RTTOV-7: A satellite radiance simulator for the
new millennium
R Saunders, M Matricardi, P Brunel
S English and G Deblonde
 What is RTTOV
 Latest developments from RTTOV-6 to 7
Validation results for RTTOV-7
 How to get it
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Acknowledgements
NWP Satellite Application Facility
A Collard, P Rayer, S English,
E Carroll/F Smith
M Matricardi, F Chevallier, G Kelly,
Erik Andersson, D Salmond
P Brunel
G Deblonde, V Sherlock, T Kleespies
EUMETSAT for partial funding
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Other RTTOV related talks/posters
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
M Matricardi New transmittance predictors/AIRS

F Chevallier Diverse profile datasets

V Sherlock Gastropod for AIRS simulations

T Kleespies Inclusion of OPTRAN in RTTOV
3
Fast Model Approaches
(profile TOA radiances)

Linear regression (profile  optical depth)
– On fixed pressure levels
– On fixed absorber overburden layers (OPTRAN)
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
Physical method

Look up tables

Neural nets
4
History of RTTOV
RTTOV-3 released in 1993 by ECMWF Eyre, (1991)

– 40 levels mixed gases, 15 levels H2O
– Based on 32 NESDIS profile dataset and ITPP TOVSRAD
RTTOV-5 released in 1999 Saunders et al (1999)

– 43 levels for mixed gases, H2O and O3.
– Based on 43 TIGR profile dataset and GENLN2/MPM-89/92
– FASTEM
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
RTTOV-6 released in Apr 2000 SAF report

RTTOV-7 released Feb 2002 SAF report
5
RTTOV-6 model
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
Statistical regression of layer optical depths with profile variables on fixed
pressure levels for mixed gases, water vapour and ozone

IR optical depths based on GENLN2, HITRAN-96/CKD2.1 in range 500 - 3000
cm-1

MW optical depths based on MPM 89/92 Line by Line models

43 diverse TIGR profile dataset used to compute coeffs for model
(dependent set)
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RTTOV-6 model (cont)
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
Includes fast surface emissivity models (ISEM for IR and FASTEM for MW) at
least over water, more work needed over land

Includes simplistic treatment of cloud

Code written in F77 & F90 and available through SAF (RTTOV-6 has > 40
users worldwide including major NWP centres)

Variety of different sensors supported (next slide)
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Recent RTTOV developments
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
Improved water vapour and ozone optical depth predictors (ECMWF)

Multi-layer clouds, more realistic emissivities and random overlap assumption have been
added for both IR and MW External routines (ECMWF)

Update of microwave sea surface emissivity model FASTEM to FASTEM-2 (METO/MSC)

Inclusion of cosmic background radiation (MSC)

Addition of high spectral resolution sounders (ECMWF) and SSMI(S) (MSC/METO)

Code rewritten in standard F90,vectorised and made threadsafe (MeteoFrance/ECMWF)

Separate coefficient files for each sensor (MeteoFrance)

