Satellite radar altimeters like CryoSat-2 estimate sea ice thickness by measuring the return-time of transmitted radar pulses, reflected from the sea ice and ocean surface, to measure the radar freeboard. Converting freeboard to thickness requires an assumption regarding the fractional depth of the snowpack from which the radar waves backscatter $(\alpha )$. We derive sea ice thickness from CryoSat-2 radar freeboard data with incremental values for $\alpha$, for the 2010–2021 winter periods. By comparing these to sea ice thickness estimates derived from upward-looking sonar moorings, we find that $\alpha$ values between 35%–80% result in the best representation of interannual variability observed over first-year ice, reduced to 55% over multi-year ice. The underestimating bias in retrievals caused by optimizing this metric can be removed by reducing the waveform retracking threshold to 20%–50%. Our results pave the way for a new generation of ‘partial penetration’ sea ice thickness products from radar altimeters.

中文翻译：

---

优化从 CryoSat-2 检索的年际海冰厚度变化


像 CryoSat-2 这样的卫星雷达高度计通过测量从海冰和海洋表面反射的发射雷达脉冲的返回时间来估计海冰厚度，以测量雷达干舷。将干舷转换为厚度需要假设雷达波反向散射的积雪的分数深度 $(\alpha )$ 。我们从 CryoSat-2 雷达干舷数据中得出海冰厚度，并增加了 $\alpha$ 2010-2021 年冬季期间的 。通过将这些与从向上看的声纳系泊得出的海冰厚度估计值进行比较，我们发现 35%-80% 之间的 $\alpha$ 值可以最好地代表在第一年冰上观察到的年际变化，而在多年冰上则降低到 55%。通过将波形回溯阈值降低到 20%–50%，可以消除优化此指标导致的检索中低估偏差。我们的结果为雷达高度计的新一代“部分穿透”海冰厚度产品铺平了道路。