ECOSTRESS estimates gross primary production at different times of day from the International Space Station

Accurate estimation of gross primary production (GPP), the amount of carbon absorbed by plants via photosynthesis, is of great importance for understanding ecosystem functions, carbon cycling, and climate-carbon feedbacks. Remote sensing has been widely used to quantify GPP at regional to global scales. However, traditional satellites (e.g., Landsat, Terra, Aqua) lack the capability to examine the diurnal cycles of GPP because they observe the Earth’s surface at the same time of day. The Ecosystem Spaceborne Thermal Radiometer Experiment on Space Station (ECOSTRESS), launched on June 2018, observes the land surface temperature (LST) at different times of day with high spatial resolution (70 m × 70 m) from the International Space Station (ISS). Here, we used ECOSTRESS data to predict instantaneous GPP with high spatial resolution based on a data-driven approach. The predictive GPP model was developed based on ECOSTRESS LST observations, along with the Enhanced Vegetation Index (EVI) from the Moderate Resolution Imaging Spectroradiometer (MODIS), land cover type from the National Land Cover Database (NCLD), and meteorological variables. Our model estimated instantaneous GPP across 56 flux tower sites fairly well (R2 = 0.88, Root Mean Squared Error (RMSE) = 2.42 μmol CO2 m-2 s-1). The predicted GPP driven by the ECOSTRESS LST captured the diurnal variations of tower GPP for different biomes. We then produced multiple ECOSTRESS GPP maps for the Central California Foothills and Coastal Mountains, Central California Valley, Sierra Nevada and Coast Range in California. We found that the ECOSTRESS GPP showed distinct changes at different times of day (e.g. higher in late morning, peak around noon, approaching zero at dusk), and clearly depicted the differences in productivity across landscapes (e.g., savannas, croplands, grasslands, and forests) for different times of day. This study demonstrates the feasibility of using ECOSTRESS data for producing instantaneous GPP for different times of day. The ECOSTRESS GPP can shed light on how plant photosynthesis and water use vary over the course of the diurnal cycle and inform agricultural management and future improvement of terrestrial biosphere/land surface models.