| DQR ID | Subject | Data Streams Affected |
|---|---|---|
| D020805.2 | SGP/MWR/B6 - Instrument replaced, calibration incorrect | sgp5mwravgB6.c1, sgpmwrlosB6.a0, sgpmwrlosB6.a1, sgpmwrlosB6.b1 |
| D020805.3 | SGP/MWR/B6 - Instrument replaced, calibration updating | sgp5mwravgB6.c1, sgpmwrlosB6.a0, sgpmwrlosB6.a1, sgpmwrlosB6.b1 |
| D040819.6 | SGP/MWR/B6 - Loss of thermal stabilization | sgp5mwravgB6.c1, sgpmwrlosB6.a0, sgpmwrlosB6.a1 |
| D050725.5 | SGP/MWR/B6 - Reprocess: Revised Retrieval Coefficients | sgp5mwravgB6.c1, sgpmwrlosB6.a1, sgpmwrlosB6.b1, sgpmwrtipB6.a1, sgpqmemwrcolB6.c1 |
| D951005.3 | SGP/5MWRAVG/B6 - Valid LWP > 1 mm excluded from 5 min avgs | sgp5mwravgB6.c1 |
| D960404.13 | SGP/MWR/B6 - Reprocess: Error in MWR calibration | sgp5mwravgB6.c1 |
| D960404.9 | SGP/MWR/B6 - Reprocess: MWR Tuning Functions | sgp5mwravgB6.c1 |
| D961117.14 | Loss of thermal stabilization | sgp5mwravgB6.c1 |
| D961117.19 | Loss of thermal stabilization | sgp5mwravgB6.c1 |
| 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 |
|---|---|---|---|
| 08/02/2002 | 1652 | 08/02/2002 | 2144 |
| Subject: | SGP/MWR/B6 - Instrument replaced, calibration incorrect |
| DataStreams: | sgp5mwravgB6.c1, sgpmwrlosB6.a0, sgpmwrlosB6.a1, sgpmwrlosB6.b1 |
| Description: | MWR serial number 18 was replaced with MWR serial number 04 at 1652 on 2 Aug 2002. Between this time and 2214, when a sufficient number of new tip curves were acquired to update the calibration, the old calibration (for serial number 18) was used. During this period the data are incorrect. |
| Measurements: | sgpmwrlosB6.a1:
sgpmwrlosB6.b1:
sgpmwrlosB6.a0:
sgp5mwravgB6.c1:
|
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 08/02/2002 | 2144 | 08/04/2002 | 0213 |
| Subject: | SGP/MWR/B6 - Instrument replaced, calibration updating |
| DataStreams: | sgp5mwravgB6.c1, sgpmwrlosB6.a0, sgpmwrlosB6.a1, sgpmwrlosB6.b1 |
| Description: | Following replacement of the MWR at B6, an automatically and continuously upated median calibration value was used based on data acquired during this period. After this period, sufficient tip curves were available to automatically and continuously determine and account for the temperature dependence of the calibration. |
| Measurements: | sgpmwrlosB6.a1:
sgpmwrlosB6.b1:
sgpmwrlosB6.a0:
sgp5mwravgB6.c1:
|
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 08/20/1995 | 0000 | 08/20/1995 | 2359 |
| 08/29/1995 | 0000 | 08/29/1995 | 2359 |
| Subject: | SGP/MWR/B6 - Loss of thermal stabilization |
| DataStreams: | sgp5mwravgB6.c1, sgpmwrlosB6.a0, sgpmwrlosB6.a1 |
| 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: | sgpmwrlosB6.a1:
sgpmwrlosB6.a0:
sgp5mwravgB6.c1:
|
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 04/16/2002 | 2200 | 06/24/2005 | 1942 |
| Subject: | SGP/MWR/B6 - Reprocess: Revised Retrieval Coefficients |
| DataStreams: | sgp5mwravgB6.c1, sgpmwrlosB6.a1, sgpmwrlosB6.b1, sgpmwrtipB6.a1, sgpqmemwrcolB6.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 at SGP.B6 20020416.2200. The MONORTM-based retrieval coefficients became active at SGP.B6 20050624.1942. Note: a reprocessing effort is already underway to apply the Rosenkranz-based retrieval coefficients to all MWR prior to April 2002. An additional reprocessing task will be undertaken to apply the MONORTM retrieval to all MWR data when the first is completed. Read reprocessing comments in the netcdf file header carefully to ensure you are aware which retrieval is in play. |
| Measurements: | sgpmwrlosB6.a1:
sgpmwrlosB6.b1:
sgpmwrtipB6.a1:
sgp5mwravgB6.c1:
sgpqmemwrcolB6.c1:
|
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 04/17/1995 | 0005 | 10/12/1995 | 2359 |
