A method for calibrating the pointing of an X-Y radio telescope

Abstract

The application discloses a kind of X-Y formula radio telescope pointing calibration method, its steps include: 1) the pointing calibration model Δy of X-Y formula telescope is constructed=C2+C3sinx-C4cosx+C7cosysinx+C8coty;Wherein, C1=α, C2=β, C5=-δ, C6=-γ, C7=χGl, α,β respectively is the corresponding code disc reading when x=0, y=0, γ is the positive direction of pointing axis Y axis deviation angle, δ is the positive direction of Y axis positive direction X axis deviation angle, ε is the deviation angle of X axis negative direction and geographic north pole, it is the angle between X axis negative direction in east-zodiacal plane and geographic east, χ is the deviation coefficient of pointing in pitch caused by gravity moment, it is the pitch angle deviation coefficient caused by atmospheric refraction;2) the numerical value of C1~C8 is obtained by using pointing error measurement data fitting calculation;3) using pointing calibration model calibrates X-Y formula telescope.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of radio astronomy, and particularly relates to a method for calibrating the pointing of an X-Y radio telescope. BACKGROUND

[0002] The invention of radio telescope has broadened the application of electromagnetic wave. With the help of radio telescope, human beings have discovered more celestial radiation, such as pulsar, fast radio burst, and neutral hydrogen in galaxy, thus deepening the understanding of the universe.

[0003] Commonly used fully movable radio telescopes include the altitude-azimuth type, the equatorial type, and the X-Y type.

[0004] The altitude-azimuth type has greater load capacity, and large radio telescopes in the prior art usually adopt this scheme. The pointing of the telescope is controlled in the form of azimuth and elevation, so that it is difficult for this type of telescope to track and observe celestial bodies near the zenith, and there is a blind area.

[0005] The equatorial type adopts a rotation axis parallel to the earth axis, which can effectively eliminate the earth rotation and better track remote celestial bodies. There is also a blind area at the two poles of the earth axis.

[0006] The X-Y type adopts the west offset east as X and the south offset north as Y, which avoids the limitations of the altitude-azimuth type near the zenith and the equatorial type at the two poles of the earth axis, and can better track fast-moving celestial bodies, such as planets, satellites, and comets. Due to the load limitation of the X-Y axis, the X-Y type telescope is usually a medium or small radio telescope.

[0007] The equatorial type and the X-Y type are similar, and are limited by the load capacity of the rotation axis, so the weight of these two types of telescopes is relatively light.

[0008] Different types of telescopes have their own advantages and disadvantages. In actual application, the most suitable telescope technical scheme should be selected according to the actual demand and objective conditions.

[0009] Due to various objective factors, such as mechanical assembly error, gravity effect, atmospheric refraction, wind load, and temperature load effect, the actual pointing of the telescope will deviate from the theoretical value. So far, many works have made in-depth research on the pointing model of the altitude-azimuth type telescope, and the commonly used methods include the spherical harmonic function expansion method and the partial correction method.

[0010] The spherical harmonic function expansion method is simple, and the model and data have high compliance accuracy. However, the model has many parameters, and the correlation between the parameters is large, which leads to poor stability of the model. Moreover, each parameter does not have actual physical meaning.

[0011] The item-by-item correction method is to establish a model according to physical factors causing the deviation. The method requires familiarity with the structure of the telescope, the ability to consider various physical factors, and accurate description of each error. The method has the characteristics of fewer parameters, faster model convergence, and each parameter has a clear physical meaning.

[0012] In the prior art, most altazimuth telescopes adopt the item-by-item correction method to correct pointing errors, such as the 13.7-meter millimeter-wave telescope of the Purple Mountain Observatory, the 65-meter radio telescope of the Shanghai Observatory, the 40-meter radio telescope of the Yunnan Observatory, and the 66-meter radio telescope of Jiamusi.

[0013] The altazimuth telescope adopts an azimuth-elevation driving mode to drive the telescope, and the polar axis direction is the zenith direction. When the observed target passes through the zenith, due to the limitation of the driving motor speed, the target cannot be normally tracked. The rotation mode adopted by the X-Y telescope is west offset south as X and south offset north as Y, and the polar axis is the geographical north-south direction. Therefore, in the observable range above the horizon, the X-Y telescope can normally track, and has the highest tracking angular velocity near the zenith. This makes the X-Y telescope very suitable for observing fast-moving celestial bodies, such as planets, satellites, and comets.

