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.

• Temperature, Sky Infra-Red(sky_ir_temp)

• Temperature, Sky Infra-Red(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.

• liqtip
• vaptip

• Total water vapor along LOS path(vap)
• Total liquid water along LOS path(liq)
• 31.4 GHz sky brightness temperature(tbsky31)
• 23.8 GHz sky brightness temperature(tbsky23)

• 31.4 GHz sky brightness temperature(tbsky31)
• 23.8 GHz sky brightness temperature(tbsky23)
• Total water vapor along LOS path(vap)
• Total liquid water along LOS 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.

• time_offset
• tipsky23
• tipsky31
• tnd31I
• r23
• bbn31
• tnd_nom23
• tkair
• actaz
• tbsky31tip
• tnd23
• tc23
• actel
• liqtip
• tnd23I
• tbsky23tip
• tknd
• tkbb
• tkxc
• wet_window
• bb23
• tnd31
• tc31
• vaptip
• bbn23
• r31
• tnd_nom31
• base_time
• bb31

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

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

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.

• Temperature, Sky Infra-Red(sky_ir_temp)

• Temperature, Sky Infra-Red(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)

• Temperature, Sky Infra-Red(sky_ir_temp)

• Temperature, Sky Infra-Red(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.

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

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

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

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

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.

• Total water vapor along LOS path(vap)
• Total liquid water along LOS path(liq)
• 31.4 GHz sky brightness temperature(tbsky31)
• 23.8 GHz sky brightness temperature(tbsky23)

• Total water vapor along LOS path(vap)
• 23.8 GHz sky brightness temperature(tbsky23)
• 31.4 GHz sky brightness temperature(tbsky31)
• Total liquid water along LOS path(liq)

• Total water vapor along LOS path(vap)
• Total liquid water along LOS path(liq)
• 31.4 GHz sky brightness temperature(tbsky31)
• 23.8 GHz sky brightness temperature(tbsky23)

• 31.4 GHz sky brightness temperature(tbsky31)
• 23.8 GHz sky brightness temperature(tbsky23)
• Total liquid water along LOS path(liq)
• Total water vapor along LOS path(vap)

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

• 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.

• Total water vapor along LOS path(vap)
• Total liquid water along LOS path(liq)
• 31.4 GHz sky brightness temperature(tbsky31)
• 23.8 GHz sky brightness temperature(tbsky23)
• wet_window

• wet_window
• 31.4 GHz sky brightness temperature(tbsky31)
• 23.8 GHz sky brightness temperature(tbsky23)
• Total water vapor along LOS path(vap)
• Total liquid water along LOS 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.

• tc23
• tnd23I
• tknd
• tkbb
• tkxc
• wet_window
• tnd31I
• tnd_nom23
• tkair
• tnd31
• tc31
• tnd_nom31
• tnd23

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

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

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).

• liqtip
• vaptip
• tbsky23tip
• tbsky31tip

• Total water vapor along LOS path(vap)
• Total liquid water along LOS path(liq)
• 31.4 GHz sky brightness temperature(tbsky31)
• 23.8 GHz sky brightness temperature(tbsky23)

• 31.4 GHz sky brightness temperature(tbsky31)
• 23.8 GHz sky brightness temperature(tbsky23)
• Total water vapor along LOS path(vap)
• Total liquid water along LOS 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.

• liqtip
• vaptip

• mean_liq_mwr
• mean_vap_mwr

• Total water vapor along LOS path(vap)
• Total liquid water along LOS path(liq)

• Total water vapor along LOS path(vap)
• Total liquid water along LOS 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.

• time_offset
• tipsky23
• tipsky31
• tnd31I
• r23
• bbn31
• tnd_nom23
• tkair
• lon
• actaz
• tbsky31tip
• lat
• tnd23
• tc23
• actel
• liqtip
• tnd23I
• tbsky23tip
• tkxc
• tknd
• tkbb
• wet_window
• bb23
• tnd31
• tc31
• vaptip
• alt
• bbn23
• r31
• tnd_nom31
• base_time
• bb31

• wet_window
• lon
• bbn31
• tkair
• sky23
• tnd23
• base_time
• tnd31
• tknd
• bbn23
• tkxc
• tnd_nom31
• tc31
• 23.8 GHz sky brightness temperature(tbsky23)
• Total liquid water along LOS path(liq)
• tkbb
• lat
• sky31
• tc23
• time_offset
• bb31
• Total water vapor along LOS path(vap)
• bb23
• tnd_nom23
• 31.4 GHz sky brightness temperature(tbsky31)
• Temperature, Sky Infra-Red(sky_ir_temp)
• 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 liquid water along LOS path(liq)
• Total water vapor along LOS path(vap)

• liqtip
• vaptip

• mean_liq_mwr
• mean_vap_mwr

• Total water vapor along LOS path(vap)
• Total liquid water along LOS path(liq)

• Total water vapor along LOS path(vap)
• Total liquid water along LOS path(liq)

• Total water vapor along LOS path(vap)
• Total liquid water along LOS 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.

