First spectral measurements of light attenuation in Greenland Ice Sheet bare ice suggest shallower subsurface radiative heating and ICESat-2 penetration depth in the ablation zone
Light transmission into bare glacial ice affects surface energy balance, bio-photochemical cycling, and light detection and ranging (LiDAR) laser elevation measurements but has not previously been reported for the Greenland Ice Sheet. We present in-ice solar irradiance measured over the spectral ran...
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ftcopernicus:oai:publications.copernicus.org:tcd83902 2023-05-15T16:21:26+02:00 First spectral measurements of light attenuation in Greenland Ice Sheet bare ice suggest shallower subsurface radiative heating and ICESat-2 penetration depth in the ablation zone Cooper, Matthew G. Smith, Laurence C. Rennermalm, Asa K. Tedesco, Marco Muthyala, Rohi Leidman, Sasha Z. Moustafa, Samiah E. Fayne, Jessica V. 2020-03-17 application/pdf https://doi.org/10.5194/tc-2020-53 https://tc.copernicus.org/preprints/tc-2020-53/ eng eng doi:10.5194/tc-2020-53 https://tc.copernicus.org/preprints/tc-2020-53/ eISSN: 1994-0424 Text 2020 ftcopernicus https://doi.org/10.5194/tc-2020-53 2020-07-20T16:22:21Z Light transmission into bare glacial ice affects surface energy balance, bio-photochemical cycling, and light detection and ranging (LiDAR) laser elevation measurements but has not previously been reported for the Greenland Ice Sheet. We present in-ice solar irradiance measured over the spectral range 350–900 nm and 12–77 cm depth collected at a site in the western Greenland ablation zone. The acquired spectral irradiance measurements are used to calculate flux attenuation coefficients using an exponential decay Bouguer law model and are compared to values calculated from two-stream radiative transfer theory. Relative to asymptotic two-stream theory, our empirical attenuation coefficients are up to one order of magnitude larger in the range 350–530 nm, suggesting light absorbing particles embedded in ice enhance visible light absorption at our field site. The empirical coefficients accurately describe light attenuation in the ice interior but underestimate light attenuation near the ice surface. Consequently, Bouguer’s law overestimates transmitted flux by up to 50 % depending on wavelength. Refraction is unlikely to explain the discrepancy. Instead, vertical variation in the ice microstructure and the concentration of light absorbing particles appears to enhance near-surface attenuation at our field site. The magnitude of this near-surface attenuation implies that optical penetration depth is lower by up to 19 cm (28 %) at wavelengths relevant to visible-wavelength lidar altimetry of ice surface elevation (e.g. 532 nm for the Ice, Cloud, and Land Elevation Satellite-2) than is suggested by e-folding depths inferred from two stream theory for optically pure glacier ice. This enhanced near-surface attenuation implies shallower light transmission and therefore lower subsurface light availability for subsurface radiative heating and bio-photochemical cycling. We recommend radiative transfer models applied to bare ice in the Greenland Ice Sheet ablation zone account for vertical variation in light attenuation due to the vertical distribution of light absorbing particles and ice microstructure, and we provide new values of flux attenuation, absorption, and scattering coefficients to support model validation and parameterization. Text glacier Greenland Ice Sheet Copernicus Publications: E-Journals Greenland |
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Open Polar |
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Copernicus Publications: E-Journals |
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ftcopernicus |
language |
English |
description |
