SGP/MWR/C1 - IRT removed

There were no IRT data during this period because MWR #10, upon
which the IRT is mounted, was returned to the vendor for upgrades and
replaced with spare MWR #33 which does not have the mounting hardware
or the electronics to accept the IRT.

• Sky infrared temperature(sky_ir_temp)

SGP/MWR/C1 - calibration checks

The MWR calibration was checked by a cryogenic (liquid nitrogen) 
blackbody target or (in the case of the Sept 2001 time period)
by pointing the mirror at an internal blackbody target.  The 
brightness temperatures and vap and liq retrievals are not
representative of the sky/atmosphere.

• Mean 31.4 GHz sky brightness temperature(tbsky31)
• 23.8 GHz sky brightness temperature(tbsky23)
• Total water vapor along LOS path(vap)
• Water, liquid, total along line-of-sight path(liq)

SGP/MWR/C1 - Time drift

On 9/18/00, I found that the time on the MWR laptop was 1m 21s slow. The Dimension4 
utility had last synchronized the time on 5/5/00. Found that the network DNS settings had been 
disabled. Added the DNS entry for ntp host CF10. Dimension4 synchronized the clock by 
adding 80.91s. The time had drifted at a rate of -0.59s/day.

• bbn23
• bb23
• tkxc
• wet_window
• tnd_nom23
• tnd_nom31
• sky23
• Mean 31.4 GHz sky brightness temperature(tbsky31)
• tnd23
• 23.8 GHz sky brightness temperature(tbsky23)
• tc31
• base_time
• Sky infrared temperature(sky_ir_temp)
• Water, liquid, total along line-of-sight path(liq)
• tkbb
• tnd31
• sky31
• tc23
• tknd
• time_offset
• bb31
• bbn31
• Total water vapor along LOS path(vap)
• tkair

SGP/MWR/C1 - IRT failure

The IRT was damaged by internal moisture causing sky temperature
measurements that are negatively biased compared to those from
the AERI. IRT#0517 was returned to the manufacturer for repair
and was replaced with spare IRT#1254.

• Sky infrared temperature(sky_ir_temp)

SGP/MWR/C1 - Reprocess: IRT insufficiently insulated

The downwelling IRT was insufficiently insulated to maintain an internal 
reference temperature above 0 degrees C. Measurements of sky temperature were 
over-estimated when instrument was below freezing.

Data will be reprocessed, but users can correct data using the following correction 
factor:

If T_reference < -5°C, then

  IRT_corrected = (IRT_original - 32.993K)/0.87238

where T_reference can be estimated with the ambient temperature (e.g.
tkair)

• Sky infrared temperature(sky_ir_temp)

SGP/MWR/B4/C1 - LOS cycle skipping

When MWR software version 4.12 was installed at the SGP, it was observed 
that the MWRs at CF and BF4 skip line-of-sight (LOS) observing cycles. In LOS mode, the 
software begins an observing cycle at 0, 20, and 40 seconds after the minute to provide 3 
LOS cycles per minute. If a cycle is delayed so that it takes more than 20 seconds to 
complete, then the next start time is missed, the cycle is skipped, and the data that would 
have been acquired are lost.  

It was demonstrated that the interaction with the IRT at CF slowed the MWR observing cycle 
noticeably and contributed significantly to the LOS cycle skipping. The IRT was removed 
from the MWR on 5 November 2002 and the LOS cycle skipping at the CF was resolved.  The 
IRT data are now available in a new separate datastream: sgpirtC1.a1 (and soon 
sgpirt2sC1.a1).

The BF4 cycle skipping may have resulted from a combination of an additional air 
temperature sensor on this instrument and the use of a fiber optic cable.  However, the cycle 
skipping on this instrument appears to have abated without modifications to the instrument 
configuration.

• bbn23
• bb23
• tkxc
• wet_window
• tnd_nom23
• sky23
• tnd_nom31
• Mean 31.4 GHz sky brightness temperature(tbsky31)
• tnd23
• tc31
• 23.8 GHz sky brightness temperature(tbsky23)
• Sky infrared temperature(sky_ir_temp)
• Water, liquid, total along line-of-sight path(liq)
• tkbb
• tnd31
• sky31
• tc23
• tknd
• time_offset
• bb31
• bbn31
• Total water vapor along LOS path(vap)
• tkair

SGP/MWR/C1 - Intermittent Negative Sky Brightness Temperatures

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.

