CN110568427A - Reverberation parameter inversion method based on ADCP flow measurement signal - Google Patents

Reverberation parameter inversion method based on ADCP flow measurement signal Download PDF

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CN110568427A
CN110568427A CN201910837086.6A CN201910837086A CN110568427A CN 110568427 A CN110568427 A CN 110568427A CN 201910837086 A CN201910837086 A CN 201910837086A CN 110568427 A CN110568427 A CN 110568427A
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adcp
tvc
data
echo
reverberation parameter
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CN110568427B (en
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王忠康
胡长和
郭冉
韩礼波
冯宏
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Hangzhou Ruili Marine Equipment Co Ltd
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Hangzhou Ruili Marine Equipment Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
    • G01P5/00—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft
    • G01P5/24—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring the direct influence of the streaming fluid on the properties of a detecting acoustical wave
    • G01P5/241—Measuring speed of fluids, e.g. of air stream; Measuring speed of bodies relative to fluids, e.g. of ship, of aircraft by measuring the direct influence of the streaming fluid on the properties of a detecting acoustical wave by using reflection of acoustical waves, i.e. Doppler-effect
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/02—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems using reflection of acoustic waves
    • G01S15/50—Systems of measurement, based on relative movement of the target
    • G01S15/58—Velocity or trajectory determination systems; Sense-of-movement determination systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
    • G01S7/539—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F2218/00—Aspects of pattern recognition specially adapted for signal processing
    • G06F2218/22—Source localisation; Inverse modelling

Abstract

The invention discloses a reverberation parameter inversion method based on an ADCP flow measurement signal. The specific operation steps are as follows: s1: acquiring actual echo data of different profile layers in a target voyage measured by ADCP, and screening to obtain effective data for inversion; s2: restoring the effective data according to an original TVC amplification formula built in the ADCP to obtain the real echo signal sound level of each effective data point without TVC amplification; s3: fitting the effective data points obtained in the step S2 according to a theoretical echo intensity formula by taking the propagation distance as an independent variable and the sound level of the real echo signal as a dependent variable to obtain a fitting curve and real values of a and A; s4: based on the value A obtained in S3, the volume scattering intensity S is further calculatedVThe true value of (d). The method has the characteristics of intuition, brief introduction, easy operation and strong pertinence, can overcome the defect that the experience value of the current reverberation parameter can not accord with the actual sea area, can accurately invert the reverberation parameter, and provides accurate data for subsequent scientific research.

Description

Reverberation parameter inversion method based on ADCP flow measurement signal
Technical Field
the invention relates to an inversion method of reverberation parameters based on ADCP flow measurement signals, which comprises an absorption coefficient and volume scattering intensity and is particularly suitable for calculating accurate reverberation parameters of different sea areas.
background
signals propagate in seawater and are attenuated by factors such as sound absorption and sound spread. With the continuous increase of the propagation distance, the attenuation is larger and larger, and the smaller the received signal energy finally reaching the transducer is, the smaller the corresponding signal amplitude is, thereby increasing the difficulty of signal processing. Therefore, in the signal preprocessing, the TVC curve amplification mode is adopted, so that the amplitudes of echo signals at different distances are kept in a certain range, and the difficulty of signal post-processing is further reduced.
One of the functions of the sonar equation is to predict the performance of the existing sonar equipment, obtain the theoretical acting distance of the designed sonar through derivation, and similarly, calculate the echo signal intensity at different distances and further calculate the amplification factor of the TVC curve at the receiving time corresponding to different distances. Therefore, the setting of the TVC curve parameters is greatly related to the sonar equation.
In the prior art, the numerical value of the parameter of the sonar equation is based on empirical parameters, such as volume scattering intensity SVthe absorption coefficient a of the seawater medium. In the practical use process of the ADCP, the passing water areas are different, and the numerical values of the parameters are different; the measurement in the same water area is carried out in different time seasons, and the parameter values are different. The TVC curve formula cannot be accurately set by adopting empirical parameters. Therefore, the problem of inaccurate parameter setting of the TVC curve is caused, and the accuracy of the equipment is affected, so that a more accurate reverberation parameter inversion method is to be provided.
