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...m multiple crops across a number of different locations indicate that general relationships between spectral properties and plant response are achievable (Wiegand et al., 1990; Wiegand et al., 1992b; =-=Richardson et al., 1992-=-). Water Management Poor irrigation timing and insufficient applications of water are ubiquitous factors limiting production in many arid and semi-arid agricultural regions. As a consequence, consider...

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...ce from all possible viewing angles under all possible illumination conditions, has seen considerable study for plants and soils (Liang and Strahler, 2000; Walthall et al., 1985) and can be approached as a source of information as well as a source of noise to be removed from remotely sensed data Th e most widely used VI is the Normalized Diff erence Vegetative Index (NDVI) proposed by Deering (1978) that now serves as somewhat of a benchmark for researchers developing new VIs. Th e NDVI has been shown to be strongly related to light interception (Hatfi eld et al., 1984a; Redelfs et al., 1987; Richardson et al., 1992; Sellers, 1987; Serrano et al., 2000; Verma et al., 1992; Wiegand and Hatfi eld, 1988; Wiegand et al., 1990, 1992; Russel et al., 1995). Interference from underlying soil refl ectance, especially for incomplete canopy cover, has been a weakness for many VIs. Th e refl ectance line for the soil (day of year 150) shown in Fig. 6 reveals a fairly linear relationship across the wavelengths compared with the changes as the canopy develops. Agronomic systems occur on many diff erent soils and accounting for these differences provides confi dence in being able to apply VIs to different regions. Mini...

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...elow. Thus, sub-index i refers here to the number of classes for each plot. The LAI was accounted for through the Normalized Difference Vegetation Index (NDVI), Eq. (4). NDVI qIR qR qIR þ qR ð4Þ In order to constrain LAI through the NDVI, different analytical relationships can be applied. A linear relationship between LAI and NDVI was established for LAI of less than three (Zhangshi and Williams 1997), but not for higher values, where the LAI-NDVI relation becomes characteristically asymptotic (Carlson and Ripley 1990). Some authors have proposed exponential relations (Eq. 5) up to LAI 7 (Richardson et al. 1992; Lu et al. 2004). LAI x1ex2NDVI ð5Þ Others (Aparicio et al. 2000) have used a modified expression like Eq. (6). LAI x1ex2NDVI þ x3 ð6Þ This expression is more suitable for low LAI values, although it introduces a third parameter. Nevertheless, x3 can be related to x1, x2, and soil reflectance when LAI is taken as being 0, and therefore, the use of the latter expression does not increase the number of parameters required. 544 Precision Agric (2013) 14:541–557 123 Leaf inclination distribution function The leaf inclination distribution functions (LIDF) in the SAIL model were originally defi...

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...lectance in Band 5 of Landsat 7 ETM+, the middle infrared band. Similarly the normalized difference vegetation index (NDVI) that employs the reflectance in Band 4, is defined for the seven images as (=-=Richardson et al., 1992-=-): NDVI = ρ(780−900 nm) − ρ(630−690 nm) ρ(780−900 nm) + ρ(630−690 nm) where ρ(630−690 nm) is the reflectance in Band 3 of Landsat 7 ETM+, the red band and ρ(780−900 nm) is the reflectance in Band 4 of...

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...es (VIs) to reduce the influence of soil reflectance and atmosphericseffects (Baret and Guyot, 1991). These VIs are then calibrated over experimentalsdatasets to estimate LAI (Price, 1993;Huete, 1988;=-=Wiegand et al., 1990-=-;Richardson etsal., 1992;Wiegand et al., 1992). These VIs were later used to derive LAI maps at globals(Feng et al., 2006) and regional scales (Chen et al., 2002a;Pandya et al., 2006;Chen etsal., 2002...

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...il [6,7]. Nutrient supply of the plants influences absorption through chlorophyll activity in the transition band from red to NIR (660 nm to 740 nm) and thereby corresponds to the stress of the plant =-=[8]-=-. Reflections in the wavelength spectrum below 740 nm are higher for plants than for soil. Hence, NIR wavebands below 780 nm are commonly used for the NDVI. Thus, the difference between NIR and red is...