Method for measuring extinction coefficient of oil film on water surface based on differential thickness fluorescence spectrum

Abstract

The invention particularly relates to a difference thickness fluorescence spectrum-based water surface oil film extinction coefficient measurement method, which comprises the following steps that a laser light source irradiates a first water surface area, the first water surface area comprises an oil film with the thickness of d, a fiber optic spectrometer tests the first water surface area at a first observation angle and a second observation angle, and a first fluorescence intensity ratio is measured; the laser light source irradiates a second water surface area, the second water surface area comprises an oil film with the thickness of 2d, the optical fiber spectrometer tests the second water surface area at a first observation angle and a second observation angle respectively, and a second fluorescence intensity ratio is measured; calculating an oil film extinction coefficient corresponding to the wave band through a calculation formula of the extinction coefficient; after full-wave band data of the spectrograph are traversed, oil film extinction coefficients corresponding to all wave bands are obtained, and an oil film extinction coefficient spectrum is constructed. According to the invention, through the difference of double oil film thickness fluorescence signals at two different observation angles, under the condition that the difference thickness is set to be a multiple, the arithmetic solution of the oil film extinction coefficient can be directly obtained, and the operand is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of oil film thickness detection, and specifically relates to a method for measuring the extinction coefficient of an oil film on the water surface based on differential thickness fluorescence spectroscopy. Background Art

[0002] As a major marine pollutant, oil spills at sea can cause serious environmental pollution and economic losses. Operational oil spills from ships' illegal discharges are one of the main sources of oil spills at sea. After an oil film on the water surface is detected, the identification of the type of spilled oil is the basis for determining the source of the oil spill and identifying the responsible ship. Different types and sources of oil spill pollutants have unique extinction coefficients. Therefore, the measurement of the extinction coefficient of the oil film on the water surface can help determine the type of spilled oil and trace the source of the oil spill.

[0003] In the prior art, in a controllable laboratory environment, an ellipsometer can be used to measure the extinction coefficient of a stable thin film sample. However, this method has high requirements for the measurement environment, and the test results need to be professionally processed to obtain the extinction coefficient. The reflection spectrum based on double-beam interference can estimate the extinction coefficient of the oil film on the water surface, but this method is based on the calculation of the reflection spectrum and is easily affected by environmental factors, resulting in large measurement errors.

[0004] The present invention constructs a physical model between the laser-induced fluorescence intensity of a thin oil film on the water surface, the oil film thickness, and the observation angle based on the laser-induced fluorescence equation, and proposes a method for measuring the extinction coefficient of the oil film on the water surface based on differential thickness fluorescence spectroscopy based on this model. The laser-induced fluorescence technology uses a stable laser as the excitation light source, with high measurement accuracy. The oil film measurement based on differential thickness can obtain an accurate extinction coefficient of the oil film. Summary of the Invention

[0005] In view of the technical problems in the prior art that the method for measuring the extinction coefficient of the oil film on the water surface has high requirements for the measurement environment, is easily affected by environmental factors, and has large measurement errors, a method for measuring the extinction coefficient of the oil film on the water surface based on differential thickness fluorescence spectroscopy is provided. The present invention mainly uses the laser-induced fluorescence technology, constructs a physical model between the laser-induced fluorescence intensity, the oil film thickness, and the observation angle, and combines the differential thickness measurement method to accurately calculate the extinction coefficient of the oil film, thereby improving the measurement accuracy, reducing environmental interference, and achieving the effect of quickly and accurately identifying the type and source of the spilled oil.

[0006] The technical means adopted by the present invention are as follows:

[0007] A method for measuring the extinction coefficient of the oil film on the water surface based on differential thickness fluorescence spectroscopy, the steps including:

[0008] Step 1: Select a first water surface area, and the first water surface area includes an oil film with a thickness of d;

[0009] Step 2: Vertically irradiate the first water surface area with a laser light source to generate a first laser spot. The fiber optic spectrometer measures the first laser spot at a first observation angle and a second observation angle respectively, obtains the first fluorescence intensity corresponding to the first observation angle and the second fluorescence intensity corresponding to the second observation angle, calculates the ratio of the first fluorescence intensity to the second fluorescence intensity, and obtains the first fluorescence intensity ratio.

