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Reprocessed global sea ice concentration

Sea ice is a part of our changing climate system. Continuous monitoring of sea ice globally on a daily basis started with the launch of SeaSat in June 1978 and October the same year Nimbus 7 both with a SMMR instrument on board. SMMR was the first multi frequency and dual polarization microwave radiometer satellite instrument which was particularly well suited for sea ice monitoring. American satellite microwave radiometer instruments still provide sea ice observations today in an unbroken record since 1978. The Nimbus 7 SMMR brightness temperature data from October 1978 to August 1987 was provided by out partner in the project, NSIDC. EUMETSAT purchased the DMSP SSM/I data from Remote Sensing Systems. SSMIS data have been collected from the operational data stream from NOAA via EUMETCast.

EUMETSAT initiated the reprocessing of both microwave radiometer datasets in 2005 and the OSI SAF team developed a new processing chain and selected new algorithms. The initial development havs been done in cooperation with the Met Office and NSIDC. Further development is ongoing. The SMMR, SSM/I and SSMIS datasets from October 1978 to April 2015 for both hemispheres have been processed using a sea ice concentration algorithm and methodology which is consistent for all 7 sensors (see table below). The global sea ice concentration dataset v1 was available in 2010, version 1.1 in late 2011 and version 1.2 in June 2015.

Version 1.2 is an extension in time of version 1.1, adding the period from October 2009 to April 2015. There is no change in the algorithms or processing chain used. Specifically, no results from the ESA CCI Sea Ice project has been applied to this version of the reprocessed data set. The next full OSI SAF reprocessing in late 2016 will include research results from the ESA CCI Sea Ice project.

This sea ice product is freely available for download on this page together with the documentation and validation report (see details below).

The following sensors have been used for producing the sea ice concentration dataset. The datasets start and end dates are listed below.

Satellite StartEnd
Nimbus 7 SMMR October 1978August 1987
DMSP F8 SSM/IJune 1987December 1991
DMSP F11 SSM/IDecember 1991May 2000
DMSP F13 SSM/IMarch 1995Operational at end of October 2009
DMSP F14 SSM/IMay 1997August 2008
DMSP F15 SSM/IDecember 1999January 2013
DMSP F17 SSMISJanuary 2013April 2015

Sea Ice concentration algorithm overview

Algorithm

The ice concentration algorithm is a linear combination of Comiso bootstrap in frequency mode over open water and the Bristol algorithm over ice. These two algorithms have low sensitivity to errors over their respective domains.

Atmospheric correction

Before the ice concentration estimation the measured brightness temperatures are compensated explicitly for the influence of atmospheric water vapor and water surface roughness caused by wind using ECMWF numerical weather prediction data and radiative transfer modeling. This practice is similar to the operational OSISAF ice concentration processing and minimizes the error due to these two error sources.

Error estimates

The remaining ice concentration estimate error is quantified for every data point using the tie-point variability and a model for the radiometer foot-print smearing. Tie-points are the typical signatures of ice and water used by all sea ice concentration algorithms.

Dynamical tie-points

Inter sensor differences and sensor drift is a serous issue when computing long time series intended for climate studies. In order to minimize these problems the algorithm is using dynamical tie-points adjusted to the typical signatures of ice and open water for each channel on a monthly basis.

Download data set

The sea ice concentration data set can be downloaded at this anonymous FTP server:

ftp://osisaf.met.no/reprocessed/ice/conc/v1p2.

Data set history

  • version 1.0: Released in March 2010, covered October 1978-2007. Had bug in uncertainty estimates.
  • version 1.1: Released in November 2011, covers October 1978-October 2009, labelled OSI-409. Bug in uncertainty estimates fixed.
  • version 1.2: Released in June 2015, covers October 1978-April 2015. Extended period with Oct 2009-Apr 2015 (labelled OSI-409-a), products from 1978 to Oct 2009 are the same as v1p1 (OSI-409).

Validation

The sea ice concentration data has been compared to National Ice Center ice charts from both northern and southern hemisphere. In general the ice charts have higher ice concentrations than the OSISAF product. However, there is no trend from year to year.

Documentation

More technical details about the data set can be found in the Product User Manual and the Algorithm Theoretical Basis Document.

Validation results can be found in the Validation Report.

Quicklooks

Quicklook of the reprocessed data can be found here:

Quicklooks, single day
Quicklooks, compare two days.

Reference

Users of this data set should acknowledge the data set by using this reference:

EUMETSAT Ocean and Sea Ice Satelitte Application Facility. Global sea ice concentration reprocessing dataset 1978-2015 (v1.2, 2015), [Online]. Norwegian and Danish Meteorological Institutes. Available from http://osisaf.met.no.

Registration

We ask all users to register at our central web site. By doing so, you can chose to get service messages about sea ice products, and we will be able to serve you better. We will also be able to better report on the use of our products. So please register at this site if you are not already registered.

Contact

Contact person for the OSI SAF Reprocessed Sea Ice Concentration products is Steinar Eastwood, met.no, osisaf-manager[at]met.no.
   
       
     

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