CN110850433A - Method for detecting mass center of space debris based on laser reflection tomography technology - Google Patents
Method for detecting mass center of space debris based on laser reflection tomography technology Download PDFInfo
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Abstract
The invention provides a space debris centroid detection method based on a laser reflection tomography imaging technology. The method mainly comprises the steps of acquisition of multi-angle echo signals of a detected target, registration of original echo data, blind deconvolution of data, multi-angle centroid distance calculation, maximum likelihood estimation of centroid coordinates, contour image reconstruction of the target, calibration of centroid positions and the like. According to the method, a laser echo pulse which is obtained by filtering and normalizing echo signals which vertically irradiate a target and are reflected back to a detector is used as a reference echo pulse, deconvolution processing is carried out on laser reflection echo data to obtain a target body reflectivity projection distribution function, and then the distance from a centroid, which is obtained by calculating the echo data of the angle, to a detection system is calculated. The method for detecting the mass center of the space debris can overcome the difficulties which cannot be solved by the traditional optical and microwave radars, such as small size, high speed, dark position, complex track and the like of the space debris, and can enable the mass center to be accurately determined.
Description
Technical Field
The invention relates to the technical field of Laser Reflective Tomography (LRT for short), in particular to a centroid detection method in Laser Reflective Tomography.
Background
With the rapid development of space and aerospace technologies, the fragment type space garbage such as abandoned spacecraft, disintegrated fragments, rocket ejecta, discards and the like is continuously accumulated, and great threats are generated on the safe flight of the spacecraft and the personal safety of astronauts around the earth orbit. Therefore, the detection and identification of the space debris are more and more emphasized by aerospace and defense departments of various countries. The space debris generally has the characteristics of small size, high speed, dark position, complex track and the like, so that the space debris is very difficult to detect, and the main detection modes comprise traditional optics, microwave radars and the like. The space debris detection can be divided into orbit determination, imaging, identification and the like according to the purpose, wherein the orbit determination is most important, because the running track has the most direct reference value for preventing collision, and the determination of the mass center has important significance for the orbit determination. The shapes of the space debris are different, the speed is high, and the high resolution of the pulse laser radar enables the accurate determination of the position of the centroid of the space debris to be possible.
In the space debris cleaning process, a cleaning means is required to push the space debris away from the running track. Because the space debris is generally a small dark target and has strong dynamic property, a high-precision and high-sensitivity detection means is needed to accurately acquire key parameters such as the centroid position, the outline, the scale and the like of the debris from a long distance in real time. There are typically optical imaging and radar detection means, and it is considered herein that a target centroid measurement method based on narrow pulse laser waveform acquisition and processing would be a more efficient way to achieve this. The basic principle of the method is a satellite-borne narrow pulse laser tomography technology, laser beams with full coverage of light spots are emitted to specific fragments from multiple angles, and pulse echo full-waveform information of the laser beams is obtained. Assuming that homogeneous planar debris is detected, determining the mass distribution of the planar debris along the direction of the laser beam by analyzing the relation between the intensity of the full waveform echo and time; then, another dimension of mass distribution data can be obtained by processing the full waveform echo acquired from another direction in the process of fly-by; furthermore, through image reconstruction processing of a plurality of angle laser echo waveforms, high-precision tomographic images of the laser echo waveforms can be obtained, and the contour and scale information of fragments can be extracted; and finally, determining the fragment centroid through comprehensive processing.
Disclosure of Invention
The invention aims at providing a method for determining the centroid position of a space debris based on laser reflection tomography. The method has reliable principle and high precision, and has important application value for small-space dark targets.
The invention is realized by the following technical scheme:
the method for detecting the mass center of the space debris based on the laser reflection tomography technology comprises the steps of irradiating a detection target by using pulse laser, detecting an echo by using a non-coherent detection system, regarding echo data as a convolution result of a target body reflectivity projection distribution function and a transmitted pulse waveform, obtaining the target body reflectivity projection distribution function after deconvolution, calculating the distance from the mass center to the detection system through a formula, and realizing accurate calibration of the mass center through observation data of a plurality of angles.
