JP4930130B2 - Active sonar device, received signal processing method for sonar, and signal processing program thereof - Google Patents

Description

  The present invention relates to an active sonar device and the like, and more particularly to an active sonar device using a linear frequency modulation signal, a received signal processing method for sonar, and a signal processing program thereof.

The active sonar device generates and transmits a sound wave, processes the received signal, and determines the direction and distance of the target based on the reflected wave (echo signal) from the target included in the received signal. It refers to the specified underwater acoustic device.
In a conventional active sonar apparatus, replica correlation is used as a method of detecting an echo signal from a received signal. Replica correlation is a signal processing method for calculating the degree of correlation between a sample signal (replica signal) and an input signal, and is also called cross-correlation. In the active sonar apparatus, the degree of correlation with a signal received as a replica signal is calculated, and an echo signal is detected.

  At this time, by repeating the replica correlation while shifting the time with respect to the input signal, the maximum value of the correlation degree appears at the time when the waveforms are most similar. Two types of transmission signals are mainly used: a linear frequency modulation (LFM) signal whose frequency is linearly modulated and a constant frequency continuous wave (CW) signal. Here, when an LFM signal whose frequency changes linearly with time is used, even if the reflected wave from the target is weak, the signal-to-noise (SN) ratio can be improved by signal processing.

On the other hand, when the target is moving, echo signals reflected from the target are observed with different frequencies of the propagating sound waves depending on the relative speed between the target and the observation point. This phenomenon is called Doppler shift. In the active sonar apparatus using the replica correlation by the LFM signal, when the Doppler shift occurs, a difference occurs between the input signal inputted to the target and the replica signal, and the degree of correlation becomes small. Therefore, when the SN ratio is small, there is a problem that detection becomes difficult and the detection area is narrowed.
On the other hand, it is easier to detect the relative speed with respect to the target and the Doppler shift by using a CW signal having only a single frequency component.

Several prior arts have been reported for the purpose of solving such problems and facilitating signal detection even when a Doppler shift occurs.
For example, an LFM signal whose frequency is increased to decreased or inverted from decreased to increased in the middle of the pulse width is transmitted, and the replica correlation for the increased frequency LFM received signal and the replica correlation for the decreased frequency LFM received signal are transmitted. A method for measuring the Doppler shift of a received signal with a time difference between detection results by two replica correlations has been reported (see Patent Document 1).
In addition, a method has been reported in which two LFM signals, an LFM signal with an increasing frequency and an LFM signal with a decreasing frequency, are transmitted, the time of the two received signals is aligned, correlation processing is performed, and the effect of Doppler shift is eliminated. (See Patent Document 2).

  Further, the LFM reception band of the input signal is divided into a plurality of parts, the signal component of each divided band is detected, the level of the detection signal is compared with a predetermined level, and the signal is converted to a 1 or 0 bit signal. The technique of detecting the Doppler shift according to the order of the pulse train (see Patent Document 3), and using two replica signals of two signals obtained by shifting the transmission signal to a higher frequency and a lower frequency by the same frequency width, By performing replica correlation, a technique for obtaining an echo signal including a Doppler shift from the ratio of the maximum amplitude values of two correlation results for a certain time (see Patent Document 4), positive Doppler shift, negative Doppler shift, no Doppler shift The three replica signals and the input signal (received signal) are subjected to correlation processing, and the three correlation results are subjected to three-value interpolation (Lagrange interpolation). Accordingly, such techniques for measuring the Doppler shift of the target (see Patent Document 5) have also been reported.

  Although not using an LFM signal, a technique for reproducing a Doppler frequency waveform by transmitting and receiving a plurality of pulse beams by PRF (Pulse Repeat Frequency) and arranging the levels in time series (see Patent Document 6). Reported is a technology that generates a pseudo continuous wave by connecting reflected echo signals that are sequentially input, and realizes high frequency resolution by Fourier transforming the pseudo continuous wave (see Patent Document 7). Has been.

JP 59-225375 A Japanese Patent Laid-Open No. 08-114672 Japanese Patent Laid-Open No. 03-115879 Japanese Patent Laid-Open No. 03-242586 Japanese Patent Laid-Open No. 07-120553 JP 2000-162317 A JP 2000-352585 A

As described above, in the conventional active sonar apparatus, various countermeasures are taken to cope with the Doppler shift.
However, the methods disclosed in Patent Documents 1 and 2 need to transmit two types of LFM signals of an increasing frequency and a decreasing frequency. In the method disclosed in Patent Document 3, it is necessary to prepare a plurality of filters and detection circuits in order to provide a plurality of reception bands. In addition, the methods disclosed in Patent Documents 4 and 5 must be prepared to generate a plurality of replica signals. Furthermore, the methods disclosed in Patent Documents 6 and 7 require complicated signal processing.
Thus, in any case, there is a disadvantage that the circuit configuration becomes complicated, the hardware increases, and the cost increases.

[Object of the present invention]
The present invention improves the inconvenience of the above-mentioned conventional example, maintains a stable signal detection performance, increases the detection accuracy of the received signal, and improves the time resolution of the signal detection time. It is an object of the present invention to provide a received signal processing method and a signal processing program thereof.

In order to solve the above problems, the active sonar device of the present invention performs sampling conversion on the received signal of the received underwater reflected echo based on the sampling frequency having the same frequency change rate as the frequency change rate of the transmission signal, and the echo signal and An echo signal detecting means for detecting the position; and a received signal cutting out means for cutting out the echo signal portion detected by the echo signal detecting means from the received signal. Replica correlation processing means is provided for performing replica correlation processing using a signal as a replica signal, thereby calculating a signal detection time of the echo signal (claim 1).
As a result, it is possible to realize an active sonar device capable of detecting a signal detection time accurately and stably by detecting a portion where an echo signal is present using sampling conversion and processing the portion by replica correlation. .

