Official HYGEOS website

TORMS

Total Ozone Retrieval from MERIS in view of application to Sentinel-3

An algorithm has been developed to retrieve total column of ozone (TCO) using MERIS data. Whereas total ozone has been usually measured from space for several decades using nadir UV backscatter sensors such as TOMS, SBUV, GOME, SCIAMACHY or OMI, we used here TOA reflectances spectrum in the MERIS spectral range [400 – 900 nm] which includes Chappuis bands .

Shortly, the method is based on the assumption that the TOA reflectance spectrum in the absence of gaseous absorption can be modelled by a third order polynomial. Excluding MERIS bands affected by water vapour and oxygen absorption, the free absorption spectrum can be derived using a 3rd order polynomial fit on bands not affected by ozone (i.e.: 412.5, 442.5, 753.75 , 778.75 and 865.0 nm). Difference between free absorption spectrum and measured spectrum is thus only due to ozone absorption. TCO is retrieved using method to minimize the chi-square difference between 3rd order polynomial values weighted by ozone transmittance and measured reflectances.

This method has been applied to MERIS archive and is valid for bright and spectrally white surface such as snow/ice surfaces and over optically thick clouds.

First comparison between MERIS TCO and ground measurements show a good correlation with a small bias of about 4 DU and an uncertainty (root mean square) of about 20 DU.

 

Client: European Space Agency (ESA) / European Space Research and Technology Centre (ESTEC)

HYGEOS is sub-contractor of the Belgian Institute for Space Aeronomy (BIRA-IASB). HYGEOS is in charge of the algorithm development, the validation and the generation of the level-2 and level-3 TCO products for the whole MERIS archive.