CN103645479A - Rapid real-time imaging method for synthetic aperture sonar - Google Patents

Abstract

The invention provides a rapid real-time imaging method for synthetic aperture sonar. According to the method, accurate propagation delay of sound waves from pixels to space sampling points is obtained according to kinematic error table look-up, and counter-propagation results of array element single sampling point echo data and process images are used for coherence stack for aperture synthesis. The method has the advantages of being accurate in imaging, small in calculation amount and capable of achieving echo data zero inventory, facilitating large-scale pipeline processing and achieving remote and large-scene high-resolution rapid real-time imaging of the seabed.

Description

A kind of quick real time imagery method of synthetic aperture sonar

Technical field

The present invention relates to the synthetic aperture sonar technical field in Underwater Acoustics Engineering, be specifically related to a kind of formation method of synthetic aperture sonar.

Background technology

Synthetic aperture sonar is ocean new and high technology of a kind of 21 century, it utilizes the rectilinear motion of small-bore basic matrix to fictionalize large aperture basic matrix, thereby the high-resolution detectivity that acquisition and signal frequency and operating distance are irrelevant, is widely used in detecting a mine, navigation channel mapping and information in ocean military field and scouts.Modern naval battle form is just being accelerated to develop to information-based, digitizing, and opportunity of combat is transient, so synthetic aperture sonar must possess at a distance, the ability of large scene, the quick real time imagery of high resolving power.

In synthetic aperture sonar field, time delay summation is a kind of theoretical optimal algorithm, it puts the sound path of each spatial sampling point on its corresponding virtual aperture by calculating pixel, obtain the propagation delay curve of pixel echo, then to echo by the sued for peace synthetic processing of virtual aperture of line.The virtual aperture that different azimuth pixel is corresponding is different, and the delay time error that kinematic error is introduced echo is relevant with the position of orientation of array element spatial sampling point in virtual aperture.Therefore, while adopting pointwise time delay to ask algorithm to the imaging of different azimuth pixel, array element needs the impact of different phase shifts ability fine compensation kinematic errors at the echo of the same space station acquisition, the calculated amount of motion compensation is very large, is difficult to meet the requirement of real time imagery.

Improved method is to carry out an aperture segmented compensation,, in the section of the sub-aperture of certain length, is similar to and thinks that the delay time error of array element kinematic error introducing is identical, and single compensation can participate in a plurality of orientation to the synthetic processing of the corresponding virtual aperture of pixel.For example sub-aperture is comprised of N array element, and echo data motion compensated result can be used for an adjacent N virtual aperture, thereby the calculated amount of motion compensation can be reduced to N doubly.In actual applications, for guaranteeing final image quality, it is excessive that sub-aperture be difficult for to be divided, although therefore this improving one's methods to a certain degree improved the synthetic speed of processing in aperture, but still is difficult to meet the requirement of remote, large scene, high resolving power real time imagery.

For guaranteeing high resolving power, the data volume that synthetic aperture sonar is processed is very large, higher to the rate request of processor.Especially under the condition of remote, large scene, the serial processing method based on uniprocessor is difficult to meet the requirement of real-time, and method for parallel processing based on multiprocessor is the effective way addressing this problem.For controlling data-interface scale, cost-saving, multiple submatrixes synthetic aperture sonar adopts pipeline and parallel design conventionally.Pipeline and parallel design distributes task serial, and data communication occurs over just adjacent subtask, and data transmission can completely asynchronously carry out, and has data-interface small scale, engineering is applied simple advantage.Due to serial distributing data, streamline scale is vulnerable to data transmission quantitative limitation.Tradition time delay summation algorithm is by accumulation original echo data formation virtual aperture, between each processing unit, volume of transmitted data is larger, data transmission holding time is longer, pipeline processes scale is restricted, and is difficult to meet the requirement of remote, large scene, the quick real time imagery of high resolution synthetic aperture sonar.

Summary of the invention

The object of the invention is to overcome the deficiency of above-mentioned technology, provide that a kind of imaging is accurate, calculated amount is little and be convenient to the synthetic aperture sonar imaging method that large-scale pipeline is processed, can realize the quick real time imagery of high resolving power to remote, large seabed scene.