[0014] Compared with the altazimuth telescope, the X-Y telescope is less used in astronomical observation at present, and the study on its pointing model is very little. Since each parameter in the pointing model has a clear physical meaning and is closely related to the rotation structure of the telescope, the pointing model of the altazimuth telescope cannot be directly applied to the X-Y telescope, and the correction result will have a large deviation. Figure 1 The differences between the altazimuth telescope and the X-Y telescope are shown.

[0015] Therefore, it is necessary to propose a corresponding pointing model and calibration method according to the rotation structure of the X-Y telescope, so as to obtain higher pointing accuracy. SUMMARY

[0016] In view of the problems in the prior art, the purpose of the present application is to provide an X-Y radio telescope pointing calibration method. According to the mechanical structure of the X-Y radio telescope, the present application first proposes a corresponding pointing correction model, which includes correction terms such as mechanical installation, gravity deformation, and atmospheric refraction. And the X-Y radio telescope pointing calibration method is given, which effectively improves the observation pointing accuracy of the X-Y telescope.

[0017] The technical scheme of the present application is as follows:

[0018] An X-Y radio telescope pointing calibration method, the steps of which include:

[0019] 1) Constructing a pointing calibration model of the X-Y telescope

[0020]

[0021] Δy = C2 + C3 sin x - C4 cos x + C7 cos y sin x + C8 cot y;

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

[0023] (x, y) is the theoretical pointing position of the X-Y telescope encoder, α is the encoder reading corresponding to x = 0, β is the encoder reading corresponding to y = 0, γ is the angle of the pointing axis of the X-Y telescope deviating from the positive direction of the Y axis of the X-Y telescope, δ is the angle of the positive direction of the Y axis deviating from the positive direction of the X axis of the X-Y telescope, ε is the angle of the negative direction of the X axis deviating from the geographic north pole, is the angle of the negative direction of the X axis deviating from the geographic east in the east-horizontal plane, χ is the coefficient of the deviation of the pointing in the elevation caused by the gravity moment, is the coefficient of the deviation of the elevation angle caused by the atmospheric refraction;

[0024] 2) fitting and calculating the values of C1-C8 in the pointing calibration model using the pointing error measurement data of a batch of radio sources;

[0025] 3) calibrating the X-Y telescope using the pointing calibration model obtained in step 2); that is, when the X-Y telescope is expected to point at (x, y), sending the encoder position (x', y') = (x, y) + (Δx, Δy) to the X-Y telescope.

[0026] Further, determining χ according to ΔEl = χGlcosEl, and determining according to wherein G is the gravity of the movable part of the X-Y telescope, l is the distance from the center of gravity of the rotatable part of the X-Y telescope to the X-Y axis of the X-Y telescope, El represents the elevation of the X-Y telescope, and ΔEl represents the deviation of the elevation.

[0027] Further, using as the evaluation function for fitting, and taking the values of C1-C8 corresponding to the minimum value of the evaluation function as the final values of C1-C8; wherein (Δx model ,Δy model ) is the deviation value calculated using the pointing calibration model.

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

[0029] 21) selecting a group of continuous spectrum radio sources as pointing calibration sources;

[0030] 22) The X-Y type telescope points at the radio source at position (x, y), and performs cross scanning along X and Y directions, and records the signal power received by the receiver and the position information;

[0031] 23) According to the recorded signal power, the change curve of power with time is generated, and the position deviation (Δx t ,Δy t ) is calculated according to the recorded position information at time t; then the relationship curve of signal power and deviations Δx t ,Δy t is generated; then the power intensity-position curve is fitted by using the Gaussian function, and the position deviation of the pointing calibration source and the cross center is obtained;

[0032] 24) When the pointing calibration source is at different positions (x, y) in the visible sky area of the telescope, steps 22) to 23) are repeated to obtain N sets of (x i ,y i ) to (Δx i ,Δy i ); wherein (x i ,y i ) represents the i-th position (x, y), and (Δx i ,Δy i ) is the position deviation of 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 by comprising 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 comprises instructions for executing steps in the above method.

