SATELLITE MONITORING OF LAKE ICE BREAKUP ON THE LAURENTIAN SHIELD (1980-1994)

Lake ice breakup dates from 1980 to 1994 for 81 selected lakes and res ervoirs in the U.S. upper Midwest and portions of Canada (60 degrees N , 105 degrees W to 40 degrees N, 85 degrees W) were determined employi ng analysis of 1,830 archival images from the visible band (0.54 to 0. 70 mu m) of the GOES-VISSR. The objectives were to investigate the uti lity of monitoring ice phenology as a climate indicator and to assess regional trends in lake ice breakup dates. The dates of imagery repres ented the range available in the national archive at the time of this study. Comparison of satellite-derived breakup dates with available gr ound reference data revealed a mean absolute difference of +/- 3.2 day s and a mean difference of -0.4 days, well within the natural variabil ity in lake ice breakup dates (sigma approximate to +/- 12 days) for a single lake over time. The predominant spatial trends of mean ice bre akup dares can be attributed to latitude and snowfall (R-2 = 93 percen t). Analysis of the pooled data for all 81 lakes revealed a significan t (p < 0.001) trend toward earlier ice breakup dates. All of the indiv idual lakes exhibiting significant trends toward earlier ice breakup f rom 1980 to 1994 are located in southern Wisconsin.