Radiance simulator

Introduction

Current version: v1.1, September 2014
The NWPSAF radiance simulator was initially proposed to support pre-launch scientific studies and pre- operational development work in support of the MTG-IRS instrument. The user requirement for the radiance simulator is, however, more general. Studies into future instruments on-board EUMETSAT’s MetOp-SG for example, such as the Microwave Sounder (MWS), the Microwave Imager (MWI) and the Ice Cloud Imager (ICI) will also soon require test datasets, based on simulations from NWP models.

The capability to model radiances from new satellite instruments, from other agencies, is normally integrated into the NWPSAF fast radiative transfer model (RTTOV) many months or years prior to launch. The purpose of the radiance simulator is to supplement this capability with a flexible interface to NWP model fields in order to enable the generation of simulated observations for all instruments supported by RTTOV in a straightforward way. The Radiance Simulator is designed to work specifically with datasets from NWP models, either analysis fields or short-range forecasts.

Any potential use for climate applications is outside the scope of this release.

Functionality

The radiance simulator will perform the following functions:

  • Ingest of NWP model fields, provided in common data formats. In the initial implementation this will include support for the following formats:
    • GRIB
    • Met Office fieldsfiles / PP files
    • NWP SAF 60L profile dataset from ECMWF analyses
    • NWP SAF 91L profile dataset from ECMWF analyses

    Model fields will consist of:

    • Level pressure
    • Temperature
    • Humidity
    • Cloud liquid water
    • Cloud ice water
    • Cloud fraction
    • Surface wind
    • Surface skin temperature
    • Surface air temperature
    • Surface humidity
  • Ingest of observation files (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.
  • Interpolation of model fields to observation locations. This is optional, dependent on the above. If no observation data are provided, simulations are performed at model profile locations.
  • Prepare input to, and run, radiative transfer model. This will be RTTOV version 11 in the first instance. Depending on the availability of the required model fields, both infrared and microwave scattering simulations will be feasible.
  • Output top-of-atmosphere brightness temperatures or radiances, emissivity values and input observation data. Options for the initial implementation will include:
    • Output of Jacobians
    • Output of layer transmittances
    • Output of model profiles