# Multi-Mode GF-3 Satellite Image Geometric Accuracy Verification Using the RPC Model

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## Abstract

**:**

## 1. Introduction

## 2. Error Sources of GF-3 Geometric Processing

#### 2.1. Ephemeris Error of the Satellite Platform

#### 2.2. Doppler Center Frequency Error

#### 2.3. Azimuthal Time Error

#### 2.4. Slant Range Measurement Error

#### 2.5. Topographic Error

## 3. General Geometric Processing Model of GF-3

_{ij}(i = 1, 2, 3, 4; j = 0, 1, …, 19) are rational polynomial coefficients (RPCs). There are 80 total parameters for the RPCs. To ensure the reliability of the calculation, the first parameter coefficient of the denominator term is often set to 1, so the 80 parameters for the RPCs turn to 78 parameters.

- Determination of an image grid and establishment of a 3D object grid of points using the RD model;
- RPC fitting;
- Accuracy checking.

## 4. Experimental Data

- Choose a crossroads intersection or a T-junction. These junctions have clear road textures in SAR images and are easy to identify in the corresponding optical image.
- Select roads of an appropriate size. Roads that are too narrow are difficult to identify clearly, whilst roads that are too wide make it difficult to determine an accurate centerline position.
- Choose straight roads. Due to speckle noise, a road boundary in SAR images is not as clear as it is in optical images, especially at intersections. If the roads are straight, the centerline at intersections can be accurately determined.
- Select roads in a flat area. Undulating roads, together with circumjacent buildings, may lead to foreshortening, layover, or shadow, which affects the accuracy of the selected GCPs.

## 5. Experimental Results

## 6. Conclusions

## Acknowledgments

## Author Contributions

## Conflicts of Interest

## References

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**Figure 3.**Residual distributions of check points of the SL mode orientation for Taiyuan. (

**a**) 0 GCP; (

**b**) 4 GCP; (

**c**) all GCP.

**Figure 4.**Residual distributions of check points of the UFS mode orientation for Tianjin: (

**a**) 0 GCP; (

**b**) 4 GCP; (

**c**) all GCP.

**Figure 5.**Residual distributions of check points of the FSI mode orientation for Mount Song: (

**a**) 0 GCP; (

**b**) 4 GCP; (

**c**) all GCP.

**Figure 6.**Residual distributions of check points of the QPSI mode orientation for Tianjin: (

**a**) 0 GCP; (

**b**) 4 GCP; (

**c**) all GCP.

**Figure 7.**Residual distributions of check points of the SS mode orientation for Mount Song: (

**a**) 0 GCP; (

**b**) 4 GCP; (

**c**) all GCP.

No. | Work Modes | Incidence Angle (°) | Look Number | Resolution (m) | Imaging Bandwidth (km) | Polarization Mode | ||||
---|---|---|---|---|---|---|---|---|---|---|

Nominal | Azimuth | Range | Nominal | Size | ||||||

1 | spotlight (SL) | 20–50 | 1 × 1 | 1 | 1.0~1.5 | 0.9~2.5 | 10 × 10 | 10 × 10 | Optional single polarization | |

2 | ultra-fine strip (UFS) | 20–50 | 1 × 1 | 3 | 3 | 2.5~5 | 30 | 30 | Optional single polarization | |

3 | fine strip I (FSI) | 19–50 | 1 × 1 | 5 | 5 | 4~6 | 50 | 50 | Optional dual polarization | |

4 | fine strip II (FSII) | 19–50 | 1 × 2 | 10 | 10 | 8~12 | 100 | 95~110 | Optional dual polarization | |

5 | standard strip (SS) | 17–50 | 3 × 2 | 25 | 25 | 15~30 | 130 | 95~150 | Optional dual polarization | |

6 | narrow scan (NSC) | 17–50 | 2 × 3 | 50 | 50~60 | 30~60 | 300 | 300 | Optional dual polarization | |

7 | wide scan (WSC) | 17–50 | 2 × 4 | 100 | 100 | 50~110 | 500 | 500 | Optional dual polarization | |

8 | global (GLO) | 17–53 | 4 × 2 | 500 | 500 | 350~700 | 650 | 650 | Optional dual polarization | |

9 | full polarized Strip I (QPSI) | 20–41 | 1 × 1 | 8 | 8 | 6~9 | 30 | 20~35 | Full polarization | |

10 | full polarized Strip II (QPS II) | 20–38 | 3 × 2 | 25 | 25 | 15~30 | 40 | 35~50 | Full polarization | |

11 | wave imaging (WAV) | 20–41 | 1 × 2 | 10 | 10 | 8~12 | 5 × 5 | 5 × 5 | Full polarization | |

