CN110554394B - ADCP flow measurement signal-based TVC curve accurate setting method - Google Patents

ADCP flow measurement signal-based TVC curve accurate setting method Download PDF

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CN110554394B
CN110554394B CN201910837050.8A CN201910837050A CN110554394B CN 110554394 B CN110554394 B CN 110554394B CN 201910837050 A CN201910837050 A CN 201910837050A CN 110554394 B CN110554394 B CN 110554394B
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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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    • 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
    • G01S15/88—Sonar systems specially adapted for specific applications
    • G01S15/89—Sonar systems specially adapted for specific applications for mapping or imaging
    • G01S15/8906—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques
    • G01S15/8979—Combined Doppler and pulse-echo imaging 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

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Abstract

The invention discloses a TVC curve accurate setting method based on ADCP flow measurement signals. The method adopted is as follows: firstly, obtaining an accurate reverberation parameter value through reverberation parameter inversion; then, calculating according to the propagation distance and the reverberation parameter value, and preliminarily obtaining the TVC amplification factor at the receiving moment by using the compensation propagation total loss as a principle; and finally, selecting discrete time points according to the resolution to obtain the propagation loss of different receiving time points, further obtaining the TVC amplification factor of the point, and fitting after correcting the amplification factor to obtain a TVC voltage control curve. The method has the characteristics of intuition, brief introduction, easy operation and strong pertinence, can overcome the problem that the current reverberation parameter can not accurately set the TVC curve by taking the empirical value, and improves the precision of the equipment.

Description

ADCP flow measurement signal-based TVC curve accurate setting method
Technical Field
The invention relates to an ADCP flow measurement signal-based TVC curve accurate setting method, which is suitable for setting an accurate TVC curve under different environmental conditions.
Background
Signals propagate in seawater and are inevitably attenuated due to factors such as sound absorption and sound spread. The larger the propagation distance, the larger the attenuation, the smaller the received signal energy finally reaching the transducer, and the smaller the corresponding signal amplitude, increasing the difficulty of signal processing. Therefore, in the actual 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.
The sonar equation can deduce and 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 precision of the equipment is further influenced.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a TVC curve accurate setting method based on an ADCP flow measurement signal so as to solve the problem that the current reverberation parameter experience value can not accurately set a TVC curve, and further improve the accuracy of equipment.
The purpose of the invention is realized by the following technical scheme:
a TVC curve accurate setting method based on ADCP flow measurement signals comprises the following steps:
s1: reducing ADCP actual flow measurement data to obtain real echo signal sound levels which are not amplified by TVC at different propagation distances, fitting based on a theoretical echo intensity formula by taking the propagation distances as independent variables and the real echo signal sound levels as dependent variables, and performing inversion to obtain the absorption loss a and the volume scattering intensity SVAn intrinsic accurate reverberation parameter;
s2: substituting the accurate reverberation parameters obtained in the step S1 into a sonar equation to obtain signal propagation total loss calculation formulas at different propagation distances, and further obtaining TVC (total harmonic distortion) amplification factor calculation formulas at corresponding distances according to the signal propagation total loss;
the calculation formula of the total signal propagation loss EL is as follows:
Figure GDA0002885829190000021
wherein: SL denotes the sound source level; sVRepresents the volume scattering intensity; RL is the true echo signal sound level on the receiving transducer; theta-3dBRepresents the-3 dB beamwidth of the transducer; l is the layer thickness; a is absorption loss; r is a propagation distance;
the TVC amplification factor TVCAmplification ofThe calculation formula of (2) is as follows:
TVCamplification of＝-EL
S3: determining the propagation distance interval, the starting change point and the ending change point of the TVC curve, and then setting the TVC magnification curve, wherein the setting mode of the curve is as follows: TVC compensation is not carried out within the initial change point; calculating TVC (transient voltage suppressor) amplification factors under different propagation distances according to a calculation formula of the TVC amplification factors between the initial change point and the termination change point by taking the initial change point as a propagation distance zero point, and performing smooth filtering on the TVC amplification factor data point; after the change point is terminated, the TVC amplification factor is always kept as the amplification factor corresponding to the position of the change point;
s4: the TVC amplification curve obtained at S3 is converted into a voltage control curve in ADCP.
