Seminar Announcement

SPEAKER H. Jay Zwally

Oceans and Ice Branch NASA Goddard Space Flight Center

TITLE: Arctic Sea-Ice Freeboard Height Distributions and Thickness Maps From ICESat Laser Altimetry

DATE: Monday, March 1, 2004

TIME: 12:00 NOON

PLACE: Spanagel Hall, Rm 316

ABSTRACT:

NASA’s Ice, Cloud and Land Elevation Satellite (ICESat) was launched in January 2003 for the primary purpose of determining the mass balances of the Greenland and Antarctic ice sheets. Data has been acquired during several laser operation periods of 36 to 54 days, which is less than the planned continuous operation for 3 to 5 years. In addition to ice-sheet, atmospheric, land, and ocean measurements, ICESat is providing a novel capability to measure sea-ice freeboard heights with a precision of several centimeters. Sea-ice thicknesses are derived from the freeboard heights using estimates of the snow cover thickness and snow and ice densities. Distributions of sea thicknesses over spatial scales provide information on the mean sea-ice thickness, ratio of thicker multi-year ice to thinner ice types, growth/decay rates, and convergence/divergence. ICESat measures the mean surface elevation over footprints 70 m in diameter spaced at 170 m along track. The along-track precision over low-slope surfaces is < 3 cm. Freeboard height distributions are derived by calculating 50 km running means of the measured elevations, plotting the distributions of the elevation deviations from the 50 km means, and using several methods for determining the open-water level. The method removes elevation variations of several meters due to inaccuracies in the geoid and will provide a basis for improved geoid mapping in polar seas. Comparison with radar images (with Ron Kwok, JPL) show good agreement with grey-ice in leads, open leads, ice ridges, and thick ice floes. Comparison with multiyear ice distributions from passive microwave and rougher ice areas from scatterometry also show good agreements, including some motion of thicker ice areas during successive ICESat 8-day mappings. Maps of sea ice thickness are in agreement with known patterns of sea-ice thicknesses.

ABOUT THE SPEAKER: Dr. H. Jay Zwally is the Project Scientist for ICESat.