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 - 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
• 23.8 GHz sky brightness temperature(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/TSI/C1 - Birds obstructing view

Birds were frequently in the the field-of-view and soiling the mirror, affecting the 
visible sky image and resulting processed cloud fraction image. Bird deterant spikes were 
installed on top of the camera housing and arm on 5/16 which prevented their perching on the 
camera so that the impact on the sky image was reduced. But birds were still present 
around the edges of the mirror until additional spikes were installed on top of the four 
corners of the enclosure on 6/14.

• Cloud decision images, Total Sky Imager, PNG format(png)

• JPEG data stream - documentation not yet available

• MPEG data stream - documentation not yet available

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 - 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)