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 - 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

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 - 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