• Mean 31.4 GHz sky brightness temperature(tbsky31)
• 23.8 GHz sky brightness temperature(tbsky23)
• Total water vapor along LOS path(vap)
• Water, liquid, total along line-of-sight path(liq)

SGP/MWR/C1 - Incorrect min and max values

The values of valid_min and valid_max applied to fields tkxc and tknd were incorrect. They 
should be 303 and 333, respectively.

• tknd
• tkxc

SGP/MWR/C1 - no air temperature signal

When the new blower was upgraded by Radiometrics and reinstalled on the MWR, the air 
temperature sensor failed to properly report. It was determined that the wires carrying the 
signal to the analog board did not conform to the standard expected by the upgraded blower. 
The problem was corrected by changing the wiring.

• tkair

SGP/MWR/C1 - Wet window flag "on" more frequently than expected

The wet window flag was set "on" more frequently than expected during the time periods 
specified.  This indicates the heater has been running more than necessary.  In most 
instances the moisture sensitivity was adjusted at the end of these periods.

• wet_window
• Mean 31.4 GHz sky brightness temperature(tbsky31)
• 23.8 GHz sky brightness temperature(tbsky23)
• Total water vapor along LOS path(vap)
• Water, liquid, total along line-of-sight path(liq)

SGP/MWR/C1 - Instrument problem

The MWR mixer temperature, blackbody temperature, and moisture flag are incorrect. This 
began when the instrument was returned to service after the analog board was temporarily 
removed to check the presence and absence of certain resistors. The board must have been 
accidently damaged during this process.

• tkbb
• tnd31
• tc23
• tknd
• tkxc
• wet_window
• tnd_nom23
• tnd_nom31
• tnd23
• tc31
• tkair

SGP/MWR/C1 - thermal instability

The analog board was replaced with a spare (D041001.3) with a reference temperature that 
was set too low (306 K) so that during periods of high ambient temperature, the instrument 
became thermally unstable. The problem was corrected when the temperature setting was 
increased (to 311 K).

• Mean 31.4 GHz sky brightness temperature(tbsky31)
• 23.8 GHz sky brightness temperature(tbsky23)
• Total water vapor along LOS path(vap)
• Water, liquid, total along line-of-sight path(liq)

SGP/MWR/C1 - Reprocess: wrong retrievals

When the computer and core configuration were upgraded, retrieval coefficients for BF1 
were accidently included in the configuration file.
The correct coefficients for CF1 were applied when the configuration file was updated.

• Total water vapor along LOS path(vap)
• Water, liquid, total along line-of-sight path(liq)

SGP/MWR/C1 - spare instrument

The spare MWR, S.N. 04, was installed while the production instrument, S.N. 10, was 
returned to the manufacturer for upgrades.

• bbn23
• tkxc
• wet_window
• East longitude(lon)
• tnd_nom31
• tc31
• 23.8 GHz sky brightness temperature(tbsky23)
• Water, liquid, total along line-of-sight path(liq)
• tkbb
• North latitude(lat)
• sky31
• tc23
• time_offset
• bb31
• Total water vapor along LOS path(vap)
• bbn31
• tkair
• bb23
• tnd_nom23
• sky23
• Mean 31.4 GHz sky brightness temperature(tbsky31)
• tnd23
• base_time
• Sky infrared temperature(sky_ir_temp)
• tnd31
• tknd
• Altitude above mean sea level(alt)

SGP/MWR/C1 - REPROCESS - Revised Retrieval Coefficients

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.

• Total water vapor along LOS path(vap)
• Water, liquid, total along line-of-sight path(liq)

SGP/MWR/C1 - Instrument noise problem

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.

