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

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 a laboratory.


na. = Not available.

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

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