TY - JOUR ID - aparicio2004 AU - Aparicio, N. AU - Villegas, D. AU - Royo, C. AU - Casadesus, J. AU - Araus, J. L. TI - Effect of sensor view angle on the assessment of agronomic traits by ground level hyper-spectral reflectance measurements in durum wheat under contrasting Mediterranean conditions UR - http://dx.doi.org/10.1080/0143116031000116967 DO - 10.1080/0143116031000116967 T2 - International Journal of Remote Sensing PY - 2004 DA - 2004/03/01 SN - 0143-1161 VL - 25 IS - 6 SP - 1131-1152 AB - The objective of this work is to study the effect of changing the sensor view angle on spectral reflectance indices and their relationships with yield and other agronomic traits. Canopy reflectance spectra of 25 durum wheat genotypes were measured with a field spectroradiometer at two view angles, nadir and 30°, from anthesis to maturity in two years and two water regimes. Nine spectral reflectance indices were calculated from reflectance measurements for correlation with yield and several agronomic traits. At off-nadir position more reflected radiation was collected, associated with the reflective characteristics of stems. The performance of the indices predicting the yield and the agronomic traits varied as a function of sensor view angle, and were moreover affected by leaf area index (LAI) value. At high LAI, simple ratio (SR) and normalized difference vegetation index (NDVI), calculated at off-nadir position, were better predictors of traits related to the density of stems and poorer predictors of traits related to green area. On the other hand, at low LAI the indices normalized pigment chlorophyll index (NPCI) and water index (WI) were better predictors of yield and all the other traits when the sensor view angle was at nadir, whereas no differences due to sensor angle were accounted for the other three indices. The different performance of indices at low and high LAI is discussed. ER - 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 - 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 - JOUR ID - pe_uelas1998 AU - Peñuelas, J. AU - Filella, I. TI - Visible and near-infrared reflectance techniques for diagnosing plant physiological status UR - http://dx.doi.org/10.1016/S1360-1385(98)01213-8 DO - 10.1016/S1360-1385(98)01213-8 T2 - Trends in Plant Science PY - 1998 SN - 13601385 VL - 3 IS - 4 SP - 151-156 ER - TY - JOUR ID - pe_uelas1994 AU - Peñuelas, J. AU - Gamon, J. A. AU - Fredeen, A. L. AU - Merino, J. AU - Field, C. B. TI - Reflectance indices associated with physiological changes in nitrogen- and water-limited sunflower leaves UR - http://www.sciencedirect.com/science/article/pii/0034425794901368 DO - 10.1016/0034-4257(94)90136-8 T2 - Remote Sensing of Environment PY - 1994 SN - 0034-4257 VL - 48 IS - 2 SP - 135-146 AB - We followed diurnal and seasonal changes in physiology and spectral reflectance of leaves throughout the canopies of sunflower plants grown in control, nitrogen (N)-limited, and water-stressed plots. Leaves from control sunflower plants had significantly higher levels of nitrogen, chlorophyll (chl), ribulose bis phosphate carboxylase / oxygenase (RuBPCase) activity and photosynthetic rates and lower starch content and leaf thickness than N-limited plants. Water-stressed plants had the highest N and chl contents (on an area basis). They also had the lowest water potential and photosynthetic rates, in spite of maintaining high RuBPCase activities. Leaves from stressed plants (especially N-limited) had significantly higher reflectances in the visible wavelengths and lower in the near IR than leaves from control plants. The only clear trend across canopy levels was the higher reflectance at all wavelengths but especially in the visible of the lower (oldest) leaves. NDVI-like parameters were useful in distinguishing stress and control leaves over the growing season. However, several narrow-band indices provided better physiological information than NDVI. The physiological reflectance index (PRI) (R550 - R530 / R550 + R530) followed diurnal changes in xanthophyll pigments and photosynthetic rates of control and N-limited leaves. The maximum of the first derivative of reflectance in the green (dG) was correlated with diurnal photosynthetic rate, and with seasonal chl and N changes. The normalized pigment chlorophyll ratio Index (NPCI) (R680 - R430 / R680 + R430) varied with total pigments / chl. The water band index (WBI) (R970 / R902) followed water status. The normalized ratio between the maxima of the first derivatives of reflectances at the red edge and green regions (EGFN) was correlated with chl and N content. Principal components analysis yielded several indicators of physiological status. The first principal component was higher in control leaves, the second was higher in N-limited leaves, and the third was higher in water-limited leaves. Discriminant analysis based on the combination of several narrow-band spectral indices clearly separated leaves into the three treatment groups. These results illustrate the promise of narrow-band spectroradiometry for assessing the physiological state of vegetation. ER - TY - JOUR ID - pe_uelas1993 AU - Peñuelas, Josep AU - Gamon, John A. AU - Griffin, Kevin L. AU - Field, Christopher B. TI - Assessing community type, plant biomass, pigment composition, and photosynthetic efficiency of aquatic vegetation from spectral reflectance UR - http://www.sciencedirect.com/science/article/pii/003442579390088F DO - 10.1016/0034-4257(93)90088-f T2 - Remote Sensing of Environment PY - 1993 SN - 0034-4257 VL - 46 IS - 2 SP - 110-118 AB - We studied the reflectance spectra of the aquatic vegetation of Searsville Lake in coastal central California using a high spectral resolution hand-held spectroradiometer. The three aquatic types—submerged, floating, and emergent—exhibited clear differences in their spectral reflectance and can be distinguished on the basis of discriminant analysis