Spatial Correlation Length Scales of Sea-Ice Concentration Errors for High-Concentration Pack Ice

The European Organisation for the Exploitation of Meteorological Satellites-Ocean and Sea Ice Satellite Application Facility–European Space Agency-Climate Change Initiative (EUMETSAT-OSISAF–ESA-CCI) Level-4 sea-ice concentration (SIC) climate data records (CDRs), named SICCI-25km, SICCI-50km and OSI...

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Autor principal:	Stefan Kern
Formato:	article
Lenguaje:	EN
Publicado:	MDPI AG 2021
Materias:	sea-ice concentration satellite microwave radiometry retrieval error bias high-concentration pack ice correlation length scale Science Q
Acceso en línea:	https://doaj.org/article/a4a391dffbe34cd2922e91bdd405b752
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spelling	oai:doaj.org-article:a4a391dffbe34cd2922e91bdd405b7522021-11-11T18:56:26ZSpatial Correlation Length Scales of Sea-Ice Concentration Errors for High-Concentration Pack Ice10.3390/rs132144212072-4292https://doaj.org/article/a4a391dffbe34cd2922e91bdd405b7522021-11-01T00:00:00Zhttps://www.mdpi.com/2072-4292/13/21/4421https://doaj.org/toc/2072-4292The European Organisation for the Exploitation of Meteorological Satellites-Ocean and Sea Ice Satellite Application Facility–European Space Agency-Climate Change Initiative (EUMETSAT-OSISAF–ESA-CCI) Level-4 sea-ice concentration (SIC) climate data records (CDRs), named SICCI-25km, SICCI-50km and OSI-450, provide gridded SIC error estimates in addition to SIC. These error estimates, called total error henceforth, comprise a random, uncorrelated error contribution from retrieval and sensor noise, <i>aka</i> the algorithm standard error, and a locally-to-regionally correlated contribution from gridding and averaging Level-2 SIC into the Level-4 SIC CDRs, <i>aka</i> the representativity error. However, these CDRs do not yet provide an error covariance matrix. Therefore, correlation scales of these error contributions and the total error in particular are unknown. In addition, larger-scale SIC errors due to, e.g., unaccounted weather influence or mismatch between the actual ice type and the algorithm setup are neither well represented by the total error, nor are their correlation scales known for these CDRs. In this study, I attempt to contribute to filling this knowledge gap by deriving spatial correlation length scales for the total error and the large-scale SIC error for high-concentration pack ice. For every grid cell with >90% SIC, I derive circular one-point correlation maps of 1000 km radius by computing the cross-correlation between the central 31-day time series of the errors and all other 31-day error time series within that circular area (disc) with 1000 km radius. I approximate the observed decrease in the correlation away from the disc’s center with an exponential function that best fits this decrease and thereby obtain the correlation length scale <i>L</i> sought. With this approach, I derive <i>L</i> separately for the total error and the large-scale SIC error for every high-concentration grid cell, and map, present and discuss these for the Arctic and the Southern Ocean for the year 2010 for the above-mentioned products. I find correlation length scales are substantially smaller for the total error, mostly below ~200 km, than the SIC error, ~200 km to ~700 km, in both hemispheres. I observe considerable spatiotemporal variability of the SIC error correlation length scales in both hemispheres and provide first directions to explain these. For SICCI-50km, I present the first evidence of the method’s robustness for other years and time series of <i>L</i> for 2003–2010.Stefan KernMDPI AGarticlesea-ice concentrationsatellite microwave radiometryretrieval errorbiashigh-concentration pack icecorrelation length scaleScienceQENRemote Sensing, Vol 13, Iss 4421, p 4421 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	sea-ice concentration satellite microwave radiometry retrieval error bias high-concentration pack ice correlation length scale Science Q
spellingShingle	sea-ice concentration satellite microwave radiometry retrieval error bias high-concentration pack ice correlation length scale Science Q Stefan Kern Spatial Correlation Length Scales of Sea-Ice Concentration Errors for High-Concentration Pack Ice
description	The European Organisation for the Exploitation of Meteorological Satellites-Ocean and Sea Ice Satellite Application Facility–European Space Agency-Climate Change Initiative (EUMETSAT-OSISAF–ESA-CCI) Level-4 sea-ice concentration (SIC) climate data records (CDRs), named SICCI-25km, SICCI-50km and OSI-450, provide gridded SIC error estimates in addition to SIC. These error estimates, called total error henceforth, comprise a random, uncorrelated error contribution from retrieval and sensor noise, <i>aka</i> the algorithm standard error, and a locally-to-regionally correlated contribution from gridding and averaging Level-2 SIC into the Level-4 SIC CDRs, <i>aka</i> the representativity error. However, these CDRs do not yet provide an error covariance matrix. Therefore, correlation scales of these error contributions and the total error in particular are unknown. In addition, larger-scale SIC errors due to, e.g., unaccounted weather influence or mismatch between the actual ice type and the algorithm setup are neither well represented by the total error, nor are their correlation scales known for these CDRs. In this study, I attempt to contribute to filling this knowledge gap by deriving spatial correlation length scales for the total error and the large-scale SIC error for high-concentration pack ice. For every grid cell with >90% SIC, I derive circular one-point correlation maps of 1000 km radius by computing the cross-correlation between the central 31-day time series of the errors and all other 31-day error time series within that circular area (disc) with 1000 km radius. I approximate the observed decrease in the correlation away from the disc’s center with an exponential function that best fits this decrease and thereby obtain the correlation length scale <i>L</i> sought. With this approach, I derive <i>L</i> separately for the total error and the large-scale SIC error for every high-concentration grid cell, and map, present and discuss these for the Arctic and the Southern Ocean for the year 2010 for the above-mentioned products. I find correlation length scales are substantially smaller for the total error, mostly below ~200 km, than the SIC error, ~200 km to ~700 km, in both hemispheres. I observe considerable spatiotemporal variability of the SIC error correlation length scales in both hemispheres and provide first directions to explain these. For SICCI-50km, I present the first evidence of the method’s robustness for other years and time series of <i>L</i> for 2003–2010.
format	article
author	Stefan Kern
author_facet	Stefan Kern
author_sort	Stefan Kern
title	Spatial Correlation Length Scales of Sea-Ice Concentration Errors for High-Concentration Pack Ice
title_short	Spatial Correlation Length Scales of Sea-Ice Concentration Errors for High-Concentration Pack Ice
title_full	Spatial Correlation Length Scales of Sea-Ice Concentration Errors for High-Concentration Pack Ice
title_fullStr	Spatial Correlation Length Scales of Sea-Ice Concentration Errors for High-Concentration Pack Ice
title_full_unstemmed	Spatial Correlation Length Scales of Sea-Ice Concentration Errors for High-Concentration Pack Ice
title_sort	spatial correlation length scales of sea-ice concentration errors for high-concentration pack ice
publisher	MDPI AG
publishDate	2021
url	https://doaj.org/article/a4a391dffbe34cd2922e91bdd405b752
work_keys_str_mv	AT stefankern spatialcorrelationlengthscalesofseaiceconcentrationerrorsforhighconcentrationpackice
_version_	1718431663966388224

Spatial Correlation Length Scales of Sea-Ice Concentration Errors for High-Concentration Pack Ice

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