• bbn23
• bb23
• tkxc
• wet_window
• tnd_nom23
• tnd_nom31
• sky23
• Mean 31.4 GHz sky brightness temperature(tbsky31)
• tnd23
• tc31
• 23.8 GHz sky brightness temperature(tbsky23)
• Sky infrared temperature(sky_ir_temp)
• Water, liquid, total along line-of-sight path(liq)
• tkbb
• tnd31
• sky31
• tc23
• tknd
• bb31
• Total water vapor along LOS path(vap)
• bbn31
• tkair

SGP/MWR/C1 - New software version (4.15) installed

A problem began with the installation of MWR.EXE version 4.12 in July 2002. The software 
had been upgraded from a "DOS" to a "Windows"-compiled program to address an earlier 
problem.  The software upgrade corrected the earlier problem but introduced a new one that 
caused line-of-sight observing cycles to be skipped, a 15% reduction in the number of tip 
curves, and saturation of CPU usage. Software versions 4.13 and 4.14 also produced these 
problems.

The new MWR software, version 4.15, was installed on 08/04/2005. As a consequence of this 
upgrade, the tip curve frequency increased. The tip cycle time decreased from ~60s to 
~50s.

• bbn23
• bb23
• tkxc
• tnd_nom23
• tnd_nom31
• sky23
• Mean 31.4 GHz sky brightness temperature(tbsky31)
• tnd23
• tc31
• 23.8 GHz sky brightness temperature(tbsky23)
• Sky infrared temperature(sky_ir_temp)
• Water, liquid, total along line-of-sight path(liq)
• tkbb
• tnd31
• sky31
• tc23
• tknd
• bb31
• bbn31
• Total water vapor along LOS path(vap)
• tkair

SGP/MWR/C1 - Spikes in ambient temperature readings

There are intermittent spikes in the Tkair temperature (T ~ 400 K). On 7/28 the sensor 
was cleaned and the instrument power cycled following a power outage. Readings came back to 
normal.

• tkair

SGP/MWR/C1/E14 - Freezing rain-Incorrect rain flag

Between 01/12 and 01/15 brightness temperatures show high values (Tb > 100 K) indicative 
of rain, however the wet_window flag is 0 (indicative of no rain). During that time there 
where freezing conditions with ice pellets that were not detected by the sensor. The high 
brightness temperatures may be due to melting ice on the window.

• wet_window

SGP/MWR/C1 - Noisy data

Since 7/14 the MWR is experiencing intermittent periods of increased noise. The cause for 
this is under investigation.

• sky31
• bbn23
• bb23
• sky23
• bb31
• Mean 31.4 GHz sky brightness temperature(tbsky31)
• 23.8 GHz sky brightness temperature(tbsky23)
• Total water vapor along LOS path(vap)
• bbn31
• Water, liquid, total along line-of-sight path(liq)

SGP/MWR/C1 - Reprocessed: Radiometer reinstalled

After the radiometer was reinstalled it had to update the calibration coefficients.

Data reprocessed 20071217.

• tnd31
• tc23
• tnd_nom23
• tnd_nom31
• Mean 31.4 GHz sky brightness temperature(tbsky31)
• tnd23
• 23.8 GHz sky brightness temperature(tbsky23)
• tc31
• Total water vapor along LOS path(vap)
• Water, liquid, total along line-of-sight path(liq)

SGP/MWR/C1 - Missing data

Data are missing and unrecoverable.

• bbn23
• tkxc
• wet_window
• East longitude(lon)
• tnd_nom31
• 23.8 GHz sky brightness temperature(tbsky23)
• tc31
• Water, liquid, total along line-of-sight path(liq)
• tkbb
• North latitude(lat)
• sky31
• tc23
• time_offset
• bb31
• Total water vapor along LOS path(vap)
• bbn31
• tkair
• bb23
• tnd_nom23
• sky23
• Mean 31.4 GHz sky brightness temperature(tbsky31)
• tnd23
• Sky infrared temperature(sky_ir_temp)
• base_time
• tnd31
• tknd
• Altitude above mean sea level(alt)

SGP/MWR/C1 - Increased noise in 31.4 GHz channel

The 31.4 GHz channel has been showing an increased level of noise which results in 
increased noise in the LWP retrievals. The instrument is tipping and all other parameters seem 
to be in the range. The elevate noise started in May, but it seems to have become slightly 
worse after summer. After November the noise level seems to have gone back to normal.

• Mean 31.4 GHz sky brightness temperature(tbsky31)
• Water, liquid, total along line-of-sight path(liq)

SGP/MWR/C1 - IRT bias

Measurements of sky temperature, especially those <250K, were positively biased compared 
with AERI because there was no compensation for the reflectivity of the gold mirror. The 
problem was corrected by changing the IRT emissivity from 1.000 to 0.987.

