Impact of Spectral Resolution on Solar Induced Fluorescence and Reflectance Indices for Monitoring Vegetation

Abstract

This study examines the impact of spectral resolution on red-edge reflectance (R) and Fraunhofer Line Depth (FLD) derived fluorescence (F) from vegetation. The goal of this investigation is to present data describing net canopy CO₂ exchange (A ₙₑₜ ) of corn (Zea mays L.) under variable N supply and present considerations for both fluorescence and reflectance sensing methodologies to remotely quantify this key regulator of ecosystem/biome productivity. A number of R indexes were investigated and consistent relationships were evident between red-edge R and R derivative (D) indexes to indicators of crop growth and condition. Through Gaussian FWHM spectral broadening of the native 3 nm data in intervals from 10 nm to 50 nm, it was determined that correlations were maintained between the top two performing indexes (Dₘₐₓ /D₇₄₄ , R₈₀₀ /R₇₅₀ ) and their respective measures of crop condition (Aₙₑₜ , C:Chl) up to a 20 nm spectral resolution. Adaxial corn leaf R was obtained from three spectrometers operating in unison with optical fibers bundled together enabling NADIR measurement of leaf R at five spectral resolutions ranging from 0.2 nm to 5 nm. In general, the increased band depth of high spectral resolution data allowed for more accurate SIF retrievals with improved relationships to plant biophysical parameters. From this investigation we conclude that indices calculated from both R and F data types supplied useful information for modeling nitrogen use for carbon sequestration by vegetation.