TY - JOUR ID - le_maire2004 AU - le Maire, G. AU - Francois, C. AU - Dufrene, E. TI - Towards universal broad leaf chlorophyll indices using PROSPECT simulated database and hyperspectral reflectance measurements DO - 10.1016/j.rse.2003.09.004 T2 - Remote Sensing of Environment PY - 2004 SN - 0034-4257 VL - 89 IS - 1 SP - 1-28 AB - Fifty-three leaves were randomly sampled on different deciduous tree species, representing a wide range of chlorophyll contents, tree ages, and leaf structural features. Their reflectance was measured between 400 and 800 nm with a 1-nm,step, and their chlorophyll content determined by extraction. A larger simulated database (11,583 spectra) was built using the PROSPECT model, in order to test, calibrate, and obtain universal indices, i.e., indices applicable to a wide range of species and leaf structure. To our knowledge, almost all leaf chlorophyll indices published in the literature since 1973 have been tested on both databases. Fourteen canonical types of indices (published ones and new ones) were identified, and their wavelengths calibrated on the simulated database as well as on the experimental database to determine the best wavelengths and, hence, the best performances in chlorophyll estimation for each index types. These indices go from simple reflectance ratios to more sophisticated indices Using reflectance first derivatives (using the Savitzky and Golay method). We also tested other nondestructive methods to obtain total chlorophyll concentration: SPAD (Minolta Camera, Osaka, Japan) and neural networks. The validity of the actual PROSPECT model is challenged by our results: Important discordances are found when the indices are calculated with PROSPECT compared to experimental data, especially for some indices and wavelengths. The discordance is even greater when the indices are determined with PROSPECT and applied on the experimental database. A new calibration of PROSPECT is therefore necessary for any study aiming at using simulated spectra to determine or to calibrate indices. The "peak jump" and the multiple-peak feature observed on the first derivative of the reflectances (e.g., in the Red-Edge Inflection Point [REIP] index) has been investigated. It was shown that chlorophyll absorption alone can explain this feature. The peak jump disqualifies' the REIP to be a valuable chlorophyll index. A simple modified difference ratio gave the best results among all published indices (cross-validated RMSE = 2.1 mug/cm(2) on the experimental database). After calibration on the experimental database, modified Simple Ratio (mSR) and modified Normalized Difference (mND) indices gave the best 2 performances (RMSECV = 1.8 mug/cm(2) on the experimental database). The new Double Difference (DD) index, although not the best on the 2), 2 experimental database (RMSECV 2.9 mug/cm(2)), has the best results on the larger simulated database (RMSE = 3.7 mug/cm(2)) and is expected to give good results on larger experimental databases. The best reflectance-based indices give better performances than the current commercial nondestructive device SPAD (RMSECV = 4.5 mug/cm(2)). In This leaf-level study, the best indices are very near from each other, so that complex methods are useless: REIP-like, neural networks, and derivative-based indices are not necessary and give worst results than simpler properly chosen indices. These conclusions will certainly be different for. a canopy-level study, where the derivative-based indices may perform significantly better than the other ones. (C) 2003 Elsevier Inc. All rights reserved. KW - universal broad leaf chlorophyll indices. PROSPECT. hyperspectral. reflectance measurements. neural-network classification. radiative-transfer models. remote-sensing. data. red-edge. vegetation indexes. spectral reflectance. optical-properties. bidirectio ER - TY - GEN ID - maccioni2001 AU - Maccioni, Andrea AU - Agati, Giovanni AU - Mazzinghi, Piero TI - New vegetation indices for remote measurement of chlorophylls based on leaf directional reflectance spectra UR - http://www.sciencedirect.com/science/article/pii/S1011134401001452 DO - 10.1016/s1011-1344(01)00145-2 T2 - Journal of Photochemistry and Photobiology B: Biology PY - 2001 SN - 1011-1344 VL - 61 IS - 1-2 SP - 52-61 AB - Directional reflectance (R) spectra from 380 to 780 nm for nadir illuminated leaves of four different plants (croton, Codiaeum variegatum; spotted eleagnus, Eleagnus