[0010] Step 3: Add a quantitative oil sample to the first water surface area to obtain a second water surface area, and the second water surface area includes an oil film with a thickness of 2d.

[0011] Step 4: Vertically irradiate the second water surface area with a laser light source to generate a second laser spot. The fiber optic spectrometer measures the second laser spot at a first observation angle and a second observation angle respectively, obtains the third fluorescence intensity corresponding to the first observation angle and the fourth fluorescence intensity corresponding to the second observation angle, calculates the ratio of the third fluorescence intensity to the fourth fluorescence intensity, and obtains the second fluorescence intensity ratio.

[0012] Step 5: Construct a calculation formula for the extinction coefficient of the oil film. According to the first fluorescence intensity ratio, the second fluorescence intensity ratio, the oil film thickness, the first observation angle, and the second observation angle, calculate the extinction coefficient of the oil film corresponding to the wavelength band through the calculation formula of the extinction coefficient.

[0013] Step 6: Repeat Step 5 to obtain the extinction coefficients of the oil film corresponding to all wavelength bands measured by the fiber optic spectrometer, and construct an extinction coefficient spectrum of the oil film based on the extinction coefficients of the oil film corresponding to all wavelength bands.

[0014] Further, according to the first observation angle and the second observation angle, based on Snell's law, calculate the first refraction angle corresponding to the first observation angle and the second refraction angle corresponding to the second observation angle. The calculation formula for the refraction angle is:

[0015] θ r =arcsin[(sinθ) / n]

[0016] where θ r is the refraction angle, θ is the observation angle, and n is the refractive index of the oil film.

[0017] Further, the specific calculation formula for the extinction coefficient is:

[0018]

[0019] where k EM is the extinction coefficient of the oil film, θ r1 is the first refraction angle, θ r2 is the second refraction angle, d is the thickness of the oil film in the first water surface area, ΔIF1 is the first fluorescence intensity ratio, and ΔIF2 is the second fluorescence intensity ratio.

[0020] Further, the first observation angle and the second observation angle satisfy:

[0021] |θ1 - θ2| > 30°

[0022] 0 < θ1 ≤ 60°

[0023] 0 < θ2 ≤ 60°

[0024] Wherein, θ1 is the first observation angle and θ2 is the second observation angle.

[0025] Further, the specific calculation formula of the fluorescence intensity is:

[0026]

[0027] Wherein, I F is the total fluorescence intensity emitted by the oil film with a thickness of d measured by the spectrometer, σ F is the fluorescence cross-section, ρ is the molar concentration of oil molecules, S is the laser spot area, I0 is the light intensity emitted by the laser, k sum is the total extinction coefficient under the influence of the observation angle, d is the thickness of the oil film,

[0028] The specific calculation formula of the total extinction coefficient under the influence of the observation angle is:

[0029] k sum = k EX + secθ r k EM

[0030] Wherein, k sum is the total extinction coefficient under the influence of the observation angle, k EX is the extinction coefficient of the oil film at the excitation wavelength, k EM is the extinction coefficient of the oil film at the fluorescence emission wavelength, θ r is the refraction angle.

[0031] Further, the laser light source is an ultraviolet laser, and the ultraviolet laser emits light with a wavelength of 355 nm, a pulse width of 8 mm, and a repetition frequency of 50 Hz.

[0032] Compared with the prior art, the present invention has the following advantages:

[0033] 1. By combining with the differential measurement of the fluorescence signals of the double oil film thickness, the present invention eliminates the influence of related medium parameters such as the fluorescence cross-section, the molar concentration of oil molecules, the laser cross-sectional area, and the excitation light intensity, and improves the measurement accuracy and reliability.

