Fig. 1. Relationship between pixel response and different input parameters. (a) Solar azimuth; (b) altitude angle of observation
Fig. 2. Schematic of network structure
Fig. 3. Structural diagrams of different network shortcut connections. (a) Overall shortcut; (b) local shortcut
Fig. 4. Convergence curves of network with different types of shortcut connection
Fig. 5. Convergence curves of network with different functional structures
Fig. 6. Processing results of different algorithms. (a) Original star image; (b) K-SVD; (c) BM3D; (d) DnCNN; (e) proposed method
Fig. 7. Renderings of real star image after denoising and subtracting background by different algorithms. (a) Original image; (b) algorithm in Ref. [7]; (c) algorithm in Ref. [8]; (d) proposed algorithm
Latitude season | Mid-latitude summer | Latitude season | Mid-latitude summer |
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Terrain | Forest | Altitude angle of observation /(°) | 70 | Weather | Sunny | Solar azimuth /(°) | 90 | Altitude H /km | 8 | Solar elevation θ /(°) | 70 |
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Table 1. Example of input parameters for ModTran software
Parameter | Value | Parameter | Value |
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F /(°) | 2 | Nx×/(pixel×pixel) | 512×512 | /μm | 11 | f /mm | 161.1 | D /mm | 41 | τ | 0.80 | ζ | 0.75 | Q | 0.40 | dw | 120000e | | 0.0001 | t /ms | 10 | n | 3 | /nm | 800 | Imin | 400 | /nm | 1100 | Imax | 3600 |
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Table 2. Optical-system parameters of detector
Latitude season | Mid-latitude summer | Latitude season | Mid-latitude summer |
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Terrain | Forest | Altitude angle of observation /(°) | 50-90 | Weather | Sunny | Solar azimuth /(°) | 55-150 | Altitude H /km | 8 | Solar elevation θ /(°) | 70 |
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Table 3. Input parameters of ModTran software
Types of convolutional network | Dilated Conv | Downsampling Conv | Plain Conv |
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/ms | 16.21 | 16.11 | 16.84 | /s | 0.87 | 0.22 | 0.86 |
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Table 4. Running time of network with different functional structures
Algorithm | PSNR /dB |
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Original star image | 22.36 | K-SVD | 25.43 | BM3D | 26.15 | DnCNN | 37.42 | Proposed algorithm | 37.43 |
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Table 5. PSNR of different algorithms
Algorithm | K-SVD | BM3D | DnCNN | Proposed |
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/ms | - | - | 45.43 | 16.84 | /s | 1.64 | 1.84 | 12.12 | 0.21 |
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Table 6. Running time of different algorithms
Algorithm | /dB |
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Original image | 5.82 | Algorithm in Ref. [8] | 7.95 | Algorithm in Ref. [7] | 7.56 | Proposed algorithm | 195 |
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Table 7. Statistical RSN of star points after denoising by different algorithms