Disclosure of Invention
the invention aims to overcome the defects of the prior art, and provides a reverberation parameter inversion method based on an ADCP flow measurement signal, which can accurately invert reverberation parameters, provide a data base for setting a TVC curve of equipment and improve the equipment precision.
the purpose of the invention is realized by the following technical scheme:
A reverberation parameter inversion method based on an ADCP flow measurement signal comprises the following steps:
S1: acquiring actual echo data of different profile layers in a target voyage measured by ADCP, and screening to obtain effective data for inversion;
S2: restoring the effective data according to an original TVC amplification formula built in the ADCP to obtain the real echo signal sound level of each effective data point without TVC amplification;
S3: fitting the effective data points obtained in the step S2 according to a theoretical echo intensity formula (1) by taking the propagation distance as an independent variable and the sound level of the real echo signal as a dependent variable to obtain a fitting curve and real values of a and A;
RL＝A-20log10(R)-2aR (1)
wherein: RL is the true echo signal sound level on the receiving transducer; a is a constant value that does not change with propagation distance; r is a propagation distance; a is absorption loss;
S4: based on the value A obtained in S3, the volume scattering intensity S is further calculated according to the formula (2)VThe true value of (d);
Wherein: SL denotes the sound source level; theta-3dBRepresents the-3 dB beamwidth of the transducer; l is the layer thickness.
Preferably, in S1, several profile layers with smooth speed, no invalid data, and no abrupt change between layers are selected for inversion.
Further, the plurality of profile layers select the profile layer after the TVC is completely released.
Further, in S1, the data in each section layer needs to be subjected to outlier rejection processing in advance.
Preferably, the method used for curve fitting is a least squares method.
The method has the advantages that the accurate reverberation parameter can be obtained, and the TVC parameter is corrected, so that the problem of inaccurate TVC curve parameter setting is solved, and the equipment accuracy is further improved. The method has the characteristics of intuition, simplicity, easy operation and strong pertinence, can overcome the defect that the experience value of the current reverberation parameter can not meet the actual sea area, can accurately invert the reverberation parameter, and provides accurate data for subsequent research.
Drawings
FIG. 1 is a flow chart of a method of the present invention;
FIG. 2 is a diagram showing the selection criteria of the operational profile layer of the voyage data in a certain spring, wherein (a) to (c) represent the synthetic speed curves of the 8 th to 10 th layers respectively;
Fig. 3 is a curve showing the variation of the average echo signal level with distance of four beams obtained by selecting certain spring voyage data according to the embodiment of the present invention and a fitting curve diagram, where (a) to (d) represent beams 0 to 3, respectively.
Detailed Description
The present invention is further illustrated by the following examples.
The inversion of reverberation parameters based on ADCP flow measurement signals provided by the invention mainly comprises a theoretical echo intensity formula, actual echo intensity data generation and curve fitting. The theoretical echo intensity formula is a generation formula used as a fitting curve, and is a theoretical calculation formula for deriving echo intensities at different distances by a sonar equation and combining with specific equipment parameters of ADCP (reverberation parameters are contained in the formula as unknown numbers). The actual echo intensity data is generated by accurately calculating actual echo intensities corresponding to different propagation distances through actual flow measurement data and by combining with specific ADCP settings. And the curve fitting is carried out by taking actual echo intensity data as a reference through a theoretical echo intensity formula to obtain a theoretical echo intensity curve, so as to obtain an accurate estimation value of the reverberation parameter.
