Methods for measuring water body attenuation coefficient

Abstract

The application discloses a kind of water body attenuation coefficient measurement methods, through a pair of underwater optical communication machine coordination work, realize high-precision, adjustable parameter water body attenuation coefficient measurement, including: optical communication machine carries out air calibration and pure water calibration to obtain transmission reference light intensity;Utilize underwater optical communication mechanism to build ranging data frame to complete ranging by measuring transmission time difference;Process the full waveform data of communication signal after underwater channel to obtain the light intensity after water attenuation;Synthesize communication distance, transmission reference light intensity, the light intensity after attenuation, calculates and processes to obtain water body attenuation coefficient.The application utilizes underwater optical communication machine communication signal to obtain water body attenuation coefficient, and it is a kind of simple operation, easy to deploy, wide application range, suitable for real-time measurement method.

Description

Technical Field

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

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

[0003] Underwater wireless optical communication is an important method for achieving high-speed underwater communication due to its extremely high bandwidth and speed. However, due to the inherent optical properties of the ocean, ocean turbulence, and the skin effect, water has a strong attenuation effect on light, limiting the transmission distance of light in seawater. As the transmission distance increases, the waveform of the received optical signal undergoes temporal and spatial broadening, leading to increased bit error rates and even communication failure. The water attenuation coefficient is a crucial factor affecting the transmission distance of light in water. Underwater optical communication devices need to adjust the communication rate according to the water attenuation coefficient in water bodies with different attenuation coefficients to achieve optimal communication performance. The water attenuation coefficient is an important basis for setting the operating parameters of underwater optical communication devices, determining the maximum communication distance in water, and is also used to evaluate their communication performance. However, current underwater optical communication devices do not have the function of measuring water attenuation coefficients themselves. They require the use of additional specialized equipment (such as AC-S) to measure the water attenuation coefficients. These devices are expensive, have complicated and cumbersome usage procedures, cannot measure in real time, and 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 devices that is widely applicable, easy to operate, and can monitor the water attenuation coefficient in real time. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method for measuring the water body attenuation coefficient, which achieves high-precision, adjustable parameter measurement of the water body attenuation coefficient through the coordinated operation of a pair of underwater optical communication devices (A and B).

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

[0007] This invention provides a method for measuring the water attenuation coefficient based on underwater optical communication signals, characterized in that it includes:

[0008] The measurement process is completed by a pair of underwater optical communication devices (hereinafter referred to as device A and device B).

[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: Construct a ranging data frame using an underwater optical communication device and measure 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 optical intensity I after water attenuation. out ;

[0012] Step S4: Combine communication distance S and transmitted reference light intensity I c Attenuated received light intensity I out Data processing is performed to obtain the water body attenuation coefficient C and then correct it.

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

[0014] S1.1 Perform air calibration by placing Unit A and Unit B in the air of the darkroom, starting them individually and checking whether the optical path is clean and dust-free to ensure the communication unit is working properly. After the optical communication unit stabilizes, record the system noise I. n Air calibration complete;

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

[0016] S1.3 sets the laser communication light intensity I of machine B. in Machine B operates according to the set laser communication light intensity I. in Send ranging data frames. After the light intensity and water body stabilize, record the measured light intensity I1 at point A, and use the calculation formula I. c =I1-I n Obtain the 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 I values.in The corresponding emission reference light intensity I c ;

[0018] Furthermore, the ranging data frame is composed of laser communication light intensity I. in The communication data, consisting of the communication content, is formed by RS encoding and scrambling and then inserted into the frame synchronization sequence. The ranging data frame includes the synchronization sequence, payload data bits, and RS check code.

[0019] Furthermore, the communication distance S is the geometric length of the laser path in the underwater channel when underwater optical communication devices A and B are aligned. Its value reflects the relative distance between devices A and B. The calculation of the communication distance S in step S2 includes the following sub-steps:

[0020] S2.1 Set the laser communication light intensity I of machine A in Machine A operates according to the set laser communication light intensity I. in Send ranging data frames and start timing; the data is received by Unit B after passing through the underwater channel.

