CN105021702A - Hydroacoustic material acoustic reflection coefficient free field wide-band width measurement method based on complex cepstrum - Google Patents

Abstract

The invention discloses a hydroacoustic material acoustic reflection coefficient free field wide-band width measurement method based on a complex cepstrum. The method comprises the following steps: generating a wide-band compressed pulse signal as a transmitting signal; receiving the signal by a pressure hydrophone; capturing the received signal and eliminating an edge diffraction wave of a hydroacoustic material to be detected to obtain a mixed signal of a direct wave signal and a reflection wave signal; obtaining a reconstructed signal of the direct wave signal; and obtaining an acoustic reflection coefficient of the hydroacoustic material to be detected. According to the method, the wide-band compressed pulse signal is used as the form of the transmitting signal so that the edge diffraction effect of a sample to be detected in free field measurement is overcome and the measurement of the acoustic reflection coefficient of the hydroacoustic material under a relative large-angle incidence condition is realized. The measurement method based on the complex cepstrum is provided so that errors caused by real cepstrum extraction and zero filling of the reflection signal in a real cepstrum method are avoided. By virtue of the method, the acoustic reflection coefficient of a measurement frequency band can be obtained only by once measurement and the operation is relatively convenient and feasible.

Description

A kind of underwater acoustic materials sound reflection coefficient free field wide-band width measurement method based on cepstrum

Technical field

The invention belongs to underwater acoustic measurement field, particularly relate to a kind of underwater acoustic materials sound reflection coefficient free field wide-band width measurement method based on cepstrum.

Background technology

The method of current measurement underwater acoustic materials sound reflection coefficient has multiple, can be divided into sound pipe method and free field method from measurement sample physical dimension.Compared with sound pipe method, the measurement result of free field method can reflect underwater acoustic materials or component acoustical behavior in actual applications better, and can obtain the sound reflection coefficient of oblique incidence situation.But because sample to be tested size is limited, free field method all can be subject to the impact of sample to be tested edge diffraction effect.For this problem, there has been proposed the measuring method of multiple improvement, as the free field broadband compression pulse method of superposition proposed in " the free field broadband compression pulse method of superposition of underwater acoustic materials performance is measured " that Li Shui in 2005, the 25th volume the 3rd phase acoustic journal is delivered.First nautical receiving set bias place by the method, the transmitting transducer battle array of recycling high directivity transmits, reduce sample edge diffraction effect, least-squares-inverse filtering technology is finally utilized to process measuring system, make the ping of transmitting transducer radiation obtain compression to a certain extent, measure the sound reflection coefficient of sample.The method can reduce the impact of edge diffraction effect, but it needs to distinguish repetitive measurement, complex operation to the direct sound wave signal without sample to be tested with there being the signal of sample to be tested respectively.Domestic and international expert Bolton.J.S, real cepstrum signal treatment technology is applied to the sound reflection coefficient wide-band width measurement of aeroacoustics material by the people such as Zhu Congyun, wherein external expert Bolton.J.S and E.Gold in " the The Application ofCepstral Techniques to The Measurement of Transfer Function and Acoustic ReflectionCoefficients " the 93rd volume the 2nd phase Journal of Sound and Vibration. to deliver in 1984 earlier proposition utilize the on-site measurement method of real cepstrum commercial measurement acoustical material sound reflection coefficient.The method uses linear FM signal as transmitting, using real cepstrum algorithm as process data means, cepstrum domain utilize regressive filter extract the unit impulse response on sample to be tested surface, and to its zero padding, and then calculate the sound reflection coefficient on sample to be tested surface.But the method is measured sound reflection coefficient phase place and be there is certain difficulty, and requires that measuring system has very high sample frequency.Domestic expert Huang Qibai, the people such as Zhu Congyun propose the method utilizing cepstrum commercial measurement acoustical material acoustical absorption coefficient in " a kind of new method measured based on the acoustical absorption coefficient of cepstrum analysis " the 32nd volume the 4th phase Central China University of Science and Technology's journal (natural science edition) to be delivered in 2004, sample to be tested is applied ointment or plaster in rigid walls by the method, utilize broadband noise signal as transmitting, first the acoustic pressure at sound wave microphone place after sample to be tested reflection that loudspeaker sends is measured, be converted into real cepstrum, again with cancel the real cepstrum that microphone records after sample to be tested acoustic pressure is transformed into and contrast, obtain the sound reflection coefficient of sample to be tested, thus obtain the acoustical absorption coefficient of acoustic absorbant sample.But the method needs twice measurement, operate more loaded down with trivial details, its loudspeaker and microphone are all placed in the dead ahead of sample to be tested, measurement be the acoustical absorption coefficient of normal direction, and the sound reflection coefficient phase measurement of the method to sample to be tested does not relate to.

