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.