New Wideband Large Aperture Open-Ended Coaxial Microwave Probe for Soil Dielectric Characterization

We present a unique open-ended coaxial probe (OECP) that can accurately measure the permittivity of heterogeneous materials due to its large aperture. The probe works at frequencies ranging from 0.5 to 18 GHz, which is an important range for microwave remote sensing applications, and more precisely the Terrestrial Snow Mass Mission (TSMM). TSMM aims at launching a new satellite equipped with a dual Ku-band radar (13.5 and 17.2 GHz) for snow monitoring. At Ku-band frequencies, the backscattered radar signal contains information not only about the snow but also about the soil underneath. Knowing the soil permittivity will allow models to better account for the soil contribution to the total signal and to obtain more accurate snow data. To demonstrate the accuracy of the probe and the repeatability of the measures, calibration solutions of known permittivity were measured, and the results were compared to their theoretical values. Then, we conducted tests for approximating the penetration depth of the probe signal with dry and wet papers. Afterward, a protocol to use the probe to compute the permittivity of soil samples in freeze/thaw cycles was developed. The permittivities of commercial sand and organic soil from Iqaluktuuttiaq (Cambridge Bay, Nunavut, Canada) are presented for different relevant frequencies for microwave remote sensing applications and different temperatures (-20 degrees C to 20 degrees C) according to the new protocol. This article aims to present the probe and its potential use in microwave remote sensing applications, especially for the active Ku-band, where little research exists.