Summary of the invention

The object of this invention is to provide a kind of simple to operate, based on the underwater acoustic materials sound reflection coefficient free field wide-band width measurement method of cepstrum.

Based on a underwater acoustic materials sound reflection coefficient free field wide-band width measurement method for cepstrum, comprise the following steps,

Step one: generate broadband compression pulse signal as transmitting;

Step 2: pressure hydrophone Received signal strength, and intercept to received signal, reject underwater acoustic materials edge diffraction waves to be measured, obtain the mixed signal P (t) of direct-path signal and reflection wave signal;

Step 3: the reconstruction signal obtaining direct-path signal

Step 4: the sound reflection coefficient obtaining underwater acoustic materials to be measured:

$\tilde{R}=F\[P\left(t\right)-{\hat{P}}_i\left(t\right)\]/F\[{\hat{P}}_i\left(t\right)\].$

A kind of underwater acoustic materials sound reflection coefficient free field wide-band width measurement method based on cepstrum of the present invention, can also comprise:

1, the method generating broadband compression pulse signal is:

(1) calculate the time delay of diffracted wave signal and reflection wave signal according to sound wave incident angle and measuring system parameter, determine the pulse width transmitted;

(2) according to measuring frequency band and the pulse width determination linear FM signal transmitted:

$u\left(t\right)=A\·rect\left(\frac{t}{\mathrm{\τ}}\right)\·e^{j(2{\mathrm{\πf}}_{0}t+\frac{1}{2}{\mathrm{\μt}}^2)}$

Wherein, $rect\left(\frac{t}{\mathrm{\τ}}\right)=\left\{\begin{array}{c}1,\left|t\right|\≤\frac{\mathrm{\τ}}{2}\\ 0,\left|t\right|>\frac{\mathrm{\τ}}{2}\end{array}\right.,$ A is amplitude, f ₀centered by frequency, Δ f is frequency modulation, and τ is frequency modulated time;

Process of pulse-compression is carried out to linear FM signal, obtains the output signal after compressing:

$u_0\left(t\right)=A\·\sqrt{D}\·\frac{sin\left(\mathrm{\π}Bt\right)}{\mathrm{\π}Bt}\·cos\left(2{\mathrm{\πf}}_{0}t\right)$

Wherein, B is signal band width, and D=B τ is the pulse compression ratio of signal;

(3) linear FM signal after compression being blocked, taking out energy concentration parts as transmitting.

2, the reconstruction signal of direct-path signal is obtained method be:

(1) cepstrum of the mixed signal P (t) of direct-path signal and reflection wave signal is calculated;

(2) on cepstrum domain by the energy filtering of reflection wave signal, obtain direct-path signal cepstrum

(3) reconstruction signal of direct-path signal is obtained

${\hat{P}}_i\left(t\right)=F^{-1}\[e^{fft\left(c_{pi}\left(t\right)\right)}\].$

Beneficial effect:

Utilize broadband compression pulse signal as the form of transmitting on the one hand, overcome the edge diffraction effect of sample to be tested in free field measurement, realize the measurement of underwater acoustic materials sound reflection coefficient under larger angle condition of incidence.On the other hand, the difficulty of sample sound reflection coefficient phase place is measured for real Cepstrum Method, propose the measuring method based on cepstrum, this measuring method avoids the real cepstrum of reflected signal in real Cepstrum Method and extracts the error brought with zero padding, realizes the measurement of underwater acoustic materials sound reflection coefficient phase place.Finally, this measuring method only needs one-shot measurement can obtain measuring the sound reflection coefficient of frequency band, and operation should be more convenient and easy.

