Sea ice surface temperature in the Weddell Sea (Antarctica), from driftingbuoy and AVHRR data

The surface temperature of sea ice is derived from infrared AVHRR measureme nts and from in situ measurements at drifting buoys in the Weddell Sea, Ant arctica. For clear sky cases, the surface temperature is calculated from AV HRR channel 4 data (10.3-11.3 mum). After calibrating and geo-referencing t he infrared measurements, an atmospheric correction is carried out using th e radiation transfer model MODTRAN and temperature and humidity data from E CMWF analyses. The results are compared with surface temperatures derived f rom air temperature measurements from drifting buoys with an energy balance model. Results from both methods are linearly related with a correlation c oefficient of 0.97 and a slope of 1.03. The bias is less than 1.3 K and the standard deviation of the residuals is 2.56 K. Accuracies and worst case e rror estimates of both methods are quantified by sensitivity studies with r espect to the relevant sources of errors. A typical accuracy of the buoy-ba sed surface temperature is 2 K and a worst case error estimate is 4-7 K dep ending on the ice thickness. The accuracy and worst case error estimate of satellite-derived surface temperature are of the same magnitude. Thus, none of the derivation methods is considered to be a validation of the other. I ce surface temperature variations in the Antarctic sea ice zone are caused by moving depressions in all seasons and cover a range of up to 20 K. Satel lite measurements with a typical accuracy of 2 K may provide surface temper atures with a satisfactory signal to noise ratio in this data-sparse region , although clouds bear a significant restriction to their application. (C) 2001 Elsevier Science B.V. All rights reserved.