Snow property characterization for improved radar altimetry estimates of sea ice thickness

地球气候正在经历前所未有的变化，监测和预测这种变化的性质是一项正在进行的全球科学努力。将海冰纳入全球气候模式是至关重要的，因为它控制着大气和海洋之间的热传递。例如，随着海冰的减少，更多的海洋热量可以转移到北极大气中，导致进一步变暖和海冰减少，这是一个特别具有破坏性的正反馈循环。据卫星估计，在过去的40年里，北极海冰面积下降了13%，变薄了近40%，预计在2050年之前，北冰洋将首次在夏季无冰。今天，超过80%的北极海冰覆盖由季节性海冰组成。这些变化将如何影响北极海洋生态系统、北极和中纬度气候和生态系统、泛北极航运和邮轮旅游等社会经济问题，以及包括加拿大北部在内的土著社区的生计，这些方面仍存在相当大的不确定性。海冰上的积雪是雪/海冰系统的重要组成部分，由于其相对较小的热导率，它控制着冰的增加和消融速率。由于积雪的高反照率，短波辐射交换主导了海冰-反照率的反馈机制，并在春夏过渡期间使海冰与变暖的大气隔绝。因此，积雪最终控制了海冰厚度和随后的融化行为，并在很大程度上决定了控制海冰夏季破裂潜力的机械强度特性。卫星遥感估算泛北极海冰厚度的准确性取决于利用雷达测高来区分海冰浮冰、海冰导冰和开放水域的统计阈值方法的性能。然而，这些简单的方法并不能完全考虑海冰积雪中季节性和空间变化的复杂地球物理过程，这些过程会影响雷达传播，并给估计增加相当大的误差和不确定性。这些显著变量包括雪深、雪密度、雪粒度和比表面积、雪电性能（包括液态水和雪盐水含量）。近年来开发的新的和改进的地球物理仪器现在可以以显着提高的精度表征这些关键的雪变量。本提案中描述的仪器套件将显著提高用于评估海冰雪厚雷达测高的介电和微波散射模型的性能。该提案还描述了一套最先进的雪地球物理仪器和HQP数据收集重点计划的紧迫性，以改善雪地球物理特性测量，改善北极范围内通过雷达测高估算海冰厚度。*****************

Earth's climate is experiencing unprecedented change and monitoring and predicting the nature of this change is an ongoing global scientific endeavor. Inclusion of sea ice in global climate models is paramount due to its control on heat transfer between the atmosphere and ocean. For example, with less sea ice, more ocean heat can transfer to the Arctic atmosphere, leading to further warming and less sea ice, a particularly damaging positive feedback loop. Arctic sea ice extent has declined by 13% and thinned by nearly 40% over the past four decades as estimated from satellites, with the Arctic Ocean predicted to become ice free in summer for the first time before 2050. Today, more than 80% of the Arctic sea ice cover is composed of seasonal sea ice. Considerable uncertainty remains as to how these changes will influence the Arctic marine ecosystem, Arctic and mid-latitude climates and ecosystems, socio-economic issues such as pan-Arctic shipping and cruise tourism, and the livelihood of indigenous communities including those in northern Canada. The snow cover on sea ice is a critical component of snow/sea ice system because it controls the ice accretion and ablation rate due to its relatively small thermal conductivity. Because of the high albedo of snow, shortwave radiative exchanges dominate the sea ice-albedo' feedback mechanism and act to insulate the sea ice from the warming atmosphere during the spring to summer transition. As a result, the snow cover ultimately controls sea ice thickness and subsequent melt behavior and largely determines the mechanical strength properties which control sea ice summer break-up potential. The accuracy of pan-Arctic sea ice thickness estimates from satellite remote sensing depends on the performance of statistical thresholding methods using radar altimetry to distinguish sea ice floes from sea ice leads and open water. However, these simple methods do not fully account for seasonally and spatially varying complex geophysical processes in the snow cover on sea ice, which affect radar propagation and add considerable error and uncertainty to estimates. These salient variables include snow depth, snow density, snow grain size and specific surface area, snow electrical properties including liquid water and snow brine content. New and improved geophysical instrumentation developed in recent years now permits characterization of these key snow variables with significantly improved accuracy. The instrumentation suite described in this proposal will significantly improve performance of dielectric and microwave scattering models for assessment of radar altimetry estimates of snow thickness on sea ice. This proposal also describes the urgency for a suite of state-of-the-art snow geophysical instrumentation and an HQP data collection focused plan towards improved snow geophysical property measurements towards Arctic-wide improvements to sea ice thickness estimates from radar altimetry. *****************