Tracking Tornados from Space

Assessment of the Tornado in Czechia with the help of high-resolution Sentinel-2 satellite data

Jul 10, 2021

3 min read

On Thursday the 24th of June at approximately 7:15 pm a major tornado hit the region of Southern Moravia in Czechia with winds of at least 219km/h (136 mph). The tornado was assigned the category F4 on the Fujita-Scale.

"It’s living hell!" – South Moravia governor Jan Grolich

Six people were killed and at least 200 injured. Locals reported hailstones the size of tennis balls. Overall six different villages (Hrušky, Moravska Nova Ves, Mikulčice, Lužice, Hodonína and Ratíškovic) suffered significant damage. The path of the tornado was assessed via an airborne mission and is depicted in the image below. Red areas indicate damage to buildings, green area damage to forests, blue areas damage to agriculture and the yellow outline shows the path of the tornado which is roughly 26km long and 700m wide.

Is it visible from space?

After I saw the videos on TV and read the reports of the devastating event, the question that popped into my head was – "Can the effects of the tornado be seen on satellite imagery?" Therefore, I decided to look into recent imagery of the Sentinel-2 satellite constellation which provides high-resolution images of the earth surface with 10m resolution roughly every 5 days (depending on the location). Even though there is a wide range of tools you can use to access the data, I decided to use the excellent Sentinelhub EO Browser which makes the search and visualisation of recent satellite data very easy.

The visualisation above shows two scenes captured by the Sentinel-2 satellites. The top scene was taken on the 21st of July and the bottom scene depicts the same area five days after the tornado on the 29th of July. You can clearly see a bright spot in the central part of the bottom scene between the cities of Breclav and Hodonin. This spot (change in spectral properties) can clearly be attributed to the effects of the tornado.

Assessing the damage

Let us zoom in a little bit closer into the region that we have just identified to be affected by the tornado: the village Moravska Nova Ves. If you look at the two satellite scenes below (that again show a before-after comparison) you can see that the northern and southern parts of the village look untouched, however, the central part again shows a significant change in the spectral properties: You can see that the red rooftops in the area highlighted in yellow basically all disappeared and now appear in blue colour. This likely means that either the roofs or the entire buildings in that area were completely destroyed. Surrounding the village (especially on the west) you can also see extensive damage that was done to the agricultural areas that appear in an orange/brownish hue after the tornado event.

Deriving the trajectory of the tornado

In the first image above we could see that through the comparison of the satellite images before and after the tornado we could identify hotspots of severe damage to agriculture and buildings. But is it possible to derive the trajectory of the tornado?

To find out, I normalized the spectral bands of the scene before and after and calculated the spectral difference between the two timesteps. The result is false-colour (8-4-3) visualized in the image below. If you look closely, especially from the central part of the image upwards to the right you can make out a clear path that shows the spectral differences due to damage in vegetation and infrastructure!