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摘要： 合成孔径雷达（SAR）测高技术已被广泛运用于内陆水位监测中，但内陆水域回波复杂，需要波形重跟踪精化才能获取有效水位。内陆水域SAR高度计回波通常包含多个子波形，重跟踪的主要思路是寻找最优子波形，在特定条件下可以获得较合理水位，但在复杂水域或小水体中容易出现最优子波形筛选错误导致水位异常。传统最优子波形筛选主要是基于沿轨或外部数据约束下进行，而本文提出一种不使用外部数据、兼顾了内陆水体水位时间变化连续且空间变化平稳特性的重跟踪算法SaTCoM，首先对波形进行插值平滑，有效提高子波形识别准确度；然后对所有周期沿轨子波形水位集合进行时间向滤波得到参考水位序列；最后将沿轨子波形水位划分为若干区间并将子波形水位“放入”最近区间，在参考水位波动约束下，根据表征沿轨水位空间稳态特性的指标函数，选择最优水位区间子波形水位计算最终水位。选择我国区域68个大中小型水体的水文站实测数据作为验证，对其附近的哨兵-3A/3B/6A卫星SAR回波数据，分别使用SaTCoM算法、OCOG、ICE1、阈值法和MWaPP+算法重跟踪后进行了比较。结果表明，SaTCoM算法所得内陆水体水位与实测数据不符值RMSE为0.34 m，相对RMSE为7.8%，相关性为0.95，在大部分内陆水体中均表现优异，较其他算法有很大优势，在中小水体中尤为明显，同时分析表明时空约束下的SaTCoM算法仍可以有效捕捉水体水位的快速变化。由此表明，本文算法SaTCoM可较好地解决小水体有效水位获取的困难，能够较大地拓展内陆测高数据的应用。

关键词: 波形重跟踪, 内陆水位, SAR, 水文站, 卫星测高

Abstract: Synthetic aperture radar (SAR) altimetry has been widely used in inland water monitoring, but the echoes from inland waters are complex and need to be retracked to retrieve effective water levels. The SAR waveforms from inland waters usually contain multiple sub-waveforms, The main idea of retracking is to find the optimal sub-waveform. A reasonable water level may be obtained under specific conditions, but the wrong sub-waveform is likely to be picked in complex waters or small water bodies, which leads to abnormal water levels. To solve this problem, we proposed a spatial and temporal constrained multi-subwaveform (SaTCoM) retarcker considering time continuity and spatial stability of inland water level changes,which is different from traditional methods that finding the optimal sub-waveform by along-track or external data. Firstly, to find the sub-waveform reflected from water bodies effectively, SaTCoM interpolates and smooths the waveform. Secondly, the reference water level is obtained by filtering the sub-waveform level point clouds from all cycles in the time direction. Then, the along-track sub-waveform water levels are divided into several intervals and all along-track water levels are put into the nearest interval. Under the constraints of the maximum fluctuation from the reference water level, the indicator function characterizing the along-track spatial stability of the water level is used, which can guide the selection of the optimal water level intervals by maximum.
In this paper, we selected 68 hydrological stations with situ level measurements of large, medium, and small water bodies in China as validation, the nearby Sentinel-3A/3B/6A satellite SAR waveforms data were used for five retrackers:SaTCoM, OCOG, ICE1, threshold, and MWaPP+. The results show that the mean RMSE of the inland water level obtained by using SaTCoM is 0.34 m, the relative RMSE is 7.8%, and the correlation with the situ level is 0.95, SaTCoM also performs excellently in most inland water surface and has an absolute advantage over the other retrackers, especially in small and medium-sized water bodies. At the same time, the analysis showed that the SaTCoM can still effectively capture the rapid water level changing signals under spatiotemporal constraints, so it indicates that the proposed retracker SaTCoM can effectively solve the difficulty of retrieving effective water levels in small water bodies, SaTCoM greatly expands the application of inland altimetry data.

Key words: waveform retracking, inland water level, SAR, hydrological station, satellite altimetry

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