## 3 Results  
The following results are examples from the 2015 study conducted at the soybean field in AmeriFlux US-B1 site located within Fermi National Accelerator Laboratory, Batavia, Illinois. Examples of spectral reflectance values of land surfaces that were collected using the EcoSpec system are shown in Figure 2. The spectral reflectance signatures presented in the figure were collected at 7:30 a.m.,10:30 a.m., 1:30 p.m., 4:30 p.m., and 7:00 p.m. at local time on 21 August 2015 (DoY 234). There are two atmospheric absorption features around the 1350-1430 and 1800-1940 nm spectral ranges that are seen across all the time periods. While spectral reflectance signatures show characteristic profiles for healthy vegetation most of the day, the signature appears noisy, and a vegetation spectral signature becomes obscured late in the day (Figure 2). This type of system could help determine the effective daytime period or sun angles and the minimum irradiance to usefully collect optical and infrared information to study plant properties and functions. Diurnal trajectories of selected spectral vegetation indices and TIR on 21 August 2015 (DoY 234) are shown in Figure 3. The NDVI and NDWI, which are known to correlate with green biomass [21; 22; 26; 27] and plant moisture [28; 29; 30; 23], respectively, follow a similar pattern throughout the day, while the PRI, which is known to indicate photosynthetic radiation use efficiency of plants, shows an opposite pattern (Figure 3a). The MSI, which is known to indicate plant's moisture stress [25; 31; 32; 33], and TIR both show gradual change during the day (Figure 3b). Plant canopy temperature represented by TIR increases from morning to mid-day and slightly decreases later in the day. On the other hand, plant water stress depicted by the MSI decreases from morning to mid-day and steadily increases toward the evening. This contrasting pattern between the MSI and TIR shows the indication of TIR measurements for plant moisture content or their responses to water availability, which has been demonstrated in a number of studies [19; 20; 34]. RGB photos on the selected dates during the 2015 growing season that were captured using the EcoSpec system are shown in Figure 4. Soybean plants planted in mid-April 2015 covered approximately 25% of the ground surface in the beginning of July. Foliage cover exceeded 60% of the ground in two weeks (Figure 4) and completely closed by early August. The plants started to show a sign of senescence in early September and completely senesced by mid-September. RGB photos of ground surface documents plant conditions (e.g., stress, disease) and phenology and would provide valuable information for interpreting optical and infrared measurements. For example, certain patterns in spectral reflectance values or signatures may be evaluated based on plant or land surface conditions captured in the photos. Causes of sudden changes in spectral reflectance and/or vegetation indices may be identified using the photos. The RGB photos may also be used to investigate the effects of soil exposure, leaf orientation, and shadow on optical and infrared measurements. Figure 2: Land surface reflectance from the visible to shortwave infrared spectral region at 7:30 a.m., 10:30 a.m., 1:30 p.m., 4:30 p.m., and 7:00 p.m. at local time on 21 August 2015 (DoY 234). Seasonal trajectories of the NDVI, NDWI, and PRI along with the trajectory of the fPAR that was measured using the eddy covariance system are shown in Figure 5. All three indices increased toward the peak growing season of late July to early August and decreased toward the end of the season. These patterns correspond to that of fPAR throughout the growing season (Figure 5).