[0034] A computer readable storage medium, which stores a computer program, characterized in that the computer program is executed by a processor to realize the steps of the above method.

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

[0036] Due to the influence of mechanical manufacturing, processing, installation, code disc and environment and other factors, the telescope has a static pointing error, which must be corrected to improve the observation accuracy. The present application proposes a pointing calibration model for the X-Y type telescope, which contains the pointing error terms caused by mechanical installation, gravity deformation, atmospheric refraction and many other factors, and gives a specific telescope pointing calibration method. After the pointing error correction of the telescope by using the technical scheme of the present application, the pointing accuracy will be obviously improved, thereby effectively improving the observation performance of the telescope. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 The difference between the altazimuth and X-Y telescope is shown;

[0038] (a) Altazimuth telescope driving mode, (b) X-Y telescope driving mode.

[0039] Figure 2 The flow chart of the present application.

[0040] Figure 3 The visible sky area of the telescope, a set of trajectories of the pointing calibration source in the azimuth and elevation diagrams.

[0041] Figure 4 The telescope scanning and the calibration source motion trajectory;

[0042] (a) The deviation of the theoretically calculated trajectory (cross center) from the real position of the source (dotted line) due to the deviation of the mechanical installation, (b) the curve of the position X versus time, (c) the curve of the position Y versus time.

[0043] Figure 5 The power versus time during the cross scanning process.

[0044] Figure 6 The power versus position deviation curve;

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

[0046] Figure 7 The distribution of the sampling positions of the cross scanning of the calibration source in the sky is shown.

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

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

[0049] The present application will be further described in conjunction with the accompanying drawings, in which the examples are used to explain the present application and are not intended to limit the scope of the present application.

[0050] The calibration flow of the present application is shown in Figure 2 Fig. 1. First, the pointing model of the X-Y radio telescope is proposed: let the ideal rotation direction of the X-Y radio telescope be (x, y), for convenience, use Δx = x ′ -x and Δy = y ′ -y (where x and y are the theoretically pointing positions, and x' and y' are the actual encoder readings) to represent the pointing deviation of the telescope caused by different factors.

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

[0052] 2. Offset due to non-orthogonality between pointing axis and Y axis: Δy = 0. Where γ is the angle between the pointing axis and the positive Y axis (right-hand rule), the pointing axis represents the direction of the maximum value in the power pattern of the telescope.

[0053] 3. Offset due to non-orthogonality between Y axis and X axis: Δx = -δ cot y, Δy = 0. Where δ is the angle between the positive Y axis and the positive X axis.

[0054] 4. Offset between X axis and geographical north-south: Where ε is the angle between the negative X axis and the geographical north pole, is the angle between the projection of the negative X axis on the east-horizontal plane and the geographical east (east deviation from the horizontal).

[0055] 5. Gravity deformation: Δy = χ Gl cos y sin x. Where G is the gravity of the movable part of the telescope, l is the distance from the center of gravity to the X-Y axis. χ is the coefficient of the pointing deviation in the elevation caused by the gravity moment, which is determined by the empirical formula ΔEl = χ Gl cos El, where El represents the elevation of the telescope, and ΔEl represents the deviation in the elevation.

[0056] 6. Atmospheric refraction: Where is the coefficient of the elevation angle deviation caused by atmospheric refraction, which is determined by .

[0057] The final pointing model of X and Y is the sum of the above deviations, replacing the constants with C1-C8, which is as follows:

[0058]

[0059] αy = C2 + C3 sin x - C4 cos x + C7 cos y sin x + C8 cot y

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

[0061] The above is the pointing calibration model of the X-Y telescope. In principle, the values of the eight parameters C1-C8 can be calculated by data fitting based on the measured pointing error data of a batch of radio sources. Bringing the eight best fitting parameters back into the above formula can obtain the deviation (Δx, Δy) in any (x, y) direction. In order to enable the telescope to point to the desired value (x, y), the code disc 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, providing a reference for adjusting the telescope. The inverse solution parameters are as follows:

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

[0064] The implementation of the present application uses simulation data to show 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 group of continuous spectrum radio sources as pointing calibration sources. The pointing calibration sources must have sufficient flux density for the calibrated telescope, the size should be less than 1 / 10 of the telescope beam, and there should be no other strong continuous spectrum sources around, and the trajectory should be uniformly distributed in the sky. Figure 3 The trajectory distribution of Cyg A and Cas A in the visible sky of the telescope is given.

