Distortion calibrating method for large-field reflex free form surface space camera

Abstract

The invention discloses a distortion calibrating method for a large-field reflex free form surface space camera, and belongs to the technical fields of optical detection and optical measurement. The method comprises the following steps: building a measurement coordinate system by using three theodolites; calibrating an azimuth angle and a pitch angle of each metering marker in a full field of an optical system by datum transformation; and then calibrating two-dimensional distortion distribution of a reflex free form surface optical system of which the field angle is 76 degrees in a disperse adjustment state by a data fitting method. According to the distortion calibrating method, reserved precision distortion measurement under the complicated scattered condition of the optical system is achieved, the development cost is reduced, the development cycle is shortened, and the test result shows that both the precision and the accuracy of the measurement and data calculation methods meet the development requirements.

Description

technical field [0001] The invention belongs to the technical field of optical detection and optical measurement, and in particular relates to a distortion calibration method for a large field of view reflective free-form surface space camera. Background technique [0002] The space remote sensor used for the census of ground crops needs to have a large field of view, so that the sub-width of the ground swath corresponding to the satellite's one-pass overhead can meet the demand for observation data such as crop growth. For this reason, the main optical load of the remote sensor—the very wide-coverage multispectral space camera (hereinafter referred to as the space camera) uses multiple reflective free-form surface optical elements to form an optical system, which can reach a field of view of 76°, but the resulting Distortion of up to 10% (theoretical value) in the imaging direction. The above distortions will cause image distortion and distortion, resulting in differences ...

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Problems solved by technology

[0004] (1) The multispectral camera adopts the push-broom imaging method, while the three-dimensional test field calibration method, the two-step calibration method (RAC) based on radial constraints, and the multi-angle imaging method of the same calibration object are only suitable for staring imaging of area array detectors Distortion calibration of the system, so it is difficult to apply to the distortion calibration of the push-broom imaging system during the adjustment stage

[0005] (2) The calibration method based on the optical diffraction element requires a large-scale diffractive optical element whose aperture covers the optical system to be tested to provide incident light at different angles, and the effective aperture of the system to be tested exceeds 750mm, so it is currently difficult to process a suitable diffraction element

[0006] (3) The conventional precision angle measurement calibration method uses a turntable, a collimator and a standard calibration object to achieve precise measurement of distortion, but for a space camera with a 76° field of view, it is necessary to develop a collimator with a diameter of more than 1500mm to be able to use it during the rotation of the turntable. Covering the entire field of view, the development cost and difficulty are unbearable

[0007] (4) The precision angle measurement method needs to place the optical system on a high-precision turntable to provide a standard angle, but the integration and adjustment process of high-performance and complex optical systems is completed on the optical platform with the help of a large number of auxiliary adjustment equipment. The size and weight of the auxiliary assembly and adjustment equipment together with the optical table are too large to be placed on the turntable for distortion calibration

[0008] (5) For an imaging system composed of reflective free-form surface optical elements, its distortion distribution law does not fully conform to the existing distortion fitting a priori rules such as the least squares law, and it is difficult to use the current distortion fitting method to solve the full Distortion value of each point in the field of view

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