Astronomical rough north introduction method based on fixed star apparent movement speed

Abstract

The invention discloses an astronomical rough north guiding method based on fixed star apparent movement speed, which comprises the following steps: measuring an azimuth angle and an elevation angle of an observed star in an east-north-sky coordinate system of a measuring point during observation as thetadir and thetah respectively, and a latitude thetalat of the known measuring point; the cosine of the included angle between the vector of the observed star and the rotation axis can be obtained according to the point product of the vector of the observed star and the vector of the rotation axis; measuring the average angular velocity of the observed star during observation, and obtaining the sine value of the included angle delta theta se between the vector of the observed star and the rotation axis of the earth according to the ratio of the average angular velocity to the rotation speed of the earth; performing closed-form solution on the azimuth angle theta dir according to the azimuth angle theta dir; the azimuth angle of the due north direction is 0 degree, the orientation of the due north direction is speculated according to the azimuth angle theta dir, the method is simple in equipment, and celestial body observation can be used as a rough north seeking mode.

Description

Technical Field

[0001] The present invention belongs to the technical field of astronomical calibration, and in particular relates to an astronomical rough north guidance method based on the apparent motion velocity of stars. Background Art

[0002] In recent years, digital theodolites equipped with astronomical north guidance or automatic target recognition capabilities have become increasingly popular, making fully automated astronomical north guidance an inevitable trend in the development of advanced azimuth reference devices. Astronomical north guidance utilizes the North Star (North Star) for determination. This is because the North Star is the star closest to the celestial axis of rotation in the Northern Hemisphere, and thus has the lowest apparent angular velocity, minimizing errors caused by dynamic measurements. To locate the North Star, one must first locate the projection of the celestial axis of rotation onto the north meridian. This requires moving the theodolite's field of view to approximately due north, pointing at the same altitude angle as the ground at the local latitude. In other words, prior to astronomical north guidance, approximate azimuth and horizontal reference information are required to ensure that the North Star falls within the observation field for further astronomical north guidance.

[0003] A rough horizontal reference can be accurately obtained by measuring the gravity component, but there is currently no simple and feasible way to obtain a rough absolute azimuth reference. Currently, there are three common north guidance methods: gyro guidance, inertial integration, and geomagnetic sensitivity. Gyro guidance uses a gyroscope to sense the spatial axis of the earth's rotation axis, and its projection on the horizontal plane is the north direction. This method requires integration for more than half an hour in a static environment to capture the rotation axis, which is too time-consuming. Inertial integration requires binding the initial azimuth information when the measurement mission is started, and then keeping the inertial equipment powered on throughout the mission to integrate in order to confirm the azimuth information of the measurement location. The method is complicated. Geomagnetic sensitivity is a highly autonomous measurement method, but its measurement accuracy is very poor and it is easily interfered with by electronic equipment. Summary of the Invention

[0004] In view of this, the present invention provides an astronomical rough north guidance method based on the apparent motion velocity of stars, which can use celestial body observation as a way to roughly find the north.

[0005] The technical solutions for implementing the present invention are as follows:

[0006] A rough astronomical north-guiding method based on the apparent motion velocity of stars. The azimuth and altitude of the observed star in the northeastern celestial coordinate system at the time of observation are θ dir and θ h , the latitude θ of the known measuring point lat , then the cosine of the angle between the observed star vector and the rotation axis can be obtained by multiplying the star vector of the observed star and the vector of the rotation axis; the average angular velocity of the observed star during observation is measured, and the angle Δθ between the observed star vector and the Earth's rotation axis can be obtained according to its ratio to the Earth's rotation speed. seThe sine value of the azimuth angle θ dir Perform closed-form solution; the azimuth of due north is 0°, according to the azimuth θ dir , and infer the direction of due north.

[0007] Furthermore, the latitude θ of the measurement location is obtained by GNSS positioning equipment. lat .

[0008] Furthermore, the digital image terminal of the theodolite is used to continuously shoot 5 frames of images, and the angle Δθ between the incident vectors of two adjacent frames of images is calculated using the calibration model of the digital camera. (i+1)i , the time of the i-th shooting is recorded as t i , then the average angular velocity w of the star target motion is:

[0009]

[0010] Furthermore, the Earth's rotation will cause the star's apparent angular velocity relative to the ground to not exceed 15" / s. The average angular velocity w of the star target motion is also the apparent angular velocity The average value of the observed star is affected by the angle Δθ between its star vector and the Earth's rotation axis. se The modulation of its apparent angular velocity The ratio of this to the Earth's rotation speed of 15" / s will be the angle Δθ se The sine value of , that is:

[0011]

[0012] make The angle Δθ between the star vector and the Earth's rotation axis can be obtained se .