Use sky temperature measurements less than 230K with caution. Biases as large as 30K have 
been observed when the actual temperature, as measured by AERI, is less than 210 K.

• Sky infrared temperature(sky_ir_temp)

SGP Site Power Outage Due to Winter Storm

On Saturday and Sunday, December 26 and 27th a powerful winter storm (Goliath) brought 
sleet and freezing rain to much of Oklahoma with wind gusts of 45 MPH at times. The result 
was very very slick roads and mass power outages.
 
The SGP central facility lost power at 8:55 PM CDT on Sunday, December 27th.  
The power was restored on 7:56 PM CDT on Wednesday, December 30th
 
Site Emergency procedures were activated and Technicians drained water out of instrument 
reservoirs and other measures as needed, early Monday morning.
 
On Wednesdays as roads and power started was restored to much of the areas east of I-35 , 
Site Technicians performed maintenance on several Extended Facilities.

During this period, data are potentially missing, incorrect, or suspect.  Carefully 
inspect the data before use.

• bbn23
• tkxc
• wet_window
• East longitude(lon)
• tnd_nom31
• 23.8 GHz sky brightness temperature(tbsky23)
• tc31
• Water, liquid, total along line-of-sight path(liq)
• tkbb
• North latitude(lat)
• sky31
• tc23
• time_offset
• bb31
• Total water vapor along LOS path(vap)
• bbn31
• tkair
• bb23
• tnd_nom23
• sky23
• Mean 31.4 GHz sky brightness temperature(tbsky31)
• tnd23
• Sky infrared temperature(sky_ir_temp)
• base_time
• tnd31
• tknd
• Altitude above mean sea level(alt)

SGP/MWR/C1 - Data System Upgrade: Data Missing

The site data system was upgraded.  Data were not collected during this period.

• bbn23
• qc_tkbb
• qc_tknd
• qc_sky31
• tkxc
• wet_window
• East longitude(lon)
• tnd_nom31
• qc_tkair
• tc31
• 23.8 GHz sky brightness temperature(tbsky23)
• Water, liquid, total along line-of-sight path(liq)
• tkbb
• North latitude(lat)
• sky31
• qc_time
• tc23
• time_offset
• qc_tbsky23
• bb31
• qc_bbn23
• bbn31
• qc_bb23
• Total water vapor along LOS path(vap)
• tkair
• qc_vap
• bb23
• qc_sky23
• qc_tkxc
• tnd_nom23
• time
• sky23
• Mean 31.4 GHz sky brightness temperature(tbsky31)
• tnd23
• Sky infrared temperature(sky_ir_temp)
• base_time
• tnd31
• tknd
• qc_tbsky31
• Altitude above mean sea level(alt)
• qc_bbn31
• qc_bb31
• qc_liq

SGP/MWR/C1 - Missing data

Data are missing

• bbn23
• qc_tkbb
• qc_tknd
• qc_sky31
• tkxc
• wet_window
• East longitude(lon)
• tnd_nom31
• qc_tkair
• tc31
• 23.8 GHz sky brightness temperature(tbsky23)
• Water, liquid, total along line-of-sight path(liq)
• tkbb
• North latitude(lat)
• sky31
• qc_time
• tc23
• time_offset
• qc_tbsky23
• bb31
• qc_bbn23
• bbn31
• qc_bb23
• Total water vapor along LOS path(vap)
• tkair
• qc_vap
• bb23
• qc_sky23
• qc_tkxc
• tnd_nom23
• time
• sky23
• Mean 31.4 GHz sky brightness temperature(tbsky31)
• tnd23
• Sky infrared temperature(sky_ir_temp)
• base_time
• tnd31
• tknd
• qc_tbsky31
• Altitude above mean sea level(alt)
• qc_bbn31
• qc_bb31
• qc_liq

SGP/MWR/C1 - Loss of thermal stabilization

As described in DQR D960405.1 during the month of August in 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 degC). 
The temperatures in July 1996 were hotter than in previous years and the loss of 
stabilization problem occurred before the instrument mentor could make the needed adjustment.

The purpose of this DQR is to 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 DQR D960405.1.

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.

