## 3 Hardware and Software Sub-Framework for Active LIF Spectroscopy Sensing (HSFW2)  
The application of the LIF spectroscopy method for the seawater detection of pollution by oil and oil products has a long history and was described in many works, for example, [21; 22; 23; 24]. However, articles using LIF spectroscopy on drones appeared recently [25; 26; 27; 28]. The use of the LIF method on small-sized drones has become possible due to the emergence of small-size laser sources, especially LED [29]. References [30; 31] described the development of the LIF spectroscopy method for monitoring oil products dissolved in seawater. According to the results of these studies, a small-sized LIF spectrometer was developed, the 3D model and assembled version of which is shown in Figure 3a,b. In the case of a slick, it is necessary to carry out an autonomous identification of the type of oil product that formed the slick; in this case, the volume of pollution is estimated by the HSFW1. In the case of monitoring bilge water, it is necessary either to identify the oil in the solution or to measure its concentration; thus, the HSFW2 is used in this case. High efficiency of fluorescence emission in dissolved oil products is observed in the range 310-360 nm when excited by radiation at wavelengths less than 290 nm. The use  
Figure 3: (a) 3D model of the LIF spectrometer, and (b) photo of the LIF spectrometer in the drone body. 1—LIF spectrometer; 2—LED; 3—collimator of the first channel (slick of oil products); 4—collimator of the second channel (solutions of oil products); 5—optical fiber; 6—computer; 7—drone body; 8—light filters and optical windows. Figure 2: (a) The result of the operation of an artificial intelligence element HSFW1 for detecting an oil slick; (b) the result of oil slick segmentation and classification by different codes. of lasers as a source of excitation of the fluorescence signal leads to a significant increase in the mass and size characteristics of the LIF spectrometer, which is difficult to use on drones. Currently, with the advanced technologies, LED ultraviolet sources with high conversion efficiency and with power characteristics appropriate for efficient excitation of the fluorescence emission signal are possible to use. In the developed HSFW, the LED LEUVA66H70 HF00--2 (LG, Seoul, South Korea) with a central wavelength of 277.7 nm and average power of 70 mW, mounted on a cooling radiator and installed in a special holder, was chosen as an excitation source. This holder also has an integrated optical lens system for the formation of quasi-parallel radiation from the LED. The emission spectrum is shown in Figure 4. The vertical axis is the value of the LED intensity in relative units, while the horizontal axis is the wavelength in nm. A small-sized highly sensitive spectrometer Maya 2000 Pro--1 (Ocean Insight, Orlando, FL, USA) was used to measure the spectral distribution of LIF with the ability to record radiation in the range from 200 to 1100 nm, with low power consumption, a wide temperature range of operation, soft development kit tools, and control via USB port. According to the proposed concept, the developed complex should provide the ability to measure the fluorescence spectra of slicks of oil products by hovering the carrier above the surface. Traces of dissolved oil products are detected by the drone landing on the water. Hence, the receiving system of the spectrometer was implemented in a two-channel design. The first channel provides the possibility of recording the backscattered signal from the slick from a distance of more than 1 m.  
The registration in the second receiving channel is performed at an angle close to 60\({}^{\circ}\) to the direction of radiation of the LED and is carried out in the immediate vicinity of the receiving window submerged in water. Radiation in the first channel is registered by a 74-uv quartz collimator (Ocean Insight, Orlando, FL, USA)--3. In the second channel, registration is carried out by a 74-ud collimator (Ocean Insight, Orlando, FL, USA)--4.