SGP/MWR/B1 - 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.

• Sky brightness temperature at 23.8 GHz(tbsky23)
• Sky brightness temperature at 31.4 GHz(tbsky31)
• MWR column precipitable water vapor(vap)
• Averaged total liquid water along LOS path(liq)

• Averaged total liquid water along LOS path(liq)
• Sky brightness temperature at 31.4 GHz(tbsky31)
• MWR column precipitable water vapor(vap)
• Sky brightness temperature at 23.8 GHz(tbsky23)

SGP/MWR/B1  - min/max/delta values incorrect

The values of valid_min, valid_max, and valid_delta for fields tkxc and tknd were 
incorrect. They should be 303, 333, and 0.5 K, respectively.

• (tknd)
• Mixer kinetic (physical) temperature(tkxc)

SGP/MWR/B1 - thermal instability

During periods of high ambient temperature, the instrument may have been thermally 
unstable.

• Sky brightness temperature at 23.8 GHz(tbsky23)
• Sky brightness temperature at 31.4 GHz(tbsky31)
• MWR column precipitable water vapor(vap)
• Averaged total liquid water along LOS path(liq)

• Averaged total liquid water along LOS path(liq)
• Sky brightness temperature at 31.4 GHz(tbsky31)
• MWR column precipitable water vapor(vap)
• Sky brightness temperature at 23.8 GHz(tbsky23)

SGP/MWR/B1 - 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 at SGP.B1 20020412.1600.  The 
MONORTM-based retrieval coefficients became active at SGP.B1 20050624.2100.

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.

• MWR column precipitable water vapor(vap)
• Averaged total liquid water along LOS path(liq)

• Averaged total liquid water along LOS path(liq)
• MWR column precipitable water vapor(vap)

• MWR column precipitable water vapor(vap)
• Averaged total liquid water along LOS path(liq)

• Total liquid water along zenith path using tip-derived brightness temperatures(liqtip)
• Total water vapor along zenith path using tip-derived brightness temperatures(vaptip)

• Ensemble average for MWR liquid in window centered about balloon release(mean_liq_mwr)
• Ensemble average for MWR vapor in window centered about balloon release(mean_vap_mwr)

SGP/MWR/B1 - thermal instability

During periods of high ambient temperature, the instrument may have been thermally 
unstable. The problem was corrected by increasing the RF deck temperature from 50 to 52 C.

• Averaged total liquid water along LOS path(liq)
• Sky brightness temperature at 31.4 GHz(tbsky31)
• MWR column precipitable water vapor(vap)
• Sky brightness temperature at 23.8 GHz(tbsky23)

• Total liquid water along zenith path using tip-derived brightness temperatures(liqtip)
• Total water vapor along zenith path using tip-derived brightness temperatures(vaptip)
• 31.8 GHz sky brightness temperature derived from tip curve(tbskytip31)
• 23.8 GHz sky brightness temperature derived from tip curve(tbskytip23)

SGP/MWR/B1 - Reprocess: mixer temp adjustment

The RF deck temperature was increased from 50 to 52 C to prevent thermal instability in 
summer.  This resulted in a change in the calibration.  The data need to be reprocessed 
with the calibration coefficients that were automatically derived after the reference 
temperature, tkmx, was adjusted.

• Temperature correction coefficient at 23.8 GHz(tc23)
• Noise injection temp at 31.4 GHz adjusted to tkbb(tnd31)
• Total liquid water along zenith path using tip-derived brightness temperatures(liqtip)
• Noise injection temp at nominal temperature at 31.4 GHz(tnd_nom31)
• Noise injection temp at nominal temperature at 23.8 GHz(tnd_nom23)
• Noise injection temp at 23.8 GHz adjusted to tkbb(tnd23)
• Total water vapor along zenith path using tip-derived brightness temperatures(vaptip)
• 31.8 GHz sky brightness temperature derived from tip curve(tbskytip31)
• Temperature correction coefficient at 31.4 GHz(tc31)
• 23.8 GHz sky brightness temperature derived from tip curve(tbskytip23)

