Wylie and Menzel (1989, 1999) and Wylie et al. (1994) describe a worldwide cloud-top altitude climatology composed from High-Resolution Infrared Radiation Sounder (HIRS) data on the National Oceanic and Atmospheric Administration (NOAA) Polar Orbiting Earth Satellites (POES). CO2 slicing is used to calculate effective emissivities (Ne) in pixels over the area from 82° N to 82°S. Pixels with Ne ³ 0.1 are considered cloudy in this study. 2° (latitude) X 3° (longitude) X 1 km (vertical) bins are defined, and cloudiness percentages are calculated from the population of pixels within each bin. Eighteen vertical levels are used.

Airborne and ground-based sensor performance is seriously degraded by the presence of clouds. This climatology allows estimates of Cloud-Free Line-of-Sight (CFLOS) probability between sensors and objects. Assessments can be made for different sensor and object altitudes, seasons, and geographic regions. Data from the central tropical Pacific is used to demonstrate the usefulness of this climatology. Aeromet has conducted numerous cloud microphysical sampling and cloud mapping missions over this area, and is very familiar with that area’s cloud characteristics.

The authors will discuss the assumptions and limitations of the data and the results from the tropical study.