TY - JOUR ID - bastiaanssen2000 AU - Bastiaanssen, Wim G. M. AU - Molden, David J. AU - Makin, Ian W. TI - Remote sensing for irrigated agriculture: examples from research and possible applications UR - http://www.sciencedirect.com/science/article/pii/S0378377400000809 DO - 10.1016/s0378-3774(00)00080-9 T2 - Agricultural Water Management PY - 2000 SN - 0378-3774 VL - 46 IS - 2 SP - 137-155 AB - Researchers in various international programs have studied the potential use of remotely sensed data to obtain accurate information on land surface processes and conditions. These studies have demonstrated that quantitative assessment of the soil-vegetation-atmosphere-transfer processes can lead to a better understanding of the relationships between crop growth and water management. Information on land surface can now be obtained at a wide range of spatial (5–5000 m) and temporal resolutions (0.5–24 days). However, even though considerable progress has been made over the past 20 years in research applications, remotely sensed data remain underutilized by practicing water resource managers. This paper seeks to bridge the gap between researchers and practitioners, first, by illustrating where research tools and techniques have practical applications and, second, by identifying real problems that remote sensing could solve, albeit with additional research and development. As freshwater becomes an increasingly scarce resource, all opportunities to better manage water uses, particularly in irrigated agriculture, must be taken. An important challenge in the field of water resources is to utilize the timely, objective and accurate information provided by remote sensing. KW - Remote sensing KW - Irrigated farming KW - Land management KW - Water resources management KW - Crop yield KW - Water use efficiency KW - Water rights ER - TY - JOUR ID - ceccato2001 AU - Ceccato, Pietro AU - Flasse, Stéphane AU - Tarantola, Stefano AU - Jacquemoud, Stéphane AU - Grégoire, Jean-Marie TI - Detecting vegetation leaf water content using reflectance in the optical domain UR - http://www.sciencedirect.com/science/article/pii/S0034425701001912 DO - 10.1016/s0034-4257(01)00191-2 T2 - Remote Sensing of Environment PY - 2001 SN - 0034-4257 VL - 77 IS - 1 SP - 22-33 AB - This paper outlines the first part of a series of research studies to investigate the potential and approaches for using optical remote sensing to assess vegetation water content. It first analyzes why most methods used as approximations of vegetation water content (such as vegetation stress indices, estimation of degree of curing and chlorophyll content) are not suitable for retrieving water content at leaf level. It then documents the physical basis supporting the use of remote sensing to directly detect vegetation water content in terms of Equivalent Water Thickness (EWT) at leaf level. Using laboratory measurements, the radiative transfer model PROSPECT and a sensitivity analysis, it shows that shortwave infrared (SWIR) is sensitive to EWT but cannot be used alone to retrieve EWT because two other leaf parameters (internal structure and dry matter) also influence leaf reflectance in the SWIR. A combination of SWIR and NIR (only influenced by these two parameters) is necessary to retrieve EWT at leaf level. These results set the basis towards establishing operational techniques for the retrieval of EWT at top-of-canopy and top-of-atmospheric levels. KW - Leaf water content KW - Fuel moisture content KW - Optical domain KW - Shortwave infrared ER - TY - JOUR ID - ceccato2002 AU - Ceccato, Pietro AU - Gobron, Nadine AU - Flasse, Stéphane AU - Pinty, Bernard AU - Tarantola, Stefano TI - Designing a spectral index to estimate vegetation water content from remote sensing data: Part 1: Theoretical approach UR - http://www.sciencedirect.com/science/article/pii/S0034425702000378 DO - 10.1016/s0034-4257(02)00037-8 T2 - Remote Sensing of Environment PY - 2002 SN - 0034-4257 VL - 82 IS - 2–3 SP - 188-197 AB - This paper describes the methodology used to create a spectral index to retrieve vegetation water content from remotely sensed