  In order to solve the above problem, an active sonar device according to the present invention includes a signal transmission unit that converts a transmission signal composed of a pulse of a frequency-modulated wave whose frequency changes with time into a sound wave, and a reflected sound wave from a target. A replica receiving unit including a signal receiving unit that receives an underwater acoustic signal including a signal and converts the signal into an electric signal to be a received signal, and a replica correlation unit that performs replica correlation processing on the received signal as a replica signal. The replica correlation processing means is an active sonar apparatus configured to measure a distance from the target by obtaining a delay time from the time of transmission of the transmission signal. The signal is subjected to sampling conversion at a sampling frequency having the same frequency change rate as the frequency change rate of the transmission signal, and an echo signal from the received signal and An echo signal detecting means for detecting the position of the received signal, and a received signal cutting out means for cutting out an echo signal portion detected by the echo signal detecting means from the received signal, wherein the replica correlation processing means is provided by the received signal cutting out means. A configuration is adopted in which the echo signal of the cut-out area is the target of the replica correlation processing (claim 2).

  As a result, stable signal detection is possible, and only the time portion when the echo signal is detected can be cut out and replica correlation processing can be performed.Therefore, even if the signal detection threshold is lowered, it is erroneous even if the signal detection threshold is reduced. Thus, it is possible to eliminate the detection of a false alarm and further narrow the signal processing section, so that an active sonar device capable of improving the time resolution of the signal detection time can be realized.

Here, the echo signal detection means includes a sampling conversion unit that performs sampling conversion of the received signal at a sampling frequency having the same frequency change rate as the frequency change rate of the transmission signal, and the sample-converted pseudo CW signal. A Fourier transform unit that performs a short-time Fourier transform, and sequentially shifts the received signal by setting a predetermined cut-out width in advance, and cuts out the CW signal each time and operates each of the transform units to change the frequency and level. It is good also as a structure containing the cut-out echo production | generation part which produces | generates an echo signal, and the signal detection part which pinpoints and detects the echo of the maximum level among the some cut-out echoes produced | generated by this cut-out echo production | generation part as an echo signal ( Claim 3).
Thereby, it is possible to realize an echo signal detection means that can accurately determine the position of the echo signal and cut out only that portion.

Further, the echo signal detection means is provided with a Doppler shift amount calculation unit that takes in an output signal of the echo signal detection means and calculates a Doppler shift amount for the transmission signal of the echo signal, and the replica correlation processing means includes: When generating the replica signal, a configuration may be provided with a correction replica signal generation function for generating a correction replica signal in which the frequency band of the transmission signal is corrected based on the Doppler shift amount output from the Doppler shift amount calculation unit. (Claim 4).
As a result, even when Doppler occurs, the detection time lag due to the replica correlation process can be corrected, and the accuracy of the signal detection time can be improved.

Here, the Doppler shift amount calculation unit interpolates a plurality of cut echoes generated by the cut echo generation unit to specify a vertex position of the interpolation curve, and uses the specified vertex position as the echo signal. The signal reception time detection function for detecting the detected time, the echo frequency interpolation function for interpolating the frequency corresponding to the detected time from the frequency of the plurality of cut echoes, and the echo frequency interpolation function are activated. It is good also as a structure provided with the shift amount calculation function which calculates the difference of the interpolation frequency obtained and the lower limit frequency in the said transmission signal, and makes this a Doppler shift amount (Claim 5).
As a result, an active sonar apparatus capable of correcting the replica correlation processing by obtaining the Doppler shift amount by calculation in the sampling conversion unit can be realized.

In addition, the replica correlation processing unit includes a correction replica signal generation unit that generates a correction replica signal in which the frequency of the transmission signal is corrected based on the Doppler shift amount output from the Doppler shift amount calculation unit, and the received signal clipping A replica correlator that performs a replica correlation process using the transmission signal as a replica signal for the echo signal portion cut out by the means to obtain a time-series correlation between the two signals, and correlation data obtained by the replica correlation And a time calculation unit that detects a time at which a signal whose level exceeds a preliminarily assumed threshold is located (claim 6).
As a result, by correcting the replica signal used for the correlation calculation, even if there is a Doppler shift, the active sonar capable of improving the detection accuracy of the correlation degree and improving the time resolution of the signal detection time in the replica correlation processing An apparatus can be realized.

In order to solve the above-described problem, the received signal processing method for a sonar of the present invention performs sampling conversion on a received signal of an underwater reflected echo based on a sampling frequency having the same frequency change rate as the frequency change rate of a transmission signal. An echo signal detection step for detecting an echo signal and its position, and a reception signal cut-out step for cutting out the detected echo signal portion from the reception signal, and replicating the transmission signal for the cut-out echo signal portion A replica correlation process is performed for performing a replica correlation process as a signal, and thereby calculating a signal detection time of the echo signal.
This realizes a sonar received signal processing method capable of detecting a signal detection time accurately and stably by detecting a portion where an echo signal is present using sampling conversion and processing the portion by replica correlation. be able to.

  In order to solve the above problems, the received signal processing method for a sonar of the present invention converts a transmission signal composed of a pulse of a frequency-modulated wave whose frequency changes with time into a sound wave and transmits the sound, and includes a reflected sound wave from a target. After receiving the acoustic signal and converting it into an electrical signal to obtain a reception signal, replica correlation processing is performed on the reception signal by the replica correlation processing means using the transmission signal as a replica signal, thereby transmitting the transmission signal. In an active sonar received signal processing method for obtaining a delay time from time and measuring a distance to the target, the received signal is sampled and converted at a sampling frequency having the same frequency change rate as the frequency change rate of the transmission signal. An echo signal detection step for detecting an echo signal from the received signal, and an echo signal detected in the echo signal detection step A reception signal cut-out step of cutting out the portion from the transmission signal, and a replica correlation processing step in which the replica correlation processing means executes the replica correlation processing using the echo signal of the area cut out in the reception signal cut-out step as the target of the replica correlation processing; (Claim 8).

  As a result, stable signal detection is possible by cutting out only the time part when the echo signal is detected and performing replica correlation processing, and even if the detection threshold of the signal is lowered except for the influence of noise outside the signal processing interval, Thus, it is possible to eliminate the detection of a false alarm and further narrow the signal processing section, so that it is possible to realize a sonar received signal processing method capable of improving the time resolution of the signal detection time.

Here, the echo signal detection step includes a first step of performing sampling conversion of the received signal at a sampling frequency having the same frequency change rate as the frequency change rate of the transmission signal, and the sampling-converted pseudo CW signal. And a second step of performing a Fourier transform for a short time, a predetermined cutout width is set in advance with respect to the received signal, and sequentially shifted, and each time the CW signal is cut out and each converter is operated to have a different frequency and level. A configuration including a third step of generating a plurality of echo signals, and a fourth step of identifying and detecting an echo of the maximum level among the plurality of cut-out echoes generated in the third step as an echo signal; (Claim 9).
As a result, it is possible to realize a sonar received signal processing method capable of accurately determining the position of the echo signal, eliminating the detection time shift in the replica correlation process, and improving the accuracy of the signal detection time.

