Radiance simulator


Current version: v2.2, September 2019

The NWP SAF Radiance Simulator is a tool designed to support pre-launch scientific studies and pre-operational development work for new satellite instruments. It provides a straightforward means of generating simulated radiance datasets from NWP model analysis or background fields using the NWP SAF fast radiative transfer model RTTOV. In addition, it is increasingly being used in studies which require comparison of observed and simulated radiances and can be viewed as a tool for running RTTOV without having to write any code.


The radiance simulator performs the following functions:

Ingest of NWP model fields provided in common data formats.
This includes support for the following formats:

  • GRIB data from ECMWF
  • NetCDF data from ECMWF
  • GRIB data from the DWD ICON model
  • Met Office fieldsfiles / PP files
  • NWP SAF 60L profile dataset from ECMWF analyses
  • NWP SAF 91L profile dataset from ECMWF analyses
  • NWP SAF 137L profile dataset from ECMWF analyses

Model fields will consist of:

  • Level pressure
  • Temperature
  • Humidity
  • Ozone
  • Cloud liquid water
  • Cloud ice water
  • Rain
  • Snow
  • Cloud fraction
  • Air density
  • Surface wind
  • Surface skin temperature
  • Surface air temperature
  • Surface humidity
  • Sea-ice fraction
  • Orography
  • Land/sea mask

Some fields are optional depending on the input data format and chosen simulation options.

Ingest of observation files, and interpolation of model fields (optional).
The user may provide observation metadata including observation locations and viewing geometry and other fields to allow simulations to be performed at those locations. Model fields are interpolated to the given observation locations and, optionally, observation times. If no observation data are provided, simulations are performed at model profile locations.

Prepare input to, and run, radiative transfer model.
The model used in Radiance Simulator v2 is RTTOV v12. Depending on the availability of the required model fields, visible/near-infrared, infrared and microwave clear-sky and cloud simulations can be run. Most RTTOV options can be specified for the simulations. Solar radiation can be included, including use of the MFASIS fast visible cloud parameterisation. Simulations can also be run using PC-RTTOV and HTFRTC, the Principal Components based models available in RTTOV.

Output simulated data to a file.
Output fields include:

  • Top-of-atmosphere brightness temperatures/reflectances or radiances
  • Input observation data
  • Simulation meta-data
  • Surface emissivities (optional)
  • Surface BRDFs (optional)
  • Jacobians for temperature, water vapour and ozone (optional)
  • Level-to-space transmittances (optional)
  • Model profiles at obs (simulation) locations (optional)


Radiance-Simulator-related Publications