Method for measuring attenuation coefficient of water body

Abstract

The invention discloses a method for measuring a water body attenuation coefficient, which realizes high-precision and parameter-adjustable water body attenuation coefficient measurement through coordination work of a pair of underwater optical communication machines, and comprises the following steps of: performing air calibration and pure water calibration by the optical communication machines to obtain emission reference light intensity; the underwater optical communication machine is used for building a ranging data frame and measuring the transmission time difference to complete ranging; processing full-waveform data of the communication signal passing through the underwater channel to obtain light intensity after water attenuation; and integrating the communication distance, the emission reference light intensity and the attenuated receiving light intensity, and calculating and processing to obtain a water body attenuation coefficient. According to the method, the water attenuation coefficient is obtained by using the communication signal of the underwater optical communication machine, and the method is simple to operate, easy to deploy, wide in application range and suitable for real-time measurement.

Description

Technical Field

[0001] The invention relates to the field of water body attenuation coefficient measurement, in particular to a method for measuring the water body attenuation coefficient. Background Art

[0002] The measurement of optical properties of ocean water is of great significance in many aspects, especially in the fields of oceanography, environmental science, water quality monitoring and underwater communication. The optical properties of ocean water are mainly divided into intrinsic optical parameters (IOP) and apparent optical parameters (AOP). In the IOP of ocean water, the water attenuation coefficient C reflects the absorption and scattering characteristics of water to light of different wavelengths, which directly affects the propagation depth of light in water. The water attenuation coefficient is generally measured by professional equipment such as spectral absorption and attenuation sensor (ac-s).

[0003] Underwater wireless optical communication is an important way to achieve underwater high-speed communication due to its extremely high communication bandwidth and communication rate. However, due to the influence of the inherent optical properties of the ocean, ocean turbulence, skin effect, etc., water has a strong attenuation effect on light, and the transmission distance of light in seawater is limited. As the transmission distance increases, the waveform of the received optical signal will be broadened in the time domain and space domain, which leads to an increase in the communication bit error rate and even failure to communicate. The water attenuation coefficient is an important factor affecting the transmission distance of light in water. When underwater optical communicators communicate in water bodies with different water attenuation coefficients, they need to adjust the communication rate according to the water attenuation coefficient of the water body to achieve the best communication effect. The water attenuation coefficient is an important basis for underwater optical communicators to set their working parameters. It determines the maximum communication distance of underwater optical communicators in water bodies and is also used to evaluate their communication performance. However, current underwater optical communication devices do not have the function of measuring the water attenuation coefficient. They need to use additional professional equipment (such as AC-S) to measure the water attenuation coefficient. These devices are expensive, the use procedures are complicated and cumbersome, they cannot measure in real time, and they are not convenient to use in some special areas (such as the deep sea).

[0004] Therefore, there is an urgent need for a method based on underwater optical communication equipment that has a wide range of applications, is easy to operate, and can monitor the water attenuation coefficient in real time. Summary of the invention

[0005] In view of the defects of the prior art, the purpose of the present invention is to provide a method for measuring the water attenuation coefficient, through a pair of underwater optical communication devices (A and B) working together to achieve high-precision, adjustable parameter water attenuation coefficient measurement.

[0006] The technical solution of the present invention is as follows:

[0007] The present invention provides a method for measuring water body attenuation coefficient based on communication signals of an underwater optical communication device, which is characterized in that it includes:

[0008] The measurement process is completed through the cooperation of a pair of underwater optical communication machines (hereinafter referred to as A machine and B machine).

[0009] Step S1: The optical communication device performs air calibration and pure water calibration to obtain the emission reference light intensity I c ;

[0010] Step S2: Use the underwater optical communication device to construct a ranging data frame by measuring the transmission time difference t ABA Complete the communication distance S measurement;

[0011] Step S3: Process the full waveform data of the communication signal after passing through the underwater channel to obtain the received light intensity I after water attenuation out ;

[0012] Step S4: Comprehensive communication distance S, emission reference light intensity I c , received light intensity after attenuation I out Perform data processing, obtain the water body attenuation coefficient C and make corrections.

