阅读说明：本技术 一种基于分数阶傅里叶变换的变频声呐测深方法 (Frequency conversion sonar depth sounding method based on fractional Fourier transform ) 是由 张建 陈晓静 耿彦章 于 2019-11-12 设计创作，主要内容包括：本发明涉及一种基于分数阶傅里叶变换的变频声呐测深方法,具体包括以下步骤：(1)线性调频信号生成；(2)功率放大；(3)信号发射；(4)监听回波信号；(5)判断收到回波：(6)计算显示距离。本发明的一种基于分数阶傅里叶变换的变频声呐测深方法基于线性调频信号在分数阶傅里叶变换域上能量高度集中的特点进行声呐测深,可以有效分辨出极低信噪比情况下的声呐回波信号,从而大大加强了声呐的远距离探测功能。(The invention relates to a frequency conversion sonar depth sounding method based on fractional Fourier transform, which specifically comprises the following steps: (1) generating a linear frequency modulation signal; (2) amplifying power; (3) signal transmission; (4) monitoring an echo signal; (5) judging the received echo: (6) the display distance is calculated. The frequency conversion sonar depth measurement method based on fractional Fourier transform carries out sonar depth measurement based on the characteristic that linear frequency modulation signals are highly concentrated in energy in a fractional Fourier transform domain, can effectively distinguish sonar echo signals under the condition of extremely low signal-to-noise ratio, and therefore greatly strengthens the remote detection function of sonar.)

1. A frequency conversion sonar depth sounding method based on fractional Fourier transform is characterized in that: the method specifically comprises the following steps:

(1) generating a Chirp signal Chirp by using a signal generating device;

(2) transmitting the linear frequency modulation signal to a power amplifier, amplifying the energy of the linear frequency modulation signal to energy AP through the power amplifier, and transmitting the linear frequency modulation signal S (t) subjected to power amplification to an ultrasonic transducer through the power amplifier;

(3) transmitting a chirp signal s (t) using an ultrasonic transducer;

(4) at transmission waiting time T_bIn the time range of the monitoring module, the echo condition generated by the signal is monitored, the monitoring method is to carry out analog-to-digital conversion on a signal wire of the ultrasonic transducer, and a digital signal obtained by the conversion is transmitted into the signal processing module;

(5) for frame-by-frame fractional Fourier analysis of echo signals, the angle parameters of the fractional Fourier analysis satisfy the following conditions:

wherein β is a corresponding fractional Fourier transform angle, the corresponding fractional Fourier transform being:

because the chirp echo signal presents an impact signal characteristic in the angle of fractional Fourier transform, the impact signal with beta is detected in each frame of echo, the spectral energy of the data frame is calculated, and the detected data frame is continuously stored;

(6) when the energy of the impact signal is continuously enhanced when continuous multiple frames appear, and reaches the maximum value in the next frames and lasts for n frames, judging that the echo signal is received;

(7) and after judging that the echo signal is received, recording the ordinal number of the current frame in the period as k, and carrying out depth measurement.

2. The frequency conversion sonar depth measurement method based on fractional Fourier transform according to claim 1, characterized in that: the Chirp signal Chirp in the step (1) satisfies the following conditions:

wherein A is the generated ChirAmplitude of p, f₁，f₂The lower limit frequency and the upper limit frequency are respectively used for generating the Chirp, T is the total duration of the Chirp, and T is the Chirp generation time.

3. The frequency conversion sonar depth measurement method based on fractional Fourier transform according to claim 1, characterized in that: the energy in the step (2) is usually AP larger than 2400W, the frequency response curve of the power amplifier is kept flat in a response frequency range, the lower limit of the frequency response range of the power amplifier is smaller than f1, and the upper limit of the frequency response range is larger than f 2.

4. The frequency conversion sonar depth measurement method based on fractional Fourier transform according to claim 1, characterized in that: when the chirp signal s (T) is transmitted in the step (3), the duration T of each transmission cycle_sExpressed as: t is_s＝T+T_bWherein, T_bRepresenting the time of transmission latency in one cycle.

5. The frequency conversion sonar depth measurement method based on fractional Fourier transform according to claim 4, characterized in that: in the step (3), T_bThe time meets the following conditions:

wherein sigma is a margin coefficient, the value of sigma is 0.1-0.3, c is the sound velocity in seawater, and L is the maximum length capable of measuring depth.

6. The frequency conversion sonar depth measurement method based on fractional Fourier transform according to claim 1, characterized in that: in the step (5), the time-division frame duration Tc is greater than T, and the frame overlap rate is 95%, i.e., the frame shift is 5%.

7. The frequency conversion sonar depth measurement method based on fractional Fourier transform according to claim 1, characterized in that: the number of frames for continuously storing the spectral energy of the data frames in the step (5) is less than or equal to k frames, wherein k is 20 Ts/T.

