Synthetic aperture radar data is used in conjunction with altimeter data to produce a terrain map corrected for platform roll angle. The technique uses two synthetic radar antennas and a ranging altimeter placed on an aircraft. The aircraft is moved in a set of substantially parallel flight paths where each flight is directly over the strip of terrain viewed by the synthetic aperture radar of an adjacent flight. During each flight the at least one antenna repeatedly transmits radar signals whose return echoes are received by both the first and second antennas. Conventional synthetic aperture radar processing yields a terrain map uncorrected for roll angle. Altimeter data from an adjacent flight determines the first order corrected aircraft roll angle when the corresponding synthetic radar data was taken. This roll angle is used to correct the height and ground range of nearby points in the uncorrected terrain map. A second order corrected roll angle is determined using the first order corrected terrain map to identify the first return point of the altimeter measurements. The measured altitude is then realigned to the first return point to produce a second order corrected roll angle and a corresponding second order corrected terrain map. The result is a terrain map corrected for aircraft roll angle.