Preferably, the method specifically comprises the following steps:
(1) the laser emits laser beams with Gaussian pulse waveforms, the emission end modulates the laser pulses by a signal generator, the emitted beams pass through an adjustable attenuation mirror and are split by a spectroscope, one beam of light is detected by a detector and records the pulse waveform, the other beam of light is expanded by a beam expanding mirror and points to a target, and a target body is completely covered by laser spots;
(2) the target body reflects the echo after being irradiated by the laser beam, an incoherent detection system is used for detecting the echo, a single-pixel detector is used at a receiving end for directly detecting the reflected echo, and a waveform is displayed by an oscilloscope and echo data are collected after an output signal of the detector passes through a radio frequency high-speed electric signal amplifier;
(3) the target body is arranged on a rotatable turntable, the rotating speed of the turntable is uniform and controllable, the rotating angle of the turntable is adjusted, and target echo data of different angles are obtained;
(4) performing registration processing by using a target characteristic point tracking echo registration algorithm according to inherent characteristic points existing on the surface of the target;
(5) observing the registered reflection echo data, wherein the reflection echo is a nontrivial convolution result of a target body reflectivity projection distribution function and a transmitted Gaussian pulse, and deconvoluting the convolution expression by adopting a multi-frame iterative blind deconvolution method to obtain a target body reflectivity projection distribution function;
(6) calculating the distance from the centroid to the detector by using a centroid distance formula for the reflectivity projection distribution function of each angle, thereby obtaining the centroid position under the reflectivity projection distribution data of each angle, wherein the intersection point of all centroid surfaces is the accurate centroid position;
(7) after data preprocessing is finished, reconstructing a two-dimensional contour image of the space debris by using a filtering back projection algorithm according to a target body reflectivity projection distribution function obtained by deconvolution;
(8) and calibrating the position of the centroid on the target by combining the laser reflection tomography image result.
Furthermore, the detector in the step (2) is a high-bandwidth high-sensitivity Si-APD detector, and the lens is an industrial standard C-shaped optical lens with adjustable aperture and variable focus.
Further, the optical path of step (2) is designed to be in a non-transceiving coaxial mode.
Further, the determination of the precise centroid position in the step (2) is to estimate the precise centroid position of the space target according to the centroid coordinates calculated by the echo data from multiple angles by using a maximum likelihood estimation method.
Further, the registration process of step (4) specifically includes the following steps:
(41) selecting a point which is obviously different from other points in the echo signal as a first characteristic point, and selecting a second characteristic point according to the principle that the angular interval between the second characteristic point and the first characteristic point is 180 degrees and has obvious characteristics;
(42) judging whether the first feature point is shielded or not, if not, calculating the projection offset of the feature point, and correcting the projection offset of the feature point;
(43) if the first characteristic point is shielded, selecting a second characteristic point and calculating the projection offset of the second characteristic point, and correcting the projection offset of the second characteristic point;
(44) and adding 1 to the projection angle until the registration of the projection data of all the sampling angles is completed.
Further, the deconvolution in the step (5) specifically includes the following steps:
(51) giving an approximate transmit waveform estimate from the echo observation data;
(52) obtaining the estimation of the projection distribution of the reflection coefficient after the discrete non-causal Wiener filter
As an initial prediction into an incremental Wiener filter, where there is a similar gradual estimate of the emitted waveform spectrum G:
p (ω), G (ω), W (ω) are frequency spectra of P, G, W, respectively, W is a discrete form of the convolution result of the reflectivity, i.e. the discrete form of the projection data, and represents the complex conjugate;
s (ω) ═ W (ω) -P (ω) G (ω) is the frequency domain deconvolution error, γgIs the inverse of the signal-to-noise ratio of the digital version of the transmitted pulse, a constant to be estimated;
(53) thus obtained
The estimation is filtered by discrete non-causal Wiener to obtain relatively accurate estimation of incident pulse waveform g
After the echo data of each angle are processed, the relatively accurate estimation of g is obtained by utilizing the least square method
(54) Handle
And performing discrete non-causal Wiener filtering on each echo data as estimation to finally obtain relatively accurate projection distribution of the target reflection coefficient.