data in the solar spectrum domain. A global sensitivity analysis (GSA) using radiative transfer models is used to understand and quantify vegetation water content effects on the signal measured at three levels: leaf, canopy, and atmosphere. An index is then created that optimises retrieval of vegetation water content (in terms of water quantity per unit area at canopy level) and minimises perturbing effects of geophysical and atmospheric effects. The new index, optimised for the new SPOT-VEGETATION sensor, is presented as an example. Limitations and robustness of the index are also discussed. ER - TY - JOUR ID - cibula1992 AU - Cibula, W. G. AU - Zetka, E. F. AU - Rickman, D. L. TI - Response of thematic mapper bands to plant water stress UR - http://dx.doi.org/10.1080/01431169208904236 DO - 10.1080/01431169208904236 PR - Taylor & Francis T2 - International Journal of Remote Sensing PY - 1992 DA - 1992-07-01 SN - 0143-1161 VL - 13 IS - 10 SP - 1869-1880 AB - Abstract Changes in leaf reflectance as water content decreases have been hypothesized to occur in the 1 55-1.75 and 2.08-2.35 ?m wavelength regions. To evaluate this hypothesis, studies were conducted on ryegrass (Lolium muitiflorum Lam.) and oats (Avena saliva L.), which were grown in a controlled, outdoor situation. Both fully-watered control beds and water-stressed beds were periodically examined with a spectroradiometer calibrated against a reflectance reference of polytetrafluoroethylene. The observed changes correspond to those predicted by stochastic leaf models employed by other investigators (leaf reflection increases in the l.55-l.75?m region as leaf water content decreases). Although the percentage changes in TM bands 1-3 are nearly as great as those found in TM bands 5 and 7, the absolute values of reflectance change are much lower. We believe that these patterns are probably characteristic of a broad range of vegetation types. In terms of phenomena detection, these patterns should be considered in any practical remote sensing sensor scenario. ER - TY - JOUR ID - curran1989 AU - Curran, Paul J. TI - Remote sensing of foliar chemistry UR - http://www.sciencedirect.com/science/article/pii/0034425789900692 DO - 10.1016/0034-4257(89)90069-2 T2 - Remote Sensing of Environment PY - 1989 SN - 0034-4257 VL - 30 IS - 3 SP - 271-278 AB - Remotely sensed data are being used to estimate foliar chemical content as a result of our need for the information and our increasing ability to understand and measure foliar spectra. This paper reviews how stepwise multiple regression and deconvolution have been used to extract chemical information from foliar spectra, and concludes that both methods are useful, but neither is ideal. It is recommended that the focus of research be modeling in the long term and experimentation in the short term. Long-term research should increase our understanding of the interaction between radiation and foliar chemistry so that the focus of research can move from leaf model to canopy model to field experiment. Short-term research should aim to design experiments in which remotely sensed data are used to generate unambiguous and accurate estimates of foliar chemical content. ER - TY - JOUR ID - datt1999 AU - Datt, Bisun TI - Remote Sensing of Water Content in Eucalyptus Leaves DO - http://dx.doi.org/10.1071/BT98042 T2 - Australian Journal of Botany PY - 1999 VL - 47 IS - 6 SP - 909-923 AB - The spectral reflectance of leaves from several Eucalyptus species was measured over the 400–2500 nm wavelengths with a laboratory spectroradiometer. The relationship of reflectance with the gravimetric water content and equivalent water thickness (EWT) of the leaves was analysed. The results showed that EWT was strongly correlated with reflectance in several wavelength regions. No significant correlations could be obtained between reflectance and gravimetric water content. It was also possible to confirm theoretically that reflectance changes of leaves could be directly linked to changes in EWT but not to changes in gravimetric water content. Several existing reflectance indices were evaluated