Publication Abstracts
Battaglia et al. 2006
Battaglia, A., C. Simmer, S. Crewell, H. Czekala, C. Emde, F. Marzano, , J.R. Pardo, and C. Prigent, 2006: Emission and scattering by clouds and precipitation. In Thermal Microwave Radiation: Applications for Remote Sensing. C. Mätzler, Ed., IET Press, pp. 101-223.
The strength of the interaction of clouds and precipitation with microwave radiation strongly increases with frequency. While at frequencies around 10 GHz and below radiances are influenced only marginally by large precipitating particles in rain, higher frequency signals emanating from the earth-surface-atmosphere system are increasingly dominated by both clouds and precipitation, especially outside the strong absorption lines of atmospheric gases. While in the infrared and solar spectral ranges clouds completely block the transmission of radiation in most of the microwave region both clouds and precipitation stay transparent at least to some degree. While only the outer surfaces of clouds can be seen in the solar and infrared spectral regions, the whole cloud and its internal structure is in principle accessible to remote sensing in the microwaves. Of importance for the spectral signal in the microwave region is the behaviour of the complex index of refraction of liquid and solid water. At low frequencies liquid precipitation dominates radiative transfer by absorption and emission processes due to the relatively large imaginary part of the index of refraction of liquid water. Atmospheric ice has almost no noticeable absorption due to its very small imaginary index of refraction. With increasing frequency, scattering at both liquid and solid hydrometeors increases dramatically in the transition region from the Rayleigh to the Lorenz-Mie regime, and at frequencies above the molecular absorption band around 60 GHz ice particles dominate the interaction in a way that, e.g. liquid precipitation in the lower parts of a cloud is almost hidden from the satellite view by the scattering effects of ice particles aloft.
Since large atmospheric hydrometeors tend to have non-spherical shapes (e.g. falling raindrops, snow and other ice crystals) polarisation becomes increasingly important. Over water surfaces all four components of the Stokes vector may become activated by radiation-surface interactions. Thus in general to take care of all important interaction processes and also to exploit significant signals for remote sensing purposes fully polarised atmospheric radiative-transfer models have a much higher importance for microwaves as compared with other spectral regions. Finally, the combination of scattering effects, the large spatial variation of the dominating hydrometeors in the atmosphere, the partly reflecting properties of the surface and the typically large footprints of microwave radiometers put weight on the consideration of three-dimensional effects in microwave radiative transfer.
This chapter reviews first the state of the art in deriving the single scattering properties of atmospheric hydrometeors, and then models are described for the computation of radiance distributions in cloudy atmospheres. The chapter finishes with the characterisation of the known signatures of clouds and precipitation in passive microwave observations.
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BibTeX Citation
@inbook{ba02200i,
author={Battaglia, A. and Simmer, C. and Crewell, S. and Czekala, H. and Emde, C. and Marzano, F. and Mishchenko, M. and Pardo, J. R. and Prigent, C.},
editor={Mätzler, C.},
title={Emission and scattering by clouds and precipitation},
booktitle={Thermal Microwave Radiation: Applications for Remote Sensing},
year={2006},
pages={101--223},
publisher={IET Press},
address={London},
}
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RIS Citation
TY - CHAP ID - ba02200i AU - Battaglia, A. AU - Simmer, C. AU - Crewell, S. AU - Czekala, H. AU - Emde, C. AU - Marzano, F. AU - Mishchenko, M. AU - Pardo, J. R. AU - Prigent, C. ED - Mätzler, C. PY - 2006 TI - Emission and scattering by clouds and precipitation BT - Thermal Microwave Radiation: Applications for Remote Sensing SP - 101 EP - 223 PB - IET Press CY - London ER -
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