Mapping Daily Net CO2 Flux From Grasslands Using Remote Sensing

The daily net carbon dioxide (CO₂) flux from extensive grassland ecosystems is an important component of the global carbon cycle. In previous studies, instantaneous net CO₂ flux was estimated using a Water Deficit Index (WDI) determined from the relation between surface reflectance and temperature. The mean absolute difference between measured and WDI-derived CO₂ flux was 0.23 over a range of CO₂ flux values from -0.10 to 1.10 (mg m^-2 s^-1). The objective of this study was to determine daily net CO₂ flux from instantaneous estimates for a semiarid grassland site in Southeast Arizona. This objective was reached through two main steps. First, a linear relationship (R² = 0.95) was found between instantaneous net CO₂ flux and net daytime (6 a.m. to 6 p.m.) flux and used to generate maps of daytime CO₂ flux. Second, a field study was conducted to relate night time flux measurements to daytime measurements. These relations made it possible to map daily (24-hour) net CO₂ flux from a single satellite image and basic meteorological information. A limitation of this approach is the dependence upon empirical relations for deriving daytime and night time estimates from instantaneous measurements. On the other hand, the empirical relations derived at this location were strong and consistent for the six-year study period.