[0034] 2. By directly obtaining the arithmetic solution of the oil film extinction coefficient under the condition of setting the differential thickness as a multiple, the present invention achieves the technical effects of low computational complexity and high computational efficiency, significantly improving the operability and practicality of the method.

[0035] 3. By combining with the laser-induced fluorescence technique, the present invention realizes the high-precision and rapid measurement of the extinction coefficient of the oil film on the water surface, providing reliable technical support for the identification of oil spill types and the tracing of oil spill sources.

[0036] Based on the above reasons, the present invention can be widely promoted in the fields such as oil film thickness detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0038] Figure 1 It is a schematic diagram of the mathematical model of the laser-induced fluorescence intensity of the oil film on the water surface of the present invention.

[0039] Figure 2 It is a schematic diagram of the comparison between the extinction coefficient of the oil film measured by the differential thickness fluorescence spectrum and the true value in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] In order to enable those skilled in the art to better understand the solution of the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0041] It should be noted that the terms "first", "second", etc. in the description, claims and above-mentioned drawings of the present invention are used to distinguish similar objects, and do not necessarily have to be used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present invention described here can be implemented in an order other than those illustrated or described here. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0042] The present invention provides a method for measuring the extinction coefficient of an oil film on the water surface based on differential thickness fluorescence spectroscopy.

[0043] A method for measuring the extinction coefficient of an oil film on the water surface based on differential thickness fluorescence spectroscopy, the steps including:

[0044] Step 1: Select a first water surface area, the first water surface area including an oil film with a thickness of d;

[0045] Step 2: Vertically irradiate the first water surface area with a laser light source to generate a first laser spot. The fiber optic spectrometer tests the first laser spot at a first observation angle and a second observation angle respectively, obtains a first fluorescence intensity corresponding to the first observation angle and a second fluorescence intensity corresponding to the second observation angle, and calculates the ratio of the first fluorescence intensity to the second fluorescence intensity to obtain a first fluorescence intensity ratio;

[0046] Step 3: Add a quantitative oil sample to the first water surface area to obtain a second water surface area, the second water surface area including an oil film with a thickness of 2d;

[0047] Step 4: Vertically irradiate the second water surface area with a laser light source to generate a second laser spot. The fiber optic spectrometer tests the second laser spot at a first observation angle and a second observation angle respectively, obtains a third fluorescence intensity corresponding to the first observation angle and a fourth fluorescence intensity corresponding to the second observation angle, and calculates the ratio of the third fluorescence intensity to the fourth fluorescence intensity to obtain a second fluorescence intensity ratio;

[0048] Step 5: Construct a calculation formula for the extinction coefficient of the oil film. According to the first fluorescence intensity ratio, the second fluorescence intensity ratio, the oil film thickness, the first observation angle and the second observation angle, calculate the extinction coefficient of the oil film corresponding to the wavelength band through the calculation formula of the extinction coefficient;

[0049] Step 6: Loop Step 5 to obtain the extinction coefficients of the oil film corresponding to all wavelength bands measured by the fiber optic spectrometer, and construct an extinction coefficient spectrum of the oil film based on the extinction coefficients of the oil film corresponding to all wavelength bands.

[0050] Furthermore, based on the first observation angle and the second observation angle, and according to the refraction theorem, the first refraction angle corresponding to the first observation angle and the second refraction angle corresponding to the second observation angle are calculated. The calculation formula for the refraction angle is:

[0051] θ r = arcsin[(sinθ) / n]

[0052] where θ r is the refraction angle, θ is the observation angle, and n is the refractive index of the oil film.

[0053] Furthermore, the calculation formula for the extinction coefficient is specifically:

[0054]

[0055] where k EM is the extinction coefficient of the oil film, θ r1 is the first refraction angle, θ r2 is the second refraction angle, d is the thickness of the oil film in the first water surface area, ΔIF1 is the first fluorescence intensity ratio, and ΔIF2 is the second fluorescence intensity ratio.