[0021] S2.2 Machine B decodes the ranging data frame to obtain the laser communication light intensity I from Machine A. in ;

[0022] S2.3 Machine B uses the laser communication light intensity I of Machine A. in A ranging data frame is sent to Unit A. After passing through the underwater channel, Unit A receives the data and immediately stops timing to obtain the time difference.

[0023] S2.4 A receiver assesses the received full waveform data. If the full waveform data is saturated, it reduces the laser communication light intensity I. in If the full waveform data is too weak, increase the laser communication light intensity I. in 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 The full waveform data received by machine A at this time is then used to receive the light intensity I. out Measurement.

[0024] S2.5 utilizes the protection time slot t p The inherent delay t of the system c Transmission time difference t ABA The communication distance S is calculated in machine A using the following formula: Where c is the speed of light in a vacuum, and n 水 This represents the current refractive index of the water body.

[0025] Furthermore, the protection time slot t in step S2.5 p and the system's inherent delay t c All are known quantities, protection time slot t pFor half-duplex communication, a guard slot is used to set communication parameters, and the system's inherent delay t is also included. c Obtained from the calibration at the time the equipment 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 laser as the carrier, and its waveform physical meaning is the received wave signal strength that changes with time.

[0027] Furthermore, the received light intensity I after water attenuation out The received light intensity I in step S3 is calculated using the full waveform data obtained in step S2.4. out The calculation includes the following sub-steps:

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

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

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

[0031] S4.1 Based on the laser communication light intensity I in Find the corresponding emission reference light intensity I in step S1. c ;

[0032] S4.2 Based on the laser emission angle θ, the diameter d of the receiver surface of the communication device, the communication distance S in step S2, the calibration distance L, and the emission reference light intensity I c The corrected reference light intensity I0 is calculated using the following formula:

[0033] S4.3 Using the communication distance S, reference light intensity I0 from step S2, and the received light intensity I from step S3 out The water body attenuation coefficient C is calculated using the following formula:

[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 Both the communication distance S and the laser communication light intensity I can be adjusted when calculating the water body attenuation coefficient. in The communication distance S is calculated to obtain a more accurate water attenuation coefficient.

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

[0037] 1. When performing underwater wireless optical communication, the present invention can complete the measurement of communication distance S and water attenuation coefficient C during the communication process without relying on additional equipment, which simplifies the measurement and the entire system.

[0038] 2. This invention allows for measurement during underwater wireless optical communication, offering high real-time performance;

[0039] 3. The measurement platform of this invention is an underwater optical communication device. This device can be installed on underwater mobile platforms such as AUVs, which is convenient to deploy, simple to operate, flexible in measurement, and has a wide range of applications.

[0040] 4. When performing measurements, the communication power and the distance between the two communication devices are adjustable. Using different power and distance measurements can improve the measurement accuracy.

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

[0042] To make the above-described features and advantages of the present invention more apparent and understandable, the present invention will be further described below with reference to examples and accompanying drawings, but this should not be construed as limiting the scope of protection of the present invention. Additional features and advantages of the present invention will be set forth in part in the following description, and such features and advantages will be apparent in part from the description or may be learned by practice of the present invention. Attached Figure Description

[0043] Figure 1 This is a flowchart of the method for measuring the water body attenuation coefficient according to the present invention.

[0044] Figure 2 This is a schematic diagram of pure water calibration in the water body attenuation coefficient measurement method of the present invention.

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

[0046] Figure 4 This is a schematic diagram of the reference light intensity correction in the water body attenuation coefficient measurement method of the present invention. Detailed Implementation

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

[0048] Please refer to the following first. Figure 1 , Figure 1This is a flowchart of the water attenuation coefficient measurement method of the present invention. This method utilizes a pair of underwater optical communication devices (A and B) working collaboratively to achieve high-precision, adjustable-parameter measurement of the water attenuation coefficient. The specific implementation steps are as follows:

[0049] Step S1: Monitor and calibrate the equipment:

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

[0051] Place machines A and B in a dark room to ensure there is no external light source interference.