Before describing a detailed reverberation parameter inversion method, the invention specifically introduces a derivation process of a theoretical echo intensity formula:
a) when an acoustic Doppler current profiler (ADCP for short) measures current, an active sonar working mode taking seawater volume reverberation as a target is adopted, and the sonar equation is as follows:
SL-2TL+TS-(NL-DI)＝DT
Wherein: SL denotes the sound source level, the propagation loss is denoted by TL, TS denotes the target intensity, NL denotes the marine environmental noise level, the reception directivity index is denoted by DI, and DT is the detection valve.
b) The sound levels of the echo signals applied to the receiving transducer are:
RL＝SL-2TL+TS
RL＝SL-2TL+TS
c) The one-way propagation loss TL includes seawater medium propagation loss and medium absorption loss, and can be expressed as:
TL＝20*log10(R)+a*R
Wherein: r is the propagation distance and a is the absorption coefficient.
d) The target intensity TS may be expressed as:
TS＝SV+10*log10(V)
e) volume scattering intensity SVIs the reaction of scatterers in the ocean to the scattering power of the sound waves. The value range of the volume scattering intensity is-90 to-70 dB (neglecting a deep sea scattering layer), and the volume scattering intensity is considered to be a constant value in one-time navigation. The-3 dB beamwidth of the circular plate transducer in ADCP is noted as: theta-3dB(should be converted to radians when calculated), the scattering volume is:where L is the layer thickness.
the above formulas are combined, and the theoretical calculation formula of the echo signal intensity at different distances is deduced:
RL＝A-20log10(R)-2aR
Wherein: a is a constant value which does not change with the propagation distance, and the expression is as follows:
Based on the above derivation, the theoretical echo intensity formula is as follows:
RL＝A-20log10(R)-2aR
Wherein: RL is the echo signal level on the receiving transducer; a is a constant value that does not change with propagation distance; r is a propagation distance; a is absorption loss; SL represents the sound source level, a known value associated with ADCP hardware; sVRepresents the volume scattering intensity; theta-3dBRepresents the-3 dB beamwidth of the transducer, a known value associated with ADCP hardware; l is the layer thickness.
Based on the theoretical echo intensity formula, the response parameter inversion can be accurately carried out. The method for inverting reverberation parameters based on ADCP current measurement signals is described in detail below with reference to FIG. 1, and comprises the following steps:
S1: and obtaining the actual data of the ADCP through sailing, and screening the actual echo data of a plurality of stable profile layers from the data of the current voyage, wherein the actual echo data are used as effective data of subsequent inversion. Generally, when selecting profile layers, the profile layers should be selected with a relatively smooth speed, without drastic fluctuation and invalid data, and without abrupt change between the profile layers, so as to avoid introducing errors. It should be noted that the echo data obtained at this time is already gain-compensated in the ADCP device by the built-in TVC amplification formula. At this time, parameters in the adopted TVC amplification formula are usually fixed empirical values, so that the output actual echo data usually has a deviation, and the actual data needs to be subjected to screening processing in the next step, and the influence of the amplification of the original TVC is eliminated.
S2: since the original TVC amplification formula built in the ADCP is known, the effective data obtained by screening in S1 may be subjected to reduction processing according to the original TVC amplification formula built in the ADCP, and the real sound level of the echo signal of each effective data point without TVC amplification is obtained through recalculation, where the sound level corresponds to the real sound level on the receiving transducer. The processed data points are connected smoothly, and a curve of the sound level of the real echo signal changing along with the distance can be approximately obtained.
S3: and (3) fitting the effective data points obtained in the step (S2) according to a theoretical echo intensity formula (1) by taking the propagation distance as an independent variable and the sound level of the real echo signal as a dependent variable, wherein the fitting method is a least square method (namely fitting the data points) to obtain a fitting curve. The estimated values of the fitting curve for a and A can be used as the true values;
RL＝A-20log10(R)-2aR (1)
Wherein: RL is the true echo signal level on the receiving transducer, i.e. the level recovered in S2; r is a propagation distance; a is absorption loss; a is a constant value which does not change with the propagation distance, and includes
S4: based on the value A obtained in S3, the volume scattering intensity S is further calculated according to the formula (2)Vthe true value of (d);
Wherein: SL represents the sound source level, theta-3dBrepresents the-3 dB beamwidth of the transducer, both of which are fixed values for a particular ADCP device and can be obtained in advance from hardware parameters; l is the layer thickness, and can also be obtained in advance.