Accompanying drawing explanation

Fig. 1 complex reflection coefficient free field wide-band width measurement model schematic;

Fig. 2 (a) acoustic pressure in transmission signal form acoustic pressure in transmission signal, Fig. 2 (b) acoustic pressure in transmission power spectrum signal acoustic pressure in transmission signal;

Fig. 3 Received signal strength schematic diagram;

Fig. 4 sound pressure signal cepstrum schematic diagram;

Cepstrum method reconstruct direct sound wave signal simulation result figure when Fig. 5 (a) sound wave incident angle θ is 0 °, cepstrum method reconstruct direct sound wave signal simulation result figure when Fig. 5 (b) sound wave incident angle θ is 60 °;

When Fig. 6 (a) sound wave incident angle θ is 0 °, cepstrum method measures underwater acoustic materials sound reflection coefficient modulus value, and when Fig. 6 (b) sound wave incident angle θ is 0 °, cepstrum method measures underwater acoustic materials sound reflection coefficient phase place;

When Fig. 7 (a) sound wave incident angle θ is 30 °, cepstrum method measures underwater acoustic materials sound reflection coefficient modulus value, and when Fig. 7 (b) sound wave incident angle θ is 30 °, cepstrum method measures underwater acoustic materials sound reflection coefficient phase place;

When Fig. 8 (a) sound wave incident angle θ is 60 °, cepstrum method measures underwater acoustic materials sound reflection coefficient modulus value, and when Fig. 8 (b) sound wave incident angle θ is 60 °, cepstrum method measures underwater acoustic materials sound reflection coefficient phase place;

Fig. 9 cepstrum method measures underwater acoustic materials sound reflection coefficient flow chart of data processing figure.

Embodiment

Below in conjunction with accompanying drawing, the present invention is described in further detail.

The object of the invention is to propose a kind of free field wide-band width measurement method measuring underwater acoustic materials sound reflection coefficient in medium and low frequency section (500Hz-10kHz), only need one-shot measurement accurately can obtain modulus value and the phase information of underwater acoustic materials sound reflection coefficient.Its technical scheme is: the pulse compression technique of linear FM signal combines with cepstrum algorithm by the method, first utilize broadband compression pulse as the form of transmitting, separate sample to be tested edge diffraction waves in time, avoid it to affect, again by cepstrum algorithm reconstruct direct-path signal, then be separated direct-path signal and reflection wave signal, finally the two compared and try to achieve the sound reflection coefficient of underwater acoustic materials sample to be measured.

The technical solution adopted for the present invention to solve the technical problems comprises the following steps:

(1) broadband compression pulse signal is generated as the form of transmitting;

(2) Rejection of samples edge diffraction waves: pressure hydrophone Received signal strength is the direct-path signal, reflection wave signal, sample edge diffracted wave signal etc. that transmitting transducer is launched, first remove in time the interference such as sample to be tested edge diffraction waves signal, obtain the mixed signal P (t) of direct-path signal and reflection wave signal;

(3) reconstruct direct-path signal: the cepstrum calculating P (t), by the energy filtering of reflection wave signal on cepstrum domain, obtain direct-path signal cepstrum, and it is carried out to the inverse operation of cepstrum computing, obtain the reconstruction signal of direct-path signal be separated direct-path signal and reflection wave signal again;

(4) sound reflection coefficient of underwater acoustic materials sample is obtained: the complex reflection coefficient being obtained sample by relative method, that is:

$\tilde{R}=F\[P\left(t\right)-{\hat{P}}_i\left(t\right)\]/F\[{\hat{P}}_i\left(t\right)\].$

Utilize broadband compression pulse signal as the form of transmitting, separating sample edge diffraction waves in time, evade its impact.The concrete generative process of broadband compression pulse signal is as follows: the time delay first calculating diffracted wave signal and reflection wave signal according to sound wave incident angle and measuring system parameter, determines the pulse width transmitted; Then, select frequency modulated time and the frequency span of suitable linear FM signal according to measurement frequency band and transmit signal pulse width, and process of pulse-compression is carried out to it; Finally intercept the part of the concentration of energy of linear FM signal pulse compression output signal as the form of transmitting.

Utilize cepstrum algorithm to reconstruct direct-path signal, then it is separated with reflection wave signal, finally by comparing the sound reflection coefficient obtaining sample.

