CN111366136B - Design method of optical ring scanning ultra-wide imaging mode - Google Patents

Abstract

The invention relates to a design method of an optical ring scan ultra-wide imaging mode. Including: designing the angle γ between the optical axis of the camera and the entire satellite-to-earth axis; designing the satellite's spin angular velocity ω _fast in fast spin mode; if the camera can clearly image at the current angular velocity, go to step 3; otherwise, go to step 4 ; Design the on-off time t _on , t _off of the camera in a fast rotation period T _fast ; Design the satellite's spin angular velocity ω _slow in the slow rotation mode; Design the on-off time t _on1 , t of the camera in a slow rotation period T _{slow off1} , t _on2 , t _off2 ; design the phase angle θ ₀ and the start-up duration τ ₁ of the camera when the camera is turned on in the variable-speed spin mode; design the satellite spin angular velocity equation when the camera is turned off; if the satellite can track the equation stably, then The variable-speed spin mode is adopted; otherwise, the slow-spin mode designed in step 5 is adopted. Each imaging mode of the present invention can ensure the integrity of the splicing of the ring-sweeping strips, and reduce the requirements of the imaging task on the processing, storage and data transmission capabilities of the satellite.

Description

Design method of optical ring scan ultra-wide imaging mode

technical field

The invention relates to a design method of an optical ring scan ultra-wide imaging mode, and belongs to the technical field of aerospace satellites.

Background technique

At present, with the development of aerospace technology, micro-nano satellites have been favored by everyone due to their low cost and miniaturization. However, low-orbit small satellites with meter-level resolution cannot meet the imaging coverage width of thousands of kilometers. Optical ring scan ultra-wide imaging is a solution that has been proposed so far. In this method, an area array optical camera is installed, so that the optical axis of the camera forms a fixed angle with the satellite-to-earth axis, and the rotation of the satellite's entire satellite around the ground-pointing axis enables the camera to achieve ultra-large wide coverage by ring-scanning imaging.

However, there is no design plan for the angle between the optical axis of the camera for optical ring-scan ultra-wide imaging and the satellite-to-earth axis, the specific calculation method of the satellite spin angular velocity, and the detailed ring-sweep strip splicing method.

SUMMARY OF THE INVENTION

The purpose of the present invention is to propose a design method of an optical ring scan ultra-wide imaging mode. The design method proposes three different ring scan imaging modes for different camera imaging capabilities and different satellite spin angular velocity control capabilities, including fast rotation mode, slow rotation mode, and variable-speed spin mode. Each imaging mode can not only ensure the integrity of the splicing of the ring scan strips, but also reduce the overlapping area between the ring scan strips through the design of the camera timing switch in each ring scan cycle, thereby reducing the imaging task's impact on satellites. Requirements for processing capacity, storage capacity, and data transmission capacity. In order to solve the problem that no design plan has been proposed for the angle between the optical axis of the camera for optical ring scan ultra-wide imaging and the entire satellite's earth axis, the specific calculation method of the satellite spin angular velocity, and the detailed ring scan strip splicing method.

The design method of optical ring scan ultra-wide imaging mode includes the following steps:

Step 1. Design the angle γ between the optical axis of the camera and the axis of the entire satellite to the earth according to the orbital height of the satellite, the imaging width required by the mission, and the field of view of the camera;

Step 2: According to the γ value designed in Step 1 and the minimum overlap ratio between two adjacent ring-sweep strips, design the spin angular velocity ω _fast and the spin period T _fast of the satellite in fast spin mode. If ω _fast can make the camera If there is enough exposure time and integration time for high-resolution imaging, go to step 3; if ω _fast is too large for the camera to perform clear imaging, go to step 4;

Step 3: In order to reduce the overlapping area between the ring-sweep strips, the on-off times t _on and t _off of the camera within a fast rotation period T _fast are designed, that is, the optical ring-sweep ultra-wide imaging mode that meets the design requirements;

Step 4, according to the γ value designed in step 1 and the minimum overlap rate requirement between two adjacent ring sweep strips, the spin angular velocity ω _slow and the self-selected period T _slow of the satellite under the design slow rotation mode;

