# Satellite-Based Sea Ice Navigation for Prydz Bay, East Antarctica
## 1 Introduction  
Accurate knowledge of the sea ice distribution is crucial for ship navigation in polar-regions. Marine vehicles should follow safe and fast tracks in ice-rich waters. Severe ice conditions can significantly reduce the progress or even beset a vessel. The variability of sea ice conditions, especiallynear the Antarctica coast, is often complex and transient as it is driven by synoptic atmospheric forcing or changing ocean currents, then modified by ice compression, divergence, shear or a mixture of all forms of deformation [1; 2]. In recent years, several vessels have been delayed or entrapped in the Antarctic sea ice. These vessels were often surrounded by highly concentrated pack ice under compression accompanied with bad weather and snowstorms (e.g., the RV _L'Astrolabe_ (France) in November 2009, RV _Xuelong_ (China) in January 2010 and December 2013, and RV _Aurora Australis_ (Australia) in November 2012). In order to plan for a smooth and fast navigation in ice-covered waters, information about sea ice concentration (SIC), sea ice extent (SIE), sea ice thickness (SIT) and deformation such as ridges is needed. The SIC and SIT may be combined with the vessel's ice-strengthened class to develop a regulatory standard in ice-cover water, which is the essence of the Arctic Ice Regime Shipping System to provide mariners with information to navigate vessels safely through the sea ice [3]. However, no similar system exists for marine navigation in the Antarctic sea ice. Therefore, it has become essential to develop a system to support a safe nautical route for marine vehicles travelling in the Antarctic. SIT can be estimated from microwave remote sensing but the estimation is limited to an upper limit of 16-50 cm pending on the frequency band [4]. Sea ice type identified in radar remote sensing images using surface features can be used as a proxy indicator of thickness of thicker ice. The spatio-temporal distribution of SIT in the Antarctic region was estimated using laser altimetry data from NASA's (National Aeronautics and Space Administration) Ice, Cloud, and land Elevation Satellite (ICESat) combined with passive microwave measurements during 2003-2008 [5]. Furthermore, a dataset of ice thickness for six regions around the Antarctic was developed by comprising 23,373 ship-based observations obtained over more than two decades [6]. None of these datasets, however, is suitable for marine operational use. For one thing, long-term average data do not represent the current ice thickness at locations that ship navigators require. Moreover, the problem with the satelite altimeter (radar or laser) is the narrow swath combined with a long repeat cycles (hundreds of days), which require numerous orbits to compile the thickness over a given area. For seasonal ice, high values of SIE and extensive SIC may cause slowing down of a marine vehicle but are not likely to impede its motion unless the ice becomes highly deformed. Charts of SIC are generated daily at a few centers, based passive microwave observations and only occasionally based on synthetic aperture radar (SAR) data. The spatial resolution of the charts varies from a few kilometers to a few tens of kilometers. This may not be appropriate for navigation in highly variable regions such as eastern rim of Prydz Bay. As for the SIE, recent studies [7; 8] have shown that since 1978, SIE around the Antarctic continent has demonstrated an increasing trend of 1.5 \(\pm\) 0.4% per decade. The increase affects the breadth of the marginal ice zone around the Antarctica, a region of interest to ice navigation. Unlike the Arctic region, only a few routine sea ice analyses are available for the Antarctic regions [9; 10]. This is partly due to the limited marine traffic in this region. The Chinese National Antarctic Research Expedition (CHINARE) Program has been operating since 1984.