The present invention is the technical scheme that technical solution problem is taked: a kind of quick real time imagery method of synthetic aperture sonar, the method is utilized the backpropagation result of array element echo data that single spatial sampling point gathers, procedural image coherence stack with buffer memory, realize fast real-time synthetic aperture processing, its concrete steps are:

Step 1: suppose that sonar platforms movement locus is straight line, the propagation delay table of the acoustical signal that prestores from each pixel in array element beam area to array element $\mathrm{\τ}=\left[{\mathrm{\τ}}_{k,n}\right]\∈Q^{L_{\mathrm{SA}}\×N},$ Wherein ${\mathrm{\τ}}_{k,n}=2\sqrt{x_k^2+{r_n}^2}/c,$ τ _k,nthe propagation delay that pixel arrives array element spatial sampling point, x _karray element spatial sampling point (x _i, 0) and to pixel (x _m, r _n) relative orientation, i.e. the position of orientation of array element in virtual aperture, x _k=x _i-x _m, k is pixel number corresponding to relative orientation, k=i-m, and n is the pixel number that pixel is corresponding with array element relative distance, L _sAbe an orientation in virtual aperture length to pixel number, N be distance to pixel number, c is the underwater sound velocity of sound, Q represents rational number set;

Step 2: reference array element beam coverage, open up the procedural image buffer area B of a formed objects, $B=\left[b_{k,n}\right]\∈C^{L_{\mathrm{SA}}\×N},$ Wherein C represents plural number set;

Step 3: echo data receives after also matched filtering, first optical fiber compass and redundancy phase center algorithm are combined and carry out multi-source estimation, and change by coordinate system, calculate sensor position uncertainties (the Δ x that carrier movement error is introduced at spatial sampling point i place _i, Δ r _i);

Step 4: according to sensor position uncertainties (Δ x _i, Δ r _i), table look-up and get the transaudient time delay of broadcasting

as pixel (x _m, r _n) to array element spatial sampling point (x _i, 0) propagation delay, Δ k wherein _i=round (Δ x _i/ δ _x), Δ n _i=round (Δ r _i/ δ _r), δ _x, δ _rbe respectively orientation to distance to pixel interval, round represents round numbers;

Step 5: according to propagation delay, array element is put to position (x in spatial sampling _i, 0) and the echo data e that receives _i(t) backpropagation is to each pixel, and with the procedural image coherence stack of buffer memory, carry out that aperture is synthetic processes, $B(k,n)=B(k,n)+e_i\left({\mathrm{\τ}}_{k+{\mathrm{\Δk}}_i,n+{\mathrm{\Δn}}_i}\right);$

Step 6:, the synthetic result in aperture is moved to a spatial sampling point interval along sonar navigation in the other direction, i.e. B (k+q, n)=B (k, n), now buffer area can overflow pixel B (L automatically _sA+ 1, n) B (L _sA+ q, n), automatically overflow the synthetic processing that pixel has all completed virtual aperture, can export and send demonstration, wherein q is that orientation corresponding to spatial sampling point interval is to pixel number;

Step 7: preserve the procedural image of buffer area, receive the echo data e that next spatial sampling point receives _i+1(t), get back to step 3.

The present invention has following remarkable result:

1, owing to there being error (Δ x _i, Δ r _i) time, pixel (x _m, r _n) to array element spatial sampling point (x _i, 0) acoustic propagation time delay be ${\mathrm{\τ}}_{k,n,i}=2\sqrt{{(x_k+{\mathrm{\Δx}}_i)}^2+{(r_n+{\mathrm{\Δr}}_i)}^2}/c,$ This time delay is just corresponding to pixel in the table that prestores

to array element spatial sampling point (x _i, 0) propagation delay value

the present invention, in the building-up process of aperture, gets

as pixel (x _m, r _n) to array element spatial sampling point (x _i, 0) propagation delay, disposable direct compensation kinematic error, the position of orientation x with array element in virtual aperture _kirrelevant, without constantly adjusting offset according to array element orientation, and the phase shift process that can avoid conventional motion to compensate, not only motion compensation is accurate, and calculated amount is very little.

2, the present invention utilizes the backpropagation result of array element echo data that single spatial sampling point gathers, with procedural image coherence stack, carry out the synthetic processing in aperture, each space adopts point to be not fully exerted to the contribution of the final imaging of virtual aperture, without forming virtual large aperture by accumulation echo data, discardable after each spatial sampling point echo data participation aperture is synthetic, realized echo data zero inventory, saved storage space.And while adopting multi-processor pipeline parallel processing, between each processing unit, only need to transmit the echo data of a spatial sampling point, volume of transmitted data is very little, greatly reduces the restriction of data transmission to streamline scale, is convenient to effectively improve aperture aggregate velocity by expanding streamline scale.

Accompanying drawing explanation

Fig. 1 is the real time signal processing process flow diagram of certain synthetic aperture sonar system of the present invention;

Fig. 2 is the aperture synthetic schemes of processor unit of the present invention.

Embodiment

Below in conjunction with the drawings and specific embodiments, the invention will be further described:

The present embodiment is certain AUV SAS system, this SAS related system element number of array 12, array element physical length 15cm, maximum detectable range 200m, imaging resolution 7.5cm * 3.75cm, real-time signal processor is completed by 7 DSP process chip, and wherein No. 1 DSP is for pulse compression and motion error extraction, and all the other 2～No. 7 DSP are for the synthesis of aperture pipeline and parallel design.SAS carries in AUV both sides, transmits, and gather the signal reflecting with some cycles.

