A high-frequency integration time adjustment method suitable for dynamic imaging

Abstract

The application relates to a high-frequency integration time adjustment method suitable for motion imaging, which has good practicability for integration time calculation and adjustment frequency determination of push-broom imaging in a satellite attitude maneuver process. The method is aimed at the problem of sharp change of image motion speed caused by the satellite attitude maneuver in the push-broom imaging process, and a push-broom integration time calculation method considering the satellite attitude maneuver angular velocity is provided, then the integration time is adjusted at a certain frequency to reduce the MTF drop, and a determination method of the integration time adjustment frequency is given. The integration time calculation method of the method is suitable for the push-broom imaging task of any attitude angular velocity, and the high-frequency integration time adjustment method is adopted to ensure the imaging quality in the whole push-broom imaging process.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of push-broom imaging, and relates to a high-frequency integration time adjustment method suitable for imaging in motion. BACKGROUND

[0002] Traditional push-broom imaging ground speed is mainly caused by track movement and earth rotation, while push-broom ground speed in satellite attitude imaging in motion is jointly composed of track movement, earth rotation and satellite attitude angular velocity. Affected by satellite attitude and attitude angular velocity change, the image plane image motion speed changes dramatically during satellite attitude maneuvering. In the state invention patents "A method for imaging a target along an inclined strip during agile satellite maneuvering" and "An attitude maneuvering adjustment method for imaging along an inclined strip", a method for imaging along an inclined strip during attitude maneuvering is proposed, which adopts a uniform ground speed mode. It can be seen that the satellite attitude and attitude angular velocity change dramatically during imaging in motion. In the traditional satellite integration time calculation method, only position speed information and attitude angle information are introduced, and the image motion speed change caused by attitude angular velocity in the imaging in motion process cannot be reflected. For imaging in motion, it is necessary to introduce attitude angular velocity information for integration time calculation.

[0003] The imaging efficiency is greatly improved in the imaging in motion mode compared with the traditional static imaging mode, but due to the combined effect of track movement and attitude maneuvering, the image plane space orientation changes in real time, which causes a large change in the image motion speed during one imaging process, affecting the imaging quality. If the rapidly changing image motion speed cannot be compensated, it will lead to serious decline in imaging quality. Traditional high-resolution remote sensing satellites usually use 1Hz integration time adjustment frequency, and the attitude information delay used in the existing satellite integration time adjustment method is very large, which is difficult to meet the image motion requirements of the imaging process in motion. MTF is usually used to measure the decline in imaging quality caused by image motion. For the rapid change of integration time in imaging in motion, it is necessary to increase the integration time frequency and reduce the attitude information delay, that is, to match the current integration time with the current image plane image motion speed. It is difficult to infinitely increase the integration time adjustment frequency in engineering implementation, and it is not necessary in practice, so it is necessary to determine the minimum integration time adjustment frequency required in the imaging in motion process according to the imaging quality as the measurement basis, which meets the imaging quality and facilitates engineering implementation. SUMMARY

[0004] The technical problem solved by the application is that, for the problem of rapid change of image motion speed caused by satellite attitude maneuvering in push-broom imaging in motion, a high-frequency integration time adjustment method suitable for imaging in motion is proposed, which reduces the MTF decline by adjusting the integration time at a certain frequency, and a determination method of the integration time adjustment frequency is given.

[0005] The technical scheme of the present application is: a high-frequency integration time adjustment method suitable for motion imaging, the calculation process uses time step Δt to calculate, and the specific steps of calculating any t n time are as follows:

[0006] (1) acquiring t n time of motion imaging, the position vector R D (t n ) from the earth center to the imaging point, the position S(t n ) from the earth center to the satellite, the velocity vector V S (t n ) of the satellite, the three-axis attitude vector X b (t n ), Y b (t n ), Z b (t n ) of the satellite, and the attitude angular velocity vector ω b (t n ) of the satellite, and calculating the imaging plane image motion velocity V D (t n ) of the imaging point;

[0007] (2) determining the image motion velocity size v 像 (t n ) of the ground object relative to the body coordinate system according to the projection of the imaging plane image motion velocity V D (t n ) of the imaging point on the X b (t n ) axis of the satellite body;

[0008] (3) calculating the integration time T int (t n ) according to the image motion velocity size v 像 (t n );