Step 5: Design the switch-on times t _on1 , t _off1 , t _on2 , and t _off2 of the camera in a slow rotation period T _slow ;

Step 6. Design a variable-speed spin mode. In each spin cycle in this mode, the satellite's spin angular velocity is equal to the satellite's spin angular velocity ω _slow in the slow spin mode when the camera is turned on, and the satellite spins rapidly when the camera is turned off. Therefore, the spin period is equal to the spin period T _fast of the fast spin mode, and the phase angle θ ₀ and the power-on duration τ ₁ of the camera in this mode are designed;

Step 7: Design the satellite spin angular velocity equation when the camera is turned off in the variable-speed spin mode. If the satellite's attitude control system can stably track and control the spin angular velocity equation designed in this mode, the variable-speed spin mode designed in this step will be used. That is, the optical ring scan ultra-wide imaging mode that meets the design requirements; if the attitude control system of the satellite is not enough to stably track and control the spin angular velocity equation designed for this mode, the slow rotation mode designed in step 5 is the one that meets the design requirements. Optical ring scan ultra-wide imaging mode.

Further, in step 1, the angle γ between the optical axis of the camera and the entire star-to-earth axis is iteratively solved by the following sine theorem equation:

为地球半径，H为轨道高度，r₁为任务要求幅宽的一半，即环扫条带外半径，α为相机的一个半视场角。in,

is the radius of the earth, H is the orbit height, r ₁ is half of the width required by the mission, that is, the outer radius of the ring sweep strip, and α is a half field of view of the camera.

如下：Further, in step 2, first define the approximate moving speed of the satellite sub-satellite point

as follows:

Among them, T _orbit is the orbital period of the satellite, then the spin angular velocity ω _fast and the spin period T _fast of the satellite in fast spin mode are calculated by the following equations:

为相邻两圈环扫条带的最小重叠率。where r ₂ is the inner radius of the ring sweep strip,

It is the minimum overlap ratio of two adjacent ring sweep strips.

和理论关机时刻

通过如下方程迭代求解：Further, in step 3, define the 0 phase angle of the ring sweep strip, the theoretical start-up time of the jth circle camera

and theoretical shutdown moment

Iteratively solves by the following equation:

令

考虑到实际的控制误差和星下点速度偏差，为了确保拼接的完整性，则相机在一个快旋周期T_fast内的开机时刻t_on应略提前于理论值t′_on，关机时刻t_off应略晚于理论值t′_off。Let the jth circle 0 phase angle moment be

make

Considering the actual control error and the speed deviation of the sub-satellite point, in order to ensure the integrity of the splicing, the startup time t _on of the camera in a fast rotation period T _fast should be slightly earlier than the theoretical value t' _on , and the shutdown time t _off should be. slightly later than the theoretical value t' _off .

Further, in step 4, the spin angular velocity ω _slow and the self-selected period T _slow of the satellite in the slow spin mode are calculated by the following equations respectively:

为相邻两圈环扫条带的最大漏缝率。In the formula,

It is the maximum leakage rate of two adjacent ring sweep strips.

其中，下角标on为开机时刻，下角标off为关机时刻，1、2表示时间的先后，通过如下方程迭代求解：Further, in step 5, there are two shutdowns and two startups in each circle, and the theoretical switching times of the camera in the jth circle are respectively:

Among them, the subscript on is the power-on time, the subscript off is the shutdown time, and 1 and 2 represent the time sequence, which is iteratively solved by the following equation:

In the formula, k is defined as: the right half circle formed by the fourth quadrant of the m-1th circle and the first quadrant of the mth circle, and the left half circle formed by the second and third quadrants of the nth circle. circle, splicing each other to fill the hollow part in the middle of the n-1th circle, then k=n-m,

令

考虑到实际的控制误差和星下点速度偏差，为了确保拼接的完整性，则相机在一个慢旋周期T_slow内的关机时刻t_off1、t_off2应略晚于理论值t′_off1、t′_off2，开机时刻t_on1、t_on2应略提前于理论值t′_on1、t′_on2。Let the jth circle 0 phase angle moment be

make

Considering the actual control error and the speed deviation of the sub-satellite point, in order to ensure the integrity of the splicing, the shutdown time t _off1 and t _off2 of the camera in a slow rotation period T _slow should be slightly later than the theoretical values t' _off1 and t' _off2 , the power-on times t _on1 and t _on2 should be slightly ahead of the theoretical values t' _on1 and t' _on2 .

