Background

Since 2005, ECMWF has generated model-simulated satellite images out to five days from the 00 UTC and 12 UTC  cycles of the operational HRES forecast for all operational geostationary satellites operated by EUMETSAT (e.g., Meteosat-7/8/9/10), NOAA (e.g., GOES-8/10/11/12/13/15) and JMA (e.g., MTSAT-1R/2). The simulated images are archived in MARS as GRIB edition 1 files and have been presented on the ECMWF website as image files. The forecast-generated satellite images have been based on the resolution of the HRES global model with 3-hourly output from T+0 to T+48 and 6-hourly output to T+120.

Up to and including IFS cycle 41r1, the satellite images in both the atmospheric window and water vapour regions were simulated over each of the 5 geostationary satellite’s disk. Simulated brightness temperatures at a number of wavelengths/bands were calculated using the same radiative transfer algorithm (e.g., RTTOV-11) as in the operational data assimilation and using the relevant atmospheric model profiles (temperature, specific humidity, ozone mass mixing ratio, cloud cover, specific cloud liquid water content, specific cloud ice water content, specific rain water content, specific snow water content) and the relevant surface parameters (skin temperature, 10m u and v wind components, 2m temperature and 2m dewpoint temperature, volumetric soil water layer 1, convective available potential energy).

Errors in simulated satellite images can derive from errors in the NWP parameters, on which the simulation is based, the resolution of the model and RTTOV model performance.

Updates to the simulated satellite data at IFS cycle 41r2

The simulated satellite data at IFS cycle 41r2 have been enhanced in various aspects.

• Global satellite images capturing detailed cloud and/or humidity features
  The new simulated satellite data product shows the high-resolution ECMWF forecasts as a weather satellite would see it (e.g. Meteosat-10). The new simulated satellite image product includes latitudes greater than 60° north and south, extending the geostationary-type imagery over high-latitude regions. The previous satellite image products were limited to the disk domains of the respective geostationary satellites.

• Nadir view for every model grid point
  The new simulated satellite data assume a nadir view for every model grid point so the effect of looking slantwise through the atmosphere is neglected. Consequently the atmosphere appears less opaque than with the old simulated images.
  
  
• Produced in post-processing within the IFS, with no mapping on satellite grid
  This is a technical advantage of the new simulated satellite data being now produced in the post-processing within the IFS and being part of the research tests for operational release to validate model developments which affect the temperature and moisture fields.
  
  
• Availability of the simulated satellite data in MARS
  The new simulated satellite data products are archived in MARS in GRIB edition 2 and are available at every post-processing step, out to 240 hours: 3 hourly from T+0 to T+144 and 6 hourly from T+150 to T+240. The previous satellite image products were available in GRIB edition 1, to T+120 only.
  
  
• Availability of the simulated satellite data in ECMWF Catalogue and dissemination in the future
  The timeliness of delivery is optimal for dissemination. The addition of the new simulated satellite data products to the ECMWF Catalogue will be proposed. It will not be available to commercial customers / researchers until then.

At present only Meteosat-10-like simulated satellite data are available. The central wavelength of the channels on other geostationary platforms is quite close to those selected to be produced, archived and disseminated based on the Meteosat-10-like data.

Example images

48-hour global simulated Meteosat-10 SEVIRI imagery at 10.8 μm (channel 9) from the ECMWF model cycle 41r2 at TCO1279 / O1280 horizontal resolution with 137 vertical levels run on 1 March 2016 at 00 UTC.	48-hour global simulated Meteosat-10 SEVIRI imagery at  6.30 μm (channel 5)from the ECMWF model cycle 41r2 at TCO1279 / O1280 horizontal resolution with 137 vertical levels run on 1 March 2016 at 00 UTC.

