RELATIONSHIP BETWEEN SATELLITE-DERIVED VEGETATION INDEXES AND AIRCRAFT-BASED CO2 MEASUREMENTS

The objective of this study was to analyze the relationship between satellite-derived vegetation indices and CO2 uptake, as an initial step in exploring the possibility of using a satellite-derived vegetation index as a measure of net photosynthesis. [-he study area included the First International Satellite Land Surface Climatology Project (ISLSCP) Field Experiment (FIFE) site located on the Konza prairie and adjacent area as well as a transect between Manhattan and Salina. One third of the transect exhibited vegetation and terrain characteristics similar to those on the FIFE site, whereas cultivated land predominated in the remaining portion of the 75-km-long flight line. In June, July, August, and October 1987, several CO2 data sets were obtained using the National Research Council of Canada's Twin Otter research aircraft. The normalized difference vegetation index (NDVI) and the simple ratio (SR) were computed from NOAA advanced very high resolution radiometer (AVHRR) data acquired as part of FIFE. Aircraft and satellite data were processed to obtain spatially coincident and locally representative flux values. Results show a linear relationship between NDVI and CO2 uptake during a single day; however, a nonlinear relationship emerged when all data sets were combined. The data from FIFE and the regional transect were consistent for one date but differed for other periods. Overall . about 60% of total variability in CO2 flux was accounted for by the NDVI and 74% by the SR.