CN105806949A - Correcting method for radial travel time in ultrasonic CT detection - Google Patents

Abstract

The invention provides a correcting method for radial travel time in ultrasonic CT detection. The correcting method is oriented to ultrasonic detection of concrete with a heterogeneity ecderon layer, wherein the reflection echo of an ultrasonic signal on an interface between the ecderon layer and the concrete is collected, the first wave travel time of the reflection echo is utilized to correct the radial travel time and the part transmitted on the ecderon layer in the radial travel time is eliminated, so that the influence of the ecderon layer on the radial travel time after being corrected can be eliminated and the signal transmission time of the ultrasonic signal in the concrete can be accurately reflected. The correcting method provided by the invention has the characteristics that the ultrasonic signal with time-varying characteristics is utilized to overcome the influences of signal attenuation, various echoes and bottom waves in the process of detecting the reflection echo of the signal emitted at each moment.

Description

A kind of ray traveltime bearing calibration in ultrasound computed tomography detection

Technical field

The present invention relates to the concrete nondestructive testing technology realized by ultrasound computed tomography, particularly relate to the ray traveltime bearing calibration in the detection of a kind of ultrasound computed tomography.

Background technology

Inside at concrete structure, likely because there is cavity, crack or being mingled with silt foreign material and produce leakiness district, and because leakage is shaken, isolated or cell that is built on stilts and that formed, or loose shape region is formed because lacking cement, and because being caused loose shape region by accidental injury.These defects destroy the seriality within concrete structure and integrity, and reduce concrete bearing strength and durability to a great extent.Effectively find out the position of drawbacks described above, scope and size in concrete structure, be the precondition carrying out toolability technical finesse for these defects.

The one quantification detection method accurate, efficient formed after the detection of concrete ultrasound computed tomography is concrete Ultrasonic Nondestructive and computerized tomography (CT) be combined with each other.In concrete ultrasound computed tomography detection process, transmitting transducer and reception transducer are separately fixed on two apparent surfaces of concrete structure, by transmitting transducer repeat its transmission ultrasonic pulse, ultrasonic pulse, at concrete structure internal communication, is then received by reception transducer.Ultrasonic pulse signal is in the communication process within concrete structure, when running into rejected regions such as there is honeycomb, cavity or crack, path can only be changed walk around these rejected regions and could continue to propagate, increase when causing walking because transmission path increases and the velocity of sound reduces；Reflection and scattering occurring in the interface of rejected region, cause that ultrasonic wave acoustic energy is decayed, the amplitude of ultrasonic signal is decreased obviously；Because the high fdrequency component in ultrasonic signal decays more significantly, thus ultrasonic signal frequency reduces under the effect of rejected region；Because of the impact of path changing and scattering, reflection, ultrasonic signal is overlapped mutually and makes signal waveform produce distortion.Thus, by gather receive transducer and receive when walking of ultrasonic signal, amplitude, the parameter such as frequency, it is possible to carry out the analysis of concrete quality.On this basis, by adopting ultrasound wave ray that is intensive and that intersect to penetrate each section of concrete structure, then inverting is carried out according to parameters such as when walking of ultrasonic signal, amplitude, frequencies, rebuild the concrete inner structure status image reflecting each section, carry out quantitative measurement and the evaluation of rejected region in combining image process and mode identification technology.

It is the key component that concrete ultrasound computed tomography detects that detection ultrasonic signal carries out inversion imaging at parameter when walking and when passing through to walk concrete structure within.Ultrasonic signal extends transmission path when running into rejected region because detouring, and causes signal to pass through increasing when walking of this position, and the velocity of wave thus corresponding to rejected region is slack-off.Therefore, by measure ultrasonic signal on each section when walking, recycle the wave speed distribution situation on suitable algorithm inversion reckoning section, the position of rejected region, size, distribution and type can be reflected according to the difference of wave speed distribution.

