Correcting the orbit drift effect on AVHRR land surface skin temperature measurements

The orbital drift of the National Oceanic and Atmospheric Administration (NOAA)-7, -9, -11, -14 series of satellites results in a significant cooling effect on their afternoon path Advanced Very High Resolution Radiometer (AVHRR) land surface skin temperature (T-s) measurements. This effect mixes with the signal of true variations in the climate system, and thus prevents T-s from being directly used in climate change and global warming studies. This paper applies a physically based 'typical pattern technique' to remove the orbit drift effect from T-s. The technique utilizes a lookup table of representative land skin temperature diurnal cycles derived from the National Center for Atmospheric Research (NCAR) Climate Community Model (CCM3) coupled with the land surface model, Biosphere-Atmosphere Transfer Scheme (BATS). The generated typical patterns of T-s diurnal cycle are functions of vegetation type, season and latitude, and are combined with satellite observations to remove the cooling effect. Applying this methodology to eighteen years of AVHRR ( 1981-1998) T-s observations yields an improved skin temperature dataset. Analysis of the drift-corrected skin temperature illustrates a warming trend at the surface over the past two decades, a result which agrees well with the observed surface air temperature trend. A discussion of uncertainties in this technique is also presented.