New web site (METO)
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Satellite sensors supported by RTTOV-6/7
Chan #
Sensor
HIRS
MSU
SSU
AMSU-A
AMSU-B
AVHRR
SSMI
VTPR1
VTPR2
TMI
SSMIS
AIRS
MODIS
ATSR
MVIRI
SEVIRI
GOES-Imager
GOES-Sounder
GMS imager
FY2-VISSR
FY1-MVISR
*channels 19-23 are not simulated accurately
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0
1
2
3
4
5
6
7
8
9
10
11
13
14
20
21
22
23
24
25
26
1 to 19
1 to 4
1 to 3
1 to 15
1 to 5
3b to 5
1 to 7
1 to 8
1 to 8
1 to 9
1 to 24
1 to 2378
1 to 17
1 to 3
1 to 2
4 to 11
1 to 4
1 to 18
1 to 2
1 to 2
1 to 3
Italics
RTTOV-7
only
How to validate RTTOV?
– Use an independent set of profiles (e.g. ECMWF diverse 117 profile set)
but with same LbL model computed transmittances
» Gives estimate of inherent model accuracy of trasmittances and TOA
radiances
– Fast model comparisons (e.g. Garand et al 2001, Gastropod) of
radiances and jacobians
» Gives performance of model compared to others
– Line-by-line model comparisons (e.g. ISSWG LIE)
» Gives estimate of underlying LbL model accuracy
– Comparisons with real satellite data using NWP fields
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Validation of AMSU-B transmittances
Dashed RTTOV-6; solid RTTOV-7
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Dependent vs independent statistics
HIRS
1-20
AMSU
21-40
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Validation of radiances
HIRS
HIRS
1-20
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AMSU
21-40
Validation of jacobians
AMSU
21-40
HIRS
1-20
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Garand fast model
intercomparison for
HIRS channels
RTTOV 5 and 6
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SSMI(S) Filters
Center
1st IF
2nd IF
Bandwidth*
PolarizaEFOV**
Frequency
(MHz)
(MHz)
per passband
tion
along scan
(GHz)
(MHz)
(km)
1
50.3
0.
0.
380.0
H
17.6
2
52.8
0.
0.
388.8
H
17.6
3
53.596
0.
0.
380.0
H
17.6
4
54.40
0.
0.
382.5
H
17.6
5
55.50
0.
0.
391.3
H
17.6
6
57.29
0.
0.
330.0
H
17.6
7
59.4
0.
0.
238.8
H
17.6
8
150.0
1250.
0.
1642.
H
13.2
9
183.31
6600.
0.
1526.
H
13.2
10
183.31
3000.
0.
1019.
H
13.2
11
183.31
1000.
0.
512.5
H
13.2
12
19.35
0.
0.
355.0
H
44.8
13
19.35
0.
0.
356.7
V
44.8
14
22.235
0.
0.
407.5
V
44.8
15
37.0
0.
0.
1615.
H
27.5
16
37.0
0.
0.
1545.
V
27.5
17
91.655
900.
0.
1418.
V
13.2
18
91.655
900.
0.
1411.
H
13.2
19
63.283248
285.271
0.
1.36
H+V
17.6
20
60.792668
357.892
0.
1.35
H+V
17.6
21
60.792668
357.892
2.
1.29
H+V
17.6
22
60.792668
357.892
5.5
2.62
H+V
17.6
23
60.792668
357.892
16.
7.32
H+V
17.6
24
60.792668
357.892
50.
26.5
H+V
17.6
* measured for this unit prior to launch
** raw data resolution (prior to on-board averaging) based on measured half-power beamwidth and
spacecraft altitude of 833 km
Channel
Number
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EFOV**
90 to scan
(km)
27.3
27.3
27.3
27.3
27.3
27.3
27.3
15.5
15.5
15.5
15.5
73.6
73.6
73.6
45.0
45.0
15.5
15.5
27.3
27.3
27.3
27.3
27.3
27.3
NeT (K)
for 305K
Scene*
0.21
0.20
0.21
0.20
0.22
0.26
0.25
0.53
0.56
0.39
0.38
0.35
0.34
0.45
0.26
0.22
0.19
0.19
1.23
1.18
0.86
0.58
0.37
0.38
SSMIS brightness temps
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Validation of jacobians
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NWP O-B scan angle stats
RTTOV-5
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RTTOV-7
Validation of HBHT
RTTOV-5
Model background error
as HIRS-12 radiance
RTTOV-7
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New water vapour spectroscopy
Using Toth revision of the water vapour spectroscopy, resulted
in a better agreement between observations and simulations
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Summary
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
RTTOV-7 now available with improved water vapour and ozone
simulation for both IR and MW channels

Smoother jacobians

More realistic cloudy radiances can be computed using RTTOVCLD
routines

Improved simulation of MW surface emissivity

AIRS/SSMIS/FY radiance simulation included
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better assimilation
Future plans  RTTOV-8

Improve interface with NWP model levels

Update LbL dependent transmittances with latest spectroscopy

Optimise predictors (number, robustness)

Improve fast land surface emissivity models and extend range of ISEM-6

Add solar reflection

Include precipitation in state vector for microwave

Add more variable gases (e.g. CH4, N2O, CO2)

Add IASI simulation capability
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RTTOV-7 Distribution
http://www.metoffice.com/research/interproj/nwpsaf/rtm/

Requests: email rttov.nwpsaf@metoffice.com or fax request to me on
+44-1344-854026

I will reply with a 2 page licence form to sign which you then fax to
number above

RTTOV-7 code is then distributed via ECMWF data services:
data.services@ecmwf.int on requested format/medium

Two formats:
» Compressed unix tar file of F90 code+files
» CDROM of F90 code+files

Media: ftp transfer or CDROM

Documentation + updates available from NWP-SAF web page above.

RTTOV-6 is also available (e.g. for F77 users)

Please give feedback on any bugs by email to: rttov.nwpsaf@metoffice.com
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RTTOV-7 Documentation/Updates
http://www.metoffice.com/research/interproj/nwpsaf/rtm/

Users guide (overview, installation, testing, interfaces)

Science and validation plan (overview of new science and links to papers/reports giving
more details, validation results documented here).

Technical report (details of software architecture, file formats and interfaces)

SAF reports on RTTOV (access from web page)

Bugs and fixes (alerts on RTTOV email list, details on web page)
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