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Microwave Brightness of Polar Firn as Measured by Nimbus 5 and 6 ESMR

  • A. T. C. Chang (a1), B. J. Choudhury (a2) and P. Gloersen (a3)

Abstract

The microwave emission from a half-space medium characterized by coordinate dependent scattering and absorbing centers has been calculated by numerically solving the radiative transfer equation by the method of invariant imbedding. A Mie scattering phase function and surface polarization have been included in the calculation. Also included are the physical temperature profile and the temperature variation of the index of refraction for ice. Using published values of grain-size and temperature-profile data of polar firn, the brightness temperature has been calculated for the 1.55 cm and 0.8 cm wavelengths. For selected regions in Greenland and Antarctica, the results of our calculations are in reasonable agreement with the observed Nimbus-5 and Nimbus-6 ESMR data.

Résumé

L’émission en micro-ondes issue d’un milieu hémispatial caractérisé par des centres coordonnés dépendants de dispersion et d’absorption a été calculée par résolution numérique de l’équation de transfert de chalcur avec la méthode de l’invariant inclus. On a pris en compte dans le calcul une fonction pour la phase de dispersion Mie et une polarisation en surface. On a également tenu compte du profil physique des températures et de la variation avec la température de l’indice de réfraction de la glace. En utilisant les valeurs publiées pour la tailie des grains et les données des profils de température du névé polaire, la température de brillance a été calculée pour les longueurs d’onde de 1,55 cm et de 0,8 cm. Pour des régions sélectionnées du Groenland et de l’Antarctique, les résultats de nos calculs sont en accord raisonnable avec les données observées par ESMR de Nimbus-5 et Nimbus-6.

Zusammenfassung

Durch numerische Lösung der Gleichung für die Strahlungsübertragung mit der Methode der invarianten Einbettung wurde die Mikrowellen-Emission im Halbraum über einem Medium, das durch Zentren mit ortsabhängiger Streuung und Absorption charakterisiert ist, berechnet. In die Rechnung wurde eine Mie’sche Phasenfunktion der Streuung und eine Polarisation an der Oberfläche einbezogen. Desgleichen wurde das physikalische Temperaturprofil und die temperaturabhängige Schwankung des Refraktionsindex für Eis berüchsichtigt. Auf der Basis veröffentlichter Werte für die Korngrösse und das Temperaturprofil in polarem Firn wurde die Farbtemperatur für Wellenlängen von 1,55 cm und 0,8 cm berechnet. Für ausgewählte Gebiete in Grönland und Antarktika stehen die Rechenergebnisse in guter Übereinstimmung zu beobachteten Werten der Satelliten Nimbus-5 und Nimbus-6 ESMR.

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Copyright

References

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Microwave Brightness of Polar Firn as Measured by Nimbus 5 and 6 ESMR

  • A. T. C. Chang (a1), B. J. Choudhury (a2) and P. Gloersen (a3)

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