The goal of the project is to retrieve total ozone column (TOC) using Ocean and Land Colour Imager (OLCI) measurements over Antarctica and other snow-covered areas. OLCI is placed on Sentinel-3A; B platforms and is planned to be launched on Sentinel-3 C, D as well.
The instruments operates in the spectral range 400-1020nm. It is known that OLCI spectrum is influenced by ozone absoption in the Chappuis band with a maximum located at 603nm. Therefore, OLCI atmospheric aerosol/ocean colour retrievals are corrected for the European Centre for Medium-Range Weather Forecast (ECMWF). On the other hand, total ozone column can be retrieved from OLCI measurements themselves over bright underlying surfaces such as snow. As a matter of fact, the snow spectral reflectance around 620nm, which is mostly due to light absorption by ozone molecules. The degree of this decrease can be related to the total ozone column. This has been demonstrated previously using the data of Medium Resolution Imaging Spectrometer (MERIS) on board ENVISAT.
The first results of TOC retrieval over Antarctica using OLCI have been published by Kokhanovsky et al. (2020).
Although the total ozone is currently retrieved by many instruments, they have quite large spatial resolution. OLCI provides TOC on the scale 300m, which makes it possible to study inter-pixel TOC variability and also improves understanding the total ozone change in areas, where gradients of TOC are large.
Current activities related to this project are aimed at the development of better cloud screening and atmospheric correction algorithms over snow.
The algorithm for the total ozone column retrieval will be prepared lather this year. It will be based on the minimization of the cost function (derived using radiative transfer theory) with respect to TOC and some other atmospheric parameters including aerosol optical thickness.
The work is performed by Telespazio Belgium’s employees Dr. Alexander Kokhanovsky and Filippo Iodice.