A comparison of satellite-derived sea-ice motion with drifting-buoy data in the Weddell Sea, Antarctica

We compare a satellite-derived sea-ice motion dataset obtained from the US National Snow and Ice Data Center with daily ice drift by drifting buoys between 1989 and 2005. The satellite data were derived from daily composites of passive-microwave satellite measurements by means of a cross-correlation method and were supplemented with data from visible and thermal channels of the Advanced Very High Resolution Radiometer. Seasonal and interannual variations of the agreement between the two datasets are discussed. In addition, regional differences in the agreement and correlation coefficients of buoy- and satellite-derived drift components are analyzed. Results show that the overall drift regime can be well described by satellite-derived drift data but 71% of the retrieved drift velocities are lower than those observed by buoys. Nevertheless, correlation coefficients, r, between the two datasets are 0.587 for the zonal and 0.613 for the meridional drift component. The correlation coefficients between monthly averages of buoy- and satellite-derived zonal and meridional drift components are on average 25.7% and 16.4% lower in summer (October-February) than in winter (March-September), with the exception of January. In January, correlation coefficients are about 62.6% (zonal) and 66.5% (meridional) lower than in winter. Furthermore, deviations between zonal buoy- and satellite-derived drift are 80% larger in the second half than in the first half of the year. The observed yearly and regional averaged agreement between the two datasets depends strongly on the season when buoy data were collected and on the number of coincident buoy and satellite data, which was often very low.