Further, the step (6) of estimating the centroid position specifically includes the following steps:
(61) for the reflectivity projection distribution function of each angle, calculating the distance from the centroid to the detection angle by using a centroid distance formula, and calculating a plurality of centroid distances through the reflectivity projection distribution function of the same target at multiple angles;
(62) for a plurality of calculated centroid distances, the rotation center is taken as a coordinate origin, and the estimated centroid coordinate is set as (x)c,yc) The coordinates of the detector at each angle are (x)φ1,yφ1),(xφ2,yφ2)…(xφN,yφN) So that the centroid distance error at all anglesMinimum, as the maximum likelihood estimate of the centroid coordinates; wherein r isc(φi) Is phiiThe distance of the centroid to the detector under the angle.
Further, the reconstructing the two-dimensional contour image of the space debris in the step (7) specifically includes the following steps:
(71) performing fast Fourier transform on each group of preprocessed projections;
(72) multiplying the Fourier transform by a Ram-Lak filter function;
(73) performing fast Fourier inverse transformation on the processed data;
(74) carrying out angle rearrangement on the data after inverse transformation, and carrying out pixel point valuing according to a nearest neighbor interpolation method to obtain a single-angle inverse projection graph;
(75) and superposing the back projection images of all the angles to obtain a final target reconstruction image.
The invention has the beneficial effects that:
according to the method, the centroid calculation data results of the same target at multiple angles are integrated, different calculation methods are adopted for different rotation forms, and the accurate position of the centroid is finally determined. The method for detecting the mass center of the space debris can overcome the difficulties which cannot be solved by the traditional optical and microwave radars, such as small size, high speed, dark position, complex track and the like of the space debris, and can enable the mass center to be accurately determined. By using the method, the centroid position of the space debris target can be accurately determined in a long distance, the actual position of the centroid on the target can be calibrated by using laser reflection tomography, the distance between the centroid and the target is 5.53cm, and the relative error is 0.11% in a detection distance of 50 m; on the basis of imaging resolution of 15cm, the image quality is improved by 2.7 times.
Drawings
FIG. 1 is a schematic diagram of a laser reflection tomography emission system;
FIG. 2 is a diagram of a laser reflection tomography receiving system;
FIG. 3 is a schematic diagram of feature points of projection data during data registration of a feature point tracking algorithm, where A is the projection of feature points and B is the center of projection;
FIG. 4 is a schematic diagram of multi-angle data after registration in the feature point tracking algorithm data registration;
FIG. 5 is a schematic view of a curved patch bin;
FIG. 6 is a schematic diagram of a multi-faceted echo superposition;
FIG. 7 is a continuous projection geometry;
FIG. 8 is a schematic illustration of laser reflection tomography and Fourier slicing principles;
FIG. 9 is a schematic diagram of a comparison of centroid detection calculated position to actual position;
FIG. 10 is a flow chart of a method for detecting the centroid of a spatial debris by laser reflection tomography.
Detailed Description
For a better understanding of the present invention, the present invention will be further described with reference to the following examples and the accompanying drawings, which are illustrative of the present invention and are not to be construed as limiting thereof.
A method for detecting the centroid of a space debris based on a laser reflection tomography technology is shown in FIG. 10, and specifically comprises the following steps:
the method comprises the following steps: the laser emits laser beams with Gaussian pulse waveforms, the signal generator is used at the emitting end to modulate the laser pulses, the emitted beams pass through an adjustable attenuation mirror and are split by a spectroscope, one beam of light is detected by a detector and records the pulse waveforms, the other beam of light is expanded by a beam expanding mirror and points to a target, and a target body is completely covered by laser spots, as shown in figure 1.
