Feasibility of Determining Cloud-Top Heights Using the Backscattered Ultraviolet Satellite Observation Technique

Abstract

A technique for determining cloud-top height by means of backscattered ultraviolet (BUV) solar radiation is presented. Cloud-top heights can be inferred using this technique if both the BUV radiance and its degree of polarization are measured by a spacecraft and compared with theoretical values. The cases of satellites with high-inclination orbits and geosynchronous satellites are discussed here. Based on calculations of radiance and polarization, the resolutions of cloud-top height determinations are roughly estimated in both cases. The estimates show that inference is possible as long as the angle between the direction of the sun and the satellite from the point of interest in the atmosphere is larger than about 10°. The estimates also indicate that the cloud-top height resolution depends on solar zenith angle ?0 in the case of nadir observation by satellites in nonequatorial orbits: The resolution is ?0.5 km for ?0 = 30° and ?0.3 km for larger ?0. On the other hand, when observations are made by geosynchronous satellites, the resolution depends strongly on the latitude of the point of interest, α1; a resolution within 0.4 km can be achieved for α1 ≤ 65° (0.2 km resolution can be obtained for middle latitudes). Resolution becomes rapidly worse with increasing latitude, and α1 ≈ 70° seems to be the limit of observations with this technique.