12 | extended (EXT) | low | 10–20 | 3 × 2 | 25 | 25 | 15~30 | 130 | 120~150 | Optional dual polarization |

high | 50–60 | 3 × 2 | 25 | 25 | 20~30 | 80 | 70~90 | Optional dual polarization |

Imaging Mode | Acquisition Date | Orbit | Image Size (Pixel) | Central Look Angle | Imaging Region |
---|---|---|---|---|---|

spotlight (SL) | 2 March 2017 | ASC | 10861/33766 | 27.17 | Taiyuan |

ultra-fine strip (UFS) | 24 February 2017 | DEC | 10352/20358 | 21.27 | Tianjin |

fine strip I (FSI) | 30 December 2016 | ASC | 16509/23002 | 38.66 | Mount Song |

full polarization strip (QPSI) | 30 March 2017 | DEC | 7750/6482 | 31.70 | Tianjin |

standard strip (SS) | 26 January 2017 | ASC | 24131/34568 | 18.77 | Mount Song |

Image Mode | Test Site | GCP Number | Check Point Number | Root Mean Square Error (RMSE) of GCP (Pixels) | Root Mean Square Error (RMSE) of Checkpoint (Pixels) | ||||
---|---|---|---|---|---|---|---|---|---|

x | y | Plane | x | y | Plane | ||||

SL | Taiyuan | 0 | 9 | - | - | - | 42.4637 | 50.2833 | 65.8147 |

4 | 5 | 0.7140 | 1.1387 | 1.3441 | 0.8867 | 1.1465 | 1.4494 | ||

9 | 0 | 0.8578 | 0.9767 | 1.2999 | - | - | - | ||

UFS | Tianjin | 0 | 11 | - | - | - | 12.5462 | 6.8061 | 14.2734 |

4 | 7 | 0.5460 | 0.3933 | 0.6729 | 1.1250 | 0.9719 | 1.4867 | ||

11 | 0 | 0.6871 | 0.7818 | 1.0408 | - | - | - | ||

FSI | Mount Song | 0 | 8 | - | - | - | 10.9848 | 4.7005 | 11.9483 |

4 | 4 | 1.3287 | 0.3376 | 1.3709 | 1.0355 | 0.7581 | 1.2834 | ||

8 | 0 | 1.1153 | 0.4758 | 1.2126 | - | - | - | ||

QPSI | Tianjin | 0 | 9 | - | - | - | 8.1886 | 1.9381 | 8.4148 |

4 | 5 | 0.1465 | 0.3220 | 0.3538 | 0.4513 | 0.5124 | 0.6828 | ||

9 | 0 | 0.3146 | 0.4059 | 0.5135 | - | - | - | ||

SS | Mount Song | 0 | 12 | - | - | - | 17.2819 | 2.5586 | 17.4703 |

4 | 8 | 0.9236 | 0.1070 | 0.9298 | 0.7041 | 0.6708 | 0.9725 | ||

12 | 0 | 0.7463 | 0.5044 | 0.9008 | - | - | - |

**Table 4.**Table of ortho-rectification accuracy comparison among the five GF-3 satellite imaging modes.

Image Mode | Test Filed | RMSE of Checkpoint (m) | ||
---|---|---|---|---|

DX | DY | Plane | ||

SL | Taiyuan | 1.1049 | 1.0061 | 1.4943 |

UFS | Tianjin | 5.7351 | 4.9067 | 4.6129 |

FS1 | Mount Song | 5.1171 | 3.5901 | 6.2509 |

QPS1 | Tianjin | 5.1347 | 4.3998 | 6.7619 |

SS | Mount Song | 14.1420 | 18.0254 | 22.9109 |

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**MDPI and ACS Style**

Wang, T.; Zhang, G.; Yu, L.; Zhao, R.; Deng, M.; Xu, K.
Multi-Mode GF-3 Satellite Image Geometric Accuracy Verification Using the RPC Model. *Sensors* **2017**, *17*, 2005.
https://doi.org/10.3390/s17092005

**AMA Style**

Wang T, Zhang G, Yu L, Zhao R, Deng M, Xu K.
Multi-Mode GF-3 Satellite Image Geometric Accuracy Verification Using the RPC Model. *Sensors*. 2017; 17(9):2005.
https://doi.org/10.3390/s17092005

**Chicago/Turabian Style**

Wang, Taoyang, Guo Zhang, Lei Yu, Ruishan Zhao, Mingjun Deng, and Kai Xu.
2017. "Multi-Mode GF-3 Satellite Image Geometric Accuracy Verification Using the RPC Model" *Sensors* 17, no. 9: 2005.
https://doi.org/10.3390/s17092005