SGP/MWR/B1 - 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 at SGP.B1 20020412.1600.  The 
MONORTM-based retrieval coefficients became active at SGP.B1 20050624.2100.

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.

• 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)

• vaptip
• liqtip

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

• mean_vap_mwr
• mean_liq_mwr

SGP/MWR/B1 - 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 9/13/2005 at 21:25. As a consequence 
of this upgrade, the tip curve frequency increased. The tip cycle time decreased from 
~60s to ~50s.

• tnd31
• bbn23
• tc23
• tknd
• tbskytip31
• liqtip
• vaptip
• r23
• tipsky23
• bb23
• tnd_nom31
• bbn31
• tc31
• tkbb
• tnd23
• tkxc
• tbskytip23
• r31
• tkair
• tnd23I
• tnd_nom23
• bb31
• tnd31I
• tipsky31

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