Further, in step 6, the theoretical value θ′ ₀ of the phase angle when the camera is turned on in one cycle is obtained by iterative calculation of the following formula:

Considering the actual control error, the phase angle θ ₀ of the actual camera startup time should be slightly smaller than the theoretical value θ′ ₀ ,

The theoretical value τ′ ₁ of the camera startup time can be calculated by the following formula:

Considering the actual control error, the actual camera startup time τ ₁ should be slightly larger than the theoretical value τ′ ₁ .

Further, in step 7, first define the state vector X(t) as follows:

Then let u(t) be the angular acceleration of the satellite, and t ₀ be the start time of a cycle. Through the Pontryagin maximum principle, the following energy optimization problem can be solved:

Obtain the satellite spin angular velocity equation ω ^* (t)t∈[t ₀ +τ ₁ ,t ₀ +T _fast ] in the camera shutdown phase.

The main advantages of the present invention are as follows: the present invention proposes a method for designing an optical ring scan ultra-wide imaging mode. In the present invention, three different ring scan imaging modes are proposed for different camera imaging capabilities and different satellite spin angular velocity control capabilities, including fast spin mode, slow spin mode, and variable-speed spin mode. Each imaging mode can not only ensure the integrity of the splicing of the ring scan strips, but also reduce the overlapping area between the ring scan strips through the design of the camera timing switch in each ring scan cycle, thereby reducing the imaging task's impact on satellites. Requirements for processing capacity, storage capacity, and data transmission capacity.

Description of drawings

Fig. 1 is the flow chart of the optical ring scan ultra-wide imaging mode design method of the present invention;

Fig. 2 is a schematic diagram of optical ring scan ultra-wide imaging;

Fig. 3 is a schematic diagram of a ring sweep width;

FIG. 4 is a schematic diagram of the minimum overlap ratio of the fast spin mode;

FIG. 5 is a schematic diagram of long-term startup of the camera in the fast rotation mode;

FIG. 6 is a schematic diagram of a long-term startup of a camera in a fast rotation mode;

Fig. 7 is a schematic diagram of the definition of quadrant and 0 phase angle;

FIG. 8 is a schematic diagram of the design result after reducing the overlapping area of the ring-sweep strips in the fast spin mode;

FIG. 9 is a schematic diagram of the maximum leakage rate in the slow rotation mode;

Figure 10 is a schematic diagram of a long-term startup (narrow field of view) of a camera in slow rotation mode;

Figure 11 is a schematic diagram of a long-term startup (wide field of view) of a camera in slow rotation mode;

Figure 12 is a schematic diagram of the design result after reducing the overlapping area of the ring sweep strip in the slow rotation mode;

Figure 13 Schematic diagram of the design result of the variable-speed spin mode.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Referring to FIG. 1-FIG. 2, the present invention proposes a method for designing an optical ring scan ultra-wide imaging mode, which includes the following steps:

Step 1. Design the angle γ between the optical axis of the camera and the axis of the entire satellite to the earth according to the orbital height of the satellite, the imaging width required by the mission, and the field of view of the camera;

Step 2: According to the γ value designed in Step 1 and the minimum overlap ratio between two adjacent ring-sweep strips, design the spin angular velocity ω _fast and the spin period T _fast of the satellite in fast spin mode. If ω _fast can make the camera If there is enough exposure time and integration time for high-resolution imaging, go to step 3; if ω _fast is too large for the camera to perform clear imaging, go to step 4;

Step 3: In order to reduce the overlapping area between the ring-sweep strips, the on-off times t _on and t _off of the camera within a fast rotation period T _fast are designed, that is, the optical ring-sweep ultra-wide imaging mode that meets the design requirements;

