Image motion compensation of off-axis two-line camera based on earth ellipsoid

Wu Xingxing; Liu Jinguo; Kong Dezhu; Zhang Liping; Long Kehui

As view axis and optical axis of reflective off-axis two-line stereo mapping camera are separate and the earth is in fact an ellipsoid, distances between objects on earth corresponding to view axis and optical axis vary with geocentric angle from substellar to ascend point. In addition imaging sensor is perpendicular to optical axis while imaging the objects on earth corresponding to view axis. All these factors lead to change of image motion speeds and drift angles along with off-axis angles. Equivalent simplified model of reflective off-axis space camera was established based on analysis of its imaging principle. Formulas of image motion speeds and drift angles of reflective off-axis two-line stereo mapping camera based on earth ellipsoid were deduced. Influence of adjusting row transfer periods and drift angles uniformly on imaging quality of a reflective off-axis two-line stereo mapping camera was analyzed. Results of analysis indicates that if no more than 5% drop of modulation transfer function is used as a constraint, row transfer periods of nadir-view camera and backward-view camera should be adjusted individually as TDI stages is greater than 4. When drift angles are adjusted uniformly, mean value of drift angles of nadir-view camera and backward-view camera should be used and TDI stages should not exceed 89.

1. Changchun Institute of Optics,Fine Mechanics and Physics,Chinese Academy of Sciences,Changchun 130033,China

Received Date: 2013-07-13

Rev Recd Date: 2013-08-14

Publish Date: 2014-03-25

Key words:

earth ellipsoid /
off-axis /
two-line /
image motion /
MTF

Abstract: As view axis and optical axis of reflective off-axis two-line stereo mapping camera are separate and the earth is in fact an ellipsoid, distances between objects on earth corresponding to view axis and optical axis vary with geocentric angle from substellar to ascend point. In addition imaging sensor is perpendicular to optical axis while imaging the objects on earth corresponding to view axis. All these factors lead to change of image motion speeds and drift angles along with off-axis angles. Equivalent simplified model of reflective off-axis space camera was established based on analysis of its imaging principle. Formulas of image motion speeds and drift angles of reflective off-axis two-line stereo mapping camera based on earth ellipsoid were deduced. Influence of adjusting row transfer periods and drift angles uniformly on imaging quality of a reflective off-axis two-line stereo mapping camera was analyzed. Results of analysis indicates that if no more than 5% drop of modulation transfer function is used as a constraint, row transfer periods of nadir-view camera and backward-view camera should be adjusted individually as TDI stages is greater than 4. When drift angles are adjusted uniformly, mean value of drift angles of nadir-view camera and backward-view camera should be used and TDI stages should not exceed 89.

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Reference (21)

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Image motion compensation of off-axis two-line camera based on earth ellipsoid

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