Level 3 Mosaics over Africa

Copernicus Sentinel-3 mission has been designed and developed mainly to focus on the climate changes effects impacting on our planet and is carrying on board several instruments with medium-low resolution in order to pursuit this goal. From this perspective the main strength of the project is not standing in the capabilities to distinguish small objects and shapes on the ground but in the evaluation, monitoring and evolution of geophysical entities on large scale. Indeed one of the best feature of the mission is the high revisit time allowing us to check and monitor a single point on our planet with high frequency.

The goal of this post is to give a taste about how the time series data belonging to Sentinel-3 can be fruitful for the study of the Earth and the evolution of geophysical phenomena all over the years. To do this we can start showing some Level 3 products of the mission, namely monthly mosaics over the Africa, processed on one of the virtual servers made available by the Copernicus RUS Service.

Vegetation Index – August 2017
Integrated Water Vapour Column – August 2017
Chlorophyll Index – August 2017
Land Surface Temperature

The four images above show three different geophysical entities acquired by OLCI and SLSTR instruments and processed mosaicing around 600 scenes sensed in August 2017. OLCI makes available to the users for land application the mapping of the vegetation index, the chlorophyll index and the Integrated Water Vapour Column (IWV) for atmospheric column. Vegetation and chlorophyll give evidence of the status and the health of the flora on the Earth and their evolution over the years is a key parameter for the study of climate change effects. We can see the most vegetated and healthy zones in the middle of Africa as well as a very low IWV in the southern part of the continent, regions extremely arid and affected by long periods of droughts. Moreover SLSTR Land Surface Temperature shows temperatures in the Sahara Desert near 50°C (scale white-red-black from 250 to 320 K).

Starting from this first month of mosaic Earth Starts Beating is going to give birth to a new initiative. ESB wants to monitor the evolution of those geophysical phenomena on monthly basis, mosaicing all the products acquired by the mission continent per continent. Both land and marine applications will be taken in consideration as well as both the optical instruments. Mosaics will be showed via a free data browser client and will be hosted and elaborated thanks a geoserver. Here below some screenshots of our prototype in development phase:

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As complementary information we have generated an RGB natural color image of the Africa using TOA reflectances from data acquired the same month. Some no data pixel are still present and this is mainly due to the extremely cloudy regions on the western coast. However the strange blue alone in the central inner regions caught our eyes. Those regions are affected by a large number of seasonal fires and according to a study published some years ago [1] (see ref: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2005JG000142) in the central/south part of the Africa fires reach their peak during the summer. So the blue alone could be explained as smoke, still present after one entire month of acquisition due to the high frequency of fires.

References:

[1] Louis Giglio, Ivan Csiszar ,Christopher O. Justice  – “Global distribution and seasonality of active fires as observed with the Terra and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) sensors” – https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2005JG000142

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