Step 4, according to the γ value designed in step 1 and the minimum overlap rate requirement between two adjacent ring sweep strips, the spin angular velocity ω _slow and the self-selected period T _slow of the satellite under the design slow rotation mode;

Step 5: Design the switch-on time t _on1 , t _off1 , t _on2 , and t _off2 of the camera in a slow rotation period T _slow ;

Step 6. Design a variable-speed spin mode. In each spin cycle in this mode, the satellite's spin angular velocity is equal to the satellite's spin angular velocity ω _slow in the slow spin mode when the camera is turned on, and the satellite spins rapidly when the camera is turned off. Therefore, the spin period is equal to the spin period T _fast of the fast spin mode, and the phase angle θ ₀ and the power-on duration τ ₁ of the camera in this mode are designed;

Step 7: Design the satellite spin angular velocity equation when the camera is turned off in the variable-speed spin mode. If the satellite's attitude control system can stably track and control the spin angular velocity equation designed in this mode, the variable-speed spin mode designed in this step will be used. That is, the optical ring scan ultra-wide imaging mode that meets the design requirements; if the attitude control system of the satellite is not enough to stably track and control the spin angular velocity equation designed for this mode, the slow rotation mode designed in step 5 is the one that meets the design requirements. Optical ring scan ultra-wide imaging mode.

In the preferred embodiment of this part, in step 1, the angle γ between the optical axis of the camera and the axis of the whole star with respect to the earth is iteratively solved by the following sine theorem equation:

为地球半径，H为轨道高度，r₁为任务要求幅宽的一半，即环扫条带外半径，α为相机的一个半视场角。in,

is the radius of the earth, H is the orbit height, r ₁ is half of the required width of the mission, that is, the outer radius of the ring sweep strip, and α is a half field of view of the camera.

如下：In the preferred embodiment of this part, in step 2, first define the approximate moving speed of the satellite sub-satellite point

as follows:

Among them, T _orbit is the orbital period of the satellite, then the spin angular velocity ω _fast and the spin period T _fast of the satellite in fast spin mode are calculated by the following equations:

为相邻两圈环扫条带的最小重叠率，其定义参照图4所示。Among them, r ₂ is the inner radius of the ring sweep strip, as shown in Figure 3,

is the minimum overlap ratio of two adjacent ring sweep strips, and its definition is shown in Figure 4.

Before performing step 3, the ring sweep trajectory designed in step 2 is shown in Fig. 5 and Fig. 6 .

和理论关机时刻

通过如下方程迭代求解：In the preferred embodiment of this part, in step 3, referring to FIG. 7 , define the 0 phase angle of the ring sweep strip, and the theoretical power-on time of the jth circle of cameras

and theoretical shutdown moment

Iteratively solves by the following equation:

令

考虑到实际的控制误差和星下点速度偏差，为了确保拼接的完整性，则相机在一个快旋周期T_fast内的开机时刻t_on应略提前于理论值t′_on，关机时刻t_off应略晚于理论值t′_off。Let the jth circle 0 phase angle moment be

make

Considering the actual control error and the speed deviation of the sub-satellite point, in order to ensure the integrity of the stitching, the startup time t _on of the camera in a fast rotation period T _fast should be slightly earlier than the theoretical value t' _on , and the shutdown time t _off should be slightly later than the theoretical value t' _off .

The ring-sweep strip designed in step 3 is shown in Figure 8.

In the preferred embodiment of this part, in step 4, the spin angular velocity ω _slow and the self-selected period T _slow of the satellite in the slow rotation mode are calculated by the following equations respectively:

为相邻两圈环扫条带的最大漏缝率，其定义如图9所示。In the formula,

is the maximum leakage rate of two adjacent ring sweep strips, and its definition is shown in Figure 9.

Before proceeding to Step 5, the ring sweep trajectory designed in Step 4 is shown in Figure 10 and Figure 11 .

