1. An interferometric synthetic aperture radar system for producing a highly precise three dimensional SAR image, said system comprising: a synthetic aperture radar system having two antennas separated by a predetermined separation distance which generates data comprising complex image pairs representative of an image scene; and processing means for processing the data comprising the complex image pairs, for calibrating the data comprising the complex image pairs to provide calibrated data, for processing the calibrated data to generate a low ambiguity SAR elevation map, for processing the low ambiguity SAR elevation map to provide an enhanced SAR elevation map, and for processing the enhanced SAR elevation map to produce a precise three dimensional SAR image, said processing means comprising: (i) means for processing the data using low frequency phase error processing to remove low frequency phase inconsistencies between same-pass image pairs; (ii) means for processing the data using inter-pass, low frequency processing to remove low frequency phase inconsistencies between inter-pass image pairs, and (iii) means for processing the data using inter-pass baseline processing to provide a coarse estimate of the elevation angel separation between each pass.