Determination of Glacial-Ice Temperature Profiles Using Radar and an Antenna-Gain Estimation Technique

Abstract

Knowledge of glacial ice temperature profiles is important to the study of glaciology. Currently, the only method of obtaining ice temperature profiles is by drilling ice cores, which is a long and arduous process. Fortunately, ice-penetrating radar can be used to obtain temperature profiles without the need of ice cores. A radar technique incorporating common mid-point geometries is presented for measuring ice temperature. However, in order for this technique to work, accurate estimates of the far-zone antenna gain within glacial ice are necessary. Currently, commercial electromagnetics software packages utilizing the finite element method (FEM) are used by academia and industry to accurately characterize antennas in free space, and near finite dielectric and conductive materials. Unfortunately, these commercial packages are incapable of accurately determining the far-zone antenna gain near a dielectric half-space such as glacial ice. Therefore, to solve this problem, a routine for determining the far-zone gain of an antenna located near glacial ice was developed, which utilizes an FEM package in conjunction with a near-to-far-field transformation (NFFT). Additionally, glacial ice imposes another complication to estimating far-zone antenna gain: the dielectric constant is a function of depth. Therefore the far-zone antenna gain within glacial ice changes as a function of depth due to increased ray bending resulting from refraction. To solve this problem, the geometric optics technique (GO) was used to propagate the far-zone antenna gain determined within the relatively shallow upper region of glacial ice, dubbed the quasi-far-zone, to any depth within glacial ice. Results are presented showing that this technique is capable of accurately determining the far-zone gain at any depth within glacial ice for an arbitrary antenna located near glacial ice. Additionally, results are presented showing that with the aid of this numerical antenna gain estimation software, ice-penetrating radar can be used to determine glacial ice temperature profiles at all depths.