Azimuth or along-track (approximately north-south) motion is critical in constructing three-dimensional ground motion with synthetic aperture radar (SAR) satellites orbiting the Earth in sun-synchronous polar orbit. The main problem of measuring azimuth motion with short-wavelength SAR data is decorrelation. A fleet of newly launched and upcoming long-wavelength L-band SAR satellites bring new opportunities for measuring azimuth motion. However, azimuth motion measured with L-band SAR data often contains large azimuth shifts caused by the Earth's ionosphere. We outline the framework of separating the azimuth motion and ionospheric azimuth shift from an analysis of the ionospheric effects on SAR images and SAR measurement precisions. We demonstrate three methods, among which one is newly proposed, can separate the azimuth motion and ionospheric azimuth shift with higher precisions. We evaluate the performances of the three methods by simulations using parameters of several selected L-band SAR satellites. The results show that, at kilometer resolutions, the azimuth motion measured by multiple-aperture SAR interferometry (MAI) can achieve centimeter precision, while the ionospheric azimuth shifts can be estimated with decimeter precision. Based on these results, a strategy for obtaining corrected azimuth motion is subsequently suggested, which achieves at least a first-order ionospheric correction of the original higher resolution MAI result. The three methods were also compared by real data processing examples. Furthermore, using real and simulated data of selected L-band SAR satellites, we present the first L-band MAI time series analysis result that measures subtle ground motion, as illustrated by the example of the postseismic deformation after the 2016 Kumamoto earthquakes in Japan. The performance is expected to be further improved with future L-band SAR missions that have much higher duty cycles. Some geophysical applications, in particular, those associated with the Earth's tectonic processes, can thus benefit from the azimuth motion measured by L-band SAR data.

中文翻译：

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L波段SAR卫星方位角运动测量潜力分析


方位角或沿轨道（大约南北）运动对于利用在太阳同步极轨道上绕地球运行的合成孔径雷达（SAR）卫星构建三维地面运动至关重要。利用短波长SAR数据测量方位运动的主要问题是去相关。新发射和即将发射的长波长 L 波段 SAR 卫星群为测量方位角运动带来了新的机遇。然而，用 L 波段 SAR 数据测量的方位角运动通常包含由地球电离层引起的大方位角偏移。我们通过分析电离层对 SAR 图像和 SAR 测量精度的影响，概述了分离方位角运动和电离层方位角偏移的框架。我们演示了三种方法，其中一种是新提出的，可以以更高的精度分离方位角运动和电离层方位角位移。我们通过使用几颗选定的 L 波段 SAR 卫星的参数进行模拟来评估这三种方法的性能。结果表明，在千米分辨率下，多孔径SAR干涉测量（MAI）测量的方位角运动可以达到厘米级精度，而电离层方位角偏移可以达到分米级精度估计。基于这些结果，随后提出了一种获得校正方位角运动的策略，该策略至少实现了原始更高分辨率MAI结果的一阶电离层校正。还通过真实的数据处理实例对三种方法进行了比较。 此外，利用选定的 L 波段 SAR 卫星的真实和模拟数据，我们提出了第一个测量微妙地面运动的 L 波段 MAI 时间序列分析结果，如 2016 年日本熊本地震后震后变形的例子所示。随着未来具有更高占空比的 L 波段 SAR 任务，预计性能将进一步提高。因此，一些地球物理应用，特别是与地球构造过程相关的应用，可以从 L 波段 SAR 数据测量的方位角运动中受益。