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A new technique for resolving the ambiguity inherent in delay-Doppler radar observations of Mars has been developed and implemented using a suite of data collected during 2001, 2003, and 2005 oppositions. New recording systems, processing techniques, and, most importantly, the addition of a fourth receiving telescope allow for the high-resolution mapping of Mars' radar properties. In this paper, we develop a maximum likelihood method to probabilistically estimate the contributions to the received radar signal from the ambiguous resolution cells. Our delay-Doppler interferometric radar observations are designed to map the radar properties of Mars surface while disregarding the historically typical goal of measuring topography, instead using Mars' topography as a priori knowledge. Example data from the September 27, 2003 observation over Mars' southern highlands, including Ma'adim Vallis and Gusev Crater, and the June 7, 2001 observation crossing Terra Meridiani are presented to demonstrate the effectiveness of the technique. Analysis of these observations predicted a root-mean-square (rms) roughness, or slopes, for the Mars Exploration Rover (MER) Spirit landing site of 1.80?? ?? 0.75??. Similarly, analysis of the Gusev Crater landing site of MER Opportunity predicted rms slopes of 1.1?? ?? 0.1??. Both predictions were validated by analysis of in situ rover images.