[0009] (4) adjusting the integration time according to the frequency , and calculating the maximum image motion error Δp(t n ) caused by the integration time adjustment in a period;

[0010] (5) calculating the MTF(t n ) of the t n time caused by the image motion according to the maximum image motion error Δp(t n );

[0011] (6) calculating the minimum MTF value in the imaging process, denoted as MTF min ;

[0012] (7) taking MTF min≥ MTF Q For requirement, modify the calculation step Δt, repeat the steps (1) to (7) to calculate the new MTF min , until the | MTF min | ≤ δ, the integral time adjustment frequency at this time is taken as the minimum integral time adjustment frequency allowed by the imaging system; MTF Q | is the minimum design value of MTF to meet the imaging quality requirement, and δ is a preset error threshold. Q For requirement, modify the calculation step Δt, repeat the steps (1) to (7) to calculate the new MTF min , until the | MTF min | ≤ δ, the integral time adjustment frequency at this time is taken as the minimum integral time adjustment frequency allowed by the imaging system; MTF Q | is the minimum design value of MTF to meet the imaging quality requirement, and δ is a preset error threshold.

[0013] Further, the image motion speed V D (t n ) of the photographic point image plane is calculated as follows:

[0014] V D (t n ) = ω e (t n ) × R D (t n ) - V S (t n ) - ω b (t n ) × L(t n )

[0015] Wherein, ω e (t n ) is the angular velocity vector of the earth rotation, L(t n ) = R D (t n ) - S(t n ) is the vector from the satellite to the photographic point, and the distance size is recorded as L(t n ) = | R D (t n ) - S(t n ) |.

[0016] Further, the image motion speed size v 像 (t n ) of the ground object relative to the body coordinate system is calculated as follows:

[0017]

[0018] Wherein F is the focal length of the optical camera.

[0019] Further, the integral time T int (t n ) is calculated as follows:

[0020]

[0021] Wherein d is the size of the detector pixel.

[0022] Further, the maximum image motion error Δp(t n ), the calculation is as follows:

[0023]

[0024] Wherein N is the number of TDI.

[0025] Further, the calculation of the image motion causes t n The MTF at the moment MTF(t n ), as follows:

[0026]

[0027] Further, the minimum integration time adjustment frequency allowed by the imaging system is to meet |MTF min -MTF Q |≤δ when And rounding to the nearest integer; Wherein δ is a small number close to 0.

[0028] The beneficial effects of the present application compared with the prior art are:

[0029] (1) The integration time calculation method of the present application considers the influence of the attitude angular velocity during the attitude maneuver. The satellite attitude and attitude angular velocity change dramatically during the imaging in motion, which is the main reason for the change of the integration time. The present application takes the attitude angular velocity into the integration time calculation.

[0030] (2) The present application method uses the method of increasing the integration time adjustment frequency to ensure the MTF of the whole push-broom imaging process. The determined integration time adjustment frequency meets the requirements of the imaging quality under any attitude and any attitude angular velocity during the imaging in motion. The determined integration time adjustment frequency is the lowest adjustment frequency, which can be directly referenced for engineering implementation. When engineering is implemented, the actual integration time adjustment frequency greater than or equal to the value can meet the imaging requirements. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The flow chart of the present application method;

[0032] Figure 2 The satellite imaging in motion part vector diagram;

[0033] Figure 3 The actual integration time usage diagram when adjusting the integration time;

[0034] Figure 4 The integration time calculation result diagram for different slanted strips; ​

[0035] Figure 5 Fig. 2 is a diagram showing the MTF calculation results of the frequency adjustment of the integral time. DETAILED DESCRIPTION

[0036] The method of the present application first provides a calculation method of the image motion speed and integral time of push-broom imaging considering the satellite attitude maneuver angular velocity, then provides a calculation method of the image motion deviation caused by the integral time adjustment, calculates the MTF drop caused by the image motion, and determines the minimum integral time adjustment frequency allowed by the imaging system according to the imaging quality requirement.

[0037] The present application will be further described below in combination with the drawings and embodiments.

