CN103645479B - A kind of quick real time imagery method of synthetic aperture sonar - Google Patents

Abstract

The invention provides a kind of quick real time imagery method of synthetic aperture sonar, the method is tabled look-up according to kinematic error and is obtained the accurate travel time delay of sound wave point from pixel to spatial sampling, and utilize backpropagation result and the procedural image coherence stack of array element single spatial sampling point echo data, carry out aperture synthetic, have that imaging is accurate, calculated amount is little, echo data zero inventory and be convenient to the advantage of large-scale pipeline process, the quick real time imagery of high resolving power that is remote, large scene to seabed can be realized.

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 one 21 century ocean new and high technology, it utilizes the rectilinear motion of small-bore basic matrix to fictionalize large aperture basic matrix, thus obtain the high-resolution detectivity had nothing to do with signal frequency and operating distance, be widely used in detecting a mine, navigation channel mapping and intelligence reconnaissance in ocean military field.Modern naval battle form is just being accelerated to develop to information-based, digitizing, and opportunity of combat is transient, therefore synthetic aperture sonar must possess at a distance, the ability of the quick real time imagery of large scene, high resolving power.

In synthetic aperture sonar field, time delay summation is a kind of theoretical optimal algorithm, it, by calculating the sound path of each spatial sampling point on pixel to its corresponding virtual aperture, obtains the propagation delay curve of pixel echo, the synthesis process of virtual aperture of then having sued for peace to echo by-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, when adopting pointwise time delay to ask algorithm to the imaging of different azimuth pixel, array element needs the impact of different phase shift ability fine compensation kinematic error at the echo of the same space station acquisition, and the calculated amount of motion compensation is very large, is difficult to the requirement meeting real time imagery.

The method of improvement carries out an aperture segmented compensation, namely in the sub-aperture section of certain length, is similar to and thinks that the delay time error that array element kinematic error is introduced is identical, and single compensation can participate in the synthesis process of multiple orientation to the corresponding virtual aperture of pixel.Such as sub-aperture is made up of N number of array element, then echo data motion compensated result can be used for adjacent N number of virtual aperture, thus the calculated amount of motion compensation can be reduced N doubly.In actual applications, for ensureing final image quality, sub-aperture not easily divides excessive, although therefore this improving one's methods to a certain degree improves the speed of aperture synthetic process, but still is difficult to meet remote, large scene, high resolving power real time imagery requirement.

For ensureing high resolving power, the data volume of synthetic aperture sonar process 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 the requirement meeting real-time, and is the effective way addressed this problem based on the method for parallel processing of multiprocessor.For control data interface scale, cost-saving, multiple submatrixes synthetic aperture sonar adopts pipeline and parallel design usually.Task serial distributes by pipeline and parallel design, and data communication occurs over just adjacent subtask, and data transmission can completely asynchronously be carried out, and has data-interface small scale, the simple advantage of engineer applied.Due to serial distributing data, streamline scale is vulnerable to the restriction of volume of transmitted data.Tradition time delay summation algorithm forms virtual aperture by accumulation raw radar data, 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 remote, large scene, the quick real time imagery of high resolution synthetic aperture sonar requirement.

Summary of the invention

The object of the invention is to the deficiency overcoming 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 of large-scale pipeline process, the quick real time imagery of high resolving power to remote, large seabed scene can be realized.

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 utilize the single spatial sampling point of array element gather the backpropagation result of echo data, with the procedural image coherence stack of buffer memory, realize quick real-time synthetic aperture process, its concrete steps are:

Step one: suppose that sonar platforms movement locus is straight line, the acoustical signal that prestores is from pixel each in array element beam area to the propagation delay table of array element wherein 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, and k=i-m, n are the pixel number that pixel is corresponding with array element relative distance, L _sAbe orientation in a virtual aperture length to pixel number, N be distance to pixel number, c is the underwater sound velocity of sound, and Q represents rational number set;

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

Step 3: after echo data receives also matched filtering, first optical fiber compass and redundant phase CENTER ALGORITHM are combined and carry out multi-source estimation, and by ordinate transform, 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 to get and transaudiently broadcast time delay as pixel (x _m, r _n) to array element spatial sampling point (x _i, 0) propagation delay, wherein Δ k _i=round (Δ x _i/ δ _x) _,Δ n _i=round (Δ r _i/ δ _r), δ _x, δ _rbe respectively orientation to and distance to pixel interval, round represents round numbers;

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

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

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

The present invention has following remarkable result:

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

2, the present invention utilize the single spatial sampling point of array element gather the backpropagation result of echo data, with procedural image coherence stack, carry out aperture synthetic process, each space adopts point to be not fully exerted to the contribution of the final imaging of virtual aperture, without the need to forming virtual large aperture by accumulation echo data, each spatial sampling point echo data is namely discardable after participating in aperture synthetic, achieves echo data zero inventory, has saved storage space.And when adopting multi-processor pipeline parallel processing, the echo data of a transmission spatial sampling point is only needed between each processing unit, volume of transmitted data is very little, greatly reduces the restriction of data transmission pipeline scale, is convenient to improve aperture synthetic speed by expanding streamline Size Portfolio.

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 process flow diagram 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 AUVSAS 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 used 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 is mounted in AUV both sides, transmits with some cycles, and gathers the signal reflected.

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

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

After each synthetic aperture processing device receives echo data, carry out aperture synthetic process by flow process shown in Fig. 2, first get 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 _ieach pixel (pixel not in beam coverage does not process) in (t) backpropagation to array element beam coverage, and with the procedural image coherence stack of buffer memory, in the other direction along sonar platforms navigation finally, aperture synthetic result is moved a spatial sampling point interval, spilling pixel is bundled to the vacancy that (p+1) Ping echo data stays after the distribution of this processor, 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 in application other amendment, change, application, and think that all such amendments, change, 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 utilize the single spatial sampling point of array element gather the backpropagation result of echo data, with the procedural image coherence stack of buffer memory, realize quick real-time synthetic aperture process, its concrete steps are:

Step one: suppose that sonar platforms movement locus is straight line, the acoustical signal that prestores is from pixel each in array element beam area to the propagation delay table of array element wherein 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, and k=i-m, n are the pixel number that pixel is corresponding with array element relative distance, L _sAbe orientation in a virtual aperture length to pixel number, N be distance to pixel number, c is the underwater sound velocity of sound, and Q represents rational number set;

Step 2: reference array element beam coverage, opens up the procedural image buffer area B of a formed objects, wherein C represents plural number set;

Step 3: after echo data receives also matched filtering, first optical fiber compass and redundant phase CENTER ALGORITHM are combined and carry out multi-source estimation, and by ordinate transform, 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 to get and transaudiently broadcast time delay as pixel (x _m, r _n) to array element spatial sampling point (x _i, 0) propagation delay, wherein Δ k _i=round (Δ x _i/ δ _x), Δ n _i=round (Δ r _i/ δ _r), δ _x, δ _rbe respectively orientation to and distance to pixel interval, round represents round numbers;

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

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

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