Further, the replica used for the replica correlation processing is provided with a Doppler shift amount calculating step for calculating the Doppler shift amount of the echo signal by incorporating the output signal in the echo signal detecting step in the echo signal detecting step. The signal may be a corrected replica signal obtained by correcting the frequency band of the transmission signal based on the Doppler shift amount calculated in the Doppler shift amount calculating step.
Thereby, even when Doppler occurs, it is possible to realize a sonar received signal processing method that can correct the detection time shift in the replica correlation processing and improve the accuracy of the signal detection time.

Furthermore, the Doppler shift amount calculating step interpolates a plurality of cut-out echoes generated in the third step of the echo signal detection step to specify the vertex position of the interpolation curve and the specified vertex position A signal reception time detection step in which the detection time of the echo signal is used, an echo frequency interpolation step of interpolating a frequency corresponding to the detected time from the frequencies of the plurality of cut-out echoes, and the echo frequency interpolation step It may be configured to include a shift amount calculating step of calculating a difference between an interpolation frequency obtained by operating and a lower limit frequency in the transmission signal and using this as a Doppler shift amount.
Thereby, the received signal processing method for sonar which can correct | amend replica correlation processing by calculating | requiring Doppler shift amount by calculation in a sampling conversion part is realizable.

Further, the replica correlation processing step includes a correction replica signal generation step of generating a correction replica signal in which the frequency band of the transmission signal is corrected based on the Doppler shift amount output in the Doppler shift amount calculation step, and the received signal A correlation degree calculation step that performs replica correlation processing using the transmission signal as a replica signal for the echo signal portion cut out in the cutout step to obtain a time series correlation between the two signals, and obtained by this correlation degree calculation step And a time calculating step in which a time at which a signal whose level exceeds a preliminarily assumed threshold is located is set as a detection time (claim 12).
As a result, by correcting the replica signal used for correlation calculation, even for Doppler shift, the detection accuracy of correlation degree can be improved and the time resolution of signal detection time in replica correlation processing can be improved. A received signal processing method can be realized.

In order to solve the above problems, the received signal processing program for sonar of the present invention performs sampling conversion on the received signal of the received underwater reflected echo based on the sampling frequency having the same frequency change rate as the frequency change rate of the transmission signal. Echo signal detection function for detecting an echo signal and its position, a received signal cut-out function for cutting out the detected echo signal portion from the received signal, replica correlation for the cut-out echo signal portion as a target and the transmission signal as a replica signal The computer is caused to execute a replica correlation processing function that performs processing and thereby calculates a signal detection time of the echo signal (claim 13).
This realizes a received signal processing program for sonar that can detect a signal detection time accurately and stably by detecting a portion where an echo signal is present using sampling conversion and processing the portion by replica correlation. be able to.

  In order to solve the above problems, the received signal processing program for sonar of the present invention includes a signal transmission unit that converts a transmission signal composed of a pulse of a frequency-modulated wave whose frequency changes with time into a sound wave, and a reflection from a target. A replica including a signal receiving unit that receives an underwater acoustic signal including a sound wave and converts it into an electric signal to be a received signal, and a replica correlation unit that performs replica correlation processing on the received signal as a replica signal. An active sonar apparatus configured to measure a distance from the target by obtaining a delay time from the time of transmission of the transmission signal. The received signal is sampled at a sampling frequency having the same frequency change rate as the frequency change rate of the transmission signal. An echo signal detection function for detecting an echo signal and its position from the received signal by ring conversion, a received signal cut-out function for cutting out the detected echo signal portion from the received signal by operating the echo signal detection function, and A replica correlation processing function for performing the replica correlation processing is executed by using an echo signal of a region cut out by the reception signal extraction function as an object of the replica correlation processing (claim 14).

  As a result, stable signal detection is possible by cutting out only the time part when the echo signal is detected and performing replica correlation processing, and even if the detection threshold of the signal is lowered except for the influence of noise outside the signal processing interval, Thus, it is possible to eliminate a false alarm and further narrow the signal processing section, so that it is possible to realize a sonar received signal processing program capable of improving the time resolution of the signal detection time.

Here, the echo signal detection function performs sampling conversion of the received signal at a sampling frequency having the same frequency change rate as the frequency change rate of the transmission signal, and this sample-converted pseudo CW A second processing function for short-time Fourier transform of the signal, and a predetermined cut-out width is set in advance with respect to the received signal and sequentially shifted, and each time the CW signal is cut out and each converter is operated to operate the frequency and level. A third processing function for generating a plurality of echo signals having different levels, and a fourth processing function for identifying and detecting an echo of the maximum level among a plurality of cut-out echoes generated by the third processing function as an echo signal (Claim 15).
Accordingly, it is possible to realize a sonar received signal processing program that can accurately determine the position of the echo signal, eliminate the detection time shift in the replica correlation processing, and improve the accuracy of the signal detection time.

In addition, a Doppler shift amount calculation function for calculating a Doppler shift amount of the echo signal by taking in a signal detected when the echo signal detection function is activated is provided, and when executing the replica correlation processing function, the Doppler shift amount is provided. The correction replica signal generated by correcting the frequency band of the transmission signal based on the Doppler shift amount calculated by operating the calculation function is configured to be the replica signal used for the replica correlation processing (Claim 16).
Thereby, even when Doppler occurs, it is possible to realize a sonar received signal processing program that can correct the detection time shift in the replica correlation processing and improve the accuracy of the signal detection time.

Further, the Doppler shift amount calculation function interpolates a plurality of cut-out echoes generated by the third processing function in the echo signal detection function to specify the vertex position of the interpolation curve and the specified vertex A signal reception time detection function having a position as the detection time of the echo signal, an echo frequency interpolation function for interpolating a frequency corresponding to the detected time from the frequency of the plurality of cut-out echoes, and the echo frequency interpolation A shift amount calculation function that calculates a difference between an interpolation frequency obtained by operating the function and a lower limit frequency in the transmission signal and uses this as a Doppler shift amount may be included.
Thereby, the received signal processing program for sonar which can correct | amend replica correlation processing by calculating | requiring Doppler shift amount by a calculation in a sampling conversion part is realizable.

