CryoSat-2 (CS2) is the first mission equipped with a pulse-limited radar altimeter capable of operating in Synthetic Aperture Radar (SAR) Interferometric (SARIn) mode. Over ice sheets and ice caps, CS2 SARIn data have been used to retrieve surface elevations over an across-track ground “swath.” This work demonstrates that retracking multiple coherent peaks of CS2 SARIn waveforms, in combination with the interferometric phase, enables to obtain more than one valid height estimate from single SARIn waveforms over Arctic sea ice. For some SARIn waveforms, the scattering from sea ice at the satellite nadir is successfully separated from returns originating from off-nadir leads. An average bias of −1.8 cm is found for absolute sea ice elevations when using a 50% threshold retracker. It is shown that including multiple SARIn peaks and the associated phase difference in the processing does not introduce any bias on the average sea ice freeboard heights compared with the estimates from regular SAR processing schemes, while significantly increasing the number of valid sea surface height retrievals (+55%) and the number of freeboard estimates in the coastal domain and in multi-year ice regions (~3 times). This results in an average ~34% reduction of the gridded random freeboard uncertainty, corresponding to a ~20% reduction of the gridded total sea ice thickness uncertainty. The results of this work show that SARIn acquisitions over Arctic sea ice provide improved spatial coverage and denser sampling of sea level and sea ice freeboard compared with the SAR mode, with accuracy being largely driven by the retracking algorithm.

中文翻译：

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北极海冰上CryoSat-2 SARIn波形的多峰跟踪

CryoSat-2（CS2）是第一个装备有脉冲限制雷达高度计的任务，能够在合成孔径雷达（SAR）干涉测量（SARIn）模式下运行。在冰盖和冰盖上，CS2 SARIn数据已用于检索跨轨道地面“条带”的表面高程。这项工作表明，结合干涉相位，重新跟踪CS2 SARIn波形的多个相干峰，可以从北极海冰上的单个SARIn波形中获得多个有效的高度估计。对于某些SARIn波形，成功地将卫星最低点处海冰的散射与离最低点导线返回的回波成功地分开了。当使用50％阈值跟踪器时，发现绝对海冰高度的平均偏差为-1.8 cm。结果表明，与常规SAR处理方案的估算值相比，在处理过程中包含多个SARIn峰和相关的相差不会对平均海冰干舷高度产生任何偏差，同时显着增加了有效海面高度检索的数量（ + 55％），以及沿海地区和多年冰区的干舷估计数量（约3倍）。这导致网格随机干舷不确定性平均降低了〜34％，相当于网格总海冰厚度不确定性降低了〜20％。这项工作的结果表明，与SAR模式相比，在北极海冰上进行SARIn采集可以改善空间覆盖范围，并提供更密集的海平面和海冰干舷采样，其精度在很大程度上受重新跟踪算法的驱动。