An observation method suitable for high-precision astronomical positioning of near-Earth targets

Abstract

The present invention provides an observation method suitable for high-precision astronomical positioning of near-Earth targets, including: tracking a target to be measured according to the ephemeris of the target to be measured; driving a high-speed CMOS camera to continuously collect N frames of images with a short exposure time as a group of short-exposure image sequences and storing them; superimposing each group of short-exposure image sequences into a long-exposure image, and extracting a reference short-exposure image at the center moment, and using the two as a group of matching images; in each group of matching images, selecting at least 3 stars from the reference short-exposure image as reference stars, and performing relative measurement on the star image of the target to be measured in the long-exposure image. The method of the present invention only needs to change the image acquisition method to obtain a matching image composed of a long-exposure image and a reference short-exposure image, so as to achieve continuous tracking and high-precision astronomical positioning of near-Earth targets. The method is not only applicable to stationary targets, but also to targets of other orbit types, and does not require additional mechanical structures, so the cost is low.

Description

Technical Field

[0001] The present invention relates to the field of astronomical observation, and in particular to an observation method suitable for high-precision astronomical positioning of near-Earth targets. Background Art

[0002] Near-Earth targets include artificial satellites and near-Earth asteroids that revolve around the Earth. Artificial satellites are generally divided into geosynchronous orbit satellites (GEO), inclined synchronous orbit satellites (IGSO), highly elliptical orbit satellites (HEO), navigation orbit satellites (MEO) and low-Earth orbit satellites (LEO) according to their orbit types. High-precision direction parameters of near-Earth targets can be obtained by using optical telescope observations and astronomical positioning methods. The basic principle of astronomical positioning is to use the stars in the observed image as reference stars and use the relative measurement method to determine the direction parameters of the target to be measured. This method can eliminate the systematic errors of the observation instrument itself and achieve higher accuracy.

[0003] At present, no matter what type of near-Earth target, its movement direction and speed are obviously different from the trajectory of star movement, and it is impossible to obtain both circular star images and circular target images at the same time during observation. Figure 1A As shown in , if the object tracked by the telescope is a star, the star image obtained by the photograph is circular, and the star image of the near-Earth target is elongated; Figure 1B As shown, if the object tracked by the telescope is a near-Earth target, the star image obtained by the capture is elongated, and the star image of the near-Earth target is circular.

[0004] At present, the following observation methods are commonly used in the field of astronomy:

[0005] (1) Telescope tracking near-Earth target mode: The telescope tracks the target to be measured, and the camera takes pictures continuously. At this time, the star image of the target to be measured is circular, but at the same time, the star image in the field of view is elongated. On the one hand, the elongated star image will cause the signal-to-noise ratio of the star image to decrease, and it will not be possible to obtain enough reference stars in the field of view. On the other hand, the accuracy of determining the center of the elongated star image is limited, resulting in a large astronomical positioning error of the target to be measured.

[0006] (2) Telescope tracking near-Earth targets in alternating long and short exposure mode: The telescope tracks the target to be measured, and the camera uses short exposure and long exposure to shoot alternately. In this case, short exposure can obtain a nearly circular star image, and long exposure can obtain a circular target image to be measured. This method has a high centering accuracy for the star image and the target image to be measured, but because the star image and the target image to be measured are not obtained at the same time, the high-frequency tracking error of the telescope will directly reduce the final astronomical positioning accuracy. Therefore, this method has very high requirements on the tracking performance of the telescope, and the hardware cost will increase exponentially.

[0007] (3) Telescope tracking star mode: The telescope tracks the stars and the camera takes pictures continuously. At this time, the star image in the field of view is circular, while the star image of the target to be measured is elongated. The elongated star image of the target to be measured reduces the signal-to-noise ratio. On the one hand, the telescope can only observe brighter near-Earth targets and cannot exert its actual detection capability. On the other hand, the accuracy in determining the center of the elongated star image is limited, resulting in a large error in the final astronomical positioning of the target to be measured.

