Characterization of Antarctic Firn by Multi-Frequency Passive Remote Sensing from Space

该项目将测试一个假设，即南极雪的物理和热特性可以从太空远程测量——部分压实的颗粒状雪处于雪和冰川冰之间的中间阶段。虽然这些性质，如内部温度、密度、粒度和层厚，与南极气候、冰盖动力学和物质平衡的研究高度相关，但它们的测量目前依赖于在具有挑战性的天气条件下进行的稀疏的原位调查。极地轨道卫星上的传感器在其长达数年的寿命中每隔几天就能观测整个南极。因此，本研究中开发的方法，与小型和低成本立方体卫星的先进技术相结合，旨在为南极科学做出贡献，并在减少人类在南极大陆上的足迹的同时，实现对南极系统的经济、方便和准确的长期分析。此外，该项目将完全基于公开可用的数据集；因此，在为受资助者所在机构的跨学科本科生和研究生研究和教育做出贡献的同时，该项目还将通过其网站鼓励公民科学家的参与。该项目的总体目标是通过多频微波辐射计从太空测量南极冰层的厚度、物理温度、密度和晶粒尺寸。冰层中电磁穿透深度随频率变化；因此，多频率辐射计能够描绘出与深度相关的地层特性。为了实现其目标，该项目将利用全球降水测量（GPM）卫星星座作为一个具有11个频率通道的单一多频微波辐射计系统来观测南极冰盖。将收集存档的南极冰原密度、粒度、温度和层厚的原位测量数据，并将其分为训练数据集和测试数据集。利用训练数据模拟的微波发射将与GPM星座测量结果进行比较，以评估和改进最先进的正演微波发射模型。在这些模型的基础上，该项目将开发南极冰层热物理性质的数值检索算法。检索结果将使用测试数据集进行验证，并进行不确定度和误差分析。最后，将通过利用GPM星座测量的长期检索研究来研究南极公司的热物理特征变化。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project will test the hypothesis that physical and thermal properties of Antarctic firn--partially compacted granular snow in an intermediate stage between snow and glacier ice--can be remotely measured from space. Although these properties, such as internal temperature, density, grain size, and layer thickness, are highly relevant to studies of Antarctic climate, ice-sheet dynamics, and mass balance, their measurement currently relies on sparse in-situ surveys under challenging weather conditions. Sensors on polar-orbiting satellites can observe the entire Antarctic every few days during their years-long lifetime. Consequently, the approaches developed in this study, when coupled with the advancing technologies of small and low-cost CubeSats, aim to contribute to Antarctic science and lead to cost-effective, convenient, and accurate long-term analyses of the Antarctic system while reducing the human footprint on the continent. Moreover, the project will be solely based on publicly-available datasets; thus, while contributing to interdisciplinary undergraduate and graduate research and education at the grantee's institution, the project will also encourage engagement of citizen scientists through its website. The overarching goal of this project is to characterize Antarctic firn layers in terms of their thickness, physical temperature, density, and grain size through multi-frequency microwave radiometer measurements from space. Electromagnetic penetration depth changes with frequency in ice; thus, multi-frequency radiometers are able to profile firn layer properties versus depth. To achieve its objective, the project will utilize the Global Precipitation Measurement (GPM) satellite constellation as a single multi-frequency microwave radiometer system with 11 frequency channels observing the Antarctic Ice Sheet. Archived in-situ measurements of Antarctic firn density, grain size, temperature, and layer thickness will be collected and separated into training and test datasets. Microwave emissions simulated using the training data will be compared to GPM constellation measurements to evaluate and improve state-of-the-art forward microwave emission models. Based on these models, the project will develop numerical retrieval algorithms for the thermal and physical properties of Antarctic firn. Results of retrievals will be validated using the test dataset, and uncertainty and error analyses will be conducted. Lastly, changes in the thermal and physical characteristics of Antarctic firn will be examined through long-term retrieval studies exploiting GPM constellation measurements.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.