TWP/MWR/C3 - Elevated Skybrightness Temperatures

For an unknown reason, the MWR began to exhibit elevated sky brightness 
temperatures. This problem was corrected when the instrument was power-cycled.

• Water, liquid, total along line-of-sight path(liq)
• Mean 31.4 GHz sky brightness temperature(tbsky31)
• Total water vapor along LOS path(vap)
• 23.8 GHz sky brightness temperature(tbsky23)

TWP/MWR/C3 - Wet Window Flag not correct

The moisture sensor threshold voltage in the MWR configuration file was 
set to the wrong value for the new heater/blower assembly. This caused the 
wet window flag to not be set high during times of rain.

• wet_window

TWP/MWR/C3 - 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 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 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 (MWR version 4.12).

• bbn23
• Water, liquid, total along line-of-sight path(liq)
• bb23
• Mean 31.4 GHz sky brightness temperature(tbsky31)
• Total water vapor along LOS path(vap)
• bbn31
• bb31
• 23.8 GHz sky brightness temperature(tbsky23)

TWP/MWR/C3 - 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
• tkxc

TWP/MWR/C3 - 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 was active at TWP.C3 from
inception of the data, 20020227.0151.  The MONORTM-based retrieval
coefficients became active at TWP.C3 20050630.2100.

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.

• Water, liquid, total along line-of-sight path(liq)
• Total water vapor along LOS path(vap)

TWP/MWR/C3 - New software version (4.15) installed

A problem began with the installation of MWR.EXE version 4.12 in October 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 9/20/2005. As a consequence of this 
upgrade, the tip curve frequency increased. The tip cycle time decreased from ~60s to ~50s.

• tknd
• Mean 31.4 GHz sky brightness temperature(tbsky31)
• tnd_nom23
• tkbb
• tnd23
• sky31
• Sky infrared temperature(sky_ir_temp)
• tc31
• sky23
• tnd31
• tnd_nom31
• tc23
• bb23
• Water, liquid, total along line-of-sight path(liq)
• bbn23
• Total water vapor along LOS path(vap)
• bbn31
• bb31
• 23.8 GHz sky brightness temperature(tbsky23)
• tkair
• tkxc

TWP/MWR/C3 - Missing data

Data are missing and unrecoverable.

• Mean 31.4 GHz sky brightness temperature(tbsky31)
• Altitude above mean sea level(alt)
• tkbb
• tnd23
• sky31
• Sky infrared temperature(sky_ir_temp)
• tc23
• tnd_nom31
• bb23
• East longitude(lon)
• bbn31
• time_offset
• tkxc
• wet_window
• tknd
• tnd_nom23
• North latitude(lat)
• tc31
• tnd31
• sky23
• base_time
• Water, liquid, total along line-of-sight path(liq)
• bbn23
• Total water vapor along LOS path(vap)
• bb31
• tkair
• 23.8 GHz sky brightness temperature(tbsky23)

TWP/MWR/C3 - REPROCESS- Updated retrieval coefficients

The statistical retrieval coefficients currently in use at the Darwin (TWP/C3) site were 
developed using radiosonde RS80 launched from Manus Island during the TOGA-COARE 
experiment.
Data from Manus Island have minimal seasonality, therefore a single, annual set of 
coefficients was used at all three sites. Retrievals using these coefficients are sufficiently 
accurate especially during the local summer months (December-January). However, the Darwin 
site displays a summer/winter seasonality resulting in larger differences during the 
southern winter (May-
June).
Since we now have enough radiosonde soundings (RS80 and RS90) available at the Darwin 
site, the Darwin coefficients were modified to better reflect the local seasonality.

• Water, liquid, total along line-of-sight path(liq)
• Total water vapor along LOS path(vap)

TWP/MWR/C3 - Sun in field of view of radiometer

Each day around local noon there is an increase in the brightness temperature due to the 
sun being in the field of view of the radiometer.

• Water, liquid, total along line-of-sight path(liq)
• Mean 31.4 GHz sky brightness temperature(tbsky31)
• Total water vapor along LOS path(vap)
• 23.8 GHz sky brightness temperature(tbsky23)

TWP/MWR/C3 - Occasional incorrect surface temperature

The surface temperature has occasional incorrect reading.

• tkair