using reflectance parameters. This technique can be used in large-area mapping of aquatic plants. The normalized difference vegetation index (NDVI) and the simple ratio (SR) were well correlated with chlorophyll content, photosynthetic efficiency, and biomass in the emergent species. New, narrow-bandwidth indices and reflectance indices calculated from first and second derivative spectra were strongly correlated with the ratio of secondary and protective pigments to chlorophyll a and with epoxidation state of the xanthophyll cycle pigments, and therefore, with photosynthetic efficiency. These new indices may be useful in the remote sensing of plant physiological status. ER - TY - JOUR ID - pinter2003 AU - Pinter, P. J. AU - Hatfield, J. L. AU - Schepers, J. S. AU - Barnes, E. M. AU - Moran, M. S. AU - Daughtry, C. S. T. AU - Upchurch, D. R. TI - Remote sensing for crop management UR - ://WOS:000221193400006 T2 - Photogrammetric Engineering and Remote Sensing PY - 2003 DA - Jun SN - 0099-1112 VL - 69 IS - 6 SP - 647-664 N1 - ISI Document Delivery No.: 817RA Times Cited: 88 Cited Reference Count: 256 Pinter, PJ Hatfield, JL Schepers, JS Barnes, EM Moran, MS Daughtry, CST Upchurch, DR Amer soc photogrammetry Bethesda AB - Scientists with the Agricultural Research Service (ARS) and various government agencies and private institutions have provided a great deal of fundamental information relating spectral reflectance and thermal emittance properties of soils and crops to their agronomic and biophysical characteristics. This knowledge has facilitated the development and use of various remote sensing methods for non-destructive monitoring of plant growth and development and for the detection of many environmental stresses which limit plant productivity. Coupled with rapid advances in computing and position-locating technologies, remote sensing from ground-, air-, and space-based platforms is now capable of providing detailed spatial and temporal information on plant response to their local environment that is needed for site specific agricultural management approaches. This manuscript, which emphasizes contributions by ARS researchers, reviews the biophysical basis of remote sensing; examines approaches that have been developed, refined, and tested for management of water, nutrients, and pests in agricultural crops; and assesses the role of remote sensing in yield prediction. It concludes with a discussion of challenges facing remote sensing in the future. KW - water-stress index KW - spectral-biophysical data KW - soil heat-flux KW - infrared KW - aerial photography KW - laser-induced fluorescence KW - constant leaf KW - temperature KW - adjusted vegetation index KW - surface-energy balance KW - clover-seed production KW - gossypium-hirsutum l ER - TY - JOUR ID - riedell1999 AU - Riedell, W.E. AU - Blackmer, T.M. TI - Leaf reflectance spectra of cereal aphid-damaged wheat T2 - Crop science PY - 1999 VL - 39 IS - 6 AB - The efficiency of field monitoring for insect pests would be improved with knowledge of reflected solar radiation from crop canopies during insect outbreaks. The objectives of this greenhouse study were to characterize leaf reflectance spectra of wheat (Triticum aestivum L.) damaged by Russian wheat aphids (Diuraphis noxia Mordvilko) and greenbugs (Schizaphis graminum Rondani) and to determine those leaf reflectance wavelengths that were most responsive to crop stress imposed by these aphid pests. When the ligule was visible on second oldest leaf, wheat plants were infested with four wingless adult Russian wheat aphids, four wingless adult greenbugs, or left uninfested (four replicate plants per treatment). Plants and aphid populations were allowed to grow under greenhouse conditions for 3 wk, after which leaf-reflected radiation (from the adaxial surface across the 350-1075 nm range), dry weight, area, and chlorophyll concentrations were measured. When compared with the control, greenbug feeding damage caused general necrosis in oldest (first) leaves and dramatically lowered the dry weight, leaf area, and chlorophyll concentration of the second, third, and fourth leaves. Russian wheat aphid feeding resulted in a reduction in leaf dry weight and area in the third and fourth leaves, and a reduction in total chlorophyll concentration in all leaves. Leaf reflectance in the 625- to 635-nm and the 680- to 695-nm ranges, as well as the normalized total pigment to chlorophyll a ratio index (NPCI), were significantly correlated with total chlorophyll concentrations in both greenbug- and Russian wheat aphid-damaged plants. Thus, both of these wavelength ranges, as well as this reflectance index, were good indicators of chlorophyll loss and leaf senescence caused by the aphid feeding damage. KW - Triticum aestivum KW - Diuraphis noxia KW - Schizaphis graminum KW - leaves KW - reflectance KW - defoliation KW - monitoring KW - methodology KW - leaf area KW - chlorophyll KW - senescence KW - spectral analysis KW - chemical constituents of plants ER - TY - JOUR ID - royo2003 AU - Royo, C. AU - Aparicio, N. AU - Villegas, D. AU - Casadesus, J. AU - Monneveux, P. AU - Araus, J. L. TI - Usefulness of spectral reflectance indices as durum wheat yield predictors under contrasting Mediterranean conditions UR - http://dx.doi.org/10.1080/0143116031000150059 DO - 10.1080/0143116031000150059 T2 - International Journal of Remote Sensing PY - 2003 DA - 2003/01/01 SN - 0143-1161 VL - 24 IS - 22 SP - 4403-4419 ER - TY - JOUR ID - zarco-tejada2001 AU - Zarco-Tejada, P. J. AU - Miller, J. R. AU - Noland, T. L. AU - Mohammed, G. H. AU - Sampson, P. H. TI - Scaling-up and model inversion methods with narrow-band optical indices for chlorophyll content estimation in closed forest canopies with hyperspectral data T2 - IEEE Transactions on Geoscience and Remote Sensing PY - 2001 VL - 39 SP - 1491−1507 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 -