[0008] (4) CCD drift scanning mode: When observing geosynchronous satellites, the telescope remains stationary after being in place, and the drift scanning mode and staring mode of the CCD camera are used to alternately observe stars and satellites, respectively obtaining circular star images and circular geosynchronous satellite images, thereby improving the astronomical positioning accuracy of geosynchronous satellites. However, this method is only applicable to satellites with a relatively slow relative speed to the ground, and is not applicable to other near-earth targets with faster moving speeds.

[0009] (5) Rotating CCD drift scanning mode: After the telescope is pointed in place, it remains stationary. First, according to the direction and speed of the star's movement, the CCD camera is rotated to make the direction of the star's movement consistent with the CCD charge transfer method, and the CCD drift scanning mode is used to track the star to obtain the star's circular image; then, according to the direction and speed of the near-Earth target's movement, the CCD camera is rotated to make the direction of the target's movement consistent with the CCD charge transfer method, and the CCD drift scanning mode is used to track the target to obtain the circular image of the target to be measured, thereby improving the astronomical positioning accuracy of the target to be measured. The advantage of this method is that it is applicable to near-Earth targets of different orbit types, but the step-by-step tracking mode adopted by this method cannot continuously obtain the observation data of the target to be measured, and the data density is low. At the same time, an additional high-precision rotating structure for rotating the CCD camera is required, resulting in high cost.

[0010] Therefore, there is an urgent need for a new observation method suitable for high-precision astronomical positioning of near-Earth targets to overcome the shortcomings of existing observation methods in this field. Summary of the invention

[0011] The object of the present invention is to provide an observation method suitable for high-precision astronomical positioning of near-Earth targets, so as to be suitable for high-precision astronomical positioning of various types of near-Earth targets under low-cost conditions.

[0012] In order to achieve the above object, the present invention provides an observation method suitable for high-precision astronomical positioning of near-Earth targets, which comprises:

[0013] S1: Using a telescope with tracking capability, track the target according to its ephemeris;

[0014] S2: driving the imaging terminal of the telescope to continuously collect N frames of images as a group of short exposure image sequences at a fixed short exposure time, and storing them in the memory of the computer; N is an odd number greater than 5; the imaging terminal of the telescope is a high-speed CMOS camera;

[0015] S3: superimposing each group of short exposure image sequences in the memory to obtain a long exposure image, and extracting the (N+1) / 2th short exposure image in the short exposure image sequence as a reference short exposure image, and taking the long exposure image and the reference short exposure image as a group of matching images;

[0016] S4: In each set of matching images, at least three stars are selected from the reference short-exposure image as reference stars, and relative measurement is performed on the star image of the target to be measured in the long-exposure image.

[0017] Before executing the step S4, the method further includes step S4': repeating steps S2 to S3 until the observation of the target to be measured is completed; or after executing the step S4, the method further includes step S5: repeating steps S2 to S4 until the observation of the target to be measured is completed.

[0018] The short exposure time is 10ms-2s.

[0019] The short exposure time is 0.5 s, and N=25 or 31.

[0020] Relative measurement refers to determining the celestial coordinates of the target to be measured based on the celestial coordinates of a certain number of stars in the field of view.

[0021] In step S2, the short exposure image sequence is stored in the memory of the computer.

[0022] The telescope includes a computer, FPGA or DSP for controlling its imaging terminal.

[0023] The observation method for high-precision astronomical positioning of near-Earth targets in this method is based on a high-speed CMOS camera. No additional mechanical structure is required. Only the image acquisition method needs to be changed to obtain a matching image composed of a long-exposure image and a reference short-exposure image. Continuous tracking and high-precision astronomical positioning of near-Earth targets can be achieved. This method is not only applicable to stationary targets, but also to targets of other orbit types. It does not require additional mechanical structures and is therefore less costly. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1A It is a long-exposure image taken when the object tracked by the telescope in the prior art is a star.

[0025] Figure 1B It is a long-exposure image taken when the object tracked by the telescope in the prior art is a near-earth target.

