A pointing model calibration method for altazimuth telescopes

Abstract

The present application relates to the technical field of altazimuth telescope, in particular to a pointing model calibration method of altazimuth telescope, the error function of the telescope is obtained by two-dimensional surface fitting, the star image is shot every 10 degrees or so in the azimuth and elevation directions, the right ascension and declination of the image center are obtained by comparing with the standard star map, the right ascension and declination are converted into the real azimuth and real elevation in the geodetic horizontal coordinate according to the shooting time, the geographical longitude and latitude of the telescope, the altitude, the air temperature and air pressure; the real azimuth and real elevation are subtracted by the azimuth and elevation read by the angle sensor of the telescope respectively, the azimuth error matrix and the elevation error matrix are obtained respectively; the error matrix is fitted to obtain the azimuth error function, the real azimuth and real elevation of any target are subtracted by the azimuth pointing error and the elevation pointing error respectively, and the accurate pointing of the telescope can be obtained.

Description

Technical Field

[0001] This invention relates to the field of altazimuth telescope technology, specifically a method for calibrating the pointing model of an altazimuth telescope. Background Technology

[0002] Altazimuth telescopes typically consist of two rotation axes: an azimuth axis and a elevation axis. Each axis is equipped with a precision angle sensor, which can rotate by a certain angle according to the telescope's input commands, thus achieving pointing and tracking of the target direction.

[0003] The adjustment of azimuth and elevation angles is based on the established geoid. Before leaving the factory, the telescope will be accurately calibrated for the angular accuracy of the azimuth and elevation axes and their relationship with the optical axis. This can be considered as an inherent systematic error in the telescope pointing model, and its magnitude is generally very small.

[0004] The pointing error of a telescope mainly comes from the deviation of the mounting plane, namely the levelness error of the telescope base and the rotation angle error. These two errors are generally difficult to measure accurately, especially the rotation angle error. Determining the due east and due north orientation of the base mounting surface is also difficult and costly.

[0005] Based on the above reasons, this invention designs a pointing model calibration method for a horizontal telescope, which calibrates the pointing error of the telescope in all directions at once, achieving high calibration accuracy in all directions. It adopts a simple sine function fitting, saving personnel and computational costs, and is highly real-time and easy to implement. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a pointing model calibration method for altazimuth telescopes. This method calibrates the pointing error of the telescope in all directions at once, achieving high calibration accuracy in all directions. It uses a simple sine function fitting method, saving personnel and computational costs, and is highly real-time and easy to implement.

[0007] To achieve the above objectives, the present invention provides a method for calibrating the pointing model of an altazimuth telescope, comprising the following steps:

[0008] S1. The azimuth and elevation angles of the telescope are injected at intervals of 10°±5° in both the azimuth and elevation directions to capture images of the night sky. The captured star charts are then matched with standard star charts to obtain the image center, which is the right ascension and declination of the telescope optical axis at epoch J2000.

[0009] S2, based on the shooting time of the starry sky image, the telescope's geographical latitude and longitude, altitude, temperature, and air pressure, converts the right ascension and declination in S1 into azimuth and elevation angles in the geodetic horizontal coordinate system, and defines them as the true azimuth and true elevation angles.

[0010] S3, subtract the telescope azimuth angle injected in S1 from the true azimuth angle, and subtract the telescope elevation angle injected in S1 from the true elevation angle in S2, to obtain the azimuth error matrix and elevation error matrix respectively.

[0011] S4. Perform function fitting on the error matrix. The error distribution satisfies the sine / cosine function distribution, which is represented by the basis function form A1sin(A2Φ+A3)+A4.

[0012] Φ represents the true azimuth angle, Θ represents the true pitch angle, and A1, A2, A3, and A4 are all functions of the pitch angle;

[0013] By fitting a function to the azimuth error matrix, azimuth error data at different azimuth angles under the same elevation angle Θ are fitted with a sine function to obtain multiple sets of coefficients:

[0014] A 11 A 21 A 31 A 41 ;

[0015] A 1i A 2i A 3i A 4i ;

[0016] A 1n A 2n A 3n A 4n ;

[0017] i = 1, 2, ..., n, where n is a positive integer, A 1i A 2i A 3i A 4i The pitch angle Θ i The corresponding basis function coefficients;

