# Presentation: 531446

## Developments of the fast RT model ‘OPTRAN’for High Spectral Sounder

**Yoshihiko Tahara (UCAR, JMA, NCEP)**
**Paul V. Delst (CIMSS, NCEP)**
**John C. Derber (NCEP)**
**Larry M. McMillin (NESDIS)**
**Xiaozhen Xiong (NESDIS)**
**Thomas J. Kleespies (NESDIS)**

## OPTRAN Meets Difficulty

**Absorption coefficient prediction**
**A huge number of equations**
**900,000 equations for 1000 channels**
**Difficult to validate all**
**Numerous coefficients**
**41 Mbytes for 1000 channels**
**A lot of computer resources**** **
**Difficult to introduce high spectral sensors**
**Difficult to keep updated**
**Difficult to be more developed**
**More absorbers, more predictors, more layers, etc**

## New Prediction Form

**  ****Coefficients traced over 300 layers by polynomial**
**Coefficients are reduced more than ****95%.**
**1 additional atmospheric predictor introduced**
**No**** vertical interpolation**

## Weight in Generating Trans Coef 

**Impossible to transfer all information of 300 equations to one**
**Weight transfers and preserves the essential information.**

**Trans**

**Error in**
**Abs Coef**

**Error in**
**Trans**

_**NOAA/HIRS Ch 3**_

**Weight**

## Atmospheric Predictors

**17 atmospheric predictors**
**2 new predictors**
**Q/T****2**** for wet continuum**
**P****1/4**** for Ozone**

## Choice of Predictors

**21778 predictor set possibilities for each gas and channel**
**Known unstable sets removed in advance**
**Stability is monitored by a stability index**
**Transmittance prediction error is monitored to select the best set.**

**Validated sets automatically**

**Less than 24 hrs to find best sets for**
**500 chs using 10 CPUs on IBM SP4**

## LBL Transmittances

**UMBC**** atmospheric profiles (for ****generating coefficients****)**
**48 profiles**
**101 levels (0.005 -- 1100 hPa)**
**CIMSS**** atmospheric profiles (for ****independent verification****)**
**32 profiles**
**101 levels (0.005 -- 1100 hPa)**
**Transmittances (Infrared)**
**LBLRTM Ver 6.12 with HITRAN2000 + AER updates**
**6 angles for each atmos profile**
**Sep 2002 AIRS SRFs**** for AIRS**
**Central frequencies generated based upon the SRFs**

## Comparison to Dependent

**S.D.**

**Bias**

## Comparison to Independent

**S.D.**

**Bias**

## Comparison to Real-time Data

**Ch 28**
**656.1**
**SD 0.76**
**MN –0.16**

**Ch 253**
**722.1**
**SD 0.39**
**MN +0.29**
**(clr sky)**

**Ch 1082**
**1036.5**
**SD 0.63**
**MN +0.33**
**(clr sky)**

**Ch 1756**
**1524.4**
**SD 1.22**
**MN +0.44**
**(clr sky)**

## Comparison to Real-time Data

**S.D.**

**Num**

**Bias**

## Impacts of New OPTRAN on Global Fcst (No AIRS, Preliminary)

**Impacts of New OPTRAN on Global Fcst ****(No AIRS, Preliminary)**

**NH**
**1000 Z**

**SH**
**1000 Z**

**SH**
**500 Z**

**NH**
**500 Z**

## Impacts of New OPTRAN on Global Fcst (No AIRS, Preliminary)

**Impacts of New OPTRAN on Global Fcst ****(No AIRS, Preliminary)**

**Trop**
**850 Vct Wind**

**Trop**
**200 Vct Wind**

## Conclusion

**Equations and coefficients are reduced significantly.**
**Predictor selection and inspection is automated.**
**Offline validation shows**
**Around 0.1 deg or less S.D. for most channels**
**0.2 – 0.3 deg S.D. for ozone channels**
**Small bias except ozone and WV channels in independent val.**
**Real-time data comparison shows**
**Stable calculation for AIRS 281 subset channels except 1**
**0.5 – 1 deg S.D. for dry and ozone, 0.5 – 1.3 deg S.D. for WV**
**Within plus minus 1 deg bias**
**Impacts of the new OPTRAN (without AIRS) on the NCEP global model are small positive or neutral over the extra tropics and neutral over the tropics.**