SOIL MOISTURE IS A KEY PARAMETER TO DETERMINE WATER AVAILABILITY; IT CONNECTS THE TERRESTRIAL WATER ENERGY AND CARBON CYCLES AND ACTS AS A CLIMATE INDICTOR. THE 2007 DECADAL SURVEY REINFORCED THE NECESSITY OF MONITORING SOIL MOISTURE BY RECOMMENDING A DEDICATED SOIL MOISTURE MISSION. MANY SENSORS CAPABLE OF SOIL MOISTURE SENSING AT DIFFERENT FREQUENCIES HAVE BEEN LAUNCHED OVER THE YEARS. EACH OF THEM PURSUES THE GOAL OF SUCCESSFULLY RETRIEVING SOIL MOISTURE BASED ON THEIR OWN CALIBRATION AND VALIDATION METRICS. FUNDAMENTALLY THE INTEREST LIES IN A CONSISTENT LONG-TERM SOIL MOISTURE RECORD SPANNING MULTIPLE SATELLITE PLATFORMS AND WE THEREFORE NEED A CONSISTENT SENSOR DATA RECORD. SOIL MOISTURE WAS NAMED AN ESSENTIAL CLIMATE VARIABLE (ECV) IN 2010 BY THE GLOBAL CLIMATE OBSERVING SYSTEM AN INITIATIVE BY THE WORLD METEOROLOGICAL ORGANIZATION THE UNITED NATIONS AND THE INTERNATIONAL COUNCIL FOR SCIENCE. IN THIS INVESTIGATION WE FOCUS ON FOUR SATELLITES THAT ARE CAPABLE OF SOIL MOISTURE RETRIEVAL VIA BRIGHTNESS TEMPERATURE OBSERVATIONS: JAXA S ADVANCED MICROWAVE SCANNING RADIOMETER-EOS (AMSR-E) LAUNCHED IN MAY 2002 ON THE NASA AQUA SATELLITE (IT STOPPED NOMINAL DATA ACQUISITION IN OCTOBER 2011) ESA S SOIL MOISTURE AND OCEAN SALINITY (SMOS) MISSION LAUNCHED IN NOVEMBER 2009 JAXA S ADVANCED MICROWAVE SCANNING RADIOMETER 2 (AMSR2) ONBOARD THE GCOM-W SATELLITE LAUNCHED IN MAY 2012 AND NASA S SOIL MOISTURE ACTIVE PASSIVE (SMAP) MISSION LAUNCHED IN JANUARY 2015. WE PROPOSE TO (A) INTER-CALIBRATE THE L- C- AND X-BAND BRIGHTNESS TEMPERATURES OF AMSR-E SMOS AMSR2 AND SMAP. WE WILL MATCH THE OBSERVATIONS OF THE INSTRUMENTS IN SPACE AND TIME OVER OCEAN AND WITH RESPECT TO THE COLD SKY. WE WILL ADAPT A HERITAGE ANTENNA TEMPERATURE SIMULATOR TO MULTI-FREQUENCY BRIGHTNESS TEMPERATURE MODELING TO MAKE THE L- C- AND X-BAND BRIGHTNESS TEMPERATURES CONSISTENT ACROSS FREQUENCIES. TEMPORAL OVERLAP OF SMOS WITH AMSR-E AND SMAP AND SMOS WITH AMSR2 WILL BE KEY IN MAKING THE BRIGHTNESS TEMPERATURE RECORDS CONSISTENT. WE FURTHER PROPOSE TO (B) APPLY A UNIFORMLY DESIGNED SOIL MOISTURE RETRIEVAL ALGORITHM TO RETRIEVE CONSISTENT SOIL MOISTURE USING THE BRIGHTNESS TEMPERATURE RECORDS AT DIFFERENT FREQUENCIES. WE WILL BRING IN IN-SITU SOIL MOISTURE DATA AS GROUND TRUTH TO PARAMETERIZE AND TEST THE PERFORMANCE OF THE SOIL MOISTURE RETRIEVAL ALGORITHM. THIS WILL ALLOW US TO REVEAL ANY HIDDEN INCONSISTENCIES BETWEEN THE DIFFERENT BRIGHTNESS TEMPERATURE DATA SETS. FINALLY WE PROPOSE TO (C) COMPENSATE FOR THE DIFFERENT SENSING DEPTHS OF THE DIFFERENT FREQUENCIES USING A MODEL AND PRESENT THE SOIL MOISTURE AT A UNIFORM DEPTH. WE WILL APPLY A SIMPLE NEAR SURFACE SOIL MOISTURE MODEL TO PROJECT THE OBSERVATIONS TO THE SMAP OBSERVATION DEPTH. THE PROPOSED WORK ENABLES A CONSISTENT GLOBAL SOIL MOISTURE DATA RECORD SPANNING FROM 2002 TO PRESENT AND CONTINUES IN THE TIME FRAME OF THE PERFORMED WORK UNTIL 2019. WE SHALL LEVERAGE THE SIGNIFICANT HERITAGE OF ANALYSIS AND TOOLS ACCUMULATED BY THE INVESTIGATOR TEAM TO CONDUCT THE PROPOSED RESEARCH. THE U.S. GLOBAL CHANGE RESEARCH PROGRAM IDENTIFIED THE IMPORTANCE OF SOIL MOISTURE OBSERVATIONS IN ITS OBJECTIVES OF EARTH SCIENCE UNDERSTANDING AND EMPHASIZES THE IMPORTANCE OF LONG-TERM INTEGRATED OBSERVATIONS. NOAA S NATIONAL CALIBRATION CENTER AIMS AT DEVELOPING UNIFORM CALIBRATION STANDARDS AND METHODOLOGIES FOR ENVIRONMENTAL SATELLITES SUCH AS THE ONES PROPOSED IN THIS RESEARCH. SIMILARLY THE PROPOSED INVESTIGATION IS RESPONSIVE TO SEVERAL INTERNATIONAL EFFORTS TO ACHIEVE INTER-CONSISTENCY OF SATELLITE PRODUCTS. THIS STUDY WILL BE RELEVANT FOR THE CEOS (COMMITTEE ON EARTH OBSERVING SATELLITES). THE OBJECTIVES AND THE WORK PLAN OF THE PROPOSAL IS ALSO ALIGNED WITH OBJECTIVES OF THE GLOBAL SPACE-BASED INTER-CALIBRATION SYSTEM (GSICS) WHICH AIMS AMONGST OTHERS AT MONITORING INSTRUMENT PERFORMANCES AT TYING THE MEASUREMENTS TO ABSOLUTE REFERENCES AND STANDARDS AND AT RECALIBRATING ARCHIVED DATA.