• Mean 31.4 GHz sky brightness temperature(tbsky31)
• 23.8 GHz sky brightness temperature(tbsky23)
• Total water vapor along LOS path(vap)
• Water, liquid, total along line-of-sight path(liq)

SGP/MWR/C1 - Missing data

Data are missing

• bbn23
• qc_tkbb
• qc_tknd
• qc_sky31
• tkxc
• wet_window
• East longitude(lon)
• tnd_nom31
• qc_tkair
• tc31
• 23.8 GHz sky brightness temperature(tbsky23)
• Water, liquid, total along line-of-sight path(liq)
• tkbb
• North latitude(lat)
• sky31
• qc_time
• tc23
• time_offset
• qc_tbsky23
• bb31
• qc_bbn23
• qc_bb23
• bbn31
• Total water vapor along LOS path(vap)
• tkair
• qc_vap
• bb23
• qc_sky23
• qc_tkxc
• tnd_nom23
• time
• sky23
• Mean 31.4 GHz sky brightness temperature(tbsky31)
• tnd23
• Sky infrared temperature(sky_ir_temp)
• base_time
• tnd31
• tknd
• qc_tbsky31
• Altitude above mean sea level(alt)
• qc_bbn31
• qc_bb31
• qc_liq

SGP/MWR/C1 - IRT rain lid removal

The IR thermometer (or IRT) was deployed at the SGP central facility in
January 1994 with an automatic mechanism which closed a protective lid
over the zenith-viewing lens when a moisture detector indicated
condensation or precipitation.

Since that time the 120 VAC-to-12 VAC transformer in the lid mechanism
has failed 5 times with an average downtime of two weeks.  In addition,
the collar by which the (normally open) lid is attached to the lens
barrel of the IRT has made it difficult for site operations personnel
to observe the condition of the IRT lens.  As a result, dirt and
insects have been able to accumulate on the lens.  This has resulted in
long periods of invalid data.

To alleviate these problems the lid mechanism was removed from service
on 16 August at my recommendation.

It is anticipated that condensation and precipitation will result in
invalid data.  However, these events should be readily detectable
because the observed IR temperature will closely match the ambient
temperature (e.g. the temperature of the moisture on the lens) which is
usually much greater than the sky or cloud base temperature normally
measured.  I believe that this will not result in a large increase in
invalid data because these data would have been invalid anyway when the
lid was closed.  (This situation is now the same as for the other 
radiometers at the site.)

In addition, removing the attaching collar from the lens barrel will
prevent insects from nesting in it, and will permit site operations
personnel easy access to the lens so that they may more easily maintain
it in a clean condition.

A summary of the quality of the IR thermometer data in general,
including notes on the performance of the protective lid, follows:

JANUARY 1994
 19-JAN:  Operational.  No IR data collected.

FEBRUARY 1994
  2-FEB:  Failure of lid reported.  Transformer burned out.
 15-FEB:  IRT returned to service.    
 24-FEB:  Valid data begin.

MARCH 1994
  3-MAR:  Failure of lid reported. Transformer burned out.
  8-MAR:  IRT returned to service.
  8-MAR:  Cable problems reported.
 17-MAR:  Cable problems resolved.  IRT returned to service.
 17-27-MAR:  Comparison with AERI indicates IRT 1-10 deg C higher; 
          increasing error with decreasing temperatures.  Probably  
          due to dirt/debris on lens.  Also, IRT calibration not valid
          below -50 deg C (223 K).
 21-MAR:  Problems with O-ring on lid sticking reported/repaired.

APRIL 1994
 Data values below -50 deg C (223 K) not valid - below range of 
 calibration.  Otherwise data within 2-3 degrees of AERI.
 24-APR: Large (10-20 Deg C) offset between IRT and AERI develops.

MAY 1994
  7-MAY: Mentor visits site, observes spider's nest and dead insects
         inside collar attaching lid to lens barrel in optical path of
         instrument. Probably the source of the offset between IRT and
         AERI during late and April.
  9-MAY: Insects removed, lens cleaned by site operations personnel.
         Agreement between IRT and AERI within 1 deg C.
 23-MAY: Failure of lid reported.  Transformer burned out.

JUNE 1994
 22-JUN: Rebuilt/redesigned lid mechanism put in service; data collection
         computer fails same day.

JULY 1994
 11-JUL: Computer returned to service.  
         Agreement between IRT and AERI within 1 deg C.
 22-JUL: Failure of lid reported.  Transformer burned out.

