阅读说明：本技术 一种小尺度分层水平二维流场观测方法 (Small-scale layered horizontal two-dimensional flow field observation method ) 是由 黄豪彩 谢心怡 许世杰 冯仁栋 郭庸 王章霖 方圆力 于 2021-05-17 设计创作，主要内容包括：本发明公开了一种小尺度分层水平二维流场观测方法,包括：将获得的原始数据进行互相关以获取声线传播时间；高精度声线模拟,获得声线模式、参考传播时间及时间窗信息；多径分辨与提取,计算不同路径的到达峰传播时间和声线长度；传播时间预处理；基于声线分布进行垂直分层；计算各层的声线长度和传播时间,构建系数矩阵,构建垂直分层流场,获得每一层的路径平均流速和反演误差；设定阈值,若反演误差超过设定值,返回步骤1进行迭代计算,直至反演误差满足要求；使用流函数法,以每一层的路径平均流速作为输入数据,反演多层水平二维流场；最后进行可视化处理。利用本发明,可以提高小尺度水域水文信息测量的精度和密度。(The invention discloses a small-scale layered horizontal two-dimensional flow field observation method, which comprises the following steps: performing cross correlation on the obtained original data to obtain sound ray propagation time; performing high-precision sound ray simulation to obtain a sound ray mode, reference propagation time and time window information; multipath resolution and extraction, calculating the arrival peak propagation time and the length of an acoustic line of different paths; preprocessing the propagation time; performing vertical layering based on sound ray distribution; calculating the sound ray length and the propagation time of each layer, constructing a coefficient matrix, constructing a vertical layered flow field, and obtaining the path average flow velocity and the inversion error of each layer; setting a threshold value, if the inversion error exceeds a set value, returning to the step 1 for iterative calculation until the inversion error meets the requirement; inverting a multi-layer horizontal two-dimensional flow field by using a flow function method and taking the path average flow velocity of each layer as input data; and finally, carrying out visualization processing. The invention can improve the accuracy and density of hydrological information measurement of small-scale water areas.)

1. A small-scale layered horizontal two-dimensional flow field observation method is characterized by comprising the following steps:

(1) acquiring original data of an observation water area by using an ultrasonic transceiver system, wherein the ultrasonic transceiver system adopts three ultrasonic transceivers to perform acoustic signal return transmission;

(2) performing cross correlation on the acquired original data to acquire sound ray propagation time;

(3) carrying out high-precision sound ray simulation, wherein the obtained sound ray simulation result comprises a sound ray mode, reference propagation time and time window information;

(4) performing multi-path resolution and extraction on the sound signals subjected to cross correlation in the step (2), setting a time window to extract sound ray information corresponding to sound ray simulation, and calculating the arrival peak propagation time and the sound ray length of different paths;

(5) preprocessing the arrival peak propagation time of different paths, eliminating abnormal data, defining the maximum difference value of mutual return propagation time, and removing the peak value which is identified by mistake;

(6) carrying out vertical layering based on sound ray distribution on the principle that each layer contains different sound rays as far as possible; calculating the length and the propagation time of the sound ray of each layer, constructing a coefficient matrix, constructing a vertical layered flow field, and obtaining the path average flow velocity and the inversion error of each layer;

(7) setting a judgment threshold, if the inversion error exceeds a set value, returning to the step (2) for iterative calculation until the inversion error meets the requirement;

(8) inverting a multi-layer horizontal two-dimensional flow field by using a flow function method and taking the path average flow velocity of each layer as input data;

(9) and carrying out visualization processing on the multilayer flow field.

2. The small-scale layered horizontal two-dimensional flow field observation method according to claim 1, wherein in the step (1), in the ultrasound transceiver system, three ultrasound transceivers all adopt a simultaneous transmission mode, so as to ensure that a bidirectional acoustic signal can be received at each moment.

