Microwave Emissivity and Accumulation Rate of Polar Firn
Abstract Radiative transfer theory is formulated to permit a meaningful definition of emissivity for bulk emitting media such as snow. The emissivity in the Rayleigh-Jeans approximation is then the microwave brightness temperature T B divided by an effective physical temperature 〈 T 〉 . The 〈 T 〉 is...
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Cambridge University Press (CUP)
1977
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Online Access: | http://dx.doi.org/10.1017/s0022143000021304 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000021304 |
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crcambridgeupr:10.1017/s0022143000021304 2024-09-09T19:11:05+00:00 Microwave Emissivity and Accumulation Rate of Polar Firn Jay Zwally, H. 1977 http://dx.doi.org/10.1017/s0022143000021304 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000021304 en eng Cambridge University Press (CUP) Journal of Glaciology volume 18, issue 79, page 195-215 ISSN 0022-1430 1727-5652 journal-article 1977 crcambridgeupr https://doi.org/10.1017/s0022143000021304 2024-06-19T04:04:34Z Abstract Radiative transfer theory is formulated to permit a meaningful definition of emissivity for bulk emitting media such as snow. The emissivity in the Rayleigh-Jeans approximation is then the microwave brightness temperature T B divided by an effective physical temperature 〈 T 〉 . The 〈 T 〉 is an average of the physical temperature, T(z), weighted by a radiative transfer function ƒ(z). Similarly, where e ( z ) is the local emittance. An approximate ƒ(z) is used to determine analytically the effects of various absorption coefficients, of scattering coefficients that vary with depth, and of the seasonal variation of T ( z ). It is shown that a mean emissivity, which is equal to the mean annual T B divided by the mean annual surface temperature T m , is a useful quantity for comparing theory and observations. Snow-crystal size measurements, r ( z ), at seven locations in Greenland and Antarctica are used to determine the Mie/Rayleigh scattering coefficient γ s ( z and to calculate the mean emissivities. The observed mean emissivities are determined by a which is the average of 12 monthly Nimbus-5 (1.55 cm) microwave observations, and the T m measured at the same locations. The calculated emissivities are about one-half of the observed values. The assumption that each snow crystal is an independent and equally effective scatterer, and the use of an approximation to ƒ(z) , tend to over-estimate the effect of scattering. Therefore, a parameter multiplying γ s ( z ) is used. The emissivities calculated with a single value of this empirical parameter for all seven locations agree well with the observed emissivities, showing that the microwave emissivity variations of dry polar urn can be characterised as a function of the crystal sizes. One optical depth corresponds to a typical fini depth of 5 m, but significant radiation emanates from up to 30 m. Since r(z) depends on the snow accumulation rate A and T m . the sensitivity of the emissivity to changes in T m or A are estimated using this semi-empirical theory. ... Article in Journal/Newspaper Antarc* Antarctica Greenland Journal of Glaciology Cambridge University Press Greenland Journal of Glaciology 18 79 195 215 |
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Open Polar |
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Cambridge University Press |
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crcambridgeupr |
language |
English |
description |
Abstract Radiative transfer theory is formulated to permit a meaningful definition of emissivity for bulk emitting media such as snow. The emissivity in the Rayleigh-Jeans approximation is then the microwave brightness temperature T B divided by an effective physical temperature 〈 T 〉 . The 〈 T 〉 is an average of the physical temperature, T(z), weighted by a radiative transfer function ƒ(z). Similarly, where e ( z ) is the local emittance. An approximate ƒ(z) is used to determine analytically the effects of various absorption coefficients, of scattering coefficients that vary with depth, and of the seasonal variation of T ( z ). It is shown that a mean emissivity, which is equal to the mean annual T B divided by the mean annual surface temperature T m , is a useful quantity for comparing theory and observations. Snow-crystal size measurements, r ( z ), at seven locations in Greenland and Antarctica are used to determine the Mie/Rayleigh scattering coefficient γ s ( z and to calculate the mean emissivities. The observed mean emissivities are determined by a which is the average of 12 monthly Nimbus-5 (1.55 cm) microwave observations, and the T m measured at the same locations. The calculated emissivities are about one-half of the observed values. The assumption that each snow crystal is an independent and equally effective scatterer, and the use of an approximation to ƒ(z) , tend to over-estimate the effect of scattering. Therefore, a parameter multiplying γ s ( z ) is used. The emissivities calculated with a single value of this empirical parameter for all seven locations agree well with the observed emissivities, showing that the microwave emissivity variations of dry polar urn can be characterised as a function of the crystal sizes. One optical depth corresponds to a typical fini depth of 5 m, but significant radiation emanates from up to 30 m. Since r(z) depends on the snow accumulation rate A and T m . the sensitivity of the emissivity to changes in T m or A are estimated using this semi-empirical theory. ... |
format |
Article in Journal/Newspaper |
author |
Jay Zwally, H. |
spellingShingle |
Jay Zwally, H. Microwave Emissivity and Accumulation Rate of Polar Firn |
author_facet |
Jay Zwally, H. |
author_sort |
Jay Zwally, H. |
title |
Microwave Emissivity and Accumulation Rate of Polar Firn |
title_short |
Microwave Emissivity and Accumulation Rate of Polar Firn |
title_full |
Microwave Emissivity and Accumulation Rate of Polar Firn |
title_fullStr |
Microwave Emissivity and Accumulation Rate of Polar Firn |
title_full_unstemmed |
Microwave Emissivity and Accumulation Rate of Polar Firn |
title_sort |
microwave emissivity and accumulation rate of polar firn |
publisher |
Cambridge University Press (CUP) |
publishDate |
1977 |
url |
http://dx.doi.org/10.1017/s0022143000021304 https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022143000021304 |
geographic |
Greenland |
geographic_facet |
Greenland |
genre |
Antarc* Antarctica Greenland Journal of Glaciology |
genre_facet |
Antarc* Antarctica Greenland Journal of Glaciology |
op_source |
Journal of Glaciology volume 18, issue 79, page 195-215 ISSN 0022-1430 1727-5652 |
op_doi |
https://doi.org/10.1017/s0022143000021304 |
container_title |
Journal of Glaciology |
container_volume |
18 |
container_issue |
79 |
container_start_page |
195 |
op_container_end_page |
215 |
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1809826744592498688 |