[0052] The system is individually activated and tested to check the cleanliness of the optical path and the working status of components such as the light source and detectors of each communication device.

[0053] After the communication device stabilizes, record the system noise I. n Complete air calibration.

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

[0055] Move machines A and B to a darkroom water tank containing purified water, such as... Figure 2 As shown, ensure both are aligned and record the calibration distance L.

[0056] Set the laser communication light intensity I of machine B in It then sends a ranging data frame. This ranging data frame is generated by the laser communication light intensity I. in The ranging data frame is formed by the communication data consisting of the communication content and RS encoding, scrambling, and insertion of a frame synchronization sequence. The ranging data frame includes a synchronization sequence, payload data bits, and RS check code.

[0057] After the light intensity and water body stabilize, record the measured light intensity I1 received by receiver A, and calculate the transmitted reference light intensity I. c The formula is as follows:

[0058] I c =I1-I n ;

[0059] Repeat the above steps, by changing 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, which reduces the influence of ambient light and improves accuracy.

[0061] Step S2: Measurement of communication distance S

[0062] S2.1 Initial Distance Measurement Preparation:

[0063] Deploy the calibrated A and B units onto the underwater platform, ensuring they are aligned.

[0064] Set the laser communication light intensity I of machine A in Prepare to send ranging data frames.

[0065] S2.2 Two-way ranging:

[0066] Machine A operates according to the set laser communication light intensity I. in Send a ranging data frame and start timing. The ranging data frame is received by Unit B after passing through the underwater channel.

[0067] Machine B decodes the data frame and obtains the laser communication intensity I from machine A. in Based on this, it sends a ranging data frame in response to machine A;

[0068] After receiving the ranging data in response, 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 based on the received full waveform data. in If the entire waveform data is saturated, then 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 suitable intensity is obtained, and use this as the final transmission time difference t. ABA ;

[0072] S2.4 Communication Distance Calculation:

[0073] Utilizing the transmission time difference t ABA Protection time slot t p The inherent delay t of the system c The speed of light in a vacuum, c, and the current refractive index of the water, n. 水 The communication distance S is calculated using the following formula:

[0074]

[0075] In the formula, the protection time slot t p For half-duplex communication, a guard slot is used to set communication parameters, and the system's inherent delay t is also included. c The values ​​are determined by the equipment at the time of manufacture.

[0076] In actual operation, the communication distance S can be measured using methods such as pseudo-random code ranging and phase ranging, and is not limited to the ranging methods mentioned in this invention. The measurement of the communication distance S is a prerequisite for calculating the water body 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] Perform waveform preprocessing on the full waveform data in step S2.3 to remove noise information from the full waveform data and extract the received waveform I with N data bits "1".

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

[0081] The average value of the preprocessed waveform intensity is calculated as the received light intensity I. out The formula is as follows:

[0082]

[0083] The full waveform data refers to the waveform shape of the ranging data frame after passing through the underwater channel with laser as the carrier. It is generated by the detector converting the received optical signal into an electrical signal, which is then processed by a high-speed acquisition and processing unit. The physical meaning of the waveform is the intensity of the received wave signal changing over time. (Received light intensity I) out This is after the water has decayed.

[0084] S4. Calculation and Correction of Water Body Attenuation Coefficient

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

[0086] S4.2 as Figure 4 As shown, based on the laser emission angle θ, the diameter d of the receiver surface of the communication device, the communication distance S, the calibration distance L, and the emission reference light intensity I... c The corrected reference light intensity I0 is calculated using the following formula:

[0087]

[0088] S4.3 Based on the communication distance S, reference light intensity I0, and received light intensity I out The water body attenuation coefficient C is calculated using the following formula:

[0089]

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

[0091] This embodiment achieves high-precision measurement of the water attenuation coefficient through a meticulous calibration process, two-way ranging technology, and data optimization processing. Simultaneously, by adjusting 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 this invention, the water attenuation coefficient can only be measured after the communication distance has been measured.

