A method for on-the-move imaging of agile optical satellite linear array

Abstract

This invention proposes an agile optical satellite linear array imaging method on the move, solving the problem of failing to obtain high-fidelity remote sensing images due to improper attitude control planning methods and imaging parameter selection and settings. The method includes: acquiring the satellite imaging task and selecting the satellite imaging mode; setting the evaluation benchmarks and their weights for each indicator in the imaging task; establishing an imaging parameter selection set, selecting one combination of imaging parameters for orbit calculation and attitude planning, calculating the imaging quality by correcting the yaw angle with the detector center point as a reference, and calculating the number of detector elements whose transfer functions meet the standards; calculating the comprehensive imaging evaluation parameter value of the imaging parameter combination based on the imaging quality value and the number of detector elements, using the set evaluation benchmarks and weights, and according to the comprehensive imaging evaluation function g; selecting the highest comprehensive evaluation parameter value from various imaging parameter combinations, and inputting the parameters of this combination to the satellite to execute the imaging task.

Description

Technical Field

[0001] This invention belongs to the field of high-resolution optical remote sensing satellite Earth observation and relates to an agile optical satellite linear array imaging method in motion. Background Technology

[0002] With the development of optical remote sensing technology, linear array imaging is increasingly being used in various types of optical remote sensing satellites. Simultaneously, the agility and maneuverability of satellite platforms are constantly evolving to ensure that satellites possess imaging capabilities while in motion, adapting to the signal-to-noise ratio and timeliness requirements of imaging missions. In particular, for high-orbit optical remote sensing satellites equipped with visible light array channels, active sweep imaging while in motion can be used for sea observation, featuring high resolution, large swath width, and high efficiency.

[0003] For optical remote sensing satellites employing active attitude maneuvering for on-the-move linear array imaging, the imaging modes are more complex and diverse, and the number of possible combinations of imaging parameters increases significantly. On the one hand, users want imaging quality parameters such as signal-to-noise ratio and modulation transfer function to meet the needs of subsequent data applications; on the other hand, users also want the satellite's imaging efficiency to be as high as possible to meet the satellite's requirements for high timeliness and rapid response.

[0004] It can be seen that imaging quality and imaging efficiency are mutually restrictive, and it is particularly important to find a balance between them to achieve the best overall imaging performance. Summary of the Invention

[0005] This invention proposes an agile optical satellite linear array imaging method on the move, which solves the problem that improper optical satellite attitude control planning and imaging parameter selection and setting can lead to the inability to obtain high-fidelity remote sensing images or low imaging efficiency.

[0006] The present invention is achieved through the following technical solution.

[0007] A method for on-the-moment imaging of agile optical satellite linear arrays, characterized by comprising:

[0008] Step 1: Obtain satellite imaging mission and select satellite imaging mode;

[0009] Step 2: Set the evaluation criteria and weighting of each indicator in the imaging task;

[0010] Step 3: Establish an imaging parameter selection set, select one of the imaging parameter combinations for trajectory calculation and attitude planning, use the detector center point as a reference to calculate the yaw angle correction and imaging quality, and calculate the number of detector elements that need to be adjusted to meet the transfer function requirements.

[0011] Step 4: Based on the imaging quality value and the number of detectors calculated in Step 3, and using the evaluation benchmark and weighting set in Step 2, calculate the imaging comprehensive evaluation parameter value of the imaging parameter combination according to the imaging comprehensive evaluation function g.

[0012] Step 5: Repeat steps 3 and 4, select the highest value from the comprehensive evaluation parameter values ​​of various imaging parameter combinations, and input the parameters of this combination to the satellite to execute the imaging task.

[0013] The beneficial effects of this invention are:

[0014] 1. This invention comprehensively considers the requirements of imaging quality and imaging efficiency, establishes a quantitative imaging comprehensive evaluation function, and solves the design problem of agile satellite linear array in motion imaging under the coupled effect of complex influencing factors.

