## Materials and Methods
### Field Experiments  
Seven independent field experiments were conducted in Beijing and in Sanya, Hainan Province, China. The distribution and location of three experimental sites are shown in Figure 1. The details are \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Parameter** & **Description** & **Value/Range** & **Default** & **Unit** \\ \hline Cab & Leaf chlorophyll a + b content & 5, 10, 20, 30, 40, 50, 60, 80 & 40 & ug/cm\({}^{2}\) \\ LAI & Leaf area index & 0.5, 1.5, 3.4, 5.7 & 3 & m\({}^{2}\)/m\({}^{2}\) \\ LIDFb + LIDFb & Leaf inclination & [1, 0], [-1, 0], [-1, 0], [1, 0], [-0.35, -0.15] & [-0.35, -0.15] & - \\ SZA & Solar zenith angle & 27, 29, 31, 36, 36, 46, 50, 57, 61, 68, 72 & - & degree \\ VZA & View zenith angle & 0 & - & degree \\ \hline \hline
[1, 0]—planophile; [–1, 0]—erectophile; [0, \(-1\)]—plagioophile; [0, 1]—extremophile; [0, 0]—uniform; [–0.35, \(-0.15\)]—spherical. & \\ \end{tabular}
\end{table} 
Table 1: Main parameters of the SCOPE model used for the simulations in this study. described below and also listed in Table 2. Corresponding to the spectral measurements, the auxiliary parameters measured simultaneously are also provided, including Cab, LAI and \(f_{c}\) (the fractional cover of green vegetation). Five experiments were carried out on winter wheat at the National Precision Agriculture Demonstration Base located at Xiao Tangshan (XTS) Farm, north of Beijing (40\({}^{\circ}\)11\({}^{\prime}\)N, 116\({}^{\circ}\)27\({}^{\prime}\)E). These experiments were conducted on two winter wheat varieties during two growth cycles, i.e., the 2015-2016 and 2016-2017 cycles. In the 2015-2016 cycle, the winter wheat (_Triticum aestivum_ L.) was cultivated using conventional fertilizer and irrigation management and had a uniform growth status. Three diurnal experiments were conducted on 8, 9 and 18 April 2016 with the corresponding growth stages being the jointing, jointing, and booting stages, respectively. In each diurnal experiment, the upwelling canopy radiance and incident irradiance spectra were measured approximately every  
Figure 1: The distribution of the three experimental sites in China. half hour from 8:30 to 17:00. In the 2016-2017 cycle, four fertilization rates were applied to two cultivated varieties of wheat (_Lunxuan 167 and Jingdong 18_). Two wheat varieties were cultivated in different columns next to each other on each field site. Four nitrogen fertilization treatments, i.e., different amount of carbamide were used: 585 kg ha\({}^{-1}\) (N3), 390 kg ha\({}^{-1}\) (N2), 195 kg ha\({}^{-1}\) (N1), and no fertilization (N0). For each fertilization rate, three duplicates were also designed. Two experiments were conducted--one on 7 November 2016 and another on 8 December 2016--when the winter wheat was at the emergence and tillering stages, respectively. Another diurnal spectral experiment was designed for gold coin grass (Lysimachia christinae [PERSON]) and conducted on 18 December 2016 at Sanya Remote Sensing Satellite Data Receiving Station (18\({}^{\circ}\)18\({}^{\prime}\)N, 109\({}^{\circ}\)18\({}^{\prime}\)E) located in Sanya City, Hainan Province, China. The upwelling canopy radiance and incident irradiance spectra were measured approximately every 20 min from 8:00 to 17:00. The canopy structure was homogeneous and its coin-like leaves were oriented very close to ground. A multi\(-\)species experiment was conducted on 18 December 2016 at Nanbin Farm (18\({}^{\circ}\)22\({}^{\prime}\)N, 109\({}^{\circ}\)10\({}^{\prime}\)E) in Sanya City, Hainan Province. The plant types at Nanbin farm included vegetables and crops such as potato, cabbage, cotton, rice and maize; their canopy structures were all planophile except for one observation made on rice. Figure 2 displays three photographs of studied canopies at XTS Farm in November (left, winter wheat), Nanbin Farm (middle, cotton) and Sanya Station (right, gold coin grass). The canopy structure of winter wheat is spherical and the leaves are more erect compared with a planophile canopy.