Comparisons of SSM/I liquid water paths with aircraft measurements

Abstract

Comparisons have been made between in situ aircraft measurements of integrated liquid water and retrievals of integrated liquid water path (LWP) from algorithms using SSM/I brightness temperatures. The aircraft measurements were made over the North Atlantic Ocean during the winter of 1992. Six case studies are presented from which trends in the LWP algorithms are discussed. SSM/I liquid water path validation has previously only been performed through comparisons with measurements from upward-looking radiometers or with calculations from radiative transfer models. The case studies presented here reflect an alternative technique for validation. Aircraft-derived liquid water paths ranged from 0.01 to 0.09 kg m-2 for the six cases presented. The SSM/I algorithms investigated predicted LWP to within ±0.02-0.03 kg m-2, provided one accounted for systematic biases in the retrievals. These biases were systematic in the range ±0.06 kg m-2 and were presumably caused by latitudinal and seasonal influences inherent in the algorithms. Algorithms based on radiative transfer models appeared to perform better than the statistically based algorithms.