X-Y type radio telescope pointing calibration method

Abstract

The invention discloses a pointing calibration method for an X-Y type radio telescope. The method comprises the following steps: 1) constructing a pointing calibration model # imgabs0 # delta y = C2 + C3sinx-C4cosx + C7cosinx + C8coty of the X-Y type radio telescope; wherein C1 = alpha, C2 = beta, # imgabs1 # imgabs2 # C5 =-delta, C6 =-gamma, C7 = xG1, # imgabs3 # alpha and beta are code disc readings corresponding to x = 0 and y = 0 respectively, gamma is a deviation angle pointing to the Y-axis positive direction, delta is a deviation angle pointing to the Y-axis positive direction, delta is a deviation angle pointing to the X-axis positive direction, epsilon is a deviation angle pointing to the X-axis positive direction, epsilon is a deviation angle pointing to the X-axis negative direction and the geographic north pole, # imgabs4 # is an included angle pointing to the projection of the X-axis negative direction on the east-zenith plane and the geographic east, and y is a deviation angle pointing to the X-axis positive direction. X is a deviation coefficient of pointing on pitching caused by gravity torque, and # imgabs5 is a pitch angle deviation coefficient caused by atmospheric refraction; 2) performing fitting calculation by using the pointing error measurement data to obtain numerical values of C1-C8; and 3) calibrating the X-Y telescope by using the directional calibration model.

Description

Technical Field

[0001] The invention belongs to the technical field of radio astronomy, and in particular relates to a method for calibrating the pointing of an XY type radio telescope. Background Art

[0002] The invention of the radio telescope has broadened the application of electromagnetic waves. Using radio telescopes, humans have discovered more celestial radiation, such as pulsars, fast radio bursts, galactic neutral hydrogen, etc., thus deepening our understanding of the universe.

[0003] Commonly used fully movable radio telescopes include: horizontal, equatorial and XY types.

[0004] The horizontal type has a greater load-bearing capacity and is commonly used by existing large radio telescopes. It uses azimuth and elevation to control the direction of the telescope, making it difficult for such telescopes to track and observe celestial bodies near the zenith, resulting in blind spots.

[0005] The equatorial type uses a rotation axis parallel to the earth's axis, which can effectively eliminate the earth's rotation and better track distant celestial bodies. There are also blind spots at the poles of the earth's axis.

[0006] The XY type uses west-by-east as X and south-by-north as Y, avoiding the limitations of the horizontal type near the zenith and the equatorial type at the poles of the earth's axis, and can better track fast-moving celestial bodies, such as planets, satellites and comets. Due to the weight limitation of the XY axis, most XY telescopes are currently small and medium-sized radio telescopes.

[0007] The equatorial type is similar to the XY type, and both types of telescopes are lightweight due to the load-bearing limitations of their rotation axes.

[0008] Different types of telescopes have their own advantages and disadvantages. In practical applications, the most suitable telescope technology solution must be selected based on actual needs and objective conditions.

[0009] Due to the influence of various objective factors, such as mechanical assembly errors, gravity, atmospheric refraction, wind load and temperature load effects, the actual pointing of the telescope will deviate from the theoretical value. To date, many works have conducted in-depth research on the pointing model of horizontal telescopes, and commonly used methods include: spherical harmonic function expansion method and partial correction method.

[0010] The spherical harmonic expansion method is simple and the model and data are consistent with high accuracy. However, the model has many parameters and the correlation between the parameters is large, resulting in poor model stability. In addition, the parameters have no actual physical meaning.

[0011] The item-by-item correction method is to establish a model based on the physical factors that produce the deviation. This method requires familiarity with the structure of the telescope, the ability to consider various physical factors, and accurate description of each error. Its characteristics are that there are fewer parameters, the model converges quickly, and each parameter has a clear physical meaning.

[0012] In the prior art, most horizontal telescopes use a partial correction method to correct pointing errors, such as the 13.7-meter millimeter-wave telescope at Purple Mountain Observatory, the 65-meter radio telescope at Shanghai Observatory, the 40-meter radio telescope at Yunnan Observatory, and the 66-meter radio telescope at Jiamusi.

[0013] The horizontal telescope uses azimuth and pitch to drive the telescope, and its polar axis direction is the zenith direction. When the observed target passes through the zenith, it cannot be tracked normally due to the speed of the drive motor. The rotation method used by the XY telescope is that the west-south direction is X and the south-north direction is Y, and its polar axis is the geographic north-south direction. Therefore, within the observable range above the horizon, the XY telescope can track normally and has the highest tracking angular velocity near the zenith. This makes the XY telescope very suitable for the observation of fast-moving celestial bodies, such as planets, satellites, and comets.

[0014] Compared with horizontal telescopes, XY telescopes are less used in astronomical observations and their pointing models are rarely studied. Since the parameters in the pointing model have clear physical meanings and are closely related to the telescope's rotation structure, if the horizontal pointing model is directly applied to the XY telescope, the correction results will have a large deviation. Figure 1 Demonstrates the difference between horizontal and XY telescopes.

[0015] Therefore, it is necessary to propose a corresponding pointing model and calibration method according to the rotation structure of the XY telescope to obtain higher pointing accuracy. Summary of the invention

[0016] In view of the problems existing in the prior art, the purpose of the present invention is to provide a pointing calibration method for an XY radio telescope. According to the mechanical structure of the XY radio telescope, the present invention proposes a corresponding pointing correction model for the first time, which includes correction items such as mechanical installation, gravity deformation and atmospheric refraction. A pointing calibration method for an XY radio telescope is also provided, which effectively improves the observation pointing accuracy of the XY telescope.

[0017] The technical solution of the present invention is:

[0018] A method for calibrating an XY-type radio telescope pointing comprises the following steps:

[0019] 1) Constructing the pointing calibration model of the XY telescope

[0020]

[0021] Δy=C2+C3sinx-C4cosx+C7cosysinx+C8coty;

[0022] Among them, C1=α,C2=β, C5=-δ, C6=-γ, C7=χGl,

[0023] (x, y) is the theoretical pointing position of the code disk of the XY telescope, α is the code disk reading corresponding to x=0, β is the code disk reading corresponding to y=0, γ is the deviation angle of the pointing axis of the XY telescope from the positive direction of the Y axis of the XY telescope, δ is the deviation angle of the positive direction of the Y axis to the positive direction of the X axis of the XY telescope, and ε is the deviation angle of the negative direction of the X axis from the geographic North Pole. is the angle between the projection of the negative direction of the X-axis on the east-zenith plane and the geographic east, χ is the deviation coefficient of the pointing in pitch caused by the gravity moment, The pitch angle deviation coefficient caused by atmospheric refraction;

[0024] 2) Using a batch of pointing error measurement data of radio sources to fit and calculate the values ​​of C1 to C8 in the pointing calibration model;

[0025] 3) Calibrate the XY telescope using the pointing calibration model obtained in step 2); that is, when the XY telescope is expected to point to (x, y), send the code disk position (x′, y′) = (x, y) + (Δx, Δy) to the XY telescope.

[0026] Further, according to ΔEl = χGlcosEl, χ is determined, according to To determine Wherein, G is the gravity of the movable part of the XY telescope, l is the distance from the center of gravity of the rotatable part of the XY telescope to the XY axis of the XY telescope, El represents the pitch of the XY telescope, and ΔEl represents the pitch deviation.

[0027] Further, using As the evaluation function during fitting, the C1-C8 values ​​corresponding to the minimum value of the evaluation function are taken as the final C1-C8 values; where (Δx model ,Δy model ) is the deviation value calculated using the pointing calibration model.

[0028] Furthermore, a method for obtaining a batch of pointing error measurement data is as follows:

[0029] 21) Select a set of continuous spectrum radiation sources as pointing calibration sources;

[0030] 22) For a position in the visible sky area, point the XY telescope to the radio source at (x, y), perform a cross scan along the X and Y directions, and record the signal power and position information received by the receiver;

[0031] 23) Generate a power-over-time curve based on the recorded signal power, and calculate the position deviation (Δx t ,Δy t ), then generate signal power and deviation Δx t , Δy t Then, the power intensity-position curve is fitted using a Gaussian function to obtain the position deviation between the pointing calibration source and the cross center;

[0032] 24) When different pointing calibration sources are at different positions (x, y) in the visible sky area of ​​the telescope, repeat steps 22) to 23) to obtain N groups (x i ,y i )~(Δx i ,Δy i ) result; where (x i ,y i ) represents the i-th position (x, y), (Δx i ,Δy i ) is the position deviation between the pointing calibration source and the cross center at the i-th position (x, y), i = 1, 2, …, N.

