HR: 0800h
AN: A41B-0444    [Abstracts]
TI: Terahertz Remote Sensing of Ice Clouds - Sensitivity on Ice Dielectric Properties
AU: * Mendrok, J
EM: mendrok@nict.go.jp
AF: National Institute of Information and Communications Technology, Japan, 4-2-1 Nukui- kitamachi, Koganei, Tokyo, 184-8795, Japan
AU: Baron, P
EM: baron@nict.go.jp
AF: National Institute of Information and Communications Technology, Japan, 4-2-1 Nukui- kitamachi, Koganei, Tokyo, 184-8795, Japan
AU: Kasai, Y
EM: ykasai@nict.go.jp
AF: National Institute of Information and Communications Technology, Japan, 4-2-1 Nukui- kitamachi, Koganei, Tokyo, 184-8795, Japan
AB: Initiated by current developments in terahertz sensor technology the application of instruments operating in the spectral region between 0.1 - 30 THz is considered for a number of remote sensing issues. Accounting for more than 50 percent of the outgoing longwave radiation and with the major component of cirrus radiative forcing in the far-infrared, satellite measurements in this spectral region will significantly support the determination of the radiation budget of the Earth. Furthermore, spanning the whole range of particle sizes found in tropospheric ice clouds, the Terahertz region bears the potential to complement existing methods and improve our knowlegde and understanding of those clouds. Both, determination of the Earth's radiation budget as well as retrieving ice cloud properties require appropriately accurate calculations of radiative transfer. Hence, a good knowledge of the input parameters to the radiative transfer models is needed. In particular, this includes spectrally dependent properties of the molecular as well as particulate atmospheric matter, i.e., spectroscopic parameters of the molecular absorption lines and continua as well as the dielectric properties of aerosol and cloud particle material. Due to the lack of Terahertz light source and receiver technology in the past, measurements of these parameters have been sparse and the knowledge about them is rather poor. In preparation to evaluate the feasibility of monitoring tropospheric ice clouds using passive Terahertz observations, we study the modeling uncertainties due to the unconfident knowledge of the complex refractive index of ice. We give an overview of the consistency and discrepancies, respectively, of the existing measurements and models for ice refractive index in the Terahertz region. Using calculations of particle optical properties according to Mie theory as well as the radiative transfer models Moliere and SARTre, we estimate the deviations in particle optical properties and simulated observation spectra arising from applying the different ice refractive index data. Furthermore, in order to derive the uncertainty in retrieved cloud properties the sensitivity of the atmospheric spectra to the ice refractive index on the one hand and cloud ice content as well as particle size on the other hand is compared. From that, conclusions will be drawn on requirements for future experiments to measure dielectric properties of ice for geophysical applications.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0360 Radiation: transmission and scattering
DE: 0394 Instruments and techniques
DE: 3360 Remote sensing
DE: 6964 Radio wave propagation
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting