Doppler differential interferometer imaging position drift monitoring method

Abstract

The invention discloses a Doppler differential interferometer imaging position drift monitoring method, which solves the problem of inaccurate wind speed measurement result caused by drift of an interferometer image surface due to temperature change and the like. According to the method, periodic grooves are etched in the grating diffraction surface of the interferometer, namely, groove patterns serve as scales, the drift distance of the interferometer to be monitored is calculated, Doppler differential interferometer image surface drift caused by temperature changes can be effectively monitored, then the drift monitoring result is used for correcting the imaging position drift of the interferometer, and the drift distance of the interferometer to be monitored is calculated. Therefore, the accuracy of Doppler phase measurement is improved, the wind measurement accuracy of the interferometer is improved, and sub-pixel monitoring of the imaging position drift of the interferometer is realized.

Description

Technical Field

[0001] The present invention relates to a method for monitoring the drift of an interferometer imaging position, and in particular to a method for monitoring the drift of an interferometer imaging position. Background Art

[0002] As an instrument for measuring atmospheric wind fields, the Doppler differential interferometer (DDI) observes the airglow radiation emitted by the movement of neutral atmospheric particles. The precise phase is obtained by inverting the interferogram, and the Doppler shift of the airglow radiation is determined by comparing it with the phase at zero wind speed, thereby calculating the atmospheric wind speed.

[0003] In actual measurements, the parameters of the interferometer's optomechanical components can change due to factors such as temperature fluctuations, leading to drift in the interferometer image plane. This drift manifests as a small, typically sub-pixel, offset of the interference pattern on the detector image plane. This overall offset in the interference direction can cause phase error, which in turn can lead to wind speed measurement errors. To obtain more accurate wind speed measurements, it is necessary to precisely monitor the offset of the interference pattern on the detector image plane. Summary of the Invention

[0004] In order to solve the technical problem that in actual measurement, the drift of the interferometer image plane due to temperature changes and other reasons leads to inaccurate wind speed measurement results, the present invention provides a Doppler differential interferometer imaging position drift monitoring method.

[0005] The inventive concept of the present invention:

[0006] Periodic grooves are etched on the diffraction grating surface of the Doppler differential interferometer as a scale to monitor the offset of the interference image on the detector. By monitoring the offset of the groove pattern on the interference image, the drift of the interferometer image plane can be monitored, and the wind speed measurement deviation caused by thermal changes in the interferometer can be corrected.

[0007] In order to achieve the above objectives and complete the above invention concept, the present invention adopts the following technical solutions:

[0008] A Doppler differential interferometer imaging position drift monitoring method is characterized in that it includes the following steps:

[0009] Step 1, etching grooves;

[0010] Etching periodic grooves on the diffraction surface of the grating of the interferometer to be monitored;

[0011] Step 2: Data preprocessing;

[0012] generating a first interference pattern and a second interference pattern using an interferometer to be monitored, obtaining a first groove pattern corresponding to the groove in the first interference pattern and a second groove pattern corresponding to the groove in the second interference pattern, respectively, and preprocessing the first groove pattern and the second groove pattern based on a preset interpolation factor; an imaging position of the first interference pattern is offset; and an imaging position of the second interference pattern is not offset;

[0013] Step 3: Position offset detection;

[0014] Based on the preset displacement, the first groove pattern is moved multiple times in the row direction to determine the quadratic function relationship between the sum of the squares of the grayscale value differences between the second groove pattern and the first groove pattern and the preset displacement. The displacement corresponding to the minimum sum of the squares of the differences is calculated by the determined quadratic function relationship, and divided by the preset interpolation multiple to obtain the actual offset of the imaging position of the first groove pattern, which is the drift of the imaging position of the interferometer to be monitored, thereby completing the drift monitoring of the interferometer imaging position.

[0015] Furthermore, step 2 specifically includes:

[0016] 2.1. Generate multiple interferogram frames using the interferometer to be monitored, and select the first interferogram and the second interferogram from them;

[0017] 2.2. Obtain a first groove pattern in the first interference pattern, obtain a second groove pattern in the second interference pattern, and align the first groove pattern with the second groove pattern;

[0018] 2.3. For the first and second groove patterns after size alignment, perform the following operations respectively:

[0019] The grayscale values are interpolated and amplified in the row direction by a preset interpolation multiple, and the interpolated and amplified grayscale values are normalized to obtain the preprocessed first groove pattern and the second groove pattern.

[0020] Furthermore, step 3 specifically includes:

[0021] 3.1. Move the first groove pattern by N preset displacements respectively, and after each movement, calculate the sum of squared differences between the grayscale values of the second groove pattern and the first groove pattern to obtain N sums of squared differences. Then, the N preset displacements and the corresponding sums of squared differences satisfy the quadratic function relationship: y = ax 2 +bx+c, where x is the preset displacement and y is the sum of squared differences; 21≤N≤41 and N is a positive integer;

[0022] 3.2. Determine the specific values of the coefficients a, b, and c in the quadratic function relationship by least squares fitting;

[0023] 3.3. y=ax determined by fitting 2 +bx+c calculates the displacement corresponding to the minimum sum of squared differences;

[0024] 3.4. Divide the displacement obtained in step 3.3 by the preset interpolation multiple to obtain the actual offset of the imaging position of the first groove pattern, which is the drift of the interferometer imaging position to be monitored, thereby completing the interferometer imaging position drift monitoring.