[0013] Furthermore, the air calibration is mainly used for instrument baseline calibration and instrument self-checking, and the pure water calibration is mainly used to eliminate the influence of water molecules themselves and correct relative measurement. The calibration of step S1 includes the following sub-steps:

[0014] S1.1 Perform air calibration, place machine A and machine B in the air of the darkroom, start them separately and check whether the optical path is clean and dust-free to ensure that the communication machine works normally. After the optical communication machine is stable, record the system noise I n , air calibration is completed;

[0015] S1.2 Perform pure water calibration. Place the A and B devices in a water tank filled with pure water in a dark room and align them. Record the distance between them. This distance is called the calibration distance L.

[0016] S1.3 Set the laser communication intensity I of machine B in , machine B sets the laser communication light intensity I in Send the ranging data frame, wait for the light intensity to stabilize and the water body to stabilize, record the measured light intensity I1 at the A machine, and use the calculation formula I c =I1-I n Get the emission reference light intensity I c ;

[0017] S1.4 Change the laser communication intensity I of machine B in Repeat step S1.3 to measure different Iin The corresponding emission reference light intensity I c ;

[0018] Further, the ranging data frame is composed of the laser communication light intensity I in The communication data composed of the communication content is RS encoded and scrambled and inserted into the frame synchronization sequence. The ranging data frame includes the synchronization sequence, the payload data bit and the RS check code;

[0019] Further, the communication distance S is the geometric length of the optical path of the laser in the underwater channel under the premise that the underwater optical communication machines A and B are aligned, and its value reflects the relative distance between the A machine and the B machine. The step S2 of calculating the communication distance S includes the following sub-steps:

[0020] S2.1 Set the laser communication intensity I of machine A in , machine A sets the laser communication light intensity I in The ranging data frame is sent and the timing is started, and it is received by the B machine after passing through the underwater channel;

[0021] S2.2 Machine B decodes the ranging data frame and obtains the laser communication light intensity I of machine A. in ;

[0022] S2.3 Machine B follows the laser communication intensity I of machine A in Send the ranging data frame to machine A, which receives it after passing through the underwater channel and immediately stops timing to obtain the time difference;

[0023] S2.4 Machine A judges the received full waveform data. If the full waveform data is saturated, the laser communication light intensity I is reduced. in ,If the full waveform data is too weak, increase the laser communication light intensity I in , and repeat steps S2.1-S2.3 to obtain the time difference when the full waveform data intensity is appropriate as the transmission time difference t ABA , and the full waveform data received by machine A at this time is used to receive the light intensity I out measurement.

[0024] S2.5 uses the protection time slot t p , system inherent delay t c , transmission time difference t ABA The communication distance S is calculated in machine A, and the calculation formula is: Where c is the speed of light in vacuum, n 水 is the current water refractive index.

[0025] Furthermore, the protection time slot t in step S2.5 p and the system inherent delay t c are all known quantities, the protection time slot t pis the protection time slot of half-duplex communication, sets the communication parameters, and the inherent delay of the system is t c Obtained from the calibration of the equipment when it leaves the factory;

[0026] Furthermore, the full waveform data is the waveform shape of the ranging data frame after passing through the underwater channel with the laser as the carrier, and the physical meaning of the waveform is the intensity of the received wave signal that changes with time;

[0027] Furthermore, the received light intensity I after water attenuation out The light intensity I is calculated using the full waveform data in step S2.4. out The calculation consists of the following sub-steps:

[0028] S3.1 performs waveform preprocessing on the full waveform data in step S2.4, and intercepts the received waveform I with N data bits "1";

[0029] S3.2 Calculate the average value of the waveform intensity value as the received light intensity I out , the calculation formula is

[0030] Further, the calculation and correction of the water body attenuation coefficient C in step S4 includes the following sub-steps:

[0031] S4.1 According to the laser communication light intensity I in , find the corresponding emission reference light intensity I in step S1 c ;