8. The frequency conversion sonar depth measurement method based on fractional Fourier transform according to claim 1, characterized in that: the sounding distance formula in the step (7) is as follows:

Technical Field

The invention relates to the technical field of sonar depth measurement, in particular to a frequency conversion sonar depth measurement method based on fractional Fourier transform.

Background

1. Active sonar technology

The active sonar is called echo locator, which is a general name of various sonars for actively transmitting underwater acoustic signals and acquiring target parameters from underwater target reflection echoes. The device is used for detecting underwater targets and measuring the moving elements such as distance, direction, navigational speed, course and the like. The sonar emits a certain detection signal, the signal meets an obstacle or a target on a path propagated in water, the signal is reflected back to reach an emitting point to be received, and target information is stored in an echo reflected back by the target, so that parameters of the target can be judged according to the received echo signal. The sonar can accurately measure the target distance and can detect a fixed target. The method has poor concealment, short action distance and reverberation interference.

2. Linear frequency modulated signal

Chirp modulation (LFM) is a spread spectrum modulation technique that does not require a pseudo-random code sequence. Because the frequency bandwidth occupied by the chirp signal is much larger than the information bandwidth, a large system processing gain can be obtained. Chirp signals are also called Chirp Spread Spectrum (CSS) because their spectral bandwidth falls within the audible range and they are heard as bird sounds. The LFM technology is widely applied to radar and sonar technologies, for example, in the radar positioning technology, the LFM technology can increase the radio frequency pulse width, improve the average transmitting power, increase the communication distance and simultaneously maintain enough signal spectrum width without reducing the distance resolution of the radar.

3. Fractional Fourier transform

Fractional fourier transform (FRFT) is a mathematical generalization of Fourier Transform (FT). The Fourier transform is to change the viewing angle from time domain to frequency domain, the fractional Fourier transform is to rotate the coordinate axis of the time-frequency plane by the angle of the viewing time-frequency plane, and then to analyze the information from the angle of the viewing frequency domain. One operator that the fractional fourier transform has added is the angle of this rotation. The rotation angle is expressed in a fractional form, and the value is 0-1, and when the value is 1, the rotation angle is equivalent to Fourier transform. The reason for performing a fractional fourier transform on the information is that: most information is non-stationary signals, the significant characteristics of the non-stationary signals cannot be analyzed only by Fourier transform, and the application of fractional Fourier transform mainly can select the angle with the most concentrated information to analyze, namely, the result with the largest amplitude is selected from the results obtained by different fractional orders, so that the fractional order of the result is the optimal order.

Disclosure of Invention

The invention aims to solve the technical problem of providing a frequency conversion sonar depth measurement method based on fractional Fourier transform to solve the problems of poor concealment and reverberation interference of a sonar depth measurement technology in the prior art.

In order to solve the technical problems, the technical scheme of the invention is as follows: a frequency conversion sonar depth sounding method based on fractional Fourier transform is characterized in that: the method specifically comprises the following steps:

(1) generating a Chirp signal Chirp by using a signal generating device;

(2) transmitting the linear frequency modulation signal to a power amplifier, amplifying the energy of the linear frequency modulation signal to energy AP through the power amplifier, and transmitting the linear frequency modulation signal S (t) subjected to power amplification to an ultrasonic transducer through the power amplifier;

(3) transmitting a chirp signal s (t) using an ultrasonic transducer;

(4) at transmission waiting time T_bIn the time range of the monitoring module, the echo condition generated by the signal is monitored, the monitoring method is to carry out analog-to-digital conversion on a signal wire of the ultrasonic transducer, and a digital signal obtained by the conversion is transmitted into the signal processing module;

(5) for frame-by-frame fractional Fourier analysis of echo signals, the angle parameters of the fractional Fourier analysis satisfy the following conditions:

wherein β is a corresponding fractional Fourier transform angle, the corresponding fractional Fourier transform being:

because the chirp echo signal presents an impact signal characteristic in the angle of fractional Fourier transform, the impact signal with beta is detected in each frame of echo, the spectral energy of the data frame is calculated, and the detected data frame is continuously stored;

(6) when the energy of the impact signal is continuously enhanced when continuous multiple frames appear, and reaches the maximum value in the next frames and lasts for n frames, judging that the echo signal is received;

(7) and after judging that the echo signal is received, recording the ordinal number of the current frame in the period as k, and carrying out depth measurement.

Further, the Chirp signal Chirp in the step (1) satisfies the following condition:

where A is the amplitude of the generated Chirp, f₁，f₂The lower limit frequency and the upper limit frequency are respectively used for generating the Chirp, T is the total duration of the Chirp, and T is the Chirp generation time.