Here, the replica correlation processing function includes a correction replica signal generation function that generates a correction replica signal in which the frequency band of the transmission signal is corrected based on the Doppler shift amount calculated and output by the Doppler shift amount calculation function; A correlation degree calculating function for performing a replica correlation process on the echo signal portion cut out by the received signal cutting out function as a replica signal and obtaining a time series correlation between the two signals, and this correlation degree calculation It may be configured to include a time calculation function in which the detection time is a time at which a signal whose correlation level data obtained by the function has a level exceeding a preliminarily assumed threshold is located (claim 18).
As a result, by correcting the replica signal used for correlation calculation, even for Doppler shift, the detection accuracy of correlation degree can be improved and the time resolution of signal detection time in replica correlation processing can be improved. A reception signal processing program can be realized.

  Since the present invention is configured and functions as described above, according to this, stable signal detection is performed by the sampling conversion method, and only the time portion where the signal is detected is cut out to perform replica correlation. It is possible to provide an active sonar device, a sonar received signal processing method, and a signal processing program thereof that can further improve the time resolution of the signal detection time while maintaining the detection performance.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, the active sonar device according to the present invention is characterized in that a sampling conversion method and a replica correlation method are used in combination when processing a received signal. In other words, signal detection is performed by a sampling conversion method having stable signal detection performance, and only a detected signal section is extracted from the received signal and replica correlation is performed, whereby high time resolution can be obtained. Furthermore, the accuracy of the signal detection time can be improved by obtaining the Doppler shift amount from the signal detection result in the sampling conversion method and correcting the replica signal.

[First Embodiment]
In FIG. 1, the whole structure of the active sonar apparatus in 1st Embodiment of this invention is shown.
In FIG. 1, in the first embodiment, the main points of the present embodiment will be described first, and then the specific contents will be described.
First, the active sonar apparatus in FIG. 1 performs sampling conversion on the received signal of the received underwater reflected echo based on the sampling frequency changed in the same manner as the rate of change of the transmission signal composed of pulses, and converts the echo signal and its position. Echo signal detection means 40 for performing detection, and reception signal cutout means 46 for cutting out the echo signal portion detected by the echo signal detection means 40 from the reception signal are provided. In addition, replica correlation processing means 5 is provided which performs replica correlation processing on the cut-out echo signal portion and uses the transmission signal as a replica signal, thereby calculating a signal detection time of the echo signal.
For this reason, it is possible to detect a signal detection time accurately and stably by detecting a portion where an echo signal is present using sampling conversion and processing the portion by replica correlation.

This will be described in further detail.
As shown in FIG. 1, the active sonar device according to the first embodiment is a signal transmission unit 1 that converts a transmission signal composed of a pulse signal (LFM signal) of a frequency-modulated wave whose frequency changes with time into a sound wave and transmits the sound wave. A signal receiving unit 3 that receives an underwater acoustic signal including a reflected sound wave from the target 2 and converts the signal into an electric signal to be a received signal, and replica correlation processing using the received signal as a replica signal as a replica signal The above-described replica correlation processing means 5 is provided. Here, the LFM signal has the same form as the LFM signal disclosed in the above-described conventional example, and means a frequency-modulated wave signal whose frequency changes linearly.

Between the replica correlation processing means 5 and the signal receiving unit 3 described above, the sampling conversion processing means 4 for processing the received signal is provided.
The sampling conversion processing means 4 includes a sampling period calculation unit 41 that calculates a sampling period having the same frequency change rate as that of the LFM signal, and the echo signal detection means 40 and the reception signal cutout means 46 described above. Yes.

  The echo signal detection means 40 samples and converts the above-mentioned received signal at a sampling frequency having the same frequency change rate as the frequency change rate of the transmission signal (LFM signal), and this sample-converted pseudo signal A Fourier transform unit 43 that performs Fourier transform of the CW signal for a short time, and sequentially shifts the received signal by setting a predetermined cut-out width in advance, and cuts out the CW signal each time to operate each of the transform units so that the frequency and level A cut-out echo generation unit 44 that generates a plurality of echo signals having different levels, a signal detection unit 45 that identifies and detects the maximum level of the plurality of cut-out echoes generated by the cut-out echo generation unit 44 as an echo signal, It has.

  Further, the replica correlation processing means 5 includes a replica signal generation unit 51 that generates a replica signal, a replica correlation unit 52 that performs replica correlation using the extracted signal and the replica signal, and a signal detection time based on the degree of correlation obtained by the replica correlation. The time calculation part 53 which calculates is provided. Reference numeral 6 denotes a display unit that superimposes and displays received signal processing results and signal detection results by the constituent members of the replica correlation processing means 5.

Next, the operation of the first embodiment will be described based on the flowchart of FIG.
First, the signal transmission unit 1 generates a pulsed LFM signal as an electric signal (step S101). As described above, this LFM signal is the same as the LFM signal in the conventional example. For example, the center frequency fc is 1 [kHz], the bandwidth B is 50 [Hz], and the pulse width T is 0.1 [msec]. ] In which the frequency increases with time. The signal transmission unit 1 amplifies the power, converts the electrical signal into an acoustic signal, and transmits the sound wave as water (step S102).

The sound wave radiated into the water is reflected by the target 2 and received by the signal receiver 3.
The signal receiving unit 3 receives an underwater acoustic signal including an echo signal of a reflected wave (step S103). At this time, when the target 2 is moving, the reflected wave is Doppler shifted and received by the signal receiving unit 3 together with noise.
The signal receiving unit 3 converts the received signal into an electric signal. The converted received electrical signal is amplified and then band-filtered by a band-pass filter that can filter the echo signal. The bandwidth of the bandpass filter is, for example, 150 [Hz] from 925 [Hz] to 1075 [Hz] in consideration of frequency fluctuation due to Doppler shift.
The band-filtered signal is A / D converted by the A / D conversion means of the signal receiving unit at a predetermined sampling frequency. The sampling frequency is, for example, 20 [kHz] (step S104). The received electrical signal that has been A / D converted in this way is converted into a digital signal and input to the sampling conversion processing means 4.