| Subject: | SGP/5MWRAVG/B6 - Valid LWP > 1 mm excluded from 5 min avgs |
| DataStreams: | sgp5mwravgB6.c1 |
| Description: | Note: These data have not been and will not be reprocessed. The MWRAVG VAP has been retired. The limit of maximum valid liquid water path was set at 1 mm. Although this limit was selected 'conservatively' so as to definitely flag precipitation-contaminated data in the 20-second (sgpmwrlos) files, the effect has been to exclude valid liquid water paths greater than 1 mm from the 5-minute averages (sgp5mwravg). The following actions are recommended: 1) the maximum limits for precipitable water vapor (PWV) and liquid water path (LWP) be removed and, 2) the averaging algorithm instead exclude data on the basis of the brightness temperature flags. These flags are set below a minimum of 2.75 K (cosmic background) and above a maximum of 100 K (precipitation). |
| Measurements: | sgp5mwravgB6.c1:
|
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 04/17/1995 | 0005 | 04/04/1996 | 2359 |
| Subject: | SGP/MWR/B6 - Reprocess: Error in MWR calibration |
| DataStreams: | sgp5mwravgB6.c1 |
| Description: | The effect of this error is small. At most, it results in a bias of
about -0.015 cm in precipitable water vapor and -0.015 mm in liquid
water path during clear sky conditions. The error is largest when the
brightness temperatures are small (i.e. clear skies and low PWV).
The error results from failing to correctly account for the effect of
the Teflon window covering the radiometer mirror. Although the
contribution of the window is subtracted when the tip curve data are
reduced to determine the true zenith brightness temperature, it is not
added back in when the zenith brightness temperature is used to
calibrate the noise diode. This would still not be a problem if the
contribution of the window where not subtracted (again) during zenith
line-of-sight (LOS) operations. But it is and the net effect is to
subtract the contribution of the window twice.
The calibrations ('Noise Injection Temperatures') are off by a factor
of 1.00164 and 1.00217 for the 23.8 and 31.4 GHz frequencies,
respectively.
The magnitude of the error is equal to the emissivity of the window
multiplied by the difference between the brightness temperature and the
temperature of the window. The latter is taken to be equal to the
temperature of the internal blackbody target (which is about 10 deg C
above ambient.) The emissivity of the window is 0.00164 at 23.8 GHz
and 0.00217 at 31.4 GHz. For a reference temperature of 292.6 K and
brightness temperatures of 32.3 and 20.8 K at 23.8 and 31.4 GHz
respectively, this amounts to errors of -0.43 and -0.59 K at the
respective frequencies. The average PWV for this date (5 April 1995)
was 1.4 cm.
At higher levels of PWV and for cloudy conditions, the brightness
temperatures are higher and so the error is smaller.
I will adjust the calibrations of all SGP radiometers to account
for this problem by the end of tomorrow (4 April 1996). |
| Measurements: | sgp5mwravgB6.c1:
|
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 04/17/1995 | 0005 | 04/04/1996 | 2359 |
| Subject: | SGP/MWR/B6 - Reprocess: MWR Tuning Functions |
| DataStreams: | sgp5mwravgB6.c1 |
| Description: | The 'tuning functions' used to adjust the equivalent brightness
temperatures (TBs) measured by the ARM microwave radiometers (MWRs) are
now believed to be both incorrect and unnecessary. They should no longer
be used and the data (going back to 1992) that incorporated them should
be reprocessed. By eliminating these tuning functions the radiometer
retrievals would be independent of the soundings.