Animation of 10 day global simulated Meteosat-10 SEVIRI imagery at 10.8 μm (channel 9) from the ECMWF model cycle 41r2 at TCO1279 / O1280 horizontal resolution with 137 vertical levels run on 1 March 2016 at 00 UTC.	Animation of 10 day global simulated Meteosat-10 SEVIRI imagery at  6.30 μm (channel 5)from the ECMWF model cycle 41r2 at TCO1279 / O1280 horizontal resolution with 137 vertical levels run on 1 March 2016 at 00 UTC.

Simulated satellite data as ECMWF web charts

Images produced from the simulated satellite data are available as ECMWF medium-range forecast charts on the web as Model simulated satellite images (Authorisation required).

Availability of the simulated satellite data in MARS

The simulated satellite data are archived in MARS under TYPE=SSD (Simulated Satellite Data).  They can be viewed in the MARS Catalogue at:

• Simulated Satellite Data from the HRES Forecasts (STREAM=OPER, CLASS=OD, TYPE=SSD)   (Authorisation required)

A sample MARS request for retrieving the fields at all post-processing time steps of a single forecast is:

RETRIEVE,
    STREAM     = OPER,
    CLASS      = OD,
    EXPVER     = 0001,
    DATE       = -1,
    TIME       = 12,
    TYPE       = SSD,
    IDENT      = 57,
    INSTRUMENT = 207,
    PARAM      = 260510,
    CHANNEL    = 9,
    STEP       = 0/TO/144/BY/3,
    TARGET     = "meteosat-10.channel9.grib2"
RETRIEVE,
    STEP       = 150/TO/240/BY/6,
    TARGET     = "meteosat-10.channel9.grib2"

The fields are stored on the model O1280 octahedral reduced Gaussian grid.  Any MARS post-processing keywords, such as AREA or GRID can be applied to the request to interpolate the fields to lower resolutions or geographical sub-areas.

Availability of the simulated satellite data in dissemination

The simulated satellite data will be available in dissemination.  Initially, the products will be made available to ECMWF Member and Co-operating States.  Availability in the real-time catalogue will need to be discussed and possibly agreed by ECMWF Committees.

Technical information

The simulated satellite data are specified using the satellite identifier, instrument, channel number and central wavelength as given in the WMO Manual on codes:

• COMMON CODE TABLE C–5: Satellite identifier

• COMMON CODE TABLE C–8: Satellite instruments

.  For the simulated satellite data based on Meteosat-10 these are as in the table below:

GRIB encoding

The simulated satellite data fields are encoded in GRIB edition 2 with the parameter set to Cloudy brightness temperature:

The product description uses productDefinitionTemplateNumber=32 (analysis or forecast at a horizontal level or in a horizontal layer at a point in time for simulated (synthetic) satellite data.  The relevant GRIB API keys are encoded as:

Other GRIB API keys describing the product are:

GRIB API version at least 1.14.5 needs to be used in order to decode the simulated satellite data products.

History of simulated satellite images at ECMWF

Prior to the implementation of IFS cycle 41r2, the simulated satellite image data were stored in MARS with TYPE=SIM and REPRES=SV (Space View) for the IDENT, INSTRUMENT and CHANNEL as specified in the table below.

These products have been encoded using GRIB edition 1.

An example MARS request for retrieving the old-style (pre-IFS cy41r2) simulated satellite images at all post-processing time steps to day 5 and for a forecast date "YYYYMMDD" prior to 20160308 is:

RETRIEVE,
    CLASS = OD, 
    TYPE = SIM,
    STREAM = OPER,
    EXPVER = 0001,
    REPRES = SV,
    DATE = YYYYMMDD,
    TIME = 0000,
    STEP = 0/3/6/9/12/15/18/21/24/27/30/33/36/39/42/45/48/54/60/66/72/78/84/90/96/102/108/114/120,
    DOMAIN = G,
    CHANNEL = 9,
    IDENT = 57,
    INSTRUMENT = 207,
    TARGET = ”old_simulated_meteosat-10.channel9.grib”