SCIENCE OBJECTIVES: THE CLASSIC PERCEPTION OF AEOLIAN TRANSPORT IS GRAIN MOTION BY SALTATION. HOWEVER STUDIES SUGGEST THAT IN DENSE ATMOSPHERES ON VENUS AND TITAN ROLLING AND SKIPPING ARE SIGNIFICANT WHILE IN THIN ATMOSPHERES SUCH AS MARS SALTATION REPTATION AND SALTATION/REPTATION HYBRID TRANSPORT MODES ARE DOMINANT. AT ONE END OF THE SPECTRUM AERODYNAMIC FORCES ARE ALMOST 100% IN CONTROL (E.G. VENUS) WHILE AT THE OTHER END OF THE SPECTRUM (E.G. MARS) BALLISTIC GRAIN INTERACTIONS PLAY A HUGELY IMPORTANT ROLE IN GOVERNING TRANSPORT MODES. MUCH OF THE INFORMATION ABOUT COMPARATIVE TRANSPORT MODES FROM EXPERIMENTS HAS NOT BEEN SYSTEMATICALLY DOCUMENTED HAS ONLY BEEN MODELED OR ACQUIRED ANECDOTALLY. OUR GOAL THEREFORE IS TO CONDUCT AN INTEGRATED AND SYSTEMATIC EXPERIMENTAL (WIND TUNNEL) STUDY OF THE RELATIVE ROLES OF AERODYNAMIC VERSUS BALLISTIC TRANSPORT MODES FOR A RANGE OF PLANETARY ENVIRONMENTS. AT PRESENT IT IS UNKNOWN AS TO WHETHER THE PHYSICS OF TRANSPORT DIFFERS ONLY BY DEGREE BETWEEN DIFFERENT AEOLIAN REGIMES OR IF IT IS RADICALLY DIFFERENT BETWEEN THEM. A PRIMARY GOAL OF THE PROJECT IS TO DEVELOP #FOR WIND TUNNEL PLANETARY SIMULATIONS #A SIMILITUDE PARAMETER APPROPRIATE FOR AEOLIAN GRAINS THAT ACTS AS AN EQUIVALENT TO THE REYNOLD#S NUMBER (WHICH IS ONLY APPROPRIATE FOR THE GAS FLOW). METHODOLOGY: EXPERIMENTS WILL BE CONDUCTED IN THE PLANETARY AEOLIAN LABORATORY (PAL) AT NASA AMES USING THE MARS WIND TUNNEL AND THE TITAN (FORMERLY VENUS) WIND TUNNEL. EXTENSIVE VIDEOGRAPHY WILL BE APPLIED TO DETERMINE THE RATIO BETWEEN AERODYNAMIC (A) AND BALLISTIC (B) TRANSPORT IN RELATION TO THE APPLIED VARIABLES. EXPERIMENTS WILL TEST A WIDE RANGE OF VARIABLES (GRAIN SIZE GRAIN DENSITY GAS DENSITY WIND SPEED ETC) WITH A PASSIVE TEST MATRIX THAT INVESTIGATES PARAMETER SPACE AND AN ACTIVE TEST MATRIX THAT IS PLANETARY-SPECIFIC. A SPLIT-BED METHOD OF TESTING WILL BE INTRODUCED IN ORDER TO COMPENSATE FOR WEIGHT-VERSUS-INERTIA PROBLEMS ENCOUNTERED IN WIND TUNNELS. FROM THESE TESTS WE WILL ACQUIRE A/B RATIOS THAT CAN BE USED TO DERIVE A SIMILITUDE PARAMETER MODEL APPROPRIATE FOR CALIBRATING FUTURE WIND TUNNEL SIMULATIONS OF PLANETARY CONDITIONS. SIGNIFICANCE: AEOLIAN PROCESSES HAVE MANIFESTATIONS ON MARS EARTH TITAN VENUS TRITON AND PERHAPS ON COMETS SUCH AS 67P/ CHURYUMOV-GERASIMENKO AND PLUTO; THEIR UBIQUITY UNDER SUCH DIVERSE CONDITIONS MAKES THEM IMPORTANT TO STUDY AND OF DIRECT RELEVANCE/SIGNIFICANCE FOR NASA. IN PARTICULAR AN UNDERSTANDING OF WHY THESE VARIOUS SYSTEMS ARE SIMILAR AND WHY THEY ARE ALSO DIFFERENT IS A CORE PRINCIPLE OF COMPARATIVE PLANETOLOGY A FOUNDATION OF NASA'S PLANETARY EXPLORATION. THIS WORK WILL BE THE FIRST SYSTEMATIC AND COMPREHENSIVE PLANETARY INVESTIGATION OF WHAT WE REFER TO AS THE A-B RATIO --THE FLUX RATIO OF AERODYNAMICALLY-DRIVEN TO BALLISTICALLY-DRIVEN GRAINS THAT DEFINES THE CHARACTER OF AEOLIAN TRANSPORT. PLANETARY COMPARISONS REQUIRE A PHYSICAL BASIS -SOME GOVERNING BEHAVIORAL LAWS THAT ENABLE SUCH COMPARISON. SEDIMENTARY GEOLOGY USES SIMILITUDE PARAMETERS SUCH AS FROUDE REYNOLDS MACH NUMBERS ETC. WHICH CHARACTERIZE THE FLUID FLOW IN AEOLIAN ENVIRONMENTS INCLUDING WIND TUNNELS. THERE IS NO SIMILITUDE PARAMETER FOR GRANULAR MATERIAL IN WIND TUNNEL INVESTIGATIONS. THIS WORK HAS A GOAL OF DEFINING A SIMILITUDE PARAMETER WITH UNIVERSAL APPLICABILITY TO THE DESIGN AND INTERPRETATION OF WIND TUNNEL EXPERIMENTS.