for estimation of leaf water content and some new indices were developed and tested. Two semi-empirical indices developed in this study, (R850 - R2218)/(R850 - R1928) and (R850 - R1788)/(R850 - R1928), were found to show significantly stronger correlations with EWT than all other indices tested. It was also shown that these new indices were least sensitive to the effects of radiation scatter. The indices (R850 - R2218)/(R850 - R1928) and (R850 - R1788)/(R850 - R1928) are therefore proposed as two new indices for the remote estimation of vegetation water content. ER - TY - JOUR ID - gao1996 AU - Gao, Bo-cai TI - NDWI—A normalized difference water index for remote sensing of vegetation liquid water from space UR - http://www.sciencedirect.com/science/article/pii/S0034425796000673 DO - 10.1016/s0034-4257(96)00067-3 T2 - Remote Sensing of Environment PY - 1996 SN - 0034-4257 VL - 58 IS - 3 SP - 257-266 ER - TY - JOUR ID - glenn2008 AU - Glenn, Edward AU - Huete, Alfredo AU - Nagler, Pamela AU - Nelson, Stephen TI - Review - Relationship Between Remotely-sensed Vegetation Indices, Canopy Attributes and Plant Physiological Processes: What Vegetation Indices Can and Cannot Tell Us About the Landscape UR - http://www.mdpi.com/1424-8220/8/4/2136/ DO - doi:10.3390/s8042136 T2 - Sensors PY - 2008 VL - 8 IS - 4 SP - 2136-2160 ER - TY - JOUR ID - hunt_jr1989 AU - Hunt Jr, E. Raymond AU - Rock, Barrett N. TI - Detection of changes in leaf water content using Near- and Middle-Infrared reflectances UR - http://www.sciencedirect.com/science/article/pii/0034425789900461 DO - 10.1016/0034-4257(89)90046-1 T2 - Remote Sensing of Environment PY - 1989 SN - 0034-4257 VL - 30 IS - 1 SP - 43-54 AB - Detection of plant water stress by remote sensing has been proposed using indices of Near-Infrared (NIR, 0.7–1.3 µm) and Middle-Infrared (MIR, 1.3–2.5 µm) wavelengths. The first objective of this study was to test the ability of the Leaf Water Content Index (LWCI) to determine leaf Relative Water content (RWC) of different species with different leaf morphologies. The second objective was to determine how the Moisture Stress Index (MSI; MIR / NIR) varies with RWC and the Equivalent Water Thickness (EWT). Reflectance factors at 0.82 µm and 1.6 µm were measured on leaves of Quercus agrifolia (sclerophyllous leaves), Liquidambar styraciflua (hardwood deciduous tree leaves), Picea rubens and Picea pungens (conifer needles), and Glycine max (herbaceous dicot leaves) as they dried on a laboratory bench. RWC and EWT were measured concurrently with the reflectance measurements. The results showed that LWCI was equal to RWC for the species tested. However, the results of a sensitivity analysis indicated the reflectances at 1.6 µm for two different RWC must be known for accurate prediction of unknown RWC; thus the LWCI is impractical for field applications. MSI was linearly correlated to RWCwith each species having a different regression equation and to log10 EWT with data of all species falling on the same regression line. Because EWT is correlated with leaf area index, MSI should also be correlated with leaf area index. Assuming that the linear regression equation of MSI to EWT can be applied to canopies, then the minimum significant change of RWC that can be detected is 52%. For most plants, the natural variation in RWC from water stress is only about 20%, so that we conclude that indices derived from NIR and MIR reflectances cannot be used to remotely-sense water stress. ER - TY - GEN ID - hunt_jr1987 AU - Hunt Jr, Raymond E. AU - Rock, Barrett N. AU - Nobel, Park S. TI - Measurement of leaf relative water content by infrared reflectance UR - http://www.sciencedirect.com/science/article/pii/0034425787900940 DO - 10.1016/0034-4257(87)90094-0 T2 - Remote Sensing of Environment PY - 1987 SN - 0034-4257 VL - 22 IS - 3 SP - 429-435 AB - From basic considerations and Beer's law, a leaf water content index incorporating reflectances of wavelengths from 0.76 to 0.90 μm and from 1.55 to 1.75 μm (Landsat Thematic Mapper Bands TM4 and TM5, respectively) was developed that relates leaf reflectance