[0066] 2. For the radio sources located in the visible sky, the telescope points at (x, y), and performs cross scanning along the X and Y directions, while recording the received signal power. As shown in Figure 4 (a), the solid and dashed lines respectively show the scanning trajectory of the telescope and the trajectory of the calibration source. Due to the deviation of mechanical installation, the theoretically calculated trajectory deviates from the true position of the source. Figure 4 (b), Figure 4 (c) respectively show the curves of the positions x and y changing with time.

[0067] 3. During the cross scanning process, record the power-time curve (as shown in Figure 5 ), and record the position information at the same time. According to the position information, calculate the position deviation (Δx t ,Δy t ), and obtain the relationship between the power and the deviations Δx t and Δy t ( Figure 6The solid line is the best fit Gaussian function. The cross-scan is repeated twice along X and Y directions, and the final position deviation is the average of the two. Thus, we get a pair of (x, y) and (Δx, Δy). Figure 6 The dashed line is the best fit Gaussian function, Figure 6 (a) is the power as a function of deviation from the position Δx t , and Figure 6 (b) is the power as a function of deviation from the position Δy t . The black arrow indicates the best fit position deviation.

[0068] 4. Repeat the cross-scan procedure for different pointing calibration sources at different positions (x, y) in the observable sky of the telescope, and get N sets of (x i ,y i )-(Δx i ,Δy i ) results, where i represents the i-th set of cross-scan results, i = 1, 2,..., N. The sampling points should be distributed as evenly as possible in the whole sky (e.g. Figure 7 ) to avoid local over-fitting.

[0069] 5. Use as the merit function. Here (Δx model ,Δy model ) is the model deviation calculated from the pointing calibration model of the X-Y telescope. Note that C1 ~ C8 are undetermined parameters at this moment. After data fitting, the merit function is minimized, and the parameters C1 ~ C8 are obtained 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. Substitute the fitted parameters back into the model, and we can get the pointing deviation (Δx, Δy) for any pointing (x, y). The final encoder reading is (x', y') = (x, y) + (Δx, Δy). Thus, we can send the pointing (x', y') to the telescope to point to the desired (i.e. theoretical) position (x, y). Figure 8 The pointing deviation distributions before and after the model correction are shown in Fig. 1 and Fig. 2, respectively. It can be seen that the model removes all systematic deviations, and the remaining error is only random.

[0071] 7. According to the fitted parameters C1 ~ C8, we can solve the physical deviations 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 a reference for telescope adjustment.

[0074] While specific embodiments of the present invention have been disclosed for illustrative purposes, intended to facilitate understanding and implementation of the present invention, those skilled in the art will appreciate that various substitutions, variations, 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 disclosure of the preferred embodiments, and the scope of protection claimed in the present invention shall be determined by the scope of the claims.

Claims

1. A method for calibrating an XY-type radio telescope pointing direction, comprising the following steps: 1) Constructing an XY telescope pointing calibration model 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 direction in pitch caused by the gravity moment, The pitch angle deviation coefficient caused by atmospheric refraction; 2) Using a batch of radio source pointing error measurement data 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 Where G is the gravity of the movable part of the XY telescope, l is the distance from the center of gravity of the movable 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 set. 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 location in the visible sky, point the XY telescope at the radio source at (x, y), perform a cross scan along the X and Y directions, and simultaneously record the signal power and position information received by the receiver; 23) Generate a power variation curve over time 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 with a Gaussian function to obtain the position deviation between the pointing calibration source and the cross center; 24) Repeat steps 22) to 23) when different pointing calibration sources are at different positions (x, y) in the visible sky area of ​​the telescope. 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 of 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.

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