## 5 Discussion  
### Novelty of the Fixed-Jilin-1 Angle Effect Correction Method  
In this study, we introduced a novel method for correcting the angular effects inherent in high-resolution, side-view satellite imagery data. The accuracy of this proposed method was substantiated through validation against measured crop reflectance data, demonstrating superior performance compared to other prevalent methodologies. Extensive research, including the present study, has confirmed the applicability of MODIS BRDF parameters and the fixed BRDF parameters of Landsat satellites for angular correction across a spectrum of satellite sensors, thereby highlighting the universality of these parameters. However, variations in sensor responsiveness, imaging conditions, observation geometry, and spatial resolution necessitate further refinements to these ostensibly universal approaches. This is particularly pertinent for satellites capable of flexible side-swing imaging, which exhibit more dynamic observation geometries, thus necessitating more specialized angular correction methodologies.  
Similar to the results of [PERSON] et al. [20], the VJB method does not show better accuracy than other methods, which is different from the results of [PERSON] et al. [22]. Both this paper and [PERSON] et al. [20] focus on crops, while [PERSON] et al. [22] focus on semi-desert biome, so it can be inferred that the VJB method is greatly affected by the type of land cover. Additionally, the fixed BRDF parameters of Landsat satellites, when compared to other  
Figure 10: Chlorophyll (T850 nm/T720 nm) validation based on field measured data. The \(X\)-axis is the measured reflectance, the \(Y\)-axis is the corrected reflectance, and the black solid line is the 1:1 line. (**a**) Original, (**b**) MODIS-based, (**c**) AFX, (**d**) VJB, (**e**) Fixed-Landsat, and (**f**) Fixed-Jilin-1.  
methods, exhibits marked discrepancies in the red band. This discrepancy is primarily attributed to the broader bandwidth of the Jilin-1 GP01/02 red band in contrast to that of the Landsat TM red band (50 nm versus 30 nm), coupled with a wider viewing angle (\(\pm 45^{\circ}\) side-view imaging versus sub-satellite point imaging).  
The AFX method achieves superior accuracy in correcting sensor angle effects compared to the MODIS parameter-based approach. This enhanced precision is attributed to AFX's capacity to limit scale differences in BRDF profiles to a significant degree. At low viewing angles, the stability of the Landsat-based fixed parameters surpasses that of the MODIS method in angle correction for Jilin-1 GP01/02 PMS data, due to their reduced sensitivity to land cover type, condition, or surface disturbance. However, the fixed BRDF parameters falter in accurately depicting BRDF variations at high viewing angles. The AFX method compensates by incorporating surface variation data, suggesting a complementary application with the fixed parameter method under large observation angles. Consequently, the proposed Fixed-Jilin-1 method integrates the strengths of both the AFX and Landsat fixed parameter methods, employing fixed BRDF parameters that are more universally applicable and leveraging AFX to diminish the impact of spatial scale discrepancies. Overall, the proposed method corrects angular effects in Jilin-1 GP01/02 PMS data more effectively, offering a distinct advantage particularly at larger zenith angles.