TWP/MWR/C2 - Uncertainty in clock time

At ARCS2, the MWR computer clock was not being updated because no NTP time service 
software was installed on the computer. During Nauru99, on 6/24/99, the clock was found to be 3 
minutes and 17 seconds fast. 

Assuming that the time was properly set at installation on 10/26/98 (which is not 
indicated in the installation report) and never reset until 6/24/99, the rate of time drift on 
the computer was about +0.8 seconds per day. However, if the time was not reset since 
integration at AIS on 1/14/98 (which is recorded in my integration notes), then the rate of 
drift is about +0.4 seconds per day.

The computer was replaced and time service started on 7/30/99.

• tipsky23
• tkair
• base_time
• tnd_nom31
• tkxc
• actaz
• wet_window
• r23
• tnd23I
• tc23
• time_offset
• tnd_nom23
• tnd23
• r31
• bb23
• bbn31
• tkbb
• bbn23
• tnd31
• tc31
• tknd
• bb31
• actel
• tnd31I
• tipsky31

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

TWP/MWR/C2 - Installation

The Nauru ARCS was installed during the period September-November
1998.  Data were being collected by the end of October, but for the
first several weeks of November, the site was undergoing considerable
change, so data from that period should be used with caution.  The
official site dedication occured on November 20.  Most on-site
activity ended following the dedication so we will consider November
20 to be the beginning of the Nauru operations.  The last members of
the installation team left Nauru on November 24.

• bb23
• tipsky23
• bbn31
• tkair
• tkbb
• tnd_nom31
• tkxc
• actaz
• tnd31
• bbn23
• wet_window
• tc31
• r23
• tknd
• tnd23I
• bb31
• tc23
• tnd_nom23
• actel
• tnd23
• tnd31I
• r31
• tipsky31

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

TWP/MWR/C2 - Excessive wet_window flags

The wet_window flag is set high more than expected from the measured value of liquid water 
path. This may be caused by dew or, if the heater sensivity is slightly misadjusted, by 
the diurnal variation in ambient temperature.

The "wet_window" flag is an indicator of moisture on the MWR window which invalidates the 
measurements of precipitable water vapor and liquid water path. Sometimes this flag can 
be incorrectly set high or low if the heater sensivity is slightly misadjusted. The heater 
adjustment is a resistive device that is dependent on ambient temperature. Another 
indicator of moisture on the window is unreasonably high ( > 3*liquid_retrieval_rms_accuracy ) 
values of "liq".

• wet_window

• wet_window

TWP/MWR/C2 - thermal instability

The MWR required an unusually long time to reach thermal stability after a 4-day outage 
due to a power failure that damaged the blower/heater assembly. Also during this period, 
the heater, which had been replaced, appears to have been on continously, causing the data 
to be inappropriately flagged.

• tipsky23
• tc23
• tnd_nom23
• tnd_nom31
• wet_window
• tc31
• tipsky31

• tnd_nom23
• sky31
• 31.4 GHz sky brightness temperature(tbsky31)
• sky23
• tnd_nom31
• Total liquid water along LOS path(liq)
• Total water vapor along LOS path(vap)
• tc31
• wet_window
• tc23
• Radiation, longwave, brightness temperature, 23.8 GHz(tbsky23)

TWP/MWR/C2 - Data collection problem

Large, frequent data gaps occurred due to a failing laptop computer. The problem was 
corrected when a new computer was installed.

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

• Raw data stream - documentation not supported

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

TWP/MWR/C2 - Heater problem

When the wiring of the air temperature sensor was checked the heater apparently began 
activating too often.

• wet_window

• water_flag_fraction

• wet_window

TWP/MWR/C2 - mixer temperature

When the wiring of the air temperature sensor was checked the mixer temperature 
unexpectedly decreased 4 degrees. It increased to its normal value when the dielectric window was 
replaced. The problem was probably caused by a loose and/or corroded connection.

• tkxc

• tkxc

TWP/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 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).

The Rosenkranz-based retrieval coefficients became active at TWP.C2 20020427.0600.  The 
MONORTM-based retrieval coefficients became active at TWP.C2 20050630.2100.

Note: The TWP.C2 data for 19981028-20050630 have been reprocessed to apply the 
MONORTM-based retrievals for all time.  The reprocessed data were archived 20061003.

• mean_vap_mwr
• mean_liq_mwr

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

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

TWP/MWR/C2 - New software version (4.15) installed

A problem began with the installation of MWR.EXE version 4.12 in November 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.