[0032] S4.2 According to the laser emission angle θ, the diameter d of the receiving surface of the communication machine, the communication distance S in step S2, the calibration distance L, and the emission reference light intensity I c Calculate the corrected reference light intensity I0, the calculation formula is:

[0033] S4.3 Use the communication distance S in step S2, the reference light intensity I0, and the received light intensity I in step S3 out , calculate the water body attenuation coefficient C, the calculation formula is:

[0034] S4.4 performs data processing and corrects the calculated water body attenuation coefficient C, such as temperature correction and humidity correction;

[0035] Furthermore, the laser communication light intensity I in The communication distance S and the laser communication intensity I can be adjusted when calculating the water attenuation coefficient. in and communication distance S to obtain a more accurate water attenuation coefficient.

[0036] Compared with the prior art, the advantages of the present invention are:

[0037] 1. When the present invention performs underwater wireless optical communication, the communication distance S and the water attenuation coefficient C can be measured during the communication process without relying on additional equipment, which makes the measurement simple and the entire system is also simplified;

[0038] 2. The present invention can perform measurements during underwater wireless optical communication, and has high real-time performance;

[0039] 3. The measuring platform of the present invention is an underwater optical communication device, which can be installed on an underwater movable platform such as an AUV, and has convenient deployment, simple operation, flexible measurement and wide application range;

[0040] 4. When the present invention is measuring, the communication power is adjustable, the distance between the two communication devices is adjustable, and the measurement accuracy can be improved by using different powers and different distances;

[0041] 5. Compared with the traditional AC-S machine, the present invention is easier to operate and can make up for the defect that the traditional AC-S machine cannot measure in special fields such as the deep sea, and has a wider range of applications.

[0042] In order to make the above features and advantages of the present invention more obvious and understandable, the present invention is further described below in conjunction with examples and drawings, but this should not limit the scope of protection of the present invention. Additional features and advantages of the present invention will be partially described in the following description, and these features and advantages will be partially obvious from the description or can be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a flow chart of the method for measuring the water body attenuation coefficient of the present invention.

[0044] Figure 2 It is a schematic diagram of pure water calibration in the method for measuring the water attenuation coefficient of the present invention.

[0045] Figure 3 It is a schematic diagram of the distance measurement timing in the method for measuring the water body attenuation coefficient of the present invention.

[0046] Figure 4 It is a schematic diagram of reference light intensity correction in the method for measuring water body attenuation coefficient of the present invention. DETAILED DESCRIPTION

[0047] The following describes the implementation methods of the present invention by means of specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification, and can also implement or apply the present invention by means of other different specific embodiments.

[0048] Please read first Figure 1 , Figure 1This is a flow chart of the method for measuring water attenuation coefficient of the present invention. The method realizes high-precision and adjustable parameter water attenuation coefficient measurement through the cooperation of a pair of underwater optical communication devices (A and B). The specific implementation steps are as follows:

[0049] Step S1: Monitor equipment and calibrate:

[0050] S1.1 Air calibration, used for instrument baseline calibration and instrument self-test:

[0051] Place the A and B cameras in a dark room to ensure that there is no interference from external light sources.

[0052] Start and inspect the cleanliness of the optical path of each communication machine and the working status of components such as light source and detector separately.

[0053] After the communication machine is stable, record the system noise I n , complete the air calibration.

[0054] S1.2 Pure water calibration is used to eliminate the influence of water molecules themselves and correct relative measurements:

[0055] Move the A and B machines to a darkroom tank filled with pure water. Figure 2 As shown, ensure that the two are aligned and record the calibration distance L.

[0056] Set the laser communication intensity of machine B to I in , and sends a distance measurement data frame. The distance measurement data frame is composed of the laser communication light intensity I in The communication data composed of the communication content is formed by RS encoding, scrambling processing and inserting a frame synchronization sequence. The ranging data frame includes a synchronization sequence, payload data bits and an RS check code.