Below in conjunction with the process flow diagram of Fig. 1 and Fig. 2, describe and utilize the present invention to carry out the synthetic process of processing in aperture to collection signal.

After signal processor starts, DSP2～DSP7 distributes according to task and array element wave beam covers, and loads propagation delay table, and the procedural image memory block of opening up formed objects.After echo data access, first DSP1 carries out matched filtering processing, improves signal to noise ratio (S/N ratio), then fully utilize optical fiber compass and RPC algorithm and estimate AUV kinematic error, and the m array element that AUV kinematic error causes while calculating pPing is put i(i=12*p+m in spatial sampling) site error (the Δ r that locates _i, Δ x _i).By sensor position uncertainties and matched filtering result e _i(t) be transferred to together synthetic aperture processing device, DSP2～DSP7 serial distributes echo data.

Each synthetic aperture processing device is received after echo data, by flow process shown in Fig. 2, carries out the synthetic processing in aperture, first gets acoustic propagation delay value

as pixel (x _m, r _n) to array element spatial sampling point (x _i, 0) propagation delay, then by echo data e _i(t) backpropagation is to interior each pixel (the pixel in beam coverage does not process) of array element beam coverage, and with the procedural image coherence stack of buffer memory, in the other direction along sonar platforms navigation finally, the synthetic result in aperture is moved to a spatial sampling point interval, overflow pixel and be bundled to the vacancy that (p+1) Ping echo data stays after this processor distribution, along with the serial distribution of data is transferred to streamline end, deliver to display terminal.

Finally should illustrate, above example is only in order to illustrate technical scheme of the present invention and not limit therewith, but can extend to other modification, variation, application in application, and think that all such modifications, variation, application are all in thought category of the present invention.

Claims (1)

1. the quick real time imagery method of synthetic aperture sonar, it is characterized in that: the method is utilized the backpropagation result of array element echo data that single spatial sampling point gathers, with the procedural image coherence stack of buffer memory, realize fast synthetic aperture processing in real time, its concrete steps are:

Step 1: suppose that sonar platforms movement locus is straight line, the propagation delay table of the acoustical signal that prestores from each pixel in array element beam area to array element $\mathrm{\τ}=\left[{\mathrm{\τ}}_{k,n}\right]\∈Q^{L_{\mathrm{SA}}\×N},$ Wherein ${\mathrm{\τ}}_{k,n}=2\sqrt{x_k^2+{r_n}^2}/c,$ τ _k,nthe propagation delay that pixel arrives array element spatial sampling point, x _karray element spatial sampling point (x _i, 0) and to pixel (x _m, r _n) relative orientation, i.e. the position of orientation of array element in virtual aperture, x _k=x _i-x _m, k is pixel number corresponding to relative orientation, k=i-m, and n is the pixel number that pixel is corresponding with array element relative distance, L _sAbe an orientation in virtual aperture length to pixel number, N be distance to pixel number, c is the underwater sound velocity of sound, Q represents rational number set;

Step 2: reference array element beam coverage, open up the procedural image buffer area B of a formed objects, $B=\left[b_{k,n}\right]\∈C^{L_{\mathrm{SA}}\×N},$ Wherein C represents plural number set;

Step 3: echo data receives after also matched filtering, first optical fiber compass and redundancy phase center algorithm are combined and carry out multi-source estimation, and change by coordinate system, calculate sensor position uncertainties (the Δ x that carrier movement error is introduced at spatial sampling point i place _i, Δ r _i);

Step 4: according to sensor position uncertainties (Δ x _i, Δ r _i), table look-up and get the transaudient time delay of broadcasting

as pixel (x _m, r _n) to array element spatial sampling point (x _i, 0) propagation delay, Δ k wherein _i=round (Δ x _i/ δ _x), Δ n _i=round (Δ r _i/ δ _r), δ _x, δ _rbe respectively orientation to distance to pixel interval, round represents round numbers;

Step 5: according to propagation delay, array element is put to position (x in spatial sampling _i, 0) and the echo data e that receives _i(t) backpropagation is to each pixel, and with the procedural image coherence stack of buffer memory, carry out that aperture is synthetic processes, $B(k,n)=B(k,n)+e_i\left({\mathrm{\τ}}_{k+{\mathrm{\Δk}}_i,n+{\mathrm{\Δn}}_i}\right);$

Step 6:, the synthetic result in aperture is moved to a spatial sampling point interval along sonar navigation in the other direction, i.e. B (k+q, n)=B (k, n), now buffer area can overflow pixel B (L automatically _sA+ 1, n) B (L _sA+ q, n), automatically overflow the synthetic processing that pixel has all completed virtual aperture, can export and send demonstration, wherein q is that orientation corresponding to spatial sampling point interval is to pixel number;

Step 7: preserve the procedural image of buffer area, receive the echo data e that next spatial sampling point receives _i+1(t), get back to step 3.

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