NSA/MWR/C2 - Wet-window flag incorrectly set

The wet window flag is set high more frequently than expected.

• wet_window

• wet_window

NSA/MWR/C2 - Elevated sky brightness temperatures

The MWR was providing unreasonable values of sky brightness temperatures and values of 
precipitable water vapor and liquid water path that were about 10 times larger than 
expected. The problem was corrected when the instrument was power-cycled. The cause of the 
problem is unknown.

• 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)

• tipsky23
• tipsky31

NSA/MWR/C2 - Missing data

Data are missing and unrecoverable.

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

• tkbb
• tbskytip31
• wet_window
• tnd23I
• vaptip
• lon
• liqtip
• alt
• bb31
• actaz
• tc23
• tipsky31
• tbskytip23
• tkair
• bbn23
• tnd_nom31
• tknd
• r23
• tkxc
• tnd23
• bbn31
• tipsky23
• actel
• lat
• tnd31
• tnd_nom23
• tnd31I
• r31
• time_offset
• base_time
• bb23
• tc31

NSA/MWR/C2 - Instrument Maintenance

Exchange of winter cover caused data corruption.

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

NSA/MWR/C2 - Intermittent Negative Sky Brightness Temperatures

Several related and recurring problems with the 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, spikes in the data, 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.

Because these all initially appeared to be hardware-related problems,
the instrument mentor and 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 did 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 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)

NSA/MWR/C2 - Thermally unstable

The MWR became thermally unstable during periods when the ambient temperature exceeded 
about 28C. This situation was corrected when the mixer temperature was manually increased to 
about 35C.

Data are suspect when the blackbody temperature, tkbb, exceeds 296 K.

• 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)

NSA/MWR/C2 - Heater problem

The MWR heater did not appear to operate when moisture was present. The heater sensitivity 
was adjusted.

• wet_window

• wet_window

NSA/MWR/C2 - 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 modifying the MWR software to read the signal from the 
appropriate corresponding channel.

• tkair

• tkair

NSA/MWR/C2 - Reprocessed: 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 water 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).

The Rosenkranz-based retrieval coefficients became active at NSA.C2
20020418.1700.	The MONORTM-based retrieval coefficients became active 
at NSA.C2 20050629.0000.

Note: The NSA.C2 MWRLOS data for 19991018-20050630 have been reprocessed
to apply the MONORTM-based retrievals for all time. The reprocessed data
were archived in March 2007.  The TIP data have not been reprocessed.

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

• vaptip
• liqtip

NSA/MWR/C2 - Thermally unstable

Between 08/12 and 08/17 the instrument displayed some intermittent thermal instability. 
Measurement accuracy may be degraded during these time periods.

Periods of thermal instability may be identified by checking the black body temperature 
Tkbb. If Tkbb > 303K (30 C) the instrument is unstable.

• 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)

• vaptip
• tbskytip23
• liqtip
• tbskytip31

NSA/MWR/C2 - 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.

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

• bbn31
• tkbb
• tipsky23
• tbskytip31
• tnd23I
• vaptip
• tnd31
• tnd_nom23
• tnd31I
• r31
• liqtip
• bb31
• tc23
• tipsky31
• tbskytip23
• tkair
• bbn23
• tnd_nom31
• r23
• tknd
• tkxc
• bb23
• tc31
• tnd23

NSA/MWR/C2 - Frosting/Condensation

Doug reported freezing winds and ice accumulation on the MWR cover and radome. This may 
affect data quality and calibration. 
On 2/24 Doug attempted to slowly thaw the cover and clear the window.
From 2/22 to 2/24 the LWP and PWV reported by the MWR are near zero. These data are 
probably affected by the frost accumulated on the radiometer window.

• sky23
• tc31
• 23.8 GHz sky brightness temperature(tbsky23)
• Total water vapor along LOS path(vap)
• Total liquid water along LOS path(liq)
• 31.4 GHz sky brightness temperature(tbsky31)
• tc23
• lon
• sky31

• tipsky23
• tipsky31
• tbskytip23
• tbskytip31
• tnd23I
• tnd_nom31
• tnd31
• vaptip
• tnd_nom23
• tnd31I
• liqtip
• tnd23

• Raw data stream - documentation not supported

NSA/MWR/C2 - Spikes in air temperature readings

The tkair variable has occasional spikes due to sensor corrosion. On 8/1, the temperature 
sensor was replaced.

• tkair

NSA/MWR/C2 - Possible bias on measurements

This instrument was refurbished at the the vendor's facility in 2008 and then sent to the 
SGP for side-by-side comparison with another MWR. During the time the instrument was at 
the SGP, it was noticed that the 23.8-GHz measurements were slightly warmer than those 
from radiometer SN10 operating at the SGP Central Facility. A comparison with radiosonde 
measurements confirmed the slight change in the measurements.

An explanation of the bias and comparison with radiosonde measurements and radiometer SN 
10 is given in the mentor's monthly data  review  for the month of April 2008.

Since there aren't radiosondes at NSA.C2, it is difficult to work around this problem. 
Based on comparison at the SGP, the bias in the 23.8-GHz channel was quantified to be ~1.5 
K. Users can attempt to subtract this amount from the 23.8-GHz measurements. 
Alternatively, use the retrieved PWV and LWV keeping in mind that there is a possible overestimation 
of PWV of ~1 mm.

On 11/16/2009 after a hardware failure of the radiometer a spare radiometer (SN15) was 
installed at the site.

• 23.8 GHz sky brightness temperature(tbsky23)

• tbskytip23

NSA/MWR/C2 - Occasional thermal instability

Between 7/1 and 7/15 the radiometer experienced a few days of thermal instability. From a 
review of the data it doesn't appear that the instability has had any major effect. It is 
not possible to quantify in detail the effect of the instability due to the lack of 
radiosonde sounding,  however users are cautioned that a higher uncertainty may be affecting 
these data.

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

• tc23
• tbskytip23
• tbskytip31
• tnd_nom31
• tnd31
• vaptip
• tnd_nom23
• tc31
• liqtip
• tnd23

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

NSA/MWR/C2 - Radiometer unstable

The radiometer had problems maintaining the thermal stabilization between 1/6 and 1/14.

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

• tbskytip23
• tbskytip31
• tnd23I
• tnd31
• vaptip
• tkxc
• tnd31I
• liqtip
• tnd23

NSA/MWR/C2 - Temperature instability

There was some temperature instability that could affect the calibration. Although the 
instability was brief users may find increased noise in the data or a slight deterioration 
of calibration accuracy during the indicated times.

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

• tc23
• tbskytip23
• tbskytip31
• tnd23I
• tnd_nom31
• vaptip
• tnd31
• tnd_nom23
• r23
• tnd31I
• r31
• tc31
• liqtip
• tnd23