HR: 0800h
AN: A21D-0902    [Abstracts]
TI: Estimation of Cirrus Parameters to use for a Priori Setting of CO₂ Retrieval Algorithm
AU: * Yoshida, Y
EM: yoshida.yukio@nies.go.jp
AF: National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, 305-8506 Japan
AU: Yokota, T
EM: yoko@nies.go.jp
AF: National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, 305-8506 Japan
AU: Inoue, G
EM: inouegen@nies.go.jp
AF: National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, 305-8506 Japan
AB: In the Greenhouse Gases Observing Satellite (GOSAT) project, we use a Gauss-Newton method for retrieving column integrated CO₂ concentration. A priori cirrus properties, such as optical thickness, effective radius, cloud-top height, and cloud geometrical thickness, are necessary as input parameters, which are used for retrieval procedure. Some sensitivity analyses showed that assumptions of cloud-top height and cloud geometrical thickness had large influence on retrieved CO₂ concentration. If we try to deal with cirrus parameters strictly in the CO₂ retrieval algorithm, we have to estimate the cirrus optical thickness and the effective radius simultaneously for every atmospheric layers from middle troposphere to lower stratosphere, where cirrus would exist. However, this problem becomes more simple if some reliable parameters are given in the retrieval procedure. In this study, we try to estimate cirrus parameters, which are used in the CO₂ retrieval algorithm in a priori setting. By using radiative transfer simulations with various sets of cirrus parameters (e.g., optical thickness, effective radius, cloud-top height, and cloud geometrical thickness), we have found that O₂ A-band spectrum around 0.76 μm and water vapor saturated band spectrum around 2.0 μm have sensitivity to detect the effects of these cirrus parameters. Although it is difficult to separate the effect of optical thickness with that of cloud geometrical thickness, we can roughly estimate these parameters, for cirrus with optical thickness larger than approximately 0.5, by having simple extension of a common method; that are widely used in passive remote sensing of cloud. The estimated cirrus parameters are useful and practical to the CO₂ retrieval algorithm.
DE: 0360 Radiation: transmission and scattering
DE: 3311 Clouds and aerosols
DE: 3360 Remote sensing
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005