Meteosat Third Generation full constellation

High Spectral Resolution Geostationary (HSR Geo) simulations

Meteosat Third Generation full constellation
Meteosat Third Generation full constellation

This study provides simulations of geostationary top of atmosphere (TOA) radiances to EUMETSAT at high spectral resolution, from which realistic imager TOA radiances may be synthesised using specific definitions of Spectral Response Functions (SRFs).

Last Updated

03 November 2020

Published on

11 May 2020

The principal driver for the acquisition of such synthetic data is to enable evaluation of geostationary satellite imagery (i.e. level 1) quality and characteristics given uncertainties or variability in detector array SRFs. For example, with detector arrays, such those of the Flexible Combined Imager (FCI) planned for the Meteosat Third Generation (MTG), the degree of striping and development of methods to reduce striping may be evaluated. A secondary driver is to enable the exercising of Atmospheric Motion Vectors on synthesised IRS Level-1 products.

 Example of a high-spectral resolution radiance spectrum (blue line) for a day-time scene over the Sahara desert. The green areas highlight the spectral regions covered by the FCI channels
Figure 1: Example of a high-spectral resolution radiance spectrum (blue line) for a day-time scene over the Sahara desert. The green areas highlight the spectral regions covered by the FCI channels

Objectives

HYGEOS/LOA will provide EUMETSAT with at least two full disks with a MSG/SEVIRI spatial grid (3 km at nadir) and the spectral characteristics as described in the table below.

Low end High end Spectral resolution
Microns Microns  
0.354 0.884 1.0 nm
0.884 1.425 0.5 nm
1.425 3.200 1.0 nm
3.200 3.623 5.0 nm
3.623 15.500 0.25 cm-1

Using the same spectral resolution, at least four scenes (1000x1000 pixels) at higher spatial resolution (~500m at nadir) will be provided.


Overview

Top of the atmosphere radiances for the full range of representative atmospheric and surface conditions will be generated. The sun and view geometries will be taken from SEVIRI observations for selected repeat cycles. The spatial grid will also be from SEVIRI/MSG. For each pixel, the surface and atmosphere is realistically described based on ancillary information obtained for the dates and times of the required simulation (including OCA products for clouds coupled with ECMWF water content profile, CAMS reanalysis for aerosols profiles, ECMWF reanalysis for atmospheric state, MODIS surface BRDF product and thermal infrared climatology for land properties). For the high resolution products, MODIS or VIIRS cloud products will be used.

To compute TOA radiance, the simulator uses the ARTDECO radiative transfer tool in the UV to SWIR domain and RTTOV in the thermal infrared domain. The computation is done individually (on-the-fly) for each pixel and each spectral channel (each wavelength). The scene definition (aerosol, cloud, gas and ground) is made consistent between the two spectral domains.