[0026] Figure 2 It is a workflow diagram of an observation method suitable for high-precision astronomical positioning of near-Earth targets according to an embodiment of the present invention.

[0027] Figure 3 It is a schematic diagram of the result of a set of N frames of short exposure image sequence.

[0028] Figure 4A It is a long exposure image obtained by superimposing N frames of a short exposure image sequence, in which the circular star image of the target is circled.

[0029] Figure 4B It is a reference short exposure image extracted from a set of short exposure image sequences, in which the approximately circular images of stars are circled. DETAILED DESCRIPTION

[0030] The observation method of the present invention applicable to high-precision astronomical positioning of near-Earth targets is performed using a telescope, and the requirements for the telescope are as follows:

[0031] (1) Based on the predicted ephemeris of the near-Earth target, the telescope has good tracking capability, and most telescopes that observe near-Earth targets have this capability. (2) The imaging terminal of the telescope should be a CMOS camera with a high frame rate.

[0032] like Figure 2 As shown, according to one embodiment of the present invention, an observation method suitable for high-precision astronomical positioning of near-Earth targets has the following workflow:

[0033] Step S1: using a telescope to track the target according to the ephemeris of the target;

[0034] Step S2: Figure 3 As shown, the imaging terminal (i.e., high-speed CMOS camera) driving the telescope continuously collects N frames of images at a fixed short exposure time as a group of short exposure image sequences, and stores them in the memory of the computer;

[0035] The total number of frames N can be any odd number greater than 5, depending on the brightness of the target to be measured. In this embodiment, N=25 or 31.

[0036] The short exposure time is determined according to the aperture of the telescope, the field of view of the telescope, and the speed of the target to be observed. The short exposure time is 10ms-2s. In this embodiment, the short exposure time is 0.5s. The total exposure time is T seconds, which is determined by the total number of frames N and the short exposure time.

[0037] The telescope may include a computer, FPGA or DSP for controlling its imaging terminal.

[0038] Step S3: Each group of short exposure image sequences (i.e., N frames of images) in the memory is superimposed to obtain a long exposure image image_Long, and the (N+1) / 2th frame of short exposure image in the short exposure image sequence is extracted as a reference short exposure image image_short, and the long exposure image and the reference short exposure image are used as a group of matching images.

[0039] Therefore, the time corresponding to the long exposure image is the middle time, in which the star image of the target to be measured is circular and the stars are elongated; the time corresponding to the reference short exposure image image_short is also the middle time, in which the star image of the target to be measured is circular (or invisible), but the star image is close to a circle; therefore, the long exposure image image_Long and the reference short exposure image image_short at the same time are a set of matching images.

[0040] Step S4: In each set of matching images, at least three stars are selected from the reference short exposure image image_short as reference stars, and the star image of the target to be measured in the long exposure image image_Long is relatively measured, so as to achieve high-precision astronomical positioning.

[0041] Relative measurement refers to determining the celestial coordinates of the target to be measured based on the celestial coordinates of a certain number of stars in the field of view. The number of reference stars is closely related to the field of view and imaging quality of the telescope. Generally, the larger the field of view (degree level, ten-degree level), the more obvious the image distortion is, and the more reference stars are needed, ranging from one hundred to several hundred; the smaller the field of view (angular classification), the smaller the image distortion is, and the fewer reference stars are needed, but at least 3. The stars selected as reference stars cannot be too dark, and it is recommended that the star image signal-to-noise ratio is greater than 3; they cannot be too bright and cannot be overexposed. Stars are celestial bodies at infinity, and the star images we observe do not reflect their size.

[0042] Figure 4A It is a long exposure image obtained by superimposing N frames of a short exposure image sequence, in which the circular star image of the target is circled. Figure 4B It is a reference short-exposure image extracted from a set of short-exposure image sequences, in which the approximately circular image of the star is circled. Since the time corresponding to these two images is T0+T / 2 (T0 is the exposure start time, T is the total exposure time), relative measurement can be performed to achieve high-precision astronomical positioning.

