A Method for Measuring the Yaw Angle of a Satellite in Orbit

Abstract

A method for measuring the on-orbit yaw angle of a satellite is disclosed. This method addresses the drawbacks of existing measurement methods, which require on-board storage capacity to ensure data delay matching in order to achieve sufficient corresponding accuracy, resulting in system complexity, significant data redundancy, high resource usage, and poor real-time performance. The method employs a rolling shutter array CMOS with a windowing function as a measurement device for autocorrelation imaging, detects the offset of the associated images through image registration, and achieves real-time measurement of the on-orbit yaw angle of the satellite. The method is implemented through the steps of calculating the imaging parameters of the rolling shutter array CMOS to obtain a sufficient overlapping imaging area, performing rolling shutter array CMOS autocorrelation imaging, calculating the image offset of the overlapping imaging area through image registration, and calculating the on-orbit yaw angle of the satellite. The method provides a data foundation for image degradation assessment and subsequent image restoration, and is of great significance in the field of aerospace engineering.

Description

Technical Field

[0001] The present invention relates to a method for measuring the on-orbit yaw angle of a satellite, and in particular to a method for measuring the on-orbit yaw angle of a satellite based on autocorrelation imaging of a rolling shutter area array CMOS camera. Background Art

[0002] The Time Delayed and Integration Charge Coupled Device (TDICCD) is a new type of CCD with a planar array structure and linear array output. It utilizes multi-level integration to increase the integration time and thus the amount of light energy by exposing the same object multiple times. Compared to conventional linear array CCDs, it offers higher responsiveness and a wider dynamic range. It can also output signals with a certain signal-to-noise ratio even in dimly lit environments, significantly improving the disadvantages of low signal-to-noise ratios caused by harsh environmental conditions. Therefore, TDICCDs are widely used in space exploration and aerospace remote sensing.

[0003] When operating a TDICCD, the image motion rate must match the charge transfer rate, and the image motion direction must be along the TDI direction. Otherwise, image quality will degrade in the TDI direction and perpendicular to the TDI direction. The multi-stage integration of the TDICCD requires that the image motion rate and charge transfer rate match over a long integration time to achieve a clear image.

[0004] The yaw angle is the angle between the projection of the satellite's optical axis onto the horizontal plane and the tangent of its planned trajectory. For a space camera, the optical axis corresponds to the TDI direction of the TDICCD imaging sensor, while the tangent of the flight trajectory determines the direction of image motion. Therefore, the satellite's yaw angle determines the degree of matching between the TDI and image motion directions. The yaw angle can cause adjacent scenes to blend during the charge accumulation and integration process, thereby reducing image quality and significantly affecting imaging metrics such as the modulation transfer function (MTF) and signal-to-noise ratio (SNR) of remote sensing images.

[0005] Existing measurement methods mostly use gyroscopes or angular displacement sensors carried by satellites. Although the accuracy is sufficient, since they are not on the same unit as the camera, it is difficult to obtain data in time when on-orbit correction, calculation or image processing is required. At the same time, data transmission will significantly squeeze precious on-board communication resources. At the same time, since they are located on different units, data matching is very complicated and requires timestamps. At the same time, a certain amount of on-board storage capacity is also required to ensure data delay matching to achieve sufficient matching accuracy. This leads to shortcomings such as bloated system, large data redundancy, high resource utilization, and poor real-time performance. Summary of the Invention

[0006] This paper proposes a method for measuring the on-orbit yaw angle of a satellite. This method uses a rolling shutter CMOS array with a windowing function as a measurement device for autocorrelation imaging. The offset of the correlated images is detected through image registration, enabling real-time measurement of the satellite's on-orbit yaw angle. The rolling shutter CMOS array with a windowing function is used as the detection device. During installation, the CMOS array shutter must be perpendicular to the direction of flight (the satellite's flight direction).

[0007] A method for measuring the on-orbit yaw angle of a satellite is implemented by the following steps:

[0008] Step 1: Use an area array CMOS with a windowing function as a satellite on-orbit yaw angle measurement device and install it on the satellite focal plane; the rolling direction of the area array CMOS is required to be perpendicular to the satellite flight direction, and the area array CMOS imaging area, i.e., the windowing range, is set;

[0009] Step 2: Adjust the window size of the area array CMOS and further adjust the image overlap area to obtain a suitable image overlap area;

[0010] Step 3: Based on the image overlapping area determined in step 2, image registration is used to calculate the image offset of the overlapping imaging area;

[0011] Step 4: Calculate the yaw angle based on the image offset obtained in step 3 to achieve real-time measurement of the satellite's on-orbit yaw angle.

[0012] Beneficial effects of the present invention:

[0013] The method for measuring the on-orbit yaw angle of a satellite disclosed in the present invention uses a rolling shutter area array CMOS with a windowing function as a measuring device for autocorrelation imaging, detects the offset of related images through an image registration method, and achieves real-time measurement of the on-orbit yaw angle of the satellite, providing guidance data for satellite attitude adjustment and forming a closed-loop control system. Furthermore, the method can quantitatively evaluate the degree of image degradation based on the yaw angle data, such as the decrease in the image modulation transfer function (MTF) from the expected value, thereby providing a data basis for subsequent image restoration and image quality improvement.