[0056] Furthermore, the first observation angle and the second observation angle satisfy:

[0057] |θ1 - θ2| > 30°

[0058] 0 < θ1 ≤ 60°

[0059] 0 < θ2 ≤ 60°

[0060] where θ1 is the first observation angle and θ2 is the second observation angle.

[0061] Furthermore, the calculation formula for the fluorescence intensity is specifically:

[0062]

[0063] where I F is the total fluorescence intensity emitted by the oil film with a thickness of d measured by the spectrometer, σ F is the fluorescence cross-section, ρ is the molar concentration of oil molecules, S is the laser spot area, I0 is the light intensity emitted by the laser, k sum is the total extinction coefficient under the influence of the observation angle, d is the thickness of the oil film,

[0064] The calculation formula for the total extinction coefficient under the influence of the observation angle is specifically:

[0065] k sum = k EX + secθ r k EM

[0066] Among them, k sum is the total extinction coefficient under the influence of the observation angle, and k EX is the extinction coefficient of the oil film at the excitation wavelength, and k EM is the extinction coefficient of the oil film at the fluorescence emission wavelength, and θ r is the refraction angle.

[0067] Furthermore, the laser light source is an ultraviolet laser with an emission wavelength of 355 nm, a pulse width of 8 mm, and a repetition frequency of 50 Hz.

[0068] The derivation method of the physical model for predicting the extinction coefficient of the oil film is as follows:

[0069] The water surface oil molecules containing conjugated π-bond structures can undergo energy level transitions under the irradiation of ultraviolet lasers in the ultraviolet band. After returning to the ground state, the energy of the high-energy level transitions escapes in the form of fluorescence. The escaped fluorescence energy is proportional to the excitation light intensity and the number of excited oil molecules, and its weight can be defined as the fluorescence cross-section σ F .

[0070] For Figure 1 the water surface oil film with a thickness of d as shown, the extremely thin oil layer dz at a depth z in the oil film is subjected to the generated fluorescence intensity dI EM (z), and its calculation formula is:

[0071] dI EM (z) = σ F I'(z)ρSdz

[0072] Among them, ρ is the molar concentration of oil molecules, S is the laser cross-sectional area, I'(z) is the excitation light intensity received by the extremely thin oil layer dz at a depth z in the oil film, dz is the thickness of the extremely thin oil layer at a depth z in the oil film, dI EM (z) is the fluorescence intensity generated by the extremely thin oil layer dz at a depth z in the oil film, and σ F is the fluorescence cross-section.

[0073] Since the laser and the spectrometer are relatively close to the oil film, the attenuation of the laser and fluorescence in the atmosphere can be ignored. According to the Lambert-Beer law, the excitation light intensity I′(z) at a depth z in the oil film is:

[0074]

[0075] Among them, I0 is the light intensity emitted by the laser, and k EX is the extinction coefficient of the oil film at the excitation wavelength, I'(z) is the excitation light intensity received by the extremely thin oil layer dz at a depth z in the oil film, and z is the depth in the oil film.

[0076] Combining the intensity I′(z) of the excitation light at a depth z in the oil film and the fluorescence intensity dI generated by the extremely thin oil layer dz at a depth z in the oil filmEM From the calculation formula of dI(z), the fluorescence intensity dI generated by the extremely thin oil layer dz at depth z can be obtained. EM Calculation formula of dI(z):

[0077]

[0078] where σ F is the fluorescence cross-section, ρ is the molar concentration of oil molecules, S is the laser spot area, k EX is the extinction coefficient of the oil film at the excitation wavelength, z is the depth in the oil film, I0 is the light intensity emitted by the laser, and dI EM (z) represents the fluorescence intensity generated by the extremely thin oil layer dz at depth z in the oil film.

