SGP/MWR/C1 - calibration checks

The MWR calibration was checked by a cryogenic (liquid nitrogen) 
blackbody target or (in the case of the Sept 2001 time period)
by pointing the mirror at an internal blackbody target.  The 
brightness temperatures and vap and liq retrievals are not
representative of the sky/atmosphere.

• liqtip
• vaptip

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

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

SGP/MWR/C1 - Time drift

On 9/18/00, I found that the time on the MWR laptop was 1m 21s slow. The Dimension4 
utility had last synchronized the time on 5/5/00. Found that the network DNS settings had been 
disabled. Added the DNS entry for ntp host CF10. Dimension4 synchronized the clock by 
adding 80.91s. The time had drifted at a rate of -0.59s/day.

• time_offset
• tipsky23
• tipsky31
• tnd31I
• r23
• bbn31
• tnd_nom23
• tkair
• actaz
• tbsky31tip
• tnd23
• tc23
• actel
• liqtip
• tnd23I
• tbsky23tip
• tknd
• tkbb
• tkxc
• wet_window
• bb23
• tnd31
• tc31
• vaptip
• bbn23
• r31
• tnd_nom31
• base_time
• bb31

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

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

SGP/MWR/C1 - Intermittent Negative Sky Brightness Temperatures

Several related and recurring problems with the SGP 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 (especially at Purcell),
spikes in the data (especially at Vici), 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 (especially at the CF).

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

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

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

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

SGP/MWR/C1 - 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 changing the wiring.

• tkair

• tkair

SGP/MWR/C1 - Instrument problem

The MWR mixer temperature, blackbody temperature, and moisture flag are incorrect. This 
began when the instrument was returned to service after the analog board was temporarily 
removed to check the presence and absence of certain resistors. The board must have been 
accidently damaged during this process.

• tc23
• tnd23I
• tknd
• tkbb
• tkxc
• wet_window
• tnd31I
• tnd_nom23
• tkair
• tnd31
• tc31
• tnd_nom31
• tnd23

• tknd
• tnd_nom31
• tc23
• tnd31
• tkbb
• tc31
• wet_window
• tkxc
• tnd23
• tkair
• tnd_nom23

• tkxc
• wet_window
• tnd_nom31
• tc31
• tkbb
• tc23
• tkair
• tnd_nom23
• tnd23
• tnd31
• tknd

SGP/MWR/C1 - thermal instability

The analog board was replaced with a spare (D041001.3) with a reference temperature that 
was set too low (306 K) so that during periods of high ambient temperature, the instrument 
became thermally unstable. The problem was corrected when the temperature setting was 
increased (to 311 K).

• liqtip
• vaptip
• tbsky23tip
• tbsky31tip

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

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

SGP/MWR/C1 - Reprocess: wrong retrievals

When the computer and core configuration were upgraded, retrieval coefficients for BF1 
were accidently included in the configuration file.
The correct coefficients for CF1 were applied when the configuration file was updated.

• liqtip
• vaptip

• mean_liq_mwr
• mean_vap_mwr

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

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

SGP/MWR/C1 - spare instrument

The spare MWR, S.N. 04, was installed while the production instrument, S.N. 10, was 
returned to the manufacturer for upgrades.

• time_offset
• tipsky23
• tipsky31
• tnd31I
• r23
• bbn31
• tnd_nom23
• tkair
• lon
• actaz
• tbsky31tip
• lat
• tnd23
• tc23
• actel
• liqtip
• tnd23I
• tbsky23tip
• tkxc
• tknd
• tkbb
• wet_window
• bb23
• tnd31
• tc31
• vaptip
• alt
• bbn23
• r31
• tnd_nom31
• base_time
• bb31

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

SGP/MWR/C1 - 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 became active as follows (BCR 456):
SGP/C1 (Lamont)     4/16/2002, 2000
SGP/B1 (Hillsboro)  4/12/2002, 1600
SGP/B4 (Vici)       4/15/2002, 2300
SGP/B5 (Morris)     4/15/2002, 2300
SGP/B6 (Purcell)    4/16/2002, 2200
SGP/E14(Lamont)     4/16/2002, 0000
NSA/C1 (Barrow)     4/25/2002, 1900 
NSA/C2 (Atqasuk)    4/18/2002, 1700
TWP/C1 (Manus)      5/04/2002, 0200
TWP/C2 (Nauru)      4/27/2002, 0600
TWP/C3 (Darwin)     inception

The MONORTM-based retrieval coefficients became active as follows (BCR 984):

