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Data Set ID:
NSIDC-0192

Sea Ice Trends and Climatologies from SMMR and SSM/I-SSMIS, Version 1

NSIDC provides a suite of value-added data sets to aid in investigations of the variability and trends of sea ice cover. These data sets provide users with information about sea ice extent, total ice-covered area, ice persistence, monthly climatologies of sea ice concentrations, and ocean masks. The maps are in ArcInfo export file format. All other data sets are in flat binary or ASCII format with accompanying Portable Network Graphics (PNG) browse images. Products are derived from Nimbus-7 SMMR; DMSP-F8, -F11, and -F13 SSM/I; and from DMSP-F17 SSMIS sea ice concentrations at a grid cell size of 25 x 25 km. Data begin in October 1978 and processing is ongoing.

Geographic Coverage

Spatial Coverage:
  • N: -39.23, S: -90, E: 180, W: -180

  • N: 90, S: 30.98, E: 180, W: -180

Spatial Resolution:
  • 25 km x 25 km
Temporal Coverage:
  • 26 October 1978 to 31 December 2013
Temporal Resolution: Not specified
Parameter(s):
  • Sea Ice > Ice Extent
  • Sea Ice > Sea Ice Concentration
Platform(s) DMSP 5D-2/F11, DMSP 5D-2/F13, DMSP 5D-2/F15, DMSP 5D-2/F8, DMSP 5D-3/F17, NIMBUS-5, NIMBUS-7
Sensor(s): ESMR, SMMR, SSM/I, SSMIS
Data Format(s):
  • Binary
  • PNG
  • JPEG
  • ASCII Text
Version: V1
Data Contributor(s): Julienne Stroeve, Walt Meier

Data Citation

As a condition of using these data, you must cite the use of this data set using the following citation. For more information, see our Use and Copyright Web page.

Stroeve, J. 2003. Sea Ice Trends and Climatologies from SMMR and SSM/I-SSMIS, Version 1. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: http://dx.doi.org/10.5067/C2HMG48G83QQ. [Date Accessed].

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Detailed Data Description

NSIDC provides this data set to aid in the investigations of the variability and trends of sea ice cover. This data set provides users with data about total ice-covered areas, sea ice extent, ice persistence, and monthly climatologies of sea ice concentrations. All data are derived from the Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS data set and/or the NASA Team Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS Passive Microwave Data data set. Polar Stereographic Valid Ice Masks Derived from National Ice Center Monthly Sea Ice Climatologies are also used in the processing to remove spurious ice caused by residual weather effects and land spillover in passive microwave data.

Total Ice-Covered Areas and Sea Ice Extent Data

Along with one historical data file from the Electrically Scanning Microwave Radiometer (ESMR), these data are derived from the Scanning Multichannel Microwave Radiometer (SMMR), the Special Sensor Microwave/Imager (SSM/I), and the Special Sensor Microwave Imager/Sounder (SSMIS).

Daily and Monthly Total Ice-Covered Area and Total Sea Ice Extent Data

Daily Arctic and Antarctic ice-covered area and total sea ice extent ASCII text data files list the total ice-covered area (km2) and total sea ice extent (km2) for both the NASA Team and Bootstrap algorithms.

Monthly mean sea ice concentrations were used to derive monthly extents for both the NASA Team and Bootstrap algorithms. Monthly ice concentration extents are provided because they will tend to average out the effects of storms and other short-term events on the location of the ice edge. However, this has not been verified by NSIDC.

Regional Graphs: Time-Series Plots

The total ice-covered area and sea ice extent data are used to create .png images of regional graphs showing monthly time-series plots of ice-covered areas, area anomalies, ice extent, and extent anomalies for both the NASA Team and Bootstrap algorithms. The methods and sources for how these regions were geographically defined are discussed in Parkinson and Cavalieri (2012), Cavalieri and Parkinson (2008), and Parkinson et al. (1999).

Ice Persistence

Monthly climatologies of ice persistence binary data files with corresponding .png images are intended for users interested in persistence of ice over a particular month during the time series, which includes January 1979 through current processing. Ice persistence fields provide information on how frequently ice occurs in a region during a given month over the time period of the data. The ice extent climatologies are derived each month from monthly-averaged sea ice concentrations using the NASA Team data.

Monthly Climatology of Sea Ice Concentration

Monthly sea ice concentration climatology binary data files with corresponding .png images represent mean ice concentration percentages for each month over the entire time period of January 1979 through current processing. The data are derived from the NASA Team data.

Format

This data set has several data formats:

Total Ice-Covered Areas and Sea Ice Extent Data

Data are stored in ASCII text and PNG browse files.

Ice Persistence Data

Data are stored in binary two-byte integer format and PNG browse files.

Monthly Climatology of Sea Ice Concentration

Data are stored in flat binary one-byte integer format and PNG browse files.

