Aircraft could not fly over (or anywhere near!) the active volcano Eyjafjallajökull. And optical satellites have been severely hampered by the ash screen. But TerraSAR-X was able to safely observe the eruption site and its surroundings with great clarity from afar.
In this image two TerraSAR-X StripMap acquisitions (3 m resolution) taken on two different dates and a change layer are combined to produce a colour composite. This enables changes in the area to be highlighted in different colours. The first image acquired on 25 March 2010 is represented by the red channel, the second image acquired on 16 April by the green channel and the difference between both images by the blue channel.
In the eastern part of the map (east of the volcano’s caldera) light blue structures are visible. These are features caused by the first eruption on 20 March, which took place a few kilometres east of the glacier on the northern slopes of the Fimmvörðuháls mountain pass.
In the centre of the map the volcano’s caldera is shown in red, green and yellow. The bright red is caused mainly by the eruptive column, which formed due to the second eruption at the top caldera of the volcano. In the image acquired on 16 April the radar signal in this area shows a very low return, which might result from water vapour within the plume. The orange, dark red, yellow and greenish colours are caused by changes of the backscatter values for the areas covered by snow, which have been affected by the eruption (coverage by ash, melting of snow etc.).
In the north of the crater a round light blue structure is visible. On the first acquisition this was a lake. Following the eruption, which started on 14 April, it was filled with debris. West of the former lake, red structures indicate the newly formed melt water flows of the melted ice, which previously covered the central crater.
The image shown here is an individual TerraSAR-X StripMap Acquisition (2.9 m resolution) of Eyjafjallajoekull Volcano, Iceland, recorded on 15 April 2010 following the volcano’s eruption the day before.
The acquisition shows that all the snow surrounding the caldera of the volcano melted away and that three black craters were formed by the volcanic activities. A crack connects the northeastern and southern craters formed by the new eruption. The fine ash from the eruption was caught by the wind and carried to the east, where it was deposited on the ice as a dense and smooth surface coating. In these areas, the microwave radiation from the radar satellite is only weakly reflected, and this appears dark in the image.
This acquisition can be compared to an image of the same area recorded prior to the volcano’s eruption. Another StripMap Acquisition (2.9 m resolution), this was recorded on 31 March 2010. At that time the caldera of the volcano was covered with about 200 m of ice, which is clearly visible as a bright spot in the satellite image.