SGP/C1 (Lamont)     6/28/2005, 2300
SGP/B1 (Hillsboro)  6/24/2005, 2100
SGP/B4 (Vici)       6/24/2005, 2100
SGP/B5 (Morris)     6/24/2005, 2100
SGP/B6 (Purcell)    6/24/2005, 1942
SGP/E14(Lamont)     6/28/2005, 2300
NSA/C1 (Barrow)     6/29/2005, 0000 
NSA/C2 (Atqasuk)    6/29/2005, 0000
TWP/C1 (Manus)      6/30/2005, 2100
TWP/C2 (Nauru)      6/30/2005, 2100
TWP/C3 (Darwin)     6/30/2005, 2100
PYE/M1 (Pt. Reyes)  4/08/2005, 1900**

** At Pt. Reyes, the original retrieval coefficients implemented in March 2005 were based 
on a version of the Rosenkranz model that had been modified to use the HITRAN half-width 
at 22 GHz and to be consistent with the water vapor continuum in MONORTM.  These 
retrievals yield nearly identical results to the MONORTM retrievals.  Therefore the Pt. Reyes 
data prior to 4/08/2005 may not require reprocessing.

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

• liqtip
• vaptip

• mean_liq_mwr
• mean_vap_mwr

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

SGP/MWR/C1 - Instrument noise problem

Various variables including the mixer temperatures were very noisy. After several attempts 
to fix the problem, the instrument was taken off line and returned to the manufacturer 
for repair.

• vap_sdev
• Temperature, brightness, longwave(ir_temp)
• number_obs_averaged
• 23tbsky
• liq_sdev
• prob_slope_change
• tbsky23_sdev
• ir_temp_sdev
• water_flag_fraction
• tbsky31_sdev
• Total water vapor along LOS path(vap)
• prob_outlier
• 31tbsky
• water_flag
• prob_level_change
• Radiation, longwave, brightness temperature, 23.8 GHz(tbsky23)
• Total liquid water along LOS path(liq)
• 31.4 GHz sky brightness temperature(tbsky31)

• tipsky23
• tipsky31
• tnd31I
• r23
• bbn31
• tnd_nom23
• tkair
• tbsky31tip
• tnd23
• tc23
• liqtip
• tnd23I
• tbsky23tip
• tkxc
• tknd
• tkbb
• wet_window
• bb23
• tnd31
• tc31
• vaptip
• bbn23
• r31
• tnd_nom31
• bb31

• 31.4 GHz sky brightness temperature(tbsky31)
• 31tbsky
• dlm_flag_fraction
• Radiation, longwave, brightness temperature, 23.8 GHz(tbsky23)
• water_flag_periods
• vap_sdev
• Total water vapor along LOS path(vap)
• tbsky31_sdev
• 23tbsky
• Total liquid water along LOS path(liq)
• ir_temp_sdev
• liq_sdev
• tbsky23_sdev
• water_flag_fraction
• Temperature, brightness, longwave(ir_temp)
• dlm_flag_periods

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

SGP/MWR/C1 - New software version (4.15) installed

A problem began with the installation of MWR.EXE version 4.12 in July 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 08/04/2005. As a consequence of this 
upgrade, the tip curve frequency increased. The tip cycle time decreased from ~60s to 
~50s.

• tc23
• liqtip
• tnd23I
• tbsky23tip
• tipsky23
• tipsky31
• tkbb
• tknd
• tkxc
• tnd31I
• r23
• bbn31
• tnd_nom23
• bb23
• tkair
• tnd31
• tc31
• vaptip
• tbsky31tip
• bbn23
• r31
• tnd_nom31
• bb31
• tnd23

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

SGP/MWR/C1 - Spikes in ambient temperature readings

There are intermittent spikes in the Tkair temperature (T ~ 400 K). On 7/28 the sensor 
was cleaned and the instrument power cycled following a power outage. Readings came back to 
normal.

• tkair

• tkair

SGP/MWR/C1/E14 - Freezing rain-Incorrect rain flag

Between 01/12 and 01/15 brightness temperatures show high values (Tb > 100 K) indicative 
of rain, however the wet_window flag is 0 (indicative of no rain). During that time there 
where freezing conditions with ice pellets that were not detected by the sensor. The high 
brightness temperatures may be due to melting ice on the window.