[0057] After the light intensity and water body are stable, record the measured light intensity I1 received by machine A and calculate the emitted reference light intensity I c , the formula is as follows:

[0058] I c =I1-I n ;

[0059] Repeat the above steps to change the laser communication light intensity I of machine B. in , measure and record different laser communication light intensities I in The emission reference light intensity I c ;

[0060] The calibration process is carried out in a dark room to reduce the impact of ambient light and improve accuracy.

[0061] Step S2: Measurement of communication distance S

[0062] S2.1 Initial ranging preparation:

[0063] Deploy the calibrated A and B machines onto the underwater platform to ensure that they are aligned;

[0064] Set the laser communication intensity of machine A to I in , prepare to send ranging data frame.

[0065] S2.2 Two-way ranging:

[0066] Machine A sets the laser communication light intensity I in Send the ranging data frame and start timing. The ranging data frame is received by machine B after passing through the underwater channel.

[0067] Machine B decodes the data frame and obtains the laser communication light intensity I of machine A. in , and accordingly sends the response ranging data frame to machine A;

[0068] After receiving the response ranging data, machine A immediately stops timing and records the transmission time difference t ABA ;

[0069] S2.3 Light intensity adjustment and data optimization:

[0070] Machine A adjusts the laser communication light intensity I according to the received full waveform data in :If the full waveform data is saturated, reduce the laser communication light intensity I in ,If the full waveform data is too weak, increase the laser communication light intensity I in ;

[0071] Repeat steps S2.2-S2.3 until full waveform data of appropriate intensity is obtained and used as the final transmission time difference t ABA ;

[0072] S2.4 Communication distance calculation:

[0073] Using the transmission time difference t ABA , protection time slot t p , system inherent delay t c , the speed of light in vacuum c and the current refractive index of water n 水 , calculate the communication distance S, the formula is as follows:

[0074]

[0075] Where, the protection time slot t p is the protection time slot of half-duplex communication, sets the communication parameters, and the inherent delay of the system is t c It is obtained by calibration when the equipment is shipped out.

[0076] During actual operation, the communication distance S can be measured by pseudo-random code ranging, phase ranging and other methods, and is not limited to the ranging method mentioned in the present invention. The measurement of the communication distance S is a prerequisite for calculating the water attenuation coefficient, and the communication distance S is finally calculated in machine A.

[0077] Step S3: Received light intensity processing

[0078] S3.1 waveform preprocessing:

[0079] The full waveform data in step S2.3 is subjected to waveform preprocessing to remove noise information in the full waveform data, and a received waveform I with N data bits "1" is intercepted.

[0080] S3.2: Calculation of received light intensity:

[0081] Calculate the average value of the pre-processed waveform intensity value as the received light intensity I out , the formula is as follows:

[0082]

[0083] Among them, the full waveform data is the waveform shape of the ranging data frame after passing through the underwater channel with laser as the carrier. It is converted by the detector into an electrical signal and then converted by the high-speed acquisition processing unit. The physical meaning of the waveform is the intensity of the received wave signal that changes with time. out After water attenuation.

[0084] S4. Calculation and correction of water attenuation coefficient

[0085] S4.1 According to the laser communication light intensity I in In step S1, the corresponding emission reference light intensity I is searched in the calibration data c ;

[0086] S4.2 As Figure 4 As shown, according to the laser emission angle θ, the diameter of the communication machine receiving surface d, the communication distance S, the calibration distance L and the emission reference light intensity I c , calculate the corrected reference light intensity I0, the formula is as follows:

[0087]

[0088] S4.3 According to the communication distance S, the reference light intensity I0 and the received light intensity I out , calculate the water body attenuation coefficient C, the formula is as follows:

[0089]

[0090] S4.4 The water body attenuation coefficient C is corrected for environmental factors such as temperature and humidity to improve the measurement accuracy.

[0091] This embodiment achieves high-precision measurement of the water attenuation coefficient through a sophisticated calibration process, two-way ranging technology and data optimization processing. At the same time, by adjusting the adjustable parameters (such as the laser communication light intensity I in and communication distance S) to obtain a more accurate water attenuation coefficient.