to leaf relative water content. For the leaf succulent, Agave deserti, the leaf water content index was not significantly different from the relative water content for either individual leaves or an entire plant. Also, the relative water contents of intact plants of Encelia farinosa and Hilaria rigida in the field were estimated by the leaf water content index; variations in the proportion of living to dead leaf area could cause large errors in the estimate of relative water content. Thus, the leaf water content index may be able to estimate average relative water content of canopies when TM4 and TM5 are measured at a known relative water content and fraction of dead leaf material. ER - TY - JOUR ID - nagler2005 AU - Nagler, Pamela L. AU - Scott, Russell L. AU - Westenburg, Craig AU - Cleverly, James R. AU - Glenn, Edward P. AU - Huete, Alfredo R. TI - Evapotranspiration on western U.S. rivers estimated using the Enhanced Vegetation Index from MODIS and data from eddy covariance and Bowen ratio flux towers UR - http://www.sciencedirect.com/science/article/pii/S0034425705001616 DO - 10.1016/j.rse.2005.05.011 T2 - Remote Sensing of Environment PY - 2005 SN - 0034-4257 VL - 97 IS - 3 SP - 337-351 AB - We combined remote sensing and in-situ measurements to estimate evapotranspiration (ET) from riparian vegetation over large reaches of western U.S. rivers and ET by individual plant types. ET measured from nine flux towers (eddy covariance and Bowen ratio) established in plant communities dominated by five major plant types on the Middle Rio Grande, Upper San Pedro River, and Lower Colorado River was strongly correlated with Enhanced Vegetation Index (EVI) values from the Moderate Resolution Imaging Spectrometer (MODIS) sensor on the NASA Terra satellite. The inclusion of maximum daily air temperatures (Ta) measured at the tower sites further improved this relationship. Sixteen-day composite values of EVI and Ta were combined to predict ET across species and tower sites (r2 = 0.74); the regression equation was used to scale ET for 2000–2004 over large river reaches with Ta from meteorological stations. Measured and estimated ET values for these river segments were moderate when compared to historical, and often indirect, estimates and ranged from 851–874 mm yr- 1. ET of individual plant communities ranged more widely. Cottonwood (Populus spp.) and willow (Salix spp.) stands generally had the highest annual ET rates (1100–1300 mm yr- 1), while mesquite (Prosopis velutina) (400–1100 mm yr- 1) and saltcedar (Tamarix ramosissima) (300–1300 mm yr- 1) were intermediate, and giant sacaton (Sporobolus wrightii) (500–800 mm yr- 1) and arrowweed (Pluchea sericea) (300–700 mm yr- 1) were the lowest. ET rates estimated from the flux towers and by remote sensing in this study were much lower than values estimated for riparian water budgets using crop coefficient methods for the Middle Rio Grande and Lower Colorado River. KW - Evapotranspiration KW - Riparian KW - Water balance KW - MODIS KW - Saltcedar KW - Remote sensing ER - TY - JOUR ID - penuelas1993 AU - Penuelas, J. AU - Filella, I. AU - Biel, C. AU - Serrano, L. AU - Save, R. TI - The reflectance at the 950–970 nm region as an indicator of plant water status UR - http://dx.doi.org/10.1080/01431169308954010 DO - 10.1080/01431169308954010 PR - Taylor & Francis T2 - International Journal of Remote Sensing PY - 1993 SN - 0143-1161 VL - 14 IS - 10 SP - 1887-1905 AB - We present new remote sensing indices of plant water status: the ratio between the reflectance at 970 nm, one of the water absorption bands, and the reflectance at a reference wavelength, 900 nm (R970/R9000; the first derivative minimum in this near-infrared region (dNIRminimum ) and the wavelength where this minimum is found ( ?NIRminimum). In order to evaluate them, we carried out three experiments. Daily irrigated gerbera plants were allowed to dry until almost wilting and then daily irrigation was restarted; pepper and bean plants were grown for four months submitted to two different irrigation treatments; and bean detached leaves were submitted to