Estimation of upward radiances and reflectances at the surface of the sea from above-surface measurements

During 4 field days in the years 2009–2011, 22 data sets of measurements were collected in the inner Oslofjord, Norway. The data consist of recordings of spectral nadir radiances in air and water as well as spectral downward irradiance in air. The studied wavelengths are 351, 400, 413, 443, 490, 51...

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Main Authors: Ø. Kleiv, A. Folkestad, J. Høkedal, K. Sørensen, E. Aas
Format: Article
Language:English
Published: Copernicus Publications 2015-10-01
Series:Ocean Science
Online Access:http://www.ocean-sci.net/11/779/2015/os-11-779-2015.pdf
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spelling doaj-74c50020d5a34ceda22a2fbf6aa436972020-11-25T01:49:10ZengCopernicus PublicationsOcean Science1812-07841812-07922015-10-0111577978810.5194/os-11-779-2015Estimation of upward radiances and reflectances at the surface of the sea from above-surface measurementsØ. Kleiv0A. Folkestad1J. Høkedal2K. Sørensen3E. Aas4Norwegian Institute for Water Research, Gaustadalleen 21, 0349 Oslo, NorwayNorwegian Institute for Water Research, Gaustadalleen 21, 0349 Oslo, NorwayNarvik University College, Lodve Langes gt. 2, 8505 Narvik, NorwayNorwegian Institute for Water Research, Gaustadalleen 21, 0349 Oslo, NorwayDepartment of Geosciences, University of Oslo, Gaustadalleen 21, 0349 Oslo, NorwayDuring 4 field days in the years 2009–2011, 22 data sets of measurements were collected in the inner Oslofjord, Norway. The data consist of recordings of spectral nadir radiances in air and water as well as spectral downward irradiance in air. The studied wavelengths are 351, 400, 413, 443, 490, 510, 560, 620, 665, 681, 709 and 754 nm. <br><br> The water-leaving radiance and the reflected radiance at the sea surface have been obtained from the measured nadir radiances in air and water, where the latter radiance has been extrapolated upwards to the surface. For comparison we present a simpler and much faster method that determines the water-leaving and reflected radiances solely from above-surface measurements of upward nadir radiance and downward irradiance. This new method is based on an assumption about similarity in spectral shape of the radiance reflected at the surface, and it makes use of the small ratio between water-leaving and reflected radiances at 351 and 754 nm in the Oslofjord. <br><br> A comparison between the quantities determined by the two mentioned methods shows that the average relative deviations between their results are less than or equal to 15 % for the reflected radiance, at the studied wavelengths. The average relative deviation of the water-leaving radiance at 560 nm is 24 %. These results are obtained for a cloudiness range of 1–8 oktas (12.5–100 %) and solar zenith angles between 37 and 51°. We consider these to be acceptable uncertainties for a first check of satellite products in the inner Oslofjord.http://www.ocean-sci.net/11/779/2015/os-11-779-2015.pdf
collection DOAJ
language English
format Article
sources DOAJ
author Ø. Kleiv
A. Folkestad
J. Høkedal
K. Sørensen
E. Aas
spellingShingle Ø. Kleiv
A. Folkestad
J. Høkedal
K. Sørensen
E. Aas
Estimation of upward radiances and reflectances at the surface of the sea from above-surface measurements
Ocean Science
author_facet Ø. Kleiv
A. Folkestad
J. Høkedal
K. Sørensen
E. Aas
author_sort Ø. Kleiv
title Estimation of upward radiances and reflectances at the surface of the sea from above-surface measurements
title_short Estimation of upward radiances and reflectances at the surface of the sea from above-surface measurements
title_full Estimation of upward radiances and reflectances at the surface of the sea from above-surface measurements
title_fullStr Estimation of upward radiances and reflectances at the surface of the sea from above-surface measurements
title_full_unstemmed Estimation of upward radiances and reflectances at the surface of the sea from above-surface measurements
title_sort estimation of upward radiances and reflectances at the surface of the sea from above-surface measurements
publisher Copernicus Publications
series Ocean Science
issn 1812-0784
1812-0792
publishDate 2015-10-01
description During 4 field days in the years 2009–2011, 22 data sets of measurements were collected in the inner Oslofjord, Norway. The data consist of recordings of spectral nadir radiances in air and water as well as spectral downward irradiance in air. The studied wavelengths are 351, 400, 413, 443, 490, 510, 560, 620, 665, 681, 709 and 754 nm. <br><br> The water-leaving radiance and the reflected radiance at the sea surface have been obtained from the measured nadir radiances in air and water, where the latter radiance has been extrapolated upwards to the surface. For comparison we present a simpler and much faster method that determines the water-leaving and reflected radiances solely from above-surface measurements of upward nadir radiance and downward irradiance. This new method is based on an assumption about similarity in spectral shape of the radiance reflected at the surface, and it makes use of the small ratio between water-leaving and reflected radiances at 351 and 754 nm in the Oslofjord. <br><br> A comparison between the quantities determined by the two mentioned methods shows that the average relative deviations between their results are less than or equal to 15 % for the reflected radiance, at the studied wavelengths. The average relative deviation of the water-leaving radiance at 560 nm is 24 %. These results are obtained for a cloudiness range of 1–8 oktas (12.5–100 %) and solar zenith angles between 37 and 51°. We consider these to be acceptable uncertainties for a first check of satellite products in the inner Oslofjord.
url http://www.ocean-sci.net/11/779/2015/os-11-779-2015.pdf
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