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Atmospheric Effects on the Performance of Geosynchronous Orbit SAR Systems
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摘要: 地球同步轨道合成孔径雷达(GEO SAR)合成孔径时间长、观测范围大，易受到大气层效应时空变化的影响，使成像的聚焦质量和差分干涉处理精度严重下降。该文针对常规对流层和背景电离层等大气层缓变的干扰部分，建立了高精度时频混合GEO SAR信号模型，分析了不同大气层参数的时间变化率对成像质量和差分干涉处理精度的影响。针对大气层干扰中对流层湍流和电离层闪烁等随机扰动造成的影响，基于幂律功率谱模型，建立了大气扰动参数和成像质量的定量化分析模型，获得了大气层随机干扰的强度与成像评估指标间的关系。最后，通过仿真验证了模型的有效性，并分析了长孔径时间内缓变和随机扰动的大气层误差对成像和差分干涉处理质量的影响，仿真结果表明：L波段GEO SAR成像和差分干涉处理受时空变电离层干扰的影响十分严重，必须予以补偿；对流层干扰对其影响较小，仅当积累时间达到数百秒时才需要考虑它对成像性能的恶化。
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关键词:
- 地球同步轨道合成孔径雷达 /
- 合成孔径雷达成像 /
- 对流层干扰影响 /
- 电离层干扰影响
Abstract: GEOsynchronous orbit Synthetic Aperture Radar (GEO SAR) has a long synthetic aperture and large observation region; therefore, it is easily affected by atmospheric spatial-temporal changes, which results in a serious degradation in the focusing quality and performance of differential interference processing. In this paper, a high-precision spatial-temporal hybrid GEO SAR signal model is established for the slowly disturbed parts of the atmosphere such as the background troposphere and the ionosphere. The effects of the time rate of different atmospheric parameters on the image quality and accuracy of differential interference processing are analyzed. Considering the influence of random disturbances such as tropospheric turbulence and ionospheric scintillation in atmosphere, a quantitative analysis model is established based on a power law power spectrum model using the atmospheric disturbance and imaging quality parameters. The relationships of the random disturbances intensity in the atmosphere and the imaging evaluation index are obtained. Finally, the model is verified by simulations, and the effects of slow-varying atmospheric errors in a long aperture time on the quality of imaging and differential interference processing are analyzed. Simulation results show that spatial-temporal variable ionospheric disturbances seriously affect L-band GEO SAR imaging and differential interference processing, which must be compensated, and they are slightly affected by tropospheric disturbances. Moreover, it is necessary to consider the tropospheric effects on imaging performance only when the integration time reaches several hundred seconds. -
图 2 基于大气折射率廓线数据获得的对流层信号延迟
Figure 2. Tropospheric signal delays based on atmospheric refractive index profile data
图 3 不同波段、不同积累时间下对流层对GEO SAR成像影响的评估结果
Figure 3. Results of tropospheric GEO SAR imaging at different wave bands and different integrate times
图 6 电离层闪烁影响下成像指标参数分析
Figure 6. Analysis of imaging quality parameters in the presence of ionospheric scintillation
图 7 时空变电离层引入的干涉相位屏误差和评估
Figure 7. The interference phase screen errors and evaluation introduced by TSV ionosphere
表 1 GEO SAR对流层延迟的各阶时间变化情况
Table 1. Temporal variability of each order of GEO SAR tropospheric delay
项目 数值 $\Delta \,{r_0}$ (m) 2.21 ${q_1}$ (m/s) 2.52×10–4 ${q_2}$ (m/s2) 2.71×10–7 ${q_3}$ (m/s3) 1.64×10–13 
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表 2 电离层TEC随时间变化情况
Table 2. Rate of ionospheric TEC changing with time
项目 数值 TEC0(TECU) 68.3 k1 (TECU/s) 0.0068 k2 (TECU/s2) 7.32×10–6 k3 (TECU/s3) 4.42×10–12
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表 3 背景电离层对GEO SAR成像影响评估结果
Table 3. Results of GEO SAR imaging effected by background ionosphere
合成孔径时间(s) 距离向PSLR (dB) 方位向PSLR (dB) 方位向移位(m) 100 –13.23 –13.21 4.3 300 –13.25 –12.11 4.3 500 –13.22 –10.39 4.3
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