AUGUST 1994
  3-AUG: IRT returned to service.
 12-AUG: Failure of lid reported.  Transformer burned out.
 16-AUG: Lid mechanism abandoned.

• Sky infrared temperature(sky_ir_temp)

SGP/MWR/C1 - Data dropouts due to serial comm problems

Conflicts between the drop shipper program and the MWR operation program resulted in 
serial communication problems which ultimately manifested as spikes and dropouts in the data.

• bbn23
• bb23
• tkxc
• wet_window
• tnd_nom23
• tnd_nom31
• sky23
• Mean 31.4 GHz sky brightness temperature(tbsky31)
• tnd23
• 23.8 GHz sky brightness temperature(tbsky23)
• tc31
• base_time
• Sky infrared temperature(sky_ir_temp)
• Water, liquid, total along line-of-sight path(liq)
• tkbb
• tnd31
• sky31
• tc23
• tknd
• time_offset
• bb31
• bbn31
• Total water vapor along LOS path(vap)
• tkair

SGP/MWR/C1 - IR thermometer calibration check

Mentor used an Everest model 1000 ambient temperature target 
(emis.=0.98) to check the calibration of the Heiman IR pyrometer
(IR thermometer).  Data collected during this period will be
anomalous due to the modifications of the instrument settings
required to facilitate the calibration.

The emissivity of the instrument was changed to match the target;
units were changed to deg C (from K) to match the target LCD units;
integration time on the instrument was changed to 3 seconds (from 1
second).

Centered the target on the instrument lens and allowed it to rest
on the lens barrel so that it filled the field of view of the
instrument. Both the instrument LCD and target LCD indicated 16.7
deg C.

Noted that although the lens appeared clean, there was some liquid
water around the edge which formed a meniscus with the inside of
the lens barrel. Wiped this away with a clean, lint-free cotton
cloth.

Replaced the target on the lens barrel; both instrument and target
then indicated 17.1 deg C.

Reset the instrument emissivity (=1.0), the units (kelvins) and
the integration time (=1 sec).

The IRT was deployed in December 1993.  Its calibration appears to
have been stable since deployment.  Liquid water around the edge of
the lens appears to be out of the field of view and does not appear
to affect the data.

• Sky infrared temperature(sky_ir_temp)

SGP/MWR/C1 - Loss of thermal stabilization

Periodically during August and September 1995 the microwave radiometer generated error 
messages in the Site Operations Log. This error indicates that the temperature of the 
microwave hardware (specifically, the cross-coupler or "xc") exceeded its controlled 
temperature (47-52 degC) 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 degC 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 degC (328 K) would prevent a 
re-occurrence 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.

• Mean 31.4 GHz sky brightness temperature(tbsky31)
• 23.8 GHz sky brightness temperature(tbsky23)
• Total water vapor along LOS path(vap)
• Water, liquid, total along line-of-sight path(liq)

SGP/MWR/C1 - Radio Frequency Interference during IOP

During the specified times a strong, continuous signal was 
measured by the 31.4 GHz of the MWR.  The signal was present
in all 31.4 GHz measurements including the sky measurement,
the internal reference target measurement, and the measurement
of the internal noise injection source from which the
instantaneous instrument gain is computed.

The source of the interference has not yet been identified.

Because the gain is computed using the difference of the
noise injection and target measurements, and because the
sky brightness temperature is computed relative to the
internal target temperature, the data appear anomalous
only for a period of an hour after the interference starts
and ends.  This is due to the low pass filter applied to
the instantaneous gain.  However the data should be
considered invalid or at least questionable during the
entire period for which the interference was present.

