Land Surface Temperature

Land Surface Temperature (LST) is the radiative skin temperature of the land derived from solar radiation. It is a basic determinant of the terrestrial thermal behaviour, as it controls the effective radiating temperature of the Earth’s surface” [1]. LST is linked to several aspects of the geoscience and in this respect the understanding of its evolution and distribution all over the Earth has high importance in the framework of the monitoring of climate change, crop management, land cover changes and many other applications [1][2].

Copernicus Sentinel-3 constellation carries on board two SLSTR instruments capable to acquire infrared radiation coming from the Earth surface with high frequency, thus allowing the estimation of the surface temperature thanks to the processing of their acquired data. Earth Starts Beating continues its own study of our Planet via the generation of Worldwide L3 products showing the nighttime and daytime land surface temperature acquired by Sentinel-3 instruments on monthly basis. Products are published in the ESB EO Browser where everyone can browse and inspect a single map at his convenience.

Daytime Temperature [June 2019]

The image above is an example of the maps generated by Earth Starts Beating. This mosaic has been processed considering all the daytime Sentinel-3 SLSTR data acquired in June 2019 and shows the land surface temperature in Kelvin. What do we mean with daytime and nighttime acquisitions? SLSTR instrument gets data systematically in a single orbit lasting around 100 minutes: some of the data acquired during the passage are acquired during the day time, thus when the direct Sun radiation impacts the Earth surface, whereas the others are sensed during the night. The surface temperature in the same spot on the ground is different depending on the presence of the direct Sun radiation or not, then this means that we have a specific temperature distribution during daytime and another one during the night.

Earth Starts Beating processors divide the two distinct kinds of data in order to generated two different monthly maps and show the two phenomena. In the daytime map above we can see the hottest place on the Northern Hemisphere (summertime). Yellow-to-black nuances shows temperature from >0°C to 50°C, cyan-to-purple shades go from <0°C to -50°C and the white colour is standing for 0°C. Several spots in the Middle East reach temperature near the 50° degrees (Arabian Peninsula, Dasht-e Lut desert), indeed there we have the highest recorded temperature ever! [3].

Nighttime Temperature [June 2019]

A different behaviour is shown in the map above, showing the surface temperature acquired in June during the night. The mean max value is obviously lower than the one observed during the daytime and we can see several places with a temperature below 0°C, like the Himalaya and The Andes. In Antarctica the mean temperature of the interior is less then -50°C.

A particular phenomenon can be observed comparing the two maps and is related to the inland waters, such as the Caspian Sea or the American Great Lakes. In the daytime map their shape is well distinguishable because the temperature is quite lower then the surrounding lands, but this is not true during the night. Indeed the thermal inertia of water is higher compared to the lands and this means that the water range temperature observed in 24 consecutive hours is not so wide. On the contrary the 24h min/max temperature range of the land is higher, the nighttime temperature is quite lower compared to the one observed during the daytime but comparable to the inland waters’: that’s the reason why lakes are not distinguishable in the nighttime map. See Dead Sea and thermal inertia for details.

Contains Copernicus modified data processed on the ONDA-DIAS infrastructure.

[1] http://lst.nilu.no/

[2] https://www.sciencedirect.com/science/article/pii/B9780124095489105226

[3] https://journals.ametsoc.org/doi/pdf/10.1175/2011BAMS3067.1

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