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These page provides three examples of gouging events and grounded ridges detected by a coastal sea ice radar system in Barrow, Alaska. More details of the radar system together with near real-time and archived data can be found here. In these animations, the time between each frame is approximately 4 minutes and we assume that radar signals from offshore are received from sea ice surfaces. Note that the absence of radar reflections does not imply an absence of sea ice. Level sea ice surfaces will not typical return a signal except very close to the radar. Also, large pressure ridges may also shadow the ice behind them.

Grounded ridges can be identified by the presence of stationary ice floes in the midst of drifting floes. In the animations linked below, we provide the unprocessed radar data alongside processed imagery, that helps distinguish stationary and moving targets. We highlight stationary targets through the use of a running pixel-wise mean filter over a 6-frame window. Moving targets are highlighted by calculating the pixel-wise standard deviation over the same window. This picks out regions of the image that change over time and the trails created by moving targets. The occurrence of seafloor gouging events can be inferred from floes which comes to rest while those around them continue to move, or from floes that exhibit stop-and-go motion.

Example 1: Grounded ridges surrounded by drifting ice floes

July 14-15, 2008

In this example, the landfast ice is in an advanced stage of break-up. Isolated grounded ridges can be seen to remain in place while ice floes drift around them on both sides. One ridge exhibits discontinuous motion, which we take as evidence of seafloor gouging taking place.

Example 2: Grounded ridges created by deformation of drifting ice floes

August 5-6, 2008

This is a relatively rare example of sea ice incursion into the coastal zone in August. The sea ice is composed of small, loosely pack floes. There is little rigid body motion exhibited and targets act largely as independent particles. However, convergence of ice floes leads to the creation of a grounded ridge, which remains stationary temporarily before being dislodged. This action may also indicate a seafloor gouging event.

Example 3: Abrupt deceleration of drifting floe

March 24-26, 2010

This example shows a target which exhibits constant motion among its neighbors before abruptly coming to a halt. We take this to be evidence of seafloor interaction. Ice floes can be seen drifting past on both its landward and seaward sides further demonstrating its grounded state. The floe becomes ungrounded during a reversal in ice motion.