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ROOT ZONE SOIL MOISTURE (RZSM)  IN PARTICULAR  IS CRITICAL FOR UNDERSTANDING  HYDROLOGIC FLUXES LINKING SURFACE AND SUBSURFACE PROCESSES AND THE INTERPLAY BETWEEN THE WATER AND  CARBON CYCLES. ONLY NEAR-SURFACE (0-10 CM) SOIL MOISTURE IS AVAILABLE THROUGH CURRENT SPACEBORNE  REMOTE SENSING  WITH DATA ASSIMILATION RELIED UPON TO PRODUCE RZSM AS LEVEL-4 DATA PRODUCTS. P-BAND  SAR HAS THE POTENTIAL TO MEASURE DEEPER MOISTURE FROM SPACE  ALTHOUGH RADIO SPECTRUM RESTRICTIONS  CURRENTLY PROHIBIT TRANSMISSION OVER EUROPE AND NORTH AMERICA. SIGNAL-OF-OPPORTUNITY REFLECTOMETRY  HAS EMERGED AS A THIRD METHOD OF SPACEBORNE MICROWAVE REMOTE SENSING COMBINING FEATURES OF ACTIVE  AND PASSIVE REMOTE SENSING. SOOP OPERATES AS AN ACTIVE REMOTE SENSING TECHNIQUE IN A FORWARD  REFLECTION BISTATIC CONFIGURATION EXPLOITING PRE-EXISTING SIGNAL SOURCES. SPACEBASED SOURCES AT  THESE FREQUENCIES INCLUDE LEO TEXT-MESSAGING SATELLITES (137-138 MHZ) AND GOVERNMENT NARROWBAND AND  BROADBAND GEOSYNCHRONOUS COMMUNICATIONS SATELLITES (240-270 MHZ AND 360-380 MHZ). ON THE OTHER HAND  THE HARDWARE IS PASSIVE (RECEIVE ONLY) AND THE MEASURAND OF FORWARD REFLECTIVITY IS  LINKED BY KIRCHOFF'S LAW AND CONSERVATION OF ENERGY TO EMISSIVITY. A GREAT ADVANTAGE OF SOOP IS  THAT THESE FEATURES ENABLE LOW-POWER INSTRUMENTS TO MEET LINK BUDGETS WITH SUFFICIENT MARGIN USING  RELATIVELY SMALL WIRE-TYPE ANTENNAS. WE PROPOSE TO DEVELOP A DEPLOYABLE BROADBAND ANTENNA COVERING 137-380 MHZ (P/1 BANDS) WITH INDUSTRY  PARTNER MMA DESIGN FOR USE IN A SOOP INSTRUMENT CONSTELLATION. THE RESULTING TECHNOLOGY WILL BE  COMPATIBLE WITH U-CLASS SATELLITE BORNE SOOP INSTRUMENTS. WE ENVISION A TRAIN OF 6-U SATELLITES   EACH WITH TWO ANTENNAS AND TRI-BAND SOOP RECEIVERS IN HIGH-INCLINATION LOW-EARTH ORBIT FOR  MEASURING SURFACE REFLECTIVITY FOR RETRIEVING SOIL MOISTURE AND OTHER SURFACE PARAMETERS. THE  DEPLOYABLE ANTENNA USES INNOVATIVE PRINTED-CIRCUIT MEMBRANE TECHNOLOGY TO ACHIEVE 1-U STOWED VOLUME. WE WILL INVESTIGATE TWO ANTENNA  TYPES: BROADBAND CROSSED DIPOLE MEMBRANE ANTENNA (BCMA) AND LOG-PERIODIC DIPOLE ARRAY (LPDA).   FOLLOWING DOWNSELECT  A SUB-SCALE MODEL WILL BE BUILT AND TESTED  TO VALIDATE THE DESIGN OF BOTH  THE ELECTROMAGNETIC (EM) PROPERTIES OF THE ANTENNA AND MECHANICAL DESIGN OF THE DEPLOYMENT  MECHANISM. 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