BACKGROUND
A recent comparison by Barry Lesht (ANL) of the precipitable water
vapor (PWV) retrieved from the MWR-measured brightness temperatures
against PWV derived by integrating along the trajectory of radiosonde
ascents has revealed that the MWR values are about 90% of those derived
from the soundings. This is directly attributable to the slope of the
tuning function for the vapor-sensing channel (23.8 GHz) of 0.915 which
is applied to the measured brightness temperatures prior to retrieval
of PWV.
The rationale behind the use of the tuning functions is that the
radiation model (Liebe 87), on which the retrieval is based, is
imperfect whereas the radiosondes represent 'ground truth.' Thus the
observed brightness temperatures must be adjusted to match those
calculated with the model using co-located soundings so that the
retrieval yields precipitable vapor amounts that agree with the
soundings.
Tuning functions were developed for the present ARM MWRs using
co-located soundings launched between October 1992 and December 1993.
These were adjusted slightly in January 1995 to account for the effects
of the 1-point calibration check performed prior to launch (see DQR
P950110.1):
23.8 GHz: TB_model = 0.789 + 0.915 TB_measured (R2 = 0.998)
31.4 GHz: TB_model = 1.142 + 0.910 TB_measured (R2 = 0.984)
However, repeating this exercise for soundings launched during 1994 and
1995 (excepting those that were mis-calibrated by the manufacturer; see
D960229.1) it now appears that the model-calculated
brightness temperatures are in much closer agreement with the measured
values and that the tuning functions account more for variations in the
radiosonde calibration than for any deficiencies in the radiation
model.
Consequently, it appears that the present tuning functions are
incorrect and bias the retrieved PWV low by 10%. In addition, given
the present agreement between measured and modeled brightness
temperatures, the tuning functions are also unnecessary.
METHODOLOGY
Brightness temperatures measured with microwave radiometer (MWR) serial
number 10, which was deployed at the central facility in December 1993,
have been compared against calculations using measurements from the
co-located Balloon-Borne Sounding System (BBSS). The results are
summarized in two tables. In each table, the calibration dates of the
sondes and MWR are listed as well as the time period and number of
samples included in each regression. Each MWR sample is a 40-minute
average, centered on the time of the sonde launch, of the microwave
brightness temperature. In order to include only clear sky conditions,
samples for which the standard deviation of the liquid-sensing (31.4
GHz) channel exceeded 0.3 K were eliminated. To assure that the water
vapor was reasonably homogeneous horizontally, samples for which the
standard deviation in the vapor-sensing (23.8 GHz) channel exceeded 0.4
K (in 1995) or 0.5 K (in 1994) were eliminated. The 1994 threshold is
larger in order to increase the number of samples and reduce the
standard error in the results.
The microwave radiometer measurements used in this comparison have been
reprocessed to account for calibration changes and other problems (see
P940813.1)
TB vs PWV
The first table is a comparison of microwave brightness temperature
(TB_mwr) regressed against the precipitable water vapor (PWV) computed
by integrating along the trajectory of the radiosonde ascent. The
sondes launched during May - December 1994 are compared against two
sets of MWR data; the first uses the May 1994 calibration, and the
second uses the calibration of July 1994. A comparison is also made of
TB_model vs PWV ('Liebe87') for reference.
The intercepts indicate the contribution due to molecular oxygen (i.e.
the tail of the 60 GHz line) which is affected by temperature and
pressure. Note that the 'Liebe87' intercepts vary seasonally as the
temperature changes. Note also that the effect of MWR calibration
changes is most evident in the intercept: offsets of 1-2 K are
observed. Because the MWR calibration values represent the slope of
the radiometer equation (see Appendix), the magnitude of the offset is
largest at 0 K (i.e. the intercept) and declines to zero at ambient
temperature (~290 K).