Preferably, the inversion method of the precise reverberation parameter is as follows:
s11: acquiring actual echo data of different profile layers measured by ADCP, and screening to obtain effective data for inversion;
s12: 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;
s13: fitting the effective data points obtained in the step S12 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: a is a constant value that does not change with propagation distance;
s14: based on the value A obtained in S13, the volume scattering intensity S is further calculated according to the formula (2)VThe true value of (d);
Figure GDA0002885829190000031
wherein: SL denotes the sound source level; theta-3dBRepresents the-3 dB beamwidth of the transducer; l is the layer thickness.
Further, in S11, the data in each section layer needs to be subjected to outlier rejection processing in advance.
Further, in S11, a plurality of profile layers with smooth speed, no invalid data, and no abrupt change between layers are selected for inversion.
Further, the method adopted by the curve fitting is a least square method.
Preferably, when the ADCP is used for the navigation measurement, the actual measured flow data of a voyage is selected as calibration data, and the accurate reverberation parameter is obtained through inversion.
Preferably, when the ADCP is used for fixed-point measurement, actual flow measurement data are acquired in different seasons, and accurate reverberation parameters in different seasons are obtained through inversion.
Preferably, the propagation distance interval is set according to TVC curve resolution.
Preferably, in the TVC curve, the initial change point is located outside a distance of a blind zone of the ADCP, and the termination change point is a position where a fluctuation range of the propagation loss is maximized compared with the initial change point.
Preferably, in S4, the TVC amplification curve is combined with the hardware of the ADCP device to accurately fit the TVC voltage control curve.
The method has the advantages that accurate reverberation parameters can be obtained through inversion of a theoretical formula, and parameters of the TVC curve are corrected by using the parameters obtained through inversion, so that the problem of inaccurate parameter setting of the TVC curve 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 problem that the current reverberation parameter can not accurately set the TVC curve by taking the empirical value, and improves the precision of the equipment.
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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.
Fig. 4 is a curve showing the variation of the average echo signal level with distance of four beams obtained by selecting certain autumn voyage data according to the embodiment of the present invention, and a fitting curve, where (a) to (d) represent beams 0 to 3, respectively.
Detailed Description
The present invention will be further described with reference to the following examples.
In the invention, the TVC curve accurate setting mainly comprises three parts of reverberation parameter inversion, TVC amplification factor calculation formula setting and TVC curve accurate calculation and fitting. The reverberation parameter inversion is to obtain an accurate reverberation parameter, and the initial calculation formula of the TVC amplification factor is to compensate the total signal propagation loss at different propagation distances and is used for initially calculating the TVC amplification factor; the TVC curve is accurately calculated and fitted to accurately set the TVC curve and thereby obtain the voltage control curve in the ADCP.
The reverberation parameter inversion of the ADCP flow measurement signal is mainly formed by curve fitting of actual echo intensity data based on a theoretical echo intensity formula. The theoretical echo intensity formula is a generation formula used as a fitting curve, and is a theoretical calculation formula for obtaining echo intensities at different distances through a sonar equation and by combining with ADCP (Acoustic Doppler current profiler) specific equipment parameter derivation (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 performed by taking actual echo intensity data as a reference through a theoretical echo intensity formula to obtain a theoretical echo intensity curve, so that an accurate estimation value of the reverberation parameter is obtained.
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
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:
Figure GDA0002885829190000051
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:
Figure GDA0002885829190000052
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:
Figure GDA0002885829190000053
based on the above derivation, the theoretical echo intensity formula is as follows:
RL＝A-20log10(R)-2aR
Figure GDA0002885829190000054
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, reverberation parameter inversion can be accurately carried out.
The method for accurately setting the TVC curve based on the ADCP flow measurement signal according to the present invention is described in detail with reference to fig. 1, and includes the following steps:
s1: reducing ADCP actual flow measurement data to obtain real echo signal sound levels which are not amplified by TVC at different propagation distances, fitting based on the theoretical echo intensity formula by taking the propagation distances as independent variables and the real echo signal sound levels as dependent variables, and performing inversion to obtain the absorption loss a and the volume scattering intensity SVThe exact reverberation parameter inside.