[0038] The present application provides a high-frequency integral time adjustment method suitable for motion imaging, as shown in Fig. 1. Figure 1 The calculation process is calculated by time step Δt, and the specific steps at any t n time are as follows:

[0039] (1) Obtain the t n time of motion imaging, the position vector R D (t n ) from the center of the earth to the photographic point, the position S(t n ) from the center of the earth to the satellite, the velocity vector V S (t n ) of the satellite, the three-axis attitude vector X b (t n ), Y b (t n ), Z b (t n ) of the satellite, the attitude angular velocity vector ω b (t n ) of the satellite, and calculate the photographic point image motion speed V D (t n );

[0040] (2) Determine the image motion speed size v 像 (t n ) of the ground object relative to the body coordinate system according to the projection of the photographic point image motion speed V D (t n ) on the X b (t n ) axis of the satellite body;

[0041] (3) Calculate the integral time T int (t n ) according to the image motion speed size v 像 (t n );

[0042] (4) by frequency The integral time adjustment is performed, and the maximum image motion error Δp(t n ) caused by the integral time adjustment in a period is calculated;

[0043] (5) According to the maximum image motion error Δp(t n ), the MTF drop at time t n caused by the image motion is calculated MTF(t n );

[0044] (6) The minimum MTF value in the imaging process is calculated, denoted as MTF min ;

[0045] (7) With the requirement of MTF min ≥ MTF Q , the calculation step Δt is modified, and steps (1)-(7) are repeated to calculate a new MTF min , until | MTF min - MTF Q | ≤ δ, and the integral time adjustment frequency at this time is taken as the minimum integral time adjustment frequency allowed by the imaging system; MTF Q is the minimum design value of MTF that meets the imaging quality requirement, and δ is a preset error threshold.

[0046] In step (1), the photographic point image plane image motion speed V D (t n ) is calculated, which specifically includes:

[0047] Given the geocentric position vector R D (t n ) to the photographic point, the geocentric position S(t n ) to the satellite, the satellite running speed vector V S (t n ), the satellite three-axis attitude vector X b (t n ), Y b (t n ), Z b (t n ), and the satellite attitude angular velocity vector ω b (t n ) at time t n of the moving imaging, part of the vectors are shown in Figure 2 .

[0048] The photographic point image plane image motion speed V D (t n ) calculation method is shown in formula (1).

[0049] V D(t n ) = ω e (t n ) x R D (t n ) - V S (t n ) - ω b (t n ) x L(t n ) (1)

[0050] where ω e (t n ) is the angular velocity vector of the earth rotation, L(t n ) = R D (t n ) - S(t n ) is the vector from the satellite to the photograph point, and its distance is denoted as:

[0051] L(t n ) = |R D (t n ) - S(t n )| (2)

[0052] In step (2), the image motion velocity of the ground object relative to the body coordinate system is denoted as v 像 (t n ), and the calculation method is as follows:

[0053] The projection of the image motion velocity V D (t n ) of the photograph point on the satellite body X b (t n ) axis is the image motion velocity of the ground object relative to the body coordinate system, and the calculation formula is as follows:

[0054]

[0055] where F is the focal length of the optical camera.

[0056] In step (3), the integral time T int (t n ) is calculated, which specifically includes:

[0057] The integral time is calculated according to the image motion velocity of the image plane, and the calculation formula is as follows:

[0058]

[0059] where d is the size of the detector pixel.

[0060] According to the above calculation method, the integral time of the camera is related to the sliding velocity of the photograph point, the orbit height of the satellite, the attitude angle, the attitude angular velocity, the focal length of the camera, and the pixel size.

[0061] In step (4), the maximum image shift error Δp(t n ) caused by the integral time adjustment in one period is calculated, specifically including:

[0062] The attitude angle and angular velocity information at the last time are used to calculate and adjust the integral time during the integral time adjustment, and the integral time used before t n is the integral time calculated according to the attitude information at t n-1 , and the integral time used before t n+1 is the integral time calculated according to the attitude information at t n . Due to the large attitude and attitude angular velocity changes in the moving imaging process, the delay will cause the decline of the imaging quality. The maximum image shift error in one period can be calculated, for example, the integral time at t n is used to calculate the integral time at t n-1 , and the calculation formula is shown in formula (5), where N is the number of TDI. The schematic diagram is shown in Figure 3 .

[0063]

[0064] In step (5), the MTF decline MTF(t n ) caused by the image shift at t n is calculated, as shown in formula (6):

[0065]

[0066] In step (6), the minimum MTF in one imaging process is calculated as:

[0067] MTF min = min[MTF(t0), MTF(t1), MTF(t2), …, MTF(t n ), …] ≥ MTF Q (7)

[0068] In step (7), the integral time adjustment frequency is determined, specifically including:

[0069] According to the imaging requirements, the MTF decline caused by the integral time should be as small as possible, and it is usually required that MTF(t n ) ≥ MTF n at any t Q , that is, MTF min ≥ MTF Q , where MTF Q is the minimum design value of MTF that meets the imaging quality requirements.