[0093] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method of measuring the attenuation coefficient of a body of water, characterized in that, The underwater optical communication is coordinated by a pair of underwater optical communication devices, including A device and B device, comprising the following steps: S1: monitoring equipment and calibration: Put A device and B device in darkroom air, start up separately and detect optical path cleanliness of each communication device and working state of light source and detector, record system noise after communication device is stable, complete air calibration; The A machine and the B machine are moved to the darkroom water tank filled with pure water, it is ensured that the two are aligned, the calibration distance is recorded, the laser communication light intensity of the B machine is set and the ranging data frame is sent, after the light intensity and the water body are stable, the measurement light intensity received by the A machine is recorded and the emission reference light intensity is calculated, the above steps are repeated, the emission reference light intensity I under different laser communication light intensities is measured and recorded by changing the laser communication light intensity of the B machine c ; S2: Constructing a ranging data frame by measuring the transmission time difference t using the underwater optical communication mechanism ABA Completing the communication distance S measurement: S3: processing the full waveform data of the communication signal after passing through the underwater channel to obtain the received light intensity I after passing through the water attenuation out ; S4: integrate the communication distance S and the emission reference light intensity I c and the received light intensity I after attenuation out perform data processing, calculate the water body attenuation coefficient C and perform correction; The calculation and correction of water body attenuation coefficient C in step S4 includes: S4.1 According to the laser communication light intensity I in Search for the corresponding emission reference light intensity I c ; S4.2 The corrected reference light intensity I0 is calculated according to the laser emission angle θ, the communication receiver surface diameter d, the communication distance S, the calibration distance L and the emission reference light intensity I0 c The corrected reference light intensity I0 is calculated according to the laser emission angle θ, the communication receiver surface diameter d, the communication distance S, the calibration distance L and the emission reference light intensity I0 S4.3 using the communication distance S, the reference light intensity I0, and the received light intensity I out The water body attenuation coefficient C is calculated; the calculation formula is: S4.4 correct the calculated water body attenuation coefficient C.

2. The method of measuring attenuation coefficient of a volume of water according to claim 1, wherein, The step S2 specifically includes: Deploy calibrated A device and B device to underwater platform, ensure alignment of both; Set laser communication light intensity of A device, A device sends ranging data frame and starts timing, B device receives and decodes data frame and sends back responding ranging data frame to A device, A device stops timing after receiving responding ranging data, record transmission time difference; A device adjusts laser communication light intensity according to received full waveform data, repeat bidirectional ranging and light intensity adjustment until suitable intensity full waveform data is obtained, and use transmission time difference at this time for final communication distance calculation; Use transmission time difference, protection time slot, system inherent delay, light speed in vacuum and current water body refractive index to calculate communication distance.

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

4. The method of measuring attenuation coefficient of a volume of water of claim 1, wherein, The received light intensity I in the step S3 out The calculating comprises: S3.1 pre-process full waveform data, intercept N data bits "1" receiving waveform I; S3.2 Calculate the average of the waveform intensity values as the received light intensity I out .

5. The method of measuring the attenuation coefficient of a volume of water according to any one of claims 1 to 4, characterized in that, The laser communication light intensity I in And the communication distance S can be adjusted, and by adjusting the different laser communication light intensity I in And the communication distance S are calculated to obtain more accurate water body attenuation coefficient C.

6. The method of measuring the attenuation coefficient of a volume of water according to any one of claims 1 to 4, characterized in that, The communication distance S is the geometric length of optical path of laser in underwater channel under the premise of alignment of underwater optical communication device A device and B device, and its value reflects relative distance of A device and B device.

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