其中，下角标on为开机时刻，下角标off为关机时刻，1、2表示时间的先后，通过如下方程迭代求解：In the preferred embodiment of this part, in step 5, there are two shutdowns and two startups in each circle, and the theoretical switching times of the camera in the jth circle are respectively

Among them, the subscript on is the power-on time, the subscript off is the shutdown time, and 1 and 2 represent the time sequence, which is iteratively solved by the following equation:

In the formula, k is defined as: the right half circle formed by the fourth quadrant of the m-1th circle and the first quadrant of the mth circle, and the left half circle formed by the second and third quadrants of the nth circle. circle, splicing each other to fill the hollow part in the middle of the n-1th circle, then k=n-m,

令

考虑到实际的控制误差和星下点速度偏差，为了确保拼接的完整性，则相机在一个慢旋周期T_slow内的关机时刻t_off1、t_off2应略晚于理论值t′_off1、t′_off2，开机时刻t_on1、t_on2应略提前于理论值t′_on1、t′_on2。Let the jth circle 0 phase angle moment be

make

Considering the actual control error and the speed deviation of the sub-satellite point, in order to ensure the integrity of the stitching, the shutdown time t _off1 and t _off2 of the camera in a slow rotation period T _slow should be slightly later than the theoretical values t' _off1 , t' _off2 , the power-on times t _on1 and t _on2 should be slightly ahead of the theoretical values t' _on1 and t' _on2 .

The ring-sweep strip designed in step 5 is shown in Figure 12.

In the preferred embodiment of this part, in step 6, the theoretical value θ′ ₀ of the phase angle at the moment when the camera is turned on in one cycle is obtained by iterative calculation of the following formula:

Considering the actual control error, the phase angle θ ₀ of the actual camera startup time should be slightly smaller than the theoretical value θ′ ₀ ,

The theoretical value τ′ ₁ of the camera power-on time can be calculated by the following formula:

Considering the actual control error, the actual camera startup time τ ₁ should be slightly larger than the theoretical value τ′ ₁ .

In the preferred embodiment of this part, in step 7, the state vector X(t) is first defined as follows:

Then let u(t) be the angular acceleration of the satellite, and t ₀ be the start time of a cycle. Through the Pontryagin maximum principle, the following energy optimization problem can be solved:

Obtain the satellite spin angular velocity equation ω ^* (t)t∈[t ₀ +τ ₁ ,t ₀ +T _fast ] in the camera shutdown phase.

The ring-sweep strip designed in step 7 is shown in Figure 13.

Claims (8)

1. The optical ring scan ultra-wide imaging mode design method, is characterized in that, comprises the following steps: Step 1. Design the angle γ between the optical axis of the camera and the axis of the entire satellite to the earth according to the orbital height of the satellite, the imaging width required by the mission, and the field of view of the camera; Step 2: According to the γ value designed in Step 1 and the minimum overlap ratio between two adjacent ring-sweep strips, design the spin angular velocity ω _fast and the spin period T _fast of the satellite in fast spin mode. If ω _fast can make the camera If there is enough exposure time and integration time for high-resolution imaging, go to step 3; if ω _fast is too large for the camera to perform clear imaging, go to step 4; Step 3: In order to reduce the overlapping area between the ring-sweep strips, the on-off times t _on and t _off of the camera within a fast rotation period T _fast are designed, that is, the optical ring-sweep ultra-wide imaging mode that meets the design requirements; Step 4, according to the γ value designed in step 1 and the minimum overlap rate requirement between two adjacent ring sweep strips, the spin angular velocity ω _slow and the self-selected period T _slow of the satellite under the design slow rotation mode; Step 5: Design the switch-on times t _on1 , t _off1 , t _on2 , and t _off2 of the camera in a slow rotation period T _slow ; Step 6. Design a variable-speed spin mode. In each spin cycle in this mode, the satellite's spin angular velocity is equal to the satellite's spin angular velocity ω _slow in the slow spin mode when the camera is turned on, and the satellite spins rapidly when the camera is turned off. Therefore, the spin period is equal to the spin period T _fast of the fast spin mode, and the phase angle θ ₀ and the power-on duration τ ₁ of the camera in this mode are designed; Step 7: Design the satellite spin angular velocity equation when the camera is turned off in the variable-speed spin mode. If the satellite's attitude control system can stably track and control the spin angular velocity equation designed in this mode, the variable-speed spin mode designed in this step will be used. That is, the optical ring scan ultra-wide imaging mode that meets the design requirements; if the attitude control system of the satellite is not enough to stably track and control the spin angular velocity equation designed for this mode, the slow rotation mode designed in step 5 is the one that meets the design requirements. Optical ring scan ultra-wide imaging mode. 2. The optical ring scan ultra-wide imaging mode design method according to claim 1, wherein in step 1, the angle γ between the optical axis of the camera and the axis of the whole star to the earth is iteratively solved by the following sine theorem equation :

