In recent years, due to the continuous expansion of China's offshore oil exploration and mining scale, offshore oil transportation has become increasingly busy, and the incidence of sudden oil spills in the oceans due to oil exploitation, transportation, storage and other reasons has increased. According to statistics, from the end of 1973 to the end of 2008, there were more than 3,000 oil spill accidents on the coast of China, including 69 oil spills from more than 50 tons of major ships. The total oil spill was 37,077 tons, with an average annual rate of 2, with an average of every oil spill. The amount of 537 t has caused great harm to the marine environment and seriously affected the lives of coastal residents.

At present, the traditional methods for detecting oil spills on the sea include aerial remote sensing and satellite remote sensing, but both have different problems. Aerial remote sensing monitoring does not have real-time performance, and satellite remote sensing has inaccuracy for small-scale pollution. Therefore, research And designing a system that can monitor floating oil spills in the sea in real time and accurately is of great significance for protecting marine environmental resources. In view of the advantages of near-infrared spectroscopy, such as high speed, low cost, no pollution, no damage to samples, and successful application in the identification of pure oil, an oil spill detection system based on near-infrared spectroscopy is designed. The system uses near-infrared light as the detection light source combined with the single-chip microcomputer-based data acquisition module. Online real-time monitoring of offshore waters is of great significance for protecting the environmental safety of offshore waters.

1 Near-infrared spectroscopy technology and its advantages

Near-infrared light (NIR) is an electromagnetic wave between visible light and infrared light with a wavelength in the range of 780-2 526 nm. It is one of the earliest non-visible light. Near-infrared spectroscopy is mainly caused by the non-resonance of molecular vibrations that causes molecular vibrations to transition from the ground state to the high energy level. In general, the near-infrared absorption of organic matter in this region is mainly the frequency doubling and frequency absorption of OH, C and NH. The main structure and composition of almost all organic materials can find signals in their near-infrared spectrum, and the spectrum is stable. Later, the researchers found that the content of the material is linear with the absorption peaks at different wavelength points in the near-infrared region, so the technology was used to determine the content of some products. Since organic substances such as oils contain OH, C and NH groups, NIR technology is continuously applied to the configuration and detection of oils.

Unlike traditional spectral analysis techniques, the application of near-infrared spectroscopy has the following advantages: (1) fast analysis, most of the measurement process can be completed in 1 min; (2) high analytical efficiency, through one-time spectral measurement and established Corresponding calibration model, continuous measurement of multi-components of infinite samples; (3) low cost of analysis, cost saving, and no pollution to the environment; (4) wide range of applicable samples, direct measurement of liquids through corresponding sample attachments , solid, semi-solid and colloidal samples of different physical states; (5) the sample generally does not require pretreatment, does not require the use of chemical reagents or high temperature, high pressure, high current and other test conditions, generally can achieve non-destructive determination; (6) operation Simple and convenient, safe to use, and not very demanding for operators.

2 Structural design of near-infrared absorption photoelectric sensor

2.1 Photoelectric sensor system structure

The system requires that the photoelectric sensing part has high detection accuracy and stability, and has high real-time performance, that is, continuous continuous measurement of seawater to be measured is required, so a near-infrared LED is used as a light source. The near-infrared light emitted by the light source is selected by the optical lens group to obtain the analysis light having characteristic absorption of the oil spill, and interacts with the sample in the sample chamber through the transmission, and then enters the photodetector to convert the optical signal into an electrical signal, thereby realizing detecting sample components shown in Figure 1.

2.2 Selection of source wavelength of light source

The optical path part uses the near-infrared light transmission absorption principle to monitor the oil content in the water on-line. Therefore, the spectral characteristics of the light source are required to be located in the near-infrared region, and the specific wavelength of near-infrared light is used as the light source, and considering that the design will eventually be a buoy. The form is packaged and has to be placed on the sea for a long time, and the sea surface environment is relatively harsh. Therefore, the light source is required to have a small volume, high mechanical strength, and high stability, so a near-infrared LED is selected as a light source device. In order to more accurately select the LEDs with specific peaks to achieve accurate measurement, different concentrations of water and oil mixture were configured to simulate the oil spill on the sea surface. The MPA near-infrared spectrometer was used to perform spectral acquisition on the configured samples to determine the peak value.

Instruments and reagents: MPA near-infrared spectrometer, gasoline, kerosene sample configuration: take a certain amount of seawater in Qinhuangdao waters, respectively, remove 100, 200, 300, 500 gasoline, kerosene into 100 mL of seawater, shake well, static This allows the sample to simulate the dispersion of oil spills in seawater.

Near infrared spectroscopy performed with samples prepared spectral acquisition, recording kerosene within the sample 8 000-12 000 cm wave number region, gasoline absorption curve shown in Figure 2.

As can be seen in FIG. 2 in a wave number region 8 300-8 500 cm, kerosene, gasoline has a distinct absorption peak, and with an oil absorption of the mixture increases gradually closer to the water sample to the peak concentration of the pure oil, calculated The peak is about 1 190 nm, and an LED having a similar characteristic peak is used as a light source of the light-emitting portion.