The ultimate principle of detection and inversion imaging when Fig. 1 illustrates away.On the detection section of shown in Fig. 1 a ultrasound computed tomography, S₁-Sn is the launch point (launch point such as transmitting transducer) of ultrasonic signal, R₁-Rn is the reception point of ultrasonic signal, it is assumed that ultrasonic signal is linearly propagated between each launch point and each reception point, thus as it is shown in figure 1, there is a ray between each launch point and reception point, amounts to N bar ray, and it is 1-N that ray sequence number is compiled.From receiving t when walking that can record every ray₁-t_N, when walking and ultrasonic signal from launch point along ray propagate receive point used time.Further, this section is decomposed into m image-generating unit, in Fig. 1, has split m=8*8 amount to 64 image-generating units, be numbered 1-m；The quantity of m is determined by imaging precision, and, when the numerical value of m ensures that each image-generating unit is sufficiently small, ultrasound wave can be approximated to be a fixed value in the slowness (slowness is the inverse of velocity of wave) of each image-generating unit, is expressed as f₁-f_m.Thus, for wherein i-th ray, t when it is walked_iCan be expressed as:Wherein a_jiRepresent this i-th ray length of process in jth image-generating unit.a_jiEngineering construction drawing or the angle of in-site measurement and ray according to concrete structure are readily available, therefore, and t when above formula also just characterizes away_iAnd the operation relation between the slowness (namely velocity of wave) on each image-generating unit, for utilize detectable walk time each image-generating unit of inverting velocity of wave lay the foundation, and the travel-time tomography of ultrasound computed tomography is exactly that velocity of wave distribution on each image-generating unit is showed in the form of images.

For when the walking of whole rays recorded, it is possible to obtain following Matrix Formula:

By length a_iiIn the coefficient matrix of composition, owing to every ray only can by the sub-fraction in whole m image-generating units, therefore the most elements in this matrix will value be 0.For the feature that coefficient matrix is sparse, it is possible to use the iterative algorithm such as ART realizes based on the inverting to wave speed distribution of measured value when walking.

T when walking to whole rays₁-t_NMeasurement, be inverting obtain wave speed distribution the basis of rejected region in concrete structure can be shown real table.In the middle of practice, arriving the time receiving point as when walking being transmitted into Mintrop wave from ultrasonic signal, the degree of accuracy measured when walking needs to reach Microsecond grade, even up to 1/10th microseconds.

Under desirable measuring state, the emitter of ultrasonic signal and receptor should be close to concrete structure surface, and at joint place daubing coupling agent to avoid the occurrence of space.But, in some cases, there is heterogeneous serving in concrete surface, such as the top layer etc. that outer surface swabbing etc. is formed, thus, in this case the measured ray traveltime obtained is strictly speaking, be not ultrasonic signal propagate in concrete structure when walking, but by its being also included within when walking in the middle of serving.Owing to prior art cannot accurately eliminate ultrasonic signal part when walking in serving, and examining and making cuts when can only walk with an estimated value based on serving thickness and prediction velocity of wave, obtain ultrasonic signal in concrete structure when walking, this obviously deviates from mutually with requirement of measurement pinpoint accuracy when walking.

Summary of the invention

For the defect overcoming above-mentioned prior art to exist, it is desirable to provide the ray traveltime bearing calibration in the detection of a kind of ultrasound computed tomography.The present invention is towards the concrete ultrasound detection with heterogeneous serving, wherein gather ultrasonic signal reflection echo at interface between serving and concrete, utilize reflection echo head wave traveltime that ray traveltime is corrected, eliminate the part in serving transmission in ray traveltime, so that the ray traveltime after correction can get rid of the impact of serving, accurately reflect the ultrasonic signal signal transmission time at inside concrete.Utilize during another feature of the present invention and there is the ultrasonic signal of time variation feature, detect each moment launch signal reflection echo process in overcome signal attenuation and the impact of each echo, end ripple time domain superposition.

