24 Aug 2023
 | 24 Aug 2023
Status: a revised version of this preprint is currently under review for the journal AMT.

Unfiltering of the EarthCARE Broadband Radiometer (BBR) observations: the BM–RAD product

Almudena Velázquez Blázquez, Edward Baudrez, Nicolas Clerbaux, and Carlos Domenech

Abstract. The methodology to determine the unfiltered solar and thermal radiances from the measured EarthCARE BBR shortwave (SW) and totalwave (TW) filtered radiances is presented. Within the EarthCARE ground processing, the correction for the effect of the BBR spectral responses, the unfiltering, is performed by the so-called BM-RAD processor which produces the level 2 BM-RAD product. The BM-RAD product refers to unfiltered broadband radiances that are derived from the BBR and the Multi-Spectral Imager (MSI) instruments onboard of the forthcoming EarthCARE satellite. The method is based on theoretical regressions between filtered and unfiltered radiances, as is done for the Clouds and the Earth's Radiant Energy System (CERES) and the Geostationary Earth Radiation Budget (GERB) instruments. The regressions are derived from a large geophysical database of spectral radiance curves simulated using radiative transfer models. Based on the radiative transfer computations, the unfiltering error, i.e., the error introduced by the small spectral variations of the BBR instrument response, is expected to remain well below 0.5 % in the shortwave (SW) and 0.1 % in the longwave (LW), at 1 standard deviation. These excellent performances are permitted by the very simple optics used in the BBR instrument: a telescope with a single paraboloid mirror. End-to-end verification of the unfiltering algorithm has been performed by running the BM-RAD processor on modeled Level 1 BBR radiances obtained for three EarthCARE orbits simulated by an integrated forecasting and data assimilation system. The resulting unfiltered radiances are eventually compared to the solar and thermal radiances derived by radiative transfer simulations over the three EarthCARE orbits. In addition, this end-to-end verification has provided further evidence on the high accuracy of the unfiltered radiance process, with accuracies better than 0.5 % for SW and better than 0.1 % for LW.

Almudena Velázquez Blázquez, Edward Baudrez, Nicolas Clerbaux, and Carlos Domenech

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on amt-2023-170', Anonymous Referee #1, 27 Sep 2023
  • RC2: 'Comment on amt-2023-170', Anonymous Referee #2, 12 Dec 2023
  • EC1: 'Comment on amt-2023-170', Robin Hogan, 26 Feb 2024
Almudena Velázquez Blázquez, Edward Baudrez, Nicolas Clerbaux, and Carlos Domenech
Almudena Velázquez Blázquez, Edward Baudrez, Nicolas Clerbaux, and Carlos Domenech


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Latest update: 01 Mar 2024
Short summary
The BBR measures shortwave and totalwave radiances filtered by the spectral response of the instrument. To obtain unfiltered solar and thermal radiances, it is needed to correct for the effect of the spectral response. This is done within the BM-RAD processor. Errors in the unfiltering are propagated into the fluxes, thus, an accurate unfiltering is required for a proper estimation of the fluxes (within BMA-FLX). Unfiltering errors are estimated to be <0.5 % for the SW and <0.1 % for the LW.