Firebreaks over Portugal

Last Saturday Portugal has faced one of the biggest wildfire in its history. Hundreds of firefighters and more than 150 vehicles have been dispatched in order to counteract the flames spreading, fires that even after 24 hours were still churning across the forested hillsides of central Portugal, causing around 62 casualties. The largest part of the impacted area belongs to the Leiria and Coimbra Districts, covering tenths of square kilometers, surrounded by Pedrogao Grande, Figueiro dos Vinhos e Castanheira de Pera.

Copernicus Sentinel-3 satellite captured the event with its two optical instruments, returning a complete overview from two different perspectives. The Ocean and Land Colour Instrument, with its visible bands and 300 meters of resolution, pictured the described area on Sunday Morning (June 18th) showing the fire still alive (image below). The smoke trails are indeed clearly visible, recognizable thanks to their grey color compared to the white clouds.

OLCI natural colors RGB image over Portugal

On the other hand the SLSTR instrument, carried by Sentinel-3 as well, with its thermal bands allows us to identify the fire advancement and perform an estimation of the impacted area. Fires are more responsive to some thermal Infrared bands than the other elements on the ground: from this perspective the image below, processed using the 3.74 μm band response, clearly highlights the fire location, its spreading and the involved region too.

SLSTR wildfire detection

The impacted area is pointed by the arrow, just south of Coimbra: the region is round-shaped where the wildfires are located around its circumference (colored in black) and are going to expand. The image is indeed acquired on Sunday morning (the same time of OLCI acquisition above) when the fire was still spreading: the ground defined by the circle, in red, represents the burned areas.

The synchronized acquisition between the two instruments allow us to observe the same phenomenon, at the same time, from two different points of view (namely, in this case, visible and infrared). Indeed overlapping the two images it is evident that the area detected by the thermal band of SLSTR is the same surrounding the smoke trails captured by OLCI, as showed in the animated gif below.

OLCI and SLSTR animation

Thanks to the several infrared bands of SLSTR is possible to process different RGB images using different band compositions for the three channels. In this way the instrument allows us to highlight the area affected by the wildfire in many and more fruitful ways, thanks to its different response compared to the surrounding not-burned ground (see below).

Flames continued to spread during all the day. SLSTR instrument can acquire also during the night, thanks to its infrared bands, and captured the state of the burning advancement around 12 hours after the first daily acquisition on Sunday morning. The animation below compares the two images and clearly shows the fire’s extension, pictured in black.

Fire spreading captured by SLSTR

Contains modified Copernicus Sentinel data 2017.

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