progressive dehydration whereas pressure-volume curves were being carried out. In gerbera plants, the trough about 950?970 nm decreased as the drought was increasing. Therefore, the R970/R900 index and the dNIRminimum closely tracked the changes in relative water content (RWC), leaf water potential, stomatal conductance and the foliage-air temperature differences. The ?dNIRminimum tracked even better these changes in gerberas. However, these water status indices began to be significant when the water stress was already well developed, at RWC smaller than 85 per cent. The same happened to detached leaves of beans which did not present differences above ?1·55 MPa water potential. Beans and peppers growing at soil matric potentials larger than ?0·04 MPa presented higher R970/R900 values than those growing at soil matric potentials only larger than ?0·01 MPa. In all the cases, the maximum response of these indices was found in the varieties or the species that lost cell wall elasticity in response to drought stress. This could indicate an important structural component in these indices changes. Relative water content itself seemed to be, however, the most important factor as shown by the highest correlation coefficients with these spectral indices. These spectral signals were more evident at canopy level than at leaf level. They seem to be useful as water status indicators at ground level, especially when there are not important changes of LAI and when plants wholly cover the soil. ER - TY - JOUR ID - penuelas1997 AU - Penuelas, J. AU - Pinol, J. AU - Ogaya, R. AU - Filella, I. TI - Estimation of plant water concentration by the reflectance Water Index WI (R900/R970) UR - http://dx.doi.org/10.1080/014311697217396 DO - 10.1080/014311697217396 T2 - International Journal of Remote Sensing PY - 1997 DA - 1997/09/01 SN - 0143-1161 VL - 18 IS - 13 SP - 2869-2875 AB - Abstract Water Index WI (R900/R970) was used for the estimation of plant water concentration (PWC) by ground-based, reflectance measurements. Reflectance and PWC were measured for adult plants growing in the field throughout an annual cycle and in potted seedlings submitted to progressive desiccation. The species studied were characteristicly Mediterranean: Pinus halepensis, Quercus ilex, Quercus coccifera, Arbutus unedo, Cistus albidus, Cistus monspeliensis, Phillyrea angustifolia, Pistacia lentiscus and Brachypodium retusum . WI was significantly correlated with PWC when all the species were considered together, and with almost all the species considered individually, especially when a wider range of PWC was obtained by extreme dessication of experimental plants. The correlations increased when normalizing WI by NDVI. The wavelength of the trough corresponding to water absorption band tended to shift from 970-980 nm to lower wavelengths 930-950 nm with decreasing PWCs. Infrared measurement of plant temperature and T leaf - T air provided worse assessment of PWC. A simple radiometer measuring plant reflectance at 680, 900, and 970nm could speed up the measurement of PWC, and be useful in wildfire risk evaluation and drought assessment. 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 - 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 - pu2003 AU - Pu, R. AU - Ge, S. AU - Kelly, N. M. AU - Gong, P. TI - Spectral absorption features as indicators of water status in coast live oak ( Quercus agrifolia ) leaves UR - http://dx.doi.org/10.1080/01431160210155965 DO - 10.1080/01431160210155965 T2 - International Journal of Remote Sensing PY - 2003 DA - 2003/01/01 SN - 0143-1161 VL - 24 IS - 9 SP - 1799-1810 AB - A total of 139 reflectance spectra (between 350 and 2500 nm) from coast live oak ( Quercus agrifolia ) leaves were measured in the laboratory with a spectrometer FieldSpec?Pro FR. Correlation analysis was conducted between absorption features, three-band ratio indices derived from the spectra and corresponding relative water content (RWC, %) of oak leaves. The experimental results indicate that there exist linear relationships between the RWC of oak leaves and absorption feature parameters: wavelength position (WAVE), absorption feature depth (DEP), width (WID) and the multiplication of DEP and WID (AREA) at the 975 nm, 1200 nm and 1750 nm positions and two three-band ratio indices: RATIO 975 and RATIO 1200, derived at 975 nm and 1200 nm. AREA has a higher and more stable correlation with RWC compared to other features. It is worthy of noting that the two three-band ratio indices, RATIO 975 and RATIO 1200, may have potential application in assessing water status in vegetation. ER - TY - JOUR ID - serrano2000 AU - Serrano, Lydia AU - Ustin, Susan L. AU - Roberts, Dar A. AU - Gamon, John A. AU - Peñuelas, Josep TI - Deriving Water Content of Chaparral Vegetation from AVIRIS Data UR - http://www.sciencedirect.com/science/article/pii/S0034425700001474 DO - 10.1016/s0034-4257(00)00147-4 T2 - Remote Sensing of Environment PY - 2000 SN - 0034-4257 VL - 74 IS - 3 SP - 570-581 AB - Spectral imaging data acquired with Advanced Visible Infrared Imaging Spectrometer over Point Dume (Los Angeles County, CA, USA) were used to assess the ability of hyperspectral reflectance data to estimate canopy Relative Water Content (RWC) at the landscape level. The study was performed on 23 vegetation stands comprised of three characteristic chaparral plant communities, with contrasting phenological stages and canopy cover. Several estimates of water content based on the near-infrared (NIR; reflectance indices and water thickness derived from reflectance and radiance data) and shortwave infrared (SWIR) water absorption bands were compared to measurements of vegetation structure and water content made on the ground. The Water Index (WI) and Normalized Difference Water Index (NDWI), reflectance indices formulated from the NIR water absorption bands, were the best indicators of canopy RWC estimated from combining leaf relative water content with measures of canopy structure. A stepwise multiple regression revealed that canopy structure explained 36% and 41% of the variation in WI and NDWI, respectively. The explained variance in WI and NDWI increased to 44% and 48% when leaf relative water content was included in the model. By contrast, the inclusion of leaf relative water content did not contribute significantly to the explained variance in indices formulated using SWIR water absorption bands and in those based on water thickness. The relationship between WI and the canopy RWC significantly improved when only data from plots with green vegetation cover >70% were considered (r2=0.88, p<0.001). All the indices studied had an important structural component (as indicated by the strong correlation with NDVI), yet only the indices WI and NDWI additionally responded to water content. These results indicate that the WI and NDWI are sensitive to variations in canopy relative water content at the landscape scale. ER - TY - JOUR ID - thenot2002 AU - Thenot, F. AU - Méthy, M. AU - Winkel, T. TI - The Photochemical Reflectance Index (PRI) as a water-stress index UR - http://dx.doi.org/10.1080/01431160210163100 DO - 10.1080/01431160210163100 T2 - International Journal of Remote Sensing PY - 2002 DA - 2002/01/01 SN - 0143-1161 VL - 23 IS - 23 SP - 5135-5139 AB - Measurements of leaf reflectance in two narrow wavelength bands centred around 531 and 570 nm were carried out during withering of two contrasting functional and structural plant types: Chenopodium quinoa (Willd.) and Arbutus unedo (L.). The Photochemical Reflectance Index (PRI)=( R 531 - R 570 )/ ( R 531 + R 570 ) was calculated. The results showed that PRI could be used as a reliable water-stress index. However, some limits to the use of PRI have to be emphasized, e.g. the wilting of leaves during dry periods. If such limits are under control, PRI could be a non-destructive and low cost method for assessing plant water status. ER - TY - JOUR ID - underwood2003 AU - Underwood, Emma AU - Ustin, Susan AU - DiPietro, Deanne TI - Mapping nonnative plants using hyperspectral imagery UR - http://www.sciencedirect.com/science/article/pii/S0034425703000968 DO - 10.1016/s0034-4257(03)00096-8 T2 - Remote Sensing of Environment PY - 2003 SN - 0034-4257 VL - 86 IS - 2 SP - 150-161 AB - Nonnative plant species are causing enormous ecological and environmental impacts from local to global scale. Remote sensing images have had mixed success in providing spatial information on land cover characteristics to land managers that increase effective management of invasions into native habitats. However, there has been limited evaluation of the use of hyperspectral data and processing techniques for mapping specific invasive species based on their spectral characteristics. This research evaluated three different methods of processing hyperspectral imagery: minimum noise fraction (MNF), continuum removal, and band ratio indices for mapping iceplant (Carpobrotus edulis) and jubata grass (Cortaderia jubata) in California's coastal habitat. Validation with field sampling data showed high mapping accuracies for all methods for identifying presence or absence of iceplant (97%), with the MNF procedure producing the highest accuracy (55%) when the classes were divided into four different densities of iceplant. KW - AVIRIS KW - Hyperspectral KW - Invasive plants KW - Nonnative plants KW - Iceplant KW - Carpobrotus edulis KW - Jubata grass KW - Cortaderia jubata KW - Mapping ER - TY - JOUR ID - zarco-tejada_p_j_sepulcre-cant_2007 AU - Zarco-Tejada P.J. AU - Sepulcre-Cantó, G. TI - REMOTE SENSING OF VEGETATION BIOPHYSICAL PARAMETERS FOR DETECTING STRESS CONDITION AND LAND COVER CHANGES T2 - Estudios de la Zona No Saturada del Suelo PY - 2007 VL - 8 ER - TY - JOUR ID - zarco-tejada2003 AU - Zarco-Tejada, P. J. AU - Rueda, C. A. AU - Ustin, S. L. TI - Water content estimation in vegetation with MODIS reflectance data and model inversion methods UR - http://www.sciencedirect.com/science/article/pii/S0034425702001979 DO - 10.1016/s0034-4257(02)00197-9 T2 - Remote Sensing of Environment PY - 2003 SN - 0034-4257 VL - 85 IS - 1 SP - 109-124 AB - Statistical and radiative-transfer physically based studies have previously demonstrated the relationship between leaf water content and leaf-level reflectance in the near-infrared spectral region. The successful scaling up of such methods to the canopy level requires modeling the effect of canopy structure and viewing geometry on reflectance bands and optical indices used for estimation of water content, such as normalized difference water index (NDWI), simple ratio water index (SRWI) and plant water index (PWI). This study conducts a radiative transfer simulation, linking leaf and canopy models, to study the effects of leaf structure, dry matter content, leaf area index (LAI), and the viewing geometry, on the estimation of leaf equivalent water thickness from canopy-level reflectance. The applicability of radiative transfer model inversion methods to MODIS is studied, investigating its spectral capability for water content estimation. A modeling study is conducted, simulating leaf and canopy MODIS-equivalent synthetic spectra with random input variables to test different inversion assumptions. A field sampling campaign to assess the investigated simulation methods was undertaken for analysis of leaf water content from leaf samples in 10 study sites of chaparral vegetation in California, USA, between March and September 2000. MODIS reflectance data were processed from the same period for equivalent water thickness estimation by model inversion linking the PROSPECT leaf model and SAILH canopy reflectance model. MODIS reflectance data, viewing geometry values, and LAI were used as inputs in the model inversion for estimation of leaf equivalent water thickness, dry matter, and leaf structure. Results showed good correlation between the time series of MODIS-estimated equivalent water thickness and ground measured leaf fuel moisture (LFM) content (r2=0.7), demonstrating that these inversion methods could potentially be used for global monitoring of leaf water content in vegetation. KW - Radiative transfer KW - Water content KW - Leaf fuel moisture KW - Equivalent water thickness KW - MODIS KW - Reflectance KW - Model inversion 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 -