Therefore, the real body reverberation scattering intensity S can be inverted by using the actual measurement data of the ADCPVand the absorption loss a, so that the real parameters can be used for accurately setting the TVC curve, correcting errors caused by empirical parameters and improving the measurement precision.
the inversion method described above is applied to specific embodiments in order to facilitate the realization of the present invention for better understanding by those skilled in the art.
Example 1
The specific implementation mode is explained by the inversion method of the invention by taking the voyage flow measurement data of certain spring of south China sea as an example.
1) actual echo data of different profile layers of the voyage are obtained through voyage, and the voyage flow measurement data are processed and screened to obtain effective data. The method comprises the steps of selecting a profile layer for operation according to an actual speed synthesis curve graph, selecting the profile layer with stable speed, no violent fluctuation and no invalid data, and having no sudden change between the profile layers.
FIG. 2 and Table 1 show the selection criteria for a spring voyage data operation profile layer. As can be seen, the layer 3-9 speeds are stable, so layer 3 to layer 9 with similar cross-sectional layers are selected as the calculation data. And (3) reserving a certain margin for the distance 24.746m of the gain of all TVCs, so that the actual echo data of the 3 rd to 9 th layers are selected for fitting calculation by selecting the current voyage.
TABLE 1
2) considering that the received data includes the influence of a TVC formula, the TVC amplification formula is removed when a real echo intensity value is restored, the TVC amplification formula is used for compensating energy loss caused by the increase of the propagation distance, the TVC value is larger and larger along with the increase of the propagation distance, but the TVC value is not infinite, a constant is kept after a certain amplification factor is reached, and at the moment, the TVC is completely released. For simplicity, the section layer with the TVC completely released is selected for calculation, so that the TVC magnification is constant and is easier to eliminate.
The original TVC amplification formula built in the ADCP may be known in advance according to original hardware and software design, so that the effective data obtained by screening in step 1) may be reduced according to the original TVC amplification formula, and the real echo signal sound level of each effective data point without TVC amplification may be obtained by recalculation. The ADCP device of this embodiment is 150kHz ADCP (SLC150-1 type), and the time for setting TVC to be completely released is 30ms, which is converted into transmissionthe propagation distance should be:(the beam inclination angle is 24.6 degrees), after the ADCP profile layer is greater than 24.746m, the TVC value is a fixed value, the TVC influence is eliminated, and the real echo intensity calculation formula is as follows:
Wherein: e is the amplitude of the received data, namely the amplitude of the amplified signal; sSensitivity of receptioncalculating the formula for the amplification factors of a receiving board, a DSP and the like: sSensitivity of reception＝-180dB；SMagnification factorFor the TVC gain, the calculation formula is: sMagnification factor＝20log10(15000)。
Through the restoration processing, the sound level in each piece of effective data can be restored to the true sound level of the echo signal without being amplified by the TVC. Before the data are used for subsequent fitting, the data in each section layer need to be subjected to outlier rejection processing in advance, and interference of poor data is eliminated. In this embodiment, taking a certain profile layer as an example, the energy mutation points are removed based on the average energy value of different batches of data of the profile layer. Similarly, such outlier culling is performed for all profile layers.
since multiple beams are typically transmitted during the measurement process, multiple sets of data are acquired to reduce errors. Therefore, the data after the abnormal value elimination processing can be averaged to obtain the data points of the actual average echo signal level along with the change of the distance for the subsequent fitting process. The smooth connection of the data points approximately obtains a curve of the change of the sound level of the real echo signal along with the distance.
