Thomas J. Kleespies
NOAA/NESDIS
Camp Springs MD USA
ITSC 12 5 March 2002
The Merger of OPTRAN and RTTOV: The Best of Both Worlds

• Informal comparisons with R. Saunders of
OPTRAN with RTTOV suggested that
– 1) OPTRAN performed better with water vapor
– 2) RTTOV performed better with mixed gases
• It seems obvious that an attempt should be made to merge the two
ITSC 12 5 March 2002
The Merger of OPTRAN and RTTOV: The Best of Both Worlds

• Used different line by line
• Used different dependent atmospheres
• Used different number of levels
• No serious independent comparison for
OPTRAN
• This work corrects most of these deficiencies
ITSC 12 5 March 2002
The Merger of OPTRAN and RTTOV: The Best of Both Worlds

• Performs regression on fixed pressure levels
• Optical depth is the predictand
ITSC 12 5 March 2002
The Merger of OPTRAN and RTTOV: The Best of Both Worlds

RTTOV
PRFIN
PRFTAU
OPDEP
RTTOV
RTTAU RTINT
RTTOV
Calls PRFIN to unpack state vector
Calls OPDEP to compute optical depths
Calls RTTAU to compute transmittances
Calls RTINT to compute radiances and brightness temperatures
PRFIN
Unpacks input state vector
Calls PRFTAU to compute predictors
PRFTAU
Computes predictors
OPDEP
Computes optical depth
RTTAU
Computes transmittances
RTINT
Integrates the radiative transfer equation to produce radiances and brightness temperatures
ITSC 12 5 March 2002
The Merger of OPTRAN and RTTOV: The Best of Both Worlds

• Regression is performed on levels of absorber amount
• Predictand is absorption coefficient, easily combined with absorber amount to give optical depth
ITSC 12 5 March 2002
The Merger of OPTRAN and RTTOV: The Best of Both Worlds

OPTRAN2 Double Interpolation
(Original OPTRAN)
OPTRAN2
OPTRAN_SPECIES
Transmittance Driver.
Set up coefficients on first invocation.
Compute absorber profile.
Call OPTRAN_SPECIES to compute optical depths.
Compute transmittances from optical depths.
Find levels in absorber space that bracket input profile.
Call GET_PREDICTORS_ALL to compute predictors.
Compute absorption coefficients in absorber space.
Interpolate absorption coefficients to pressure space.
Compute optical depth in pressure space.
GET_PREDICTORS_ALL
Compute predictors in absorber space.
ITSC 12 5 March 2002
The Merger of OPTRAN and RTTOV: The Best of Both Worlds

OPTRAN1 Single Interpolation
OPTRAN1
OPTRAN_SPECIES
Transmittance Driver.
Set up coefficients on first invocation.
Compute absorber profile.
Call OPTRAN_SPECIES to compute optical depths.
Compute transmittances from optical depths.
Find levels in absorber space that bracket input profile.
Call GET_PREDICTORS_ALL to compute predictors on pressure levels.
Compute absorption coefficients by interpolating regression coefficients from absorber space to pressure space.
Compute optical depth in pressure space.
GET_PREDICTORS_ALL Compute predictors in pressure space.
ITSC 12 5 March 2002
The Merger of OPTRAN and RTTOV: The Best of Both Worlds

• Merge OPTRAN into the RTTOV 6.7 framework
• Permit switching of individual absorbers between OPTRAN and RTTOV
• Permit switching off individual absorbers
• Perform a ‘clean test’ comparison
ITSC 12 5 March 2002
The Merger of OPTRAN and RTTOV: The Best of Both Worlds

OPTRAN1-RTTOV
PRFIN
PRFTAU
GET_PREDICTORS_ALL
OPDEP
RTTOV
RTTAU
OPTRAN_SPECIES
RTINT
RTTOV
Calls PRFIN to unpack state vector
Calls OPDEP to compute optical depths
Calls RTTAU to compute transmittances
Calls RTINT to compute radiances and brightness temperatures
PRFIN
Unpacks input state vector
Computes absorber profile (vice OPTRANS)
Calls PRFTAU to compute predictors
PRFTAU
Computes predictors.
Find levels in absorber space that bracket input profile
(vice OPTRANS_SPECIES).
Calls GET_PREDICTORS_ALL.
OPDEP
Computes optical depth
Calls OPTRANS_SPECIES
Code is switchable between OPTRAN and RTTOV for each absorbing species: UMG, H2O, O3 RTTAU
Computes transmittances
RTINT
Integrates the radiative transfer equation to produce radiances and brightness temperatures
ITSC 12 5 March 2002
The Merger of OPTRAN and RTTOV: The Best of Both Worlds

