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JCSDA Briefing


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									Modeling Stratospheric Sounding Unit
   (SSU) Radiance in Reanalysis
Quanhua (Mark) Liu, Yong Chen, Paul van Dulst, and Yong Han
 Cooperative with NESDIS, NCEP, NASA, ECMWF scientists

                  November 7, 2007

Joint Center for Satellite Data Assimilation, Maryland, U.S.A
                 Satellite Data for Reanalysis

                         Previous generation             current generation

            SSU+MSU                               HIRS                        AMSU

SSU part: Dashed line is for 1/1/1995.
Red line is for 1/1/2003, indicate the shift of
the weighting function due to the leaking.
  Time series of a composite of 3 SSU channels and MSU channels 3 and 4

Averaged over 60º S to the South pole     Averaged over 60º N to the North pole
                          SSU Data
Stratospheric Sounding Unit data is a three-channel sensor onboard
NOAA series satellites (started from TIROS-N in 1978 and ended
at NOAA-14 in 2006).
The data in past 29 years is unique for middle and upper
stratospheric temperatures.

Using CO2 cell pressure modulation onboard satellite, the single
CO2 15 μm is split into 3 channels and shifted up to middle and
upper stratosphere.

In absent of a fast and accurate transmittance model, the SSU data has
    not been used in NCEP analysis and reanalysis.
             Sensor Response Function (SRF)

Different from a conventional sensor response function, the SSU SRF is a product
of traditional broadband and the CO2 cell absorption line responses.


                                                       CO2 cell

               Weighting Function

Split into 3 channels and shifted upward middle and upper stratosphere

           GSI model top height

                                            without CO2 cell
CO2 Leaking in cell pressure modulator

   This figure is from Dr. Shinya Kobayashi at ECMWF.
                              Error budget

Brindley et al. (1999) showed the variation of SSU brightness temperature at
channel 1 due to the leaking is between -0.3 and 0.3 K during entire SSU mission.
But, the variation for SSU channels 2 and 3 can be between 0.5 ~ 1.5 K
for single mission.
By considering the CO2 cell pressure as a variable in the CRTM,
this part error is < 0.1 K.

By choosing a constant CO2 concentration in a mission (e.g. NOAA-14),
the brightness temperature change for CO2 between 370 and 380 ppmv is 0.15 K.

The fitting error in the CRTM fast model against line-by-line model
is very small ( < 0.05 K).

The channel 3 is affected by the input atmospheric profile above the model height
(~0.2 hPa). The error is not quantitatively evaluated.
                             Comparisons between observation and modeling
                       260                                                                          270
                                std=0.87                                                                     std=1.78
                       250      bias=2.21                                                           260      bias=3.85
SSU ch.1 Cal.

                                                                                    SSU ch.2 Cal.
                       240                                                                          250
                       230                                                                          240
                       220                                                                          230
                       210                                                                          220
                       200                                                                          210
                       190                                                                          200
                          190    200         210    220   230     240   250   260                      200    210        220    230   240     250   260   270
                                                   SSU ch.1 Obs                                                                SSU ch.2 Obs

                       280                                                                            The peaks of the SSU weighting function
                       270       bias=0.74                                                            approximately locate at 15, 5, and 1.5 hPa.
       SSU ch.3 Cal.

                                                                                                      The simulated BT bias at channels 1 and 2
                       250                                                                            could be caused by a cold bias in
                       240                                                                            stratosphere in the NCEP analysis.
                                                                                                      The large scatters for channel 3 is partly
                          210      220       230    240    250    260   270   280                     due to the limited top height (~ 0.2 hPa)
                                                   SSU ch.3 Obs                                       in analysis.
       CO2 cell pressure effect on SSU observation

                                          US Standard       Tropic

                                                        SSU 1
       Difference (K)

                                                                                 Channel 1
                            106   108     110    112      114        116   118
                                        CO2 cell pressure (hPa)

The difference depends on both cell pressure and atmospheric state.
The difference for channels 2 and 3 are larger.
         Accomplishment and Future Work

1. We extended the CRTM to include the SSU radiance simulation.
2. The CRTM model takes care of the leaking problem by using the variable
  CO2 cell pressure calculated from satellite ID and analysis time.
3. The transmittance coefficients have been generated for
TIROS-N, NOAA-6, 7, 8, 9, 11, and 14.

Future works are to add extra layers above the GSI model height (~0.2 hPa).
It is also an issue, which relates to unrealistic radiance jacobi for some
of stratospheric channels in current CRTM model.

Support and help NCEP colleagues to implement the new CRTM in the reanalysis
system and maximize the usage of the SSU information content in reanalysis.

Including the atmospheric CO2 concentration in the CRTM.
                   Correction on atmospheric CO2 concentration

                                black for ch. 1
                                red for ch. 2
                   0.3          solid line for US Standard
                                dashed line for Tropic
Difference (K) .

                          330   335     340      345         350   355   360   365   370   375   380
                                                  CO2 concentration (ppmv)

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