A precise calibration method for the ground focal plane position of a space camera

Abstract

The present invention proposes a precise calibration method for the ground focal position of a space camera, applies a component temperature measurement method to the focal position calibration test, and uses a collimator calibration method to calibrate the camera's focal position in a laboratory; uses the space camera focal position calibration method to calibrate the camera's focal position in a laboratory, collects the temperature states of the collimator and each component of the camera under test in real time, and calculates and compensates to eliminate the defocusing effect caused by the change in the temperature of the collimator and the inconsistency between the temperature of the camera component under test and the on-orbit operating temperature state, thereby achieving precise calibration of the ground focal position of the space camera.

Description

Technical Field

[0001] The invention belongs to the field of space remote sensing technology, in particular to the field of remote sensor calibration and detection, and relates to a method for accurately calibrating the ground focal plane position of a space camera. Background Art

[0002] When a space camera is working in orbit, the inconsistency between the focal plane calibration position in the laboratory and the actual focal plane position in orbit will greatly affect the imaging quality and work efficiency of the space camera in orbit. With the increasing application of space cameras, in order to simplify the design form of space cameras and meet the requirements of lightweight design, the structural design form without focusing mechanism is more urgently needed; the demand for rapid imaging response of real-time downlink images after entering orbit, shortening the time of in-orbit parameter adjustment and improving work efficiency is becoming increasingly strong. The above requirements have put forward higher requirements on the accuracy of the focal plane calibration position in the laboratory.

[0003] The traditional methods for calibrating the focal plane position of space cameras are mainly the following: 1) self-collimating pentaprism method combined with microscope observation to determine focus; 2) determining focus by judging the amplitude strength of the imaging electrical signal; 3) determining focus by measuring the transmission function in a vacuum tank. The method of visual observation with a microscope cannot accurately and quantitatively calibrate the focal plane position of the camera. Its calibration accuracy is low, and the human eye has a large error in interpretation. This calibration method is no longer applicable to space cameras that require high imaging quality. Although the determination of focal plane position changes is achieved by collecting electrical signals, the imaging quality of the camera cannot be determined. The calibration process in a vacuum tank ensures consistency with the on-orbit state, but its calibration process is complicated and greatly increases the calibration cost.

[0004] In response to this practical need, this patent proposes a temperature measurement and focus method, that is, to paste thermocouples [other temperature collection devices] on the parallel light tube and each component of the camera under test to collect real-time temperature, so as to calculate and compensate for the change in the focal position of the camera on track caused by the temperature change of each component, and realize the precise calibration of the focal position in the laboratory. The patent's precise calibration method for the focal position of a space camera [referred to as the temperature measurement and focus method] can ensure that the camera's on-orbit working state is basically consistent with the focal position in the laboratory. The camera can download images as soon as it enters orbit, and the imaging response is fast, eliminating the on-orbit focusing process and shortening the on-orbit focusing cycle. It is of great significance in the field of space camera imaging calibration and detection. Summary of the invention

[0005] The present invention proposes a method for accurately calibrating the ground focal position of a space camera, applies the component temperature measurement method to the focal position calibration test, and proposes to calculate, compensate and eliminate the defocus problem caused by the temperature change of the component by collecting the temperature of the component, so as to realize the accurate calibration of the focal position in the laboratory.

[0006] The present invention is achieved through the following scheme:

[0007] A method for accurately calibrating the ground focal plane position of a space camera: the method specifically comprises the following steps:

[0008] Step 1: Use the collimator calibration method to calibrate the camera's focal plane position in the laboratory;

[0009] Step 2: Use the space camera focal plane position calibration method to calibrate the camera focal plane position in the laboratory;

[0010] Step 3: The focal plane position changes caused by the temperature changes of the components of the above two parts are controlled by real-time temperature sampling. The defocus caused by the temperature change of the parallel light tube (3) and the defocus effect caused by the inconsistency between the temperature of the component of the camera under test (8) and the temperature state of the on-orbit operation are eliminated by calculating compensation. The camera defocus is compensated by adjusting the target position of the light tube, thereby realizing the accurate calibration of the ground focal plane position of the space camera.

[0011] Furthermore, in step 1

[0012] The specific steps of the collimator calibration are:

[0013] Step 11: Paste thermocouples or other temperature measuring devices (5) on the primary and secondary mirrors and focal plane components of the collimator (3), and use a temperature collection device (6) to collect real-time temperatures of the primary and secondary mirrors and focal plane components of the collimator (3);

[0014] Step 12: Use a large-aperture plane reflector (4) and a 4D interferometer (1) to build a self-collimating interference detection optical path for the parallel light tube (3);

[0015] Step 13: Collect the interference pattern power value through the 4D interferometer (1), and adjust the power value to 0 to accurately calibrate the initial focal plane position of the collimator (3);

[0016] Step 14: During the test, the temperature of the light pipe component is collected in real time to ensure that it is consistent with the initial calibration temperature state. When the temperature changes, the change in the focal plane position of the light pipe can be calculated based on the collected component temperature changes, and the change in the focal plane position of the camera introduced by it can be removed.