[0015] 2. This invention proposes a comprehensive evaluation method for linear array optical satellite imaging with agile on-the-moment imaging capabilities, simplifying the process of satellite imaging mode selection and imaging parameter design under the combined influence of complex factors;

[0016] 3. This invention ensures that the important imaging quality and imaging efficiency indicators of the satellite imaging area meet the application requirements, and helps similar satellites to carry out related overall design work;

[0017] 4. This invention is the first to propose a comprehensive imaging evaluation function and imaging design method that takes into account both imaging quality and imaging efficiency, ensuring that the important imaging quality and imaging efficiency indicators of the satellite imaging area meet application requirements.

[0018] 5. This invention can also help evaluate the actual on-orbit application effectiveness of satellites. Attached Figure Description

[0019] Figure 1 This is a flowchart of the agile optical satellite linear array imaging method of the present invention. Detailed Implementation

[0020] Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be understood that the embodiments shown and described in the drawings are merely exemplary and are intended to illustrate the principles and spirit of the present invention, and are not intended to limit the scope of the present invention.

[0021] like Figure 1 As shown, the present invention provides an agile optical satellite linear array imaging method in motion, which specifically includes:

[0022] Step 1: Obtain satellite imaging mission and select satellite imaging mode;

[0023] In this embodiment, the imaging conditions of the imaging task include: imaging time T, latitude and longitude of the imaging target area (L0, B0), illumination conditions (measured by solar altitude angle) and typical target reflectivity.

[0024] The existing satellite imaging modes mainly include the following three types:

[0025] Uniform ground velocity mode: that is, uniform geocentric angular velocity, meaning that the linear velocity of the point on the ground surface pointed to by the satellite camera's line of sight remains constant.

[0026] Uniform angular velocity mode: that is, uniform satellite sweep angular velocity, meaning that the angular velocity of the satellite camera relative to its optical axis center point remains constant in the pitch direction;

[0027] Uniform integral time mode: also called uniform velocity-to-height ratio sweeping imaging mode, meaning the "velocity-to-height ratio" remains constant throughout the imaging process. Here, "velocity" refers to the velocity component along the imaging direction (perpendicular to the optical axis) of the camera's line of sight pointing to the ground projection point; "height" refers to the distance from the center of the camera's primary mirror to the ground projection point. In attitude planning, the imaging trajectory is generally determined first, then the "height" is determined based on the satellite position and the imaging trajectory, and finally the "velocity" is planned.

[0028] Therefore, in this embodiment, the selected satellite imaging mode is selected in order of priority based on the actual capabilities of the satellite, namely, uniform integral time mode, uniform ground velocity mode, and uniform angular velocity mode.

[0029] Step 2: Set the evaluation criteria and weighting of each indicator in the imaging task; specifically, this includes the following steps:

[0030] S201, Calculate the comprehensive imaging evaluation function g:

[0031] g = (ma + nb + pc) × 100

[0032] Where a is the evaluation value of the imaging quality parameter {A}, b is the evaluation value of the imaging efficiency parameter B, c is the evaluation value of the number of detectors that meet the transfer function standard (i.e. the proportion of detectors that meet the transfer function standard), and m, n, and p are weighting coefficients assigned according to the importance of the indicators, m+n+p=1.

[0033] S202. Calculate the evaluation value a of the imaging quality parameter {A}:

[0034] a = x1a1 + x2a2

[0035] Among them, a iLet xi be the evaluation value of the imaging quality parameter Ai, which is the ratio of the actual imaging parameter to the evaluation benchmark parameter, and xi be the corresponding weighting coefficient, x1 + x2 = 1; the imaging quality parameter {A} includes: A1 Modulation Transfer Function (MTF), A2 Signal-to-Noise Ratio (SNR); where A1 can be further decomposed into A1, A2, and A3 based on the actual imaging spectrum of the satellite. 11 Visible light panchromatic channel MTF, A 12 ~A 15 MTF and A of multispectral channels 1-4 16 Infrared channel MTF, etc.; A2 can also be decomposed accordingly;

[0036] S203. Calculate the evaluation value b of the imaging efficiency parameter B:

[0037]

[0038] Where L is the length of the imaging strip, T is the total time from attitude adjustment to imaging to attitude return to zero, and v0 is the maximum ground velocity of the satellite.

