Using SMAP Soil Moisture Measurements in Carbon Flux Studies in Ohio.

NASA’s Soil Moisture Active/Passive (SMAP) satellite was launched on January, 31^st 2015 to measure global surface (5 cm) volumetric soil moisture content (θ_v) at 36 km spatial and 3 day temporal resolution. Furthermore, net ecosystem exchange (NEE) is also being measured to assess the terrestrial biosphere capacity as a net source or sink for atmospheric carbon dioxide (CO₂) and its ability to offset or reinforce anthropogenic greenhouse gas emissions at 9 km spatial and 3 day temporal resolution. The advantages of taking measurements at these large scales include a stronger linkage between weather and NEE when compared to finer scales, where the effects of soil physical and biological process are the major determinates for plant growth. Current methods used to characterize the influence of moisture on C fluxes in agroecosystems at a large scale (>1 ha), primarily used rainfall impacts on plant growth. However, θ_v  is more appropriate for describing the influence of changes in water availability controlling the biological processes involved in microbial respiration (C losses due to decomposition) and plant growth. Currently, the link between SMAP satellite data and NEE is the strongest in humid regions where the predominant limitation to plant productivity is energy from solar radiation, which occurs in synchrony with plant C uptake via photosynthesis. However, this may be over simplifying when considering moisture stresses on plants specifically in agricultural fields during water logging and drought, which are heavily dependent on soil texture and management practices. Therefore, this study will assess the impact of θ_v on NEE in agroecosystems in Ohio.