The Feasibility of Detecting Supercooled Liquid With a Forward-Looking Radiometer

Icing due to supercooled liquid poses a threat to manned and unmanned aircraft. Particularly with the proliferation of unmanned systems, lightweight passive sensors could allow the remote detection of supercooled liquid. A three-dimensional radiative transfer model is utilized to determine the feasibility of a forward-viewing passive sensor for remotely detecting hazardous icing conditions. An analysis of simulated passive microwave spectra for a forward-viewing passive sensor finds dependencies on the liquid water content, cloud distance, and temperature, and sensitivity is noted across the millimeter-wave spectrum. Spectral flattening in the shoulders of molecular resonances corresponds to the presence of clouds, while saturated brightness temperatures near the transition lines are linked to the ambient temperature. A principal component analysis shows significant information content at
G
-band near the water vapor molecular transition, suggesting compact radiometer systems to detect and range supercooled liquid are feasible. Additional information content may be available at
K
$_a$
-band, suggesting such observations would be useful when size and mass are not constrained.