• Noise injection temp at 23.8 GHz adjusted to tkbb(tnd23)
• Noise injection temp at nominal temperature at 23.8 GHz(tnd_nom23)
• Noise injection temp at nominal temperature at 31.4 GHz(tnd_nom31)
• Noise injection temp at 31.4 GHz adjusted to tkbb(tnd31)
• Sky brightness temperature at 23.8 GHz(tbsky23)
• Temperature correction coefficient at 31.4 GHz(tc31)
• Averaged total liquid water along LOS path(liq)
• Sky brightness temperature at 31.4 GHz(tbsky31)
• Temperature correction coefficient at 23.8 GHz(tc23)
• MWR column precipitable water vapor(vap)

SGP/MWR/B1 - 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 9/13/2005 at 21:25. As a consequence 
of this upgrade, the tip curve frequency increased. The tip cycle time decreased from 
~60s to ~50s.

• Blackbody kinetic temperature(tkbb)
• 23.8 GHz sky signal(tipsky23)
• 23.8 GHz blackbody+noise injection signal(bbn23)
• 23.8 GHz Blackbody signal(bb23)
• Noise injection temp at 23.8 GHz derived from this tip(tnd23I)
• Noise injection temp at 23.8 GHz adjusted to tkbb(tnd23)
• Noise injection temp at 31.4 GHz derived from this tip(tnd31I)
• 31.4 GHz blackbody(bb31)
• Total water vapor along zenith path using tip-derived brightness temperatures(vaptip)
• 31.8 GHz sky brightness temperature derived from tip curve(tbskytip31)
• Temperature correction coefficient at 31.4 GHz(tc31)
• Mixer kinetic (physical) temperature(tkxc)
• 23.8 GHz sky brightness temperature derived from tip curve(tbskytip23)
• (tknd)
• Ambient temperature(tkair)
• Total liquid water along zenith path using tip-derived brightness temperatures(liqtip)
• Noise injection temp at 31.4 GHz adjusted to tkbb(tnd31)
• Temperature correction coefficient at 23.8 GHz(tc23)
• Noise injection temp at nominal temperature at 31.4 GHz(tnd_nom31)
• 23.8 GHz goodness-of-fit coefficient(r23)
• Noise injection temp at nominal temperature at 23.8 GHz(tnd_nom23)
• 31.4 GHz sky signal(tipsky31)
• 31.4 GHz goodness-of-fit coefficient(r31)
• 31.4 GHz blac2body+noise injection signal(bbn31)

• Noise injection temp at 23.8 GHz adjusted to tkbb(tnd23)
• Sky Infra-Red Temperature(sky_ir_temp)
• Noise injection temp at 31.4 GHz adjusted to tkbb(tnd31)
• 31.4 GHz blac2body+noise injection signal(bbn31)
• Ambient temperature(tkair)
• IR Brightness Temperature(ir_temp)
• 23.8 GHz sky signal(sky23)
• Averaged total liquid water along LOS path(liq)
• Temperature correction coefficient at 23.8 GHz(tc23)
• 23.8 GHz blackbody+noise injection signal(bbn23)
• Noise injection temp at nominal temperature at 23.8 GHz(tnd_nom23)
• 31.4 GHz sky signal(sky31)
• (tknd)
• Noise injection temp at nominal temperature at 31.4 GHz(tnd_nom31)
• 31.4 GHz blackbody(bb31)
• Mixer kinetic (physical) temperature(tkxc)
• Sky brightness temperature at 23.8 GHz(tbsky23)
• Temperature correction coefficient at 31.4 GHz(tc31)
• Sky brightness temperature at 31.4 GHz(tbsky31)
• Blackbody kinetic temperature(tkbb)
• MWR column precipitable water vapor(vap)
• 23.8 GHz Blackbody signal(bb23)

SGP/MWR/B1 - Reprocessed: Corrected calibration

The radiometer was thermally unstable. Calibration coefficients for the time interval were 
re-derived after screening for bad values of TKxc and the data were reprocessed.  
Reprocessed MWRLOS data were archived January 2007.  MWRTIP data will not be reprocessed.

