problem at the SGP. The manufacturer, Radiometrics, concurs that raising the set point will fix this problem and will not cause other problems. I will have to carefully examine the MCTEX data to determine whether this will be a problem for the TWP. The manufacturer and I had discussed this possibility prior to building the TWP MWRs (S/N 015, 016, and 017) and those instruments have set points above 50 deg C. Note that MWR 018 has a set point near 52 deg C (like the TWP models) but it still experienced a few loss-of-stabilization events. Note that the instruments with the lowest set points had the most loss-of-stabilization events. |
| Measurements: | sgp5mwravgC1.c1:
sgpmwrlosC1.b1:
sgp1mwravgC1.c1:
sgpmwrlosC1.a1:
|
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 08/01/1996 | 0000 | 08/31/1996 | 2359 |
| Subject: | SGP/MWR/B1/B4/B5/B6/C1 - Thermal Stabilization Adjustment |
| DataStreams: | sgp1mwravgC1.c1, sgp5mwravgB1.c1, sgp5mwravgB4.c1, sgp5mwravgB5.c1, sgp5mwravgB6.c1, sgp5mwravgC1.c1, sgpmwrlosB1.a0, sgpmwrlosB1.a1, sgpmwrlosB4.a0, sgpmwrlosB4.a1, sgpmwrlosB5.a0, sgpmwrlosB5.a1, sgpmwrlosB6.a0, sgpmwrlosB6.a1, sgpmwrlosC1.a1, sgpmwrlosC1.b1 |
| Description: | In order to correct a thermal stabilization problem identified earlier I adjusted the thermal set point of the microwave radiometers at the SGP upward from 48-50 deg C to 55 deg C in early August 1996 according to the schedule given below. B6 5 August 1996 C1 6 August 1996 B1 7 August 1996 B5 8 August 1996 Subsequent to making this adjustment the MWRs were put in TIP mode to check on whether the change in set point temperature affected their calibration. Because clear sky conditions were quite intermittent, it is difficult to determine whether the substantial variability in the tip data were attributable to the change in thermal set point. The instrument calibration was not altered in August. Tip data were again collected with these instruments in September prior to the beginning and at the close of the Water Vapor IOP. For example, the calibration of the instrument at the central facility (S/N 10) derived from the September data was essentially the same as that derived from calibration data acquired in February 1996. Although this would lead one to believe that altering the thermal set point did not affect the instrument calibration, it may be that some transient effect was induced. In comparing soundings launched from the central facility with the microwave radiometer there, I noticed that those sondes calibrated in June 1996 consistently reported lower integrated water vapor than the radiometer in July and September (during the IOP) but were in better agreement with the radiometer for the two weeks period immediately after the set point was adjusted. I suspect that adjusting the thermal set point may have temporarily increased the radiometer gain (kelvins/volt) thereby lowering the measured brightness temperature and the retrieved integrated water vapor. It is not clear why a temporary change in gain should occur or even whether it did. But users of the data should be aware that the data from the microwave radiometers at the SGP may be anomalous during August 1996. |
| Measurements: | sgpmwrlosB5.a1:
sgp5mwravgC1.c1:
sgp5mwravgB6.c1:
sgpmwrlosB4.a0:
sgpmwrlosB6.a0:
sgpmwrlosC1.b1:
sgpmwrlosB1.a0:
sgp1mwravgC1.c1:
sgpmwrlosC1.a1:
sgpmwrlosB4.a1:
sgpmwrlosB1.a1:
sgp5mwravgB1.c1:
sgp5mwravgB5.c1:
sgpmwrlosB5.a0:
sgp5mwravgB4.c1:
sgpmwrlosB6.a1:
|