**3.5. Chlorophyll indices based on reflectance indices**

Five reflectance indices for chlorophyll content estimation found in the literature are described in **Table 2**. They considered the visible, red edge, and near infrared ranges. Chlorophyll content was estimated by applying linear or polynomial models for specific plant species when deriving these models. Selection criteria for reflectance indices were based on their ability to estimate chlorophyll content in a wide range of plant species, plant physiology, phenology, and growing conditions, which is a characteristic of the vegetation in tropical forests.

#### **3.6. PROSPECT radiative transfer model**

The inversion of the PROSPECT model using leaf reflectance and transmittance was applied in this chapter in order to estimate chlorophyll concentration. Foliar chlorophyll content (*Cab*) was computed by the inversion process of PROSPECT 5 for the range of 400–1075 nm using reflectance and transmittance in the sampling interval of 1 nm for the 1134 leaf samples. Brown pigments (*Cbp*) and water content (*Cw*) were neutralized since foliar samples are green vegetation and the spectra does not show water absorption features.


na. = Not available.

**3.4. Chlorophyll indices based on SPAD-502 readings (transmittance)**

60 Tropical Forests - The Challenges of Maintaining Ecosystem Services while Managing the Landscape

**ID Model Units Tested in Number of**

species

Source: (1) Ref. [35], (2) Ref. [15], (3) Ref. [31], (4) Ref. [33], (5) Ref. [28], (6) Ref. [28], and (7) Ref. [28].

µg cm−2 13 Amazonian trees species

1 Chl = 62.05*e*(*X*\*0.0408) mg cm−2 6 Amazonian trees

**3.5. Chlorophyll indices based on reflectance indices**

**3.6. PROSPECT radiative transfer model**

a laboratory.

2 Chl = (117.1\**X*)/ (148.84–*X*)

3 Chl = 2*E*-05*X*<sup>2</sup>

+ 1E-04X + 0.0038

4 Chl = 5.52*E*-04 + 4.04*E* -04*X* + 1.25*E*-05*X*<sup>2</sup>

5 Chl = 10.6 + 7.39*X* + 0.114*X*<sup>2</sup>

na. = Not available.

this study.

Several published calibration models based on SPAD-502 readings were applied in this study. **Table 1** describes seven published polynomial, exponential, or homographic calibration models for chlorophyll content estimation from SPAD-502 chlorophyll meter readings. Selected calibration models cover a heterogeneous range of plants species, plant physiology, phenology, and growing conditions, which is a characteristic of the vegetation in tropical forests. All selected models have shown good agreement with traditional methods applied in

6 Chl = 10(*X*0.265) µmol m−2 Soybean and maize na. na. ~0–90 0.94 7 Chl = 10(*X*0.264) µmol m−2 Maize na. na. na. 0.79

**Table 1.** Indices of chlorophyll content estimation (µm cm−2) based on SPAD-502 chlorophyll meter models applied in

Five reflectance indices for chlorophyll content estimation found in the literature are described in **Table 2**. They considered the visible, red edge, and near infrared ranges. Chlorophyll content was estimated by applying linear or polynomial models for specific plant species when deriving these models. Selection criteria for reflectance indices were based on their ability to estimate chlorophyll content in a wide range of plant species, plant physiology, phenology,

The inversion of the PROSPECT model using leaf reflectance and transmittance was applied in this chapter in order to estimate chlorophyll concentration. Foliar chlorophyll content (*Cab*) was computed by the inversion process of PROSPECT 5 for the range of 400–1075 nm using reflectance and transmittance in the sampling interval of 1 nm for the 1134 leaf samples. Brown

and growing conditions, which is a characteristic of the vegetation in tropical forests.

**samples** 

mg cm−2 Lindera melissifolia 145 3.8–47.3 4–50 0.90

mg cm−2 Paper birch 100 ~0–45 0.4–45.5 0.96

µmol m−2 Soybean and maize na. 0–70 ~0–90 0.96

30–50 leaves per specie **SPAD-502 range** 

391 0–80 0–150 0.89

**Chl range (µm cm−2)** 

3–80 ~0–100 0.79

*R***2**

Source: (8) Ref. [25], (9) Ref. [25], (10) Ref. [25], (11) Ref. [40], and (12) Ref. [42].

**Table 2.** Chlorophyll content indices based on reflectance derived from spectroradiometer data.

#### **3.7. MTCI index**

In this study, MTCI was applied to foliar reflectance data collected at leaf level by the following equation:

$$MTCI\_{\text{follow reflex\\_data}} = \frac{R\_{\gamma \lesssim 4} - R\_{\gamma 09}}{R\_{709} - R\_{681}} \tag{2}$$

where *R*754, *R*709.75, and *R*681 are the foliar reflectance at wavelength 754, 709, and 681 nm, respectively.

#### **3.8. REP: first derivative method**

The red-edge inflection point was estimated by the first derivative method:

$$D\_{\lambda(i)} = \frac{R\_{\lambda(i)} - R\_{\lambda(i-1)}}{\Delta \mathcal{X}} \tag{3}$$

where *Rλ(i*) and *Rλ(i*-1) are reflectance at wavelength *i* and (*i* − 1), respectively.