• 23.8 GHz sky signal(tipsky23)
• Noise injection temp at 23.8 GHz adjusted to tkbb(tnd23)
• Noise injection temp at 23.8 GHz derived from this tip(tnd23I)
• Noise injection temp at 31.4 GHz derived from this tip(tnd31I)
• Total water vapor along zenith path using tip-derived brightness temperatures(vaptip)
• 31.8 GHz sky brightness temperature derived from tip curve(tbskytip31)
• Temperature correction coefficient at 31.4 GHz(tc31)
• Mixer kinetic (physical) temperature(tkxc)
• 23.8 GHz sky brightness temperature derived from tip curve(tbskytip23)
• (tknd)
• Temperature correction coefficient at 23.8 GHz(tc23)
• Noise injection temp at 31.4 GHz adjusted to tkbb(tnd31)
• Total liquid water along zenith path using tip-derived brightness temperatures(liqtip)
• Noise injection temp at nominal temperature at 31.4 GHz(tnd_nom31)
• 23.8 GHz goodness-of-fit coefficient(r23)
• Noise injection temp at nominal temperature at 23.8 GHz(tnd_nom23)
• 31.4 GHz sky signal(tipsky31)
• 31.4 GHz goodness-of-fit coefficient(r31)

• Noise injection temp at 23.8 GHz adjusted to tkbb(tnd23)
• Noise injection temp at 31.4 GHz adjusted to tkbb(tnd31)
• Temperature correction coefficient at 23.8 GHz(tc23)
• Noise injection temp at nominal temperature at 23.8 GHz(tnd_nom23)
• (tknd)
• Noise injection temp at nominal temperature at 31.4 GHz(tnd_nom31)
• Mixer kinetic (physical) temperature(tkxc)
• Sky brightness temperature at 23.8 GHz(tbsky23)
• Temperature correction coefficient at 31.4 GHz(tc31)
• Sky brightness temperature at 31.4 GHz(tbsky31)
• MWR column precipitable water vapor(vap)

• null(Raw data stream - documentation not supported)

SGP/MWR/B1 - Calibration failure

The radiometer suddenly stopped performing successful tip curve calibrations. Brightness 
temperatures are inaccurate during this time. The instrument was removed from service 
20071126.  Reprocessing is not possible.

• 23.8 GHz sky signal(tipsky23)
• Noise injection temp at 23.8 GHz adjusted to tkbb(tnd23)
• Noise injection temp at 23.8 GHz derived from this tip(tnd23I)
• Noise injection temp at 31.4 GHz derived from this tip(tnd31I)
• Total water vapor along zenith path using tip-derived brightness temperatures(vaptip)
• 31.8 GHz sky brightness temperature derived from tip curve(tbskytip31)
• Temperature correction coefficient at 31.4 GHz(tc31)
• 23.8 GHz sky brightness temperature derived from tip curve(tbskytip23)
• Noise injection temp at 31.4 GHz adjusted to tkbb(tnd31)
• Temperature correction coefficient at 23.8 GHz(tc23)
• 23.8 GHz goodness-of-fit coefficient(r23)
• Noise injection temp at nominal temperature at 31.4 GHz(tnd_nom31)
• Noise injection temp at nominal temperature at 23.8 GHz(tnd_nom23)
• 31.4 GHz sky signal(tipsky31)
• 31.4 GHz goodness-of-fit coefficient(r31)