The slope of the regression is essentially unaffected by the MWR
calibration. Variations in the slope of the regression correlate with
sonde calibration date. The sondes calibrated in May 1994 or later
appear to yield much closer agreement between the measured brightness
temperatures and those calculated with the Liebe 87 model than those
calibrated in January 1994 or earlier, with which the present tuning
functions were developed.
TABLE 1. Microwave brightness temperature vs. precipitable water vapor
Relationship: TB_mwr (K) = intercept (K) + slope (K/cm) * PW_sonde (cm)
Standard Error of the intercepts and slopes are given in parentheses.
Date of Date of Period ------ 23.8 GHz ----- ----- 31.4 GHz -----
Sonde Cal MWR tip Covered N intercept slope intercept slope
1991-93 92-93 Oct92-Dec93 91 6.7 14.7 8.1 5.3
1992,93 Dec 93 Jan-Feb 94 85 6.9(0.19) 15.8(0.26) 8.8(0.13) 5.6(0.17)
1992,93 Liebe87 Jan-Feb 94 85 6.5(0.02) 13.8(0.03) 8.9(0.07) 4.5(0.09)
Jun 93 Dec 93 Apr 94 16 10.6(1.11) 14.8(0.55) 10.1(0.51) 5.6(0.25)
Jun 93 Liebe87 Apr 94 16 6.9(0.05) 13.6(0.02) 8.1(0.09) 5.0(0.05)
1992,93 May 94 May-Jun 94 48 7.0(1.03) 14.9(0.45) 7.8(0.41) 5.7(0.17)
1992,93 Jul 94 May-Jun 94 48 5.1(1.03) 14.9(0.44) 6.6(0.39) 5.7(0.17)
1992,93 Liebe87 May-Jun 94 48 7.1(0.11) 13.5(0.05) 8.4(0.16) 4.9(0.07)
Jan 94 Dec 93 Feb-May 94 95 7.6(0.27) 14.3(0.14) 8.5(0.15) 5.5(0.08)
Jan 94 Liebe87 Feb-May 94 95 6.9(0.05) 13.6(0.02) 8.1(0.09) 5.0(0.05)
May 94 May 94 Jun-Aug 94 78 12.3(1.04) 13.0(0.34) 11.0(0.39) 4.8(0.13)
May 94 Jul 94 Jun-Aug 94 78 10.3(1.04) 13.1(0.34) 9.8(0.39) 4.8(0.13)
May 94 Liebe87 Jun-Aug 94 78 7.8(0.22) 13.3(0.07) 8.6(0.29) 4.9(0.10)
Jun 94 May 94 Jul-Dec 94 57 8.3(0.37) 13.6(0.21) 8.8(0.19) 5.2(0.11)
Jun 94 Jul 94 Jul-Dec 94 57 6.4(0.37) 13.6(0.21) 7.7(0.18) 5.2(0.10)
Jun 94 Liebe87 Jul-Dec 94 57 6.9(0.08) 13.5(0.04) 8.3(0.10) 4.9(0.06)
Aug 94 May 94 Sep-Dec 94 90 7.4(0.15) 13.5(0.09) 8.8(0.11) 5.1(0.07)
Aug 94 Jul 94 Sep-Dec 94 90 5.5(0.14) 13.6(0.09) 7.8(0.12) 5.0(0.07)
Aug 94 Liebe87 Sep-Dec 94 90 6.8(0.05) 13.6(0.03) 8.6(0.09) 4.9(0.06) |
| Measurements: | sgp5mwravgB6.c1:
|
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 07/01/1996 | 2015 | 07/23/1996 | 0000 |
| Subject: | Loss of thermal stabilization |
| DataStreams: | sgp5mwravgB6.c1 |
| Description: | DQR No: Platform: sgpmwrlos, sgp5mwravg,
sgpqmemwrlos
Subject: Loss of thermal stabilization
Date Submitted:
Submitted By: JIM LILJEGREN _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:
What level data: a0,a1,c1
What location was the data collected at: SGP B1 (Hillsboro, KS)
SGP B4 (Vici, OK)
SGP B5 (Morris, OK)
SGP B6 (Purcell, OK)
SGP C1 (Lamont, OK)
Period of time in question (see table below)
Data should be labeled:
___ questionable ___ All data fields affected
_X_ incorrect _X_ Only some data fields affected:
___ wrong calibration
___ others "23tbsky","31tbsky","vap","liq"
Discussion of Problem:
I pointed out in a previous DQR (P960405.1) that during August of 1994
and 1995 the microwave radiometers would lose thermal stabilization on
very hot, sunny days when the temperature in the radiometer enclosure
rose above the set point for thermal stabilization (~50 deg C). Although
I had planned to travel to the SGP prior to August 1996 to adjust the
set points upward to prevent this problem from occuring this year, the
temperatures in July 1996 were hotter than in previous years and the
loss of stabilization problem occurred before I could make the needed
adjustment.