“If you’ve made up your mind to test a theory, or you want to explain some idea, you should always decide to publish it whichever way it comes out. If we only publish results of a certain kind, we can make the argument look good. We must publish both kinds of results.”
Richard Feynman
ITSC 12 5 March 2002
The Merger of OPTRAN and RTTOV: The Best of Both Worlds

Independent Profile Mean Error
0.3
0.2
0.1
OPTRAN1
OPTRAN2
RTTOV
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
-0.1
-0.2
-0.3
NOAA 16 HIRS Channel
Independent Profile Mean Error
0.3
0.2
0.1
OPTRAN1
OPTRAN2
RTTOV
-0.2
-0.3
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
-0.1
NOAA 16 AMSU Channel
ITSC 12 5 March 2002
The Merger of OPTRAN and RTTOV: The Best of Both Worlds

Independent Profile Std Error
1.4
1.2
1
0.8
0.6
0.4
OPTRAN1
OPTRAN2
RTTOV
0.2
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
NOAA 16 HIRS Channel
Independent Profile Std Error
0.25
0.2
0.15
0.1
0.05
OPTRAN1
OPTRAN2
RTTOV
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
NOAA 16 AMSU Channel
ITSC 12 5 March 2002
The Merger of OPTRAN and RTTOV: The Best of Both Worlds

HIRS9 Fit to dependent data
1.00
0.90
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.00
Regression
OPTRAN1
OPTRAN2
ITSC 12 5 March 2002
The Merger of OPTRAN and RTTOV: The Best of Both Worlds

Independent Profile Mean Error
RTTOV for UMG and O3, indicated for H2O
0.3
0.2
0.1
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
-0.1
-0.2
OPTRAN1
OPTRAN2
RTTOV
-0.3
NOAA 16 HIRS Channel
Independent Profile Mean Error
RTTOV for UMG and O3, indicated for H2O
-0.03
-0.04
-0.05
-0.06
0.04
0.03
0.02
0.01
0
-0.01
-0.02
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
OPTRAN1
OPTRAN2
RTTOV
NOAA 16 AMSU Channel
ITSC 12 5 March 2002
The Merger of OPTRAN and RTTOV: The Best of Both Worlds

Independent Profile Std Error
RTTOV for UMG and O3, indicated for H2O
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
OPTRAN1
OPTRAN2
RTTOV
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
NOAA 16 HIRS Channel
Independent Profile Std Error
RTTOV for UMG and O3, indicated for H2O
0.18
0.16
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
OPTRAN1
OPTRAN2
RTTOV
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
NOAA 16 AMSU Channel
ITSC 12 5 March 2002
The Merger of OPTRAN and RTTOV: The Best of Both Worlds

Temperature Jacobians Atm 116
K code
0
600
800
200
400
1000
0.000
0.050
0.100
0.150
dTb/dT
0.200
ITSC 12 5 March 2002
The Merger of OPTRAN and RTTOV: The Best of Both Worlds
O4
R4
O26
R26
O39
R39
O10
R10
O15
R15
0.250

0
0
Brute Force
Brute Force
0.100
dTb/dq dTb/dq
0.100
ITSC 12 5 March 2002
The Merger of OPTRAN and RTTOV: The Best of Both Worlds
O10
R10
O11
R11
O12
R12
O10
R10
O11
R11
O12
R12

600
800
1000
0.000
0
200
400
0.050
Brute Force
AMSU-B Water Vapor Jacobians Atm 116
0.100
dTb/dq
0.150
0.200
O38
R38
O39
R39
O40
R40
0.250
ITSC 12 5 March 2002
The Merger of OPTRAN and RTTOV: The Best of Both Worlds

• RTTOV/OPTRAN1 with TL,AD,K done
• RTTOV/OPTRAN2 only forward model
• Nagging question of OPTRAN1/2 ozone
• H
2
O Jacobians incorrect
ITSC 12 5 March 2002
The Merger of OPTRAN and RTTOV: The Best of Both Worlds

NWP models have to interpolate to RTTOV model levels
NWP models do not have to interpolate to OPTRAN levels, this is done internally.
These comparisons to LBL data on RTTOV levels give a bit in favor to RTTOV.
A clean test would compare the two within the context of NWP analysis, or independent profiles with arbitrary pressure levels.
ITSC 12 5 March 2002
The Merger of OPTRAN and RTTOV: The Best of Both Worlds

• OPTRAN H2O combined with to
RTTOV UMG&O3 improves overall performance for most channels.
•This may be a moot point given the results of Matricardi et al.
ITSC 12 5 March 2002
The Merger of OPTRAN and RTTOV: The Best of Both Worlds

This work was sponsored by the SAF-NWP, The
Metoffice, Bracknell UK. Appreciation to Roger Saunders and others who made my visit a memorable experience.
ITSC 12 5 March 2002
The Merger of OPTRAN and RTTOV: The Best of Both Worlds

ITSC 12 5 March 2002
The Merger of OPTRAN and RTTOV: The Best of Both Worlds