Sea-Ice Reflectivity Modelling and Estimation: Results on GNSS Reflectometry from Expeditions to the Arctic

Abstract

GNSS signals are transmitted in L-band and provide a promising source for sea-ice remote sensing as they partly penetrate into ice upon reflection. The sea-ice surface and its composing layers below contribute to the reflected signal. Analysing these contributions allow to investigate sea-ice properties (ice thickness and ice type). We present here calculations of sea-ice reflectivity for GNSS signals based on a multilayer reflection model including: underlying water, a sea-ice layer and an additional snow cover. The calculations assume coherent reflection conditions, elevation angles of the GNSS satellite between 3° and 30°, as well as, the different media with their relative permittivity (dry snow ~1, multiyear ice ~3, high-salinity ice ~5 and sea water ~70). The model-based results show that oscillation pattern occur in the reflectivity profiles when the permittivity and conductivity (the permittivity's imaginary part) are low in the considered layers (ice and snow). The model results are compared to reflectivity profiles estimated from reflectometry data recorded during Arctic expeditions of research vessels. The comparison shows that the calculated oscillation pattern can also be found in the estimated profiles. This result fits the rather old ice types (second- or multiyear ice) reported for the expeditions by ancillary data. These results are promising for further investigations of sea-ice reflectometry preparing the upcoming ESA satellite mission PRETTY with coverage in the Arctic. However, agreement of applied model and observations is still limited to coherent reflection conditions. A future extension of the model to diffuse scatter contribution might be beneficial as well.