A remote sensing approach for estimating distributed daily net carbon dioxide flux in semiarid grasslands

Semiarid systems compose a significant portion of the world's terrestrial area and may play an important role in the global carbon cycle. A model was developed using the relation between surface reflectance and temperature obtained from satellite imagery to determine a Water Deficit Index (WDI) that estimated distributed plant transpiration, and by extension carbon dioxide (CO 2 ) flux, for a point in time. Relationships were developed to scale these instantaneous flux measurements up to daytime estimates, which were then used to obtain measures of nighttime flux. Satellite images were acquired for a 5‐year period (1996–2000) during which transpiration and net CO 2 flux were measured for a semiarid grassland site in southeastern Arizona. Manual and automatic chamber data were also collected at the same site during the monsoon growing seasons of 2005 and 2006 and used to develop the relationship between and daytime and nighttime CO 2 flux. Strong linear relationships were found between WDI‐derived instantaneous and daytime net CO 2 flux estimates (R 2 = 0.97), and between daytime and nighttime fluxes (R 2 = 0.88). These relations were used to generate maps of distributed total daily net CO 2 flux. The error for the model was within the range of error inherent in the data sets used to create it and remained reasonable when used with WDI values less than 0.9. This study demonstrated that remote sensing can offer a physically based means of obtaining daily net CO 2 flux in semiarid grasslands.