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

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

TWP/MWR/C2 - software upgrade (version 3.29)

The MWR operating program was upgraded to version 3.29 on 30 July 1999. This version 
included a beam width correction as well as provided the capability to automatically level the 
elevation mirror (that is, to automatically detect and correct offsets in the elevation 
angle stepper motor position.)
   
The improvement in the quality of the tip curves resulting from the auto-leveling has been 
dramatic: differences in the brightness temperatures at 3 airmasses (19.5 and 160.5 
degrees) have been reduced from +/- 5 K to +/- 0.5 K. In order to take full advantage of this 
improvement to detect and reject cloudy tip curves, the minimum value of the 
goodness-of-fit coefficient for a valid tip curve has been increased from 0.995 to 0.998.

The data prior to July 30 1999 do not include beam-width and mirror-leveling corrections.

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

TWP/MWR/C2 - Missing data

The heater blower assembly was causing the fuse to blow.  The instrument was taken offline 
until a replacement arrives.

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

• tbsky31_sdev
• Total liquid water along LOS path(liq)
• time_offset
• lat
• vap_sdev
• ir_temp_sdev
• Temperature, brightness, longwave(ir_temp)
• base_time
• Radiation, longwave, brightness temperature, 23.8 GHz(tbsky23)
• tbsky23_sdev
• alt
• water_flag_fraction
• lon
• 31.4 GHz sky brightness temperature(tbsky31)
• liq_sdev
• num_obs
• num_obs_irt
• Total water vapor along LOS path(vap)

• Raw data stream - documentation not supported

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

TWP/MWR/C2 - Missing Data

Data are missing and unrecoverable.

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

TWP/MWR/C2 - Reprocessed: New Calibration coefficients

On 11/27 a spare radiometer was installed to replace a faulty radiometer. Once the 
radiometer started to collect data it used the default calibration coefficients until it 
collected enough tip data to determine its own coefficients.

The data were reprocessed to apply corrected calibrations and the reprocessed data were 
archived 20061222.

• tc23
• tnd_nom23
• tnd_nom31
• tnd23
• tnd31
• tc31

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

TWP/MWR/C1/C2 - Sun in the field of view

Every day between around noon local time (usually between 1 and 2 AM UTC time) there is an 
increase in the brightness temperatures due to the sun in the field of view of the 
radiometer.

The effect lasts less than an hour around local noon (usually between 1 and 2 AM UTC 
time).  The effect appears as a smooth increase and decrease in brightness temperature.

• tipsky23
• tipsky31

• vaptip
• liqtip
• tbskytip23
• tbskytip31

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

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

TWP/MWR/C2 - Incorrect ambient temperature during rain

The ambient temperature was approximately 15 degree higher than what it should be when it 
was raining and the heater came. On Jan 9 2009 the dewblower was replaced which solved 
the problem.

The increased ambient temperature (tkair) was happening during times of rain and users 
should always disregard MWR data during rain events.  Therefore this DQR is colored 
transparent.

• tkair

• tkair

TWP/MWR/C2 - Intermittent data

There are several short data gaps (usually 2 to 7 hours) in the data due to computer 
malfunction. The problem was solved by replacing the computer.

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

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

TWP/MWR/C2 - Software Change

The MWR operating software was changed on 19 November 1998 to provide additional 
functionality as described below.
   
NEW FEATURES
1. Faster sampling rate
   
Standard line-of-sight (LOS) observations can now be acquired at 15-second intervals vs. 
20-second intervals previously. (The standard LOS cycle is comprised of one sky sample per 
blackbody sample and gain update.)
   
2. More flexible sampling strategy
   
Multiple sky observations can be acquired during a LOS cycle, up to 1024 per gain update. 
This permits sky samples to be acquired at intervals of 2.67 seconds for improved 
temporal resolution of cloud liquid water variations and better coordination with the millimeter 
cloud radar during IOPs.
   
3. Separation of zenith LOS observations from TIP data
   
When the radiometer is in TIP mode, the zenith LOS observations are now extracted, the PWV 
and LWP computed and reported separately in the output file. This eliminates the periods 
of missing LOS data during calibration checks/updates.
   
4. Automatic self-calibration
   
The software now permits the calibration to be updated at specified intervals or 
continuously. In the first case, LOS mode is automatically changed to TIP mode at user-specified 
intervals or whenever clear sky conditions occur, the tip data reduced, the calibration 
updated, and the radiometer returned to LOS mode without operator intervention. In the 
second case, the radiometer is continuously is TIP mode until changed by the operator.
   
5. Graphical user display
   
The graphical display is comprised of a status display, a message display, a temperature 
plot, a plot of the retrieved PWV and LWP, and (in TIP mode) a plot of the latest tip 
curves.

• tnd23
• tkair
• tknd
• tnd31