A Review of Recent Developments in Low-Frequency Ultra-Wideband Microwave Radiometry for Studies of the Cryosphere

Kenneth Jezek^1*, J T. Johnson¹, L Tsang², M Brogioni³, G Macelloni³, M Aksoy⁴, L Kaleschke⁵, Shujie Wang⁶, M Leduc-Leballeur³, C Yardim¹, M Andrews¹, Haokui Xu², O Demir¹, S Tan^{7, 8} and J Miller⁹

• ¹The Ohio State University, United States
• ²University of Michigan, United States
• ³Nello Carrara Institute of Applied Physics, Department of Engineering, ICT and Technology for Energy and Transport, National Research Council (CNR), Italy
• ⁴The State University of New York (SUNY), United States
• ⁵Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI), Germany
• ⁶The Pennsylvania State University (PSU), United States
• ⁷University of Illinois at Urbana-Champaign, United States
• ⁸Zhejiang University, China
• ⁹Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, United States

Over the past decade, a series of airborne experiments in the Arctic and Antarctica explored microwave emission from sea ice and ice sheets at frequencies from 0.5 to 2 GHz. The experiments were motivated by the fact that lower frequencies penetrate deeper into frozen surface, thus offering the possibility to measure physical temperatures at great depths in ice sheets and, subsequently, other unique geophysical observables including sea ice salinity. These experiments were made feasible by recent engineering advances in electronics, antenna design, and noise removal algorithms when operating outside of protected bands in the electromagnetic spectrum. These technical advances permit a new type of radiometer that not only operates at low frequency, but also obtains continuous spectral information over the band from 0.5 to 2 GHz. Spectral measurements facilitate an understanding of the physical processes controlling emission and also support the interpretation of results from single frequency instruments.
This paper reviews the development of low-frequency, wide band radiometry and its application to cryosphere science over the past 10 years. The paper summarizes the engineering design of an airborne instrument and the associated algorithms to mitigate radio frequency interference. Theoretical models of emission built around the morphologic and electrical properties of cryospheric components are also described that identify the dominant physical processes contributing to emission spectra. New inversion techniques for geophysical parameter retrieval are summarized for both Arctic and Antarctic scenarios. Examples that illustrate how the measurements are used to inform on glaciological problems are presented. The paper concludes with a description of new instrument concepts that are foreseen to extend the technology into operation from space.