# Satellite-Based Sea Ice Navigation for Prydz Bay, East Antarctica
## 4 Results
### CHINARE2013 Ice Navigation  
Ice concentrations in the Bay exceeded 90% in November 2013, which is considerably higher than the previous years, with barely any leads visible (Figure 4). MODIS imagery acquired on 20-29 November confirmed this distribution. Therefore, the SatSINS process recommended that SAR data had to be ordered to guide the nautical sea ice analysis. On 25 November, a cyclone centered at approximately 78.5\({}^{\circ}\)E, 59.5\({}^{\circ}\)S (Figure 5) moving southeast from the northern Prydz Bay was soon followed by second cyclone moving eastward from the western Prydz Bay (53.8\({}^{\circ}\)E, 63.2\({}^{\circ}\)S). A third, albeit weaker, cyclone was located over the bay on 27 November moving to the east, and two other cyclones covered Prydz Bay on 29 November. Winds at RV _Xuelong_ location were quiescent (less than 5-6 ms\({}^{-1}\)) and clouds prevailed from 27 to 30 November. This suggested that sea ice conditions were unlikely to have changed greatly by that time.  
The two Radarsat-2 images acquired on 27 and 29 November (Figure 9) showed very large ice floes across almost the entire ice pack with a number of very small leads once south of 65\({}^{\circ}\)S (hundreds of meters to a few kilometers in length). It appeared impossible for RV _Xuelong_ to navigate through the compact pack ice region without detailed ice distribution and a proposed route based on remote sensing data. Though part of the Prydz Bay was cloud-covered on 29 November, a MODIS image was sufficiently clear over the region of interest to identify ice floe boundaries and a few leads. Consequently, a route with 12 waypoints was first proposed based on information from the MODIS data, recommending RV _Xuelong_ sail towards 65\({}^{\circ}\)S, 73\({}^{\circ}\)E and from there travel along the defined zone in a southeasterly direction towards Zhongshan Station (Figure 9). The waypoint information was sent to the vessel on 29 November. At 20:00 (UTC) of the same day a refined route with 13 waypoints was derived according to sea ice conditions obtained from Radarsat-2 SAR image acquired at 15:14 (UTC) (less than 5 h from vessel entry into the ice in Prydz Bay) (Figure 9). The differences between the waypoints of the first and second proposed routes were minor. The SAR image was acquired one day before the start of the vessel's path shown in Figure 9. Therefore, it is possible that the vessel encountered ice distribution slightly different from the one based on MODIS data only. For most of the route, the vessel speed was between 8 and 12 knots. Figure 9 includes a line separating an areas of ice cover with leads (concentration < 90%) and an area of fully consolidated ice (100%). Locations of a few selected points on that line were included in the proposed route with an advice for the vessel not to cross over it into the fully consolidated pack. The SAR-based route follows locations of apparent leads or thin ice. The deviation of the actual route from the first route ranged between 1.5 km and 15.7 km, with a standard deviation of 4.2 km. For the second route, the deviation ranged between 245 m to 11.0 km with a standard deviation of 3.0 km.  
Because the region east of 75\({}^{\circ}\)E was almost 100% ice concentration, navigation of RV _Xuelong_ was considered risky without any satellite-assisted sea ice analysis. The vessel succeeded in passing through the pack ice at an average speed of 5.7 knots over 2 days along the proposed route, arriving at the fast-ice edge within 22 km of Zhongshan Station at 19:30 (UTC) on 2 December 2013.