[0018] For A respectively 1i A 2i A 3i A 4i For pitch angle Θ i (i = 1, 2, ..., n) are fitted with functions A1(Θ), A2(Θ), A3(Θ), and A4(Θ) to obtain the four coefficients and Θ, or arbitrary pitch angle Θ can be obtained through interpolation. x The coefficient below;

[0019] An azimuth error function was established: ΔΦ(Θ,Φ)=A1(Θ)sin(A2(Θ)Φ+A3(Θ))+A4(Θ);

[0020] For the pitch angle error matrix, the same fitting method as the azimuth angle error matrix is ​​used to establish the pitch angle error function: ΔΘ(Θ,Φ)=B1(Θ)sin(B2(Θ)Φ+B3(Θ))+B4(Θ);

[0021] S5, Telescope pointing error correction:

[0022] First, the true azimuth and true elevation angles of the observed target are calculated using astronomical ephemeris. Then, these are substituted into the azimuth error function and elevation error function to obtain the azimuth error and elevation error in this direction; the corresponding telescope azimuth angle Φ is then calculated. T The telescope elevation angle Θ equals the true azimuth angle minus the azimuth error. T Equals the true pitch angle minus the pitch angle error, Φ T and Θ T The input can be sent to the telescope control system to achieve accurate pointing of the target.

[0023] Compared with existing technologies, this invention establishes an error dataset between the telescope's pointing direction and the actual pointing direction by photographing targets with different directions across the entire sky. It then obtains an accurate pointing error correction function through two-dimensional surface fitting, thereby simultaneously correcting the telescope's own systematic errors. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the coordinate system and errors of an altazimuth telescope. Detailed Implementation

[0025] The present invention will now be further described with reference to the accompanying drawings.

[0026] See Figure 1 :

[0027] E: Due east in the local horizontal plane;

[0028] N: Due north in the local horizontal plane;

[0029] Z: The zenith direction of the telescope in the local horizontal plane;

[0030] E1: The projection of E onto the telescope mounting plane;

[0031] N1: The projection of N onto the actual mounting plane of the telescope;

[0032] Z1: The direction of the zenith normal to the actual mounting plane of the telescope;

[0033] T: Represents the position of the telescope's azimuth 0 and elevation 0 positions on the actual mounting plane;

[0034] Among them, E, N, and Z constitute the local actual geodetic horizontal coordinate system;

[0035] E1, N1, and Z1 constitute the horizontal coordinate system of the actual installation plane;

[0036] The azimuth and elevation angles of the telescope itself are defined in E1, N1, and Z1, while the azimuth and elevation angles of the observed target are defined in E, N, and Z. The deviation between the two is the pointing error of the telescope, and the error distribution is a function of the true azimuth and the true elevation angle.

[0037] Specifically:

[0038] All-sky pointing calibration (excluding the telescope's blind zone, i.e., elevation angle greater than 86 degrees) was achieved on the 80-centimeter planetary atmospheric spectroscopic telescope at the Lenghu Planetary Geological Observatory. The telescope has a field of view of 15 arcminutes and a pixel resolution of 0.5 arcseconds. Image stabilization and tracking are achieved using a fast-swinging mirror with a field of view of 2 arcminutes, requiring a pointing accuracy within 0.5 arcminutes.

[0039] Referring to the specific parameter settings described above, the specific implementation steps of this invention are as follows:

[0040] Step 1: By injecting pointing commands into the telescope at azimuth intervals of 15 degrees (-165 degrees to 165 degrees, with due south at 0 degrees, clockwise being positive and counterclockwise being negative) and elevation intervals of 10 degrees (from 20 degrees to 80 degrees), a total of 161 sets of star images were captured. By comparing them with standard star images, the right ascension and declination values ​​corresponding to the center of each of the 161 images (i.e., the telescope's optical axis) were obtained.

[0041] Step 2: Based on the shooting time, telescope's geographical latitude and longitude, altitude, temperature and air pressure recorded in the image, convert right ascension and declination into azimuth and elevation angles in the geodetic horizontal coordinate system, which are called true azimuth and true elevation angles.

[0042] Step 3: Subtract the injected telescope azimuth from the true azimuth and subtract the injected telescope elevation from the true elevation to obtain the azimuth error matrix and elevation error matrix, respectively.

