## 1 Introduction
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Measurement Approach** & **Location Frequency** & **Parameters (units)** \\ \hline \multirow{3}{*}{Eddy covariance} & \multirow{3}{*}{10 m tower 30 min} & Gross primary production (GPP, mg/m\({}^{2}\)/s), photosynthetically active radiation (PAR, \(\upmu\)mol/m\({}^{2}\)/s) and absorbed PAR (APAR, \(\upmu\)mol/m\({}^{2}\)/s), light use efficiency (LUE, mg CO\({}_{2}\)/\(\upmu\)mol PAR) \\ \hline \multirow{3}{*}{MoniPAM} & \multirow{3}{*}{leaf-level 10 min} & PAM light-adapted fluorescence metrics (i.e., F maximum-F\({}_{m}\)’, and F steady state–F\({}_{s}\)), used to estimate the operating efficiency of PSII (YII, arbitrary units or au) and electron transport rate (ETR, \(\upmu\)mol electrons/m\({}^{2}\)/s) \\ \hline \multirow{3}{*}{FLoX} & \multirow{3}{*}{1.5 m above Canopy \textless{} 2 min} & Solar induced fluorescence (SIF, mW/m\({}^{2}\)/nm/sr) in the Q\({}_{2}\)A (SIF\({}_{A}\)) and O\({}_{2}\)B (SIF\({}_{B}\)) bands and their sum (SIF\({}_{A+B}\)), SIF yields (SIF\({}_{A}\), SIF\({}_{B}\), SIF\({}_{B+A}\)), normalized difference vegetation index (NDVI, au), chlorophyll index (Clred, au), photochemical reflectance index (PRI, au) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Complementary measurements of corn (_Zea mays_ L.), collected across the 2017 growing season at OPE3, Greenbelt, MD. An approach for the remote estimation of Chl content, broadly used in precision agriculture and forestry, estimates leaf Chl content using VIs that are less sensitive to LAI, so as not to saturate under high LAI [3,4,8]. [PERSON] et al. [3,4] and [PERSON] et al. [5] investigated the use VIs as Chl surrogates for gross primary productivity (GPP, the carbon uptake by the process of photosynthesis) estimation, suggested the use of Clred (Table 1) for optimal Chl assessment, and validated canopy Chl in crops and deciduous canopies as the main seasonal driver of productivity. Chlorophyll fluorescence offers a strong potential to assess vegetation photosynthesis at local and regional levels using Earth observation technology [13]. Chlorophyll fluorescence signals are comprised of red and far-red emissions released from the chloroplasts as a by-product of photosynthesis, which are emitted from both sides of a leaf [14, 15, 16]. Chlorophyll fluorescence theory and its applications for evaluation of photosynthetic function are well understood [1,3,17, 18, 19, 20, 21]. Fluorescence is driven by the available photosynthetic pigments (i.e., chlorophyll) and APAR. The fluorescence signal originates in the antennae complexes of both photosystems I and II, however, most of its contribution originates in photosystem II (PSII) [22, 23]. Leaf-level chlorophyll fluorescence, measured by the pulse amplitude modulated (PAM) approach, is commonly used for evaluation of photosynthetic performance of vegetation [1,21, 24], measuring leaf-level photosynthetic efficiency and the associated chlorophyll fluorescence (F) parameters. Metrics collected in the presence of sunlight include steady state F (Fs, i.e., F) and F maximum (i.e., Fm'), which were used to derive photochemical quantum yield of PS II or the operating efficiency of PSII (YII) and electron transport rate (i.e., ETR, photochemical transport of electrons through PSII) [1,18,19,23,24], providing non-invasive means to evaluate photosynthetic activity. Since most of the regulation of photosynthesis takes place in PS II, the F signal provides a good indicator of the functional status of photosynthesis, as it is related to its light use [20,21]. While current PAM systems are capable of continuously measuring photosynthetic performance [24] on a number of plants for extended time periods (e.g., complete growing seasons), these measurements remain restricted to the leaf level. The eddy covariance approach measures the net exchange of carbon, water, and energy between an ecosystem and the atmosphere nearly continuously, providing time series of canopy level measurements over multiple seasons and years at flux tower sites [25].