Next, the operation of the sampling conversion processing means 4 will be described.
In the sampling conversion processing means 4, the sampling cycle calculation unit 41 calculates a non-uniform sampling cycle using the transmitted LFM signal data (step S107). The sampling period calculator 41 is non-uniform based on the center frequency, bandwidth, pulse width, signal type of the transmission signal input from the transmission signal generator 1 and the sampling frequency in the A / D conversion means. The sampling period is calculated and output to the sampling converter 42. Here, it is assumed that the sampling frequency in the A / D conversion means of the signal receiving unit 3 is registered in the sampling period calculation unit 41 in advance.

The sampling conversion unit 42 captures the A / D converted received signal while shifting the cut-out time portion (time window) little by little (step S105), and according to the sampling cycle obtained by the calculation in the sampling cycle calculation unit 41. Then, sampling conversion is performed (step S106: sampling conversion step).
Although the frequency after conversion when the LFM signal is converted into the CW signal can be arbitrarily set, in this embodiment, the sampling period is set so as to convert the frequency to the lower limit frequency of the LFM signal. The echo signal sampled and converted by the sampling converter 42 becomes a pseudo CW signal having a slight frequency bandwidth.

The Fourier transform unit 43 performs a short-time Fourier transform on the pseudo CW signal sampled and converted by the sampling conversion unit 42 and outputs the result to the cut-out echo generation unit 44. The cut-out echo generator 44 sequentially outputs the echo signals sampled and converted by the sampling converter 42 to the signal detector 45.
The signal detection unit 45 detects a frequency component having a level exceeding a preset threshold from the frequency spectrum obtained by Fourier transform, and specifies this as an echo signal (step S108).

Then, the processing result is output to the signal cutout means 46. The signal cutout unit 46 cuts out only the portion corresponding to the portion where the echo signal is all included and the level is maximum among the plurality of detection results that have appeared, and the cut out received signal is sent to the replica correlation processing unit 5. Input (step S110: signal extraction step).
The echo signal sampled and converted by the sampling converter 42 becomes a pseudo CW signal having a slight frequency bandwidth.
In the sampling conversion processing means 4, the sampling conversion section 42, the Fourier transform section 43, the cut-out echo generation section 44 and the sequential signal detection section 45 constitute an echo signal detection means 40.

  In the process of detecting the echo signal, it is determined whether or not the time length of the received electrical signal captured in step S105 is equal to or greater than a predetermined time width sufficient to capture the echo signal corresponding to the LFM signal transmitted this time ( In step S109), the process is repeated until the predetermined time width is reached, and the process from step 105 to step 108 is repeated.

The operation of the sampling conversion processing means 4 will be described more specifically with reference to FIG.
The sampling conversion unit 41 performs sampling conversion by loop processing that continuously repeats signal processing while shifting the position where the signal is cut out. In FIG. 3A, the signal cut-out position is indicated by a horizontally long rectangle.
In this case, when the shift width of the cutout position is made smaller than the cutout width, the sampling signal overlaps with the previously cutout signal. When the overlap occurs, the echo signal is included in a plurality of processing results. Therefore, when the spectrogram display is performed, a plurality of detection results of echo signals having different frequencies and levels are displayed on the spectrogram as shown in FIG. appear. In the spectrogram shown in FIG. 3B, the horizontal axis represents time and the vertical axis represents frequency, and the display luminance is the signal level. The number of echo signal detection results that appear varies depending on the cutout width and shift width.

Then, when the cutout width is twice the pulse width and the shift width is 1/3 times the cutout width as shown in FIG. 3, four or more echo signal detection results appear.
Here, the signal cutout means 46 cuts out only the time portion in which all the echo signals are included and the level is maximum from the plurality of detection results that have appeared. The extracted signal is input to the replica correlation processing means 5.
FIG. 3C and FIG. 3D show examples of correlations that appear as replica correlation processing results corresponding to levels in two of the spectrograms shown in FIG.

Next, the operation of the replica correlation processing unit 5 will be described.
In the replica correlation processing means 5, first, the replica signal generation unit 51 generates a replica signal using the transmitted LFM signal data.
The replica correlation unit 52 calculates the replica correlation between the signal extracted by the signal extraction unit 45 and the generated replica signal (FIG. 2, step S111: replica correlation processing step). Ask for. The time calculation unit 53 calculates the time when the correlation level exceeds the set threshold in the time-series correlation data as the echo signal detection time (step S112).
Then, the processing result is converted into a spectrogram and a graph, and the detection result is superimposed and displayed on the display unit 6 (step S113).
The operations from step S101 to step S113 may be repeatedly executed continuously.

In the first embodiment, a sampling conversion method for sampling and converting a received signal using a non-uniform sampling frequency to detect an echo signal, and a replica correlation operation between the extracted received signal and a replica signal are performed. A replica correlation method for calculating the detection time is used in combination.
Therefore, it is possible to accurately detect an echo signal by a sampling conversion method having stable signal detection performance, cut out only a signal section in which the echo signal is detected from the received signal, calculate a replica correlation, and obtain a high time resolution.

By doing this, it is possible to perform replica correlation calculation by extracting only the cut-out portion that includes all echo signals and has the maximum level, and by limiting the range of signal data for performing replica correlation calculation to a narrow resolution. Can be improved. Furthermore, false alarms that occur outside the signal processing interval can be ignored, and echo signals with few false alarms can be detected even if the detection threshold of the echo signal is reduced.
In addition, since the replica correlation calculation continuously detects the echo signal detection time, the time resolution and accuracy of the signal detection time can be improved as compared with the case of using only the sampling conversion method for discontinuous time detection.

  Here, the execution contents in each step disclosed in the operation description of the active sonar apparatus described above may be programmed to be executed by a computer. Even if it does in this way, the effect equivalent to the effect in 1st Embodiment mentioned above can be acquired.

[Second Embodiment]
Next, a second embodiment will be described with reference to FIG.
Here, the same reference numerals are used for the same components as those in the embodiment of FIG. 1 described above.