Light transmission into bare glacial ice affects surface energy balance, bio-photochemical cycling, and light detection and ranging (LiDAR) laser elevation measurements but has not previously been reported for the Greenland Ice Sheet. We present in-ice solar irradiance measured over the spectral range 350–900 nm and 12–77 cm depth collected at a site in the western Greenland ablation zone. The acquired spectral irradiance measurements are used to calculate flux attenuation coefficients using an exponential decay Bouguer law model and are compared to values calculated from two-stream radiative transfer theory. Relative to asymptotic two-stream theory, our empirical attenuation coefficients are up to one order of magnitude larger in the range 350–530 nm, suggesting light absorbing particles embedded in ice enhance visible light absorption at our field site. The empirical coefficients accurately describe light attenuation in the ice interior but underestimate light attenuation near the ice surface. Consequently, Bouguer’s law overestimates transmitted flux by up to 50 % depending on wavelength. Refraction is unlikely to explain the discrepancy. Instead, vertical variation in the ice microstructure and the concentration of light absorbing particles appears to enhance near-surface attenuation at our field site. The magnitude of this near-surface attenuation implies that optical penetration depth is lower by up to 19 cm (28 %) at wavelengths relevant to visible-wavelength lidar altimetry of ice surface elevation (e.g. 532 nm for the Ice, Cloud, and Land Elevation Satellite-2) than is suggested by e-folding depths inferred from two stream theory for optically pure glacier ice. This enhanced near-surface attenuation implies shallower light transmission and therefore lower subsurface light availability for subsurface radiative heating and bio-photochemical cycling. We recommend radiative transfer models applied to bare ice in the Greenland Ice Sheet ablation zone account for vertical variation in light attenuation due to the vertical distribution of light absorbing particles and ice microstructure, and we provide new values of flux attenuation, absorption, and scattering coefficients to support model validation and parameterization. |
format |
Text |
author |
Cooper, Matthew G. Smith, Laurence C. Rennermalm, Asa K. Tedesco, Marco Muthyala, Rohi Leidman, Sasha Z. Moustafa, Samiah E. Fayne, Jessica V. |
spellingShingle |
Cooper, Matthew G. Smith, Laurence C. Rennermalm, Asa K. Tedesco, Marco Muthyala, Rohi Leidman, Sasha Z. Moustafa, Samiah E. Fayne, Jessica V. First spectral measurements of light attenuation in Greenland Ice Sheet bare ice suggest shallower subsurface radiative heating and ICESat-2 penetration depth in the ablation zone |
author_facet |
Cooper, Matthew G. Smith, Laurence C. Rennermalm, Asa K. Tedesco, Marco Muthyala, Rohi Leidman, Sasha Z. Moustafa, Samiah E. Fayne, Jessica V. |
author_sort |
Cooper, Matthew G. |
title |
First spectral measurements of light attenuation in Greenland Ice Sheet bare ice suggest shallower subsurface radiative heating and ICESat-2 penetration depth in the ablation zone |
title_short |
First spectral measurements of light attenuation in Greenland Ice Sheet bare ice suggest shallower subsurface radiative heating and ICESat-2 penetration depth in the ablation zone |
title_full |
First spectral measurements of light attenuation in Greenland Ice Sheet bare ice suggest shallower subsurface radiative heating and ICESat-2 penetration depth in the ablation zone |
title_fullStr |
First spectral measurements of light attenuation in Greenland Ice Sheet bare ice suggest shallower subsurface radiative heating and ICESat-2 penetration depth in the ablation zone |
title_full_unstemmed |
First spectral measurements of light attenuation in Greenland Ice Sheet bare ice suggest shallower subsurface radiative heating and ICESat-2 penetration depth in the ablation zone |
title_sort |
first spectral measurements of light attenuation in greenland ice sheet bare ice suggest shallower subsurface radiative heating and icesat-2 penetration depth in the ablation zone |
publishDate |
2020 |
url |
https://doi.org/10.5194/tc-2020-53 https://tc.copernicus.org/preprints/tc-2020-53/ |
geographic |
Greenland |
geographic_facet |
Greenland |
genre |
glacier Greenland Ice Sheet |
genre_facet |
glacier Greenland Ice Sheet |
op_source |
eISSN: 1994-0424 |
op_relation |
doi:10.5194/tc-2020-53 https://tc.copernicus.org/preprints/tc-2020-53/ |
op_doi |
https://doi.org/10.5194/tc-2020-53 |
_version_ |
1766009437751869440 |