• bbn23
• tkxc
• wet_window
• East longitude(lon)
• tnd_nom31
• tc31
• 23.8 GHz sky brightness temperature(tbsky23)
• Water, liquid, total along line-of-sight path(liq)
• tkbb
• North latitude(lat)
• sky31
• tc23
• time_offset
• bb31
• bbn31
• Total water vapor along LOS path(vap)
• tkair
• bb23
• tnd_nom23
• sky23
• Mean 31.4 GHz sky brightness temperature(tbsky31)
• tnd23
• base_time
• Sky infrared temperature(sky_ir_temp)
• tnd31
• tknd
• Altitude above mean sea level(alt)

SGP/MWR/C1 - IRT lens replaced

The lens of the uplooking "IR thermometer" (a 10 micrometer pyrometer)
was replaced on 28 October 1996 at 16:18 GMT.  At the time the sky was
heavily overcast (0.1-0.5 mm liquid water path, IR temperature =
281-285 K) with about 4 cm integrated water vapor.  A comparison was
carried out against the Atmospheric Emitted Radiance Interferometer
(AERI) both prior to and subsequent to the lens change.  The statistics
of the differences (IRT-AERI) are as follows:

         Mean (K)  Std Dev (K)   No.
Before:    0.64      0.24       122
After:     0.35      0.20        89

In addition, the downward step change in the time series plot of the
temperature difference (IRT-AERI) at the time of the lens replacement
is obvious.

This suggests, but is not conclusive evidence, that the primary cause
of the differences between the IRT and AERI reported previously
(PIF no. P960809.2) may have been the weather-worn lens.  However,
as this instrument has not been calibrated since it was deployed in
December 1993, there may also be calibration drift to contend with.

Arrangements are being pursued with NREL to check the calibration of
this instrument.

It is preferable to carry out the IRT vs AERI comparison for clear sky
conditions to be certain that both instruments are observing the same
scene at the moment when they make sky measurements.  However, it is
not possible at this time of the year to carry out a clear sky
comparison because the integrated water vapor is generally less than
2.0 cm which means that the IR temperature is less than 223 K, the
lower limit of the D/A converter on the IRT.

On the positive side, the AERI and the IRT are within 10 m of each
other and have similar fields of view (about 2 degrees) so their
scenes should be comparable for clear or cloudy skies.

• Sky infrared temperature(sky_ir_temp)

SGP/MWR/B1/B4/B5/B6/C1 - Thermal Stabilization Adjustment

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.

• Mean 31.4 GHz sky brightness temperature(tbsky31)
• 23.8 GHz sky brightness temperature(tbsky23)
• Total water vapor along LOS path(vap)
• Water, liquid, total along line-of-sight path(liq)

SGP/MWR/C1 - IRT Calibration check

IRT was out of service for calibration check.  MWR was powered
down on 96/12/03 1937-1949 to remove IRT and on 96/12/12 1848-1920
to re-install IRT.

The following is from the NREL Metrology Laboratory test report of 12/10/97:

Temperature     Nominal Value     Measured Value
-----------     -------------     --------------
  0 C             273.2 K           274.1 K
 10               283.2             283.6
 20               293.2             293.6
 30               303.2             303.2
 40               313.2             313.2

In the range tested, the temperature difference is within the
resolution of the instrument, so the IRT was not adjusted and
the calibration factor was not changed.

• Sky infrared temperature(sky_ir_temp)

SGP/MWR/C1 - IRT Calibration

Comparison of the uplooking IRT with AERI for 5 May 1997 during a time
when the 9-11 micrometer sky temperature was in the range 220-228 K,
according to AERI, the IRT indicated approximately 3 K higher.  This is
outside of the specified uncertainty in the IRT and indicates that the
calibration needs to be revised.

• Sky infrared temperature(sky_ir_temp)

SGP/MWR/C1 - IRT offline

The IRT was removed from the MWR to perform a comparison/calibration check prior to the 
Integrated IOP.

• Sky infrared temperature(sky_ir_temp)

SGP/MWR/C1 - IRT lens replaced

During my recent trip to the SGP I noticed that the IRT was reading
too high (about 250 K for clear sky with less than 2 cm PWV).  The
anti-reflective coating on the lens appeared to have deteriorated
significantly.  Because I observed no change in the measurements
after cleaning the lens, I replaced it with the original lens which
had been saved as a spare.

The measured sky temperature fell to 232 K, which appeared more reasonable.

The next morning I realized that I had forgotten to clean the lens
after replacing it.  After cleaning the IR temperature fell from 219
to 213 K with about 1.2 cm PWV.  This appeared to be in agreement
with Martin Platt's radiometer which measures the same passband
(10 micrometers.)

Upon returning to Ames, I compared the IRT with AERI for April 1998.
It appears that at least as far back as 1 April the IRT data are bad.