[0070] The calculation step Δt is modified, and the MTF is recalculatedmin , find MTF min closest MTF Q i.e.

[0071] | MTF min - MTF Q |≤δ (8)

[0072] δ is a small number close to 0, for example 0.005. At this time, the integration time adjustment frequency is and rounding off to the nearest integer as the minimum integration time adjustment frequency allowed by the imaging system.

[0073] Example 1

[0074] Figure 4 The integration time along the imaging process of the slanted strip at different angles is given. Taking the imaging of the vertical subspace point trajectory by the slanted strip as an example (i.e. 90° slanted strip), Figure 5 The MTF of the whole imaging process when the integration time adjustment is 1 Hz, 2 Hz and 4 Hz during the imaging process of the vertical subspace point trajectory is given. It can be seen that when 4 Hz is used, the MTF exactly meets the imaging requirement of more than 97%, therefore the integration time adjustment frequency of the scanning imaging system needs to be greater than 4 Hz to meet the imaging quality requirement.

[0075] Although the present application has been disclosed with the preferred embodiments as above, it is not intended to limit the present application, and any person skilled in the art can make possible changes and modifications to the technical solutions of the present application by using the disclosed methods and technical contents without departing from the spirit and scope of the present application. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application, which does not depart from the content of the technical solutions of the present application, belongs to the protection scope of the technical solutions of the present application.

[0076] The contents not described in detail in the specification of the present application are the known technology of the person skilled in the art.​

Claims

1. A high-frequency integration time adjustment method suitable for in-motion imaging, characterized in that, The calculation process uses a time step of 1. Perform calculations, any The specific steps for time calculation are as follows: (1) Acquiring in-motion imaging Time, vector from Earth's center to the location of the photographing point The position from the Earth's center to the satellite The velocity vector of satellite orbit The satellite's three-axis attitude vector , , , satellite attitude angular velocity vector Calculate the image movement velocity of the image plane at the shooting point. ; (2) Based on the image movement speed of the image plane at the shooting point In the satellite body The projection on the axis determines the magnitude of the image displacement velocity of the ground feature relative to the body coordinate system. ; (3) Based on the magnitude of the image movement velocity Calculation time of integration ; (4) By frequency Perform integration time adjustment and calculate the maximum image shift error caused by the integration time adjustment within one cycle. ; (5) Based on the maximum image shift error Calculate image shift caused MTF decrease at time ; (6) Calculate the minimum MTF value during a single imaging process, denoted as ; (7) with To meet the requirements, modify the calculation step size. Repeat steps (1) to (7) to calculate the new... until satisfied The integral time adjustment frequency at this time is taken as the minimum allowable integral time adjustment frequency of the imaging system. Minimum design value of MTF to meet imaging quality requirements, This is a preset error threshold.

2. The high-frequency integration time adjustment method for in-motion imaging according to claim 1, characterized in that, The calculation of the image motion velocity of the photographic point image plane As shown below: in, This is the angular velocity vector of the Earth's rotation. Let be the vector distance from the satellite to the photography point, and let its magnitude be denoted as . .

3. The high-frequency integration time adjustment method for in-motion imaging according to claim 2, characterized in that, The magnitude of the image displacement velocity of the ground feature relative to the body coordinate system The calculation method is as follows: Where F is the focal length of the optical camera.

4. The high-frequency integration time adjustment method for in-motion imaging according to claim 3, characterized in that, The calculation time of integration As shown below: Where d is the detector pixel size.

5. A high-frequency integration time adjustment method for in-motion imaging according to claim 4, characterized in that, The maximum image shift error The calculation method is as follows: Where N is the number of levels in TDI.

6. The high-frequency integration time adjustment method for in-motion imaging according to claim 5, characterized in that, The calculated image shift caused MTF decrease at time As shown below: 。 7. A high-frequency integration time adjustment method for in-motion imaging according to claim 6, characterized in that, The minimum allowable integration time adjustment frequency of the imaging system is to meet the following requirements. time and to Rounding down; where It is a decimal number close to 0.

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