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Laser altimeter is the key configuration to improve the accuracy of the mapping satellite, the position accuracy of the laser spot emitted by the laser transmitter and the pointing accuracy of the laser beam received by the laser receiver will directly affect the plane and elevation positioning accuracy of the mapping satellite. Because the change of the spot position of the reference beam and the measurement beam can be calculated, the direction measurement of the laser altimeter can be realized. According to the need of quantitative measurement of the laser altimeter emitting and receiving spot direction, an optical system of direction measurement is designed in this paper. The technical indicators: The optical system focal length is 396mm, F number is 4.5, field of view is 2°× 2°,the operating wave band are 532nm±5nm，660±5nm，880±5nm. The encircled energy of the 532nm±5nm in 3×3 pixel is above 92% all over the field of view, the encircled energy of the 660nm±5nm in 3×3 pixel is above 90% all over the field of view, the encircled energy of the 880nm±5nm in 3×3 pixel is above 89% all over the field of view. The absolute distortion of the optical system is less than 1μm，the non-parallel degree of the chief ray in the whole field of view of the optical system is less than 0.015° . At present, considering the calibration error, the centroid extraction error, the optical component thermal deformation error and the laser jitter error, it can be calculated by the error synthesis theory that the pointing accuracy of the laser altimeter directional measurement optical system is about 0.36″.
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