pungens Maculata; Japanese pittosporum, Pittosporum tobira and Benjamin fig, Ficus benjamina Starlight) were acquired at a viewing angle of 30° from the nadir direction. Chlorophyll-a and -b content of leaves covered a range of 1–60 and 0.5–21 μg/cm2, respectively. In contrast with previous results from hemispherical reflectance measurements, directional reflectance data does not correlate well with chlorophyll concentration. This is mainly due to the external reflectance (RE) at the leaf epidermis, caused by the mismatch of the refractive index at the air–epidermis and epidermis–inner layer boundary. The external reflectance can be identified with the blue flat reflectance between 380 and 480 nm. The inner reflectance (RI), obtained by subtracting the external reflectance from the measured spectra, was found to be linearly related to the logarithm of the chlorophyll content. Good fitting of the log (Chl) versus RI(λ) curves were obtained for RI in the green band (around 550 nm) and close to the inflection point in the red edge (around 700 nm). The coefficient of determination, r2, of curve fitting improved (up to 0.97) when the normalised inner reflectance NRI(λ)=RI(λ)/RI(λ0), with λ0≥750 nm, was used instead of the absolute reflectance. The best indices for Chl, Chl-a and Chl-b determination were RI542/RI750, RI706/RI750 and RI556/RI750, respectively. However, since the content of Chl-a relative to Chl-b was almost constant for the plants investigated, the two last indices must be further validated on leaves with a high variability in the Chl-a:Chl-b ratio. The error in the determination of chlorophyll content was found to be of the order of 10%. This value was lower than those obtained by applying the vegetation indices previously suggested. Therefore, the normalised inner reflectance in the green and in the red edge represents a more suitable index for the chlorophyll determination than those up to now used. KW - Chlorophyll, Leaf directional reflectance, Leaf reflectance spectra, Remote sensing of chlorophyll ER - TY - JOUR ID - main2011 AU - Main, Russell AU - Cho, Moses Azong AU - Mathieu, Renaud AU - O’Kennedy, Martha M. AU - Ramoelo, Abel AU - Koch, Susan TI - An investigation into robust spectral indices for leaf chlorophyll estimation UR - http://www.sciencedirect.com/science/article/pii/S092427161100089X DO - 10.1016/j.isprsjprs.2011.08.001 T2 - ISPRS Journal of Photogrammetry and Remote Sensing PY - 2011 SN - 0924-2716 VL - 66 IS - 6 SP - 751-761 AB - Quantifying photosynthetic activity at the regional scale can provide important information to resource managers, planners and global ecosystem modelling efforts. With increasing availability of both hyperspectral and narrow band multispectral remote sensing data, new users are faced with a plethora of options when choosing an optical index to relate to their chosen or canopy parameter. The literature base regarding optical indices (particularly chlorophyll indices) is wide ranging and extensive, however it is without much consensus regarding robust indices. The wider spectral community could benefit from studies that apply a variety of published indices to differing sets of species data. The consistency and robustness of 73 published chlorophyll spectral indices have been assessed, using leaf level hyperspectral data collected from three crop species and a variety of savanna tree species. Linear regression between total leaf chlorophyll content and bootstrapping were used to determine the leafpredictive capabilities of the various indices. The indices were then ranked based on the prediction error (the average root mean square error (RMSE)) derived from the bootstrapping process involving 1000 iterative resampling with replacement. The results show two red-edge derivative based indices (red-edge position via linear extrapolation index and the modified red-edge inflection point index) as the most consistent and robust, and that the majority of the top performing indices (in spite of species variability) were simple ratio or normalised difference indices that are based on off-chlorophyll absorption centre wavebands (690–730 nm). KW - Leaf level reflectance KW - Leaf chlorophyll KW - Red-edge KW - Vegetation indices KW - Photosynthetic activity ER - TY - ELEC ID - idb AU - Henrich, V. AU - Krauss, G. AU - Götze, C. AU - Sandow, C. TI - The IndexDatabase UR - https://www.indexdatabase.de/ CY - Bonn PY - 2011 DA - 2011 ER -