SSM/I sea ice algorithm inter-comparison: operational case studies from the National Ice Center

The National Ice Center (NIC) routinely provides weekly global sea ice analyses, daily analyzed and forecasted ice edge products, and tailored high-resolution satellite imagery in support of various U.S. Government agency requirements. Heavy reliance is placed on visible and infrared imagery from the civilian and defense meteorological satellites; however, in areas of persistent cloud cover the NIC takes advantage of passive microwave satellite data to fill these gaps. Currently the NIC analysts use the NIC Hybrid sea ice algorithm in the Northern Hemisphere and the Bootstrap sea ice algorithm in the Southern Hemisphere to complete their products. This particular choice of algorithms was initially based on the personal preference of individual analysts, and was then perpetuated through ongoing training programs. No rigorous assessment of the merit of each algorithm was undertaken. In July 2001 the NIC began an ongoing evaluation of the NASA Team, Bootstrap, NIC Hybrid, and NASA Team II sea ice algorithms. The evaluation was performed by comparing available, time-coincident, visible and infrared satellite imagery with the SSM/I products. To date, 13 cases have been collected and analyzed. The NASA Team II provides the consistently best estimate of the ice edge and the 90% concentration boundary. This paper discusses the study undertaken by the NIC and presents select case studies to illustrate the performance characteristics of the various algorithms.