Ray traveltime bearing calibration in ultrasound computed tomography of the present invention detection, it is characterised in that including:

At the launch point of serving surface configuration ultrasonic signal, launch point launches the ultrasonic signal with time variation characteristic parameter one by one；Wherein, the described time variation characteristic parameter that ultrasonic signal has at each x time of launch point is different；

Point is received in the side surface configuration first group relative with the surface arranging launch point；The described point that receives in first group measures the time of the signal Mintrop wave receiving described ultrasonic signal, as the ray traveltime connecting described launch point and this reception point；

The described surface that launch point is set arranges second group and receives point；Described reception point in second group receives and goes out the described ultrasonic signal reflection echo that interface produces between described serving and xoncrete structure according to described time variation characteristic parameter extraction, and metering receives the time of the signal Mintrop wave of reflection echo as when correcting；

The spacing between thickness and reception point and the launch point of second group according to described serving, obtain the reflection echo ray put that receives of described launch point to second group, and and then draw each reflection echo ray and from launch point to the ray angle received between the ray put of first group；

According to the ray angle calcu-lation modifying factor as this ray angle linear function；Ray traveltime correction it is converted into based on described modifying factor when described correction being walked；

Utilize described ray traveltime correction, apply to revise to the ray traveltime of the ray receiving point of launch point to first group.

Preferably, described time variation characteristic parameter is the mid frequency of ultrasonic signal.It may further be preferable that launch point launches ultrasonic signal with predetermined fixed center frequency, and the mid frequency of the ultrasonic signal of each moment transmitting of launch point is time-varying；Second group receive is put received ultrasonic signal and records the mid frequency of echo-signal；Judge that the skew of mid frequency of the ultrasonic signal of echo-signal mid frequency and the transmitting of particular transmission moment is whether within estimating threshold range, if within threshold range, then determine and receive the reflection echo that the ultrasonic signal that receives of point comprises the ultrasonic signal that this x time is launched, and this reception point is detected first reflection echo when walking as described correction walk time.

Preferably, described time variation characteristic parameter is wavelet-based attribute vector.It may further be preferable that frequency range when being decomposed into N number of by the ultrasonic signal that each for launch point moment launches, after Denoising disposal, calculate ultrasonic signal energy coefficient in frequency range when each；Energy distribution coefficient table is shown as characteristic vector (E1, E2 ... EN), and the characteristic vector of the ultrasonic signal of each moment transmitting of launch point is time-varying；Second group receive is put received ultrasonic signal and decomposes the characteristic vector that acquisition receives；The relatively characteristic vector of the ultrasonic signal that particular moment launches and the degree of association receiving the characteristic vector that point receives；When the two degree of association is more than threshold value, it is determined that receive the reflection echo that the ultrasonic signal that receives of point comprises the ultrasonic signal that this particular moment launches, and this reception point is detected first reflection echo when walking as described correction walk time.

Preferably, the revised ray traveltime of each ray is substituted into following Matrix Formula:

In formula, t₁’-t_n' for revising the ray traveltime after just；a_jiRepresent this i-th ray length of process in jth image-generating unit；Concrete body A is divided m image-generating unit, and ultrasonic signal is approximately fixed value f in the slowness of each image-generating unit₁-f_m；Utilize the iterative algorithm such as ART realize based on revised walk time the numerical value inverting to wave speed distribution.

Preferably, for arbitrary launch point S1 ultrasonic signal launched, metering connects this launch point and first group n the ray traveltime t receiving point₁-t_n；

For this launch point S1 ultrasonic signal launched, measure this launch point to second group n and receive t when the correction put is walked_C1-t_Cn；

The thickness HB of serving can be obtained according to engineering construction drawing or in-site measurement, and each spacing receiving point and this launch point according to second group, obtain reflection echo ray, and then draw each reflection echo ray and from the ray angle α between first group of ray respectively received a little of this launch point₁-α_n；

Calculate the modifying factor β as this ray angle linear function₁-β_n；

Based on modifying factor, it is possible to t when correction is walked_C1-t_CnIt is converted into ray traveltime correction, it may be assumed that

Δt₁=β₁·t_C1

Δt₂=β₂·t_C2

…

Δt_n=β_n·t_Cn

Utilize above ray traveltime correction, this launch point to first group is respectively received whole n ray traveltime t a little₁-t_nApply to revise, revised ray traveltime t₁’-t_n' as follows:

t₁'=t₁-Δt₁

t₂'=t₂-Δt₂

…

t_n'=t_n-Δt_n

Revised ray traveltime t₁’-t_n' as ultrasonic signal within concrete body A actual walk time.