[0043] Step 4: Fit the error matrix to obtain the azimuth error function:

[0044] ΔΦ(Θ,Φ)=A1(Θ)sin(A2(Θ)Φ+A3(Θ))+A4(Θ)

[0045] Pitch angle error function:

[0046] ΔΘ(Θ,Φ)=B1(Θ)sin(B2(Θ)Φ+B3(Θ))+B4(Θ);

[0047] Step 5: Using astronomical ephemeris, first calculate the true azimuth and true elevation angles of the observed target. Substitute these values ​​into the azimuth error function and elevation error function, respectively, to obtain the azimuth error and elevation error in this direction; the corresponding telescope azimuth angle Φ T The telescope elevation angle Θ equals the true azimuth angle minus the azimuth error. T It equals the true pitch angle minus the pitch angle error. Φ T and Θ T By inputting the information into the telescope control system, accurate pointing to the target can be achieved.

[0048] The above are merely preferred embodiments of the present invention, intended only to aid in understanding the method and core ideas of this application. The scope of protection of the present invention is not limited to the above embodiments; all technical solutions falling within the scope of the present invention's concept are within its protection. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

[0049] This invention comprehensively solves the problems in existing technologies where it is difficult to accurately measure the horizontality error and rotation angle error of the telescope base, and the determination of the due east and due north orientations of the base mounting surface is difficult and costly. By measuring targets pointing in different directions across the entire sky to establish an error matrix, and by fitting a mathematical model, a pointing error correction function is obtained. At the same time, the system error of the telescope itself is corrected, thereby significantly improving the pointing accuracy of the system. High calibration accuracy can be achieved in all directions. Because a simple sine function fitting is used, it saves personnel and computing costs, has strong real-time performance, and is easy to implement.

Claims

1. A pointing model calibration method for an alt-azimuth telescope, characterized by, The method comprises the following steps: S1, injecting the telescope azimuth and the telescope elevation at intervals of 10°±5° in both azimuth and elevation directions, shooting the star image, matching the shot star image with a standard star image, and obtaining the image center, i.e. the right ascension and declination in the J2000 epoch corresponding to the optical axis of the telescope; S2, converting the right ascension and declination in S1 into the azimuth and elevation in the geodetic horizontal coordinate according to the shooting time of the star image, the geographical longitude and latitude of the telescope, the altitude, the air temperature and the air pressure, and defining the azimuth and elevation as the real azimuth and real elevation; S3, subtracting the telescope azimuth in S1 from the real azimuth, and subtracting the telescope elevation in S1 from the real elevation in S2, to obtain the azimuth error matrix and the elevation error matrix respectively; S4, performing function fitting on the error matrix, and expressing the error distribution by a base function form A1sin(A2Φ+A3)+A4, wherein the Φ represents the real azimuth, the Θ represents the real elevation, and A1, A2, A3 and A4 are all functions of the elevation; Performing function fitting on the azimuth error matrix, and performing the sine function fitting on the azimuth error data of different azimuths under the same elevation Θ to obtain a plurality of coefficients: An azimuth error function is established: ΔΦ(Θ,Φ)=A1(Θ)sin(A2(Θ)Φ+A3(Θ))+A4(Θ); A 11 ,A 21 ,A 31 ,A 41 ; A 1i ,A 2i ,A 3i ,A 4i ; A 1n ,A 2n ,A 3n ,A 4n ; where i = 1, 2,... n, n is a positive integer, A 1i ,A 2i ,A 3i ,A 4i is the pitch angle Θ i corresponding to the basis function coefficient; A 1i ,A 2i ,A 3i ,A 4i the function fitting of the pitch angle Θ i (i = 1, 2, … n) to obtain the function A1(Θ), A2(Θ), A3(Θ), A4(Θ) of the four coefficients and Θ, or through interpolation to obtain the coefficients under any pitch angle Θ x ; For the elevation error matrix, the same fitting method as that for the azimuth error matrix is adopted to establish an elevation error function: ΔΘ(Θ,Φ)=B1(Θ)sin(B2(Θ)Φ+B3(Θ))+B4(Θ); S5, correcting the pointing error of the telescope: ​ The real azimuth and the real elevation of the observed target are calculated by using astronomical ephemeris, and are respectively brought into the azimuth error function and the elevation error function to obtain the azimuth error and the elevation error of the direction; the corresponding telescope azimuth Φ T is equal to the real azimuth minus the azimuth error, and the telescope elevation Θ T is equal to the real elevation minus the elevation error, and Φ T and Θ T are input into the telescope control system, so that the accurate pointing to the target can be realized.

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