Step two: the target body reflects the echo after being irradiated by the laser beam, and the echo is detected by using an incoherent detection system. The receiving end directly detects the reflection echo by using a single-pixel detector, and the detector adopts a high-bandwidth high-sensitivity Si-APD detector. The lens adopts an industrial standard C-shaped aperture adjustable and zooming optical lens. After the output signal of the detector passes through a radio frequency high-speed electric signal amplifier, the oscilloscope displays the waveform and collects echo data (the maximum sampling rate is 20 GHz). Because the system is in an incoherent detection system and the target generates diffuse reflection on the laser, the optical path is designed to be in a non-transceiving coaxial mode, as shown in fig. 2.
Step three: the target body is arranged on a rotatable turntable, and the rotating speed of the turntable is uniform and controllable. Setting the rotary index value of the rotary table to be 1 degree, detecting a target laser reflection echo once when the rotary table rotates by an angle index value, obtaining a target full-angle echo after the rotary table rotates by a circle (360 degrees), and recording data as W1(t1,φ1),W2(t2,φ2)…,WN(tN,φN) Wherein N is 360.
Step four: because the imaging system has target or detector shake in the working process and the registration processing is needed to be carried out on the projection echoes of all angles, the invention carries out the registration processing by using a characteristic point tracking echo registration algorithm according to the inherent characteristic points existing on the surface of the target (as shown in figures 3 and 4):
(1) selecting a point which is obviously different from other points in the echo signal as a first characteristic point, and selecting a second characteristic point according to the principle that the angular interval between the second characteristic point and the first characteristic point is about 180 degrees and has obvious characteristics;
(2) judging whether the first feature point is shielded or not, if not, calculating the projection offset of the feature point, and correcting the projection offset of the feature point;
(3) if the first characteristic point is shielded, selecting a second characteristic point and calculating the projection offset of the second characteristic point, and correcting the projection offset of the second characteristic point;
(4) and adding 1 to the projection angle until the registration of the projection data of all the sampling angles is completed.
Step five: and observing the registered reflection echo data, wherein the reflection echo is a non-trivial convolution result of the reflectivity projection distribution and the emitted Gaussian pulse. Deconvolving the convolution expression by adopting a multi-frame iterative deconvolution method to obtain a target body reflectivity projection distribution function:
(1) giving an approximate transmit waveform estimate from the echo observation data;
(2) obtaining an estimation of the reflection coefficient projection distribution after a discrete non-causal Wiener filter (NCWF)
As an initial prediction into an incremental Wiener filter, where there is a similar gradual estimate of the emitted waveform spectrum G:
p (ω), G (ω), W (ω) are frequency spectra of P, G, W, respectively, W is a discrete form of the convolution result of the reflectivity, i.e. the discrete form of the projection data, and represents the complex conjugate.
S (ω) ═ W (ω) -P (ω) G (ω) is the frequency domain deconvolution error, γgIs the inverse of the signal-to-noise ratio of the digital version of the transmitted pulse, a constant to be estimated;
(3) thus obtained
The estimation is filtered by discrete non-causal Wiener to obtain relatively accurate estimation of incident pulse waveform g
After the echo data of each angle are processed, the relatively accurate estimation of g is obtained by utilizing the least square method
(4) Handle
And performing discrete non-causal Wiener filtering on each echo data as estimation to finally obtain relatively accurate projection distribution of the target reflection coefficient.
Step six: for the reflectivity projection distribution function of each angle, the distance from the centroid to the detection angle is calculated by using a centroid distance formula, and the intersection point of all centroid planes is the position of the centroid:
(1) first, the space debris object is simplified into a finite plane without thickness, the surface density is ρ, and the division plane is an infinitesimal surface element ds, then the centroid coordinate can be expressed by the following formula:
in the formula (x)c,yc,zc) Is the Cartesian coordinate of the centroid of the patch cluster, the integration limit obj indicates that the integration is valid in the target spatial domain, A is the area of the target, and a vector is usedThe written form is as follows:
this means that in order to solve the centroid of a planar object, the distribution rule of its mass with distance must be known.
