A Feasibility Study of a Microwave Water Vapor Measurement from a Space Probe Along an Occultation Path

摘要

The work presented is a preliminary feasibility study of stratospheric and mesospheric water vapor measurements using the microwave lines at 22 GHz (22.235 GHz) and 183 GHz (183. 31 GHz). The resonant cross sections for both the 22 GHz and the 183 GHz lines are presented and used to model the optical depth of atmospheric water vapor. The range of optical depths seen by a microwave radiometer through the earth's limb is determined from radiative transfer theory. Radiometer sensitivity, derived from signal theory, is compared with calculated optical depths to determine the maximum height to which water vapor can be measured using the following methods: passive emission, passive absorption, and active absorption.nThe report concludes that measurements using the 22 GHz line are limited to about 50 km whereas the 183 GHz line will enable measurements up to and above 100 km for water vapor mixing ratios as low as 0. 1 ppm under optimum conditions.