[0033] An information processing terminal, characterized in that it includes a memory and a processor, the memory stores a computer program, the computer program is configured to be executed by the processor, and the computer program includes instructions for executing each step in the above method.

[0034] A computer-readable storage medium stores a computer program, wherein the computer program implements the steps of the above method when executed by a processor.

[0035] The advantages of the present invention are as follows:

[0036] Due to the influence of mechanical manufacturing, processing, installation, as well as factors such as the code disk and the environment, the telescope has a static pointing error, which must be corrected to improve the observation accuracy. The present invention proposes a pointing calibration model for an XY telescope, which includes pointing error terms caused by many factors such as mechanical installation, gravity deformation, and atmospheric refraction, and provides a specific telescope pointing calibration method. After the pointing error of the telescope is corrected using the technical solution of the present invention, the pointing accuracy will be significantly improved, thereby effectively improving the observation performance of the telescope. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Demonstrates the difference between horizontal and XY telescopes;

[0038] (a) Horizontal telescope driving mode, (b) XY telescope driving mode.

[0039] Figure 2 It is a flow chart of the present invention.

[0040] Figure 3 The trajectory of a set of pointing calibration sources in the azimuth and elevation diagrams for the area of ​​sky visible to the telescope.

[0041] Figure 4 Scan and calibrate source motion trajectories for the telescope;

[0042] (a) Due to the deviation of mechanical installation, the theoretical calculation trajectory (cross center) deviates from the actual position of the source (dotted line), (b) the curve of position X changing with time, (c) the curve of position Y changing with time.

[0043] Figure 5 This is the variation of power over time during the cross scanning process.

[0044] Figure 6 is the curve of power changing with position deviation;

[0045] (a) Power versus deviation position Δx t Change curve, (b) power versus deviation position Δy t Change curve.

[0046] Figure 7 The distribution of sampling positions on the sky for a cross scan of the calibration source is shown.

[0047] Figure 8 is the pointing deviation distribution before and after model correction;

[0048] (a) The deviation distribution of the telescope, (b) The deviation distribution of the telescope after correction using the model. DETAILED DESCRIPTION

[0049] The present invention is further described in detail below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention but not to limit the scope of the present invention.

[0050] The calibration process of the present invention is as follows Figure 2 As shown in the figure, the XY radio telescope pointing model is first proposed: Assume that the ideal rotation direction of the XY radio telescope is (x, y). For convenience, Δx = x ′ -x and Δy = y ′ -y (where x and y are theoretical pointing positions, and x′ and y′ are actual code disk readings) represents the telescope pointing deviation caused by different factors.

[0051] 1. Code disk zero point deviation: Δx = α, Δy = β. α and β are the corresponding code disk readings when x = 0 and y = 0 respectively.

[0052] 2. Deviation caused by the non-orthogonality between the pointing axis and the Y axis: Δy=0. Wherein γ is the deviation angle of the pointing axis from the positive direction of the Y axis (right-hand rule), and the pointing axis represents the direction of the maximum value in the telescope power pattern.

[0053] 3. Deviation caused by non-orthogonality between the Y axis and the X axis: Δx = -δcoty, Δy = 0. δ is the deviation angle from the positive direction of the Y axis to the positive direction of the X axis.

[0054] 4. X-axis and geographic north-south deviation: Where ε is the deviation angle between the negative direction of the X-axis and the geographic North Pole, It is the angle between the projection of the negative direction of the X-axis on the east-zenith plane and the geographic east (east zenith).

[0055] 5. Gravity deformation: Δy=χGlcosysinx. G is the gravity of the movable part of the telescope, l is the distance from the center of gravity to the XY axis. χ is the deviation coefficient of the pointing in pitch caused by the gravitational torque, which is determined by the empirical formula ΔEl=χGlcosEl, where El represents the pitch of the telescope and ΔEl represents the pitch deviation.

[0056] 6. Atmospheric refraction: in is the pitch angle deviation coefficient caused by atmospheric refraction, given by to be sure.