3. The observation method for the small-scale layered horizontal two-dimensional flow field according to claim 1, wherein in the step (1), all three ultrasonic transceivers are fixed underwater by means of bottom surface mooring so as to ensure that the positions of the ultrasonic transceivers are unchanged.

4. The observation method of the small-scale layered horizontal two-dimensional flow field according to claim 1, wherein the specific process of the step (3) is as follows:

inputting a corresponding temperature profile and topographic data of a water area to be measured to perform sound ray simulation, and accurately calculating reference propagation time according to high-precision sound ray simulation;

and setting a time window according to the propagation delay of each sound ray so as to separate each sound ray path from the multi-path signal, thereby obtaining the propagation time of each sound ray for inversion and the corresponding sound ray length.

5. The observation method of the small-scale layered horizontal two-dimensional flow field according to claim 1, wherein the specific process of the step (4) is as follows:

for the sound signals subjected to cross correlation in the step (2), firstly extracting a peak value corresponding to a direct path, and realizing the subsequent peak value by means of high-precision sound ray simulation; comparing the propagation time corresponding to the related arrival peak with the sound ray simulation result, and selecting to obtain all the identified sound rays; and setting a time window and a signal-to-noise ratio threshold, and distinguishing and extracting all related arrival peaks and corresponding propagation time.

6. The small-scale layering horizontal two-dimensional flow field observation method according to claim 1, characterized in that in the step (6), j layers are layered on the vertical section of every two standing positions when vertical layering is performed;

for each sound ray, we obtain:v_jrepresents the path average flow rate of the j-th layer; t is t_i ^±Representing the forward and backward propagation time of the ith sound ray; l_ijRepresents the length of the ith sound ray passing through the jth layer; c_0jAnd δ C_jRespectively, the reference sound speed and the deviation of the actual sound speed from the reference sound speed of the j-th layer.

7. The observation method of the small-scale layered horizontal two-dimensional flow field according to claim 6, wherein the specific process of constructing the vertical layered flow field is as follows:

to formulaTaylor expansion was performed to obtain:will be provided withDefined as a matrix of coefficients, x ═ v_iIs defined as the vector to be inverted, n is defined as the observation error, y ═ Δ t_iThe measured reciprocal return sound propagation time difference is obtained;

obtaining the optimal solution of x expectation by adopting Lagrange methodThe lambda is determined by constraining the squared error value to be less than a preset value, which is calculated from the expected maximum error value, and then introducing an H-regularization matrix to smooth the result.

8. The small-scale layered horizontal two-dimensional flow field observation method according to claim 7, wherein an inversion error formula is as follows:

in the formula (I), the compound is shown in the specification,<nn^T>as a difference in propagation time Δ t_iThe desired variance value of.

9. The small-scale layered horizontal two-dimensional flow field observation method according to claim 1, wherein the specific process of the step (8) is as follows:

taking the path average flow rate of each layer as input data, carry into:

V_mjrepresents the path average flow velocity, L, of the j-th layer along each path_iRepresents the distance between two station positions corresponding to the ith path, D_k、Q_kRespectively a coefficient matrix to be solved and a known coefficient matrix; using a tapered least squares method to obtain the optimal solution for x expectationAnd determining the alpha value by combining an L curve method, solving the inverse problem again, and performing inversion to obtain a multilayer two-dimensional horizontal flow field.

Technical Field

The invention belongs to the technical field of hydrological monitoring, and particularly relates to a small-scale layered horizontal two-dimensional flow field observation method.

Background

The flow field distribution of small-scale water areas such as a marine ranch, a shallow sea hot liquid port, artificial upwelling and the like is closely related to the marine environment, the flow field observation of the small-scale water areas has very important scientific significance for the research of marine physics, chemistry, ecology and the like, and the research of providing a long-term, effective and high-precision flow field observation method for the small-scale water areas is widely concerned by scholars at home and abroad.

For example, chinese patent publication No. CN212872519U discloses an airborne acoustic doppler flow profiler and apparatus. The current acoustic doppler current profiler generally used for current velocity observation can obtain a vertical section two-dimensional flow field by navigation, but it is difficult to realize synchronous observation of a long time sequence.

Chinese patent publication No. CN109900256A discloses a self-adaptive marine mobile acoustic tomography system and method, which can significantly improve the accuracy of marine hydrological information measurement.

However, although the existing acoustic tomography technology can acquire large-area flow field information through an inversion method, the existing acoustic tomography technology can only calculate the average flow velocity along an acoustic line path or the horizontal flow field of the depth of an instrument, and the acquired flow field information is very limited, so that the requirements of monitoring small-scale water areas with high time and spatial resolution cannot be met.

Disclosure of Invention

The invention provides a small-scale layered horizontal two-dimensional flow field observation method which can improve the accuracy and density of small-scale water hydrological information measurement.

A small-scale layered horizontal two-dimensional flow field observation method comprises the following steps:

(1) acquiring original data of an observation water area by using an ultrasonic transceiver system, wherein the ultrasonic transceiver system adopts three ultrasonic transceivers to perform acoustic signal return transmission;

(2) performing cross correlation on the acquired original data to acquire sound ray propagation time;

(3) carrying out high-precision sound ray simulation, wherein the obtained sound ray simulation result comprises a sound ray mode, reference propagation time and time window information;

(4) performing multi-path resolution and extraction on the sound signals subjected to cross correlation in the step (2), setting a time window to extract sound ray information corresponding to sound ray simulation, and calculating the arrival peak propagation time and the sound ray length of different paths;

(5) preprocessing the arrival peak propagation time of different paths, eliminating abnormal data, defining the maximum difference value of mutual return propagation time, and removing the peak value which is identified by mistake;

(6) carrying out vertical layering based on sound ray distribution on the principle that each layer contains different sound rays as far as possible; calculating the length and the propagation time of the sound ray of each layer, constructing a coefficient matrix, constructing a vertical layered flow field, and obtaining the path average flow velocity and the inversion error of each layer;

(7) setting a judgment threshold, if the inversion error exceeds a set value, returning to the step (2) for iterative calculation until the inversion error meets the requirement;

(8) inverting a multi-layer horizontal two-dimensional flow field by using a flow function method and taking the path average flow velocity of each layer as input data;

(9) and carrying out visualization processing on the multilayer flow field.

Preferably, in the step (1), in the ultrasound transceiving system, three ultrasound transceivers all adopt a simultaneous transmission and reception transmission mode, so as to ensure that a bidirectional acoustic signal can be received at each time.

Furthermore, the three ultrasonic transceivers are all fixed under water in a bottom surface mooring mode so as to ensure that the positions of the ultrasonic transceivers are unchanged.

The specific process of the step (3) is as follows:

inputting a corresponding temperature profile and topographic data of a water area to be measured to perform sound ray simulation, and accurately calculating reference propagation time according to high-precision sound ray simulation;

and setting a time window according to the propagation delay of each sound ray so as to separate each sound ray path from the multi-path signal, thereby obtaining the propagation time of each sound ray for inversion and the corresponding sound ray length.

The specific process of the step (4) is as follows:

for the sound signals subjected to cross correlation in the step (2), firstly extracting a peak value corresponding to a direct path, and realizing the subsequent peak value by means of high-precision sound ray simulation; comparing the propagation time corresponding to the related arrival peak with the sound ray simulation result, and selecting to obtain all the identified sound rays; and setting a time window and a signal-to-noise ratio threshold, and distinguishing and extracting all related arrival peaks and corresponding propagation time.

In the step (6), j layers are formed on the vertical sections of every two standing positions when vertical layering is carried out,

for each sound ray, we obtain:v_jrepresents the path average flow rate of the j-th layer; t is t_i ^±Representing the forward and backward propagation time of the ith sound ray; l_ijRepresents the length of the ith sound ray passing through the jth layer; c_0jAnd δ C_jRespectively, the reference sound speed and the deviation of the actual sound speed from the reference sound speed of the j-th layer.

