## 3 Results  
### Simulation Results by the Fluspect Model with/without the FQE Inversion Code  
To simulate fluorescence under natural conditions more accurately and validate the results, we used an improved approach with measured data for the simulation. Reflectance and transmittance data were used to retrieve the leaf composition and structure using the RTM inversion model. The model aimed to calibrate \(R\) and \(T\) to find the vegetation parameters that best fit the simulated and measured \(R\) and \(T\). ChlF can also be simulated using the Fluspect model. The upward and downward curves of the simulated fluorescence were calculated; the total fluorescence (upward and downward fluorescence) is shown as two curves from 680 nm to 800 nm and compared with each measured curve. Normally, the fluorescence will show two peaks at 687 nm and 740 nm. In the tests, upward fluorescence (ventral), and downward fluorescence (dorsal) of high-chlorophyll-content leaves (WT) and low-chlorophyll-content leaves (MG) in the top and middle layers are simulated with/without the FQE inversion code. A comparison among the measured, modeled, and improved simulation values (with the FQE inversion) for two soybean varieties (WT and MG) based on representative leaf samples are explored. To obtain a better comparison of the model performance, the simulated fluorescence and measured data are compared in Figure 4, along with the results that include FQE inversion. The statistical relationships between the measured and modeled fluorescence for these representative leaf samples, before and after adding the FQE inversion code, are listed in Table 2.  
Figure 4: A comparison among the measured, modeled, and improved simulation values (with the FQE inversion) for two soybean varieties (WT and MG) based on four representative leaf samples. **(a)** High WT and **(b)** Low MG. Note: HT (HM) is the high WT top (middle); LT (LM) is the low MG top (middle). From Figure 4 with Table 2, we can see that, for all the simulations without inversion code, most of the reflectance and transmittance values for the top and middle layers of the WT and MG leaves were simulated reasonably accurately with a decent \(R^{2}=0.7\)-\(0.9\) and \(RMSE=0.55\times 10^{-4}\)-\(2.49\times 10^{-4}\) Wm\({}^{-2}\)um\({}^{-1}\)sr\({}^{-1}\) by the Fluspect model. However, the simulated fluorescence was overestimated, especially in two peaks. For leaves with high chlorophyll content, the simulated upward fluorescence was higher than in the measured data, especially in the first peak at 687 nm. The simulation for the upward fluorescence in the second peak was better than that in the first peak. For leaves with low chlorophyll content, the simulated fluorescence is always overestimated in both the upward and downward fluorescence, especially around 740 nm. We noticed that the first peaks in the downward fluorescence (ventral) curves were not easy to identify in the actual measurements because the chlorophyll absorbed some of the fluorescence. Hence, the first peak in the downward fluorescence is more noticeable in leaves with low chlorophyll content. Under certain conditions, the model underestimated the fluorescence on the second peak for both the upward and downward fluorescence. This situation may occur due to weather conditions, which means that the default FQE values are not sufficient for performing an accurate simulation. For leaves with low chlorophyll content, the upward and downward fluorescence values were overestimated in most