Optical Design and Stray-Light Analysis of Urban Night-Light Remote Sensing Imaging System

Fig. 1. Optical path diagrams of three total-reflection optical systems. (a) Coaxial three-mirror Cassegrain system; (b) off-axis three-mirror secondary imaging system; (c) off-axis three-mirror primary imaging system

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Fig. 2. Optical path diagram of proposed optical system

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Fig. 3. Spot diagram

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Fig. 4. MTF curves

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Fig. 5. System diagram of night-light remote sensing camera

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Fig. 6. Curve of point-source transmittance in X direction

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Fig. 7. Curve of point-source transmittance in Y direction

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Table 1. Main optical parameters of night-light remote sensing camera

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Table 1. Main optical parameters of night-light remote sensing camera

Parameter	Value
Orbit altitude /km	600
Focal length /mm	500
F number	3.8
Field angle	5°×2°
Pixel /(μm×μm)	20×20
GSD at 600 km/m	24
Spectral region /nm	400-800
Optical transmittance	≥90%
Point source transmittance atsolar depression angle	≤1×10^-9
Modulation transfer function at25 lp·mm^-1	≥0.7

Table 2. Advantages and disadvantages of three total-reflection optical systems

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Table 2. Advantages and disadvantages of three total-reflection optical systems

System type	Advantage	Disadvantage
TMC	Be suitable for space remote sensorwith long focal length and large field(perpendicular to the orbital direction);there is an intermediate image plane,having a strong ability to eliminate straylight; easy to install and adjust	There is a light shield in the center,and the optical efficiency is relativelylow; angle of view along the orbitaldirection is small, about 1°-1.5°
RUGER TMA	There is an intermediate image plane, havinga strong ability to eliminate stray light;optical efficiency is relatively high;easy to install and adjust	System is not rotationally symmetric,and the off-axis of the mirror is large;angle of view is small, about 1.5°-3°
COOK TMA	Field of view is larger, about3°-20°; optical efficiency is relativelyhigh; focal length is wide	There is no intermediate imageplane, and stray light suppression is moredifficult; mirror is off-axis, and thesystem is not rotationally symmetric;difficult to install and adjust

Table 3. Parameters of mirrors
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Table 3. Parameters of mirrors
Mirror Off-axis distance /mm Radius /mm Conic coefficient 4^thorder term
PM -103.6 -1382.49 -2.786 -5.1460×10^-11
SM — -404.84 0.759 —
TM 105.5 -561.99 0.246 2.2440×10^-11

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Shouwang Jiang, Zhentao Xia, Yongxue Sun, Ke Wang. Optical Design and Stray-Light Analysis of Urban Night-Light Remote Sensing Imaging System[J]. Laser & Optoelectronics Progress, 2020, 57(1): 012201

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