**2. Materials and methods**

#### **2.1. Field experiment**

A field experiment was designed and conducted in 2004 to collect measured data at both the leaf and canopy level for foliar Car content assessment. The experiment site was located at the National Experimental Station for Precision Agriculture (40°10.6′ N, 116°26.3′ E), Beijing, China. Winter wheat (*Triticum aestivum* L.) was used in this experiment, and 21 cultivars of winter wheat were grown in plots of 30 × 5.4 m size in the experiment site. Fertilization and irrigation were applied according to local standard practice so as to provide nonlimiting conditions. During the whole growing season, field measurements were conducted on specific growth stages including booting (April 28), head emergence (May 11), pollination (May 28) and milk development (June 08). For each growth period, different cultivars were used for sampling at both the canopy and leaf levels.

Chl*a* (mg/L) = 12.21 × A663 − 2.81 × A646 (1)

Chl*b* (mg/L) = 20.13 × A646 − 5.03 × A663 (2)

C*ar* (mg/L) = (1000 × A470 − 3.27 × *Chla* − 104 × *Chlb*)/229 (3)

where A*X* is the absorbance of the extract solution at wavelength x, VT (ml) is the volume of

LAI was determined using a dry weight method [30]. Leaf segments of approximate area 0.06 m<sup>2</sup> were cut from the central part of about 30 leaves selected from all the green leaves in the 1 m2 quadrat as standard leaves for LAI calculation. Both the standard leaves and the remaining leaves were oven dried at 70°C to constant weight and weighed. LAI was calculated as Eq. (6):

(*ml*)

) = [*Car*(*mg*/*g*) × *DW*(*g*)]/leaf area(*cm*2) (5)

) and *Wr*

]/[DW(*g*) × 1000] (4)

http://dx.doi.org/10.5772/intechopen.78239

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Monitoring Crop Carotenoids Concentration by Remote Sensing

)/(*Sl* × *Wr*) (6)

(g) is the total dry weight of the 1 m2

(g) is the dry weight of the

C*ar* (mg/g) = [*Car*(*mg*/*L*) × *VT*

LAI = (*Sr* × *Wt*

leaf pigment extract solution and DW (g) is the leaf dry weight.

) is the area of the standard leaves, *Wt*

is the sampled land area (m2

Besides the winter wheat measured data, the ANGERS dataset, which contains various plant species and different growth conditions, was also used. The dataset was collected in 2003 on temperate plants at the National Institute for Agricultural Research (INRA), ANGERS, France. It contains leaf directional-hemispherical reflectance and transmittance spectra measured at 1 nm resolution from 400 to 2400 nm using ASD FieldSpec instruments equipped with integrating spheres. Chlorophyll *a* and *b* (Chl), total carotenoids (Car), water (also named equivalent water thickness (EWT)) and dry matter (also named leaf mass per area (LMA)) content

PROSPECT-5 simulates leaf directional-hemispherical reflectance and transmittance from 400 to 2500 nm with six input variables: LChl, LCar, LMA, EWT, leaf structure parameter (N) and brown pigments (Cbrown). Generally, pigments absorb light in the visible range (400– 760 nm), whereas water has a high absorbance in the near-infrared band (1000–2500 nm). Dry matter and refractive index variations extend through the whole wave range (400–2500 nm) [18]. Since the goal was to estimate leaf Car content mainly from visible wavebands, and the

C*ar* (*μ*g/cm2

where *Sr*

(m2

**2.3. ANGERS dataset**

standard leaves.

quadrat sampled leaves, *Sl*

are available for each sample [18].

**2.4. Simulated datasets**