• wet_window

• wet_window

• wet_window

• wet_window

SGP/MWRHF/C1 - 90-GHz questionable calibration

Between 20061103 and 20070301 one of the parameters thresholds used to select good tip 
curves used in the calibratio process was not optimal. This resulted in data that have a 
high standard deviation and a unsatisfactory agreement with model computations.
After collecting enough points needed to conduct a model comparison the threshold was 
changed on March 1.
From a limited data analysis for the month pf March it appears that the change in 
threshold has improved the agreement between measurements and the model.

• Sky brightness temperature (90 GHz)(tbsky90)

SGP/MWRHF/C1 - 150-Ghz channel not working

Starting on 2/23 the 150-Ghz channel is showing a temperature of 310 K. The suspected 
cause of the problem is a hardware failure. The instrument was removed and sent for repair on 
4/2

• Sky brightness temperature (150 GHz)(tbsky150)

SGP/MWRHF/C1 - Instrument removed

Due to a hardware failure the instrument was removed and sent for repairs

• Raw data stream - documentation not supported

• Rain flag(rain_flag)
• Sky brightness temperature (90 GHz)(tbsky90)
• Barometric pressure(pressure)
• Sky brightness temperature (150 GHz)(tbsky150)
• base_time
• Humidity, relative(rh)
• time_offset
• alt
• lat
• time
• lon
• elevation
• Temperature, air(temp)

SGP/MWR/C1 - Noisy data

Since 7/14 the MWR is experiencing intermittent periods of increased noise. The cause for 
this is under investigation.

• liqtip
• vaptip
• tbsky23tip
• tbsky31tip
• tipsky23
• bbn23
• tipsky31
• bbn31
• bb23
• bb31

• bbn23
• bb23
• sky23
• 31.4 GHz sky brightness temperature(tbsky31)
• Radiation, longwave, brightness temperature, 23.8 GHz(tbsky23)
• Total liquid water along LOS path(liq)
• sky31
• bb31
• Total water vapor along LOS path(vap)
• bbn31

SGP/MWRHF/C1 - Dew formation on window

During night time, when the humidity is very high (RH ~ 100%) data are strongly affected 
by
dew formation on the window. 
This results in a smooth and large (80-150 K) increase of the brightness temperature from
early night to sunrise. Data are affected mostly at night.

• Sky brightness temperature (90 GHz)(tbsky90)
• Sky brightness temperature (150 GHz)(tbsky150)

SGP/MWR/C1 - Reprocess: Radiometer reinstalled- Please reprocess

After the radiometer was reinstalled it had to update the calibration coefficients.
Data will be reprocessed

• Total water vapor along LOS path(vap)
• 31tbsky
• Radiation, longwave, brightness temperature, 23.8 GHz(tbsky23)
• Total liquid water along LOS path(liq)
• 23tbsky
• 31.4 GHz sky brightness temperature(tbsky31)

• tc23
• liqtip
• tbsky23tip
• tipsky23
• tipsky31
• tnd_nom23
• tnd31
• tc31
• vaptip
• tbsky31tip
• tnd_nom31
• tnd23

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

SGP/MWR/C1 - Increased noise in 31.4 GHz channel

The 31.4 GHz channel has been showing an increased level of noise which results in 
increased noise in the LWP retrievals. The instrument is tipping and all other parameters seem 
to be in the range. The elevate noise started in May, but it seems to have become slightly 
worse after summer. After November the noise level seems to have gone back to normal.

• liqtip
• tbsky31tip

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

SGP/MWR/C1 - Loss of thermal stabilization

Periodically during August and September 1995 all microwave radiometers
at the SGP CART generated error messages in the Site Operations Log
like:

  Time: Sat Aug 19 18:41:20 1995
  MWRLOS.C1, tkxc: Value above Maximum.

This indicates that the temperature of the microwave hardware
(specifically, the cross-coupler or "xc") exceeded its controlled
temperature (47-52 deg C) at which point it was no longer thermally
stabilized and the gain was uncontrolled.  During these periods which
typically last about 8 hours from about local noon until about sunset
the data behave anomalously and should be considered invalid.

Specifically the precipitable water vapor increases and the liquid
water path decreases (and becomes SIGNIFICANTLY NEGATIVE (-0.1 mm) on
clear sky days).  The RMS noise level in the data also increases
sharply.  The 'Tkxc' field appears ONLY in the a0-level data and does
NOT appear in either the a1 (mwrlos) or c1 (mwr5avg) files.  Therefore
THESE ANOMALOUS VALUES HAVE BEEN INCLUDED IN THE 5-MINUTE AVERAGES.

