Abstract: A method of evaluating the phase shift associated with a wave emitted by a space radar propagating through the ionosphere. The method comprises the steps of forming first and second interferograms from pairs of radar images obtained by using two respective space radars operating at respective wavelengths .lambda..sub.1 and .lambda..sub.2 satisfying the relationship m.lambda..sub.1 =n.lambda..sub.2 where m and n are integers, the radars being placed on the same satellite; and performing the linear combination n.phi..sub.1 -m.phi..sub.2 of respective phases .phi..sub.1 -.phi..sub.2 of the first and second interferograms, with the fractional portion of the linear combination being representative of the non-Euclidean effects affecting the images of the space radars used in making the interferograms.