in,

is the radius of the earth, H is the orbit height, r ₁ is half of the width required by the mission, that is, the outer radius of the ring sweep strip, and α is a half field of view of the camera. 3. The optical ring scan ultra-wide imaging mode design method according to claim 1, characterized in that, in step 2, at first an approximate satellite sub-satellite point moving speed is defined

as follows:

Among them, T _orbit is the orbital period of the satellite, then the spin angular velocity ω _fast and the spin period T _fast of the satellite in fast spin mode are calculated by the following equations:

where r ₂ is the inner radius of the ring sweep strip,

It is the minimum overlap ratio of two adjacent ring sweep strips. 4. The optical ring scan ultra-wide imaging mode design method according to claim 1, characterized in that, in step 3, the 0 phase angle of the ring scan strip is defined, and the theoretical start-up time of the jth circle camera is defined.

and theoretical shutdown moment

Iteratively solves by the following equation:

Let the jth circle 0 phase angle moment be

make

Considering the actual control error and the speed deviation of the sub-satellite point, in order to ensure the integrity of the stitching, the startup time t _on of the camera in a fast rotation period T _fast should be slightly earlier than the theoretical value t' _on , and the shutdown time t _off should be slightly later than the theoretical value _t'off . 5. optical ring scan ultra-wide imaging mode design method according to claim 1, is characterized in that, in step 4, the spin angular velocity ω _slow of satellite under slow rotation mode and self-selected period T _slow carry out respectively by following equation. calculate:

In the formula,

It is the maximum leakage rate of two adjacent ring sweep strips. 6. The optical ring scan ultra-wide imaging mode design method according to claim 1, wherein in step 5, there are two shutdowns and two startups in each circle, and the theoretical switch of the camera in the jth circle is turned on and off. The times are

Among them, the subscript on is the power-on time, the subscript off is the shutdown time, and 1 and 2 represent the time sequence, which is iteratively solved by the following equation:

In the formula, k is defined as: the right half circle formed by the fourth quadrant of the m-1th circle and the first quadrant of the mth circle, and the left half circle formed by the second and third quadrants of the nth circle. circle, splicing each other to fill the hollow part in the middle of the n-1th circle, then k=n-m, Let the jth circle 0 phase angle moment be

make

Considering the actual control error and the speed deviation of the sub-satellite point, in order to ensure the integrity of the splicing, the shutdown time t _off1 and t _off2 of the camera in a slow rotation period T _slow should be slightly later than the theoretical values t' _off1 and t' _off2 , the power-on times t _on1 and t _on2 should be slightly ahead of the theoretical values t' _on1 and t' _on2 . 7. The optical ring scan ultra-wide imaging mode design method according to claim 1, characterized in that, in step 6, the theoretical value θ' ₀ of the phase angle at the time when the camera is turned on in one cycle is obtained by iterative calculation of the following formula :

Considering the actual control error, the phase angle θ ₀ of the actual camera startup time should be slightly smaller than the theoretical value θ′ ₀ , The theoretical value τ′ ₁ of the camera power-on time can be calculated by the following formula:

Considering the actual control error, the actual camera startup time τ ₁ should be slightly larger than the theoretical value τ′ ₁ . 8. The optical ring scan ultra-wide imaging mode design method according to claim 1, characterized in that, in step 7, the state vector X(t) is first defined as follows:

Then let u(t) be the angular acceleration of the satellite, and t ₀ be the start time of a cycle. Through the Pontryagin maximum principle, the following energy optimization problem can be solved:

The satellite spin angular velocity equation ω ^* (t)t∈[t ₀ +τ ₁ ,t ₀ +T _fast ] in the camera shutdown phase is obtained.

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