THE CYCLONE GLOBAL NAVIGATION SATELLITE SYSTEM (CYGNSS) CONSISTING OF EIGHT SATELLITES WAS LAUNCHED IN DECEMBER 2016. COVERINGTHE EARTH BETWEEN 38S AND 38N LATITUDES THE CYGNSS MEASURES GPS SIGNALS WITH SCATTERING CROSS SECTIONS OVER BOTH OCEAN AND LANDSURFACES AT A 10-15 KM SPATIAL RESOLUTION. THE ADVANTAGES OF THE CYGNSS MEASUREMENTS FOR RETRIEVAL OF SOIL MOISTURE INCLUDE THESTRONG FORWARD SCATTERING SIGNAL FROM SOIL SURFACES WHICH CAN MAKE POSSIBLE THE RETRIEVAL OF SOIL MOISTURE BEYOND VWC OF 5 KG/M2 WHERE SMAP AND SMOS RETRIEVALS SHOW LARGE UNCERTAINTIES. WE PROPOSE TO DEVELOP SOIL MOISTURE RETRIEVAL ALGORITHM BASED ON PHYSICALMODELS OF BISTATIC SCATTERING. THE PROPOSAL TEAM ARE WITH THE SMAP SCIENCE TEAM AND WOULD LEVERAGE THE PRIOR EXPERIENCE OF ACTIVE ANDPASSIVE REMOTE SENSING OF SOIL MOISTURE AT L-BAND. THE TEAM HAS PERFORMED THE FOLLOWING IN SMAP.1. DEVELOPED THE BASELINE ACTIVE RETRIEVAL ALGORITHM USING TIME-SERIES OF RADAR BACKSCATTERING BASED ON DATA CUBES OF PHYSICAL MODELS.THE BACKSCATTERING RADAR PHYSICAL MODELS WERE BASED ON DISTORTED BORN APPROXIMATION (DBA) AND NUMERICAL SOLUTIONS OF MAXWELLEQUATIONS (NMM3D) OF ROUGH SURFACE SCATTERING.2. THE BASELINE ACTIVE RETRIEVAL ALGORITHM HAS BEEN VALIDATED WITH EXTENSIVE FIELD CAMPAIGNS AND WITH THE SMAP RADAR DATA OVER THEWHOLE PERIOD.3. EXTENSIVE GROUND MEASUREMENTS OF GEOMETRIC PARAMETERS OF VEGETATION AND ROUGHNESS CHARACTERISTIC OF SOIL SURFACES WERE MADE INTHE SMAP SITES THAT ARE USED IN THE VALIDATION OF THE AIRBORNE ACTIVE AND PASSIVE MICROWAVE MEASUREMENTS.4. PHYSICAL MODELS OF BISTATIC SCATTERING USING DBA FOR VEGETATION AND NMM3D FOR ROUGHNESS WERE DEVELOPED TO CALCULATE EMISSIVITY FORPASSIVE REMOTE SENSING AND USED IN CONJUNCTION WITH BACKSCATTERING FOR A COMBINED ACTIVE-PASSIVE MODEL.IN CYGNSS WE PROPOSE TO PERFORM THE FOLLOWING1. WE USE THE BISTATIC SCATTERING MODELS TO FORM DATA CUBES AND DEVELOP TIME SERIES RETRIEVAL ALGORITHM BASED ON THE DATA CUBES. FORVEGETATION BISTATIC MODELS WERE DEVELOPED BASED ON DBA FOR GRASS AND WHEAT. WE WILL COMPLETE THE BISTATIC DBA MODELS FOR CROPS SHRUBS AND TREES. USING THE DERIVED BISTATIC SCATTERING FOR THE THREE CONTRIBUTIONS: SURFACE SCATTERING VOLUME SCATTERING AND DOUBLEBOUNCE SCATTERING DATA CUBES WILL BE CONSTRUCTED.2. ABSOLUTE SOIL MOISTURE VALUES ARE RETRIEVED BY THE MULTI-ANGULAR TIME-SERIES INVERSION OF THE DATA CUBES OF THE PHYSICAL FORWARDMODELS. ITS NOVELTY LIES IN THE PHYSICAL MODELS ABILITY TO PREDICT SCATTERING FROM WIDE-RANGING INCIDENCE ANGLE AND THE TIME-SERIESCONCEPTS EXPLOITING FAST REPEAT (<12 HOURS). THESE NOVEL ASPECTS ADD TO THE PAST SUCCESS WITH VEGETATION CORRECTION AND ROUGHNESSRETRIEVAL ON SMAP RADAR DATA. THE RETRIEVALS WILL BE VALIDATED OVER THE SMAP CORE VALIDATION SITES AND SPARSE NETWORKS BETWEEN 38NAND 38S AND COMPARED WITH SMAP/SMOS RETRIEVALS.3. WE STUDY THE CONTRIBUTIONS OF COHERENT AND INCOHERENT SCATTERING. IN NMM3D BISTATIC ROUGH SURFACE COHERENT AND INCOHERENTSCATTERING COEFFICIENTS WERE DERIVED USING FINITE SURFACE AREAS. THESE ARE TO BE COMBINED TAKING INTO THE ACCOUNT THE TOPOGRAPHY ANDROUGHNESS OF VARIOUS FRESNEL ZONES IN A SINGLE CYGNSS PIXEL.4. THE LARGE SOIL SURFACE FORWARD SCATTERING MAKES POSSIBLE RETRIEVAL OF SOIL MOISTURE FOR LARGE VWC MUCH BEYOND THE VWC OF 5KG/M2OF THE SMAP MISSION. THIS REQUIRES PHYSICAL MODELLING OF THE ATTENUATION OF VEGETATION/FORESTS BETWEEN 5KG/M2 TO 20 KG/M2. RECENTLY WE HAVE PERFORMED NMM3D OF VEGETATION AND TREES WITH A NEW HYBRID METHOD. WE SHOWED THAT THE ATTENUATION RATES CALCULATED FROMNMM3D CAN BE MUCH SMALLER THAN THAT OF THE DBA/RTE METHODS PARTICULARLY FOR THE LARGE VWC CASES. WE WILL APPLY NMM3D TOTHESE CASES TO CALCULATE MORE ACCURATE RESULTS FOR THE DATA CUBES.THE PROPOSED RESEARCH AND RESULTS WILL BE AN INTEGRAL PART OF ATBD AND WILL ENHANCE THE TECHNOLOGY READINESS (TRL) OF SOIL MOISTURERETRIEVAL USING CYGNSS SIGNALS.