More than one hundred years ago the Endurance sank in the Antarctic, enclosed and crushed by pack ice. The crew survived and the superhuman rescue operation turned the expedition of the polar researcher Ernest Shackleton into a legend. Now the wreck has been located with support from the German Aerospace Center (DLR). DLR generated TerraSAR-X satellite images that supported safe navigation in the ice covered Weddell sea. The DLR researchers on board the search vessel also studied the characteristics of sea ice in order to improve navigation in polar regions.
Wreck of the Endurance at a depth of 3008 meters © Falklands Maritime Heritage Trust, National Geographic
Sea ice is subject to constant change. Winds and ocean currents can shove large masses of ice together within hours and close up open shipping lanes. and if the ice is under enough pressure, ice floes are shoved over or under each other or reorient themselves vertically. Such compressed ice ridges often prevent the passage even of icebreakers. Radar satellites like TerraSAR-X supply images of the land and ice surfaces and show the different structures of sea ice – thanks to the active radar antenna they can do this also through clouds and in the dark. These images are extremely valuable for the navigation of ships operating in polar regions.
TerraSAR-X satellite data and sea ice drift
The Endurance22 search expedition with its icebreaker, S.A. Agulhas II also relied on this technology. Thanks to high resolution satellite data it was able to find a way through the labyrinth of shipping lanes between metre-thick sea ice floes. Two researchers from DLR‘s Earth Observation Center (EOC) and Microwaves and Radar Institute were also on board. They used every overflight of the TerraSAR-X radar satellite to order recordings for S.A. Agulhas II, which enabled them to keep an eye on the sea ice situation.
TerraSAR-X image for route planning of the Endurance22 expedition © DLR (CC BY-NC-ND 3.0)
Thanks to the satellite’s near-polar orbit that could be done up to several times a day. Algorithms provided by the EOC Maritime Safety and Security Lab in Bremen used the data to calculate in addition the sea ice drift at high resolution – valuable supplementary local information. The remote sensing experts on board were also supported by the DLR ground station in Neustrelitz.
Expedition ship "S.A. Agulhas II" in search © Falklands Maritime Heritage Trust, Nick Birtwistle
In the current research projects EisKlass2 and FastCast2 the DLR scientists want to go a step further. Instead of consulting individual up-to-date radar images for navigation purposes, the sea ice is to be classified according to navigability using new algorithms, and by incorporating prediction models hourly forecasts can be made about the future situation, so that customized ship routing proposals can be computed. In order to develop the required algorithms, DLR researchers on board S.A. Agulhas II collected in situ measurement data. These included images from a infrared camera in order to better analyse sea ice characteristics.
Spectacular discovery in the Weddell Sea
Early in February 2022 the Endurance22 research and search expedition put to sea from Cape Town to find Shackleton’s polar ship with modern technology. The Endurance has now been located at a depth of 3,008 metres some six and a half kilometres south of the location Captain Frank Worsley had last indicated in 1915. The wooden wreck is lying upright in the water and is in excellent condition, as is confirmed in photographs made by the underwater robot. Even the lettering “Endurance” on the stern can be clearly recognized. Tor the expedition, an international team of globally renowned marine archaeologists, engineers, technicians and sea ice specialists was brought together on the S.A. Agulhas II research icebreaker. Endurance will, however, not be salvaged. She is strictly protected by the Antarctic Treaty as a relic of human cultural heritage. The expedition team documented this find of the century with photographs, video recording and 3D images of the sea floor. The return of the expedition is planned for end of March, with spectacular pictures and unique science data for future generations.
Underwater robot "Sabertooth" © Falklands Maritime Heritage Trust, Nick Birtwistle