Thus, the ultrasonic signal that the present invention has time variation feature in utilization correctly detects on the basis of reflection echo that each moment launches signal, accurately determine when correction is walked, and then according to above projectional technique, the ray traveltime in xoncrete structure ultrasound computed tomography detection process is carried out rate correction.Ray traveltime after calibrated can get rid of the impact of serving, accurately reflects the ultrasonic signal signal transmission time at inside concrete, thus for setting up good measurement data basis towards the wave speed distribution inverting of inside concrete and imaging.

Accompanying drawing explanation

Below in conjunction with the drawings and specific embodiments, the present invention is further detailed explanation:

The basic principle schematic of detection and inversion imaging when Fig. 1 is to walk；

Fig. 2 is the some position schematic diagram of launch point and reception point in ray traveltime bearing calibration of the present invention；

Fig. 3 is rate correction principle schematic of the present invention.

Detailed description of the invention

By the examples below, technical scheme is done more specifically bright.

The point position schematic diagram of launch point and reception point in ray traveltime bearing calibration of the present invention shown in Figure 2.Detect on section shown in Fig. 2, it is seen that structural member includes concrete body A and serving B.Serving B and concrete body A is mutually heterogeneous, thus forms interface between, and this interface is expressed as A-B.S₁-Sn is the launch point (launch point such as transmitting transducer) of ultrasonic signal；R₁-Rn is the reception point measured when walking for realizing ultrasonic signal, R₁-Rn is arranged at the side surface that the surface at launch point place is relative.Further, in order to correct serving B to R₁Impact when-Rn records away, at launch point S₁The phase the same side, surface at-Sn place is arranged to the reception point C of correction₁-Cn。

In ultrasound computed tomography detection process, launch point S₁-Sn launches ultrasonic signal one by one, when each launch point launches ultrasonic signal, and each reception point R₁-Rn metering receives the time of signal Mintrop wave, as connecting this launch point and each ray traveltime receiving point.For example, for S₁Point R is received to each₁Whole n bar rays of-Rn, the ray traveltime that metering obtains is t₁-t_n。

Ultrasonic signal is incident to interface A-B at a certain angle in communication process, it may occur that reflection, produces reflection echo, and reflection echo can by receiving some C₁When-Cn receives and determines that it is walked the time of advent according to Mintrop wave, it is referred to as correction when walking；Such as, for S₁The ultrasonic signal launched, receives some C₁The correction that-Cn obtains is referred to as t when walking_C1-t_Cn.And ultrasonic signal is at interface A-B it also occur that refraction, and the ultrasonic signal after refraction continues to propagate in concrete body A, until it reaches with the opposite side surface, surface at launch point place, it is achieved receive some R₁The signal of-Rn receives, it is thus achieved that described ray traveltime t₁-t_n.The described opposite side surface, surface with launch point place also may proceed to reflectance ultrasound ripple signal, and the ultrasonic signal of reflection, as end ripple first, returns to the surface of emitter and received some C₁-Cn receives；By that analogy, some C is received₁-Cn also can receive ripple etc. at the bottom of second trip echo and secondary, and each time echo can progressively be decayed with end ripple.