• Noise injection temp at 23.8 GHz adjusted to tkbb(tnd23)
• Noise injection temp at 31.4 GHz adjusted to tkbb(tnd31)
• 23.8 GHz sky signal(sky23)
• Temperature correction coefficient at 23.8 GHz(tc23)
• 31.4 GHz sky signal(sky31)
• Noise injection temp at nominal temperature at 23.8 GHz(tnd_nom23)
• Noise injection temp at nominal temperature at 31.4 GHz(tnd_nom31)
• Sky brightness temperature at 23.8 GHz(tbsky23)
• Temperature correction coefficient at 31.4 GHz(tc31)
• Sky brightness temperature at 31.4 GHz(tbsky31)
• MWR column precipitable water vapor(vap)

SGP/MWR/B1 - Noisy data

After the instrument was returned to service, the brightness temperature data came up 
extremely noisy.  Disregard brightness temperature data as well as PWV and LWP retrievals 
collected during the indicated time.

• Averaged total liquid water along LOS path(liq)
• Sky brightness temperature at 31.4 GHz(tbsky31)
• MWR column precipitable water vapor(vap)
• Sky brightness temperature at 23.8 GHz(tbsky23)

• Total liquid water along zenith path using tip-derived brightness temperatures(liqtip)
• Total water vapor along zenith path using tip-derived brightness temperatures(vaptip)
• 31.8 GHz sky brightness temperature derived from tip curve(tbskytip31)
• 23.8 GHz sky brightness temperature derived from tip curve(tbskytip23)

SGP/MWR/B1 - Missing data

Data are missing and unrecoverable.

• Noise injection temp at 23.8 GHz adjusted to tkbb(tnd23)
• Sky Infra-Red Temperature(sky_ir_temp)
• Noise injection temp at 31.4 GHz adjusted to tkbb(tnd31)
• Dummy altitude for Zeb(alt)
• 31.4 GHz blac2body+noise injection signal(bbn31)
• Ambient temperature(tkair)
• IR Brightness Temperature(ir_temp)
• 23.8 GHz sky signal(sky23)
• Averaged total liquid water along LOS path(liq)
• Water on Teflon window (1=WET, 0=DRY)(wet_window)
• lon(lon)
• Temperature correction coefficient at 23.8 GHz(tc23)
• 23.8 GHz blackbody+noise injection signal(bbn23)
• lat(lat)
• 31.4 GHz sky signal(sky31)
• Noise injection temp at nominal temperature at 23.8 GHz(tnd_nom23)
• (tknd)
• Time offset of tweaks from base_time(time_offset)
• Noise injection temp at nominal temperature at 31.4 GHz(tnd_nom31)
• 31.4 GHz blackbody(bb31)
• Mixer kinetic (physical) temperature(tkxc)
• Sky brightness temperature at 23.8 GHz(tbsky23)
• Temperature correction coefficient at 31.4 GHz(tc31)
• base time(base_time)
• Sky brightness temperature at 31.4 GHz(tbsky31)
• Blackbody kinetic temperature(tkbb)
• MWR column precipitable water vapor(vap)
• 23.8 GHz Blackbody signal(bb23)

SGP/MWR/B1 - Noisy data

After a software crash data were very noisy.

• 31.4 GHz sky signal(sky31)
• Averaged total liquid water along LOS path(liq)
• Sky brightness temperature at 31.4 GHz(tbsky31)
• MWR column precipitable water vapor(vap)
• Sky brightness temperature at 23.8 GHz(tbsky23)
• 23.8 GHz sky signal(sky23)

• Total liquid water along zenith path using tip-derived brightness temperatures(liqtip)
• 31.4 GHz sky signal(tipsky31)
• Total water vapor along zenith path using tip-derived brightness temperatures(vaptip)
• 23.8 GHz sky signal(tipsky23)
• 31.8 GHz sky brightness temperature derived from tip curve(tbskytip31)
• 23.8 GHz sky brightness temperature derived from tip curve(tbskytip23)