This TerraSAR-X image shows a thunderstorm cell with unusually heavy rainfall off the Caribbean coast of Panama, visible across in the upper half of this image as a blurred area. The scene recorded here extends over an area of about 18 by 64 kilometres and was generated in dual-polarisation mode, a method that substantially increases the information content of an image.
The colours are created by superimposing two separate images (red and green) of the same area taken simultaneously in this mode using two signals having different polarisation settings, together with a third image (blue) which is calculated from the difference between the original images. Now, the different reflection mechanisms become visible – the green colouration indicates a surface reflection, where the radar signal is being reflected straight back to the antenna. Red tones indicate a double reflection, and there is virtually no indication of this in the scene depicted here, since it occurs primarily in urban areas. Blue tones can be seen in the area of the thunderstorm cell, and are designated as 'volume scatter' because the signal is reflected back to the radar antenna by a multiplicity of individual raindrops and hailstones.