*3.5. Comparison of the DLARI and MDATT*

The difference between the MDATT and DLARI was the substitution of λ<sup>1</sup> with an additional wavelength (λ4). We evaluated the improvement of incorporating this additional wavelength by calculating the maximum *R*<sup>2</sup> of all band combinations for the DLARI formula based on the three datasets.

The maximum *R*<sup>2</sup> was derived from combinations by fixing λ<sup>4</sup> while changing λ1, λ2, and λ<sup>3</sup> from 700 nm to 760 nm. The wavelength regions for λ<sup>4</sup> were from 700 nm to 900 nm. The results are plotted in Figure 9. It shows that when λ<sup>4</sup> was at 700 nm to 760 nm, the maximum *R*<sup>2</sup> derived from adaxial DLARIs and abaxial DLARIs were similar to those of the adaxial MDATT (0.95) and abaxial MDATT (0.94), while bifacial DLARIs achieved higher correlations with LCC than the bifacial MDATT (0.91) since λ<sup>4</sup> was higher than 709 nm. When λ<sup>4</sup> was higher than 760 nm, all three DLARIs were much more correlated to LCC than the three MDATTs. The highest *R*<sup>2</sup> of the adaxial DLARI and bifacial DLARI were obtained at λ<sup>4</sup> equal to 819 nm and 773 nm, respectively, and then rapidly became lower than those of the MDATT when λ<sup>4</sup> was located above 890 nm. For the abaxial dataset, the highest *R*<sup>2</sup> appeared at λ<sup>4</sup> equal to 774 nm and then became lower than the abaxial MDATT when λ<sup>4</sup> was above 840 nm. Compared to the MDATT, the effective regions of λ<sup>4</sup> for the adaxial DLARI were from 760 nm to 890 nm and for the abaxial DLARI when they were from 760 nm to 840 nm. For the bifacial DLARI, the robust wavelength regions of λ<sup>4</sup> were from 709 nm to 890 nm.

**Figure 9.** Maximum *R*<sup>2</sup> between LCC and MDATTs, DLARIs with λ1, λ2, and λ<sup>3</sup> from 700 nm to 760 nm and λ<sup>4</sup> from 700 nm to 900 nm.

The above bifacial DLARI was derived from a dataset composed of the same quantity of adaxial and abaxial reflectance measurements. In order to evaluate the impact of the abaxial reflectance on the performance of the two dorsiventral leaf adjusted indices, we divided the 84 abaxial reflectance samples into 6 parts and accumulated them into the adaxial dataset, then we calculated the optimal DLARIs and MDATTs and their accuracies, estimating LCC for each sub-dataset. The results are shown in Figure 10, which shows that the RMSEcv of MDATT dramatically increased from 2.52 to 3.35 when adding one-sixth of the abaxial samples into the adaxial dataset and then linearly increased to 3.55. With the increase of abaxial reflectance, the RMSEcv of DLARI stably increased from 2.37 to 2.82. Compared to the MDATT, the DLARI possessed a linear response to the impact of abaxial reflectance. The optimal wavelengths for the DLARI and MDATT derived from each sub-dataset showed unobvious changes with the addition of the abaxial reflectance. It can be concluded that the presence of abaxial leaves decreased the accuracy of DLARI and MDATT for LCC retrieval, but had no obvious influence on the optimal wavelengths for DLARI and MDATT.

**Figure 10.** The impact of the dorsiventral leaf structure on DLARI and MDATT in terms of the estimation accuracy and optimal wavelengths. The numbers in the brackets are the optimal wavelengths for DLARI and MDATT with a unit of nm.