[0017] Furthermore, in step 2,

[0018] The specific steps of calibrating the focal plane position of the space camera are:

[0019] Step 21: Welding a temperature collection connector or other temperature measuring device (9) at the thermal control outlet of each component of the camera (8) to collect the temperature of each component of the camera in real time;

[0020] Step 22: Using an integrating sphere (7) to illuminate the test stripe plate target (2), a camera focal plane position calibration test light path is constructed by measuring the transmission function;

[0021] Step 23: Calculate the focal plane position change caused by the temperature change of the camera (8) components under the on-orbit temperature state by collecting the temperature state of each camera component, and eliminate and compensate the ground calibration test results.

[0022] Beneficial effects of the present invention

[0023] (1) The method of the present invention is referred to as the temperature measurement and focus determination method. The method proposes a method of pasting thermocouples [or other temperature measuring devices] at the positions of the collimator used for calibration and testing and the components of the space camera under test, collecting the temperature status of the collimator and the components of the camera under test in real time, and calculating and compensating to eliminate the defocusing effect caused by the temperature change of the collimator and the inconsistency between the temperature of the camera components under test and the temperature status of the on-orbit operation, thereby realizing the accurate calibration of the ground focal plane position of the space camera;

[0024] (2) Based on the previous method of realizing the focal plane position calibration of space cameras by measuring the transmission function, the present invention introduces the idea of ​​real-time temperature collection of components, which can directly and accurately monitor the deviation between the focal plane position calibration state of the camera laboratory and the focal plane position of the on-orbit operation state, and can realize more accurate focal plane position calibration;

[0025] (3) The method for accurately calibrating the focal plane position of a space camera of the present invention can ensure that the on-orbit working state of the camera is basically consistent with the focal plane calibration position in the laboratory. The camera can download images as soon as it enters orbit, which reduces the on-orbit parameter adjustment time. The position calibration is accurate, eliminating the on-orbit focusing process and shortening the on-orbit focusing cycle. It is of great significance in the field of space camera imaging calibration and detection.

[0026] (4) The present invention accurately calculates the focal plane position of the on-orbit camera, and can achieve that the focal plane position in the laboratory is basically consistent with the on-orbit imaging position, eliminating the need for the traditional space camera to use a focusing mechanism [or other focusing methods] to focus on the orbit, greatly reducing the mass of the space camera, and saving the development cost and launch cost of the space camera. The invention of this calibration method has a great impact on the development of the structural form of the space camera. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A schematic diagram of the calibration light path of the collimator of the present invention;

[0028] Figure 2 A schematic diagram of the optical path for calibrating the focal plane position of a space camera of the present invention;

[0029] Among them, (1) is a 4D interferometer, (2) is a stripe plate target for testing, (3) is a collimator, (4) is a large-aperture plane reflector, (5) is a thermal couple or other temperature measuring device, (6) is a temperature acquisition system (0 degree thermostat), (7) is an integrating sphere, (8) is a wave measurement camera, and (9) is a temperature acquisition connector or other temperature measuring device. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0031] Combination Figure 1 to Figure 2 ,

[0032] A method for accurately calibrating the ground focal plane position of a space camera: the method specifically comprises the following steps:

[0033] Step 1: Use the collimator calibration method to calibrate the focal position of the camera in the laboratory; (Use the collimator assembly temperature sampling method to calibrate the focal position of the test collimator);

[0034] Step 2: Use the space camera focal plane position calibration method to calibrate the camera's focal plane position in the laboratory; (Use the space camera component real-time temperature sampling method to calibrate the space camera's focal plane position in the laboratory)

[0035] Step 3: The focal plane position changes caused by the temperature changes of the components of the above two parts are controlled by real-time temperature sampling. The defocus caused by the temperature change of the parallel light tube (3) and the defocus effect caused by the inconsistency between the temperature of the component of the camera under test (8) and the temperature state of the on-orbit operation are eliminated by calculating compensation. The camera defocus is compensated by adjusting the target position of the light tube, thereby realizing the accurate calibration of the ground focal plane position of the space camera.

