# Satellite-Based Sea Ice Navigation for Prydz Bay, East Antarctica
## 4 Results
### CHINARE2011 Ice Navigation  
Ice concentration in Prydz Bay was generally above 90%, while there was a region between 77\({}^{\circ}\)E and 78\({}^{\circ}\)E with SIC as low as 70% at some latitudes in November 2011 (Figure 4). A small open-water area existed between these two longitudes around 68\({}^{\circ}\)S. A ridge of high atmospheric surface pressure moved north of Prydz Bay from 25 to 29 November, imposing some minor modifications to the regional MSLP distribution (Figure 5, top). Quiescent conditions (25 November) changed to moderate (wind speed less than 10 ms\({}^{-1}\)) on 27 November and 29 November with similar benign weather forecast for the following days. The ice conditions and the associated weather patterns triggered a request for SAR.  
On 27 November a proposed route with 20 waypoints was sent to RV _Xuelong_ based on the sea ice analysis of ASAR-WSM (Wide Swath Mode) images acquired on 25 and 26 November when RV _Xuelong_ entered into the sea ice region at approximately 63.5\({}^{\circ}\)S, 77.5\({}^{\circ}\)E (Figure 7). She was advised to enter the sea ice zone east of 76\({}^{\circ}\)E. Consequently, with slight adjustments to the proposed route, she progressed smoothly at a speed of 3.4 to 14.8 knots through the pack ice zone.  
A narrow bright straight line was barely visible in the ASAR images of 22, 25 and 27 November (Figure 7), contrasting the darker signature of the surrounding smooth land-fast ice. It started as a 7-km short line on 22 November and extended further south within the land-fast ice to just north of Zhongshan Station by 25 November before turning to the Indian Bharati Station (76.19\({}^{\circ}\)E, 69.40\({}^{\circ}\)S) on 27 November. This was interpreted as a narrow refrozen lead or a rough ice track of a vessel. As RV _[PERSON]_ approached this feature, communication with staff at Bharati Station confirmed that the Russian icebreaker _[PERSON]_ had provided icebreaking support for MV (Motor Vessel) _[PERSON]_, resupplying the station. It was then confirmed that the bright line represented an opening  
Figure 7: ASAR images acquired on 25 and 26 November 2011 (**left**), with the navigation points of RV _[PERSON]_ (blue) from 27 November to 29 November 2011 and the 20 planned waypoints (red). The waypoints were based on analysis of the ASAR images. Images at the right are enlargement of the area marked by the red box in the left panel on different days, showing the progress of the wake of the Russian [PERSON] through the land-fast ice off the Zhongshan Station.  
with water and broken ice in the wake of the Russian ice breaker. Consequently, after leaving the 16 th waypoint, [PERSON] _[PERSON]_ changed course to follow that opening. This led to abandonment of the proposed waypoints 17 and 18. Entering the lead through the fast ice on 29 November, she moved at an average speed of 3.5 knots (with a maximum speed of 7.7 knots), following the lead towards the Zhongshan Station to all but the last 10 km of land-fast ice.  
To assess the performance of the sea ice routing, we calculated the deviation of the actual trajectory of the vessel from the proposed route. This ranged from 165 m to 25.3 km with a standard deviation of 6.1 km. However, with the exclusion of the waypoints 17 and 18 as described before, the range reduced to a maximum of 6.9 km and the standard deviation to 2.8 km.