A Comparison Of Ice Concentration Estimates From Sar And SSSM/I Data

Abstract

Remote sensing data collected during the March 1988 Alaska survey is used to compare multiyear ice concentration estimates derived from a satellite mounted passive microwave radiometer to those generated by an aircraft mounted Synthetic Aperture Radar (SAR) system. The passive microwave radiometer data used is produced by the Special Sensor Microwave Imager (SSMII) which is a multichannel system. The SSMII ice concentration estimates are produced by a multichannel algorithm which utilizes both the polarization and spectral gradient radiance ratios to determine the percent of multiyear ice. These estimate are compared to concentration estimates produced by a manual interpretation of mosaicked SAR imagery. A 30 percent discrepancy was found in the multiyear ice concentration estimates for coincident imagery which crosses the first-yearlmultiyear ice edge. KEYWORDSSARI SSM/I, Sea Ice Concentration, Sea Ice Comparison, Passive Microwave Radiometer, Multichannel Concentration Algorithm 1.0 INTRODUCTIONThe SSM/I system is a multichannel coarse resolution passive microwave radiometer mounted on the Defense Meteorological Satellite Program (DMSP-8) satellite. It has been providing nearly full coverage of the arctic region every day since the beginning of 1988, and specifically has been generating large scale ice concentration maps giving the percent concentration of open water, first-year, and multiyear sea ice. The daily production of these sea ice concentration maps is of great interest to both ship navigation and offshore drilling platforms since they can be used to track the motion of the ice edge (the boundary between ice-covered and ice-free water) in the polar regions.However, verifying the SSMII ice concentrations is often difficult due to the lack of available ground truth. One solution is to compare SSMII ice concentration estimates to those derived by other sensors. High resolution aircraft SAR systems can provide such a verification since manual generation of ice concentrations can reliably by done [1,2]. These studies show that the high spatial resolution associated with SAR imagery provides the ability to delineate individual floes which makes the determination o f ice concentration easier. both active and passive sensors have been performed [1,3]. However, the current analysis will use sea ice concentration estimates generated from high resolution SAR imagery to validate ice concentration estimates produced specifically from the multichannel SSM/I data. The SAR derived ice concentration estimates are produced by a manual analysis of mosaicked imagery while the SSMII estimates are generated by a multichannel concentration algorithm which utilizes both the polarization and spectral gradient ratios to determine the percentage of multiyear sea ice [4,5,6]. These ice concentration estimates were produced from imagery gathered during the March 1988 Alaska collection which is coincident with SSM/I overflights. Section 2 of this paper summarizes the sensors and gives a brief description of the Alaskan collection. ...