Further, the energy in step (2) should generally be AP greater than 2400W, the frequency response curve of the power amplifier is kept flat in the response frequency range, the lower limit of the frequency response range of the power amplifier is less than f1, and the upper limit of the frequency response range is greater than f 2.

Further, when the chirp signal s (T) is transmitted in the step (3), the duration T of each transmission cycle is_sExpressed as: t is_s＝T+T_bWherein, T_bRepresenting the time of transmission latency in one cycle.

Further, in the step (3), T_bThe time meets the following conditions:

wherein sigma is a margin coefficient, the value of sigma is 0.1-0.3, c is the sound velocity in seawater, and L is the maximum length capable of measuring depth.

Further, the time frame duration Tc is greater than T when performing frame-by-frame analysis in step (5), and the frame overlap rate is 95%, that is, the frame shift is 5%.

Further, the number of frames of the spectrum energy of the data frames continuously saved in the step (5) is less than or equal to k frames, wherein k is 20 Ts/T.

Further, the sounding distance formula in step (7) is as follows:

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

the frequency conversion sonar depth measurement method based on fractional Fourier transform carries out sonar depth measurement based on the characteristic that linear frequency modulation signals are highly concentrated in energy in a fractional Fourier transform domain, can effectively distinguish sonar echo signals under the condition of extremely low signal-to-noise ratio, and therefore greatly strengthens the remote detection function of sonar.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments are briefly described below, and it is obvious that the drawings in the following description are only some embodiments described in the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.

Fig. 1 is a flow chart of a frequency conversion sonar depth sounding method based on fractional order fourier transform.

Fig. 2 is a spectrum energy diagram of a frequency conversion sonar depth sounding method based on fractional order fourier transform when echo signals are received.

Detailed Description

The technical solution of the present invention will be clearly and completely described by the following detailed description.

The invention provides a fractional Fourier transform-based frequency-conversion sonar depth sounding method, which specifically comprises the following steps:

(1) using a signal generating device to generate a Chirp signal Chirp, wherein the Chirp signal Chirp satisfies the following conditions:

wherein A is the formed CAmplitude of hirp, f₁，f₂Respectively generating a lower limit frequency and an upper limit frequency of the Chirp, wherein T is the total duration of the Chirp, and T is the Chirp generation time;

(2) the method comprises the steps of transmitting a chirp signal to a power amplifier, amplifying the energy of the chirp signal to energy AP through the power amplifier, and transmitting the power-amplified chirp signal S (t) to an ultrasonic transducer through the power amplifier, wherein the energy AP is generally larger than 2400W, the frequency response curve of the power amplifier is kept flat in a response frequency range, the lower limit of the frequency response range of the power amplifier is smaller than f1, and the upper limit of the frequency response range is larger than f 2.

(3) Transmitting a chirp signal S (T) using an ultrasonic transducer, each transmission cycle having a duration T_sExpressed as:

T_s＝T+T_b

wherein, T_bRepresents the time of transmission latency in one cycle; t is_bThe time meets the following conditions:

wherein sigma is a margin coefficient, the value of sigma is 0.1-0.3, c is the sound velocity in seawater, and L is the maximum length capable of measuring depth.

(4) At transmission waiting time T_bIn the time range of the monitoring module, the echo condition generated by the signal is monitored, the monitoring method is to carry out analog-to-digital conversion on a signal wire of the ultrasonic transducer, and a digital signal obtained by the conversion is transmitted into the signal processing module;

(5) and carrying out frame-by-frame fractional Fourier analysis on the echo signal, wherein the frame-by-frame analysis is carried out, the time Tc of a time frame is greater than T, the frame overlapping rate is 95%, namely the frame shift is 5%. The angle parameters using fractional fourier analysis should satisfy the following condition:

wherein β is a corresponding fractional Fourier transform angle, the corresponding fractional Fourier transform being:

because the chirp echo signal presents an impact signal characteristic in the angle of fractional Fourier transform, the impact signal existing in beta is detected in each frame of echo, the spectral energy of the data frame is calculated, and the detected data frame is continuously stored, wherein the frame number of the spectral energy of the data frame is continuously stored is less than or equal to k frames, and k is 20 Ts/T. When the energy of the impact signal is continuously enhanced when a plurality of continuous frames appear, reaches the maximum value in the following frames and lasts for n frames, judging that the echo signal is received as shown in figure 2;

(6) after judging that the echo signal is received, recording the ordinal number of the current frame in the period as k, and carrying out depth measurement by a final depth measurement distance formula, wherein the depth measurement distance formula is as follows:

the above-mentioned embodiments are merely descriptions of the preferred embodiments of the present invention, and do not limit the concept and scope of the present invention, and various modifications and improvements made to the technical solutions of the present invention by those skilled in the art should fall into the protection scope of the present invention without departing from the design concept of the present invention, and the technical contents of the present invention as claimed are all described in the technical claims.