The single angle target reflectivity profile projection can be expressed in the form of radon integration:
where l (r) is the length of the target surface over the distance r. For a planar target, the normal vector n is a constant vector (ψ)0,φ01), the target is segmented into a series of bands by distance, and the echo power intensity can be expressed as:
wherein SipIs the incident power intensity, η (phi) is a distance-independent parameter, neglecting the propagation factor r-2We get an expression for the reflectivity distribution:
p(r,φ)≡η(φ)l(r)
this indicates that the original formula can be written:
combining the above three formulas, a centroid solution formula based on the reflectance projection distribution can be obtained:
therefore, the centroid distance information can be calculated by echo signals of one angle. But for accurate positioning, multi-angle collection projection is required, and different resolving methods exist for different rotation forms.
(2) For fragmented objects that approximate polyhedral shapes and incomplete curved shapes, normal vectors
Varies with the target surface. Dividing the target into a series of ring-shaped bins according to the distance, and then dividing the ring-shaped bins into a series of small bins according to the angle, as shown in fig. 5, the formula according to the echo power intensity is as follows:
in the formula sisIs the incident power intensity, ξ is the sum of phi, zn,αnThe relevant parameters, d is the distance from the origin of coordinates to the laser, and dA is the area of the small bin, which can be expressed as
The incident power intensity and the reflected power intensity of the entire target satisfy the formula:
the reflectance projection distribution is expressed as
The mass of the annular surface element is
The distance of the mass center can be derived from z
If the target can not be completely covered by the limited angle, the reflectivity distribution information at the back shadow can be synthesized to the conjugate angle by using a conjugate projection superposition mode.
p*(z,φ)＝p(z,φ)+p(-z,φ+π)
For a fragmented object with a very complex shape, it is difficult to construct a relationship between the centroid distance and the reflectivity distribution, but for special cases such as spherical shells, a typical reflectivity distribution can be expressed as
Wherein R is the radius of the spherical shell. It is clear that p (z, phi) is an odd function with respect to z, which means that the centroid must lie at the sphere center z-0. Another special case is polyhedral shells and debris clusters, which can treat echoes as a superposition of individual surface echoes:
where n is the number of surfaces, the echo can be decomposed into sub-echoes of each surface, and as shown in fig. 6, the centroid positions are calculated respectively, and then the total centroid position is calculated comprehensively.
Step seven: after obtaining echoes of a plurality of angles, two methods for determining the position of the center of mass are available according to the relative position of the rotation center of the fragment target. One is that the centroid coincides with the center of rotation, which is a more ideal estimate for the expectation of multi-angle echo solution results:
the other is that the center of mass is not coincident with the center of rotation, and the motion trail of the center of mass is a circle taking the rotating shaft as the center of the circle, so that the center of mass distance equation satisfies
rc(φ)＝d+Rcos(φ+φ0)
Where d is the distance from the center of rotation to the laser and R is the radius of the circle.
From the relationship between successive projections, as in FIG. 7, the formula for the centroid radius of rotation and the initial angle can be derived:
wherein, Δ r1＝rc(φi+1)-rc(φi),Δr2＝rc(φi+2)-rc(φi+1) Then the estimate of the centroid distance can be written as:
step eight: for a plurality of calculated centroid distances, the rotation center is taken as a coordinate origin, and the estimated centroid coordinate is set as (x)c,yc) The coordinates of the detector at each angle are (x)φ1,yφ1),(xφ2,yφ2)…(xφN,yφN) So that the centroid distance error at all angles
Minimum, as the maximum likelihood estimate of the centroid coordinates; wherein r isc(φi) Is phiiThe distance of the centroid to the detector under the angle.
