###### Abstract
The peaks in the fluorescence simulation curve are changed by changing the values of FQE I and II. [PERSON] et al. [22] concluded that spectral changes due to photochemical downregulation are subtle and overshadowed by changes in structure and chlorophyll. Moreover, the conditions under which the data were measured (closed chamber with no free gas exchange) may not be ideal to measure in vivo photosystem activity. According to the leaf and canopy analysis of [PERSON] et al. [22], caution should be taken when attributing the large changes in the shape of the remote sensing solar-induced fluorescence (SIF) spectrum to plant stress, especially when the data collection time is short. Challenges remain regarding how to retrieve the efficiencies of PSI and PSII and whether they make sense physiologically. Chlf is closely related to photosynthesis and can be used to directly probe photosynthetic mechanical function [23; 24; 25; 26; 27]. Several models, such as FluorMODEL [28], Fluspect [29; 30], the newly adopted Monte Carlo ray-tracing model [31], and FluLCVRT [32], can simulate the radiative transfer of ChlF in plant leaves. There are two major techniques to measure canopy level ChlF: a laser-induced fluorescence transient (LIFT) method and a SIF method. The LIFT method uses a laser beam to excite chemical species (molecules or atoms) in the plant. Upon absorbing the laser beam photons, the species will be in a short-lived excited electronic state. To return to a stable state, the molecule releases this extra energy through several pathways--fluorescence, heat, or photochemistry [33; 34]. With this technology, fluorescence directly reflects information about the molecular structure. The fluorescence of a leaf is affected by vegetation fluorescence spectral properties, i.e., pigment composition, pigment content, and plant biomass [35; 36; 37]. LIFT is a good indicator of plant photosynthesis; however, it cannot be used at large scales, and vegetation monitoring by LIFT from satellite platforms is not yet possible [38]. In SIF, passive detection of fluorescence is used to estimate vegetation properties [39; 40]. The signals containing these properties, which are produced by the plants themselves, are measured by a detector attached to unmanned aerial vehicles, airborne vehicles or satellites, and acquired as remote sensing data [41]. Retrieval techniques are used to extract the reflectance and fluorescence values from remote sensing data; however, the spatial resolution of the data is too coarse for the soil-vegetation-atmosphere-transfer (SVAT) model. The input data must have higher resolution, which requires field-scale data [42]. There is only an indirect relationship between the radiative transfer parameters and the model parameters in the SVAT model because they were developed to serve different purposes. For example, parameters used in the PROSPECT and algorithmic bidirectional surface scattering types of leaf radiative transfer model [43] are incompatible with each other because their leaf composition handling approach and solutions are fundamentally different, with distinct end-purposes. Therefore, the relationship between the radiative transfer parameters and SVAT parameters is often indirect; for example, an optical leaf is an index that was retrieved from a radiative transfer model into a one-sided leaf area index that is used in a photosynthesis model [29]. Fiuspect-B (hereinafter, Fluspect) is a radiative transfer model for the PS I and PS II emissions that simulates leaf reflectance, transmittance, and ChlF for a given emission efficiency and a given spectral shape of ChlF [30]. It is a component of the Soil Canopy Observation, Photochemistry and Energy (SCOPE) model that simulates radiative transfer in the leaf and canopy as well as variations in the quantum efficiency [29]. Separate evaluations of Fluspect by various researchers [30; 44; 45; 46] have mostly been performed under artificial light.