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

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

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

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

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

• 23.8 GHz sky signal(tipsky23)
• 31.4 GHz sky signal(tipsky31)

NSA/MWR/C2 - Missing data

Data are missing and unrecoverable.

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

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

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.

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

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.

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

• 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/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.

• Sky brightness temperature at 23.8 GHz(tbsky23)

• 23.8 GHz sky brightness temperature derived from tip curve(tbskytip23)