The purpose of this note is the identify the time periods for which
this problem occurred. More specific information about the problem,
including how the problem is detected and its effect on the reported
values of integrated water vapor and integrated cloud liquid water are
provided in the earlier DQR.
It is useful to repeat here that when the thermal stabilization is
lost, the reported 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. THESE ANOMALOUS VALUES HAVE BEEN INCLUDED IN THE 5-MINUTE
AVERAGES.
LOCATION BEGINNING DATE AND TIME ENDING DATE AND TIME
C1 (Central Facility)
1 July 96 18:25 GMT 2 July 96 02:00 GMT
2 16:45 3 02:30
3 17:40 4 02:15
4 15:50 4 17:10
5 17:00 6 03:30
6 16:00 7 03:00
7 20:20 8 01:30
18 20:00 18 23:45
19 18:30 20 01:20
20 19:45 21 02:25
21 17:00 22 02:20
22 19:30 23 23:00
B1 (Hillsboro, KS)
1 July 96 20:30 2 July 96 01:15
2 17:00 3 02:00
17 20:30 18 00:15
18 19:25 19 02:00
19 19:00 20 02:30
20 18:35 21 00:30
21 20:20 22 01:40
28 20:55 28 00:15
B4 (Vici, OK) 2 July 96 19:25 2 July 96 23:15
3 19:35 3 21:15
4 20:40 5 00:30
5 19:15 6 02:00
6 19:00 6 22:40
7 20:45 8 00:30
21 19:45 22 02:00
B5 (Morris, OK)
1 July 96 18:35 2 July 96 00:45
2 17:20 3 01:15
3 17:25 4 02:00
5 20:20 6 01:45
6 16:45 7 02:30
7 18:10 8 01:00
19 20:00 20 00:20
20 19:30 21 00:55
21 18:15 22 01:30
22 19:30 23 01:15
23 22:00 24 00:15
B6 (Purcell, OK)
1 July 96 20:15 2 July 96 00:10
2 18:40 3 00:05
3 20:40 4 00:35
4 20:15 5 00:10
5 19:45 6 01:15
6 19:10 7 01:40
19 21:30 19 23:00
20 20:15 21 00:05
21 21:45 22 01:00
22 21:45 23 00:00
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.)