• Sky infrared temperature(sky_ir_temp)

SGP/MWR/C1 - Erroneous internal temperature

After the new internal temperature sensor was installed it was discovered
that the scaling resistor was incorrect.  (The 24.9 kohm 0.1% resistor
had accidently been replaced with a 24.0 kohm resistor when the analog
board was repaired by the manufacturer several years ago.)  A resistor
having the correct value was installed 981112.

• tkair

SGP/MWR/B1/B4/B6/C1 - software change

The MWR operating software was changed on 12 October 1998 to provide additional 
functionality as described below. This change affects the format of the raw and ingested data. 
   
NEW FEATURES
1. Faster sampling rate
   
Standard line-of-sight (LOS) observations can now be acquired at 15-second intervals vs. 
20-second intervals previously. (The standard LOS cycle is comprised of one sky sample per 
blackbody sample and gain update.)
   
2. More flexible sampling strategy
   
Multiple sky observations can be acquired during a LOS cycle, up to 1024 per gain update. 
This permits sky samples to be acquired at intervals of 2.67 seconds for improved 
temporal resolution of cloud liquid water variations and better coordination with the millimeter 
cloud radar during IOPs.
   
3. Separation of zenith LOS observations from TIP data
   
When the radiometer is in TIP mode, the zenith LOS observations are now extracted, the PWV 
and LWP computed and reported separately in the output file. This eliminates the periods 
of missing LOS data during calibration checks/updates.
   
4. Automatic self-calibration
   
The software now permits the calibration to be updated at specified intervals or 
continuously. In the first case, LOS mode is automatically changed to TIP mode at user-specified 
intervals or whenever clear sky conditions occur, the tip data reduced, the calibration 
updated ,and the radiometer returned to LOS mode without operator intervention. In the 
second case, the radiometer is continuously is TIP mode until changed by the operator.
   
5. Graphical user display
   
The graphical display is comprised of a status display, a message display, a temperature 
plot, a plot of the retrieved PWV and LWP, and (in TIP mode) a plot of the latest tip 
curves.

Editor's Note: The SGP.C1 data were reprocessed in 2004 and enhancement #3 described above 
was applied to the data prior to Oct 1998.  The SGP.BF data are queued for reprocessing 
as well.

• tnd31
• tknd
• tnd23
• tkair

SGP/MWR/B1/B4/B5/B6/C1 - software upgrade (version 3.27)

At 00:00 GMT on 7 January version 3.27 of the MWR operating program was installed and made 
operational at the SGP central facility (C1).  No problems were noted over the next few 
days and the boundary facility MWRs (B1, B4, B5, B6) were upgraded at 20:00 GMT on 11 
January.  This version includes a beam width correction I developed as well as providing the 
capability to automatically level the elevation mirror (that is, to automatically detect 
and correct offsets in the elevation angle stepper motor position.)

On 12 January I discovered that the '486-based MWR computers at B1, B4 and B6 were not 
executing the system command to move and rename the data files so that the ARM data system 
could retrieve them.  Reducing the length of the storage arrays in the auto-leveling 
feature from 1000 to 250 resolved the problem.  This results in the auto-leveling being based 
on only 4 hours of clear sky data rather than 16 hours at B5 and C1.  This version of the 
program is 3.28. Version 3.27 (running at B5 and C1) can be installed if and when these 
computers are upgraded to Pentium-class machines.

The improvement in the quality of the tip curves resulting from the auto-leveling has been 
dramatic: differences in the brightness temperatures at 3 airmasses (19.5 and 160.5 
degrees) have been reduced from +/- 5 K to +/- 0.5 K.  The goodness-of-fit coefficient for 
the tip curves has improved from about 0.995 to over 0.998.  In order to take full 
advantage of this improvement to detect and reject cloudy tip curves, the minimum value of the 
goodness-of-fit coefficient for a valid tip curve has been increased from 0.995 to 0.998.

Editor's Note: The SGP.C1 data were reprocessed in 2004 to produce a common DOD for all 
time.  The 1996-1998 data reprocessing included beam width and mirror-leveling corrections, 
but the data prior to that range did not have these corrections applied.

• Mean 31.4 GHz sky brightness temperature(tbsky31)
• 23.8 GHz sky brightness temperature(tbsky23)
• Total water vapor along LOS path(vap)
• Water, liquid, total along line-of-sight path(liq)