# Satellite-Based Sea Ice Navigation for Prydz Bay, East Antarctica
## 5 Discussion
Radar remote sensing, with its fine resolution (e.g., the spatial resolution ranges from 20 to 100 m) and sensitivity to surface roughness and structure, provides the required information though only qualitatively. This is part of the procedures in the SatSINS. It enables a flexible framework to assist in decision-making for the route planning yet the best information is still generated by ship masters based on local ice observations. For a given ice concentration, the weight of its impact on the ship structure is doubled if the ice is deformed by ridges, rubble or hummocking. On the other hand, it may be reduced by half for decayed ice [3]. It should be noted that ice parameters critically needed for ice navigation can be highly variable (spatial- and temporal-wise), depending upon the climatological and local environmental history in the region (mainly wind and temperature). That was the motivation behind the inclusion of meteorological data in the system. Moreover, most of the readily available parameters for polar marine navigation are based on observations from the Arctic region. Ice climatology in the Antarctic is different in many ways; namely the type of pack ice, fast ice, perennial ice, polynyas, and the amount of highly deformed ice. Additionally, different site-dependent environmental conditions that dominate during initial ice growth such as air temperature, wind and oceanic conditions strongly affect key parameters that contribute to ice mechanical properties. Examples include ice crystalline structure (e.g., frazil or columnar), porosity, and bulk salinity. Obviously, many of these macroscopic parameters are too difficult to measure or retrieve to provide useful operational information. Therefore, only higher-level ice information is used in SatSINS. _Question 2: What are the spatio-temporal requirements from remote sensing data and the maximum allowable time gap between data acquisition and the actual operation?_  
Spatial resolution of remote sensing data is needed at two scales to reveal gross and detailed conditions of the ice cover. Coarse resolution images and daily SIC maps (a few kilometers in resolution) available 3-7 days before the vessel encounters the ice can be used to delineate ice edge and confirm whether SIC will exceed the threshold of 70% or not. Below this threshold, only medium-resolution imagery data from an optical sensor (250-500 m resolution) are likely to be sufficient to develop waypoints for a proposed vessel route. MODIS data were used in the case study of CHINARE2012 when most of the Prydz Bay was covered by thin ice within a large polynya. The only limitation here would be the availability of cloud-free images. Coarse resolution data are also needed to reveal the synoptic-scale ice picture. The Southern Ocean circumpolar currents causes the ice cover to spread freely off shore, covering a wide area. Fine resolution data, on the other hand, are needed for a few purposes. The first is to estimate the average size of the ice floes. The probability of collisions of ice floes increases at higher ice concentration of smaller floes. This reduces the overall speed of the ice pack but exerts extra ice loads on the ship (assuming same ice type and thickness are encountered) due to repeated collisions with the smaller floes. The second is to obtain ice information in small water areas (e.g., polynyas and fjords). This was particularly important for the last phase of the RV _Xuelong_ as it approached its destination. The data are also needed in regimes of highly-mixed ice types. Case studies of CHINARE2011 and CHINARE2013 demonstrate this situation. The spatial resolution of 75 m from ASAR and 50 m from Radarsat-2 was sufficient to extract the required information, which is mainly about ice type, ridged zones (unfavorable features) and opening in the cover (favorable features). Ice motion is the factor that dictates the requirement for the temporal resolution of ice information in regimes of high SIC.