Step nine: and after the data preprocessing is finished, reconstructing a two-dimensional contour image of the space debris by using a filtering back projection algorithm according to the target body reflectivity projection distribution function obtained by deconvolution. The method specifically comprises the following steps:
(1) performing fast fourier transform on each set of the preprocessed projections, as shown in fig. 8;
(2) multiplying the Fourier transform by a Ram-Lak filter function;
(3) performing fast Fourier inverse transformation on the processed data;
(4) carrying out angle rearrangement on the data after inverse transformation, and carrying out pixel point valuing according to a nearest neighbor interpolation method to obtain a single-angle inverse projection graph;
(5) and superposing the back projection images of all the angles to obtain a final target reconstruction image.
Step ten: and calibrating the position of the centroid on the target by combining a target profile map reconstructed by laser reflection tomography.
By using the method, the centroid position of the space debris target can be accurately determined in a long distance, and the actual position of the centroid on the target can be calibrated by using laser reflection tomography, as shown in fig. 9, the distance between the centroid and the target is 5.53cm, and the relative error is 0.11% in a detection distance of 50 m; on the basis of 15cm imaging braid dividing rate, the imaging braid dividing rate is improved by 2.7 times.
The above-mentioned embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements made to the technical solution of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.
Claims (9)
1. The method for detecting the mass center of the space debris based on the laser reflection tomography technology is characterized in that: the method comprises the steps of irradiating a detection target by using pulse laser, detecting an echo by using a non-coherent detection system, regarding echo data as a convolution result of a target body reflectivity projection distribution function and a transmitted pulse waveform, obtaining the target body reflectivity projection distribution function after deconvolution, calculating the distance from a centroid to the detection system through a formula, and realizing accurate calibration of the centroid through observation data of a plurality of angles.
2. The method for detecting the centroid of the space debris based on the laser reflection tomography technology as claimed in claim 1, is characterized by comprising the following steps:
(1) the laser emits laser beams with Gaussian pulse waveforms, the emission end modulates the laser pulses by a signal generator, the emitted beams pass through an adjustable attenuation mirror and are split by a spectroscope, one beam of light is detected by a detector and records the pulse waveform, the other beam of light is expanded by a beam expanding mirror and points to a target, and a target body is completely covered by laser spots;
(2) the target body reflects the echo after being irradiated by the laser beam, an incoherent detection system is used for detecting the echo, a single-pixel detector is used at a receiving end for directly detecting the reflected echo, and a waveform is displayed by an oscilloscope and echo data are collected after an output signal of the detector passes through a radio frequency high-speed electric signal amplifier;
(3) the target body is arranged on a rotatable turntable, the rotating speed of the turntable is uniform and controllable, the rotating angle of the turntable is adjusted, and target echo data of different angles are obtained;
(4) carrying out echo data registration processing by using a characteristic point tracking echo registration algorithm according to inherent characteristic points existing on the surface of the target;
(5) observing the registered reflection echo data, wherein the reflection echo is a nontrivial convolution result of a target body reflectivity projection distribution function and a transmitted Gaussian pulse, and deconvoluting the convolution expression by adopting a multi-frame iterative blind deconvolution method to obtain a target body reflectivity projection distribution function;
(6) calculating the distance from the centroid to the detector by using a centroid distance formula for the reflectivity projection distribution function of each angle, thereby obtaining the centroid position under the reflectivity projection distribution data of each angle, wherein the intersection point of all centroid surfaces is the accurate centroid position;
(7) after data preprocessing is finished, reconstructing a two-dimensional contour image of the space debris by using a filtering back projection algorithm according to a target body reflectivity projection distribution function obtained by deconvolution;
(8) and calibrating the position of the centroid on the target by combining the laser reflection tomography image result.
3. The method for detecting the centroid of the space debris based on the laser reflection tomography technology as claimed in claim 2, wherein: the detector in the step (2) is a high-bandwidth high-sensitivity Si-APD detector, and the lens is an industrial standard C-shaped optical lens with adjustable aperture and zooming.
4. The method for detecting the centroid of the space debris based on the laser reflection tomography technology as claimed in claim 2, wherein: and (3) designing the optical path in the step (2) into a non-transceiving coaxial mode.