[0025] Furthermore, in step 3.1:

[0026] The displacement directions of the N preset displacements are symmetrically distributed based on the center line of the second groove pattern.

[0027] Furthermore, in step 3.1:

[0028] Said N=21.

[0029] Beneficial effects of the present invention:

[0030] 1. The Doppler differential interferometer imaging position drift monitoring method provided by the present invention uses periodic grooves etched on the grating diffraction surface of the interferometer, that is, the groove pattern as a scale to calculate the drift of the interferometer to be monitored. This method can effectively monitor the Doppler differential interferometer image plane drift caused by temperature changes, and then use the drift monitoring results to correct the imaging position drift of the interferometer, thereby improving the accuracy of Doppler phase measurement, and then improving the wind measurement accuracy of the interferometer, realizing sub-pixel monitoring of the interferometer imaging position drift.

[0031] 2. Traditional methods for monitoring groove pattern drift rely on monitoring the edges of the groove pattern. This requires fitting the edge parameters of the groove pattern, resulting in low monitoring efficiency. The Doppler differential interferometer imaging position drift monitoring method provided by the present invention can monitor the deviation of the groove pattern without fitting the edge parameters of the groove pattern, thus achieving higher monitoring efficiency.

[0032] 3. The Doppler differential interferometer imaging position drift monitoring method provided by the present invention only needs to calculate the sum of squares of the differences in the groove patterns in the interference pattern, avoiding the monitoring error that may be introduced by fitting the groove edge parameters, thereby improving the monitoring accuracy and further enhancing the accuracy of the Doppler differential interferometer wind speed measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is the first interferogram generated by the interferometer to be monitored;

[0034] Figure 2 2 is a schematic diagram of the distribution of the first groove pattern data obtained in step 1.2 of an embodiment of the present invention;

[0035] Figure 3 3 is a schematic diagram of data distribution of the first groove pattern after pre-processing in step 1.3 of an embodiment of the present invention;

[0036] Figure 4 This is a schematic diagram of fitting a quadratic function relationship between the sum of squared differences and a preset displacement in step 2 of an embodiment of the present invention;

[0037] Figure 5 Schematic diagram of the displacement (red dot) corresponding to the minimum sum of squared differences in step 2.3 in an embodiment of the present invention. DETAILED DESCRIPTION

[0038] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the accompanying drawings and embodiments. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0039] An embodiment of the present invention provides a Doppler differential interferometer imaging position drift monitoring method, comprising the following steps:

[0040] Step 1, etching grooves;

[0041] Etching periodic grooves on the diffraction surface of the grating of the interferometer to be monitored;

[0042] Step 2: Data preprocessing;

[0043] Generate a first interference pattern and a second interference pattern by using an interferometer to be monitored, obtain a first groove pattern in the first interference pattern and a second groove pattern in the second interference pattern, and pre-process the first groove pattern and the second groove pattern based on a preset interpolation factor; specifically comprising:

[0044] 2.1. Generate multiple interferograms through the interferometer to be monitored, and select the first interferogram and the second interferogram from them; Figure 1 As shown, the imaging position of the first interference pattern is offset; the imaging position of the second interference pattern is not offset;

[0045] 2.2. Obtain the first groove pattern in the first interference pattern and the second groove pattern in the second interference pattern, align the first groove pattern with the second groove pattern to ensure that the first groove pattern and the second groove pattern have the same size; the data distribution of the first groove pattern is as follows: Figure 2 As shown;

[0046] 2.3. For the first and second groove patterns after size alignment, perform the following operations respectively:

[0047] The grayscale value is interpolated and amplified in the row direction by a preset interpolation multiple to achieve upsampling of the groove pattern, thereby improving the imaging drift detection accuracy.

[0048] Then, the grayscale value of the groove pattern after interpolation and amplification is normalized to make the mean grayscale value of the groove pattern 1, eliminating the influence of the overall brightness difference of the groove pattern on the image offset monitoring, and obtaining the first and second groove patterns after preprocessing; the data distribution of the first groove pattern after preprocessing is as follows: Figure 3 shown.