In this embodiment, the reverberation parameter inversion method of S1 is specifically implemented by the following sub-steps:
s11: 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 target voyage number to be 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.
S12: since the original TVC amplification formula built in the ADCP is known, the effective data obtained by screening in S11 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.
S13: and (3) fitting the effective data points obtained in the step (S12) 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 that does not vary with propagation distance.
S14: based on the value A obtained in S13, the volume scattering intensity S is further calculated according to the formula (2)VThe true value of (d);
Figure GDA0002885829190000071
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 volume scattering intensity S can be inverted by using the actual measurement data of the ADCPVAnd absorption loss a, and then the subsequent accurate setting of the TVC curve can be carried out by utilizing the real parameters.
Because the reverberation parameters are different in different sea areas and different seasons, different inversion modes should be selected according to the measurement mode when the accurate reverberation parameter is inverted:
a) when the ADCP is used for the navigation measurement, the actual measured flow data of one voyage can be selected as calibration data, and the accurate reverberation parameter is obtained through inversion. The inversion parameters can be adopted in the subsequent measurement process in the same sea area and the same season.
b) When the ADCP is used for fixed-point measurement, the measurement position is usually fixed, but the measurement may be performed at different times, so that the actual flow measurement data should be acquired in different seasons respectively, and the inversion results in accurate reverberation parameters in different seasons. And during subsequent fixed-point measurement, selecting corresponding inversion parameters according to the season of the measurement time.
S2: after the signal is transmitted, the receiving and transmitting combined transducer in the ADCP can generate aftershock, so that the echo signal is not received in the time, namely a blind zone, and the transducer normally receives the echo signal after the blind zone. The signal propagation distance can be determined by the time the transducer receives the signal, and the total loss of propagation at that propagation distance can be calculated by sonar equations. Therefore, the accurate reverberation parameter obtained in step S1 is substituted into the sonar equation to obtain the total signal propagation loss calculation formula at different propagation distances, where the calculation formula of the total signal propagation loss EL is:
Figure GDA0002885829190000072
wherein: SL denotes the sound source level; sVRepresents the volume scattering intensity; RL is the true echo signal sound level on the receiving transducer; theta-3dBRepresents the-3 dB beamwidth of the transducer; l is the layer thickness; a is absorption loss; r is a propagation distance;
to compensate for total loss of propagationBased on the loss, a TVC amplification factor calculation formula at the corresponding distance can be obtained according to the total loss of signal propagation, and the TVC amplification factor TVCAmplification ofThe calculation formula of (2) is as follows:
TVCamplification of＝-EL (4)
S3: and setting a propagation distance interval according to the resolution required by the TVC curve, and determining a starting change point and a terminating change point of the TVC curve according to hardware configuration. In order to avoid aftershocks after the transducer transmits signals and facilitate calculation, the distance r (unit: m) is taken as a TVC initial change point, r is the blind zone distance of the transducer in the ADCP, the TVC is set according to the recommendation value of a transducer manufacturer, and the TVC is not compensated within the distance r. Of course the initial change point may also be slightly offset from the blind spot distance. In addition, the TVC dynamic range is YdB, that is, the maximum amplification factor of TVC is YdB, and when the propagation loss reaches YdB compared with the starting point at a certain propagation distance, the position corresponding to the propagation distance is the end change point of the TVC curve.
After determining the above parameters of the TVC curve, the TVC amplification factor curve can be set in the following manner: TVC compensation is not carried out within the initial change point; calculating TVC (transient voltage suppressor) amplification factors under different propagation distances (namely, the position of each propagation distance interval node is a series of discrete points) according to calculation formulas (4) and (3) of the TVC amplification factors between the initial change point and the final change point by taking the initial change point as a propagation distance zero point, and performing smooth filtering on the TVC amplification factor data point to form a smooth curve; after the termination of the change point, the TVC amplification is always maintained at the amplification corresponding to the termination of the change point, i.e., YdB is maintained and is not increased. Thus, the final TVC magnification curve is obtained.