The present invention relates to a kind of free field wide-band width measurement method of the underwater acoustic materials sound reflection coefficient based on cepstrum algorithm, the pulse compression technique of linear FM signal combines with cepstrum algorithm by the method, first broadband compression pulse signal is obtained by the pulse compression technique of linear FM signal, it can be used as the form of transmitting, separate sample edge diffracted wave in time, recycling cepstrum algorithm reconstruct direct-path signal, it is separated with reflection wave signal, finally the two is compared and try to achieve the sound reflection coefficient of underwater acoustic materials sample to be tested.The method overcome the difficulty of real Cepstrum Method phase measurement, and effectively prevent the impact of sample edge diffraction effect, obtain lower measurement greatest lower band, achieve the sound reflection coefficient free field measurement of broadband, large angle incidence situation; The method is real easy and simple to handle, only needs one-shot measurement can obtain being concerned about the sample sound reflection coefficient in frequency band.This method is applicable to the large sample free field wide-band width measurement of underwater acoustic materials sound reflection coefficient, is equally applicable to the measurement of aeroacoustics material.

Cepstrum measures underwater acoustic materials sound reflection coefficient free field measurement model as shown in Figure 1, and concrete technical scheme of the present invention is as follows, as shown in Figure 9:

The first step, generates broadband compression pulse signal.The form of transmitting is broadband compression pulse signal, and obtained by linear FM signal pulse compression technique, concrete steps are as described below:

1) pulse compression of linear FM signal: the time-domain expression of linear FM signal is:

$u\left(t\right)=A\·rect\[\frac{t}{\mathrm{\τ}}\]\·e^{j(2{\mathrm{\πf}}_{0}t+\frac{1}{2}{\mathrm{\μt}}^2)}---\left(1\right)$

In formula, $rect\left(\frac{t}{\mathrm{\τ}}\right)=\left\{\begin{array}{c}1,\left|t\right|\≤\frac{\mathrm{\τ}}{2}\\ 0,\left|t\right|>\frac{\mathrm{\τ}}{2}\end{array}\right.,$ A is amplitude, f ₀centered by frequency, Δ f is frequency modulation, and τ is frequency modulated time.After matched filter, output signal and be:

$u_0\left(t\right)=A\·\sqrt{D}\·\frac{sin\left(\mathrm{\π}Bt\right)}{\mathrm{\π}Bt}\·cos\left(2{\mathrm{\πf}}_{0}t\right)---\left(2\right)$

In formula, B is signal band width, and D=B τ is the pulse compression ratio of signal.Visible, linear FM signal is sinc function through matched filtering output signal envelope, and side lobe peak is f (x)=1/x rule decay, and the time interval between curve zero point is 1/B second.

2) output linearity FM signal pulse compression signal is intercepted: the energy of LFM compression of signal pulse output signal mainly concentrates on signal main lobe, its secondary lobe amplitude oscillatory extinction.In order to prevent sample to be tested edge diffraction waves signal and reflection wave signal generation aliasing, so block linear FM signal pulse compression output signal, take out the part of concentration of energy as the form of transmitting, its time domain waveform and frequency spectrum are as shown in Figure 2.

Second step, removes diffracted wave signal.The signal waveform schematic diagram that pressure hydrophone receives as shown in Figure 3.Visible, sample edge diffracted wave and sample surface reflection wave are what to separate in time, can intercept the impact avoiding sample to be tested edge diffraction effect to signal.

3rd step, reconstruct direct-path signal.

Ignore sample thickness, in Fig. 1, S is transmitting transducer, and R is pressure hydrophone, r _ifor the distance of transmitting transducer and nautical receiving set, r _r=r _i+ d is the distance of virtual source and pressure hydrophone, and nautical receiving set is d, P to material surface distance _i, P _rrepresent that transmitting transducer transmits and sample surface reflection wave signal respectively, sound wave presses the expansion of spherical wave rule.The concrete steps of reconstruct direct-path signal are as described below:

1) signal cepstrum is calculated.If the unit impulse response function of the reflection coefficient of sample is h (t), then letter P (t) that nautical receiving set receives is:

P(t)＝P _i(t)+P _r(t)＝P _i(t)+(r _i/r _r)·h(t)*P _i(t-τ _r) (3)

In formula, τ _r=(r _r-r _i)/c, c is the velocity of sound in water.(3) are carried out Fourier transform, obtain:

$\begin{array}{c}P\left(\mathrm{\ω}\right)=P_i\left(\mathrm{\ω}\right)+\frac{r_i}{r_r}h\left(\mathrm{\ω}\right)\·P_i\left(\mathrm{\ω}\right)\·e^{-{\mathrm{j\ω\τ}}_r}\\ =P_i\left(\mathrm{\ω}\right)\left(1+\frac{r_i}{r_r}h\left(\mathrm{\ω}\right)\·e^{-{\mathrm{j\ω\τ}}_r}\right)\end{array}---\left(4\right)$

