BACKGROUND: REMOTE COMPOSITIONAL INVESTIGATIONS IN THE THERMAL INFRARED WAVELENGTH REGION (E.G. 6-50M) HAVE LONG RELIED UPON THE ASSUMPTION OF LINEAR MIXING OF ENDMEMBER RADIANT ENERGY TO DETERMINE SURFACE MINERALOGY. VARIATIONS OF THIS TECHNIQUE HAVE BEEN SUCCESSFULLY APPLIED TO PLANETARY SURFACE INVESTIGATIONS AND IN THE LABORATORY. HOWEVER THE VALIDATION OF THIS CRITICAL ASSUMPTION HAS RELIED UPON A SURPRISINGLY SMALL NUMBER OF STUDIES [E.G. RAMSEY AND CHRISTENSEN 1998; FEELY AND CHRISTENSEN 1999; HAMILTON AND CHRISTENSEN 2000; WYATT ET AL. 2001] AND THE FULL PARAMETER SPACE UNCERTAINTIES AND ULTIMATE MINERAL ABUNDANCE RETRIEVAL ACCURACIES HAVE BEEN INSUFFICIENTLY EXPLORED. THIS IS IN LARGE PART DUE TO THE FACT THAT IT IS NOT PRACTICAL TO TEST THE LIMITS OF LINEAR MIXING PURELY IN THE LABORATORY AS MULTI-COMPONENT MIXTURES AS COMPLICATED SURFACES CANNOT BE READILY CONSTRUCTED. SIMILARLY SIMULATING SPECTRA VIA NUMERICAL MODELING OF REPRESENTATIVE (MULTI-COMPONENT LAYERED ETC.) MIXTURES HAS PROVED TO BE A SIGNIFICANT CHALLENGE DUE TO THE COMPLEX NATURE OF MODELS AND THE TYPICAL REQUIREMENT OF OPTICAL CONSTANTS AS MODEL INPUTS. TO DATE THERE HAS BEEN NO COMPREHENSIVE STUDY TO INVESTIGATE THE LIMITATIONS OF LINEAR SPECTRAL UNMIXING AND MINERAL ABUNDANCE RETRIEVALS IN TERMS OF COMPLEX MIXTURES OF MINERALS AND SIZE FRACTIONS. METHODOLOGY: IN THIS WORK WE PROPOSE TO TEST THE LIMITS OF MINERAL ABUNDANCE RETRIEVALS IN THE THERMAL INFRARED THROUGH MULTIPLE APPROACHES ENABLED BY BOTH LABORATORY STUDIES AND RADIATIVE TRANSFER MODELING. THIS ULTIMATE GOAL IS ACHIEVED BY FOUR DISTINCT TASKS: TASK 1. ACQUIRE THERMAL INFRARED EMISSION SPECTRA OF A SUITE OF MINERAL MIXTURES IN THE LABORATORY TASK 2. VALIDATE A NOVEL RADIATIVE TRANSFER MONTE CARLO EMISSION MODEL IN ORDER TO SIMULATE MINERAL MIXTURES TASK 3. EXPLORE PARTICLE SIZE LIMITATIONS OF THE RADIATIVE TRANSFER MONTE CARLO EMISSION MODEL TASK 4. GENERATE SYNTHETIC MODEL MIXTURES TO TEST MINERAL ABUNDANCE RETRIEVAL UNCERTAINTIES USING WELL-ESTABLISHED TECHNIQUES IN THE PLANETARY SCIENCE COMMUNITY RELEVANCE: THIS PROPOSAL IS DIRECTLY RELEVANT TO THE SOLAR SYSTEM WORKINGS PROGRAM AS IT SEEKS TO ENABLE OUR ABILITY TO BETTERCHARACTERIZE AND UNDERSTAND THE CHEMICAL MINERALOGICAL AND PHYSICAL FEATURES OF PLANETARY SURFACES AND MORE SPECIFICALLY DEVELOPS THETHEORETICAL AND EXPERIMENTAL BASES FOR UNDERSTANDING THESE FEATURES ON PLANETARY SURFACES. BY REFINING THE LIMITS OF THE COMMONLY USED LINEARMIXTURE MODELING WE ENABLE A RE-EVALUATION OF SPACECRAFT DATA RETURN FROM MULTIPLE PAST MISSIONS (E.G. MARS GLOBAL SURVEYOR MARS ODYSSEY LUNAR RECONNAISSANCE ORBITER) AS WELL AS FUTURE MISSIONS SUCH AS THE OSIRIS-REX AND LUCY MISSIONS. THE MODEL VALIDATED AS A PART OF THIS WORK SERVES TO FURTHER ENABLE THE REFINEMENT OF FUTURE MINERAL ABUNDANCE RETRIEVAL TECHNIQUES INCLUDING PARTIAL-LEAST SQUARES FITTING AND MAY IN FACT ITSELF BE USED TO RETRIEVE MINERAL ABUNDANCES ASSUMING THERMAL GRADIENTS ARE COMMON TO AIRLESS BODIES. WHILE THIS WORK FOCUSES ON THE LINEAR-MIXTURE MODELING TECHNIQUES THAT ARE WIDELY APPLIED TO MARS AND EARTH THE VALIDATION.