[0079] Since the emitted fluorescence is isotropic, the fluorescence intensity dI EM (z) escaping from the extremely thin oil layer dz is attenuated again by the oil film along the observation direction of the fiber optic spectrometer. From Figure 1 the geometric relationship, the optical path of the fluorescence in the oil film is zsecθ r . Where θ r is the refraction angle of the fluorescence when the observation angle is θ, which can be calculated according to the refraction law. Therefore, the fluorescence intensity dI F (z) finally received by the spectrometer can be expressed as:

[0080]

[0081] where dI F (z) is the fluorescence intensity generated by the extremely thin oil layer dz at depth z received by the spectrometer, k EM is the extinction coefficient of the oil film at the fluorescence emission wavelength, z is the depth in the oil film, k EX is the extinction coefficient of the oil film at the fluorescence emission wavelength, θ r is the refraction angle, dI EM (z) represents the fluorescence intensity generated by the extremely thin oil layer dz at depth z in the oil film, σ F is the fluorescence cross-section, and ρ is the molar concentration of oil molecules.

[0082] Define the extinction coefficient affected by the observation angle and k sum as:

[0083] k sum = k EX + secθ r k EM

[0084] where k sum is the extinction coefficient sum of the oil film on water, k EX is the extinction coefficient of the oil film at the excitation wavelength, k EMis the extinction coefficient of the oil film at the fluorescence emission wavelength, and θ r is the refraction angle.

[0085] Then the fluorescence intensity dI F (z) received by the spectrometer can be simplified as:

[0086]

[0087] where dI F (z) is the fluorescence intensity generated by the extremely thin oil layer dz at depth z received by the spectrometer, σ F is the fluorescence cross-section, ρ is the molar concentration of oil molecules, S is the laser spot area, k EX is the extinction coefficient of the oil film at the excitation wavelength, z is the depth in the oil film, I0 is the light intensity emitted by the laser, k sum is the sum of the extinction coefficients of the oil film on the water surface.

[0088] The fluorescence intensity I emitted by the oil film with thickness d measured by the spectrometer F is the definite integral of dI F (z) from 0 to d. The calculation formula for the total fluorescence intensity emitted by the oil film with thickness d measured by the spectrometer is as follows:

[0089]

[0090] where I F is the total fluorescence intensity of the oil film with thickness d measured by the spectrometer, σ F is the fluorescence cross-section, ρ is the molar concentration of oil molecules, S is the laser spot area, I0 is the light intensity emitted by the laser, k sum is the sum of the extinction coefficients of the oil film on the water surface, and d is the oil film thickness.

[0091] Using the same laser and spectrometer to measure two oil films with thicknesses d1 and d2 respectively, the fluorescence intensities I F1 and I F2 can be obtained, and the calculation formulas are as follows:

[0092]

[0093] where I F1 is the total fluorescence intensity of the first oil film thickness, I F2 is the total fluorescence intensity of the second oil film thickness, σ F is the fluorescence cross-section, ρ is the molar concentration of oil molecules, S is the laser spot area, I0 is the light intensity emitted by the laser, k sum is the sum of the extinction coefficients of the oil film on the water surface, d1 is the first oil film thickness, and d2 is the second oil film thickness.

[0094] Define ΔIF is the ratio of the fluorescence intensities of the oil films at two thicknesses, i.e., ΔI F = I F1 / I F2 , and the ratio calculation formula is as follows:

[0095]

[0096] where ΔI F is calculated by measuring the fluorescence intensities I F1 and I F2 of the oil films at two thicknesses, k sum is the sum of the extinction coefficients of the oil film on water, d1 is the thickness of the first oil film, d2 is the thickness of the second oil film, and the thicknesses d1 and d2 are known set values. Therefore, there is only one unknown, the sum of the extinction coefficients of the oil film on water k sum , which can be solved by computer iteration.

[0097] If you want to obtain the arithmetic solution of the sum of the extinction coefficients k sum , you can set the thickness d2 to be twice that of d1, i.e., d2 = 2d1 = 2d. At this time, the ratio of the fluorescence intensities of the oil films at two thicknesses is specifically:

[0098]

[0099] where k sum is the sum of the extinction coefficients of the oil film on water, ΔI F is the ratio of the fluorescence intensities of the oil films at two thicknesses, and d is the thickness of the first oil film.