[0039] Step 3: Establish an imaging parameter selection set, select one of the imaging parameter combinations for trajectory calculation and attitude planning, use the detector center point as a reference to calculate the yaw angle correction and imaging quality, and calculate the number of detector elements that need to be adjusted to meet the transfer function requirements.

[0040] In specific implementation, the imaging parameter selection set can be composed of imaging parameters that do not exceed the capabilities of the detector and satellite, forming an optional imaging parameter set M; specifically:

[0041]

[0042] Where s is the number of configurable imaging parameter combinations, w is the retrace factor (for high-orbit satellites, it is a multiple of their minimum line frequency), and q is the integration series.

[0043] In this embodiment, the calculated imaging quality includes the modulation transfer function (MTF) and the signal-to-noise ratio (SNR). Specifically, when calculating the MTF, the influence of the drift angle residual should be considered. In the prior art, the drift angle is defined as the angle between the image motion direction and the linear array push-broom direction, influenced by factors such as Earth's rotation and satellite attitude maneuvers. After drift angle correction based on the detector center point, the remaining value of this angle is called the drift angle residual.

[0044] In this embodiment, the number of detectors whose transfer function meets the standard is calculated as follows: a threshold MTF0 is set, the MTF value of each detector is judged, and if it is less than the threshold MTF0, the detector does not meet the standard. The number of detectors with an MTF value greater than the threshold MTF0 is recorded as B1.

[0045] Step 4: Based on the imaging quality value and the number of detectors calculated in Step 3, and using the evaluation benchmark and weighting set in Step 2, calculate the imaging comprehensive evaluation parameter value of the imaging parameter combination according to the imaging comprehensive evaluation function g.

[0046] The comprehensive evaluation parameter values ​​include: evaluation value a of imaging quality parameter {A}, evaluation value b of imaging efficiency parameter B, and proportion of detectors that meet the transfer function standard.

[0047] Where a1 and a2 are the ratios of the actual MTF and SNR to the evaluation benchmark determined in step two. If the imaging parameters are weighted in step two, then the weighting decomposition is also performed accordingly when calculating the imaging quality evaluation value a; c is the ratio of the number of detector elements B1 to the total number of detector elements.

[0048] Step 5: Repeat steps 3 and 4, select the highest value from the comprehensive evaluation parameter values ​​of various imaging parameter combinations, and input the parameters of this combination to the satellite to execute the imaging task.

[0049] The present invention will now be described in detail using a high-orbit optical remote sensing satellite with linear array imaging capability and agile maneuverability as an example.

[0050] 1) Acquire satellite imaging mission.

[0051] Obtain the input for this imaging mission. A certain high-orbit imaging satellite plans to observe a target at 22°N, 90°E at 9:00 UTC on March 20, 2021. The strip length is 300km. The calculated solar altitude angle at the imaging time is 30 degrees, and the surface reflectivity is 0.2.

[0052] 2) Select the satellite imaging mode.

[0053] Based on the actual capabilities of this high-orbit satellite, uniform integral time planning will be selected for subsequent imaging parameter design. If the satellite has the attitude planning capability for uniform integral time imaging mode, then uniform ground velocity mode will be used; if the satellite does not have the attitude planning capability for uniform ground velocity imaging mode, then uniform angular velocity mode will be selected.

[0054] The main factors considered in the selection process include: the maximum value of the deflection angle residual, the frame frequency uniformity of each detector, and the frame frequency variation amplitude during the imaging period. These are not the focus of this invention and will not be elaborated here.

[0055] 3) Set the evaluation criteria and weighting of each indicator in this imaging mission evaluation.

[0056] (3.1) Evaluation Indicators for Imaging Missions

[0057] A1: Transfer function MTF (at Nyquist frequency): Average MTF across the entire field of view is better than 0.1.

[0058] A2: Signal-to-noise ratio (SNR): better than 40dB.

[0059] The maximum ground speed is v0 = 50 km / s.