[0014] The satellite on-orbit yaw angle measurement method of the present invention uses detector images to calculate yaw parameters, which can achieve sufficient accuracy and sufficient real-time performance without the need for additional data transmission and is simple and direct.

[0015] The method for measuring the on-orbit yaw angle of a satellite described in the present invention uses a rolling shutter area array CMOS with window opening operation as a detection device, which can measure the on-orbit yaw angle of the satellite in real time, providing a data basis for image degradation assessment and subsequent image restoration, and is of great significance in the field of aerospace engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of overlapping imaging of the ground by an area array imaging device.

[0017] Figure 2 Schematic diagram of the installation of the yaw angle detection detector.

[0018] Figure 3 Schematic diagram of adjusting the overlapping area by adjusting the detector window size, (a) is full pixel imaging, (b) is 1 / 2 pixel imaging, and (c) is 1 / 4 pixel imaging.

[0019] Figure 4 Schematic diagram of using image comparison algorithm to calculate the relative offset between images along the flight direction and perpendicular to the flight direction. DETAILED DESCRIPTION

[0020] Specific implementation method 1. A method for measuring the yaw angle of a satellite on orbit. To achieve real-time measurement of the yaw angle on orbit, it is necessary to calculate the imaging parameters of a rolling shutter array CMOS to obtain a sufficient overlapping imaging area, perform rolling shutter array CMOS autocorrelation imaging, apply image registration to calculate the image offset of the overlapping imaging area, and calculate the satellite's on-orbit yaw angle.

[0021] Rolling CMOS imaging parameter calculation is primarily used to determine the appropriate window size for the rolling CMOS, ensuring sufficient overlap between two adjacent frames. For an area array CMOS, the frame rate is fixed in full-frame mode. When the satellite's flight speed exceeds a certain threshold, there may be no overlap between two consecutive frames. Therefore, the area array CMOS requires a windowing capability. By reducing the image frame size and increasing the detector's operating frame rate, sufficient overlap is achieved between two consecutive frames.

[0022] The use of a rolling area array CMOS sensor increases the sampling frequency and improves the accuracy of yaw angle data acquisition, providing a more accurate data foundation for subsequent image restoration and enhancing restoration results. When all pixels in a global shutter sensor are exposed for imaging at the same time, this is equivalent to a single sampling within that time period, and the sampling frequency is equal to the frame rate. The rolling shutter's time-sharing, line-by-line imaging is equivalent to sampling the scene sequentially along the direction of the rolling shutter. The sampling time is the exposure time of a single line, and the sampling interval is the interval between the start of exposure of each line. Using a rolling area array CMOS as the detection element significantly increases the sampling frequency and achieves better sampling results.

[0023] Rolling shutter area array CMOS autocorrelation imaging refers to the characteristic of mutual correlation of overlapping areas during rolling shutter area array CMOS imaging. Due to the special imaging method of the rolling shutter, the rolling shutter area array CMOS image has row-by-row differences and coupled correlation characteristics. This characteristic is the fundamental reason for increasing the sampling frequency.

[0024] Image registration is used to calculate the image offset of the overlapping imaging area. First, the overlapping images are partitioned and windowed. Then, the image registration method is applied to the partitioned images to calculate the relative offset along the flight direction and perpendicular to the flight direction. The image registration methods mainly include grayscale projection algorithm, normalized cross-correlation algorithm, etc.

[0025] After obtaining the relative offset data, the satellite's on-orbit yaw angle is calculated. This data can be used to assess the extent of image degradation and can also serve as a data basis for subsequent image restoration.

[0026] Specific implementation method 2: Figures 1 to 4 This embodiment is described as an example of a method for measuring the yaw angle of a satellite in orbit as described in Specific Embodiment 1: the method includes the steps of installing a yaw angle detection detector, adjusting the overlapping area by adjusting the size of the detector window, rolling shutter array CMOS autocorrelation imaging, applying image registration to calculate the image offset of the overlapping imaging area, and calculating the yaw angle of the satellite in orbit. The method is described in detail below with reference to the accompanying drawings.

[0027] like Figure 1 As shown, this embodiment uses a planar array CMOS detector to continuously image the ground, and obtains two adjacent frames of images with overlapping imaging areas. Figure 1 The diagram shows overlapping imaging of the ground by an area array imaging device. When the area array imaging device is at position k and position k+1, the area array imaging device images the kth frame image and the k+1th frame image respectively. There is an overlapping imaging area between the kth frame image and the k+1th frame image. The overlapping imaging area is used to calculate the relative offset along the flight direction and the vertical flight direction, and finally calculate the real-time yaw angle of the satellite in orbit. The specific process is as follows:

[0028] 1. As Figure 2 As shown, this embodiment uses a rolling shutter area array CMOS with a windowing function as a satellite on-orbit yaw angle measurement device. When installed on the satellite focal plane, the detector rolling shutter direction is perpendicular to the satellite flight, and the detector imaging area (i.e., the windowing range) can be adjusted by setting the windowing start row and the windowing end row.

