Author Affiliations
1College of Geoscience and Surveying Engineering, China University of Mining and Technology-Beijing, Beijing 100083, China2Land Satellite Remote Sensing Application Center, MNR, Beijing 100048, China3School of Earth Sciences and Engineering, Hohai University, Nanjing 211100, Chinashow less
Fig. 1. Flowchart of multi-feature parameters constraints algorithm
Fig. 2. Schematic of invalid data phenomenon
Fig. 3. Display of the original waveform intensity count
Fig. 4. Schematic diagram of the full-length waveform
Fig. 5. Verified data of GF-7 spaceborne laser
Fig. 6. Comparison chart of echo characteristic parameters about six ground objects
Fig. 7. Scatter diagram of correlation between echo characteristic parameters
Fig. 8. Comparison between satellite image and original waveform about special points
Fig. 9. Comparison between satellite image and original waveform
| Parameter | Value | | Laser beam | 2 | | Laser working wavelength/µm | 1.064 | | Laser divergence angle/µrad | ≤60 | | Laser ranging range/km | 450-550 | | Receiving telescope aperture/mm | 600 | | Laser repetition rate | 3 Hz （6 Hz at calibration mode） | | Sampling rate/GSps | 2 | | Spot size/m | 15 | | Ranging accuracy/m | ≤0.1 | | Transmitting pulse energy/mJ | ≤180 | | Transmitting pulse width/ns | 4-8 | | Laser emission efficiency | 99.4% | | Laser receiving efficiency | 79.0% |
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Table 1. Laser altimeter parameters of GF-7
| Orbit | Beam 1 | | Beam 2 | | Total points | Valid points | Unimodal points | Total points | Valid points | Unimodal points | | 2085 | 648 | 551 | 179 | | 648 | 454 | 271 | | 2086 | 938 | 849 | 424 | 939 | 819 | 503 | | 2088 | 1125 | 679 | 473 | 1125 | 649 | 448 | | 3419 | 1101 | 504 | 219 | 1101 | 518 | 240 |
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Table 2. Basic information of experimental data
| Orbit | Beam 1 | Beam 2 | Acquisition time | | Points | Points | | 672 | 53 | 65 | 2019.12.17 | | 5973 | 74 | 96 | 2020.11.30 | | 11430 | 65 | 55 | 2021.11.19 | | 11583 | 99 | 98 | 2021.11.29 |
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Table 3. Basic information of the verified data
| Feature type | SNR min | SNR max | Kurtosis min | Kurtosis max | Skewness min | Skewness max | | Grass land | 22.75 | 29.19 | 2.32 | 4.87 | 0.92 | 1.76 | | Gobi | 19.67 | 26.11 | 1.84 | 3.79 | 0.66 | 1.49 | | Land | 20.82 | 26.33 | 1.90 | 5.10 | 0.69 | 1.87 | | Water body | 19.61 | 29.71 | 1.88 | 5.89 | 0.66 | 2.03 | | Sand | 18.83 | 25.28 | 1.89 | 4.53 | 0.63 | 1.72 | | Arable land | 17.19 | 28.66 | 1.67 | 5.24 | 0.42 | 1.86 | | 17.19 | 29.71 | 1.67 | 5.89 | 0.42 | 2.03 |
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Table 4. The min and max value of each characteristic parameter in typical feature type
| Mean value | RMSE | | SNR min | 20.34 | 1.36 | | Kurtosis min | 1.97 | 0.18 | | Skewness min | 0.71 | 0.11 | | Skewness max | 1.74 | 0.14 |
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Table 5. Statistical calculation of echo parameters
| Orbit | Beam | Elevation difference/m | | Mean value/m | | RMSE/m | | Min/m | | Max/m | | ① | ② | ③ | ① | ② | ③ | ① | ② | ③ | ① | ② | ③ | | 注：①基于有效性筛选后数据；②基于峰值个数筛选后数据；③基于回波特征参数筛选后数据 | | 672 | 1 | −0.47 | −0.44 | −0.24 | | 2.92 | 2.71 | 1.49 | | 0.12 | 0.12 | 0.12 | | 5.67 | 2.59 | 0.55 | | 2 | −0.80 | −0.49 | −0.38 | 2.80 | 0.63 | 0.44 | 0.00 | 0.00 | 0.00 | 21.82 | 3.13 | 1.14 | | 5973 | 1 | −0.95 | −0.90 | −0.48 | 0.84 | 0.71 | 0.29 | 0.01 | 0.01 | 0.01 | 3.41 | 2.84 | 1.06 | | 2 | −1.98 | −1.03 | −0.42 | 2.45 | 0.58 | 0.45 | 0.07 | 0.07 | 0.07 | 8.65 | 2.29 | 1.17 | | 11430 | 1 | −0.22 | −0.16 | −0.09 | 0.92 | 0.69 | 0.42 | 0.00 | 0.00 | 0.00 | 4.18 | 1.90 | 0.83 | | 2 | 0.28 | 0.10 | 0.06 | 2.81 | 0.88 | 0.72 | 0.00 | 0.00 | 0.00 | 8.32 | 2.84 | 0.97 | | 11583 | 1 | 0.15 | 0.08 | 0.04 | 0.60 | 0.61 | 0.54 | 0.01 | 0.01 | 0.01 | 2.89 | 1.95 | 0.97 | | 2 | 0.38 | 0.19 | 0.15 | 1.74 | 0.69 | 0.46 | 0.00 | 0.00 | 0.00 | 9.25 | 3.95 | 1.40 |
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Table 6. Verification results of elevation accuracy before and after screening
| Orbit | Laser points | | Percentage | | ① | ② | ③ | ④ | ⑤ | ⑥ | ⑦ | | 注：①筛选前验证区域内总点数；②基于有效性筛选后有效点数；③基于峰值个数筛选后单峰值点数；④基于回波特征参数筛选后阈值范围内点数；⑤符合文中设定精度要求内点数；⑥筛选后点数的保留率；⑦符合精度点数在筛选后中的占比 | | 672 | Beam 1 | 53 | 50 | 37 | 29 | 25 | | 54.72% | 86.21% | | Beam 2 | 65 | 60 | 50 | 28 | 28 | 43.08% | 100.00% | | 5973 | Beam 1 | 74 | 73 | 63 | 48 | 40 | 64.86% | 83.33% | | Beam 2 | 96 | 94 | 83 | 77 | 66 | 80.21% | 85.71% | | 11430 | Beam 1 | 65 | 64 | 59 | 44 | 42 | 67.69% | 95.45% | | Beam 2 | 55 | 53 | 45 | 37 | 36 | 67.27% | 97.30% | | 11583 | Beam 1 | 99 | 86 | 79 | 50 | 46 | 50.51% | 92.00% | | Beam 2 | 98 | 91 | 72 | 52 | 43 | 53.06% | 82.69% |
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Table 7. Verification results of laser points before and after screening