S4: and (5) after the TVC amplification factor curve obtained in the step (S3) is subjected to amplification factor correction according to hardware parameters, fitting and converting the TVC amplification factor curve into a voltage control curve in the ADCP. The specific conversion method can be performed by any existing technology, and is not limited.
The TVC curve accurate setting method described above is applied to a specific embodiment to facilitate a better understanding of the implementation process of the present invention for those skilled in the art.
Example 1
The specific implementation mode is explained by the accurate TVC curve setting method in the south China sea by taking the voyage flow measurement data in a certain spring of the 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
Figure GDA0002885829190000091
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 (SLC 150)Type-1), which sets the time for complete release of TVC to 30ms, which translates to a propagation distance:
Figure GDA0002885829190000092
(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:
Figure GDA0002885829190000093
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)
Figure GDA0002885829190000101
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);
Figure GDA0002885829190000102
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
Figure GDA0002885829190000111
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.
5) The signal propagation distance can be determined by the time the transducer receives the signal, and the total loss of propagation at that propagation distance can be calculated by sonar equations. Therefore, substituting the accurate reverberation parameters obtained in the step 1) into a sonar equation to obtain a signal propagation total loss calculation formula at different propagation distances, wherein the calculation formula of the signal propagation total loss EL is as follows:
Figure GDA0002885829190000112
wherein: SL denotes the sound source level; sVRepresents the volume scattering intensity; RL is the true echo signal sound level on the receiving transducer; theta-3dBRepresents the-3 dB beamwidth of the transducer; l is the layer thickness; a is absorption loss; r is a propagation distance;
further, based on the compensation of the total propagation loss, a TVC amplification factor calculation formula at the corresponding distance can be obtained according to the total signal propagation loss, wherein the TVC amplification factor TVCAmplification ofThe calculation formula of (2) is as follows:
TVCamplification of＝-EL (4)
6) And setting a propagation distance interval according to the resolution required by the TVC curve, and determining a starting change point and a terminating change point of the TVC curve according to hardware configuration. In order to avoid aftershocks after the transducer transmits signals and facilitate calculation, the distance r (unit: m) is taken as a TVC initial change point, r is the blind zone distance of the transducer in the ADCP, the TVC is set according to the recommendation value of a transducer manufacturer, and the TVC is not compensated within the distance r. In addition, the TVC dynamic range is YdB (depending on hardware), that is, the maximum amplification factor of TVC is YdB, and when the propagation loss reaches YdB compared with the starting point at a certain propagation distance, the position corresponding to the propagation distance is the end change point of the TVC curve.
After the 3 parameters of the TVC curve are determined, the TVC amplification factor curve can be set in the following manner: TVC compensation is not carried out within the initial change point; calculating TVC (transient voltage suppressor) amplification factors under different propagation distances according to calculation formulas (4) and (3) of the TVC amplification factors between the initial change point and the termination change point by taking the initial change point as a propagation distance zero point, and performing smooth filtering on the TVC amplification factor data point to form a smooth curve; after the termination of the change point, the TVC amplification is always maintained at the amplification corresponding to the termination of the change point, i.e., YdB is maintained and is not increased. Thus, the final TVC magnification curve is obtained.
7) Converting the TVC amplification factor curve obtained in the step 6) into a voltage control curve in the ADCP according to hardware parameters. The specific conversion method can be performed by any existing technology, and is not limited.
Example 2
The specific setting process of this embodiment is the same as that of embodiment 1, except that the accurate TVC curve setting method of the present invention is used to describe a specific implementation manner by taking the measured current data of voyage times in certain season of south sea as an example.
Autumn voyage data the average echo signal level versus distance curves (raw curves) for the four beams obtained in the same manner as in example 1 and the fitted graph are shown in fig. 4. Table 3 is a statistical table of the absorption coefficient values and the volume scattering intensity values corresponding to the transformations of FIG. 4.
TABLE 3
Beam 0 Beam 1 Beam 2 Beam 3 Mean value of
Absorption coefficient dB/m 0.0423 0.0422 0.0430 0.0430 0.0426
Volume scattering intensity dB -84.4 -84.2 -84.3 -84.0 -84.2
By using the inversion parameters, the TVC curve can be accurately set in the same manner as in example 1.