Rate correction principle schematic shown in Figure 3, can obtain the thickness HB of serving B, and receive some C according to each according to engineering construction drawing or in-site measurement₁-Cn and launch point S₁Spacing, it is easy to obtain shown in Fig. 3 from launch point S₁Point C is received to each₁The reflection echo ray of-Cn, and and then draw each reflection echo ray with from launch point S₁Point R is received to each₁Ray angle α between the ray of-Rn₁-α_n.In order to avoid irrelevance is excessive, described ray angle should be maintained in the scope of 3.5-15.5 degree.As seen from Figure 3, launch point S₁Point R is received to each₁There is fixing progressive error with reflection echo ray in the ray of-Rn, when thickness HB determines, ray angle is poor with this fixed journey system is corresponding, therefore, it can, according to ray angle, calculate the modifying factor β as this ray angle linear function₁(α₁)-β_n(α_n).Based on this modifying factor, it is possible to t when correction is walked_C1-t_CnIt is converted into ray traveltime correction, it may be assumed that

Δt₁=β₁·t_C1

Δt₂=β₂·t_C2

…

Δt_n=β_n·t_Cn

Utilize above ray traveltime correction, to S₁Point R is received to each₁Whole n ray traveltime t of-Rn₁-t_nApply to revise, revised ray traveltime t₁’-t_n' as follows:

t₁'=t₁-Δt₁

t₂'=t₂-Δt₂

…

t_n'=t_n-Δt_n

Revised ray traveltime t₁’-t_n' as ultrasonic signal within concrete body A actual walk time.And then, it is possible to for launch point S₁Each launch point and R in-Sn₁Whole N bar rays between each reception point of-Rn, calculate the revised ray traveltime of each ray, then substitute into following Matrix Formula:

In formula, a_jiRepresent this i-th ray length of process in jth image-generating unit；Concrete body A is divided m image-generating unit, as in figure 2 it is shown, ultrasound wave is approximately fixed value f in the slowness (slowness is the inverse of velocity of wave) of each image-generating unit₁-f_m。

Utilize the iterative algorithm such as ART realize based on revised walk time the numerical value inverting to wave speed distribution.Difference according to wave speed distribution can reflect the position of rejected region, size, distribution and type, and wave speed distribution imaging is showed.

Ultrasound computed tomography detects duration, any point of geodesic structure is existed incidence wave (launch point S all simultaneously₁-Sn directly provides ultrasonic signal) and various reflection echo, thus each receives superposing of incidence wave that point receives and reflection echo.Wherein, some R is received₁-Rn receives and measures launch point S₁The incidence wave that-Sn directly provides, because of incidence wave because conducting path is short, thus arrives and receives some R₁-Rn's is little when walking, and signal attenuation is also smaller.But, with a reception point R₁-Rn receives different with measuring incidence wave, receives some C₁-Cn receives and measures the head wave traveltime of the reflection echo produced by interface A-B, the signal attenuation of reflection echo is obvious, and long relative to incidence wave during because walking, it is not easily distinguishable time domain is mixed in together with ripple at the bottom of other each echo and each time, this just gives and receives a some C₁T when correction is walked by-Cn_C1-t_CnMeasurement bring obstacle.

For solving this difficult problem, present invention employs feature and there is the ultrasonic signal of time variation as the detection signal of application in ultrasound computed tomography detection and rate correction.Such as, for a certain moment T1 ultrasonic signal launched, the Mintrop wave of its reflection echo arrives and receives some C₁Moment be T2；Receive some C₁Each echo and the end ripple signal of signal is also launched at T2 reception to other moment, but these echoes or end ripple signal are different from T1 due to x time, therefore the feature of its time variation is necessarily different from reflection echo Mintrop wave produced by the ultrasonic signal that the T1 moment launches.Thus, it is possible to by extracting time variation feature, the reflection echo Mintrop wave accurately obtaining T1 moment ultrasonic signal from the signal that time domain mixes arrives t when the correction receiving some C1 is walked_C1, thus avoiding error detection or inspection does not measure the Mintrop wave of reflection echo.

