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RTTOV-7: A satellite radiance simulator for the new

millennium

What is RTTOV Latest developments from RTTOV-6 to 7Validation results for RTTOV-7 How to get it

R Saunders, M Matricardi, P BrunelS English and G Deblonde

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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

M Matricardi New transmittance predictors/AIRS

F Chevallier Diverse profile datasets V Sherlock Gastropod for AIRS simulations T Kleespies Inclusion of OPTRAN in RTTOV

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Fast Model Approaches (profile TOA radiances)

Linear regression (profile optical depth)– On fixed pressure levels

– On fixed absorber overburden layers (OPTRAN)

Physical method Look up tables Neural nets

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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 RTTOV-6 released in Apr 2000 SAF report RTTOV-7 released Feb 2002 SAF report

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RTTOV-6 model 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)

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 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

HIRS 0 1 to 19MSU 1 1 to 4SSU 2 1 to 3

AMSU-A 3 1 to 15AMSU-B 4 1 to 5AVHRR 5 3b to 5SSMI 6 1 to 7

VTPR1 7 1 to 8VTPR2 8 1 to 8

TMI 9 1 to 9SSMIS 10 1 to 24

AIRS 11 1 to 2378MODIS 13 1 to 17ATSR 14 1 to 3MVIRI 20 1 to 2SEVIRI 21 4 to 11

GOES-Imager 22 1 to 4GOES-Sounder 23 1 to 18

GMS imager 24 1 to 2FY2-VISSR 25 1 to 2FY1-MVISR 26 1 to 3

*channels 19-23 are not simulated accurately

Italics RTTOV-7only

Sensor Chan #

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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

HIRS1-20

AMSU21-40

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Validation of radiances

HIRSHIRS1-20

AMSU21-40

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Validation of jacobians

HIRS1-20

AMSU21-40

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Garand fast modelintercomparison forHIRS channels

RTTOV 5 and 6

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SSMI(S) FiltersChannelNumber

CenterFrequency

(GHz)

1st IF(MHz)

2nd IF(MHz)

Bandwidth*per passband

(MHz)

Polariza-tion

EFOV**along scan

(km)

EFOV** 90 to scan

(km)

NeT (K)for 305KScene*

1 50.3 0. 0. 380.0 H 17.6 27.3 0.212 52.8 0. 0. 388.8 H 17.6 27.3 0.203 53.596 0. 0. 380.0 H 17.6 27.3 0.214 54.40 0. 0. 382.5 H 17.6 27.3 0.205 55.50 0. 0. 391.3 H 17.6 27.3 0.226 57.29 0. 0. 330.0 H 17.6 27.3 0.267 59.4 0. 0. 238.8 H 17.6 27.3 0.258 150.0 1250. 0. 1642. H 13.2 15.5 0.539 183.31 6600. 0. 1526. H 13.2 15.5 0.56

10 183.31 3000. 0. 1019. H 13.2 15.5 0.3911 183.31 1000. 0. 512.5 H 13.2 15.5 0.3812 19.35 0. 0. 355.0 H 44.8 73.6 0.3513 19.35 0. 0. 356.7 V 44.8 73.6 0.3414 22.235 0. 0. 407.5 V 44.8 73.6 0.4515 37.0 0. 0. 1615. H 27.5 45.0 0.2616 37.0 0. 0. 1545. V 27.5 45.0 0.2217 91.655 900. 0. 1418. V 13.2 15.5 0.1918 91.655 900. 0. 1411. H 13.2 15.5 0.1919 63.283248 285.271 0. 1.36 H+V 17.6 27.3 1.2320 60.792668 357.892 0. 1.35 H+V 17.6 27.3 1.1821 60.792668 357.892 2. 1.29 H+V 17.6 27.3 0.8622 60.792668 357.892 5.5 2.62 H+V 17.6 27.3 0.5823 60.792668 357.892 16. 7.32 H+V 17.6 27.3 0.3724 60.792668 357.892 50. 26.5 H+V 17.6 27.3 0.38

* measured for this unit prior to launch** raw data resolution (prior to on-board averaging) based on measured half-power beamwidth andspacecraft altitude of 833 km

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SSMIS brightness temps

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Validation of jacobians

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NWP O-B scan angle statsRTTOV-5 RTTOV-7

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Validation of HBHT

RTTOV-5

RTTOV-7

Model background erroras HIRS-12 radiance

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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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RTTOV-7 now available with improved water vapour and ozone simulation for both IR and MW channels

Smoother jacobians better assimilation More realistic cloudy radiances can be

computed using RTTOVCLD routines Improved simulation of MW surface emissivity AIRS/SSMIS/FY radiance simulation included

Summary

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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 Distributionhttp://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)