3) According to the foregoing derivation, the theoretical echo intensity formula is as follows:
RL＝A-20log10(R)-2aR (1)
In the above theoretical echo intensity formula (1), a and a are parameters to be determined by fitting. Therefore, the propagation distance is used as an independent variable, the sound level of a real echo signal is used as a dependent variable, the data points obtained in the previous step are fitted according to a theoretical echo intensity formula (1), and the fitting principle is that the theoretical echo intensity RL and the actual echo intensity RL under the condition of the same distance R are fittedtrueThe least difference, the least squares method. Thus, obtaining a fitting curve and the true values of a and A;
RL＝A-20log10(R)-2aR (1)
Wherein: RL is the true echo signal sound level on the receiving transducer; a is a constant value that does not change with propagation distance; r is a propagation distance; a is absorption loss;
4) Based on the A value obtained by fitting in the step 3), the volume scattering intensity S can be further calculated according to a theoretical echo intensity formula (2)Vthe true value of (d);
Wherein: SL denotes the sound source level; theta-3dBRepresents the-3 dB beamwidth of the transducer; l is the layer thickness. For a particular ADCP device and voyage, the three parameters are known quantities. Wherein: the sound source level SL is a fixed value and is simplified to 220 dB; the-3 dB beamwidth (beam opening angle taken as 3.8 degrees) of the circular plate transducer in this embodiment is: theta-3dB(conversion to radians in calculation); the layer thickness L is reduced to 16 m.
In this embodiment, the spring voyage data may obtain a change curve (original curve) of the average echo signal level with distance and a fitting curve graph of the four beams shown in fig. 3 according to the above process.
Table 2 shows the absorption coefficient a and the volume scattering intensity S inverted from the theoretical echo intensity formula corresponding to FIG. 3Vand (5) a numerical value statistical table.
TABLE 2
Therefore, the method can utilize the direct measurement data of the ADCP to carry out inversion, correct errors caused by built-in TVC experience parameters in the ADCP equipment, obtain accurate reverberation parameters and improve the measurement accuracy.
The above embodiment is an example of the technical solution of the present invention, the scope of the disclosure of the present invention is not limited thereto, and any equivalent replacement of the technical solution of the present invention falls within the scope of the present invention.

Claims (5)

1. a reverberation parameter inversion method based on an ADCP flow measurement signal is characterized by comprising the following steps:
S1: acquiring actual echo data of different profile layers in a target voyage measured by ADCP, and screening to obtain effective data for inversion;
s2: restoring the effective data according to an original TVC amplification formula built in the ADCP to obtain the real echo signal sound level of each effective data point without TVC amplification;
S3: fitting the effective data points obtained in the step S2 according to a theoretical echo intensity formula (1) by taking the propagation distance as an independent variable and the sound level of the real echo signal as a dependent variable to obtain a fitting curve and real values of a and A;
RL＝A-20log10(R)-2aR (1)
wherein: RL is the true echo signal sound level on the receiving transducer; a is a constant value that does not change with propagation distance; r is a propagation distance; a is absorption loss;
S4: based on the value A obtained in S3, the volume scattering intensity S is further calculated according to the formula (2)Vthe true value of (d);
wherein: SL denotes the sound source level; theta-3dBrepresents the-3 dB beamwidth of the transducer; l is the layer thickness.
2. the ADCP current signal-based reverberation parameter inversion method of claim 1, wherein in S1, several profile layers with smooth speed, no invalid data and no abrupt change between layers are selected for inversion.
3. the ADCP flow signal-based reverberation parameter inversion method of claim 2, wherein the profile layers are selected from the profile layers after the TVC is completely released.
4. The ADCP flow measurement signal-based reverberation parameter inversion method of claim 2, wherein in S1, data in each section layer needs to be processed by outlier rejection in advance.
5. The ADCP flow measurement signal-based reverberation parameter inversion method of claim 1, wherein the curve fitting is performed by least squares.
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