[0013] Furthermore, θ h The measurement process is as follows: place the target star at the center of the target star in the visual or digital image, and read the angle θ between the star point vector and the ground plane at this time. h .

[0014] Further, solving θ dir The expression is:

[0015]

[0016] Stellar azimuth θ dir The value range of is 0° to 360°, so the azimuth angle calculated according to the above formula has 2 solutions each time, and the reasonable azimuth angle value needs to be determined based on the polarity.

[0017] Beneficial effects:

[0018] 1. The present invention's astronomical rough north guidance method innovatively uses the measurement of the apparent velocity of star points to calculate the azimuth of the observed star, thereby achieving rapid and accurate north determination. Compared with traditional gyroscopic and inertial north finding methods, this method requires simpler equipment and only takes about one to two minutes to measure north.

[0019] 2. Compared to traditional geomagnetic north-finding methods, the present method is less susceptible to environmental influences and offers a measurement accuracy better than 0.2°. Requiring only digital imaging and navigation satellites to determine the astronomical latitude of the measurement point, this method is particularly suitable for automated astronomical north-finding applications using theodolites.

[0020] 3. The method of the present invention is simple and easy to implement, and is used for rapid initial orientation based on an embedded platform. The theodolite can quickly generate an observation window for the North Star based on the orientation results and leveling information, and then seamlessly enter the next stage of precise north guidance based on the North Star. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the process of the present invention.

[0022] Figure 2 Schematic diagram of the relationship between the northeast celestial reference system and the Earth's rotation axis at the measuring point.

[0023] Figure 3 A schematic diagram of the angular velocity of any star. DETAILED DESCRIPTION

[0024] The present invention is described in detail below with reference to the accompanying drawings and embodiments.

[0025] The present invention provides an astronomical rough north guidance method based on the apparent motion velocity of stars. The method obtains a closed-form solution based on the relationship between the apparent motion of stars caused by the rotation of the earth and the modulation effect of the star vector pointing. On a leveled platform such as a theodolite, only the altitude angle and the apparent motion angular velocity of the star point are measured for a specific star, and the position information of the prior information is obtained by using the position guide, so as to obtain the azimuth information of the target. The astronomical north guidance equipment generally represented by the theodolite, its own electronic bubble and horizontal compensation technology and the long focal length and high resolution digital image system just provide favorable conditions for the accurate measurement of altitude angle and the angular velocity of the star point motion. The star selection conditions of this method are loose, the measurement process is fast, the calculation method is simple, there is no additional hardware requirement for the astronomical north guidance equipment, and it is very suitable as a fast method for astronomical rough north guidance.

[0026] like Figure 2 As shown in the figure, the problem of observing the north direction at any point on the earth's surface can be converted into the problem of observing the translation vector of the earth's rotation axis at that point. Starting from the observation point as the origin, it can be seen that Figure 3The spatial geometric relationship shown in the figure. As can be seen from the figure, with the rotation axis as the central axis, circles of latitude with different declinations are formed. Stars in different latitude circles rotate relative to the Earth's surface at different angular velocities. The smallest angular velocity occurs at the rotation axis, where the speed is stationary; the largest angular velocity occurs at the celestial equator, where the speed reaches the speed of Earth's rotation.

[0027] like Figure 1 FIG. 1 is a flow chart of the method of the present invention, and the implementation method will be described in detail in the following step sequence.

[0028] 1. Theodolite leveling

[0029] After coarse leveling with a physical bubble and fine leveling with an electronic bubble, the theodolite's azimuth disk (for rough north-finding) is essentially aligned with the horizontal plane. Only after fine leveling can accurate elevation measurements of observed stars be made. Generally, the degree of misalignment should not exceed 1", and the theodolite's misalignment compensation function should be used.

[0030] 2. GNSS positioning

[0031] The latitude of the measurement location is obtained by the GNSS positioning equipment. The astronomical latitude of the measurement point is recorded as: θ lat .

[0032] 3. Capture and aim at any star

[0033] Find a star in the night sky using either eyepiece observation or an automated star-finding algorithm. The altitude angle of the star should not be too low, as this will cause significant obscuration due to the atmospheric gradient. However, the altitude angle should not be too high, as this will underweight the azimuth angle and increase the uncertainty of the calculated azimuth. Generally, the altitude angle should be between 30° and 60°.