[0057] The final X and Y pointing models are the sum of the above deviations, with the constants replaced by C1 to C8, in the following form:

[0058]

[0059] αy=C2+C3sinx-C4cosx+C7cosysinx+C8coty

[0060] Where C1 = α, C2 = β, C5=-δ, C6=-γ, C7=χGl,

[0061] The above is the pointing calibration model of the XY telescope. In principle, the values ​​of the eight parameters C1 to C8 can be obtained by measuring the pointing error data of a batch of radio sources through data fitting calculation. Substituting these eight best fitting parameters back into the above formula, the deviation (Δx, Δy) in any (x, y) direction can be obtained. In order to make the telescope point to the expected value (x, y), the code disk position (x′, y′) = (x, y) + (Δx, Δy) can be sent to the telescope, thereby improving the pointing accuracy of the telescope.

[0062] The fitting parameters C1-C8 can be used to inversely solve the physical deviations of the telescope and provide a reference for telescope adjustment. The inverse solution parameters are as follows:

[0063] α=C1, β=C2, γ=-C6, δ=-C5, χGl=C7,

[0064] The implementation of the present invention uses simulation data to demonstrate the specific operation process. In the simulation, the telescope is located in Beijing, the antenna aperture is 7 meters, the antenna efficiency is 0.6, the system temperature is 50K, and the L-band bandwidth is 20MHz.

[0065] 1. Select a set of continuous spectrum radio sources as pointing calibration sources. The pointing calibration source must have a sufficiently strong flux density for the telescope being calibrated, the scale should be smaller than 1 / 10 of the telescope beam, and there should be no other strong continuous spectrum sources around, and the tracks should be evenly distributed in the sky. Figure 3 The distribution of the trajectories of stars such as Cyg A and Cas A in the sky visible through the telescope is given.

[0066] 2. For a position in the visible sky, point the telescope to the radio source at (x, y), perform a cross scan along the X and Y directions, and record the signal power received by the receiver. Figure 4 As shown in (a), the solid line and dashed line show the telescope scanning trajectory and calibration source trajectory respectively. Due to the deviation of mechanical installation, the theoretical calculated trajectory deviates from the actual position of the source. Figure 4 (b) Figure 4 (c) shows the curves of position x and y changing with time, respectively.

[0067] 3. During the cross scan process, record the power change curve over time (such as Figure 5 ), and record the position information at the same time. Calculate the position deviation (Δx t ,Δy t ), and the power and the deviation Δx are obtained respectively t with Δy t The relationship ( Figure 6Solid line in the middle). The power intensity-position (x or y) curve is fitted with a Gaussian function to obtain the position deviation (Δx, Δy) between the calibration source and the cross center. In the cross scanning process, the X and Y directions are generally scanned twice each, and the final position deviation is the average of the two times. Thus, a relationship between a pair of positions (x1, y1) and position deviations (Δx1, Δy1) is obtained. Figure 6 The dashed line in is the best fitting Gaussian function. Figure 6 (a) is the power variation with the deviation position Δx t Change curve, Figure 6 (b) Power versus deviation position Δy t Variation curves. Black arrows indicate the deviation from the best fit position.

[0068] 4. In the visible sky area of ​​the telescope, when different pointing calibration sources are at different positions (x, y), repeat the above cross scanning process to obtain N groups (x i ,y i )-(Δx i ,Δy i ) results, where i represents the i-th group of cross scan results, i = 1, 2, ..., N. The sampling points should be evenly distributed over the entire sky (e.g. Figure 7 ) to avoid local overfitting.

[0069] 5. Utilize As the evaluation function. model ,Δy model ) is the model deviation calculated using the pointing calibration model of the XY telescope mentioned above. Note that C1 to C8 are undetermined parameters at this time. After data fitting, the evaluation function is minimized, and the results of parameters C1 to C8 are as follows: C1 = 0.253, C2 = -0.298, C3 = 0.430, C4 = -0.248, C5 = 0.388, C6 = -0.359, C7 = 0.437, C8 = 0.485

[0070] 6. Substituting the fitting parameters back into the above model, we can get the pointing deviation (Δx, Δy) corresponding to any pointing position (x, y). The final code disk reading is (x′, y′) = (x, y) + (Δx, Δy). Thus, by sending the pointing (x′, y′) to the telescope, the telescope can be pointed to the desired (theoretical) position (x, y). Figure 8 The distribution of pointing deviations before and after model correction is shown. It can be seen that the model removes all systematic deviations, leaving only random errors.