By the principle that each layer contains as different sound rays as possible, we mean: the most preferred way of vertical layering is to include different sound rays in each layer, allowing for situations where some layers do not include sound rays or where different layers include the same sound rays, in particular practice.

The specific process of constructing the vertical layered flow field comprises the following steps:

to formulaTaylor expansion was performed to obtain:will be provided withDefined as a matrix of coefficients, x ═ v_iIs defined as the vector to be inverted, n is defined as the observation error, y ═ Δ t_iThe measured reciprocal return sound propagation time difference is obtained;

obtaining the optimal solution of x expectation by adopting Lagrange methodThe lambda is determined by constraining the squared error value to be less than a preset value, which is calculated from the expected maximum error value, and then introducing an H-regularization matrix to smooth the result. .

The inversion error formula is:

in the formula (I), the compound is shown in the specification,<nn^T>as a difference in propagation time Δ t_iThe desired variance value of.

The specific process of the step (8) is as follows:

taking the path average flow rate of each layer as input data, carry into:

V_mjrepresents the path average flow velocity, L, of the j-th layer along each path_iRepresents the distance between two station positions corresponding to the ith path, D_k、Q_kRespectively a coefficient matrix to be solved and a known coefficient matrix; using a tapered least squares method to obtain the optimal solution for x expectationAnd determining the alpha value by combining an L curve method, solving the inverse problem again, and performing inversion to obtain a multilayer two-dimensional horizontal flow field.

Compared with the prior art, the invention has the following beneficial effects:

1. the invention only needs few observation stations to carry out acoustic tomography high-resolution imaging inversion without setting a plurality of fixed-point flow measurement.

2. The invention adopts a reciprocal transmission mode of sound and adopts the design of simultaneous transmission and reception signals to distinguish and extract a plurality of sound rays passing through different depths in a small scale range and obtain accurate transmission time of ultrasonic signals.

3. According to the invention, the horizontal flow fields at different depths are inversely drawn by solving the inverse problem twice. Under the condition that the vertical flow ratio is small and negligible, the multilayer two-dimensional flow field can well represent a three-dimensional flow field structure in an observation area, and a fine water flow distribution space is obtained.

4. The cyclic iteration method provided by the invention can effectively improve the observation precision of the small-scale flow field, and the inversion result of the multilayer horizontal flow field and the ADCP measurement result have good consistency.

Drawings

FIG. 1 is a schematic flow diagram of the process of the present invention;

FIG. 2 is a schematic diagram of the vertical layering between two stations in a preferred embodiment of the present invention;

FIG. 3 is a schematic diagram of the construction of a layered horizontal two-dimensional flow field according to a preferred embodiment of the present invention;

FIG. 4 is a graph of bottom horizontal flow field test results at a time in accordance with a preferred embodiment of the present invention.

Detailed Description

The invention will be described in further detail below with reference to the drawings and examples, which are intended to facilitate the understanding of the invention without limiting it in any way.

As shown in fig. 1, a small-scale layered horizontal two-dimensional flow field observation method includes the following steps:

step 1: raw data obtained by the system are cross-correlated to obtain the sound ray travel time. A first ultrasonic transceiver S1, a second ultrasonic transceiver S2 and a third ultrasonic transceiver S3 are respectively fixed under water of a water area to be observed to carry out mutual return transmission of acoustic signals. In this embodiment, a 10-order M-sequence acoustic signal is selected for signal design, where Q is 2(Q represents the number of carrier cycles occupied by M-sequence bits), so as to ensure that the acoustic signal has a high signal-to-noise ratio while satisfying simultaneous transmission and reception (i.e., transmission intervals between respective ultrasound transceivers are 0 s).

