Development of a synergetic sea ice retrieval method for the ERS-1 AMI wind scatterometer and SSM/I radiometer

Sea ice retrievals from the standard passive microwave NASA team algorithm for the Special Sensor Microwave/Imager (SSM/I) are compared to retrievals from a new ERS-1 Active Microwave Instrument (AMI) wind scatterometer sea ice retrieval algorithm. The main objective of the comparison is to develop a synergetic algorithm, with the combined advantages of both of the individual algorithms. The scatterometer algorithm is validated in reference to the SSM/I NASA team algorithm, and a high accuracy of 98-99% is obtained when a NASA team pixel is determined as ice covered when the concentration is 85% or higher. This rather high concentration threshold eliminates most mixed pixels from being treated as ice covered, as many of these mixed pixel signatures are in fact caused by atmospheric effects. It is evident from the results that the NASA team weather correction for SSM/I sea ice retrievals works well over ice-free ocean surfaces, although it cannot he applied over mixed pixels or ice. The scatterometer algorithm presented, however, does not appear to need a weather correction. Therefore, especially mixed pixel estimates, e.g., around ice edges or polynyas, could be enhanced by the use of both active (ERS-1 AMI wind scatterometer) and passive (SSM/I) microwaves. In addition, the results show that late summer ice type classification by the scatterometer algorithm is more reliable than the present SSM/I NASA team classification. This is due to the scatterometer classification procedure, which adapts to the ice season considered. Based on the results obtained, a synergetic algorithm for the ERS-1 AMI wind scatterometer and the SSM/I is introduced.