(4) formula is got natural logarithm and is obtained:

$ln\[P\left(\mathrm{\ω}\right)\]=ln\[P_i\left(\mathrm{\ω}\right)\]+ln\[1+\frac{r_i}{r_r}h\left(\mathrm{\ω}\right)\·e^{-{\mathrm{j\ω\τ}}_r}\]---\left(5\right)$

Because $|\frac{r_i}{r_r}h\left(\mathrm{\&omega;}\right)\&CenterDot;e^{-{\mathrm{j\&omega;\&tau;}}_r}|<1,$ By in (5) formula $ln\&lsqb;1+\frac{r_i}{r_r}h\left(\mathrm{\&omega;}\right)\&CenterDot;e^{-{\mathrm{j\&omega;\&tau;}}_r}\&rsqb;$ Expansion in Taylor series, has:

$ln\&lsqb;P\left(\mathrm{\&omega;}\right)\&rsqb;=ln\&lsqb;P_i\left(\mathrm{\&omega;}\right)\&rsqb;+\underset{n=1}{\overset{\mathrm{\&infin;}}{\&Sigma;}}\frac{{(-1)}^n}{n+1}{(\frac{r_i}{r_r}H\left(\mathrm{\&omega;}\right)\&CenterDot;e^{-{\mathrm{j\&omega;\&tau;}}_r})}^{n+1}---\left(6\right)$

(6) formula is carried out Fourier inversion, obtains:

$\begin{array}{c}{c}_p\left(t\right)=c_{p_i}\left(t\right)+\frac{r_i}{r_r}H\left(t-{\mathrm{\&tau;}}_r\right)-\frac{1}{2}{\left(\frac{r_i}{r_r}\right)}^{2}H\left(t-{\mathrm{\&tau;}}_r\right)*H\left(t-{\mathrm{\&tau;}}_r\right)\\ +\frac{1}{3}{\left(\frac{r_i}{r_r}\right)}^{3}H\left(t-{\mathrm{\&tau;}}_r\right)*H\left(t-{\mathrm{\&tau;}}_r\right)*H\left(t-{\mathrm{\&tau;}}_r\right)+L\\ =c_{p_i}\left(\mathrm{\&tau;}\right)+\frac{r_i}{r_r}H\left(t\right)\&CenterDot;\mathrm{\&delta;}\left(t-{\mathrm{\&tau;}}_r\right)-\frac{1}{2}{\left(\frac{r_i}{r_r}\right)}^{2}H\left(t\right)*H\left(t\right)\&CenterDot;\mathrm{\&delta;}\left(t-2{\mathrm{\&tau;}}_r\right)\\ +\frac{1}{3}{\left(\frac{r_i}{r_r}\right)}^{3}H\left(t\right)*H\left(t\right)*H\left(t\right)\mathrm{\&delta;}\left(t-3{\mathrm{\&tau;}}_r\right)+L\end{array}---\left(7\right)$

In formula, for the cepstrum of direct-path signal.As shown in Figure 4, visible, reflection wave signal shows as a series of pulse signal to signal cepstrum result of calculation schematic diagram on cepstrum domain, and pulse time of occurrence is reflection wave and arrives time delay.During calculating, in order to avoid the phase-wrapping that DFT brings, must phase only pupil filter be carried out to the imaginary part of formula (5) signal log spectrum and remove linear phase component.Correction factors formula is:

φ(0)＝0；

2) reflection wave signal cepstrum is removed.According to the time delay that measuring system parameter and sound wave incident angle calculation reflection wave cepstrum occur, windowing, by the filtering of reflected signal cepstrum, obtains

3) direct wave reconstruction signal is obtained.Finally the reconstruction signal that inverse operation just can obtain direct wave is carried out to it that is:

${\hat{P}}_i\left(t\right)=F^{-1}\&lsqb;e^{fft\left(c_{p_i}\left(t\right)\right)}\&rsqb;---\left(9\right)$

4th step, obtains sample to be tested sound reflection coefficient.

In sum, the sound reflection coefficient in frequency band is measured for:

$\tilde{R}=F\&lsqb;P\left(t\right)-{\hat{P}}_i\left(t\right)\&rsqb;/F\&lsqb;{\hat{P}}_i\left(t\right)\&rsqb;---\left(10\right)$

Calculate below by numerical simulation and the present invention is described further.