  The active sonar apparatus shown in FIG. 2 includes a signal transmission unit 1 that transmits an LFM signal in water, a signal reception unit 3 that receives an underwater acoustic signal including an echo signal reflected by the target 2, and the reception signal is the same as the LFM signal. Sampling conversion is performed with a sampling signal that changes at a frequency change rate, Fourier transform is performed, a signal portion where the maximum level is detected is cut out, and a sampling conversion processing means 7 that calculates a Doppler shift amount is transmitted, and a frequency correction corresponding to the Doppler shift amount is performed It comprises a replica correlation processing means 8 that performs a replica correlation calculation between the LFM electric signal and the cut signal portion, and a display unit 6 that displays a processing result and a signal detection result in a superimposed manner.

This embodiment is different from the first embodiment shown in FIG. 1 in that a sampling conversion processing unit 7 is provided with a Doppler shift amount calculation unit (Doppler shift amount calculation unit) 77 and a replica correlation processing unit 8. Thus, the replica signal is corrected in accordance with the result calculated by the Doppler shift amount calculation unit 77.
When replica correlation is performed at the time of occurrence of Doppler shift, not only the maximum value of the correlation degree is reduced, but also a time lag occurs when the correlation degree is maximum.
FIG. 5 and FIG. 6 show conceptual diagrams of replica correlation processing results with and without Doppler shift. If there is no Doppler shift and the degree of correlation becomes maximum at the start position of the signal as shown in FIG. 5, when the frequency of the signal is lowered by Doppler shift, the lower limit frequency of the replica signal is set as shown in FIG. Since the maximum value of the correlation appears at the coincident location, a deviation occurs from the true signal position.

  In order to solve this problem, a Doppler shift amount calculation unit 77 is provided together with the signal detection unit 75 of the sampling conversion processing means 7. Here, the signal detection unit 75 outputs the detection result to the reception signal cutout unit 76 and the Doppler shift calculation unit 77. The Doppler shift amount calculation unit 77 calculates the Doppler shift amount from the detection result.

Here, a calculation method of the Doppler Doppler shift amount in the Doppler shift amount calculation unit 77 will be described with reference to FIG.
The sampling converter 72 performs loop processing while shifting the signal cutout position as shown in FIG. 7A (1). At this time, when the shift width is made smaller than the cut-out width, an overlap with the previously cut-out signal occurs. When the overlap occurs, the echo signal is included in a plurality of processing results, and as shown in FIG. 7B, a plurality of detection results of echo signals having different frequencies and levels appear on the spectrogram (2).
As shown in FIG. 7 (c), an interpolation curve for interpolating the levels of a plurality of detected echo signals is drawn, and the vertex is obtained (3). Then, the time corresponding to the vertex is specified as the detection time tp (4).

Next, as shown in FIG. 7B, a frequency fp corresponding to the specified detection time tp is obtained (5). The frequency obtained here is a frequency obtained by correcting a frequency shift due to a mismatch between the signal cutout position and the signal position. The difference between this frequency and the conversion target frequency for sampling conversion is the Doppler shift amount.
In the second embodiment, the difference from the lower limit frequency of the transmitted LFM signal is obtained. The calculated Doppler shift amount is output to the replica signal generation unit 81.

Here, the processing in the replica correlation processing means 8 will be described.
First, the correction replica signal generation unit 81 generates a replica signal from the data of the transmission signal. At this time, using the Doppler shift amount calculated by the Doppler shift amount calculation unit 76, a corrected replica signal that is corrected by shifting the frequency band of the transmission signal by the Doppler shift amount is generated.
The replica correlation unit 82 calculates the degree of correlation between a part of the received electrical signal cut out by the received signal cutout unit 76 and the corrected replica signal generated by correction by the corrected replica signal generation unit 81, and the time calculation unit 83. Output the processing result to. The time calculation unit 83 calculates the time when the correlation level exceeds the set threshold value from the input time-series correlation data as the echo signal detection time, and outputs it to the display unit 6.

Here, the effect of limiting the signal processing section will be described with reference to the explanatory diagram of FIG.
As shown in FIG. 8A, when the received electrical signal is loop-processed and replica correlation is executed in the entire interval, a noise component exceeding the threshold is detected and a false alarm is generated. To reduce false alarms, the threshold value must be set large. However, if the threshold value is increased, it becomes difficult to detect the echo signal.

On the other hand, if the signal processing section is limited by narrowing the existing section of the echo signal as in this embodiment, a false alarm that occurs outside the signal processing section can be ignored. Therefore, even if the threshold value is reduced as shown in FIG. 8B, there are few false alarms, and the echo signal can be detected stably.
When the replica signal is corrected using the Doppler shift amount obtained by the Doppler shift amount calculation unit 76 as in the case of the second embodiment, the maximum value of the correlation degree as shown in FIG. And the time lag is also reduced.

  The processing result input to the display unit 6 is displayed using a spectrogram in which the horizontal axis represents time, the vertical axis represents frequency, and the luminance represents level, and the horizontal axis represents time, and the vertical axis represents correlation. The signal detection result and the time detection result are superimposed and displayed on these graphs.

As described above, the active sonar device according to the present invention includes a sampling conversion method in which a received signal is sampled and converted using a non-uniform sampling frequency to detect an echo signal, and a replica correlation between the extracted received signal and a replica signal. A replica correlation method for performing calculation and calculating a signal detection time is used in combination.
Therefore, echo signal detection can be performed by a sampling conversion method having stable signal detection performance, and stable signal detection performance can be obtained even when a Doppler shift occurs. Furthermore, by cutting out only the signal section where the echo signal was detected from the received signal and limiting the signal processing section and performing replica correlation, higher time resolution and accuracy can be obtained than when only the sampling conversion method is used. .

Further, in the second embodiment, the Doppler shift amount is calculated from the detection result in the sampling conversion method, thereby correcting the replica signal, and using the corrected replica signal, the signal detection time of the Doppler shift is calculated. Reduce the deviation. Thereby, the accuracy of the signal detection time when the Doppler shift occurs can be improved.
Other configurations and the effects thereof are the same as those of the first embodiment described above.

  Here, the execution contents in each step disclosed in the operation description of the active sonar apparatus described above may be programmed to be executed by a computer. Even if it does in this way, the effect equivalent to the effect in 2nd Embodiment mentioned above can be acquired.

  Since the present invention is configured and functions as described above, it can be used for an active sonar device, particularly an active sonar device using an LFM signal, and has a possibility to be used in the industrial field of signal processing related thereto. ing.

