Shipborne GNSS-IR for Sea Ice Freeboard Monitoring: A Case Study From the Chinese Polar Expedition

Abstract

Sea ice is a critical component of the global climate system and a key indicator of climate change. Its accurate monitoring is vital for understanding polar environmental dynamics and ensuring maritime safety. Building upon traditional sea ice detection techniques, global navigation satellite system interferometric reflectometry (GNSS-IR) introduces new possibilities that may address existing methodological constraints. This article proposed two methodological approaches for freeboard retrieval using shipborne GNSS equipment, and verified the feasibility with an experiment during the Chinese Antarctic Research Expedition in 2022–2023. To adapt to the challenging environmental conditions, several algorithmic improvements were made. The method based on ship draft shows higher accuracy during both stationary and sailing in sea ice. Its root mean square error (RMSE) is within 0.14 m when field observations are taken as true values. The GNSS elevation positioning method has poor positioning accuracy with an RMSE of 0.17 m when stationary, but it provides automated data collection without relying on manual measurement methods such as draft depth measurement. These findings provide valuable reference for advancing the application of shipborne GNSS-IR in polar sea ice monitoring. However, it should be noted that the current results are limited by the sampling rate and the conclusions are drawn under the constraint of data aliasing. Further validation with higher rate observations remains an important next step to strengthen the applicability of the proposed methods. With increasing observational data and advancing GNSS/GNSS-IR technologies, along with improved sea level height products and elevation models, the proposed methods are expected to achieve broader applicability.