[0092] It should be noted that in the present invention, the water body attenuation coefficient can be measured only after the communication distance is measured.

[0093] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for measuring water attenuation coefficient, characterized in that: The work is coordinated by a pair of underwater optical communication machines (hereinafter referred to as A and B), including the following steps: S1: Monitor equipment and calibrate: Place the A and B devices in the dark room air, start each device separately and test the cleanliness of the optical path and the working status of the light source and detector. After the devices are stable, record the system noise and complete the air calibration. Move the A and B machines to a darkroom tank filled with pure water, ensure that they are aligned, record the calibration distance, set the laser communication light intensity of the B machine and send the ranging data frame. After the light intensity and the water body are stable, record the measured light intensity received by the A machine and calculate the emission reference light intensity. Repeat the above steps, by changing the laser communication light intensity of the B machine, measure and record the emission reference light intensity I under different laser communication light intensities. c ; S2: Use underwater optical communication equipment to construct ranging data frames by measuring the transmission time difference t ABA Complete the communication distance S measurement: S3: Process the full waveform data of the communication signal after passing through the underwater channel to obtain the received light intensity I after water attenuation out ; S4: Comprehensive communication distance S, emission reference light intensity I c and the attenuated received light intensity I out Process the data, calculate the water attenuation coefficient C and make corrections.

2. The method for measuring the water attenuation coefficient according to claim 1, characterized in that: The step S2 specifically includes: Deploy the calibrated A and B machines onto the underwater platform to ensure that they are aligned; Set the laser communication light intensity of machine A. Machine A sends a ranging data frame and starts timing. Machine B receives and decodes the data frame and sends a response ranging data frame to machine A. Machine A stops timing after receiving the response ranging data and records the transmission time difference. Machine A adjusts the laser communication light intensity according to the received full waveform data, repeats the two-way distance measurement and light intensity adjustment until full waveform data of appropriate intensity is obtained, and uses the transmission time difference at this time for the final communication distance calculation; The communication distance is calculated using the transmission time difference, protection time slot, system inherent delay, speed of light in vacuum and current refractive index of water.

3. The method for measuring the water attenuation coefficient according to claim 2, characterized in that: The ranging data frame is composed of the laser communication light intensity I in The communication data formed by the communication content is formed by RS encoding, scrambling processing and insertion of a frame synchronization sequence, including a synchronization sequence, payload data bits and an RS check code.

4. The method for measuring the water attenuation coefficient according to claim 1, characterized in that: The received light intensity I in step S3 out The calculations include: S3.1 pre-processes the full waveform data and intercepts the received waveform I with N data bits "1"; S3.2 Calculate the average value of the waveform intensity value as the received light intensity I out .

5. The method for measuring the water attenuation coefficient according to claim 1, characterized in that: The calculation and correction of the water body attenuation coefficient C in step S4 includes: S4.1 According to the laser communication light intensity I in Find the corresponding emission reference light intensity I c ; S4.2 According to the laser emission angle θ, the diameter of the receiving surface of the communication machine d, the communication distance S, the calibration distance L and the emission reference light intensity I c Calculate the corrected reference light intensity I0; S4.3 Using the communication distance S, reference light intensity I0 and received light intensity I out Calculate the water attenuation coefficient C; S4.4 Correct the calculated water attenuation coefficient C.

6. The method for measuring the water attenuation coefficient according to any one of claims 1 to 5, characterized in that: The laser communication light intensity I in The communication distance S can be adjusted by adjusting the different laser communication light intensity I in and communication distance S to obtain a more accurate water attenuation coefficient C.

7. The method for measuring the water attenuation coefficient according to any one of claims 1 to 5, characterized in that: The communication distance S is the geometric length of the optical path of the laser in the underwater channel under the premise that the underwater optical communication machines A and B are aligned, and its value reflects the relative distance between the A and B machines.

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