Ultrawide-Band Polarimetric Multi-Channel Radar for Measurements of Polar Ice Sheets

Abstract

Accelerated loss of polar ice sheets from retreating glaciers and fast-flowing ice streams is the major contributor to the increasing sea level rise in the past decades. Current models are generally predicting the continued worsening situation in the short-term future. However, these predictions still have an appreciable uncertainty due to the incomplete understanding of the ice sheet processes and boundary conditions. To assist the study of the ice flow dynamics to improve the prediction of future sea level rise, a high-resolution full-polarimetric radar system is developed in this dissertation to measure and characterize various glacial ice properties. Polarimetric measurement of polar ice sheets is a useful tool to understand ice flow dynamics associated with crystal orientation fabric (COF). To provide high-quality data of anisotropic COF over a large area, two generations of ultra-wideband (UWB) multi-channel radars were developed and deployed to the East Greenland Ice Core Project (EGRIP) site to assist the study of the Northeast Greenland Ice Stream (NEGIS). The first-generation radar, supporting dual co-polarized measurements (VV and HH) with a bandwidth of 160 MHz was deployed to Greenland in 2019 as a concept validation. The second upgraded generation, which will be deployed to Greenland in Summer 2022, supports single-pass quad-polarized measurements (VV, VH, HH, and HV) will enable the characterization of COF as a function of depth. With an improved bandwidth of 300 MHz, the new radar is capable of mapping ice sheet stratigraphy with less than 0.3 m vertical resolution.This dissertation focuses on the system level design, hardware development, system integration and performance characterization of two-generation UWB polarimetric radars. To enable the quad-polarized measurement with more than 3:1 bandwidth, I designed a UWB, co-planar tightly coupled array (TCA) with a novel balun-less feed structure. This antenna array is designed for ground-based and airborne radars which require low-profile and deployable structure. For the upgraded radar system, I also developed a high-power Transmit/Receive—Polarization (T/R-Pol) switch to enable single-pass full polarimetric measurements. With these enabling technologies, the UWB polarimetric multi-channel radar presented in this dissertation can characterize multiple ice sheet properties, including spatial anisotropic COF, high-resolution ice sheet stratigraphy, and basal condition. This information provides us the ice flow history from different aspects and helps us predict the future sea level rise.