Block Adjustment without GCPs for Chinese Spaceborne SAR GF-3 Imagery
<p>Flow chart of geometric calibration algorithm.</p> "> Figure 2
<p>Flowchart of RPC model solution process.</p> "> Figure 3
<p>Flowchart of planar block adjustment and ortho-rectification.</p> "> Figure 4
<p>Selection of control/check points in SAR image.</p> "> Figure 5
<p>DOM and DEM of Hubei province, China.</p> "> Figure 6
<p>Residual distributions of IPs of block adjustments for Wuhan without GCPs.</p> "> Figure 7
<p>Residual distributions of ICPs of block adjustments for Hubei without GCPs.</p> "> Figure 8
<p>Residual distributions of ICPs of block adjustments for Hubei with GCPs.</p> "> Figure 9
<p>The ortho-map of Hubei province made by GF-3.</p> "> Figure 10
<p>The mosaic maps of adjacent images after ortho-rectification.</p> ">
Abstract
:1. Introduction
2. Principles and Methods
2.1. Geometric Calibration of Spaceborne SAR
2.2. General Geometric Processing Model of Spaceborne SAR
- (1)
- Determination of an image grid and establishment of a 3D object grid of points using the RD model;
- (2)
- RPC fitting; and
- (3)
- Accuracy checking.
2.3. Planar Block Adjustment Based on RPC
- (1)
- Adjustment input file preparation. Including GCP File, TP File, and RPC File. GCP File and TP File are obtained by manual measurement.
- (2)
- Weak convergence determined. Calculating the intersection angle of two SAR images. If the angle is less than 10°, the planar block adjustment process will be executed. Otherwise, the stereo block adjustment will be executed.
- (3)
- Planar block adjustment. First, the initial values of TPs are obtained by forward intersection. Considering the situation of weak intersection. Second, the elevations of TPs are obtained by DEM interpolation. Third, adjustment calculation. Fourth, the posteriori weight method is used to assign weights again. Fifth, if adjustment convergence, it can go to step 4. Otherwise, continue the implementation step 3.
- (4)
- Ortho-rectification.
3. Test Results and Analysis
4. Conclusions
Author Contributions
Funding
Conflicts of Interest
References
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Item | Wuhan City | Hubei Province |
---|---|---|
Imaging mode | QPSI | FS2 |
Nominal resolution (m) | 8 | 10 |
Width of image (km) | 30 | 100 |
Number of orbit | 4 | 9 |
Number of images | 11 | 31 |
Number of GCPs/ICPs | 8 | 134 |
Number of tie points | 33 | 1038 |
terrain | plain | Mountains, hills, plain |
area (km2) | 8594 | 185,900 |
Test Area | Scheme | GCP | ICP | Maximum Error (m) | RMSE (m) | ||||
---|---|---|---|---|---|---|---|---|---|
x | y | plane | x | y | plane | ||||
Wuhan | before calibration | 0 | 13 | −41.50 | 16.55 | 41.91 | 29.03 | 7.31 | 29.93 |
after calibration | 0 | 13 | 7.75 | −9.45 | 9.73 | 4.99 | 5.34 | 7.31 |
Test Area | Scheme | TP | Maximum Error (pixel) | RMSE (pixel) | ||||
---|---|---|---|---|---|---|---|---|
x | y | plane | x | y | plane | |||
Wuhan | before calibration | 33 | 0.96 | −0.95 | 0.96 | 0.35 | 0.23 | 0.42 |
after calibration | 33 | 0.86 | −0.98 | 0.99 | 0.34 | 0.23 | 0.41 |
Test Area | Scheme | GCP | ICP | Maximum Error (m) | RMSE (m) | ||||
---|---|---|---|---|---|---|---|---|---|
x | y | plane | x | y | plane | ||||
Hubei | before calibration | 0 | 135 | 54.80 | 13.74 | 55.01 | 38.70 | 4.54 | 38.97 |
13 | 122 | 32.32 | −13.95 | 32.63 | 11.35 | 4.88 | 12.35 | ||
after calibration | 0 | 135 | 14.90 | −17.98 | 19.10 | 4.60 | 7.70 | 8.97 | |
13 | 122 | −13.10 | −16.51 | 18.81 | 4.82 | 5.42 | 7.26 |
Test Area | Scheme | GCP | TP | Maximum Error (pixel) | RMSE (pixel) | ||||
---|---|---|---|---|---|---|---|---|---|
x | y | plane | x | y | plane | ||||
Hubei | before calibration | 0 | 1038 | −2.72 | 2.65 | 2.92 | 0.67 | 0.61 | 0.91 |
13 | 1038 | −5.05 | −2.80 | 5.05 | 0.95 | 0.65 | 1.15 | ||
after calibration | 0 | 1038 | 3.12 | 2.66 | 3.13 | 0.66 | 0.61 | 0.90 | |
13 | 1038 | 3.11 | −2.79 | 3.11 | 0.70 | 0.65 | 0.95 |
Test Area | Scheme | GCP | Maximum Error (m) | RMSE (m) | ||||
---|---|---|---|---|---|---|---|---|
x | y | plane | x | y | plane | |||
Hubei | After calibration | 1 | 15.00 | −17.42 | 18.41 | 4.53 | 6.55 | 7.96 |
4 | 10.93 | −17.14 | 18.12 | 4.38 | 5.50 | 7.03 | ||
9 | −12.74 | −16.27 | 18.39 | 4.59 | 5.50 | 7.17 | ||
13 | −13.10 | −16.51 | 18.81 | 4.82 | 5.42 | 7.26 |
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Zhang, G.; Wu, Q.; Wang, T.; Zhao, R.; Deng, M.; Jiang, B.; Li, X.; Wang, H.; Zhu, Y.; Li, F. Block Adjustment without GCPs for Chinese Spaceborne SAR GF-3 Imagery. Sensors 2018, 18, 4023. https://doi.org/10.3390/s18114023
Zhang G, Wu Q, Wang T, Zhao R, Deng M, Jiang B, Li X, Wang H, Zhu Y, Li F. Block Adjustment without GCPs for Chinese Spaceborne SAR GF-3 Imagery. Sensors. 2018; 18(11):4023. https://doi.org/10.3390/s18114023
Chicago/Turabian StyleZhang, Guo, Qingwei Wu, Taoyang Wang, Ruishan Zhao, Mingjun Deng, Boyang Jiang, Xin Li, Huabin Wang, Yu Zhu, and Fangting Li. 2018. "Block Adjustment without GCPs for Chinese Spaceborne SAR GF-3 Imagery" Sensors 18, no. 11: 4023. https://doi.org/10.3390/s18114023