The first, second and third ultrasonic transceivers may each receive or transmit an ultrasonic signal having a center frequency of 50 kHz. The three ultrasonic transceivers are all fixed underwater in a bottom surface mooring mode, specifically, one end of each ultrasonic transceiver is anchored by a heavy object, the other end of each ultrasonic transceiver is connected by a floating ball, the connecting wire, the ultrasonic transceivers, the connecting wire and the heavy objects are all underwater, the connecting wire is always in a tight state during an experiment, and the fixing mode can ensure that the positions of the ultrasonic transceivers are almost unchanged. The temperature profile can be acquired by CTD (thermohalimeter) or TD chain (thermodepth meter). High-precision topographic data can be acquired through schemes such as CTD, shipborne ADCP (Doppler current profiler), single-beam sonar and multi-beam sonar, wherein the multi-beam sonar has the highest observation precision and can directly acquire three-dimensional topographic data. A bottom tracking mode of an on-board ADCP (doppler flow profiler) is used to acquire the terrain and slice profile flow velocities. High-precision sound ray simulation needs to be based on high-precision terrain data, so that the ADCP sailing observation carries out sailing back and forth for multiple times to collect enough terrain data, and the terrain data along the transmission line can be obtained by carrying out interpolation and projection on the terrain data obtained by the ADCP. The topographic data can also adopt schemes such as CTD, single-beam sonar, multi-beam sonar, wherein the multi-beam sonar observes the precision the highest, can directly acquire three-dimensional topographic data.

Step 2: and (3) high-precision sound ray simulation is carried out to obtain sound ray mode, reference propagation time and time window information. And inputting corresponding temperature profiles and topographic data to perform sound ray simulation, and accurately calculating the reference propagation time according to the high-precision sound ray simulation. And setting a time window according to the propagation delay of each sound ray so as to separate each sound ray path from the multi-path signal, thereby obtaining the propagation time of each sound ray for inversion and the corresponding sound ray length.

And step 3: step 1, after the sound signals received at a certain moment are subjected to cross correlation pairwise, the first arrival signal is a direct path, the peak value corresponding to the direct path is extracted firstly, and the subsequent peak value is realized by means of high-precision sound ray simulation. And comparing the propagation time corresponding to the correlation peak with the sound ray simulation result, and selecting to obtain all the sound rays which can be identified. And setting a time window and a signal-to-noise ratio threshold, and distinguishing and extracting all correlation peaks and corresponding propagation time.

And 4, step 4: and (5) preprocessing the propagation time and checking the system error. Firstly, abnormal data are removed, the maximum difference value of mutual return propagation time is defined, the peak value of error identification is removed, and system errors are detected and corrected to obtain high-quality observation data.

And 5: the vertical layering is performed based on the sound ray distribution on the principle that each layer contains different sound rays as much as possible. The vertical sections of every two standing positions are divided into 3 layers, and for each sound ray, the following sound ray can be obtained:

taylor expansion was performed to obtain:

the above equation is written in matrix form as follows:

order toDefining a coefficient matrix, x ═ v_iDefining the vector to be inverted, defining n as the observation error, y ═ Δ t_iThe measured inter-return sound propagation time difference is obtained.

Step 6: and calculating the sound ray length and the propagation time of each layer, constructing a coefficient matrix, constructing a vertical layered flow field, and obtaining the path average flow velocity and the inversion error of each layer. Using Lagrange's method to obtain the optimal solution of x expectationThe lambda is determined by constraining the squared error value to be less than a preset value, which is calculated from the expected maximum error value, and then introducing an H-regularization matrix to smooth the result. The H matrix here can be written as:

according to inversion errorAnd (4) continuously improving the inversion calculation precision by using an iterative method in the steps 1 to 4 in a reciprocating circulation manner, and further obtaining the path average flow velocity of each layer.

