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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 CO 2 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 (D max /D 744 , R 800 /R 750 ) and their respective measures of crop condition (A net , 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.

Abstract. This study evaluates the potential of the DLR Earth Sensing Imaging Spectrometer (DESIS) visible through near-infrared (VNIR) surface reflectance to augment the EO-1 Hyperion full spectrum (400–2400 nm) reflectance collection over vegetated flux sites, to extend the reflectance time series up to the present. We compared DESIS and Hyperion surface reflectance magnitude and variability at a pseudo-invariant site (PICS) and a vegetated flux site (VFS). VNIR reflectance magnitudes between the two sensors did not significantly differ at the PICS. However, DESIS variability was higher, likely due to differences in the data acquisition time and observation geometry. Using empirical and biophysical models, both DESIS and Hyperion datasets captured the seasonal variations in gross primary production (GPP) and canopy bio-physical parameters such as chlorophyll content, leaf area index (LAI), and senescent material at the VFS. Differences in the magnitudes of the bio-physical parameters were observed, likely due to the differences in the sensors spectral range and resolution. Using together VNIR reflectance from EO-1 Hyperion and DESIS convolved to Hyperion spectral resolution to estimate canopy chlorophyll and GPP, we demonstrate that combining historic and current space-based reflectance data in a common multi-sensor approach is feasible. This is of importance for extending the reflectance record established with EO-1 Hyperion to provide continuity with the current orbital instruments (e.g., DESIS/ISS, PRISMA/ASI) and the forthcoming NASA Surface Biology and Geology (SBG), ESA CHIME and DLR EnMAP satellite missions, which is of key importance for comparisons of current and past trends in the seasonal dynamics of vegetation traits and photosynthetic function.

Abstract-Vegetation productivity is driven by nitrogen (N) availability in soils. Both excessive and low soil N induce physiological changes in plant foliage. In 2001, we examined the use of spectral fluorescence and reflectance measurements to discriminate among plants provided different N fertilizer application rates: 20%, 50%, 100% and 150% of optimal N levels. A suite of optical, fluorescence, and biophysical measurements were collected on leaves from field grown corn (Zea mays L.) and soybean plants (Glycine max L.) grown in pots (greenhouse + ambient sunlight daily). Three types of steady state laser-induced fluorescence measurements were made on adaxial and abaxial surfaces: 1) fluorescence images in four 10 nm bands (blue, green, red, far-red) resulting from broad irradiance excitation; 2) emission spectra (5 nm resolution) produced by excitation at single wavelengths (280,380 or 360, and 532 nm); and 3) excitation spectra (2 nm resolution), with emission wavelengths fixed at wavelengths centered on selected solar Fraunhofer lines (532,607,677 and 745 nm). Two complementary sets of high resolution (< 2 nm) optical spectra were acquired for both adaxial and abaxial leaf surfaces: 1) optical properties (350-2500 nm) for reflectance, transmittance, and absorptance; and 2) reflectance spectra (500-1000 nm) acquired with and without a short pass filter at 665 nm to determine the fluorescence contribution to "apparent reflectance" in the 650-750 spectrum, especially at the 685 and 740 nm chlorophyll fluorescence (ChlF) peaks. The strongest relationships between foliar chemistry and optical properties were demonstrated for C/N content and two optical parameters associated with the "red edge inflection point". Select optical properties and ChlF parameters were highly correlated for both species. A significant contribution of ChlF to "apparent reflectance" was observed, averaging 10-25% at 685 nm and 2-6% at 740 nm over all N treatments. Discrimination of N treatment groups was possible with specific fluorescence band ratios (e.g., F740/F525 obtained with 380EX). From all measurements assessing fluorescence, higher ChlF and blue/green emissions were measured fiom the abaxial leaf surfaces; Abaxial surfaces also produced higher reflectances in the 400-800 nm spectrum. Fluorescence information collected in Fraunhofer regions located on the shoulders of ChlF features compared favorably with peak emissions. This supports the potential capability of a hture space-born interferometer sensor to capture plant canopy fluorescence.