• vap_sdev
• Temperature, brightness, longwave(ir_temp)
• number_obs_averaged
• 23tbsky
• liq_sdev
• prob_slope_change
• tbsky23_sdev
• ir_temp_sdev
• water_flag_fraction
• tbsky31_sdev
• Total water vapor along LOS path(vap)
• prob_outlier
• 31tbsky
• water_flag
• prob_level_change
• 23.8 GHz sky brightness temperature(tbsky23)
• Total liquid water along LOS path(liq)
• 31.4 GHz sky brightness temperature(tbsky31)

• tipsky23
• tipsky31
• tnd31I
• r23
• bbn31
• tnd_nom23
• tkair
• tbsky31tip
• tnd23
• tc23
• liqtip
• tnd23I
• tbsky23tip
• tkxc
• tknd
• tkbb
• wet_window
• bb23
• tnd31
• tc31
• vaptip
• bbn23
• r31
• tnd_nom31
• bb31

• 31.4 GHz sky brightness temperature(tbsky31)
• 31tbsky
• dlm_flag_fraction
• 23.8 GHz sky brightness temperature(tbsky23)
• water_flag_periods
• vap_sdev
• Total water vapor along LOS path(vap)
• tbsky31_sdev
• 23tbsky
• Total liquid water along LOS path(liq)
• ir_temp_sdev
• liq_sdev
• tbsky23_sdev
• water_flag_fraction
• Temperature, brightness, longwave(ir_temp)
• dlm_flag_periods

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

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.

• tc23
• liqtip
• tnd23I
• tbsky23tip
• tipsky23
• tipsky31
• tkbb
• tknd
• tkxc
• tnd31I
• r23
• bbn31
• tnd_nom23
• bb23
• tkair
• tnd31
• tc31
• vaptip
• tbsky31tip
• bbn23
• r31
• tnd_nom31
• bb31
• tnd23

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

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

• 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

• wet_window

• wet_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.

• liqtip
• vaptip
• tbsky23tip
• tbsky31tip
• tipsky23
• bbn23
• tipsky31
• bbn31
• bb23
• bb31

• bbn23
• bb23
• sky23
• 31.4 GHz sky brightness temperature(tbsky31)
• 23.8 GHz sky brightness temperature(tbsky23)
• Total liquid water along LOS path(liq)
• sky31
• bb31
• Total water vapor along LOS path(vap)
• bbn31

SGP/MWR/C1 - Reprocess: Radiometer reinstalled- Please reprocess

After the radiometer was reinstalled it had to update the calibration coefficients.
Data will be reprocessed

• Total water vapor along LOS path(vap)
• 31tbsky
• 23.8 GHz sky brightness temperature(tbsky23)
• Total liquid water along LOS path(liq)
• 23tbsky
• 31.4 GHz sky brightness temperature(tbsky31)

• tc23
• liqtip
• tbsky23tip
• tipsky23
• tipsky31
• tnd_nom23
• tnd31
• tc31
• vaptip
• tbsky31tip
• tnd_nom31
• tnd23

• tnd_nom31
• tc31
• 23.8 GHz sky brightness temperature(tbsky23)
• Total liquid water along LOS path(liq)
• tc23
• Total water vapor along LOS path(vap)
• tnd_nom23
• 31.4 GHz sky brightness temperature(tbsky31)
• tnd23
• tnd31

SGP/MWR/C1 - Missing data

Data are missing and unrecoverable.

• bbn23
• tkxc
• wet_window
• lon
• tnd_nom31
• tc31
• 23.8 GHz sky brightness temperature(tbsky23)
• Total liquid water along LOS path(liq)
• tkbb
• lat
• sky31
• tc23
• time_offset
• bb31
• Total water vapor along LOS path(vap)
• bbn31
• tkair
• bb23
• tnd_nom23
• sky23
• 31.4 GHz sky brightness temperature(tbsky31)
• tnd23
• Temperature, Sky Infra-Red(sky_ir_temp)
• base_time
• tnd31
• tknd
• 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.

• liqtip
• tbsky31tip

• 31.4 GHz sky brightness temperature(tbsky31)
• Total liquid water along LOS path(liq)

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.

• Temperature, Sky Infra-Red(sky_ir_temp)

• Temperature, Sky Infra-Red(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.

• Temperature, Sky Infra-Red(sky_ir_temp)

• Temperature, Sky Infra-Red(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.

• Temperature, Sky Infra-Red(sky_ir_temp)

• Temperature, Sky Infra-Red(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.

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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.

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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.

• Total liquid water along LOS path(liq)
• Total water vapor along LOS path(vap)
• 31tbsky
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• Total water vapor along LOS path(vap)
• Total liquid water along LOS path(liq)
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• 31tipsky
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• Total water vapor along LOS path(vap)
• Total liquid water along LOS path(liq)
• 23.8 GHz sky brightness temperature(tbsky23)
• 31.4 GHz sky brightness temperature(tbsky31)

• 31tipsky
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• 23.8 GHz sky brightness temperature(tbsky23)
• Total liquid water along LOS path(liq)
• Total water vapor along LOS path(vap)
• 31.4 GHz sky brightness temperature(tbsky31)

• 31tipsky
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• Total water vapor along LOS path(vap)
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• Total liquid water along LOS path(liq)

• Total water vapor along LOS path(vap)
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• Total liquid water along LOS path(liq)
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