CN113280932B - Method for removing and compensating sub-aperture light spot dead pixel in coherent light communication wavefront correction - Google Patents
Method for removing and compensating sub-aperture light spot dead pixel in coherent light communication wavefront correction Download PDFInfo
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Abstract
The invention discloses a method for removing and compensating sub-aperture light spot dead pixels in coherent light communication wavefront correction, which specifically comprises the following steps: step 1, defining a response rate parameter R (i, j) as a reference variable based on the irradiation power and response voltage characteristics of a sensor sub-aperture array to a light spot; step 2, setting a threshold value T according to the response rate parameter R (i, j) defined in the step 1, judging and detecting a dead pixel of a focal plane, and setting the response rate value of the dead pixel to zero and removing the value; step 3, carrying out interpolation prediction and substitution compensation on the information of the dead point position detected in the step 2 by adopting effective point information around the dead point; and 4, repeatedly executing the steps 2-3, removing and compensating the dynamic wavefront dead pixel until the dead pixel cannot be detected within the threshold range set in the step 2, and outputting the light spot array diagram at the moment. The invention can effectively remove and compensate the dead pixel to reduce the correction error of the AO system.
Description
Technical Field
The invention belongs to the technical field of wireless laser communication, and relates to a method for removing and compensating a sub-aperture light spot dead pixel in coherent light communication wavefront correction.
Background
When laser is transmitted in the atmosphere, atmospheric turbulence can cause distortion phenomena such as optical image jitter, light intensity flicker and the like, an Adaptive Optics (AO) technology is widely used for correcting distorted wavefront caused by the atmospheric turbulence, a wavefront sensor is an important component of an AO system, and a shack-Hartmann wavefront sensor (SHWS) is a wavefront sensor which is widely applied at present. It consists of a micro lens array and a photoelectric detector arranged on the focal plane of the micro lens array. The micro lens array divides the incident wavefront into a plurality of tiny sub-apertures, the incident wavefront is focused on the focal plane of the sub-apertures through the micro lenses, and then the light intensity distribution condition at the focal plane in each sub-aperture is obtained by using a photoelectric detection device such as a CCD camera. Although the manufacturing process of the camera is continuously developed, a certain number of bad spots (failed signal spots) may still exist on the target surface of the camera.
When the laser is influenced by the strong turbulence motion of the atmosphere, or the optical path of the system is covered by noise, or the observation target signal is weak, part of the sub-apertures of the Hartmann wavefront sensor cannot receive effective optical signals or receive wrong signals. This situation can cause increased wavefront sensing errors through constant superposition in the closed loop AO system and can cause instability of the anamorphic mirror driver, thus requiring efficient handling of the sub-aperture dead spots.
Disclosure of Invention
The invention aims to provide a method for removing and compensating sub-aperture light spot dead pixels in coherent light communication wavefront correction, which can effectively remove and compensate the dead pixels so as to reduce correction errors of an AO system.
The technical scheme adopted by the invention is that the method for removing and compensating the sub-aperture light spot dead pixel in the coherent light communication wavefront correction specifically comprises the following steps:
and 4, repeatedly executing the steps 2-3, removing and compensating the dynamic wavefront dead pixel until the dead pixel cannot be detected within the threshold range set in the step 2, and outputting the light spot array diagram at the moment.
The invention is also characterized in that:
the specific process of the step 1 is as follows:
assuming that the wave front sensor is an MxN focal plane sub-aperture array, M and N are respectively the row number and the column number of focal plane sub-aperture pixels, when a plane wave front laser beam with stable working frequency is aligned to incidence without being influenced by atmospheric turbulence, the response rate R (i, j) of each sub-aperture to a light spot signal is defined as the output voltage of each pixel under unit irradiation power, and the expression is as follows:
in the formula, i is 1-M, j is 1-N, P (i, j) is the irradiation power received by the (i, j) th pixel, and V (i, j) is the response voltage of the (i, j) th pixel to the irradiation power P (i, j).
The specific process of the step 2 is as follows:
the dead pixel comprises an abnormal over-bright pixel and an abnormal over-dark pixel, and if the response rate of the actually obtained (i, j) th pixel meets the following formula, the pixel is judged to be an over-bright dead pixel:
wherein the content of the first and second substances,
h and d are the number of over-bright image elements and over-dark image elements respectively;
if the actually obtained response rate of the (i, j) th pixel meets the following relational expression, the pixel is judged to be an excessively dark dead pixel:
and setting the response value of the detected sub-aperture containing the dead pixel to zero to remove the lacking sub-aperture.
