Sea ice leads (fractures in the ice sheet) play a critical role in the exchange of mass and energy between the ocean and atmosphere in the Polar Regions, particularly in the Arctic. Leads absorb more solar energy than the surrounding ice, warming the water and accelerating melt. In the winter, spring, and autumn, leads impact the local boundary layer structure (Lüpkes et al., 2008) and cloud properties because of the large fluxes of heat and moisture into the atmosphere. Given the rapid thinning and loss of Arctic sea ice over the last few decades (Wadhams and Davis, 2000), changes in the distribution of leads can be expected in response. Leads are largely wind driven, so their distributions will also be affected by the changes in atmospheric circulation that have occurred. From a climate perspective, identifying trends in lead characteristics (width, orientation, area coverage and spatial distribution) will advance our understanding of both thermodynamic and mechanical processes in the Arctic. From an operational perspective, knowledge of lead characteristics can aid in navigation, with direct benefits to security, subsistence hunting, and recreation.
This project developed a methodology to detect and characterize sea ice leads with optical (visible, infrared) satellite data from the Moderate Resolution Imaging Spectroradiometer (MODIS). The generated data set will be used to assess the spatial and temporal distributions of Arctic sea ice leads and their changes since 2000. The algorithm starts with the cloud masking. The reflective and emissive channels are then used to derive ice concentration for a 1 km grid over the entire Arctic Ocean. This analysis is used to create a mask of potential lead pixels. The algorithm then identifies and characterizes leads with a combination of image processing techniques that examine shape characteristics. We have developed and run the algorithm over the MODIS time period to yield lead characteristics across the Artic ice sheet.
We are extending this methodology to Visible Infrared Imaging Radiometer Suite (VIIRS), producing a continuous record of sea ice leads through the MODIS and VIIRS era.