## 2 Materials and Methods  
### Hardware and Physical Architecture  
The EcoSpec system is equipped with five types of optical and infrared sensors powered by solar energy (Figure 1, Table 1, Supplementary Materials, Video S1) installed at two locations on the tower, called the upper and lower packages, respectively.  
\begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt}} \hline \hline
**Instrument** & **Description** \\
**(Model, Manufacture)** & \\ \hline Spectrometer & Spectral reflectance of land surface using 2150 spectral channels ranging from 350 to 2500 nm. Instrument with a 1.5 m fiber optic cable having a 25 degree field of view (FOV). Height of installation: 3–7 m above ground. Variables: Spectral reflectance (350–2500 nm) and spectral vegetation indices. 1 Frequency of measurement \(-1\) min 2. \\ \hline Thermal IR sensor (SI-111, Apogee Instruments Inc.; Logan, KY, USA) & Radiant temperature of canopy and ground surface. Height of installation: 3–7 m above ground. Variables: Surface temperature (plants and exposed soil) and sky temperature. Frequency of measurement: 1 min. \\ \hline Red-green-blue (RGB) camera (Q1604, Axis; Lund, Sweden) & Plant conditions; visual and contextual information within the field of view of the spectrometer and its surroundings. Height of installation: 3–7 m above ground. Variable: Contexture information of land surface, such as plant conditions and land cover composition and structure. Frequency of measurement: 1 min. \\ \hline Diffuse radiometer (RSR2, Irradiance Inc.; Cambridge, MA, USA) & Components of incoming light, such as direct and diffused light (2–6 m above ground). Variables: Total incoming light, direct light, sky light, sky temperature, and air temperature. Frequency of measurement: 1 min. \\ \hline Albedometer (Dual-Pyranometer 8104, Schenk; Grass Valley, CA, USA) & Albedo of incoming and outgoing light. Height of installation: 2–6 m above ground. Variables: Downwelling irradiance and upwelling irradiance. Frequency of measurement: 1 min. \\ \hline Pan-tilt unit (FTU-D300, FLIR; Wilsonville, AL, USA) & Rotating platform for the upper package, including spectrometer, thermal IR sensor, and RGB camera, in order to collect measurements at 12 positions around the tower (300\({}^{\circ}\)). Payloads: 70 lbs. \\ \hline Enclosure (ENC 14/16-MM-NC, Campbell Scientific Inc.; Logan, KY, USA) & House spectrometer and RGB camera. \\ \hline Actuator (PA-15-8-11, Progressive Automations; Arlington, TX, USA) & Extend and retract the white reference panel to enable white reference measurement right before each measurement from land surface. \\ \hline White reference panel (Spectraron, Labsphere; North Sutton, NH, USA) & Provide a reference surface for white reflectance calibration. The highly reflective surface has 99\% reflectivity across the spectral range. \\ \hline Single-board computers (Raspberry Pi) & Provide commands to all system components and temporary data storage. \\ \hline DC/AC converter & Convert DC power from the solar power system to AC to power the instruments. \\ \hline Enclosure (Campbell Scientific Inc.; Logan, KY, USA) & House single-board computer, CR1000 data logger, and cellular modem. \\ \hline \hline \end{tabular}  
* \({}^{1}\) Reflectance values are transformed to 100+ spectral vegetation indices that are known to correlate with plant and ecosystem properties such as biomass, plant greenness or pigment, structure, and moisture including Normalized Difference Vegetation index (NDVI), Normalized Difference Water Index (NDWI), Photochemical Reflectance Index (PRI), Enhanced Vegetation Index (EVI), Chlorophyll Index (CI), Moisture Stress Index (MSI), Water Band Index (WBI), and Modified Chlorophyll Absorption in Reflectance Index (MCARI). 2 Depending on the level of irradiance.  
\end{table}
Table 1: EcoSpec System Sensors and Components.