Effects of a refractive atmosphere on interferometric processing

An application of synthetic aperture radar (SAR) interferometry is the production of digital elevation models (DEM). Once an interferogram is unwrapped, the altitude of each point on the interferogram is calculated thanks to the two satellite positions. The underlying hypothesis in this derivation is that the propagation of the wave through the atmosphere follows a straight line. In fact, the atmosphere is refractive and the ray is bent. In this paper the authors try to assess the effects of ray bending on DEM generation. At first, they model the wave propagation through a refractive medium and model the interferometric processing. Then, they study the refractive index distribution in both the troposphere and ionosphere. They also study spatial and time fluctuations of the refractive index at scales of interest in interferometry. Finally, they simulate different cases of atmospheric disturbances on an interferogram. They show in which cases a refractive atmosphere creates artifacts on an interferogram. In each case, they determine the order of magnitude of the expected error and its signature on the interferogram. Finally they establish which processing method could minimize the effect of the atmosphere on DEM generation.