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Proceedings Paper

Statistical model for atmospheric limb radiance structure: application to airborne infrared surveillance systems
Author(s): Carine Quang; Francis Dalaudier; Antoine Roblin; Valérie Rialland; Patrick Chervet
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Paper Abstract

Infrared (IR) detectors can be used as airborne limb-viewing surveillance systems for missile detection. These systems' performances are impacted by the atmospheric inhomogeneous background. In fact, the probability of target detection can be heavily affected. Consequently, the knowledge of these radiance small-scale fluctuations and their statistical properties is required to assess these systems' detection capability. A model of two-dimensional radiance spatial fluctuations autocorrelation function (ACF) is developed. This model is dedicated to airborne limb-viewing conditions in the thermal IR. In the stratosphere and in clear-sky conditions, the structured background is mainly due to internal-gravity-wave-induced temperature and density spatial fluctuations. Moreover, in the particular case of water vapour absorption bands, the mass fraction fluctuations play a non negligible role on the radiative field. Thereby, considering the temperature field and the water vapour field as stochastic processes, the radiance ACF can be expressed as a function of the temperature ACF and the water vapor mass fraction ACF. A local thermodynamic equilibrium model is sufficient for stratospheric conditions and sunlight scattering is neglected in the thermal IR. In addition, determination of the radiance fluctuations ACF requires the knowledge of the absorption coefficient and its first derivatives with respect to the temperature and water vapour mass fraction. Thus, a line-by-line model specific to water vapor absorption bands has been developed. This model is used to precalculate the absorption coefficients and their derivatives. This look-up table method allows circumventing the computational cost of a line-by-line calculation. A detailed description of the radiance fluctuations ACF model is presented and first results are discussed.

Paper Details

Date Published: 14 October 2008
PDF: 9 pages
Proc. SPIE 7108, Optics in Atmospheric Propagation and Adaptive Systems XI, 710805 (14 October 2008); doi: 10.1117/12.799815
Show Author Affiliations
Carine Quang, ONERA (France)
Francis Dalaudier, Service d’Aéronomie, CNRS (France)
Antoine Roblin, ONERA (France)
Valérie Rialland, ONERA (France)
Patrick Chervet, ONERA (France)

Published in SPIE Proceedings Vol. 7108:
Optics in Atmospheric Propagation and Adaptive Systems XI
Anton Kohnle; Karin Stein; John D. Gonglewski, Editor(s)

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