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，经历了季节性的冰川发育和消融。在气候变暖加剧的情况下，北极地貌的物理成分发生变化的速度对栖息地、可持续社区发展和基础设施考虑都很重要。特别是，季节性冰增长、物候(冻结和解冻的时间)和冰厚度是监测气候的指标，是全球气候观测系统中的基本气候变量。利用微波频率的遥感对于恢复冰的性质特别有用。最近的研究已经确定，湖冰的后向散射的来源是冰底的粗糙度，这使得有可能得出冰的厚度和绘制冰-水界面的等高线。绘制冰底图的一个必要条件是保持相干性，它描述了目标的雷达反射和两幅图像之间的入射角的相似性。现在，使用两个新的传感器：Radarsat星座任务(RCM)和Nisar，保持冰的一致性可能是可能的。RCM(C波段5.5厘米)允许每4天重复通过一次，提高了时间分辨率，并减少了两次采集之间的结冰数量。NISAR是一项计划于2022年发射的极化干涉合成孔径雷达任务，L波段(24厘米)和S波段(12厘米)和12天重复通行证。Nisar观测到的长波长可能超过两次采集之间的冰层增长，从而保留了相干性。RCM的发射呈现了一种新的光束模式：紧凑型偏振(CP)。CP发送圆极化波形，接收垂直极化和水平极化。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，可以恢复冰参数(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新传感器和波束模式的应用，这些传感器和波束模式与淡水冰相互作用，以检索冰参数并将其传达给投资的利益相关者。此外，这项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收购数据库。随着加拿大的旗舰卫星过渡到主要以CP模式收集，该研究计划具有独特的优势，可以开发初步的CP冰算法，并将在Nisar开始收购时，为泛加拿大规模和全球范围的冰反演算法奠定基础。这项工作对于理解加拿大亚北极和北极地区的水文过程至关重要，取回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的水资源)。

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).