[0049] Step 3: Position offset detection;

[0050] like Figure 4 As shown, the first groove pattern is moved multiple times based on a preset displacement, thereby determining a quadratic function relationship between the sum of the squared differences in the grayscale values of the second groove pattern and the first groove pattern and the preset displacement. The displacement corresponding to the minimum sum of the squared differences is calculated using the determined quadratic function relationship, and divided by the preset interpolation factor to obtain the actual offset of the imaging position of the first groove pattern, which is the drift of the imaging position of the interferometer to be monitored, thereby completing the interferometer imaging position drift monitoring; specifically, the method includes:

[0051] 3.1. Move the first groove pattern by N preset displacements respectively, and after each movement, calculate the sum of squared differences between the grayscale values of the second groove pattern and the first groove pattern to obtain N sums of squared differences;

[0052] Since the first and second groove patterns drift only in the interference direction, and the groove pattern area primarily consists of the grooves and the interference fringes between them, their data distribution exhibits periodic characteristics. Furthermore, the offset of the interference image on the detector only changes the imaging position of the groove pattern on the detector. Therefore, the sum of the squares of the N preset displacements and the corresponding differences satisfies the quadratic function relationship:

[0053] y=ax 2 +bx+c;

[0054] Where x is the preset displacement and y is the sum of squared differences;

[0055] 21≤N≤41 and N is a positive integer;

[0056] The displacement directions of the N preset displacements are symmetrically distributed based on the center line of the second groove pattern.

[0057] In this embodiment, N=21.

[0058] The sum of squared differences is calculated by first interpolating the grayscale values of the second groove pattern and the first groove pattern, then square all the interpolated values, and then summing the squared values.

[0059] 3.2. Determine the specific values of the coefficients a, b, and c in the quadratic function relationship by fitting using the least squares method; in this embodiment, a=0.0073, b=-0.0052, and c=1.8020.

[0060] 3.3, such as Figure 5 As shown, using the property that the derivative of the quadratic function is zero at the minimum value, the y=ax determined by fitting 2 +bx+c calculates the displacement corresponding to the minimum sum of squared differences;

[0061] 3.4. Divide the displacement obtained in step 3.3 by the preset interpolation multiple to obtain the actual offset of the imaging position of the first groove pattern, which is the drift of the interferometer imaging position to be monitored, thereby completing the interferometer imaging position drift monitoring.

[0062] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present invention shall be covered by the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A Doppler differential interferometer imaging position drift monitoring method, characterized in that: The following steps are involved: Step 1, etching grooves; Etching periodic grooves on the diffraction surface of the grating of the interferometer to be monitored; Step 2: Data preprocessing; generating a first interference map and a second interference map by the interferometer to be monitored, respectively obtaining a first groove pattern corresponding to the groove in the first interference map and a second groove pattern corresponding to the groove in the second interference map, and preprocessing the first groove pattern and the second groove pattern based on a preset interpolation multiple; The imaging position of the first interference pattern is shifted; The imaging position of the second interference pattern does not shift; Step 3: Position offset detection; Based on the preset displacement, the first groove pattern is moved multiple times in the row direction to determine the quadratic function relationship between the sum of the squares of the grayscale value differences between the second groove pattern and the first groove pattern and the preset displacement. The displacement corresponding to the minimum sum of the squares of the differences is calculated by the determined quadratic function relationship, and divided by the preset interpolation multiple to obtain the actual offset of the imaging position of the first groove pattern, which is the drift of the imaging position of the interferometer to be monitored, thereby completing the drift monitoring of the interferometer imaging position.

2. The Doppler differential interferometer imaging position drift monitoring method according to claim 1, characterized in that: Step 2 specifically includes: 2.

1. Generate multiple interferogram frames using the interferometer to be monitored, and select the first interferogram and the second interferogram from them; 2.

2. Obtain a first groove pattern in the first interference pattern, obtain a second groove pattern in the second interference pattern, and align the first groove pattern with the second groove pattern; 2.

3. For the first and second groove patterns after size alignment, perform the following operations respectively: The grayscale values are interpolated and amplified in the row direction by a preset interpolation multiple, and the interpolated and amplified grayscale values are normalized to obtain the preprocessed first groove pattern and the second groove pattern.

3. The Doppler differential interferometer imaging position drift monitoring method according to claim 1 or 2, characterized in that: Step 3 specifically includes: 3.

1. Move the first groove pattern by N preset displacements respectively, and after each movement, calculate the sum of squared differences between the grayscale values of the second groove pattern and the first groove pattern to obtain N sums of squared differences. Then, the N preset displacements and the corresponding sums of squared differences satisfy the quadratic function relationship: y = ax 2 +bx+c, where x is the preset displacement and y is the sum of squared differences; 21≤N≤41 and N is a positive integer; 3.

2. Determine the specific values of the coefficients a, b, and c in the quadratic function relationship by least squares fitting; 3.

3. y=ax determined by fitting 2 +bx+c calculates the displacement corresponding to the minimum sum of squared differences; 3.

4. Divide the displacement obtained in step 3.3 by the preset interpolation multiple to obtain the actual offset of the imaging position of the first groove pattern, which is the drift of the interferometer imaging position to be monitored, thereby completing the interferometer imaging position drift monitoring.

4. The Doppler differential interferometer imaging position drift monitoring method according to claim 3, characterized in that: In step 3.1: The displacement directions of the N preset displacements are symmetrically distributed based on the center line of the second groove pattern.

5. The Doppler differential interferometer imaging position drift monitoring method according to claim 4, characterized in that: In step 3.1: Said N=21.

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