The specific process of the step 3 is as follows:
selecting 8 interpolation compensation points adjacent to the dead pixel sub-aperture, specifically:
the irradiation powers of 8 adjacent sub-apertures with P (i, j) as the center are respectively expressed as P (i, j-1), P (i, j +1), P (i-1, j-1), P (i-1, j +1), P (i-1, j), P (i +1, j-1), P (i +1, j +1) and P (i +1, j);
if the 8 adjacent sub-aperture light spots are all effective points, directly selecting to carry out the step 4;
if one sub-aperture spot of the 8 adjacent sub-aperture spots is a dead spot, a next normal element is selected as an interpolation point near the adjacent position of the spot.
In step 3, determining a weighting coefficient of interpolation compensation according to the correlation of 8 adjacent sub-apertures, specifically:
if 8 adjacent points are not dead spots, that is, 8 adjacent sub-aperture light spots are valid points, the interpolation compensation value is:
in this case, the signal contributions of 8 points to the central dead point are equal, where a, b, c, d, f, h, 1/8;
if one of the 8 neighboring points is a dead point, assuming that P (i-1, j) is a dead point, the next point P (i-2, j) is used instead, and the compensation value is:
in this case, a, c, d, f, h, 1/8, b, 1/16, and g, 3/16 are given.
The invention has the beneficial effects that based on the focal plane data response characteristic of the shack-Hartmann wavefront sensor and the correlation between adjacent pixels, the invention provides an algorithm for effectively detecting and interpolating the sub-aperture light spot dead pixel in the wireless coherent communication wavefront correction, thereby realizing the effective removal and compensation of the dead pixel and reducing the correction error of an AO system.
Drawings
Fig. 1 is a working schematic diagram of a wavefront sensor applied in the method for removing and compensating the sub-aperture speckle dead spot in the coherent optical communication wavefront correction of the present invention.
In the figure, 1 is a signal incident ray, 2 is a lens array, 3 is a CCD camera, and 4 is a CCD focal plane imaging array.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
The invention relates to a method for removing and compensating a sub-aperture light spot dead pixel in coherent light communication wavefront correction, which specifically comprises the following steps:
And defining a response rate parameter as a reference variable based on the irradiation power and response voltage characteristics of the sensor sub-aperture array to the light spot. As shown in fig. 1, a signal incident light 1 is irradiated onto a lens array 2, and the lens array 2 is connected to a CCD camera 3, thereby forming a CCD focal plane imaging array 4.
Assuming that the wavefront sensor is an M × N focal plane sub-aperture array, M and N are the number of rows and columns of focal plane sub-aperture pixels, respectively. Under the condition of not being influenced by atmospheric turbulence and adopting a plane wave front laser beam with stable working frequency to aim at incidence, the response rate R (i, j) of each sub-aperture to a light spot signal is defined as the output voltage of each pixel under the unit irradiation power, and the expression is as follows:
in the formula, i is 1-M, j is 1-N, P (i, j) is the irradiation power received by the (i, j) th pixel, and V (i, j) is the response voltage of the (i, j) th pixel to the irradiation power P (i, j).
And 2, detecting and removing the dead pixel.
And (3) setting a threshold value T according to the response rate defined in the step (1), judging and detecting a dead pixel of the focal plane, and setting the value of the response rate at the dead pixel to zero and removing the value.
And the dead pixel comprises an abnormal over-bright pixel and an abnormal over-dark pixel, and if the response rate of the actually obtained (i, j) th pixel meets the following formula, the pixel is judged to be an over-bright dead pixel.
In the formula (2), the threshold T is selected to be 10%.
The average value of the effective pixel response rate on the focal plane is:
in the formula, M and N are the number of rows and columns of the focal plane sub-aperture pixel respectively, and h and d are the number of over-bright pixels and over-dark pixels respectively.
And if the actually obtained response rate of the (i, j) th pixel meets the following relational expression, judging that the pixel is an excessively dark dead pixel.
In the formula (4), the threshold T is selected to be 10%.
The missing photon aperture is processed by zeroing the response of the detected sub-aperture containing the dead spot.
And 3, a linear interpolation compensation algorithm.
And (3) because adjacent sub-aperture light spots have extremely high correlation, carrying out interpolation prediction and substitution compensation on the information of the dead point position detected in the step (2) by adopting effective point information around the dead point.
Selecting adjacent 8-point effective data around the dead pixel for interpolation calculation;
and 3.1, selecting 8 interpolation compensation points adjacent to the dead pixel sub-aperture. The irradiation powers of 8 adjacent sub-apertures with P (i, j) as the center are respectively expressed as P (i, j-1), P (i, j +1), P (i-1, j-1), P (i-1, j +1), P (i-1, j), P (i +1, j-1), P (i +1, j +1) and P (i +1, j). If the adjacent 8 sub-aperture light spots are all effective points, directly selecting to carry out the next step; if one of the sub-aperture spots is a dead spot, the next normal element is selected as an interpolation point in the neighborhood. The distribution of the 8 interpolation compensation points is shown in table 1 below:
TABLE 1
| (i-1,j-1) | (i-1,j) | (i-1,j+1) |
| (i,j-1) | (i,j) | (i,j+1) |
| (i+1,j-1) | (i+1,j) | (i+1, |
And 3.2, determining an interpolation weighting coefficient.