5. The method for detecting the centroid of the space debris based on the laser reflection tomography technology as claimed in claim 2, wherein: and (2) determining the accurate centroid position, namely estimating the accurate centroid position of the space target by utilizing a maximum likelihood estimation method according to the centroid coordinates calculated by the echo data from multiple angles.
6. The method for detecting the centroid of the space debris based on the laser reflection tomography technology as claimed in claim 2, wherein the registration process of the step (4) comprises the following steps:
(41) selecting a point which is obviously different from other points in the echo signal as a first characteristic point, and selecting a second characteristic point according to the principle that the angular interval between the second characteristic point and the first characteristic point is 180 degrees and has obvious characteristics;
(42) judging whether the first feature point is shielded or not, if not, calculating the projection offset of the feature point, and correcting the projection offset of the feature point;
(43) if the first characteristic point is shielded, selecting a second characteristic point and calculating the projection offset of the second characteristic point, and correcting the projection offset of the second characteristic point;
(44) and adding 1 to the projection angle until the registration of the projection data of all the sampling angles is completed.
7. The method for detecting the centroid of the space debris based on the laser reflection tomography technology as claimed in claim 2, wherein the deconvolution of the step (5) specifically comprises the steps of:
(51) giving an approximate transmit waveform estimate from the echo observation data;
(52) obtaining the estimation of the projection distribution of the reflection coefficient after the discrete non-causal Wiener filter
As an initial prediction into an incremental Wiener filter, where there is a similar gradual estimate of the emitted waveform spectrum G:
p (ω), G (ω), W (ω) are frequency spectra of P, G, W, respectively, W is a discrete form of the convolution result of the reflectivity, i.e. the discrete form of the projection data, and represents the complex conjugate;
s (ω) ═ W (ω) -P (ω) G (ω) is the frequency domain deconvolution error, γgIs the inverse of the signal-to-noise ratio of the digital version of the transmitted pulse, a constant to be estimated;
(53) thus obtained
The estimation is filtered by discrete non-causal Wiener to obtain relatively accurate estimation of incident pulse waveform g
After the echo data of each angle are processed, the relatively accurate estimation of g is obtained by utilizing the least square method
(54) Handle
And performing discrete non-causal Wiener filtering on each echo data as estimation to finally obtain relatively accurate projection distribution of the target reflection coefficient.
8. The method for detecting the centroid of the space debris based on the laser reflection tomography technology as claimed in claim 2, wherein the step (6) of estimating the centroid position specifically comprises the steps of:
(61) for the reflectivity projection distribution function of each angle, calculating the distance from the centroid to the detection angle by using a centroid distance formula, and calculating a plurality of centroid distances through the reflectivity projection distribution function of the same target at multiple angles;
(62) for a plurality of calculated centroid distances, the rotation center is taken as a coordinate origin, and the estimated centroid coordinate is set as (x)c,yc) The coordinates of the detector at each angle are (x)φ1,yφ1),(xφ2,yφ2)…(xφN,yφN) So that the centroid distance error at all angles
Minimum, as the maximum likelihood estimate of the centroid coordinates; wherein r isc(φi) Is phiiThe distance of the centroid to the detector under the angle.
9. The method for detecting the centroid of the space debris based on the laser reflection tomography technology as claimed in claim 2, wherein the step (7) of reconstructing the two-dimensional profile image of the space debris specifically comprises the following steps:
(71) performing fast Fourier transform on each group of preprocessed projections;
(72) multiplying the Fourier transform by a Ram-Lak filter function;
(73) performing fast Fourier inverse transformation on the processed data;
(74) carrying out angle rearrangement on the data after inverse transformation, and carrying out pixel point valuing according to a nearest neighbor interpolation method to obtain a single-angle inverse projection graph;
(75) and superposing the back projection images of all the angles to obtain a final target reconstruction image.
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| Publication number | Priority date | Publication date | Assignee | Title |
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