Abstract This paper applies the Fully-Focussed SAR (FF-SAR) algorithm to CryoSat-2 full-bit-rate data to measure water levels of lakes and canals in the Netherlands, and validates these measurements by comparing them to heights measured by gauges. Over Lake IJssel, a medium-sized lake, the FF-SAR height is biased about 6 cm below the gauge height, and a similar bias is found at six sites where CryoSat-2 crosses rivers and canals. The precision of the FF-SAR measurements depends on the extent of multi-looking (incoherent averaging along-track) applied. Over Lake IJssel the precision varies from 4 to 11 cm, decreasing as multi-looking increases. The precision of FF-SAR with 100 m of multi-looking is equivalent to that of the standard delay/Doppler processing, which has an along-track resolution of about 300 m. The width and orientation of rivers and canals limits the maximum available multi-looking. After removing the 6 cm bias, FF-SAR heights of rivers and canals have an accuracy between 2 cm and several decimeters, primarily depending on the presence of other water bodies lying within the cross-track measurement footprint, as these contaminate the waveform. We demonstrate that FF-SAR processing is able to resolve and measure small ditches only a few meters in width. The visibility of these signals depends on the angle at which CryoSat-2 crosses the ditch and on whether or not the ditch remains straight within CryoSat-2’s field of view. In the best-case scenario, straight ditches at nearly 90° to the CryoSat-2 ground track, the ditch signal has high enough signal-to-noise to allow sub-decimeter accuracy of FF-SAR height measurement.

中文翻译：

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CryoSat-2 全聚焦 SAR 内陆水位估算的性能

摘要 本文将全聚焦 SAR (FF-SAR) 算法应用于 CryoSat-2 全比特率数据来测量荷兰湖泊和运河的水位，并通过将它们与仪表测量的高度进行比较来验证这些测量结果。在艾瑟尔湖（一个中等大小的湖泊）上空，FF-SAR 高度偏向标准高度以下约 6 厘米，在 CryoSat-2 穿越河流和运河的六个地点发现了类似的偏向。FF-SAR 测量的精度取决于所应用的多视（非相干沿航迹平均）的程度。在艾瑟尔湖上，精度从 4 厘米到 11 厘米不等，随着多视度的增加而降低。100 m多视FF-SAR的精度相当于标准延迟/多普勒处理的精度，沿航迹分辨率约为300 m。河流和运河的宽度和方向限制了最大可用的多视性。去除 6 厘米偏差后，河流和运河的 FF-SAR 高度的精度在 2 厘米到几分米之间，这主要取决于跨轨道测量足迹内是否存在其他水体，因为这些会污染波形。我们证明 FF-SAR 处理能够解析和测量只有几米宽的小沟渠。这些信号的可见性取决于 CryoSat-2 穿过沟渠的角度以及沟渠是否在 CryoSat-2 的视野内保持笔直。在最佳情况下，与 CryoSat-2 地面轨道成近 90° 的直沟渠信号具有足够高的信噪比，以允许 FF-SAR 高度测量的亚分米精度。