[0100] According to the calculation formula of the ratio of the fluorescence intensities of the oil films at two thicknesses, the sum of the extinction coefficients k sum of the oil film on water can be obtained as:

[0101]

[0102] where k sum is the sum of the extinction coefficients of the oil film on water, ΔI F is the ratio of the fluorescence intensities of the oil films at two thicknesses, and d is the thickness of the first oil film.

[0103] In order to further obtain the extinction coefficients k EX and k EM at the excitation wavelength and the fluorescence emission wavelength, it is necessary to measure the ratios ΔI r1 and ΔI r2 of the fluorescence intensities of the oil films at two thicknesses respectively at the refraction angles θ F1 and θ F2 corresponding to two different observation angles. By combining the two calculation formulas of the sum of the extinction coefficients k sum of the oil film on water, the following system of equations can be obtained:

[0104]

[0105] Among them, k EM is the extinction coefficient of the oil film at the fluorescence emission wavelength, and k EX is the extinction coefficient of the oil film at the fluorescence emission wavelength, θ r1 is the first refraction angle, and θ r2 is the second refraction angle. d is the thickness of the oil film in the first water surface area, ΔIF1 is the first fluorescence intensity ratio, and ΔIF2 is the second fluorescence intensity ratio.

[0106] By subtracting the equations, the extinction coefficient k EX at the excitation wavelength can be further eliminated, and then the extinction coefficient at the fluorescence emission wavelength can be obtained. The calculation formula for the extinction coefficient at the fluorescence emission wavelength is as follows:

[0107]

[0108] Among them, k EM is the extinction coefficient of the oil film, θ r1 is the first refraction angle, θ r2 is the second refraction angle. d is the thickness of the oil film in the first water surface area, ΔIF1 is the first fluorescence intensity ratio, and ΔIF2 is the second fluorescence intensity ratio.

[0109] Example

[0110] 0.05 ml and 0.1 ml of oil samples were respectively dropped into a glass bottle of 40 mm × 25 mm, and 4 ml of water was added. After standing for 3 hours, uniform oil films with thicknesses of 40 μm and 80 μm were formed respectively. During the standing process, the bottle was capped with a bottle cap with a frosted joint to prevent the evaporation of the oil sample.

[0111] Considering that the excitation wavelength of the oil film is in the ultraviolet band, a UV laser with a wavelength of 355 nm was used as the excitation light source, and a portable ground object spectrometer ASD FieldSpec3 was used to measure the fluorescence spectrum of the oil film, and the test optical path shown in Figure 1 was constructed. The experiment was carried out in a dark room environment to eliminate the interference of ambient light on the fluorescence simulation of the oil film on the water surface. The experimental conditions of all samples were kept the same. The fluorescence intensity differences ΔI F1 and ΔI F2 of the two oil films with different thicknesses were measured at two observation angles θ1 and θ2 respectively.

[0112] By substituting the two observation angles θ1 and θ2, and the measured fluorescence intensity differences ΔI F1 and ΔI F2 and the oil film thickness d into the calculation formula for the extinction coefficient at the fluorescence emission wavelength, the extinction coefficient spectra of the oil film in different bands can be measured as shown in Figure 2As shown by the orange curve. Comparing the extinction coefficient measured in the present invention with the true value ( Figure 2 the blue curve in), it can be found that the extinction coefficient measured in the present invention is basically consistent with the true value, indicating the feasibility of measuring the extinction coefficient of the oil film in the present invention.