[0060] The number of detector elements involved in imaging is C = 18.

[0061] (3.2) Weighting of Imaging Indicators

[0062] Based on the actual requirements of this imaging mission for imaging quality and efficiency, the weighting coefficients are assigned as 0.6, 0.3, and 0.1, respectively:

[0063] g = (0.6a + 0.3b + 0.1c) × 100 (Equation 4)

[0064] Where a is the evaluation value of the imaging quality parameter {A}, b is the evaluation value of the imaging efficiency parameter B, and c is the proportion of detectors that meet the transfer function standard.

[0065] The evaluation value 'a' of the imaging quality parameter {A} is decomposed as follows:

[0066] a = 0.6a1 + 0.4a2 (Equation 5)

[0067] Where a1 is the MTF evaluation value and a2 is the signal-to-noise ratio evaluation value.

[0068] 4) Establish a set of possible imaging parameters, including retrace magnification, integration series, etc.

[0069] The possible set of imaging parameters for a certain high-orbit satellite includes: retrace factor m = {1, 2, 4, 5, 10}, and integral series q = {24, 48, 96}.

[0070] 5) Select a combination of imaging parameters, perform trajectory calculation and attitude planning, and use the detector center point as a reference to correct the drift angle and calculate the imaging quality;

[0071] (5.1) Select an imaging parameter combination

[0072] The following explanation uses a retracement multiple of 1 and an integral series of 24 levels as an example.

[0073] (5.2) The yaw angle is defined as the angle between the image motion direction and the linear array push-broom direction due to factors such as Earth's rotation and satellite attitude maneuvers.

[0074]

[0075] Wherein, v1 and v2 are the projection components of the camera's line of sight pointing to the ground projection point on the image plane (perpendicular to the optical axis) perpendicular to the push-broom direction and the push-broom direction.

[0076] After correcting the deflection angle based on the detector's center point, the remaining value of this angle is called the deflection angle residual.

[0077] (5.3) Calculate the imaging quality value of each detector.

[0078] Imaging quality parameters, including modulation transfer function (MTF) and signal-to-noise ratio (SNR), are calculated using methods well-known in the industry. It is particularly important to note that the influence of the drift angle residual should be considered when calculating the MTF.

[0079] Specifically as follows:

[0080]

[0081] Where MTFp is the decrease in MTF caused by the deflection angle residual θ, and q is the integral series.

[0082] 6) Calculate the number of detector elements whose transfer function meets the requirements.

[0083] Set a threshold MTF0. If the MTF value of each detector is less than the threshold MTF0, the detector is considered substandard. Record the number B1 of detectors whose MTF value is greater than the threshold MTF0.

[0084] Calculations showed that the MTF values ​​of detectors 1 and 18 did not meet the requirements, so they were removed, resulting in B1 = 16.

[0085] 7) Based on the imaging quality value calculated in (5) and the number of detectors calculated in (6), the imaging comprehensive evaluation parameter value of the imaging parameter combination is calculated using the evaluation benchmark and weight obtained in (3) and the imaging comprehensive evaluation function g.

[0086] (7.1) Calculate the imaging quality evaluation value a.

[0087] After removing detectors that do not meet the performance standards, the average MTF within the field of view is 0.12. Therefore, a1 = 0.12 / 0.1 = 1.2.

[0088] If the signal-to-noise ratio is 32dB, then a2 = 32 / 40 = 0.8.

[0089] Therefore, the image quality evaluation value a = 0.6 * 1.2 + 0.4 * 0.8 = 1.04.

[0090] (7.2) Calculate the imaging efficiency evaluation value b.

[0091] The imaging strip length L = 300 km, the total time from satellite attitude adjustment to imaging to attitude return to zero is T = 27 s, the maximum ground speed of the satellite is v0 = 50 km / s, then b = 0.22.

[0092] (7.3) Calculate the proportion of detectors that meet the transfer function standard, c.

[0093] There are 16 detectors with the MTF value meeting the standard, so c = 16 / 18 = 0.89.