[0034] 4. Take 5 consecutive star images to estimate their angular velocity

[0035] Use the digital image terminal of the theodolite to continuously shoot 5 frames of images, and use the calibration model of the digital camera to calculate the incident vector angle Δθ between two adjacent frames of images (i+1)i , and then the average angular velocity is obtained. The time of each shooting is t i , then the average angular velocity w of the star target motion is:

[0036]

[0037] like Figure 2 As shown, the Earth's rotation will cause the star to produce an apparent angular velocity of no more than 15" / s relative to the ground. The average angular velocity w of the star target motion is also the apparent angular velocity The average value of the observed star is affected by the angle Δθ between its star vector and the Earth's rotation axis. se The modulation of its apparent angular velocity The ratio of this to the Earth's rotation speed of 15" / s will be the angle Δθ se The sine value of , that is:

[0038]

[0039] make Combining equations (1) and (2), we can obtain the angle Δθ between the star vector and the Earth's rotation axis: se .

[0040] 5. Read the altitude angle of the star

[0041] Place the target star at the center of the target star in the visual or digital image, and read the angle θ between the star point vector and the ground plane at this time. h When measuring, please note that steps 4 and 5 should be completed consecutively within a short period of time to avoid changes in the spatial constraints.

[0042] 6. Calculate the azimuth of the star

[0043] At this time, the star azimuth θ can be measured according to the following formula: dir :

[0044]

[0045] The stellar azimuth θ dir The value range of is 0° to 360°, so the azimuth angle calculated according to the above formula has 2 solutions each time, and the reasonable azimuth angle value needs to be determined based on the polarity.

[0046] 7. Roughly select stars in 4 quadrants for repeated measurements

[0047] The accuracy of single-point observation is not high. We can observe four stars in four quadrants with a 90° angle to each other from step 3 to step 6 to obtain the average azimuth information of the observed stars. The azimuth angle to the north is 0°. According to the azimuth angle θ dir , and infer the direction of due north.

[0048] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A rough astronomical north guidance method based on the apparent motion velocity of stars, characterized in that: The azimuth and altitude angles of the observed star in the northeastern sky coordinate system of the observation point are measured to be θ dir and θ h , the latitude θ of the known measuring point lat , then the cosine of the angle between the observed star vector and the rotation axis can be obtained by multiplying the star vector of the observed star and the vector of the rotation axis; the average angular velocity of the observed star during observation is measured, and the angle Δθ between the observed star vector and the Earth's rotation axis can be obtained according to its ratio to the Earth's rotation speed. se The sine value of the azimuth angle θ dir Perform closed-form solution; the azimuth of due north is 0°, according to the azimuth θ dir , and infer the direction of due north.

2. The astronomical rough north guidance method according to claim 1, characterized in that: The latitude θ of the measurement location is obtained by GNSS positioning equipment lat .

3. The astronomical rough north guidance method according to claim 1, characterized in that: Use the digital image terminal of the theodolite to continuously shoot 5 frames of images, and use the calibration model of the digital camera to calculate the incident vector angle Δθ between two adjacent frames of images (i+1)i , the time of the i-th shooting is recorded as t i , then the average angular velocity w of the star target motion is:

4. The astronomical rough north guidance method according to claim 3, characterized in that: The rotation of the Earth will cause the apparent angular velocity of the star relative to the ground to not exceed 15" / s. The average angular velocity w of the star target motion is also the apparent angular velocity The average value of the observed star is affected by the angle Δθ between its star vector and the Earth's rotation axis. se The modulation of its apparent angular velocity The ratio of this to the Earth's rotation speed of 15" / s will be the angle Δθ se The sine value of , that is: make The angle Δθ between the star vector and the Earth's rotation axis can be obtained se .

5. The astronomical rough north guidance method according to claim 1 or 2, characterized in that: θ h The measurement process is as follows: place the target star at the center of the target star in the visual or digital image, and read the angle θ between the star point vector and the ground plane at this time. h .

6. The astronomical rough north guidance method according to claim 4, characterized in that: Solving for θ dir The expression is: Stellar azimuth θ dir The value range of is 0° to 360°, so the azimuth angle calculated according to the above formula has 2 solutions each time, and the reasonable azimuth angle value needs to be determined based on the polarity.

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