It is a block diagram which shows the whole structure of 1st Embodiment of the active sonar apparatus of this invention. It is an operation | movement flowchart of 1st Embodiment shown in FIG. It is explanatory drawing of operation | movement of the sampling conversion process means in 1st and 2nd embodiment. It is a block diagram which shows the whole structure of 2nd Embodiment of the active sonar apparatus of this invention. It is a conceptual diagram of the replica correlation processing result when there is no Doppler shift in the first embodiment. It is a conceptual diagram of the replica correlation process result in case there exists a Doppler shift in 1st Embodiment. It is explanatory drawing of the calculation method of the Doppler shift amount in the Doppler shift amount calculation part of 2nd Embodiment. It is explanatory drawing which shows the effect by the restriction | limiting of the signal processing area in 1st and 2nd embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Signal transmission part 2 Target object 3 Signal receiving part 4,7 Sampling conversion process means 5,8 Replica correlation process means 6 Display part 40,70 Echo signal detection means 41,71 Sampling period calculation part 42,72 Sampling conversion part 43, 73 Fourier transform unit 44, 74 Cut-out echo generation unit 45, 75 Signal detection unit 46, 76 Received signal cut-out unit 77 Doppler shift amount calculation unit (Doppler shift amount calculation unit)
81 Correction replica signal generator

Claims (18)