[0094] (7.4) Calculate the comprehensive imaging evaluation value g

[0095] g=(0.6*1.04+0.3*0.22+0.1*0.89)*100=77.9.

[0096] 8) Repeat steps (5) to (7).

[0097] 9) Select the highest value from the comprehensive evaluation parameter values ​​of various imaging parameter combinations, and input the parameters of this combination to the satellite to perform the imaging task.

[0098] After exploring various combinations of imaging parameters, the group with the highest comprehensive evaluation value g was selected: retrace magnification of 4 times and integration level of 48. At this time, a = 1.21, b = 0.14, c = 0.83, and the comprehensive evaluation value g = 85.2.

[0099] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A method for agile optical satellite linear array motion imaging, characterized in that, The method comprises the following steps: Step one, obtaining a satellite imaging task and selecting a satellite imaging mode; Step two, setting evaluation criteria and proportion weight of each index in the imaging task; Step three, establishing an imaging parameter selection set, selecting one imaging parameter combination for orbit calculation and attitude planning, taking the center point of the detector as a reference to correct the drift angle, calculating the imaging quality, and calculating the number of detector pieces that meet the adjustment transfer function; Step four, according to the imaging quality value and the number of detector pieces calculated in step three, using the evaluation criteria and proportion weight set in step two, calculating the imaging comprehensive evaluation parameter value of the imaging parameter combination according to the imaging comprehensive evaluation function g; Step five, repeating steps three and four, selecting the highest value from the comprehensive evaluation parameter values of various imaging parameter combinations, and inputting the parameters of the combination into the satellite to execute the imaging task; Step two specifically comprises the following steps: S201, calculating the imaging comprehensive evaluation function g: Wherein, a is the evaluation value of the imaging quality parameter {A}, b is the evaluation value of the imaging efficiency parameter B, c is the evaluation value of the number of detector pieces that meet the transfer function, m, n, p are weight coefficients allocated according to the importance of the index, m+n+p=1; S202, calculating the evaluation value a of the imaging quality parameter {A}: wherein, is the evaluation value of the imaging quality parameter Ai, i.e. the ratio of the actual imaging parameter and the evaluation reference parameter, xi is the corresponding weight coefficient, ; the imaging quality parameters {A} include: A1 modulation transfer function MTF, A2 signal-to-noise ratio SNR; wherein, A1 is further decomposed into A 11 : visible light panchromatic channel MTF, A 12 A 15 MTF of multi-spectral channels 1~4, A 16 infrared channel MTF; A2 can also be decomposed accordingly; S203, calculating the evaluation value b of the imaging efficiency parameter B: Wherein, L is the imaging strip length, T is the time length of the whole process from attitude adjustment to imaging to attitude reset, and v0 is the maximum ground speed value of the satellite.

2. The agile optical satellite linear array motion imaging method of claim 1, wherein, The imaging conditions of the imaging task include: imaging time T, imaging target area longitude and latitude (L0, B0), illumination condition and typical target reflectivity.

3. The agile optical satellite linear array imaging while moving method according to claim 1 or 2, characterized in that, The selected satellite imaging mode adopts the mode of sequentially selecting the uniform integration time mode, the uniform ground speed mode and the uniform angular velocity mode according to the actual capacity of the satellite.

4. The agile optical satellite linear array motion imaging method of claim 1, wherein, The calculation of the imaging quality includes the modulation transfer function MTF and the signal-to-noise ratio SNR.

5. The agile optical satellite linear array motion imaging method of claim 4, wherein, The calculation of the number of detector pieces that meet the adjustment transfer function adopts the following method: setting a threshold MTF0, judging the MTF value of each piece of detector, if the MTF value is less than the threshold MTF0, the detector does not meet the standard, and recording the number of detector pieces B1 whose MTF value is greater than the threshold MTF0.

6. The agile optical satellite linear array imaging while moving method according to claim 4 or 5, characterized in that, The comprehensive evaluation parameter value includes: the evaluation value a of the imaging quality parameter {A}, the evaluation value b of the imaging efficiency parameter B, and the proportion c of the detector that meets the transfer function.

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