Flag with this comment. |
| Measurements: | sgp5mwravgB6.c1:
|
| Start Date | Start Time | End Date | End Time |
|---|---|---|---|
| 07/01/1996 | 2015 | 07/23/1996 | 0000 |
| Subject: | Loss of thermal stabilization |
| DataStreams: | sgp5mwravgB6.c1 |
| Description: | DQR No: Platform: sgpmwrlos, sgp5mwravg,
sgpqmemwrlos
Subject: Loss of thermal stabilization
Date Submitted:
Submitted By: JIM LILJEGREN _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:
What level data: a0,a1,c1
What location was the data collected at: SGP B1 (Hillsboro, KS)
SGP B4 (Vici, OK)
SGP B5 (Morris, OK)
SGP B6 (Purcell, OK)
SGP C1 (Lamont, OK)
Period of time in question (see table below)
Data should be labeled:
___ questionable ___ All data fields affected
_X_ incorrect _X_ Only some data fields affected:
___ wrong calibration
___ others '23tbsky','31tbsky','vap','liq'
Discussion of Problem:
I pointed out in a previous DQR (D960405.1) that during August of 1994
and 1995 the microwave radiometers would lose thermal stabilization on
very hot, sunny days when the temperature in the radiometer enclosure
rose above the set point for thermal stabilization (~50 deg C). Although
I had planned to travel to the SGP prior to August 1996 to adjust the
set points upward to prevent this problem from occuring this year, the
temperatures in July 1996 were hotter than in previous years and the
loss of stabilization problem occurred before I could make the needed
adjustment.
The purpose of this note is the identify the time periods for which
this problem occurred. More specific information about the problem,
including how the problem is detected and its effect on the reported
values of integrated water vapor and integrated cloud liquid water are
provided in the earlier DQR.
It is useful to repeat here that when the thermal stabilization is
lost, the reported 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. THESE ANOMALOUS VALUES HAVE BEEN INCLUDED IN THE 5-MINUTE
AVERAGES.
LOCATION BEGINNING DATE AND TIME ENDING DATE AND TIME
C1 (Central Facility)
1 July 96 18:25 GMT 2 July 96 02:00 GMT
2 16:45 3 02:30
3 17:40 4 02:15
4 15:50 4 17:10
5 17:00 6 03:30
6 16:00 7 03:00
7 20:20 8 01:30
18 20:00 18 23:45
19 18:30 20 01:20
20 19:45 21 02:25
21 17:00 22 02:20
22 19:30 23 23:00
B1 (Hillsboro, KS)
1 July 96 20:30 2 July 96 01:15
2 17:00 3 02:00
17 20:30 18 00:15
18 19:25 19 02:00
19 19:00 20 02:30
20 18:35 21 00:30
21 20:20 22 01:40
28 20:55 28 00:15
B4 (Vici, OK) 2 July 96 19:25 2 July 96 23:15
3 19:35 3 21:15
4 20:40 5 00:30
5 19:15 6 02:00
6 19:00 6 22:40
7 20:45 8 00:30
21 19:45 22 02:00
B5 (Morris, OK)
1 July 96 18:35 2 July 96 00:45
2 17:20 3 01:15
3 17:25 4 02:00
5 20:20 6 01:45
6 16:45 7 02:30
7 18:10 8 01:00
19 20:00 20 00:20
20 19:30 21 00:55
21 18:15 22 01:30
22 19:30 23 01:15
23 22:00 24 00:15
B6 (Purcell, OK)
1 July 96 20:15 2 July 96 00:10
2 18:40 3 00:05
3 20:40 4 00:35
4 20:15 5 00:10
5 19:45 6 01:15
6 19:10 7 01:40
19 21:30 19 23:00
20 20:15 21 00:05
21 21:45 22 01:00
22 21:45 23 00:00
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.)
Flag with this comment. |
| Measurements: | sgp5mwravgB6.c1:
|
| 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: | sgpmwrlosB1.a1:
sgpmwrlosB1.a0:
sgp1mwravgC1.c1:
sgpmwrlosC1.a1:
sgpmwrlosC1.b1:
sgp5mwravgB5.c1:
sgp5mwravgB1.c1:
sgp5mwravgB4.c1:
sgpmwrlosB6.a1:
sgp5mwravgC1.c1:
sgpmwrlosB6.a0:
sgpmwrlosB4.a0:
sgpmwrlosB5.a0:
sgpmwrlosB4.a1:
sgpmwrlosB5.a1:
sgp5mwravgB6.c1:
|