UNVEILING CYGNSS LAND SIGNATURES FOR HIGH SPATIOTEMPORAL SOIL MOISTURE ESTIMATION SOIL MOISTURE (SM) IS A KEY FACTOR THAT GOVERNS THE WATER ENERGY AND CARBON CYCLES THROUGH THE GROUND-AIR BOUNDARY OF THE EARTH. THE IMPACT OF SM SHOULD BE UNDERSTOOD WITH HIGH SPATIOTEMPORAL RESOLUTIONS ON A GLOBAL BASIS TO IMPROVE LAND APPLICATIONS SUCH AS WEATHER AND HAZARD FORECAST AND CROP YIELD ESTIMATION. MICROWAVE REMOTE SENSING HAS BEEN USED FOR MONITORING SM AND OTHER LAND PARAMETERS FOR DECADES BECAUSE OF ITS SENSITIVITY TO THE SURFACE FEATURES. CONVENTIONAL METHODS USE ACTIVE/PASSIVE MONO-STATIC RADAR AND OFFER EITHER LOW TEMPORAL RESOLUTION OR COARSE SPATIAL SENSITIVITY FOR AGRICULTURAL AND HYDROMETEOROLOGICAL PURPOSES. GLOBAL NAVIGATION SATELLITE SYSTEM-REFLECTOMETRY (GNSS-R) HAS BEEN ACHIEVING RECENT ATTRACTION IN EARTH SCIENCE DUE TO ITS GLOBAL COVERAGE WITH HIGH SPATIOTEMPORAL RESOLUTION BY USE OF SMALL FORM FACTOR RECEIVERS. IT IS BASED ON THE RECEPTION OF THE REFLECTED SIGNALS FROM THE EARTH THAT ARE ALREADY EMITTED BY EXISTING GNSS SATELLITES IN A MULTI-STATIC SCHEME. GNSS-R HAS BEEN MATURATED ON OCEAN STUDIES SUCH AS WIND VECTORS ESTIMATION AND ALTIMETRY. THIS MATURITY LED TO THE NASAS CYCLONE GNSS (CYGNSS); IT AIMS TO DEVELOP OCEAN WINDS ESTIMATION IN A LARGE TROPICAL COVERAGE. IT HAS A REMARKABLY HIGH TEMPORAL RESOLUTION OF<12 HOURS AND NATIVE SPATIAL RESOLUTION OF 10-25 KM. MOREOVER IT OBSERVES LARGE LAND DATA THAT CAN BE EXPLOITED FOR SM ESTIMATION AND SPATIAL RESOLUTION FOR LAND CAN BE ASSUMED 1 KM BY 7 KM DUE TO THE DOMINATION OF THE COHERENT REFLECTIONS FROM THE FIRST FRESNEL ZONE. SEVERAL STUDIES ASSESS THE POTENTIAL OF GNSS-R FOR RETRIEVAL OF SM AND OTHER PARAMETERS. WHILE THE EXPERIMENTAL OBSERVATIONS AND QUALITATIVE INTERPRETATIONS FROM THOSE STUDIES INVALUABLY CONTRIBUTE TO THE POTENTIAL FEASIBILITY DEMONSTRATION OF GNSS-R ON LAND QUANTIFICATION OF THE IMPACT OF ALL THE LAND PARAMETERS STILL REQUIRE COMPREHENSIVE ANALYSIS. ANALYTICAL SCATTERING MODELS CAN PLAY A SIGNIFICANT ROLE TO UNVEIL THE FEASIBILITY OF SPACEBORNE GNSS-R FOR LAND OBSERVATIONS BY THEIR PARAMETRIC CONCRETIZATION ABILITY. THE MAIN CONSTRAINT FOR IMPROVEMENT OF SPACEBORNE GNSS-R THROUGH LAND APPLICATIONS IS THE SMALL AMOUNT OF SUCH STUDIES. THE KEY PROPOSAL OF THIS RESEARCH IS TO ESTIMATE SM BY USING ANALYTICAL MODEL-BASED SIMULATIONS ON THE CYGNSS LAND OBSERVATION DATA QUANTIFYING THE IMPACT OF OTHER LAND PARAMETERS SUCH AS VEGETATION WATER CONTENT (VWC) AND ROUGHNESS. WE HAVE DEVELOPED A COHERENT BISTATIC VEGETATION SCATTERING MODEL CALLED SIGNALS OF OPPORTUNITY COHERENT BISTATIC VEGETATION MODEL (SCOBI-VEG) THAT ACCOUNTS FOR THE BISTATIC REFLECTOMETRY USING A MONTE CARLO SCHEME. IT AIMS TO ASSESS SOOP REMOTE SENSING OF LAND PARAMETERS SUCH AS SM AND BIOMASS. IT ENABLES COMPREHENSIVE ANALYSIS ON THE EFFECTS OF THESE AGENTS CALCULATING THE COHERENT AND INCOHERENT RECEIVED FIELD AND POWER TERMS BY USING THE ANTENNA EFFECTS (POLARIZATION CROSSTALK/MISMATCH ORIENTATION ETC.) AND SCENE CONDITIONS. WE HAVE ALSO DEVELOPED AND CURRENTLY BEEN OPEN-SOURCING A SIMULATOR THAT EMPLOYS SCOBI-VEG MODEL TO CREATE A FRAMEWORK FOR SUCH USE. WE HAVE ANALYZED SIGNATURES BETWEEN THE SM VWC DURING THE CORN GROWING SEASON AND THE RECEIVED POWER VIA SCOBI-VEG. THE FIRST RESULTS HAVE SHOWN REASONABLE TRENDS FOR ALTERING SM AND VWC. WE HAVE ALSO DEVELOPED AN INVERSION MODEL USING SUPPORT VECTOR MACHINE (SVM) TO RETRIEVE GROWTH STAGES (I.E. VWC) OF ARBITRARY CORN FIELDS UNDER ALTERING SCENE CONDITIONS. THE PRELIMINARY RESULTS HAVE SHOWN PROMISING LINEAR RELATIONS BETWEEN THE RECEIVED POWER AND VWC. THIS PROPOSAL AIMS TO (1) MAKE QUANTITATIVE ANALYSIS OF CYGNSS LAND DATA BY USING THE SCOBI-VEG (2) FIND THE GNSS-R SIGNATURES AND THEIR CAUSES (3) PROPOSE RULES FOR GNSS-R LAND OBSERVATION AND (4) CREATE ANALYTICAL MODELS FROM THESE RULES FOR SM ESTIMATION AND VERIFY THESE MODELS OVER SOIL MOISTURE ACTIVE PASSIVE (SMAP) CORE VALIDATION SITES