NSA/MWR/C1 - Reprocess: Revised Calibration 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 NSA.C1 
20020425.1900.  The MONORTM-based retrieval coefficients became active 
at NSA.C1 20050629.0000.

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)

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

• 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)

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

NSA/MWR/C1 - Possible loss of accuracy due to missing blower

On 7/09 the MWR blower failed. The blower prevents snow and liquid drop from accumulating 
on the window. Accumulation of snow or liquid results in a loss of accuracy of the 
instrument. The loss of accuracy has consequencies on the retrieved liquid water path and 
precipitable water vapor. Usually there will be an overestimation of liquid and vapor. The 
blower was repaired and reinstalled on 7/20. Between 7/9 and 7/20 the tkair variable is 
unavailable as well.

• 23.8 GHz sky signal(tipsky23)
• 31.8 GHz sky brightness temperature derived from tip curve(tbskytip31)
• Ambient temperature(tkair)
• Total water vapor along zenith path using tip-derived brightness temperatures(vaptip)
• 23.8 GHz sky brightness temperature derived from tip curve(tbskytip23)
• 31.4 GHz sky signal(tipsky31)
• Water on Teflon window (1=WET, 0=DRY)(wet_window)
• Total liquid water along zenith path using tip-derived brightness temperatures(liqtip)

• Water on Teflon window (1=WET, 0=DRY)(wet_window)
• Averaged total liquid water along LOS path(liq)
• MWR column precipitable water vapor(vap)
• Sky brightness temperature at 31.4 GHz(tbsky31)
• 23.8 GHz sky signal(sky23)
• Sky brightness temperature at 23.8 GHz(tbsky23)
• 31.4 GHz sky signal(sky31)
• Ambient temperature(tkair)

NSA/MWR/C1 - Missing Data

Instrument was removed for repair.

• Sky brightness temperature at 23.8 GHz(tbsky23)
• Fraction of data in averaging interval with water on Teflon window(water_flag_fraction)
• Time offset of tweaks from base_time(time_offset)
• Standard deviation about the mean for the total liquid water amount(liq_sdev)
• lon(lon)
• Sky brightness temperature at 31.4 GHz(tbsky31)
• Standard deviation about the mean for the IR brightness temperature(ir_temp_sdev)
• Number of points included in the ir_temp ensemble(num_obs_irt)
• Standard deviation about the mean for the 23.8 GHz sky brightness temperature(tbsky23_sdev)
• lat(lat)
• IR Brightness Temperature(ir_temp)
• Standard deviation about the mean for the 31.4 GHz sky brightness temperature(tbsky31_sdev)
• Number of data points averaged for 23tbsky, 31tbsky, vap & liq(num_obs)
• MWR column precipitable water vapor(vap)
• Averaged total liquid water along LOS path(liq)
• Dummy altitude for Zeb(alt)
• base time(base_time)
• Standard deviation about the mean for the total water vapor amount(vap_sdev)

• null(Raw data stream - documentation not supported)

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

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

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

A problem began with the installation of MWR.EXE version 4.12 in September 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 9/15/2005. As a consequence of this 
upgrade, the tip curve frequency increased. The tip cycle time decreased from ~60s to ~50s.

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

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

NSA/MWR/C1 - Reprocess: wrong calibration

When MWR#20 was returned to service on 9/1/2005, the calibration had changed as a result 
of the repairs made by Radiometrics and the RF deck temperature had been set to 325K for 
testing. On 9/2, the temperature was decreased to 307K to prevent thermal instability in 
winter and the calibration was changed in the configuration file with the values supplied 
on the repair report.  

The data need to be reprocessed with the calibration coefficients that were automatically 
derived after these changes were put into affect. They are: tnd_nom23=185.621, 
tnd_nom31=158.801, tc23=-0.022, tc31=-0.039.

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

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

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

NSA/MWR/C1 - Rain sensor always on

The rain sensor was always on between 10/5 and 10/23 2006.
The user should be aware that not all data flagged as rainy are actually rainy. The 
problem was caused by a shift in the sensitivity of the rain sensor and was corrected by 
changing the sensor threshold in the configuration file.

• Water on Teflon window (1=WET, 0=DRY)(wet_window)

• Water on Teflon window (1=WET, 0=DRY)(wet_window)

NSA/MWR/C1 - Spikes in air temperature readings

During this month there are occasional negative spikes in the Tkair variable. The problem 
may be corrosion in the temperature sensor or the infiltration of water from melting snow.
The dewblower was replaced and a new sensor installed

• Ambient temperature(tkair)

• Ambient temperature(tkair)

NSA/MWR/C1 - Missing surface air temperature data

Some wires in the dewblower were not correctly configured.

• Ambient temperature(tkair)

• Ambient temperature(tkair)