Echo signal detection means for sampling and converting the received signal of the received underwater reflected echo based on a sampling frequency having the same frequency change rate as the frequency change rate of the transmission signal, and detecting the echo signal and its position, and this echo signal A reception signal cut-out means for cutting out the echo signal portion detected by the detection means from the reception signal;
An active sonar apparatus comprising replica correlation processing means for performing a replica correlation process on the cut-out echo signal portion and using the transmission signal as a replica signal, thereby calculating a signal detection time of the echo signal. . A signal transmission unit that converts a transmission signal composed of a pulse of a frequency-modulated wave whose frequency changes with time into a sound wave, and receives an underwater acoustic signal including a reflected sound wave from a target, converts it into an electrical signal, and a reception signal And a replica correlation processing unit including a replica correlation unit that performs replica correlation processing on the received signal as a replica signal, and the replica correlation processing unit includes the transmission signal. In an active sonar apparatus configured to measure and measure the distance to the target by obtaining a delay time from the time of transmission of
Echo signal detection means for detecting the echo signal and its position from the received signal by sampling conversion of the received signal at a sampling frequency having the same frequency change rate as the frequency change rate of the transmission signal, and detection by the echo signal detection means A reception signal cutout means for cutting out the echo signal portion that has been cut out from the reception signal,
An active sonar apparatus, wherein the replica correlation processing means uses the echo signal of the area cut out by the received signal cut-out means as a target of the replica correlation processing. In the active sonar device according to claim 1 or 2,
The echo signal detecting means comprises: a sampling conversion unit that performs sampling conversion of the received signal at a sampling frequency having the same frequency change rate as the frequency change rate of the transmission signal; and a short-time Fourier transform of the sampled and converted pseudo CW signal A Fourier transform unit for transforming and sequentially shifting the received signal by setting a predetermined cut-out width in advance and cutting out the CW signal each time to operate each transform unit to generate a plurality of echo signals having different frequencies and levels. It is characterized by including a cut-out echo generation unit to be generated and a signal detection unit that specifies and detects an echo of the maximum level among a plurality of cut-out echoes generated by the cut-out echo generation unit as an echo signal Active sonar device. In the active sonar device according to claim 1, 2, or 3,
In addition to the echo signal detecting means, an output signal of the echo signal detecting means is taken in, and a Doppler shift amount calculating section for calculating a Doppler shift amount with respect to the transmission signal of the echo signal is provided,
The replica correlation processing means generates a corrected replica signal that generates a corrected replica signal in which the frequency band of the transmission signal is corrected based on the Doppler shift amount output from the Doppler shift amount calculation unit when generating the replica signal. An active sonar device characterized by comprising: In the active sonar device according to claim 4,
The Doppler shift amount calculation unit interpolates a plurality of cut echoes generated by the cut echo generation unit to specify a vertex position of the interpolation curve, and uses the specified vertex position as a detection time of the echo signal. A signal reception time detection function, an echo frequency interpolation function for generating a frequency corresponding to the detected time from the frequency of the plurality of cut echoes, and an interpolation obtained by operating the echo frequency interpolation function An active sonar device comprising a shift amount calculation function for calculating a difference between a frequency and a lower limit frequency in the transmission signal and using the difference as a Doppler shift amount. In the active sonar device according to claim 4,
The replica correlation processing means includes
A correction replica signal generation unit that generates a correction replica signal in which the frequency of the transmission signal is corrected based on the Doppler shift amount output from the Doppler shift amount calculation unit, and an echo signal portion cut out by the reception signal cutout unit A replica correlation unit that performs replica correlation processing using the transmission signal as a replica signal to obtain a time-series correlation of the two signals, and a correlation level data obtained by the replica correlation, the level of which is assumed in advance An active sonar device comprising: a time calculation unit that detects a time at which a signal exceeding a threshold is located as a detection time. Based on a sampling frequency having the same frequency change rate as the frequency change rate of the transmission signal, an echo signal detection step for detecting the echo signal and its position by sampling and converting the received signal of the received underwater reflected echo; and
A reception signal cut-out step of cutting out the detected echo signal portion from the reception signal,
For a sonar characterized by performing a replica correlation process for the cut out echo signal part and performing a replica correlation process using the transmission signal as a replica signal, thereby calculating a signal detection time of the echo signal. Received signal processing method. After transmitting a transmission signal consisting of a pulse of a frequency-modulated wave whose frequency changes with time into a sound wave, receiving an underwater acoustic signal including a reflected sound wave from the target and converting it into an electrical signal to obtain a reception signal The replica correlation processing unit performs replica correlation processing using the transmission signal as a replica signal with respect to the received signal, thereby obtaining a delay time from the time of transmission of the transmission signal and measuring the distance from the target. In the received signal processing method for sonar,
An echo signal detecting step of detecting the echo signal from the received signal by sampling conversion of the received signal at a sampling frequency having the same frequency change rate as the frequency change rate of the transmission signal, and an echo detected in the echo signal detecting step A reception signal cutout step of cutting out a signal portion from the reception signal, and a replica correlation processing step in which the replica correlation processing means executes replica correlation processing with the echo signal of the region cut out in the reception signal cutout step as the target of the replica correlation processing And a received signal processing method for a sonar. In the sonar received signal processing method according to claim 7 or 8,
The echo signal detection step includes a first step of sampling conversion of the received signal at a sampling frequency having the same frequency change rate as the frequency change rate of the transmission signal, and the sampling-converted pseudo CW signal for a short time. A second step of Fourier transform, and a predetermined cutout width is set in advance with respect to the received signal and sequentially shifted, and each time the CW signal is cut out to operate each conversion unit and a plurality of echoes having different frequencies and levels A configuration including a third step of generating a signal, and a fourth step of identifying and detecting an echo of the maximum level among the plurality of cut-out echoes generated in the third step as an echo signal. A sonar received signal processing method. The received signal processing method for a sonar according to claim 7, 8 or 9,
In addition to the echo signal detection step, a Doppler shift amount calculation step of calculating the Doppler shift amount of the echo signal by taking in the output signal in the echo signal detection step,
The replica signal used in the replica correlation process is a corrected replica signal obtained by correcting the frequency band of the transmission signal based on the Doppler shift amount calculated in the Doppler shift amount calculation step. Received signal processing method for sonar. The received signal processing method for a sonar according to claim 10,
The Doppler shift amount calculating step interpolates a plurality of cut-out echoes generated in the third step of the echo signal detection step to specify the vertex position of the interpolation curve and to determine the specified vertex position The signal reception time detection process for detecting the detection time of the echo signal, the echo frequency interpolation process for interpolating the frequency corresponding to the detected time from the frequency of the plurality of cut echoes, and the echo frequency interpolation process are activated. A sonar received signal processing method comprising: a shift amount calculating step of calculating a difference between an interpolation frequency obtained in this way and a lower limit frequency in the transmission signal and using this as a Doppler shift amount. The received signal processing method for a sonar according to claim 10 or 11 ,
The replica correlation processing step includes
A correction replica signal generation step for generating a correction replica signal in which the frequency band of the transmission signal is corrected based on the Doppler shift amount output in the Doppler shift amount calculation step; and an echo signal portion cut out in the reception signal cutout step. Correlation degree calculation step for obtaining a time-series correlation degree of the two signals by performing replica correlation processing using the transmission signal as a replica signal, and the correlation degree data obtained by the correlation degree calculation step. A sonar received signal processing method characterized by comprising: a time calculation step in which a time at which a signal that exceeds a threshold assumed in advance is located is a detection time. An echo signal detection function for detecting the echo signal and its position by sampling and converting the received signal of the received underwater reflected echo based on the sampling frequency having the same frequency change rate as the frequency change rate of the transmission signal, and the detected echo A received signal cut-out function for cutting out a signal part from the received signal, replica correlation processing for the cut-out echo signal part and performing replica correlation processing using the transmission signal as a replica signal and thereby calculating a signal detection time of the echo signal A received signal processing program for a sonar that causes a computer to execute a processing function. A signal transmission unit that converts a transmission signal composed of a pulse of a frequency-modulated wave whose frequency changes with time into a sound wave, and receives an underwater acoustic signal including a reflected sound wave from a target, converts it into an electrical signal, and a reception signal And a replica correlation processing unit including a replica correlation unit that performs replica correlation processing on the received signal as a replica signal, and the replica correlation processing unit includes the transmission signal. In the active sonar apparatus configured to measure the distance from the target by obtaining a delay time from the time of transmission of the computer, the computer provided in the received signal processing unit,
An echo signal detection function for detecting and processing an echo signal and its position from the received signal by performing sampling conversion on the received signal at a sampling frequency having the same frequency change rate as the frequency change rate of the transmission signal. A replica that performs the replica correlation process using the received signal cutout function that cuts out the detected echo signal portion from the received signal, and the echo signal of the area cut out when the received signal cutout function is activated Correlation processing function,
The received signal processing program for sonar characterized by the above. In the sonar received signal processing program according to claim 13 or 14,
The echo signal detection function performs sampling conversion of the received signal at a sampling frequency having the same frequency change rate as the frequency change rate of the transmission signal, and shortens the pseudo-CW signal subjected to the sampling conversion. A second processing function for time Fourier transform, and a predetermined cutout width is set in advance with respect to the received signal and sequentially shifted, and each time the CW signal is cut out to operate each conversion unit and a plurality of different frequencies and levels. And a fourth processing function for specifying and detecting an echo of the maximum level among a plurality of cut-out echoes generated by the third processing function as an echo signal. A received signal processing program for sonar characterized by having a configuration. In the sonar received signal processing program according to claim 13, 14 or 15,
Provided with a Doppler shift amount calculation function for calculating a Doppler shift amount of the echo signal by taking in a signal detected by operating the echo signal detection function;
When executing the replica correlation processing function, a corrected replica signal generated by correcting the frequency band of the transmission signal based on the Doppler shift amount calculated by operating the Doppler shift amount calculating function A sonar received signal processing program configured to be the replica signal used for correlation processing. In the received signal processing program for sonar according to claim 16,
The Doppler shift amount calculation function specifies the vertex position of the interpolation curve by interpolating a plurality of cut-out echoes detected by operating the third processing function in the echo signal detection function and specifying the vertex position of the interpolation curve. A signal reception time detection function in which the vertex position is a detection time of the echo signal, an echo frequency interpolation function for interpolating a frequency corresponding to the detected time from the frequency of the plurality of cut-out echoes, and the echo frequency A sonar reception characterized in that it includes a shift amount calculation function for calculating a difference between an interpolation frequency obtained by operating an interpolation function and a lower limit frequency in the transmission signal and using this as a Doppler shift amount. Signal processing program. In the received signal processing program for sonar according to claim 16 or 17,
The replica correlation function is
A corrected replica signal generation function for generating a corrected replica signal in which the frequency band of the transmission signal is corrected based on the Doppler shift amount calculated and output by the Doppler shift amount calculation function, and an echo cut out by the received signal cutout function There is a correlation degree calculation function that performs replica correlation processing for the signal portion and using the transmission signal as a replica signal to obtain a time series correlation degree between the two signals, and correlation degree data obtained by the correlation degree calculation function. And a sonar reception signal processing program characterized by comprising a time calculation function for detecting a time at which a signal whose level exceeds a preliminarily assumed threshold is located.

Images