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 (i.e., Meteosat-7, Meteosat-10, MTSAT-2, GOES-13 and GOES-15). The simulated images are archived in MARS as GRIB edition 1 files and have been presented on the ECMWF website as PostScript 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 window and water vapour (WV) channels were simulated over each of the 5 geostationary satellite’s disk. Brightness temperatures 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 images at IFS cycle 41r2

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

• Global satellite images capturing detailed cloud and/or humidity features
  The new simulated images product shows the high-resolution ECMWF forecasts as a weather satellite will 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. This is an enhancement with respect to the previous satellite image product which was limited to the Meteosat-10 disk domain.

• Nadir view for every model grid point
  The new simulated satellite images 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 and so lower lying clouds and other features are better presented.
  
  
• Produced in post-processing within the IFS, with no mapping on satellite grid
  This is a technical advantage of the new simulated satellite images being now produced in the post-processing within the IFS and being part of the research tests for operational release. This is an enhancement with respect to the previous product generated only in the early delivery cycles of the operational suite as they can be now used routinely in ECMWF Research Department experiments to validate model developments which affect the temperature and moisture fields.
  
  
• Availability of the simulated satellite images in MARS
  The new images product 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+48,  6 hourly from T+54 to T+120 and  then 12 hourly from T+132 to T+240. This is an enhancement with respect to the previous  satellite image product available in GRIB edition 1, out to T+120.
  
  
• Availability of the simulated satellite images in ECMWF Catalogue and dissemination
  The timeliness of delivery is optimal for dissemination. The new simulated images will be added to the list of products that can be requested in dissemination.

For the time being only Meteosat-10-like simulated satellite data will be made available. The central wavelength of the channels on other platforms is quite close to those selected to be produced, archived and disseminated.

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.

Technical information

The simulated satellite data are specified using the satellite identifer, 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.

Availability of the simulated satellite images in MARS

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

• Simulated Satellite Data from the HRES Forecasts (STREAM=OPER, CLASS=OD, TYPE=SSD)   (Login 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       = 0/3/6/9/12/15/18/21/24/27/30/33/36/39/42/45/48/54/60/66/72/78/84/90/96/102/108/114/120/132/144/156/168/180/192/204/216/228/240,
    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 images in dissemination

History of simulated satellite images at ECMWF

Prior to the implementation of IFS cycle 41r2, the simulated satellite images 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”