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The study was commissioned by EUMETSAT as an Invitation To Tender. HYGEOS and the University of Lille 1 won the ITT. HYGEOS was the prime contractor.

METimage is intended to provide high quality imagery data for global and regional Numerical Weather Prediction and NoW Casting, and to support the sounding instruments on EPS-SG. Taking advantage of its large spectral range (0.44-13.5 μm), METimage will provide, among others, Cloud Top Pressure (CTP) products based on the use of visible imaging in the oxygen A- band. The goal of the study “O2 band Cloud Top Pressure for METimage” was (i) to inform EUMETSAT with respect to all aspects of CTP-O2 retrieval as well as (ii) to establish and demonstrate an appropriate CTP-O2 retrieval scheme based on METimage observations. 


(Left) Schematic representation of the variety of possible photon path in cloudy atmosphere. (Right) AFGL Tropical atmosphere transmittance spectrum around A-band O2 band for an airmass of 1. METimage filters VII-4 and VII-5 are over-plotted in blue and red respectively. The ISRF are modelled as a rectangle function on the present graph.


The study included a review of the state of the art of retrieval algorithms applied to comparable instruments and with a particular focus on the Look-Up Table (LUT) based methods. It reported on the suitability of candidate Radiative Transfer Models (RTMs) required to generate LUTs (or equivalent). It also focused on the required inputs to the RTMs and the contents and organisation of the LUTs. An algorithm based on the use of the optimal estimate technique and the LUTs as direct model was developped and tested. The testing was performed on METimage synthetic data (see 4MSDS project) and on MERIS data.