CAREER: Enabling the Next Generation Wideband Microwave Radiometers for the Remote Sensing of the Cryosphere

了解冰雪圈，即被冰雪覆盖的地球表面，并预测其冰量和质量的未来变化，对于追踪我们星球上的气候和水循环至关重要。由于极端的环境条件，稀疏的原位测量的高成本，以及对与这些地区相关的人类足迹增加的担忧，遥感仪器是监测冰冻圈的首选。在这些仪器中，微波辐射计，即测量目标微波辐射的被动接收器，具有许多优势，因为它们可以提供独立于云条件和太阳光照的数据，并且它们的测量对重要的冰性质（如厚度、温度、密度和粒度）高度敏感。假设，如果有足够的带宽，这些仪器就能够描绘出从表面到深层冰的这些特性。然而，目前观测冰冻圈的辐射计操作还远远不够理想。首先，它们被限制在几个狭窄的频带内，以避免来自雷达和无线通信系统等有源的干扰。其次，冰的电学性质决定了它发出的电磁辐射量，但它并没有完全随频率和温度而变化。这项CAREER研究通过对冰在宽频率和温度范围内的电学特性进行建模，并开发有效的干扰缓解算法，将使下一代微波辐射计能够利用宽微波频段全面探测地球冰体。此外，通过与研究活动相结合的教育计划，该项目将使研究人员成长为杰出的科学家-教育家，并为其所在机构的学生提供实用的，动手操作的电磁学培训。电磁在冰中的穿透深度随频率变化；因此，宽带微波辐射计可以用来描述冰体的热学和物理性质与深度的关系。这一职业发展项目的总体目标是使下一代这种仪器能够遥感冰冻圈。为了实现这一目标，冰的复杂介电常数将在宽频率（0-50 GHz）和温度（200-273 K）范围内进行测量，以获得其电气特性。将通过比较南极和北极上空的模拟微波辐射与极轨空间载微波辐射计的测量值来核实所测得的介电常数值。此外，将开发用于微波辐射计的多维、基于机器学习的射频干扰检测和缓解算法，使其能够在主动服务占用和共享的宽频带上运行。最后，将在受资助机构开发一个数字宽带辐射计原型，以实施这些算法，并通过在完全表征的地面站点进行雪地遥感测量来验证项目结果。研究活动将纳入工程课程，作为研究人员应用电磁学教育理念的一部分，以培养未来微波遥感领域的工程师和科学家。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。

Understanding the Cryosphere, Earth's surface covered by snow and ice, and predicting future changes in its ice volume and mass are critical to track the climate and the water cycle on our planet. Because of the extreme environmental conditions, high costs of sparse in-situ measurements, and concerns about increasing human footprint associated with these regions, remote sensing instruments are preferred to monitor the Cryosphere. Among these instruments, microwave radiometers, i.e., passive receivers measuring microwave radiations from their targets, have many advantages since they can provide data independent of cloud conditions and solar illumination, and their measurements are highly sensitive to important ice properties such as thickness, temperature, density, and grain size. Provided with enough bandwidth, these instruments are, hypothetically, capable of profiling these properties from the surface to the deep ice. However, radiometer operations to observe the Cryosphere are currently far from ideal. First, they are limited to a few narrow frequency bands to avoid interference from active sources such as radars and wireless communication systems. Second, the electrical properties of ice, which determine the amount of electromagnetic radiation it emits, are not fully characterized versus frequency and temperature. This CAREER research, by modeling the electrical properties of ice across wide ranges of frequencies and temperatures and developing efficient interference mitigation algorithms, will enable the next generation of microwave radiometers capable of utilizing wide microwave frequency bands to fully probe Earth's ice bodies. Furthermore, with an education plan integrated with the research activities, this project will grow the investigator as a prominent scientist-educator and provide an applied, hands-on electromagnetics training for students at his institution. Electromagnetic penetration depths vary with frequency in ice; thus, wideband microwave radiometers can be used to profile thermal and physical properties of ice bodies versus depth. The overarching goal of this career development project is to enable next generation of such instruments for the remote sensing of the Cryosphere. In pursuit of this goal, the complex permittivity of ice will be measured across wide frequency (0-50 GHz) and temperature (200-273 K) ranges for its electrical characterization. Measured permittivity values will be verified by comparing simulated microwave radiations over the Antarctic and the Arctic to the measurements of polar-orbiting space-borne microwave radiometers. Furthermore, multi-dimensional, machine learning based radio frequency interference detection and mitigation algorithms for microwave radiometers will be developed to allow their operations across wide frequency bands occupied and shared by active services. Lastly, a digital wideband radiometer prototype will be developed at the grantee's institution to implement these algorithms and validate the project outcomes through snow remote sensing measurements at fully characterized ground sites. The research activities will be incorporated into the engineering courses as a part of the investigator's applied electromagnetics education philosophy to educate future engineers and scientist in the field of microwave remote sensing.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.