Implications and Applications of Emerging Polarimetric Synthetic Aperture Radar for the Retrieval of Freshwater Ice Properties

地球上超过四分之一的湖泊位于北部地区，经历着季节性的冰的形成和消融。面对日益加剧的变暖，北极景观的物理组成部分的变化速度对栖息地、可持续社区发展和基础设施的考虑具有重要意义。特别是，季节性冰的生长、物候（冻结和破裂的时间）和冰厚为监测气候提供了替代指标，是全球气候观测系统的基本气候变量。利用微波频率的遥感对检索冰的性质特别有用。最近的研究已经确定了湖冰中反向散射的来源是冰底的粗糙度，从而有可能获得冰的厚度和绘制冰-水界面的轮廓。在测绘冰底时必须保持相干性，相干性描述了目标雷达反射和两幅图像入射角的相似性。现在有可能使用两种新的传感器：雷达卫星星座任务（RCM）和NISAR来保持冰的相干性。RCM （c波段5.5 cm）允许每4天重复通过一次，提高时间分辨率并减少两次采集之间的冰增长量。NISAR是一项计划中的偏振干涉合成孔径雷达任务，计划于2022年发射，L-（24厘米）和s -波段（12厘米），12天重复通过。NISAR观测到的长波长可能超过两次捕获之间的冰生长，从而保留相干性。RCM的推出提出了一种新的光束模式：紧凑型偏振法（CP）。CP发送圆极化波形并接收垂直和水平极化。很少有研究涉及淡水冰的CP观测，只使用了Radarsat-2场景的CP模拟。模拟CP数据的初步结果表明，可以检索冰的参数（冰的范围和破裂），但测试没有使用实际的RCM采集。我的研究计划的总体目标是改进与淡水冰相互作用的新传感器和波束模式的应用，以检索和传达冰参数给投资的利益相关者。此外，本研究将提供检索基线作为蓝图，应用于不断增长的RCM CP和NISAR获取数据库。该研究项目具有独特的定位，可以开发初步的CP冰算法，作为加拿大的旗舰卫星过渡到主要以CP模式收集，并将在NISAR的收购开始时为泛加拿大规模和全球范围内的冰检索算法奠定基础。这项工作对于了解加拿大亚北极和北极地区的水文过程至关重要，因为检索到的冰参数直接有利于社区获得生态系统服务（例如冰上运输、越冬鱼类栖息地和可用水资源）。

Over one-quarter of Earth's lakes are located in northern regions and experience seasonal ice development and decay. The rate at which physical components of the Arctic landscape are changing in the face of amplified warming is of importance for habitat, sustainable community development, and infrastructure considerations. In particular, seasonal ice growth, phenology (timing of freeze-up and break-up), and ice thickness provide a proxy for monitoring climate, and are Essential Climate Variables in the Global Climate Observing System. Remote sensing utilizing microwave frequencies have been particularly useful for retrieving ice properties. Recent studies have identified the source of backscatter in lake ice is roughness at the ice bottom, allowing for the potential to derive ice thickness and map the contour of the ice-water interface. A necessity in mapping the ice bottom is to retain coherence, which describes the similarity of radar reflection of a target and incidence angle between two images. Retaining coherence for ice may now be a possibility using two new sensors: Radarsat Constellation Mission (RCM), and NISAR. RCM (C-band 5.5 cm) allows for repeat passes every 4 days, improving temporal resolution and reducing the amount of ice growth between acquisitions. NISAR is a planned polarimetric interferometric Synthetic Aperture Radar mission scheduled to launch in 2022 with L- (24 cm) and S-band (12 cm) and 12 day repeat pass. The long wavelengths observed by NISAR could exceed ice growth between acquisitions, allowing for retained coherence. RCM's launch presents a new beam mode: compact polarimetry (CP). CP sends circularly polarized waveforms and receives vertical and horizontal polarizations. There have been few studies that have addressed CP observations of freshwater ice, having only used CP simulations from Radarsat-2 scenes. Preliminary results from simulated CP data indicate that ice parameters can be retrieved (ice extent and break-up), but tests have not used actual RCM acquisitions. The overarching goal of my research program is to improve the application of new sensors and beam modes interacting with freshwater ice to retrieve and communicate ice parameters to invested stakeholders. Additionally, this research will provide a baseline of retrievals as a blueprint to be applied to the growing database of RCM CP and NISAR acquisitions. This research program is uniquely positioned to develop preliminary CP ice algorithms as Canada's flagship satellite transitions to collect predominantly in CP mode, and will lay the foundation of ice retrieval algorithms at a Pan-Canadian scale, and globally when NISAR's acquisitions begin. The work is of critical importance for the understanding of hydrological processes in Canada's sub-Arctic and Arctic regions, with retrieved ice parameters directly benefitting communities' access to ecosystem services (e.g. transportation over ice, overwintering fish habitat, and available water resources).