The NASA SMAP Mission Level 4 Carbon Product: A New Tool for Global Monitoring of Terrestrial Carbon Exchange

Abstract:

The NASA SMAP (Soil Moisture Active Passive) mission was successfully launched January 31^st 2015, inaugurating new operational low frequency (L-band) microwave observations of land surface conditions. SMAP provides for global monitoring of dynamic landscape freeze-thaw (FT) and soil moisture conditions, with model enhanced estimation of terrestrial carbon fluxes and environmental controls. Science objectives enabled by these data include improving understanding of water, energy and carbon cycle linkages, and reducing uncertainty regarding land-atmosphere CO₂ exchange and the purported missing carbon sink. The Level 4 Carbon (L4_C) product uses SMAP FT retrievals and data assimilation enhanced soil moisture estimates with other ancillary inputs to quantify daily net ecosystem CO₂ exchange (NEE), component carbon fluxes and surface soil organic carbon (SOC) stocks globally. The L4_C product also quantifies underlying soil moisture and frozen season constraints to vegetation growth and respiration. Here we describe initial L4_C observations and performance, including global variations in carbon fluxes and anomalous impacts from recent climate extremes; example illustrations show the northern migration of spring thawing, growing season onset and subsequent summer drought decline in photosynthetic carbon uptake. Initial performance assessments indicate that the L4_C product achieves targeted NEE accuracy requirements within 1.6 g C m^-2 d^-1 (RMSE) over more than 80% of the global domain, and similar to tower eddy covariance based observations. Public release of the L4_C data is expected in late 2015. Early results from L4_C Cal/Val intensive activities and anticipated science applications are discussed.