SGP/MWR/B5 - 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.

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

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

SGP/MWR/B5  - 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/B5 - 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.B5 
20020415.2300.  The MONORTM-based retrieval coefficients became active 
at SGP.B5 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)

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

• 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)

SGP/MWR/B5 - 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. As a consequence of this 
upgrade, the tip curve frequency increased. The tip cycle time decreased from ~60s to ~50s.

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

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

SGP/MWR/B5 - 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 BF5 were applied when the software was upgraded to ver. 4.14 
and the configuration file was updated.

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

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

SGP/MWR/B5 - Mixer temp unstable

The radiometer mixer temperature was unstable during this time interval. The instability 
will slightly affect calibration.  On 8/21, the instrument was sent to the vendor for 
repair.

June and July data are suspect, the calibration may be slightly incorrect. August data 
should not be used.

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

• Mixer kinetic (physical) temperature(tkxc)
• Temperature correction coefficient at 31.4 GHz(tc31)
• 23.8 GHz sky signal(sky23)
• MWR column precipitable water vapor(vap)
• Noise injection temp at 31.4 GHz adjusted to tkbb(tnd31)
• (tknd)
• Noise injection temp at 23.8 GHz adjusted to tkbb(tnd23)
• Sky brightness temperature at 31.4 GHz(tbsky31)
• Averaged total liquid water along LOS path(liq)
• 31.4 GHz sky signal(sky31)
• Sky brightness temperature at 23.8 GHz(tbsky23)
• Noise injection temp at nominal temperature at 23.8 GHz(tnd_nom23)
• Temperature correction coefficient at 23.8 GHz(tc23)
• Noise injection temp at nominal temperature at 31.4 GHz(tnd_nom31)

SGP/MWR/B5 - Intermittent missing data

Starting on 9/2/07 data have been intermittent due to frequent software crash. Large 
chunks (several days in duration) of data are missing. In March 2008 the fiber optics 
connections were checked and several faulty points were identified. The connections were 
repaired. Since then the instances of software crashes are much reduced.

• Actual Azimuth(actaz)
• Blackbody kinetic temperature(tkbb)
• 23.8 GHz Blackbody signal(bb23)
• Temperature correction coefficient at 31.4 GHz(tc31)
• Total liquid water along zenith path using tip-derived brightness temperatures(liqtip)
• Ambient temperature(tkair)
• 23.8 GHz sky signal(tipsky23)
• Water on Teflon window (1=WET, 0=DRY)(wet_window)
• 23.8 GHz goodness-of-fit coefficient(r23)
• Noise injection temp at nominal temperature at 23.8 GHz(tnd_nom23)
• lat(lat)
• Noise injection temp at 23.8 GHz adjusted to tkbb(tnd23)
• 31.4 GHz sky signal(tipsky31)
• (tknd)
• Noise injection temp at 31.4 GHz adjusted to tkbb(tnd31)
• 31.8 GHz sky brightness temperature derived from tip curve(tbskytip31)
• 31.4 GHz goodness-of-fit coefficient(r31)
• 23.8 GHz blackbody+noise injection signal(bbn23)
• Noise injection temp at 31.4 GHz derived from this tip(tnd31I)
• Temperature correction coefficient at 23.8 GHz(tc23)
• 31.4 GHz blackbody(bb31)
• Noise injection temp at nominal temperature at 31.4 GHz(tnd_nom31)
• Mixer kinetic (physical) temperature(tkxc)
• lon(lon)
• Noise injection temp at 23.8 GHz derived from this tip(tnd23I)
• 23.8 GHz sky brightness temperature derived from tip curve(tbskytip23)
• Actual elevation angle(actel)
• Time offset of tweaks from base_time(time_offset)
• Total water vapor along zenith path using tip-derived brightness temperatures(vaptip)
• base time(base_time)
• 31.4 GHz blac2body+noise injection signal(bbn31)
• Dummy altitude for Zeb(alt)

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

SGP/MWR/B5 - Some rain events flagged

March 18 there was a strong rain event. During this time the brightness temperatures where 
> 100 K due to water accumulating on the radiometer, however the wet window flag 
indicator was not tripped.  Users should not rely on the wet window flag to screen 
rain-contaminated data.  Instead, apply a brightness temperature threshold of 100 K instead to both 
channels.

• Total liquid water along zenith path using tip-derived brightness temperatures(liqtip)
• 23.8 GHz sky brightness temperature derived from tip curve(tbskytip23)
• 31.8 GHz sky brightness temperature derived from tip curve(tbskytip31)
• Total water vapor along zenith path using tip-derived brightness temperatures(vaptip)
• Water on Teflon window (1=WET, 0=DRY)(wet_window)

• Sky brightness temperature at 31.4 GHz(tbsky31)
• Averaged total liquid water along LOS path(liq)
• MWR column precipitable water vapor(vap)
• Water on Teflon window (1=WET, 0=DRY)(wet_window)
• Sky brightness temperature at 23.8 GHz(tbsky23)

SGP/MWR/B5 - Missing data

Data are missing and unrecoverable.

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