Cancellation of Singularities in SAR for Curved Flight Paths and   Non-Flat Topography
  We consider a mathematical model of synthetic aperture radar (SAR) with a known, possibly non-flat, topography. In this context we consider the problem of recovering the wavefront set of the ground reflectivity, given radar data measured along a curved flight path. We show that if singularities are located at "mirror points," then the resulting data may be smooth; in effect, the singularities "cancel." With a flat topography, these mirror points are always discrete, but we show that in a non-flat topography there may be infinite families of mirror points. 
Andrew Homan
math.AP