The microwave hardware is thermally stabilized to about +/- 0.1 deg C
by resistive heating.  When the internal temperature rises above the
set point the thermal stabilization of the instrument gain is lost.
>From an examination of the component temperature data it appears that
increasing the set point temperature to about 55 deg C (328 K) would
prevent a re-ocurrance of this problem at the SGP.  The manufacturer,
Radiometrics, concurs that raising the set point will fix this problem
and will not cause other problems.

I will have to carefully examine the MCTEX data to determine whether
this will be a problem for the TWP.  The manufacturer and I had
discussed this possibility prior to building the TWP MWRs (S/N 015,
016, and 017) and those instruments have set points above 50 deg C.
Note that MWR 018 has a set point near 52 deg C (like the TWP models)
but it still experienced a few loss-of-stabilization events.

Note that the instruments with the lowest set points had the most
loss-of-stabilization events.

• Total water vapor along LOS path(vap)
• Total liquid water along LOS path(liq)
• 23tbsky
• 31tbsky

• Total water vapor along LOS path(vap)
• 23tbsky
• Total liquid water along LOS path(liq)
• 31tbsky

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

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

SGP/MWR/B1/B4/B5/B6/C1 - Thermal Stabilization Adjustment

In order to correct a thermal stabilization problem identified earlier
I adjusted the thermal set point of the microwave radiometers at the
SGP upward from 48-50 deg C to 55 deg C in early August 1996 according
to the schedule given below.

B6    5 August 1996
C1    6 August 1996
B1    7 August 1996
B5    8 August 1996

Subsequent to making this adjustment the MWRs were put in TIP mode to
check on whether the change in set point temperature affected their
calibration.  Because clear sky conditions were quite intermittent, it
is difficult to determine whether the substantial variability in the
tip data were attributable to the change in thermal set point.  The
instrument calibration was not altered in August.

Tip data were again collected with these instruments in September prior
to the beginning and at the close of the Water Vapor IOP.  For example,
the calibration of the instrument at the central facility (S/N 10)
derived from the September data was essentially the same as that
derived from calibration data acquired in February 1996.  Although this
would lead one to believe that altering the thermal set point did not
affect the instrument calibration, it may be that some transient effect
was induced.

In comparing soundings launched from the central facility with the
microwave radiometer there, I noticed that those sondes calibrated in
June 1996 consistently reported lower integrated water vapor than the
radiometer in July and September (during the IOP) but were in better
agreement with the radiometer for the two weeks period immediately
after the set point was adjusted.  I suspect that adjusting the thermal
set point may have temporarily increased the radiometer gain
(kelvins/volt) thereby lowering the measured brightness temperature and
the retrieved integrated water vapor.

It is not clear why a temporary change in gain should occur or even
whether it did.  But users of the data should be aware that the data
from the microwave radiometers at the SGP may be anomalous during
August 1996.

• 23tbsky
• Total liquid water along LOS path(liq)
• Total water vapor along LOS path(vap)
• 31tbsky

• 23tbsky
• Total water vapor along LOS path(vap)
• 31tbsky
• Total liquid water along LOS path(liq)

• 31tbsky
• Total water vapor along LOS path(vap)
• 23tbsky
• Total liquid water along LOS path(liq)

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

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

• Total liquid water along LOS path(liq)
• Total water vapor along LOS path(vap)
• 23tbsky
• 31tbsky

• Total water vapor along LOS path(vap)
• 31tbsky
• 23tbsky
• Total liquid water along LOS path(liq)

• 31tbsky
• Total liquid water along LOS path(liq)
• 23tbsky
• Total water vapor along LOS path(vap)

• 23tbsky
• Total water vapor along LOS path(vap)
• Total liquid water along LOS path(liq)
• 31tbsky

• 23tbsky
• Total water vapor along LOS path(vap)
• 31tbsky
• Total liquid water along LOS path(liq)

• Total water vapor along LOS path(vap)
• Total liquid water along LOS path(liq)
• 31tbsky
• 23tbsky

• Total water vapor along LOS path(vap)
• Total liquid water along LOS path(liq)
• 31tbsky
• 23tbsky

• Total liquid water along LOS path(liq)
• 31tbsky
• Total water vapor along LOS path(vap)
• 23tbsky

• 31tbsky
• Total liquid water along LOS path(liq)
• Total water vapor along LOS path(vap)
• 23tbsky

• Total water vapor along LOS path(vap)
• 23tbsky
• Total liquid water along LOS path(liq)
• 31tbsky

• 23tbsky
• Total liquid water along LOS path(liq)
• Total water vapor along LOS path(vap)
• 31tbsky

SGP/MWR/B6/C1 - Instrument moved, tip field of view not clear

During the water vapor IOP in September 1997 it was observed that the
ARM MWR reported about 2 mm more water vapor than other sensors.  Unlike
the 1996 WVIOP, only one ARM MWR was used.  To assess the performance of 
the MWR used during the 1997 WVIOP, it was recomended that another ARM MWR
should be operated in close proximity to the unit at the SGP central
facility.