Emulation illustrates: sample to be tested is aluminium sheet, thickness of slab 0.006m, geometry length of side 1m × 1m, nautical receiving set is to material surface distance d=0.1m, and sound source is to sample distance H=0.5m, and measuring-signal is broadband compression pulse signal, signal initial frequency is 50Hz, and bandwidth is 50kHz, sample frequency f _s=1 × 10 ⁶hz, transmit pulsewidth 0.1ms, and signal to noise ratio (S/N ratio) is 60dB, velocity of sound c=1500m/s in water, analyze sound wave incident angle θ be 0 °, 30 ° and 60 ° time sound reflection coefficient measurement result.

Fig. 5 ~ Fig. 8 sets forth the sound reflection coefficient measurement result of direct-path signal reconstruction result under above-mentioned simulated conditions and underwater acoustic materials sample.Numerical result shows: (1) the present invention utilizes broadband compression pulse signal to reach the object avoiding sample edge diffraction effect as the form of transmitting; (2) the present invention utilizes cepstrum algorithm to complete the reconstruct of direct-path signal, reaches the object that reflection wave signal is separated with direct-path signal, achieves the free field wide-band width measurement of sound reflection coefficient modulus value and phase place under larger angle condition of incidence.(3) the method is easy and simple to handle, and one-shot measurement can obtain being concerned about the underwater acoustic materials sound reflection coefficient in frequency band.

Claims (3)

1., based on a underwater acoustic materials sound reflection coefficient free field wide-band width measurement method for cepstrum, it is characterized in that: comprise the following steps,

Step one: generate broadband compression pulse signal as transmitting;

Step 2: pressure hydrophone Received signal strength, and intercept to received signal, reject underwater acoustic materials edge diffraction waves to be measured, obtain the mixed signal P (t) of direct-path signal and reflection wave signal;

Step 3: the reconstruction signal obtaining direct-path signal

Step 4: the sound reflection coefficient obtaining underwater acoustic materials to be measured:

$\tilde{R}=F\&lsqb;P\left(t\right)-{\hat{P}}_i\left(t\right)\&rsqb;/F\&lsqb;{\hat{P}}_i\left(t\right)\&rsqb;.$

2. a kind of underwater acoustic materials sound reflection coefficient free field wide-band width measurement method based on cepstrum according to claim 1, is characterized in that: the method for described generation broadband compression pulse signal is:

(1) calculate the time delay of diffracted wave signal and reflection wave signal according to sound wave incident angle and measuring system parameter, determine the pulse width transmitted;

(2) according to measuring frequency band and the pulse width determination linear FM signal transmitted:

$u\left(t\right)=A\&CenterDot;rect\left(\frac{t}{\mathrm{\&tau;}}\right)\&CenterDot;e^{j(2{\mathrm{\&pi;f}}_{0}t+\frac{1}{2}{\mathrm{\&mu;t}}^2)}$

Wherein, $rect\left(\frac{t}{\mathrm{\&tau;}}\right)=\left\{\begin{array}{c}1,\left|t\right|\&le;\frac{\mathrm{\&tau;}}{2}\\ 0,\left|t\right|>\frac{\mathrm{\&tau;}}{2}\end{array}\right.,$ A is amplitude, f ₀centered by frequency, Δ f is frequency modulation, and τ is frequency modulated time;

Process of pulse-compression is carried out to linear FM signal, obtains the output signal after compressing:

$u_0\left(t\right)=A\&CenterDot;\sqrt{D}\&CenterDot;\frac{sin\left(\mathrm{\&pi;}Bt\right)}{\mathrm{\&pi;}Bt}\&CenterDot;cos\left(2{\mathrm{\&pi;f}}_{0}t\right)$

Wherein, B is signal band width, and D=B τ is the pulse compression ratio of signal;

(3) linear FM signal after compression being blocked, taking out energy concentration parts as transmitting.

3. a kind of underwater acoustic materials sound reflection coefficient free field wide-band width measurement method based on cepstrum according to claim 1, is characterized in that: the reconstruction signal of described acquisition direct-path signal method be:

(1) cepstrum of the mixed signal P (t) of direct-path signal and reflection wave signal is calculated;

(2) on cepstrum domain by the energy filtering of reflection wave signal, obtain direct-path signal cepstrum

(3) reconstruction signal of direct-path signal is obtained

${\hat{P}}_i\left(t\right)=F^{-1}\&lsqb;e^{fft\left(c_{pi}\left(t\right)\right)}\&rsqb;.$