Assessing the impact of cloud morphology on infrared sounder scan geometry

Next generation infrared sounders from satellites are expected to provide temperature and moisture soundings with an improved vertical resolution. However, this goal could be severely limited by clouds, since infrared sounders are not able to sense through dense clouds. This paper examines the impact of cloud morphology on the scan geometry. More specifically, the problem of how many clear soundings can be achieved, in cloudy areas, as a function of the scan geometry has been addressed. The analysis is particularly devoted to frontal cloud systems which are typically associated with active weather phenomena. These systems are characterized by many spatial scales and result in fractal structures. This particular geometry has been exploited to formulate and check a power law for the dependence of the probability of achieving a clear sounding on the size of the field of view of the sounder. Six Advanced Very High Resolution Radiometer (AVHRR) scenes over north Europe form the basis of our database and various scan geometries, including mono-pixel and multi-pixel configurations, have been analysed.