Last week SGP operations staff set up MWR 18, normally located at
BF-6 (Purcell), in proximity to MWR 10 at the SGP central facility
near Lamont, OK.  I travelled to Oklahoma to carry out the comparison
of the radiometers.  Although it rained or was cloudy until Thursday
evening, I was able to make a good comparison.  The results are summarized
below and in the attached GIF plots.

On or a about 20 November 1996 (after the 1996 WVIOP) a 10-m tower was
erected approximately 200 feet south of the MWR and directly in the
plane of the elevation scan used during tip mode.  The top of the tower
has an elevation angle of about 10 degrees relative to the radiometer
position, whereas the lowest tip angle is 19.5 degrees.  However, the
first sidelobe in the antenna pattern is 11 degrees from center, so it
is possible that the tips were influenced by the tower.  Looking back
at the calibration data it appears that the quality of the tips
deteriorated in 1997.  I had to lower the acceptance criterion from
R=0.995 to R=0.990 in order to get a reasonable number of tips.  (R is
the correlation coefficient of the Langley regression of opacity vs
airmass; 1.00=perfect co-linearity.) The situation worsened as the
ambient temperature increased, which supports the notion of tower
contamination.

Much to my surprise, rotating the radiometers 90 degrees so that they
could not view the tower did not greatly affect the derived brightness
temperatures or PWV and LWP estimates, although the quality of the tip
curves did dramatically increase (e.g. the R values were in the range
0.995-0.999).  This is revealed in plot1.gif which presents the PWV and
LWP dervied from both radiometers and the PWV from the radiosondes.

NOTE that the difference between the radiometers and the radiosondes
depends strongly on the sonde calibration lots.  Note that during the
1997 WVIOP sondes from lots 733 and 726 (weeks 33 and 26 of 1997) were
launched.  These were very close in time to lots 729, 730 and 735
launched last week which also showed a bias of about -2 mm relative to
the MWR.

The brightness temperatures derived from the tip curves are presented
in plot2.gif.  These reveal a slight offset (0.3-0.5 K) in both
channels, with MWR 18 (Purcell) higher.  I suspect that this may be due
to the temperature sensors in the blackbody target.  In MWR 18 the two
sensors are offset by about 0.75 K, whereas in MWR 10 the offset is
only about 0.25 K.  I use the average of the two readings in
calculating the brightness temperature, so an error of 0.3-0.5 K could
result if one sensor is high.  The sondes exhibit the same
batch-dependent behavior as in plot1.gif.

Brightness temperature differences at each pair of elevation angles are
presented in plot3a.gif and plot3b.gif for MWR 10 and 18 respectively.
The orientation of the radiometer and the direction of the differences
are printed along the bottom of the plot. For example, E-W means that
the scan is from east to west and the differences are east minus west.
These reveal several things:

1. I located the radiometers too close to each other in the north-south
   plane.  When both radiometers were scanning East-West, MWR 18, which
   was east of MWR 10, was in the sidelobe of the MWR 10 antenna
   pattern, as indicated by the large differences for 10 when the
   differences for 18 were small.  Rotating MWR 10 180 degrees to scan
   west-east moved its antenna about 2 feet farther north and its
   differences dramatically decreased and were the mirror image of
   those from MWR 18.

2. Although the polycarbonate foam window on MWR 10 was significantly
   weathered and more so on one side than the other, replacing the
   window did not noticeably affect the measurements.  (I initially 
   thought that the window was the cause of the large differences and
   later discovered that the radiometers were too close together.)

3. Significant east-west or north-south differences resulted in only
   small (~0.5 K) offsets in the derived brightness temperatures.
   (Note the change in brightness temperature differences in plot3a.gif
   at 05:00 on day 121 when MWR 10 was rotated 180 degrees to scan
   west-east and then examine the corresponding changes in TB or PWV
   and LWP in plot1.gif and plot2.gif.)

The results of the September 1997 and May 1998 calibrations
for MWR 10 are presented below.