[0113] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for measuring the extinction coefficient of oil film on water surface based on differential thickness fluorescence spectroscopy, characterized in that the steps include: Step 1: Select a first water surface area, wherein the first water surface area includes an oil film with a thickness of d; Step 2, irradiating the first water surface area vertically with a laser light source to generate a first laser spot, and testing the first laser spot with a fiber optic spectrometer at a first observation angle and a second observation angle respectively to obtain a first fluorescence intensity corresponding to the first observation angle and a second fluorescence intensity corresponding to the second observation angle, and calculating a ratio of the first fluorescence intensity to the second fluorescence intensity to obtain a first fluorescence intensity ratio; Step 3, adding a quantitative oil sample to the first water surface area to obtain a second water surface area, wherein the second water surface area includes an oil film with a thickness of 2d; Step 4, irradiating the second water surface area with a laser light source vertically to generate a second laser spot, and testing the second laser spot with a fiber optic spectrometer at a first observation angle and a second observation angle respectively to obtain a third fluorescence intensity corresponding to the first observation angle and a fourth fluorescence intensity corresponding to the second observation angle, and calculating a ratio of the third fluorescence intensity to the fourth fluorescence intensity to obtain a second fluorescence intensity ratio; Step 5, constructing a calculation formula for the oil film extinction coefficient, and calculating the oil film extinction coefficient corresponding to the band through the calculation formula of the extinction coefficient according to the first fluorescence intensity ratio, the second fluorescence intensity ratio, the oil film thickness, the first observation angle and the second observation angle; Step 6, looping step 5, obtaining the oil film extinction coefficient corresponding to all the wavebands measured by the fiber optic spectrometer, and constructing the extinction coefficient spectrum of the oil film based on the oil film extinction coefficient corresponding to all the wavebands.

2. The method for measuring the extinction coefficient of oil film on water surface based on differential thickness fluorescence spectroscopy according to claim 1 is characterized in that: According to the first observation angle and the second observation angle, based on the refraction theorem, the first refraction angle corresponding to the first observation angle and the second refraction angle corresponding to the second observation angle are calculated. The calculation formula of the refraction angle is: i r =arcsin[(sinθ) / n] Among them, θ r is the refraction angle, θ is the observation angle, and n is the refractive index of the oil film.

3. The method for measuring the extinction coefficient of oil film on water surface based on differential thickness fluorescence spectroscopy according to claim 1 or 2, characterized in that: The calculation formula of the extinction coefficient is specifically: Among them, k EM is the oil film extinction coefficient, θ r1 is the first refraction angle, θ r2 is the second refraction angle, d is the thickness of the oil film in the first water surface area, ΔIF1 is the first fluorescence intensity ratio, and ΔIF2 is the second fluorescence intensity ratio.

4. The method for measuring the extinction coefficient of oil film on water surface based on differential thickness fluorescence spectroscopy according to claim 1 is characterized in that: The first observation angle and the second observation angle satisfy: |θ1-θ2|>30° 0<θ1≤60° 0<θ2≤60° Wherein, θ1 is the first observation angle, and θ2 is the second observation angle.

5. The method for measuring the extinction coefficient of oil film on water surface based on differential thickness fluorescence spectroscopy according to claim 1, characterized in that: The calculation formula of the fluorescence intensity is specifically: Among them, I F is the total fluorescence intensity of the oil film with a thickness of d measured by the spectrometer, σF is the fluorescence cross section, ρ is the molar concentration of oil molecules, S is the laser spot area, I0 is the light intensity emitted by the laser, and k sum is the total extinction coefficient under the influence of observation angle, d is the oil film thickness, The calculation formula of the total extinction coefficient under the influence of the observation angle is specifically: k sum =k EX +secθ r k EM Among them, k sum is the total extinction coefficient under the influence of observation angle, k EX is the extinction coefficient of the oil film at the excitation wavelength, k EM is the extinction coefficient of the oil film at the fluorescence emission wavelength, θ r is the refraction angle.

6. The method for measuring the extinction coefficient of oil film on water surface based on differential thickness fluorescence spectroscopy according to claim 1, characterized in that: The laser light source is emitted by an ultraviolet laser, the wavelength of the ultraviolet laser is 355nm, the pulse width is 8mm, and the repetition frequency is 50Hz.

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