Retrieval of total ozone over Antarctica using Ocean and Land Colour Instrument on-board Sentinel-3A/B
The Vitrociset Belgium team has started releasing the first results of the ANREO project devoted to the determination of total ozone over Antarctica ice sheet.
The ozone layer is necessary to help life survive on Earth. The Antarctic ozone hole typically reaches its annual peak in September or October before rebounding in December. Last year, the Antarctic ozone hole was the smallest it has been since its discovery 35 years ago. The 2020 Antarctic ozone hole is one of the largest and deepest in recent years.
The total ozone column (TOC) is derived by the team using the top-of-atmosphere measurements of the Ocean and Land Colour Instrument (OLCI) on board Sentinel-3 A/B. OLCI operates in the spectral range 400-1020nm. The TOC has been derived using Sentinel-3 OLCI Level 1 product at full resolution (300m). This is the first attempt to derive the total ozone column at such high spatial resolution. The team also created a cloud mask, a snow mask and an atmospheric correction procedure.
The OLCI ozone processor is planned to be delivered to ESA in April 2021 providing the ozone research community with a total ozone product from OLCI / S-3 in Antarctica and also over other snow-covered areas including Greenland. The benefit of using OLCI / S-3 over other ozone monitoring tools is its high spatial resolution combined with 21 spectral bands sensitive to the optical properties of snow and atmosphere. Providing data on a 300m grid has a clear advantage for the user community (e.g. to monitor rapid changes in total ozone at the edges of the ozone hole and to understand the variation of ozone within pixels). Currently, ozone-based products exist on a much coarser spatial grid (say, 13 km x 24 km OMI aboard NASA's Aura satellite and 7km x 3.5km TROPOMI/S5p). The accuracy of the recoveries will be validated in the coming months using ground (Brewer and Dobson spectrophotometers) and satellite measurements (e.g, TOC as derived from OMI, TROPOMI and GOME-2 measurements).
The first results of the comparison of TOC derived from OMI/Aura, TROPOMI/S5p and OLCI/S3 (Vitrociset ozone processor) are shown in the figure. The total ozone column patterns derived from different instruments over Antarctica ice sheet are similar. The differences are due to different times of measurements and spatial resolutions.
Graphic representation of the vertical column of ozone, OMI-Aura_L3 OMTO satellite. Represented with a fixed scale expressed in Dobson (DU).
Graphical representation of the vertical column of ozone, Sentinel-5P satellite. Sentinel-5P Level 2 source data (S5P_OFFL_L2__O3) predefined without a fixed grid (Pixels in Sentinel-5P Level-2 products are defined by latitude and longitude, forming an irregular grid that makes combining multiple images more difficult). This representation solves the problem by converting to processing level 3: the data is resampled in a normal grid of spatial pixels and converted from mol / m2 to DU.
Graphical representation of the vertical column of ozone, Sentinel-3 OLCI satellite. Sentinel-5p level 1 source data (S3A-B_OL_1_EFR) is reprocessed using Total Ozone Retrieval based on OLCI measurements (TORO) measurement software. The image shows the representation of the Ozone column over the whole territory of Antarctica (DU) with the exclusion of the ocean. The absence of data on the Sentinel-3 elevation rate in the region surrounding the South Pole is due to the latitudinal limit of 81.35 of the satellite orbit.