  Date          R min  N tips   TND23    tc23  dev23    TND31    tc31   dev31
                                 (K)     (K/K)  (K)      (K)     (K/K)  (K)
26-30 Sep 97	0.990	 408	205.45	-0.079	0.36	191.02	-0.031	0.20
01-04 May 98	0.995	2768	205.27	-0.074	0.39	189.41	-0.011	0.27

There appears to have been a significant change in the 31 GHz (liquid-
sensing) channel calibration since the IOP.  However, the 23 GHz
(vapor-sensing) channel calibration does not appear to have changed.
Moreover, reprocessing the September 1997 data using the May 1998
calibration reduces the PWV by only about 0.4-0.5 mm but introduces a
significant bias (0.04 mm) in the LWP.  Thus, the May 1998 calibration
does not appear to be appropriate for September 1997.

The bottom line is that there does NOT appear to be any problem with
MWR 10 at the Central Facility.  The agreement between the two MWRs is
within the manufacturer's specification, although it does appear that
one of the temperature sensors in the blackbody target on MWR 18 may
need to be replaced or recalibrated.  From now on tip curves at the CF
should be done west-east rather than north-south to avoid any possible
influence of the SIRS tower.

• tkbb
• bbn31
• bb23
• wet_window
• 23tbsky
• Total water vapor along LOS path(vap)
• bb31
• tnd23
• actel
• Temperature, brightness, longwave(ir_temp)
• Total liquid water along LOS path(liq)
• lat
• tkxc
• bbn23
• tnd31
• sky31
• lon
• tkair
• tc23
• alt
• sky23
• 31.4 GHz sky brightness temperature(tbsky31)
• Radiation, longwave, brightness temperature, 23.8 GHz(tbsky23)
• actaz
• Temperature, Sky Infra-Red(sky_ir_temp)
• tc31
• tknd
• time_offset
• tnd_nom31
• base_time
• tnd_nom23
• 31tbsky

• actel
• 23skyn
• 23unoise
• bbn23
• 31bbn
• sky23
• tnd23
• 31bb
• Radiation, longwave, brightness temperature, 23.8 GHz(tbsky23)
• time_offset
• 23sky
• 23bbn
• bb23
• tnd31
• alt
• tkbb
• losn
• lon
• 23tbsky
• bbn31
• bb31
• Total water vapor along LOS path(vap)
• 23bb
• temperature_correction_coef_31
• noise_injection_temp_31
• actaz
• Total liquid water along LOS path(liq)
• lat
• tkxc
• base_time
• 31unoise
• wet_window
• 31sky
• noise_injection_temp_23
• temperature_correction_coef_23
• tkair
• sky31
• 31.4 GHz sky brightness temperature(tbsky31)
• tknd
• 31tbsky
• Temperature, brightness, longwave(ir_temp)
• 31skyn

• 23tipbb
• 31r
• alt
• 31tbzenith
• 23gain
• 31expave
• 23tbzenith
• 31tipskynd
• time_offset
• base_time
• 23bb
• 31bb
• 31ndiode
• tkxc
• lat
• tipn
• 31tipbb
• 23ndiode
• 31gain
• 23r
• airm
• actel
• actaz
• 23expave
• 23tipsky
• wet_window
• 31tipsky
• 31bbn
• 23bbn
• 23tipskynd
• tkbb2
• tkbb1
• lon
• Temperature, brightness, longwave(ir_temp)

• 23r
• tipsky23
• lon
• airm
• r31
• 23bb
• 23tipsky
• Temperature, brightness, longwave(ir_temp)
• r23
• 31bbn
• actaz
• tipsky31
• 31bb
• 23gain
• 31ndiode
• base_time
• tipn
• bbn31
• 23tbzenith
• 31tbzenith
• 23tipskynd
• 23expave
• bbn23
• time_offset
• tnd31I
• 23tipbb
• 31tipbb
• tkxc
• 31gain
• 23ndiode
• actel
• bb23
• tkbb2
• tkbb1
• 31expave
• bb31
• tnd23I
• wet_window
• 31r
• alt
• 31tipsky
• lat
• 23bbn
• 31tipskynd

SGP/MWR/C1 - Erroneous internal temperature

After the new internal temperature sensor was installed it was discovered
that the scaling resistor was incorrect.  (The 24.9 kohm 0.1% resistor
had accidently been replaced with a 24.0 kohm resistor when the analog
board was repaired by the manufacturer several years ago.)  A resistor
having the correct value was installed 981112.

• tkair

• tkair

• tkair