Foreword to the Special Issue on Multichannel Space-Based SAR

The papers in this special section focus on space-based synthetic aperture radar (SAR)technology. With the advent of active electronically steerable phased-array SAR antennas equipped with more than one receive channel (i.e., analog-/digital converter) on the most recent generation of commercial/civilian spacecraft, such as RADARSAT-2, TerraSAR-X & TanDEM-X, PAZ, and ALOS-2, relatively mature singlechannel SAR imaging is now rapidly evolving into advanced, multiaperture SAR concepts. The spatial diversity of multiple parallel receive channels can, for instance, be used to discriminate moving objects from the stationary background, to determine the underlying topography of the backscattering terrain, or to measure the large-scale surface motion using single-pass interferometry. The flexible programmability of this newest generation of SAR satellites offers quasi-seamless antenna beamsteering at a rate equivalent to the pulse repetition frequency and, in conjunction with sophisticated array signal processing algorithms, opens up novel radar concepts and capabilities that were not previously possible.