[0071] 7. According to the fitting parameters C1~C8, the physical deviations are solved as follows:

[0072] α=0.253, β=-0.298, γ=0.359, δ=-0.388, ε=0.496, χGl=0.437,

[0073] The above parameters can provide reference for telescope adjustment.

[0074] Although the specific embodiments of the present invention are disclosed for the purpose of illustration, the purpose is to help understand the content of the present invention and implement it accordingly, those skilled in the art will understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the content disclosed in the best embodiment, and the scope of the present invention is subject to the scope defined in the claims.

Claims

1. A method for calibrating an XY-type radio telescope pointing, comprising: 1) Constructing the pointing calibration model of the XY telescope αy=C2+C3sinx-C4cosx+C7cosysinx+C8coty; Among them,C1=α,C2=β, C5=-δ, C6=-γ, C7=xGl, (x, y) is the theoretical pointing position of the code disk of the XY telescope, α is the code disk reading corresponding to x=0, β is the code disk reading corresponding to y=0, γ is the deviation angle of the pointing axis of the XY telescope from the positive direction of the Y axis of the XY telescope, δ is the deviation angle of the positive direction of the Y axis to the positive direction of the X axis of the XY telescope, and ε is the deviation angle of the negative direction of the X axis from the geographic North Pole. is the angle between the projection of the negative direction of the X-axis on the east-zenith plane and the geographic east, χ is the deviation coefficient of the pointing in pitch caused by the gravity moment, The pitch angle deviation coefficient caused by atmospheric refraction; 2) Using a batch of pointing error measurement data of radio sources to fit and calculate the values ​​of C1 to C8 in the pointing calibration model; 3) Calibrate the XY telescope using the pointing calibration model obtained in step 2); that is, when the XY telescope is expected to point to (x, y), send the code disk position (x′, y′) = (x, y) + (Δx, Δy) to the XY telescope.

2. The method according to claim 1, characterized in that Determine χ according to ΔEl = χGlcosEl, and To determine Wherein, G is the gravity of the movable part of the XY telescope, l is the distance from the center of gravity of the rotatable part of the XY telescope to the XY axis of the XY telescope, El represents the pitch of the XY telescope, and ΔEl represents the pitch deviation.

3. The method according to claim 1, characterized in that use As the evaluation function during fitting, the C1-C8 value corresponding to the minimum value of the evaluation function is taken as the final C1-C8 value; where (Δx model ,Δy model ) is the deviation value calculated using the pointing calibration model, (x i ,y i ) represents the i-th position (x, y), (Δx i ,Δy i ) is the position deviation between the calibration source and the cross center when the i-th position (x, y) is i=1,2,…,N; N is the number of pointing error measurement data sets.

4. The method according to claim 1, 2 or 3, characterized in that: The method to obtain a batch of pointing error measurement data is: 21) Select a set of continuous spectrum radiation sources as pointing calibration sources; 22) For a position in the visible sky area, point the XY telescope to the radio source at (x, y), perform a cross scan along the X and Y directions, and record the signal power and position information received by the receiver; 23) Generate a power-over-time curve based on the recorded signal power, and calculate the position deviation (Δx t ,Δy t ), then generate signal power and deviation Δx t , Δy t Then, the power intensity-position curve is fitted using a Gaussian function to obtain the position deviation between the pointing calibration source and the cross center; 24) When different pointing calibration sources are at different positions (x, y) in the visible sky area of ​​the telescope, repeat steps 22) to 23). Get N groups (x i ,y i )~(Δx i ,Δy i ) result; where (x i ,y i ) represents the i-th position (x, y), (Δx i ,Δy i ) is the position deviation between the pointing calibration source and the cross center at the i-th position (x, y), i = 1, 2, …, N.

5. An information processing terminal, characterized in that: The method comprises a memory and a processor, wherein the memory stores a computer program, the computer program is configured to be executed by the processor, and the computer program comprises instructions for executing each step in the method according to any one of claims 1 to 4.

6. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 4 are implemented.

Images