The mid frequency of ultrasonic signal can be adopted as the parameter of the time variation feature of ultrasonic signal.At particular moment T1, launch point launches ultrasonic signal with predetermined fixed center frequency；For the T2 reception point C1 reflection echo signal received, power spectrum method is adopted to record the mid frequency of echo-signal；Because the decay of reflection echo high frequency components is big, low frequency component decay is little, thus mid frequency can offset.Judge that the skew of mid frequency is whether within estimating threshold range, if within threshold range, determine and receive the reflection echo that the some C1 ultrasonic signal received comprises the ultrasonic signal that the T1 moment launches；T when walking as correction when walking of detection reflection echo first_C1.The mid frequency of the ultrasonic signal launched due to each moment is time-varying, thus each the echo of ultrasonic signal that beyond T1, other moment launches and end ripple be not because possessing the mid frequency within threshold range, because the reflection echo without being taken as the ultrasonic signal that the T1 moment launches is detected.

In order to improve reflection echo detection reliability further, the parameter of the time variation feature of ultrasonic signal can select wavelet-based attribute vector.Frequency range when being decomposed into N number of by ultrasonic signal, after Denoising disposal, calculates ultrasonic signal energy coefficient in frequency range when each；Energy distribution coefficient table is shown as characteristic vector (E1, E2 ... EN), the degree of association of characteristic vector with the characteristic vector of the T2 reception point C1 reflection echo received by comparing the particular moment T1 ultrasonic signal launched, when the two degree of association is more than threshold value, it is determined that receive the reflection echo that the some C1 ultrasonic signal received comprises the ultrasonic signal that the T1 moment launches；T when walking as correction when walking of detection reflection echo first_C1.Time variation because of the ultrasonic signal that each moment launches, thus each the echo of ultrasonic signal that beyond T1, other moment launches and end ripple be not because possessing the characteristic vector within relevance threshold, because the reflection echo without being taken as the ultrasonic signal that the T1 moment launches is detected.

Thus, the ultrasonic signal that the present invention has time variation feature in utilization correctly detects on the basis of reflection echo that each moment launches signal, accurately determine when correction is walked, and then according to above projectional technique, the ray traveltime in xoncrete structure ultrasound computed tomography detection process is carried out rate correction.Ray traveltime after calibrated can get rid of the impact of serving, accurately reflects the ultrasonic signal signal transmission time at inside concrete, thus for setting up good measurement data basis towards the wave speed distribution inverting of inside concrete and imaging.

Above example is merely to illustrate the present invention; and it is not limitation of the present invention; those of ordinary skill about technical field; without departing from the spirit and scope of the present invention; can also make a variety of changes and modification; therefore all equivalent technical schemes fall within scope of the invention, and the scope of patent protection of the present invention should be defined by the claims.

Claims (7)

1. the ray traveltime bearing calibration in a ultrasound computed tomography detection, it is characterised in that including:

At the launch point of serving surface configuration ultrasonic signal, launch point launches the ultrasonic signal with time variation characteristic parameter one by one；Wherein, the described time variation characteristic parameter that ultrasonic signal has at each x time of launch point is different；

Point is received in the side surface configuration first group relative with the surface arranging launch point；The described point that receives in first group measures the time of the signal Mintrop wave receiving described ultrasonic signal, as the ray traveltime connecting described launch point and this reception point；

The described surface that launch point is set arranges second group and receives point；Described reception point in second group receives and goes out the described ultrasonic signal reflection echo that interface produces between described serving and xoncrete structure according to described time variation characteristic parameter extraction, and metering receives the time of the signal Mintrop wave of reflection echo as when correcting；

The spacing between thickness and reception point and the launch point of second group according to described serving, obtain the reflection echo ray put that receives of described launch point to second group, and and then draw each reflection echo ray and from launch point to the ray angle received between the ray put of first group；

According to the ray angle calcu-lation modifying factor as this ray angle linear function；Ray traveltime correction it is converted into based on described modifying factor when described correction being walked；

Utilize described ray traveltime correction, apply to revise to the ray traveltime of the ray receiving point of launch point to first group.

2. the ray traveltime bearing calibration in ultrasound computed tomography according to claim 1 detection, it is characterised in that described time variation characteristic parameter is the mid frequency of ultrasonic signal.