And determining a weighting coefficient of interpolation compensation according to the correlation of 8 adjacent sub-apertures.
If none of the 8 neighboring points is a dead point, the interpolation compensation value is:
when the signal contributions of the 8 points to the central dead point are equal, take
a＝b＝c＝d＝e＝f＝g＝h＝1/8；
If one of the adjacent points is a dead point, assuming that P (i-1, j) is a dead point, the next point P (i-2, j) is used instead, and at this time, the compensation value is:
in this case, a, c, d, f, h, 1/8, b, 1/16, and g, 3/16 are given. And the like in other cases.
And 4, repeating the steps 2-3, removing and compensating the dynamic wavefront dead pixel until the dead pixel can not be detected within the threshold range set in the step 2, and outputting the light spot array diagram at the moment.
Claims (4)
1. The method for removing and compensating the sub-aperture light spot dead pixel in the coherent light communication wavefront correction is characterized in that: the method specifically comprises the following steps:
step 1, defining a response rate parameter R (i, j) as a reference variable based on the irradiation power and response voltage characteristics of a sensor sub-aperture array to a light spot;
the specific process of the step 1 is as follows:
assuming that the wave front sensor is an MxN focal plane sub-aperture array, M and N are respectively the row number and the column number of focal plane sub-aperture pixels, when a plane wave front laser beam with stable working frequency is aligned to incidence without being influenced by atmospheric turbulence, the response rate R (i, j) of each sub-aperture to a light spot signal is defined as the output voltage of each pixel under unit irradiation power, and the expression is as follows:
wherein i is 1-M, j is 1-N, P (i, j) is the irradiation power received by the (i, j) th pixel, and V (i, j) is the response voltage of the (i, j) th pixel to the irradiation power P (i, j);
step 2, setting a threshold value T according to the response rate parameter R (i, j) defined in the step 1, judging and detecting a dead pixel of a focal plane, and setting the response rate value of the dead pixel to zero and removing the value;
step 3, carrying out interpolation prediction and substitution compensation on the information of the dead point position detected in the step 2 by adopting effective point information around the dead point;
and 4, repeatedly executing the steps 2-3, removing and compensating the dynamic wavefront dead pixel until the dead pixel cannot be detected within the threshold range set in the step 2, and outputting the light spot array diagram at the moment.
2. The method of claim 1, wherein the sub-aperture speckle dead spot is removed and compensated for in the wavefront correction of coherent optical communication, and the method comprises: the specific process of the step 2 is as follows:
the dead pixel comprises an abnormal over-bright pixel and an abnormal over-dark pixel, and if the response rate of the actually obtained (i, j) th pixel meets the following formula, the pixel is judged to be an over-bright dead pixel:
wherein the content of the first and second substances,
h and d are the number of over-bright image elements and over-dark image elements respectively;
if the actually obtained response rate of the (i, j) th pixel meets the following relational expression, the pixel is judged to be an excessively dark dead pixel:
and setting the response value of the detected sub-aperture containing the dead pixel to zero to remove the lacking sub-aperture.
3. The method of claim 2, wherein the sub-aperture speckle noise is removed and compensated for in the wavefront correction of coherent optical communication, and the method comprises: the specific process of the step 3 is as follows:
selecting 8 interpolation compensation points adjacent to the dead pixel sub-aperture, specifically:
the irradiation powers of 8 adjacent sub-apertures with P (i, j) as the center are respectively expressed as P (i, j-1), P (i, j +1), P (i-1, j-1), P (i-1, j +1), P (i-1, j), P (i +1, j-1), P (i +1, j +1) and P (i +1, j);
if the 8 adjacent sub-aperture light spots are all effective points, directly selecting to carry out the step 4;
if one sub-aperture spot of the 8 adjacent sub-aperture spots is a dead spot, a next normal element is selected as an interpolation point near the adjacent position of the spot.
4. The method of claim 3, wherein the sub-aperture speckle noise is removed and compensated for in the wavefront correction of coherent optical communication, and the method comprises: in step 3, a weighting coefficient of interpolation compensation is determined according to the correlation of 8 adjacent sub-apertures, specifically:
if 8 adjacent points are not dead spots, that is, 8 adjacent sub-aperture light spots are valid points, the interpolation compensation value is:
in this case, the signal contributions of 8 points to the central dead point are equal, where a, b, c, d, f, h, 1/8;
if one of the 8 neighboring points is a dead point, assuming that P (i-1, j) is a dead point, the next point P (i-2, j) is used instead, and the compensation value is:
in this case, a, c, d, f, h, 1/8, b, 1/16, and g, 3/16 are given.
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