GNSS remote sensing to study sea-ice and ionospheric irregularities in the central Arctic

Abstract

An expedition through the Central Arctic has been conducted between October 2019 and October 2020. During the expedition, a Multidisciplinary Observatory (MOSAiC) has been established around the German research icebreaker Polarstern as a core facility. The observatory drifted for an eightmonth period with the pack ice through the central Arctic Ocean. The observatory comprised various instruments for different disciplines. Remote sensing using GNSS (Global Navigation Satellite System) signals was one of those disciplines. Three GNSS receiver setups were operated during this period on the ship for remote sensing applications. We report, here, on results from two of the setups: one for GNSS reflectometry dedicated to study reflected signals' sensitivity to sea-ice conditions and one to retrieve GNSS scinitillation indices for detection of ionospheric irregularities. A major goal of these studies is to assess monitoring opportunities of Artic sea ice and atmosphere using GNSS remote sensing from research vessels and other ships that are operated at high latitudes beyond the coverage of ground-based GNSS stations. In the reflectometry study, we demonstrated that power ratio observations including the left-handed circular polarization (LHCP) data are sensitive to the presence of compact sea ice and allows to estimate its permittivity. In the scintillation study, we found that in the given period disturbance of the GNSS signal phase ($\sigma_\phi$ index) did not exceed weak scintillation level (0.3 rad). The generally observed weak scintillation level can be explained by the solar minimum in the 2019/2020 period. Occasionally, signal amplitude disturbance (S4 index) increased to moderate level (0.5). Several factors for these occasional disturbances have been identified (shadowing by ship structure, sea surface multipath or quick changes of ship attitude). A designated filtering of observations can mitigate these factors. In conclusion, GNSS remote sensing data gathered aboard vessels can contribute to monitoring of sea ice and of ionosphere conditions in the central Arctic. Designated GNSS receiver setups (dual-polarization and high-rate data), as well as, adapted processing (attitude-dependent masking) are required.