[0029] 2. If Figure 3 As shown in the figure, by increasing the frame rate of the area array CMOS detector, two adjacent frames can overlap or increase the overlapping imaging area. Using image windowing to reduce the imaging area can increase the frame rate. By adjusting the detector window size, the overlapping area can be adjusted. Assume that the number of pixels in the area array CMOS detector along the flight direction is n, the number of pixels in the perpendicular flight direction is m, the pixel size is a, and the exposure start time interval between rows is T. row , the image motion speed is v I , then the length of the overlapping area ΔL is:

[0030] ΔL=na-mT row v I

[0031] The length of the overlapping area can be changed by changing the value of m. The smaller m is, the larger the overlapping area is. Figure 3 Figure 2 shows how the overlap varies with different values of m (full pixel, 1 / 2 pixel, and 1 / 4 pixel). Choosing an appropriate m ensures that the overlap is large enough and the window size is large enough to facilitate subsequent offset calculations.

[0032] 3. After obtaining the appropriate overlapping area, image registration is applied to calculate the image offset of the overlapping imaging area. First, the overlapping area of two adjacent continuous frames of images is partitioned, and the overlapping area of a frame of image is divided into several equal-sized continuous areas according to a certain spacing. The partition spacing is the actual sampling interval time, which determines the sampling frequency. Figure 3 As shown, the overlapping area is divided into several blocks in sequence along the rolling direction.

[0033] like Figure 4 As shown, the horizontal and vertical offsets at time ti1, ti2, ..., tim can be obtained in sequence. The longitudinal coordinate Offset is the offset, which is the relative offset along the flight direction and perpendicular to the flight direction. The difference between the moments is determined by the number of image rows between the partitions Δl, that is, Δt = Δl·T row .

[0034] Fourth, use an image contrast algorithm to calculate the relative offset between the overlapping image partitions processed in the previous step, both along the flight direction and perpendicular to the flight direction. For two frames with overlapping imaging areas, the relative offset between them can be calculated using an image contrast algorithm. This image contrast algorithm can utilize existing offset detection algorithms, such as grayscale projection algorithms, feature point algorithms, and normalized correlation image matching algorithms. These algorithms can all be used to determine the relative offset between the two frames. The calculated relative offset along the flight direction is ΔN (number of pixels), and the relative offset perpendicular to the flight direction is ΔM (number of pixels).

[0035] 5. Calculate the yaw angle based on the relative offset along the flight direction and the relative offset perpendicular to the flight direction. Based on the relative offset ΔN along the flight direction and the relative offset ΔM perpendicular to the flight direction obtained in the previous step, the yaw angle α is:

[0036]

[0037] This data can be used to assess the extent of image degradation and can also serve as a data basis for subsequent image restoration.

[0038] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0039] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for measuring the on-orbit yaw angle of a satellite, characterized by: The method is implemented by the following steps: Step 1: Use an area array CMOS with a windowing function as a satellite on-orbit yaw angle measurement device and install it on the satellite focal plane; the rolling direction of the area array CMOS is required to be perpendicular to the satellite flight direction, and the area array CMOS imaging area, i.e., the windowing range, is set; Step 2: Adjust the window size of the area array CMOS and further adjust the image overlap area to obtain a suitable image overlap area; Step 3: Based on the image overlapping area determined in step 2, image registration is used to calculate the image offset of the overlapping imaging area; The specific process of calculating the image offset is: Step 31: partition the overlapping area of two adjacent continuous frames of image, and divide the overlapping area of one frame of image into several continuous areas of equal size according to a certain interval, and the partition interval is the actual sampling interval time; Step 32: Calculate the relative offset between overlapping image partitions along the flight direction and perpendicular to the flight direction using an image contrast algorithm; Step 4: Calculate the yaw angle based on the image offset obtained in step 3 to achieve real-time measurement of the satellite's on-orbit yaw angle.

2. The method for measuring the on-orbit yaw angle of a satellite according to claim 1, wherein: The window range set in step 1 is adjusted by the window start row and window end row.

3. The method for measuring the on-orbit yaw angle of a satellite according to claim 1, wherein: In step 2, set the number of pixels in the direction of flight of the area array CMOS to n, the number of pixels in the vertical direction of flight to m, the pixel size to a, and the exposure start time interval between rows to T. row , the image motion speed is v I , then the length of the overlapping area ΔL is: ΔL=na-mT row v I The length of the overlapping area can be changed by changing the value of m. The smaller m is, the larger the overlapping area is.

4. The method for measuring the on-orbit yaw angle of a satellite according to claim 1, wherein: The yaw angle α is calculated based on the relative offset along the flight direction and the relative offset perpendicular to the flight direction; it can be expressed as follows: Where ΔN is the relative offset along the flight direction, and ΔM is the relative offset in the vertical flight direction.

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