Ice dielectric measurements for the CryoRad mission

CryoRad is a candidate mission under ESA’s Earth Explorer 12 program, aimed at advancing our understanding of the cryosphere and its role in the Earth system (https://www.cryorad.eu/). The satellite will carry a novel P- to L-band microwave radiometer (0.4–2 GHz), representing the first deployment of a P-band radiometer in space. A primary mission objective is to remotely sense the vertical temperature profile of ice sheets. A central advantage of including P-band (0.4 –1 GHz) in the sensor design lies in its exceptionally long wavelength compared to traditional microwave remote sensing frequencies.  Because microwave penetration depth increases with increasing wavelength, CryoRad’s broad low-frequency coverage enables temperature sensing at different depths within the ice. When combined with glaciological models, these measurements will allow reconstruction of ice sheet temperature profiles down to several kilometers, providing unprecedented insights into subsurface processes.

Microwave radiometers sense objects in their dielectric constants, like human eyes see colors. Accurate retrieval of ice temperature requires precise knowledge of the dielectric constant of ice at this wide frequency range. While the knowledge of ice dielectric constant at L-band or higher frequency is relatively good, the information for P-band ice dielectric constant remain sparse.  To meet this need, we are developing a novel cylindrical cavity sensor, which has a resonance at P-band, within this ESA-funded project. The ice sample will be placed inside the cavity,  and the real and imaginary parts of the dielectric constant of sample ice will be determined by the changes in the resonant frequency and the quality factor of the cavity, respectively.  The approach offers excellent sensitivity at P-band, enabling accurate laboratory measurements of ice dielectric properties that will support the scientific concept and retrieval algorithms of the CryoRad mission.