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A new global sea ice concentration climate data record

OSI-450 is the second major version of the OSI SAF Global Sea Ice Concentration Climate Data Record (SIC CDR v2.0). The first version was called OSI-409, and was initiated in 2006 through visiting scientist activities with the UK Met Office (Stark, 2008) and NSIDC (Meier, 2008). OSI-409 was extended at several occasions, using operational SSMIS and ECMWF data after 2009, but keeping the algorithms and processing chains unchanged. It is described in Tonboe et al. 2016. A table reports an overview of the main differences and similarities between OSI-450 and OSI-409.

OSI-450 is a full reprocessing of sea ice concentration, with improved algorithms and an upgraded processing chain, covering the period 1979 to 2015. The sea ice concentration is computed from the SMMR (1979-1987), SSM/I (1987-2008), and SSMIS (2006-2015) instruments, as well as ECMWF ERA-Interim data (Dee et al., 2011).

The basic principles and methodologies that were the backbone of OSI-409 are also on board OSI-450 (e.g. atmospheric correction of brightness temperature with NWP re-analysis data, dynamic tie-points, uncertainties, etc.) but they were all revisited through dedicated R&D in the OSISAF project and, notably, through the ESA CCI Sea Ice projects, whose contribution is acknowledged.

Input data

The SMMR, SSM/I, and SSMIS data are all from the Fundamental Climate Data Record (FCDR) V3 (2016) from the EUMETSAT Climate Monitoring Satellite Application Facility (CM-SAF, DOI: 10.5676/EUM_SAF_CM/FCDR_MWI/V003).
The table below lists the satellite platforms used in OSI-450:
Satellite StartEnd
Nimbus 7 SMMR January 1979August 1987
DMSP F8 SSM/IJuly 1987December 1991
DMSP F10 SSM/IJanuary 1991November 1997
DMSP F11 SSM/IJanuary 1992December 1999
DMSP F13 SSM/IMarch 1995December 2008
DMSP F14 SSM/IMay 1997August 2008
DMSP F15 SSM/IFebruary 2000July 2006
DMSP F16 SSMISNovember 2005December 2013
DMSP F17 SSMISDecember 2006December 2015
DMSP F18 SSMISMarch 2010December 2015

OSI-450 (like OSI-409) use all DMSP platforms (for SSM/I and SSMIS instruments) available at any time, taking advantage of the overlap of satellite missions. This strategy greatly reduces the occurrence of missing data in the final sea ice concentration fields.

OSI-450 also use the global 3-hourly fields from ECMWF's ERA-Interim (Dee et al., 2011), which are accessed from the MARS archive. The following prognostic variables are taken from the ERA-Interim files and collocated with satellite swath data: wind speed, 2m air temperature, and total column water vapour. They are used for RTM-based corrections of the brightness temperatures.

More details are available from the PUM and the ATBD.

Algorithms and processing schemes

The processing steps can be divided in three main steps; Level 1 and 2, Level 3 and Level 4. An overview of these three steps is shown in the figure below, and the scope of each step is presented in full details in the ATBD.

OSI-450 processing chain
The three main processing elements in the ice concentration processing chain. The processing is the same for all three data inputs; SMMR, SSM/I and SSMIS.

File format and content

The dataset is a collection of netCDF files with daily sea ice concentration products. There are separate files for the Northern Hemisphere and Southern Hemisphere grids.

Each file contains six variables (in addition to latitude, longitude, time, and other CF- related information):

  • main (filtered) sea ice concentration (ice_conc)
  • raw sea ice concentration values (raw_ice_conc_values)
  • total uncertainty (total_standard_error)
  • smearing uncertainty (smearing_standard error)
  • algorithm uncertainty (algorithm_standard_error)
  • status flag (status_flag)

All are netCDF-4 CLASSIC MODEL files, following the netCDF Climate and Forecast (CF) conventions for data layers, and the Attribute Convention for Data Discovery (ACDD) convention for metadata.

Download data set

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

ftp://osisaf.met.no/reprocessed/ice/conc/v2p0.

The files are also served by a number of other protocols (THREDDS, OpenDap, WMS,...) here:

http://thredds.met.no/thredds/osisaf/osisaf_cdrseaiceconc.html.

Before you access the files, please note below the section about user registration.

Data set history

  • version 2.0: Released in Mai 2017, covers 1979-2015.

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

Quicklooks can be viewed in a browser tool. The tool can also be used to compare sea ice at two different dates in the data record, or compare sea ice in the new data record to that in the old data record. See this link.

Quicklooks can also be viewed and downloaded one file at a time from the ftp server:

  • grey scales quicklooks here
  • colors quicklooks here

Reference

EUMETSAT Ocean and Sea Ice Satellite Application Facility. Global sea ice concentration climate data record 1979-2015 (v2.0, 2017), [Online]. Norwegian and Danish Meteorological Institutes. doi: 10.15770/EUM_SAF_OSI_0008

Registration

We invite all users to register at our central web site www.osi-saf.org. By doing so, you can choose 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.

Contact

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

Associated ESA CCI data record from AMSR-E and AMSR2 data

A global sea ice concentration dataset is released by the ESA CCI Sea Ice project (http://esa-seaice-cci.org). It uses the same algorithms (and processing chain) as OSI-450, but processes the AMSR-E (2002-2011) and AMSR2 (2012-onwards) satellite sensors. Prospective users are invited to visit the ESA CCI Data Portal to access the data.
   
       
     

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