[0043] In addition, before executing the step S4, the method further includes step S4': repeating steps S2 to S3 until the observation of the target to be measured is completed; or after executing the step S4, the method further includes step S5: repeating steps S2 to S4 until the observation of the target to be measured is completed.

[0044] That is to say, step S4 is a data processing flow, which can be performed after each repetition of step S2-step S3 is completed, or after all repetitions of step S2-step S3 are completed.

[0045] Therefore, the advantages of the observation method applicable to high-precision astronomical positioning of near-Earth targets of the present invention are as follows:

[0046] (1) There is no need for special requirements on the tracking performance of the telescope; any conventional telescope used to observe near-Earth targets can be used;

[0047] (2) It does not require the installation of other special mechanical and electrical control mechanisms, and can be realized only by data acquisition and processing methods;

[0048] (3) In order to ensure the accuracy of astronomical positioning, in the prior art, the commonly used observation methods in this field, such as CCD drift scanning mode, are only applicable to near-Earth targets of one or two orbit types. The observation method for high-precision astronomical positioning of near-Earth targets described in the present invention uses the tracking mode of the telescope to track the target to be measured, which is not only applicable to slow geosynchronous orbit satellites (GEO), inclined synchronous orbit satellites (IGSO),

[0049] Highly elliptical orbit satellites (HEO) are also suitable for relatively fast navigation orbit satellites (MEO), low-orbit satellites (LEO) and some fast near-Earth asteroids. Based on the observation images obtained by the method of the present invention, high-precision astronomical positioning results can be obtained.

[0050] (5) In addition to the above-mentioned types of near-Earth targets, the present invention is also applicable to the observation of natural satellites (satellites of the eight major planets).

[0051] (6) In addition to ground-based telescopes, the present invention is also applicable to space-based telescope observations.

[0052] The above is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. The above embodiment of the present invention can also be modified in various ways. That is, all simple, equivalent changes and modifications made according to the claims and the description of the present invention fall within the scope of protection of the claims of the present invention. The contents not described in detail in the present invention are all conventional technical contents.

Claims

1. An observation method suitable for high-precision astronomical positioning of near-Earth targets, It is characterized in that include: Step S1: using a telescope with tracking capability to track the target according to the ephemeris of the target; Step S2: driving the imaging terminal of the telescope to continuously collect N frames of images as a group of short exposure image sequences with a fixed short exposure time, and storing them; N is an odd number greater than 5; the imaging terminal of the telescope is a high-speed CMOS camera; Step S3: superimpose each group of short exposure image sequences to obtain a long exposure image, and extract the (N+1) / 2th short exposure image in the short exposure image sequence as a reference short exposure image, and use the long exposure image and the reference short exposure image as a set of matching images; Step S4: In each set of matching images, at least three stars are selected from the reference short-exposure image as reference stars, and relative measurement is performed on the star image of the target to be measured in the long-exposure image.

2. The observation method for high-precision astronomical positioning of near-Earth targets according to claim 1, It is characterized in that Before executing the step S4, the method further includes step S4': repeating steps S2 to S3 until the observation of the target to be measured is completed; or after executing the step S4, the method further includes step S5: repeating steps S2 to S4 until the observation of the target to be measured is completed.

3. The observation method for high-precision astronomical positioning of near-Earth targets according to claim 1, It is characterized in that The short exposure time is 10ms-2s.

4. The observation method for high-precision astronomical positioning of near-Earth targets according to claim 3, It is characterized in that The short exposure time is 0.5 s, and N=25 or 31.

5. The observation method for high-precision astronomical positioning of near-Earth targets according to claim 1, It is characterized in that Relative measurement refers to determining the celestial coordinates of the target to be measured based on the celestial coordinates of a certain number of stars in the field of view.

6. The observation method for high-precision astronomical positioning of near-Earth targets according to claim 1, It is characterized in that In step S2, the short exposure image sequence is stored in the memory of the computer.

7. The observation method for high-precision astronomical positioning of near-Earth targets according to claim 1, It is characterized in that The telescope includes a computer, FPGA or DSP for controlling its imaging terminal.

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