The retrieval of cloud height and emissivity from passive measurements: comparison of techniques

Knowledge of the global vertical distribution of cloud is a critical gap in the current satellite observing system. While limited compared to the capabilities of active instruments such as lidars and cloud radars, data from the passive instruments on board operational and research satellites have been proven capable of providing estimates of cloud height and emissivity, which are critical pieces of information concerning cloud vertical structure. Given the approximately 30 years of data from some of the operational sensors, the relevance of cloud height and emissivity climatologies is very high. In this paper, retrieval techniques that utilize long wave CO2 absorption channels will be compared to window channel based techniques and the implications on the quality of long-term cloud height/emissivity climatologies will be discussed. Finally, cloud height and emissivity retrievals are often prone to larger errors when multilayered clouds are present. A methodology for improving retrievals in multilayered cloud regimes will be presented along with a proposed technique to infer the height of two cloud layers that are overlapped.