## 1 Introduction  
Optical remote sensing may serve as a tool for monitoring ecosystem dynamics and photosynthesis, both spatially and temporally. Photosynthesis by trees is typically a seasonal response to a complex set of variables, including vegetation type, photoperiod, solar angle, and weather. It is, therefore, important to identify and validate remote sensing approaches to facilitate phenology predictions across vegetation types and to identify the environmental and physiological factors that influence the optical signals. Ultimately, we expect this approach will lead to a deeper understanding of canopy photosynthesis in relation to climatic change and management [1]. Chlorophyll fluorescence is considered as an indicator of vegetation functionality. However, there is still a lack of knowledge of how the observed changes in fluorescence are influenced by canopy structural properties and the concentration of chlorophyll and other pigments. Structural properties may refer to the branches' layout on the trees and foliar distribution on the branches, which can result in shading of portions of foliar area during the day at certain sun azimuth and zenith configurations [2]. As a result, the effect of canopy self-shading can impact upon remote sensing parameters [3, 4]. foliar chlorophyll content is closely related to canopy NDVI index, which refers also to the quantity of biomass in the vegetative period [5]. Fluorescence is a radiative signal arising deep within the photosynthetic system. It offers information about photosynthesis due to its link to non-photochemical quenching [6; 7]. Large-scale detections of fluorescence signals from sensors deployed in the field are now possible with advances in measuring techniques. The network of spectral measurements at flux towers may provide opportunities to study passive fluorescent signals as a measure of plant stress and photosynthesis [8]. Two characteristic peaks of fluorescent emission are present in the red and far-red parts of the spectrum at 685 and 740 nm. Two photosystems (PSI and PSII) in plant leaves contribute to both peaks. The peak at 685 nm is closely connected to emission from PSII and has received greater attention in the earlier photosynthesis studies that have relied on artificial light excitation. This peak, however, may vary during the season along with variations in chlorophyll content as a consequence of the overlap between the spectra of fluorescent emission and chlorophyll absorption [9; 10]. The far-red peak at 740 nm consists of fluorescent emissions from both PSII and PSI and generally increases with chlorophyll content [11]. The most frequently used methods to estimate fluorescence from passive unattended measurements of the radiance spectra rely on Fraunhofer line depth discrimination of the oxygen absorption bands near 687 nm (O\({}_{2}\)B) and 760 nm (O\({}_{2}\)A) by using infilling methods for the spectra [12; 13; 14]. The use of SIF has increased in the last decade. Maps of the global distribution of fluorescence have been developed using data from the satellites GOSAT [15], GOME-2 [16], and OCO-2 [17]. These studies evaluated mostly fluorescence near the oxygen absorption band at 760 nm. The efforts have also led to attempts to link SIF emissions estimated from satellite sensors to carbon fluxes at the canopy level (e.g., [18]). However, insufficient understanding of the dynamics of fluorescence precludes scaling-up to longer-term observations. It has been documented that the relation of fluorescence emission in the O\({}_{2}\)A band to photosynthesis is more straightforward and dependent on APAR [19] and is, therefore, becoming widely used. However, some recent studies have suggested that the fluorescence of PSII with the peak value set directly to the O\({}_{2}\)B waveband is less affected by absorbed photosynthetically active radiation (APAR) and, therefore, provides more information on photosynthesis [20; 21].