# WaveConv-sLSTM-KET: A Novel Framework for the Multi-Task Analysis of Oil Spill Fluorescence Spectra
## 3 Results and Discussion  
### Spectral Analysis  
Figure 6 presents the fluorescence spectra of five oils measured at the laser powers of 60 mW, 70 mW, and 80 mW. Solid lines indicate the average spectra, while shaded areas  
represent spectral variability under specific film thickness and laser power conditions. The spectra reveal similar features across the oils, with prominent peaks around 490 nm and 530 nm. A peak near 470 nm corresponds to the Raman signal of seawater, and a peak near 610 nm likely originates from organic matter in the seawater. These findings are consistent with those reported by [PERSON] et al. [26]. As laser power increases, the fluorescence intensity of the oils also increases. For example, Figure 6a-c demonstrate that the fluorescence spectra of Shell HELIX 0W-40 tend to saturate at 80 mW, leading to a diminution of the two primary peaks. In contrast, the other oils do not exhibit noticeable saturation at a high laser power, indicating that intrinsic differences among oils result in varied laser responses. Additionally, as oil film thickness increases, the seawater Raman peak diminishes; however, the degree of attenuation varies among different oils. Even for the same oil, the intensity variation of the Raman peak differs under different laser powers. These observations suggest that differences in the optical absorption properties of each oil affect the suppression of the seawater Raman signal. Consequently, traditional oil film thickness estimation methods, such as Raman suppression techniques, often require adjusting model parameters based on oil type and laser power, increasing workflow complexity and reducing model practicality. Moreover, the predictive thickness range varies among different oils, which severely limits the generalizability of these methods. Furthermore, since spectral acquisition occurs during dynamic processes, the relative position of the oil film and detector (horizontal and vertical distances, as well as angles) is constantly changing. For oil films with similar thicknesses, the spectral intensity may overlap. Existing thickness prediction methods rely on static data collected in laboratories to fit models. However, significant spectral variations in real-world environments can lead to model failure. The relationship between oil thickness and fluorescence intensity in Figure 6 is nonlinear for different oils. Even for the same oil, due to the simulated wave action, the transformation between thickness and fluorescence intensity is inconsistent under different laser powers (e.g., Figure 6j-l). Figure 7 illustrates the fitting relationship between fluorescence intensity and oil film thickness for Helix 0W-40 and Mobil 2000 5W-40 under static conditions at three different laser power levels. This figure shows that fluorescence intensity increases with oil film thickness, exhibiting an exponential-like trend. A cubic polynomial model was used to effectively capture this nonlinear relationship. Moreover, due to inherent differences in light absorption, the thickness-intensity relationship varies among oils, as evidenced by the distinct fitted curves for Helix 0W-40 and Mobil 2000 5W-40. This phenomenon indicates that oil type and film thickness are interrelated and must be analyzed comprehensively. To illustrate the effects of oil type and film thickness on spectral distribution, pure oil spectra were collected for 100 mL samples of five different engine oils, as shown in Figure 8. A comparison revealed differences in both spectral features and distribution between the pure oil spectra and the spectra of oil films with varying thicknesses. For example, the pure oil spectrum of Mobil Super 1000 X1 Diesel 15W-40 shows two prominent fluorescence peaks near 490 nm and 530 nm, with an intensity ratio close to 1:1. However, as Figure 6j-l demonstrates, the spectral profile of Mobil Super 1000 X1 Diesel 15W-40 initially resembles that of the pure oil when the film is thin but changes as the film thickens.