3.2.1. Spectral Curve

1. Validation of the sum of the reflectance during the growing season using field data

In Figure 9, the sum of the reflectance simulated by the row model and the field data have high consistency in the growing season of row crops (it can be described as an increase of LAI and change in row structure in Table 2), except for the spectrum less than 1500 nm measured on 20 May (Figure 9a). As the crop grows over time, the photosynthetically active radiation (400–700 nm) gradually decreases. This phenomenon is especially noticeable at the "red edge" (700–750 nm, the area where the vegetation reflectance from the red band to the near-infrared band increases sharply). On 25 May (Figure 9b), the "red edge" gradually formed, and it was increasingly obvious with the growth of crops (Figure 9b–f). The sum of the reflectance in the near-infrared (NIR) region (700–1100 nm) gradually increases with the growth of crops; after that, it reaches a maximum value (0.51) on 1 July (Figure 9f).

**Figure 7.** The distribution of reflectances in the single scattering in the NIR band and the multiple scattering in the NIR band simulated by the RGM model and the row model in four viewing modes: (**a**) principal plane (PP) mode in the single scattering in the NIR band, (**b**) principal plane (PP) mode in the multiple scattering in the NIR band, (**c**) orthogonal plane (OP) mode in the single scattering in the NIR band, (**d**) orthogonal plane (OP) mode in the multiple scattering in the NIR band, (**e**) along-row plane (AR) mode in the single scattering in the NIR band, (**f**) along-row plane (AR) mode in the multiple scattering in the NIR band, (**g**) orthogonal row plane (OR) mode in the single scattering in the NIR band, and (**h**) orthogonal row plane (OR) mode in the multiple scattering in the NIR band. Here, VZA is the viewing zenith angle.

**Figure 8.** The distribution of reflectances for the single scattering near the hotspot (principal plane) model. (**a**) Single scattering near the hotspot in the red band, and (**b**) single scattering near the hotspot in the NIR band. Here, VZA is the viewing zenith angle.

**Figure 9.** Comparison of the sum of the reflectance simulated by the row model and field data at the wavelength in the vertical viewing direction on (**a**) 20 May, (**b**) 25 May, (**c**) 1 June, (**d**) 16 June, (**e**) 22 June, and (**f**) 1 July. Here, the noise in the water vapor absorption was removed.

2. Validation of the reflectance for different types of row crops using satellite data

We used remote sensing data to validate the row model. The sum of the reflectance simulated by the row model and the sum of the reflectance measured by the World-View 3 satellite have high consistency. In the simulation of each species, the accuracy of the simulation of corn and wheat is the best, while the simulations of wolfberry had a slight deviation (Figure 10).

**Figure 10.** Comparison of the sum of the reflectance simulated by the row model and the reflectance at the top of the canopy measured by the World-View 3 satellite in the vertical viewing direction. (**a**) Corn; (**b**) rice; (**c**) matrimony vine. Here, M represents the data measured by the World-View 3 satellite and S represents the simulated data of the row model.

### 3.2.2. Distribution of the Sum of the Reflectance on the Multiangle Observation

In the distribution of the sum of the reflectance (Figure 11), the results simulated by the row model and the measured data have a slight systematic deviation from some angles. In the forward direction of the PP mode in the NIR band, the reflectance has the largest computational deviation between the simulation and measurement. However, from the statistical results, we can find that the R-values are greater than 0.8317 (except R = 0.5392 in the PP mode in the NIR band) and RMSE values less than 0.0403 (Figure 12). The MAD results show that the difference between the sum of the reflectance simulated by the row model and field data is less than 13%, except for the OR mode in the red band (24.11% in Figure 12). Similar to the computer simulation in Figures 6 and 7, the consistency of the red band (MAD = 0.25 × (10.71% + 12.4% + 6.29% + 24.11%) ≈ 13.38%) is greater than that in the NIR band (MAD = 0.25 × (9.65% + 5.29% + 1.61% + 3.76%) ≈ 5.08%) (Figure 12). Generally speaking, the consistency between the two is still relatively high, simulating multiangle changes in the PP mode, OP mode, AR mode, and OR mode.

**Figure 11.** Comparison of the distribution of the sum of the reflectance simulated by the row model and field data in the multiangle observation for the principal plane (PP) mode (**<sup>a</sup>**,**<sup>e</sup>**), orthogonal plane (OP) mode (**b**,**f**), along-row plane (AR) mode (**<sup>c</sup>**,**g**), and orthogonal row plane (OR) mode (**d**,**h**). (**<sup>a</sup>**–**d**) Red band (670 nm); (**<sup>e</sup>**–**h**) NIR band (860 nm). VZA is the viewing zenith angle. The black box is the abnormal point in the measurement.

**Figure 12.** Statistics of the distribution of the sum of the reflectance simulated by the row model and field data in the multiangle observation for the principal plane (PP) mode (**<sup>a</sup>**,**<sup>e</sup>**), orthogonal plane (OP) mode (**b**,**f**), along-row plane (AR) mode (**<sup>c</sup>**,**g**) and orthogonal row plane (OR) mode (**d**,**h**). The red line is a 1:1 line. R is the correlation coefficient, RMSE is the root mean square error, and MAD is the mean absolute deviation, which represents the difference between Data *A* and Data *B*, expressed as a percentage. Its expression is *m <sup>m</sup>*=1 1 *m* (*A* − *<sup>B</sup>*)/*<sup>B</sup>*. Here, *m* is the number of comparison groups, *A* is the sum of the reflectance simulated by the row model, and *B* is field data.