3. the ray traveltime bearing calibration in ultrasound computed tomography according to claim 2 detection, it is characterised in that launch point launches ultrasonic signal with predetermined fixed center frequency, and the mid frequency of the ultrasonic signal of each moment transmitting of launch point is time-varying；Second group receive is put received ultrasonic signal and records the mid frequency of echo-signal；Judge that the skew of mid frequency of the ultrasonic signal of echo-signal mid frequency and the transmitting of particular transmission moment is whether within estimating threshold range, if within threshold range, then determine and receive the reflection echo that the ultrasonic signal that receives of point comprises the ultrasonic signal that this x time is launched, and this reception point is detected first reflection echo when walking as described correction walk time.

4. the ray traveltime bearing calibration in ultrasound computed tomography according to claim 1 detection, it is characterised in that described time variation characteristic parameter is wavelet-based attribute vector.

5. the ray traveltime bearing calibration in ultrasound computed tomography according to claim 4 detection, it is characterized in that, frequency range when being decomposed into N number of by the ultrasonic signal that each for launch point moment launches, calculates ultrasonic signal energy coefficient in frequency range when each after Denoising disposal；Energy distribution coefficient table is shown as characteristic vector (E1, E2...EN), and the characteristic vector of the ultrasonic signal of each moment transmitting of launch point is time-varying；Second group receive is put received ultrasonic signal and decomposes the characteristic vector that acquisition receives；The relatively characteristic vector of the ultrasonic signal that particular moment launches and the degree of association receiving the characteristic vector that point receives；When the two degree of association is more than threshold value, it is determined that receive the reflection echo that the ultrasonic signal that receives of point comprises the ultrasonic signal that this particular moment launches, and this reception point is detected first reflection echo when walking as described correction walk time.

6. the ray traveltime bearing calibration in ultrasound computed tomography according to claim 1 detection, it is characterised in that the revised ray traveltime of each ray is substituted into following Matrix Formula:

$\left[\begin{array}{c}{t_1}^{,}\\ {t_2}^{,}\\ ...\\ {t_N}^{,}\end{array}\right]=\left[\begin{array}{cccc}{a}_{11}& a_{21}& ...& a_{m1}\\ a_{12}& a_{22}& ...& a_{m2}\\ ...& & & \\ a_{1n}& a_{2n}& ...& a_{mn}\end{array}\right]\left[\begin{array}{c}{f}_1\\ f_2\\ ...\\ f_m\end{array}\right]$

In formula, t₁’-t_n' for revising the ray traveltime after just；a_jiRepresent this i-th ray length of process in jth image-generating unit；Concrete body A is divided m image-generating unit, and ultrasonic signal is approximately fixed value f in the slowness of each image-generating unit₁-f_m；Utilize the iterative algorithm such as ART realize based on revised walk time the numerical value inverting to wave speed distribution.

7. the ray traveltime bearing calibration in ultrasound computed tomography according to claim 1 detection, it is characterised in that for arbitrary launch point S1 ultrasonic signal launched, metering connects this launch point and first group n the ray traveltime t receiving point₁-t_n；

For this launch point S1 ultrasonic signal launched, measure this launch point to second group n and receive t when the correction put is walked_C1-t_Cn；

The thickness HB of serving can be obtained according to engineering construction drawing or in-site measurement, and each spacing receiving point and this launch point according to second group, obtain reflection echo ray, and then draw each reflection echo ray and from the ray angle α between first group of ray respectively received a little of this launch point₁-α_n；

Calculate the modifying factor β as this ray angle linear function₁-β_n；

Based on modifying factor, it is possible to t when correction is walked_C1-t_CnIt is converted into ray traveltime correction, it may be assumed that

Δt₁=β₁·t_C1

Δt₂=β₂·t_C2

…

Δt_n=β_n·t_Cn

Utilize above ray traveltime correction, this launch point to first group is respectively received whole n ray traveltime t a little₁-t_nApply to revise, revised ray traveltime t₁’-t_n' as follows:

t₁'=t₁-Δt₁

t₂'=t₂-Δt₂

…

t_n'=t_n-Δt_n

Revised ray traveltime t₁’-t_n' as ultrasonic signal within concrete body A actual walk time.