THE USE OF NARROW SPECTRAL BANDS FOR IMPROVING REMOTE SENSING ESTIMATIONS OF FRACTIONALLY ABSORBED PHOTOSYNTHETICALLY ACTIVE RADIATION

Abstract

Most remote sensing estimations of vegetation variables such as leaf area index (LAI), absorbed photosynthetically active radiation (Apar,), and primary production are made using broad band sensors with a bandwidth of approximately 100 nm. However, high resolution spectrometers are available and have not been fully exploited for the purpose of improving estimates of vegetation variables. The study was directed to investigate the use of high spectral resolution spectroscopy for remote sensing estimates of f apar in vegetation canopies in the presence of nonphotosynthetic background materials such as soil and leaf litter. A high spectral resolution measure defined as the chlorophyll absorption ratio index (CARI) was developed for minimizing the effects of nonphotosynthetic materials in the remote estimates of f apar CARI utilizes three bands at 550, 670, and 700 nm with bandwidth of 10 nm. Simulated canopy reflectance of a range of leaf area index (LAI) were generated with the SAIL model using measurements of 42 different soil types as canopy background. CARI calculated from the simulated canopy reflectance was compared with the broad band vegetation indices such as normalized difference vegetation index (NDVI), soil adjusted vegetation index (SAVI), and simple ratio (SR). CARI reduced the effect of nonphotosynthetic background materials in the assessment of vegetation canopy f apar more effectively than broad band vegetation indices.