And 7: and (4) setting a judgment threshold, and if the inversion error of each layer exceeds a set value, returning to the step 1 to perform iterative calculation until the inversion error meets the requirement. According to inversion error<nn^T>As a difference in propagation time Δ t_iThe desired variance value of. And (3) continuously improving the inversion calculation precision by using an iterative method to circulate from the step 1 to obtain the path average flow velocity of each layer.

And 8: using a flow function method, taking the average flow velocity of the path of each layer asTo input data, a multi-layer horizontal two-dimensional flow field is inverted. Taking the average flow velocity of each layer as input dataV_mjRepresents the path average flow velocity, L, of the j-th layer along each path_iRepresents the distance between two station positions corresponding to the ith path, D_k，Q_kThe coefficient matrix to be solved and the known coefficient matrix are respectively. Herein can be written as:

using a tapered least squares method to obtain the optimal solution for x expectationAnd determining the alpha value by combining an L curve method, solving the inverse problem again, and performing inversion to obtain a multilayer two-dimensional horizontal flow field.

And step 9: and finally, carrying out visualization processing on the multilayer flow field.

In order to verify the effect of the invention, the observation experiment is carried out on a certain water body area of the Changsha yellow material reservoir by utilizing the invention to obtain the flow field spatial distribution of the bottom flow, and the method specifically comprises the following steps:

the ultrasonic extension set comprises the following devices, three ultrasonic extension sets have the same structure and mainly comprise an SH7145F single chip microcomputer, a GPS positioning module, an SD memory card, a matched filter, a power amplifier, a filtering amplifier, a band-pass filter, a low-pass filter, an ultrasonic receiving and transmitting dual-purpose transducer and an external power supply.

The station spacing of the three ultrasonic extension sets S1, S2 and S3 is not more than 300m, the ultrasonic receiving and transmitting dual-purpose transducers of each station are arranged at about 20m under water, and a simultaneous transmitting and receiving sound reciprocal transmission mode is adopted in the experimental process. Firstly, time synchronization is carried out on 3 ultrasonic extension sets, 10-order M-sequence acoustic signals are selected, and Q is 2(Q represents the number of carrier cycles occupied by M-sequence bits) so as to ensure that the acoustic signals have higher signal-to-noise ratio while meeting simultaneous transmission and reception (namely, the transmission interval between each ultrasonic transceiver is 0 s). The first, second and third ultrasonic transceivers can receive or transmit ultrasonic signals with the center frequency of 50 kHz.

According to the step 2, the direct path is a straight line which only passes through almost no temperature change, so that the station distance between two stations can be accurately estimated by using the sound ray length of the direct path: S1-S2 are 270m, S1-S3 are 283.64m, and S2-S3 are 224.01 m.

The plurality of transmission lines on the three transmission sections of S1-S2, S1-S3, S2-S3 are identified and extracted through step 3: the direct path, the surface reflection path and the bottom reflection path, and the sound ray length and the propagation time of each transmission path after layering are calculated and obtained, as shown in table 1 below. TL represents Total Length (Total Length) and TT represents Travel Time (Travel Time).

TABLE 1

The program corresponding to the method is written by MATLAB, a vertical layered flow field is constructed firstly, the path average flow velocity of each layer on the transmission section of S1-S2, S1-S3 and S2-S3 is calculated, and the flow velocity of the third layer is found to be large and the fluctuation is obvious. And taking the average flow velocity of the path of the third layer as a known quantity, solving the inverse problem again by using a flow function method, and drawing the distribution condition of the flow field at the third layer, namely the bottom. As shown in FIG. 4, from the calculation results, the size of the observed bottom flow is 0.5-1.2m/s, and the fluctuation is large, which shows the effectiveness of the method in observing the layered horizontal two-dimensional flow field in a small-scale water area.

The embodiments described above are intended to illustrate the technical solutions and advantages of the present invention, and it should be understood that the above-mentioned embodiments are only specific embodiments of the present invention, and are not intended to limit the present invention, and any modifications, additions and equivalents made within the scope of the principles of the present invention should be included in the scope of the present invention.