London appears as a cluster of bright radar reflections along the River Thames in this radar image from Sentinel-1A.
The satellite captured this image on 4 March 2015 in its Interferometric Wide Swath mode and dual polarisation, from which the artificial colour composite was generated.

This image was released to mark the signing, in Paris, of an agreement between ESA and the UK Space Agency that establishes access to data from the Sentinel satellites in the UK. More details:
UK joins Sentinel Collaborative Ground Segment

Credit: Copernicus data/ESA (2015) Larger image