## Materials and Methods  
### Study Area and Field Measurements  
The study area was at the Huailai experimental field (40\({}^{\circ}\)20\({}^{\prime}\)55.093\({}^{\prime\prime}\)N, 115\({}^{\circ}\)46\({}^{\prime}\)59.569\({}^{\prime\prime}\)E, altitude 488 m) in Hebei Province, China. This field is affiliated with the Chinese Academy of Sciences (CAS) (Figure 1). The study area is in a temperate and semi-arid region with four distinct seasons, abundant sunshine, simultaneous heat and moisture, and large temperature differences. The annual average temperature and average precipitation are approximately 9.5 \({}^{\circ}\)C and 392 mm, respectively. The primary vegetation type around the Huailai experimental field is farmland, and other land cover types are water, wetland beach, and residential. Maize is the dominant crop type in this study area. The soil type of the study area is brown soil.  
Several vegetation structure parameters (e.g., leaf reflectance and transmittance, average leaf angle, canopy spectral measurements, and LAI) and biophysical and biochemical parameters (e.g., leaf chlorophyll-\(a\) and -\(b\) content (C\({}_{\text{ab}}\)), leaf water content (C\({}_{\text{w}}\)), and leaf dry matter content (C\({}_{\text{m}}\))) were acquired at the Huailai experimental field. The leaf reflectance and transmittance from 400 nm to 2500 nm were measured using a UV molecular spectroscopy (Lambda 900, PerkinElmer Inc., Waltham, MA, USA). The leaf inclination angle was the angle between a leaf and its normal direction, and was measured using a protractor. The average leaf angle is the mean leaf inclination angle for an entire plant. The canopy and soil spectra were measured using a spectroradiometer (Analytical Spectral Devices, ASD, Longmont, CO, USA) covering wavelengths from 400 nm to 1100 nm with a 5\({}^{\circ}\) field of view at noon on sunny days. C\({}_{\text{ab}}\) was based on an average of six points on each leaf three times using the SPAD 502 DL plus Chlorophyll meter (Spectrum technologies, Inc., Bridgend, UK). The fresh leaves were weighed and placed into an envelope bag. The envelope bag was then put in the oven at 105 \({}^{\circ}\)C for 30 min and then at 85 \({}^{\circ}\)C for 24 h. C\({}_{\text{m}}\) is the weight of leaves after oven drying, and C\({}_{\text{w}}\) is the proportion of leaf water (fresh weight minus dry weight) to the dry weight.  
In this study, LAI field measurements from maize sample plots were acquired on 31 July 2014 (yellow dots in Figure 1b). The sample plots were selected based on NDVI values from Landsat-8 OLI according to [PERSON] et al. [52]. Then, the sample plots were selected in the field with a single plant type and uniform growth base on the coordinates from global positioning system (GPS). Finally, 17 sample plots were acquired in the study area. LAI field measurements were acquired using an LAI-2200 PlantCanopy Analyzer (LI-COR, Inc., Lincoln, NE, USA). The LAI of each sample plot was measured from one above-canopy reading and nine below-canopy readings with a 45\({}^{\circ}\) view cup. The measurements were obtained from 06:30 to 10:00 and from 16:30 to 19:30 to avoid measurement errors caused by the direct sunlight, and the LAI value was measured twice at each site. To reduce the observer effects and other sources of error during LAI field measurements, except for the records of the fifth view angle (centered at 68\({}^{\circ}\)) acquired from the LAI-2200 instrument, all of the LAI field measurements were calculated based on a standard error LAI (SEL) of less than 0.5.