TECs (v1): A Terrestrial Ecosystem Carbon Cycle Simulator Integrated With Spectral Reflection and Emission

Abstract

Accurately estimating carbon fluxes in terrestrial biosphere models (TBMs) is of great significance for Earth system science. Using satellite observations to optimize TBMs is an effective approach to achieve this goal. Radiative transfer is the physical linkage between TBMs and satellite observations. Therefore, a sophisticated radiative transfer model in TBMs, which explicitly links satellite-observable surface reflectance to biophysical and biochemical processes within the vegetation canopy, and allows directly using remote sensing data to effectively constrain or optimize TBMs. Here, we developed the terrestrial ecosystem carbon cycle simulator (TECs) with a strategic design that incorporates an advanced radiative transfer model (RTM) based on the spectral invariant theory. This model simultaneously simulates carbon fluxes and high-resolution spectral signals across optical to thermal wavelengths under any specified sun-sensor geometry. We calibrated and tested TECs simulations at the Harvard Forest (HARV) National Ecological Observation Network site using a range of ecological and satellite data. After calibrating parameters, TECs accurately simulates net ecosystem exchange (NEE) (hourly: R² = 0.80, mean absolute error (MAE) = 1.85 μmol/m²/s; daily: R² = 0.71, MAE = 1.25 μmol/m²/s), hyperspectral reflectance (R²: 0.85, MAE: 0.04), and land surface temperature (LST) (R²: 0.85, MAE: 3.04°C). These results demonstrate that TECs is a promising tool for enhancing terrestrial carbon flux modeling using next-generation hyperspectral observations. TECs lays a strong foundation for future integration of hyperspectral data and models to improve carbon flux predictions.