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 (10)

1. A TVC curve accurate setting method based on ADCP flow measurement signals is characterized by comprising the following steps:
s1: reducing ADCP actual flow measurement data to obtain real echo signal sound levels without TVC amplification at different propagation distances, and then carrying out real echo signal sound level reductionFitting based on theoretical echo intensity formula by using propagation distance as independent variable and real echo signal sound level as dependent variable, and obtaining absorption loss a and volume scattering intensity S by inversionVAn intrinsic accurate reverberation parameter;
s2: substituting the accurate reverberation parameters obtained in the step S1 into a sonar equation to obtain signal propagation total loss calculation formulas at different propagation distances, and further obtaining TVC (total harmonic distortion) amplification factor calculation formulas at corresponding distances according to the signal propagation total loss;
the calculation formula of the total signal propagation loss EL is as follows:
Figure FDA0002885829180000011
wherein: SL denotes the sound source level; sVRepresents the volume scattering intensity; theta-3dBRepresents the-3 dB beamwidth of the transducer; l is the layer thickness; a is absorption loss; r is a propagation distance;
the TVC amplification factor TVCAmplification ofThe calculation formula of (2) is as follows:
TVCamplification of＝-EL
S3: determining the propagation distance interval, the starting change point and the ending change point of the TVC curve, and then setting the TVC magnification curve, wherein the setting mode of the curve is as follows: TVC compensation is not carried out within the initial change point; calculating TVC (transient voltage suppressor) amplification factors under different propagation distances according to a calculation formula of the TVC amplification factors between the initial change point and the termination change point by taking the initial change point as a propagation distance zero point, and performing smooth filtering on the TVC amplification factor data point; after the change point is terminated, the TVC amplification factor is always kept as the amplification factor corresponding to the position of the change point;
s4: the TVC amplification curve obtained at S3 is converted into a voltage control curve in ADCP.
2. The method for accurately setting the TVC curve based on the ADCP flow measurement signal as claimed in claim 1, wherein the method for inverting the accurate reverberation parameter is:
s11: acquiring actual echo data of different profile layers measured by ADCP, and screening to obtain effective data for inversion;
s12: 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;
s13: fitting the effective data points obtained in the step S12 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: a is a constant value that does not change with propagation distance;
s14: based on the value A obtained in S13, the volume scattering intensity S is further calculated according to the formula (2)VThe true value of (d);
Figure FDA0002885829180000021
wherein: SL denotes the sound source level; theta-3dBRepresents the-3 dB beamwidth of the transducer; l is the layer thickness.
3. The method for accurately setting the TVC curve based on the ADCP flow measurement signal as claimed in claim 2, wherein in S11, the data in each section layer needs to be processed by outlier rejection in advance.
4. The method for accurately setting the TVC curve based on the ADCP flow measurement signal as claimed in claim 2, wherein in S11, a plurality of profile layers with smooth speed, no invalid data and no abrupt change between layers are selected for inversion.
5. The method for accurately setting the TVC curve based on the ADCP flow measurement signal as claimed in claim 2, wherein the curve fitting is performed by a least square method.
6. The method for accurately setting the TVC curve based on the ADCP flow measurement signal as claimed in claim 1, wherein when the ADCP is used for the voyage measurement, the actual flow measurement data of a voyage is selected as the calibration data, and the accurate reverberation parameter is obtained by inversion.
7. The method for accurately setting the TVC curve based on the ADCP flow measurement signal as claimed in claim 1, wherein when the ADCP is used for fixed-point measurement, actual flow measurement data are obtained in different seasons respectively, and accurate reverberation parameters in different seasons are obtained through inversion.
8. The method for accurately setting TVC curve based on ADCP flow measurement signal as claimed in claim 1, wherein said propagation distance interval is set according to TVC curve resolution.
9. The method as claimed in claim 1, wherein the TVC curve is set such that the initial change point is located outside the distance of the blind zone of the ADCP transceiver transducer and the final change point is a position where the fluctuation range of the propagation loss compared to the initial change point reaches the maximum amplification factor.
10. The method as claimed in claim 1, wherein in S4, the TVC amplification curve is combined with the hardware of the ADCP device to precisely fit the TVC voltage control curve.
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