[0036] In step 1, the collimator calibrates the light path as follows Figure 1 As shown:

[0037] The specific steps of the collimator calibration are:

[0038] Step 11: Paste thermocouples or other temperature measuring devices (5) on the primary and secondary mirrors and focal plane components of the collimator (3), and use a temperature collection device (6) to collect real-time temperatures of the primary and secondary mirrors and focal plane components of the collimator (3);

[0039] Step 12: Use a large-aperture plane reflector (4) and a 4D interferometer (1) to build a self-collimating interference detection optical path for the parallel light tube (3);

[0040] Step 13: Collect the interference pattern power value through the 4D interferometer (1), and adjust the power value to 0 to accurately calibrate the initial focal plane position of the collimator (3);

[0041] Step 14: During the test, the temperature of the light pipe component is collected in real time to ensure that it is consistent with the initial calibration temperature state. When the temperature changes, the change in the focal plane position of the light pipe can be calculated based on the collected component temperature changes, and the change in the focal plane position of the camera introduced by it can be removed.

[0042] In step 2, the focal plane position of the space camera is calibrated as follows: Figure 2 As shown:

[0043] The specific steps of calibrating the focal plane position of the space camera are:

[0044] Step 21: Welding a temperature collection connector or other temperature measuring device (9) at the thermal control outlet of each component of the camera (8) to collect the temperature of each component of the camera in real time;

[0045] Step 22: Illuminate the test stripe plate target (2) through the integrating sphere (7) according to Figure 2 As shown, the camera focal plane position calibration test optical path is built by measuring the transmission function;

[0046] Step 23: Calculate the focal plane position change caused by the temperature change of the camera (8) components under the on-orbit temperature state by collecting the temperature state of each camera component, and eliminate and compensate the ground calibration test results.

[0047] A precise calibration method for the focal plane position of a space camera proposed in the present invention has been successfully applied in the calibration and testing process of the Jilin-1 high-resolution satellite. The ground focal plane calibration position of this model of camera is basically consistent with the on-orbit focal plane position. The first picture taken is downloaded within a few hours on the day of the successful launch of the satellite. The image is clear and can be directly applied to the product without obvious defocusing. The on-orbit operation is in good condition. The calibration method proposed in the present invention is applied to the ground focal plane position calibration process of the Jilin-1 high-resolution series satellites. The calibration method is real-time and effective.

[0048] The above is a detailed introduction to the precise calibration method of the ground focal plane position of a space camera proposed in the present invention, and the principles and implementation methods of the present invention are explained. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for accurately calibrating the ground focal plane position of a space camera, characterized in that: The method specifically comprises the following steps: Step 1: Use the collimator calibration method to calibrate the camera's focal plane position in the laboratory; The specific steps of the collimator calibration are: Step 11: Paste thermocouples or other temperature measuring devices (5) on the primary and secondary mirrors and focal plane components of the collimator (3), and use a temperature collection device (6) to collect real-time temperatures of the primary and secondary mirrors and focal plane components of the collimator (3); Step 12: Use a large-aperture plane reflector (4) and a 4D interferometer (1) to build a self-collimating interference detection optical path for the parallel light tube (3); Step 13: Collect the interference pattern power value through the 4D interferometer (1), and adjust the power value to 0 to accurately calibrate the initial focal plane position of the collimator (3); Step 14: During the test, the temperature of the optical tube component is collected in real time to ensure that it is consistent with the initial calibration temperature state. When the temperature changes, the change in the focal plane position of the optical tube can be calculated based on the collected component temperature change, and the change in the focal plane position of the camera introduced by it can be removed; Step 2: Use the space camera focal plane position calibration method to calibrate the camera focal plane position in the laboratory; The specific steps of calibrating the focal plane position of the space camera are: Step 21: Welding a temperature collection connector or other temperature measuring device (9) at the thermal control outlet of each component of the camera (8) to collect the temperature of each component of the camera in real time; Step 22: Using an integrating sphere (7) to illuminate the test stripe plate target (2), a camera focal plane position calibration test light path is constructed by measuring the transmission function; Step 23: Calculate the focal plane position change caused by the temperature change of the camera (8) components under the on-orbit temperature state by collecting the temperature state of each camera component, and perform elimination compensation on the ground calibration test result; Step 3: The focal plane position change caused by the component temperature change is controlled by real-time temperature sampling. The defocus caused by the temperature change of the collimator (3) and the defocus effect caused by the inconsistency between the component temperature of the camera under test (8) and the on-orbit operating temperature state are calculated and compensated to eliminate the defocus. The camera defocus is compensated by adjusting the target position of the collimator, thereby achieving accurate calibration of the ground focal plane position of the space camera.

Images