EVALUATING CROP PRODUCTIVITY USING SOLAR INDUCED CHLOROPHYLL FLUORESCENCE MEASURED FROM GROUND AND SPACE REMOTELY SENSED SOLAR INDUCED CHLOROPHYLL FLUORESCENCE (SIF) CAN BE A VERY EFFECTIVE PROXY FOR GROSS PRIMARY PRODUCTION IN AGRICULTURAL ENVIRONMENTS. AGRICULTURAL SYSTEMS EXHIBIT THE LARGEST PEAK CARBON FLUXES AND ARE PLAYING AN INCREASINGLY IMPORTANT ROLE IN THE GLOBAL CARBON CYCLE. CO2 DRAWDOWN IN SUMMER CAN RESULT IN BOUNDARY LAYER CO2 CONCENTRATIONS CLOSE TO PRE-INDUSTRIAL LEVELS POTENTIALLY LIMITING GROWTH FOR C3 CROPS AND NATURAL LANDSCAPES. INTENSIFICATION OF AGRICULTURE ALSO IMPACTS CHANGES IN CO2 SEASONAL AMPLITUDES AS ARE RELATED TO COOLING OF US MIDWEST SUMMER TEMPERATURE EXTREMES (MUELLER ET AL NATURE CC 2015). IN SUMMARY CROPS ESP. IN THE MIDWEST ALTER THE REGIONAL AND GLOBAL CARBON CYCLE AS WELL AS LATENT AND SENSIBLE HEAT FLUXES AFFECTING SUMMER TEMPERATURES REGIONAL CLIMATE AND PRECIPITATION. SIF CAN PROVIDE UNIQUE INSIGHTS IN THE CARBON CYCLE OF AGRICULTURAL SYSTEMS AND FOREST CANOPIES. FOR CROPS BOTH REMOTE SENSING INDICES FOR GREENNESS AS WELL AS CARBON CYCLE MODELS THAT ARE LARGELY CALIBRATED IN FOREST SYSTEMS FAIL TO REPRODUCE THE OBSERVED LARGE CARBON UPTAKE RATES. HOWEVER SIF CLEARLY IDENTIFIES THE HIGHER CARBON FLUXES (GUANTER ET AL PNAS 2014) AND CARBON USE EFFICIENCY (GUAN ET AL GBC 2015) OF CROP SYSTEMS. INITIAL COMPARISONS WITH OCO-2 HAVE ALREADY SHOWN STRONG LOCAL FEATURES OF CO2 DRAWDOWN ASSOCIATED WITH HIGH FLUORESCENCE VALUES IN THE MIDWEST CROP AREAS STRONGLY CONTRASTING FORESTED SYSTEMS. DESPITE THIS POTENTIAL MANY UP-SCALING APPROACHES USING SIF ARE STILL EMPIRICAL AND LACK VALIDATION AND MECHANISTIC UNDERSTANDING. WE POSIT THAT AGRICULTURAL SYSTEMS ARE AN IDEAL STUDY AREA TO ADDRESS THIS AS I) TRADITIONAL VEGETATION INDICES FAIL TO REPRODUCE HIGH CARBON UPTAKES II) CANOPY STRUCTURE IS WELL DEFINED AND CAN BE TREATED IN 1-DIMENSIONAL RADIATIVE TRANSFER MODELS AND III) PROVIDE A WEALTH OF ADDITIONAL INFORMATION VIA HARVEST STATISTICS. THE GOAL OF THIS PROPOSAL IS TO PROVIDE A SOLID FRAMEWORK FOR USING SIF TO ESTIMATE GROSS AND NET CARBON FLUXES IN AGRICULTURAL SYSTEMS. WE WILL LEVERAGE RECENT DEVELOPMENTS FOR MEASURING CHLOROPHYLL FLUORESCENCE AND CARBON EXCHANGE FROM THE LEAF TO THE CANOPY AND LANDSCAPE SCALE. THIS INCLUDES A MODIFIED FLUORESCENCE AND GAS EXCHANGE SYSTEM (WALZ) A SET OF NOVEL HIGH-RESOLUTION GROUNDBASED SIF SPECTROMETERS (PHOTOSPEC UCLA/CALTECH/JPL) ENABLING INDEPENDENT MEASUREMENTS OF SIF AT 680 AND 740NM AS WELL AS SURFACE REFLECTANCE (300-900NM) WITH FULL 2D SCANNING CAPABILITIES AIR-BORNE OBSERVATION ALREADY ACQUIRED WITH THE CHLOROPHYLL FLUORESCENCE IMAGING SPECTROMETER (CFIS JPL) AS WELL AS SPACE-BASED DATA FROM OCO-2 AND TROPOMI TO BE LAUNCHED IN OCTOBER 2016 (ESUSPI PROPOSAL FOR SIF RETRIEVALS IS FUNDED). WE WILL DEPLOY THREE GROUND-BASED PHOTOSPEC SYSTEMS AT SELECTED FLUXTOWER SITES IN DIFFERENT AGRICULTURAL SYSTEMS TO MEASURE SIF AND REFLECTANCE (BI-DIRECTIONAL) AT<10MIN TEMPORAL RESOLUTION OVER THE FULL GROWING CYCLE IN PARALLEL WITH DIRECT CARBON EXCHANGE MEASUREMENTS (NEE GPP) FROM THE FLUXTOWER AT 30MIN RESOLUTION. SIF DIRECTIONALITY AND IMPACT OF SPATIAL AVERAGING WHICH HAS THUS FAR BEEN POORLY DEFINED WILL BE ASSESSED USING THE 2D SCANNING CAPABILITY OF PHOTOSPEC. IN ADDITION LEAF-LEVEL MEASUREMENTS OF GAS EXCHANGE AND THE FULL FLUORESCENCE SPECTRAL SHAPE WILL BE PERFORMED AT DIFFERENT GROWING STAGES. THIS FULL SET OF OBSERVATIONS IN CONJUNCTION WITH SIF/GPP MODELING (SOIL-CANOPY OBSERVATION OF PHOTOSYNTHESIS AND ENERGY SCOPE) WILL ENABLE US TO DERIVE A ROBUST SCALING APPROACH FROM THE LEAF TO THE CANOPY AND LANDSCAPE SCALE. ULTIMATELY WE WILL USE SATELLITE DATA TO DETERMINE CARBON UPTAKE AT THE COUNTY LEVEL (BI-WEEKLY) AND COMPARE ANNUAL TOTALS AGAINST AVAILABLE YIELD STATISTICS. GROUND-BASED MEASUREMENTS IN IRRIGATED VS. RAINFED WILL ALSO BE USED TO EVALUATE THE RELATIONSHIP OF SIF WITH LATENT HEAT FLUXES AND THE