Reprocessed Sea Ice Concentration

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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.

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. Both the SMMR and SSM/I datasets from October 1978 to December 2007 for both hemispheres has been processed using a sea ice concentration algorithm and methodology which is consistent for all 7 sensors (see table below). The first version the global sea ice concentration dataset was complete in 2010. Updates are planned with current satellites.

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 Start End

Nimbus 7 SMMR October 1978 August 1987

DMSP F8 June 1987 December 1991

DMSP F11 December 1991 May 2000

DMSP F13 March 1995 Operational at the end of 2007

DMSP F14 May 1997 Operational at the end of 2007

DMSP F15 December 1999 Operational at the end of 2007

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/v1.

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.

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 1978-2007 (v1, 2010), [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.

Updated August 30. 2010 - Webmaster Steinar Eastwood