ARCTIC SEA-ICE CONCENTRATIONS FROM SPECIAL SENSOR MICROWAVE IMAGER AND ADVANCED VERY HIGH-RESOLUTION RADIOMETER SATELLITE DATA

Nearly coincident data from the special sensor microwave imager (SSM/I ) and the advanced very high resolution radiometer (AVHRR) are used to compute and compare Arctic sea ice concentrations for different regio ns and times of the year. To help determine overall accuracies and to highlight sources of differences between passive microwave, optical wa velength, and thermal wavelength data, ice concentrations are estimate d using two operational SSM/I ice concentration algorithms and with vi sible- and thermal-infrared wavelength AVHRR data. All algorithms capt ure the seasonal patterns of ice growth and melt. The ranges of differ ences fall within the general levels of uncertainty expected for each method and are similar to previous accuracy estimates. The estimated i ce concentrations are all highly correlated, with uniform biases, alth ough differences between individual pairs of observations can be large . On average, the NASA Team algorithm yielded 5% higher ice concentrat ions than the Bootstrap algorithm, while during nonmelt periods the tw o SSM/I algorithms agree to within 0.5%. These seasonal differences ar e consistent with the ways that the 19-GHz and 37-GHz microwave channe ls are used in the algorithms. When compared to the AVHRR-derived ice concentrations, the Team-algorithm results are more similar on average in terms of correlation and mean differences. However, the Team algor ithm underestimates concentrations relative to the AVHRR output by 6% during cold months and overestimates by 3% during summer. Little seaso nal difference exists between the Boostrap and AVHRR results, with a m ean difference of about 5%. Although the mean differences are less bet ween the SSM/I-derived concentrations and concentrations estimated usi ng AVHRR channel 1, the correlations appear substantially better betwe en the SSM/I data and concentrations derived from AVHRR channel 4, par ticularly for the Team algorithm output.