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File and Directory Structure

Data are available on the FTP site in the ftp://sidads.colorado.edu/pub/DATASETS/nsidc0192_seaice_trends_climo/ directory. Within this directory there are three folders:

  • ice-persistence/ - contains monthly climatologies of ice persistence binary data files and a browse/ folder with corresponding .png images of ice persistence
  • monthly-climatology/ - contains monthly sea ice concentration climatology binary data files and a browse/ folder with corresponding .png images of monthly climatologies
  • total-ice-area-extent/ - contains three sub folders:
    • bootsrap/ - this folder contians ASCII text data files and a browse/ folder with .png files of regional graphs showing monthly time-series plots of ice-covered area, area anomalies, ice extent, and extent anomalies
    • esmr-smmr-ssmi-merged/ - this folder contains ASCII text data files of daily and monthly sea ice extent summaries from 01 January 1972 to 31 December 2002 for the Northern Hemisphere and 01 January 1973 to 31 December 2002 for the Southern Hemisphere
    • nasateam/ - this folder contians ASCII text data files and a browse/ folder with .png files of regional graphs showing monthly time-series plots of ice-covered area, area anomalies, ice extent, and extent anomalies
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File Naming Convention Used for Data Files

The following sections explain the file naming convention used for these data files with an example.

Ice Persistence Data Files

Example File Name: persistence.apr.1979-2013.n

persistence.mmm.yyyy1-yyyy2.h

Where:

Table 1. File Naming Convention for Ice Persistence Data Files
Variable Description
persistence Identifies this as an ice persistence data file
mmm 3-character month
yyyy1 4-digit year of the first year for which data was available
yyyy2 4-digit year of the last year for which data was available
h Hemisphere (n: Northern, s: Southern)

Monthly Climatology of Sea Ice Concentration Data Files

Example File Name: mean.apr.1979-2013.n

mean.mmm.yyyy1-yyyy2.h

Where:

Table 2. File Naming Convention for Monthly Climatology of Sea Ice Concentration Data Files
Variable Description
mean Identifies this as a mean ice concentration percentage data file
mmm 3-digit month
yyyy1 4-digit year of the first year for which data was available
yyyy2 4-digit year of the last year for which data was available
h Hemisphere (n: Northern, s: Southern)

Total Ice Area Extent Data Files

Bootstrap and Nasateam Files

This section explains the file naming convention used for these files with an example. The following file naming conventions pertain to both the NASA Team and Bootstrap algorithm data files. Data are provided in two different temporal resolutions: daily and monthly.

There are two different types of daily files: ice covered area files and sea ice extent files.

There are six different types of monthly files: ice covered area files, sea ice extent files, ice covered area anomaly files, sea ice extent anomaly files, monthly mean ice covered area files, and monthly mean sea ice extent files.

Monthly anomalies of ice-covered area and ice extent are calculated from monthly mean ice concentrations throughout the period of study. These anomalies show the deviations from the mean monthly values averaged over the entire time series.

Example File Names

gsfc.algorithm.xxxx.area.1978-yyyy.r
gsfc.algorithm.xxxx.extent.1978-yyyy.r
gsfc.algorithm.xxxx.anomaly.area.1978-yyyy.r
gsfc.algorithm.xxxx.anomaly.extent.1978-yyyy.r

gsfc.algorithm.xxxx.mean.area.1978-yyyy.r
gsfc.algorithm.xxxx.mean.extent.1978-yyyy.r

Where:

Table 3. File Naming Convention for Total Ice Area Extent Files
Variable Description
gsfc Indicates that this is GSFC data
algorithm Algorithm used to process the data (nasateam or bootstrap)
xxxx Indicates that this file is either daily or monthly
anomaly Indicates that this file contains the difference between the monthly data (area or extent) and the total monthly mean for the entire temporal coverage
area Indicates that this file contains ice covered area measurements
extent Indicates that this file contains sea ice extent measurements
1978 4-digit year of the first year for which data was available
yyyy 4-digit year (most recent year of processing)
r Region (n: Arctic, s: Antarctic)

ESMR-SMMR-SSM/I-SSMIS-Merged Sea Ice Extent Files

Data are provided in two different temporal resolutions: daily and monthly.

Example File Names
gsfc.nasateam.extent.1972-2002.n
gsfc.nasateam.month.extent.1972-2002.n

gsfc.nasateam.extent.1972-yyyy.r
gsfc.nasateam.month.extent.1972-yyyy.r

Where:

Table 4. File Naming Convention for ESMR-SMMR-SSM/I-SSMIS-Merged Sea Ice Extent Files
Variable Description
gsfc.nasateam Indicates this is GSFC data processed with the NASA Team algorithm
extent Indicates that this file contains sea ice extent measurements
month Indicates that this file contains monthly averaged data (otherwise daily)
1972 4-digit year of the first year for which data was available
yyyy 4-digit year (most recent year of processing)
r Region (n: Arctic, s: Antarctic)
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Column Header Naming Conventions Used for ASCII Text Files

Total Ice Area Extent ASCII Text File Column Header Names

Data are in ASCII text format arranged in columns as described in Table 5.

Table 5. Column Header Descriptions for Total Ice Area Extent ASCII Text Files
Column Description
Year 4-digit year
Mon 1-digit and 2-digit month
Day 1-digit and 2-digit day of month
DOY 3-digit day of year
Ver Version number (pre: preliminary, v01: version 01, v02: version 02)
Region The remaining columns of the Arctic and Antarctic daily area and daily extent files list the total ice-covered area (km2) and total sea ice extent (km2), respectively. The columns are labeled by region. Refer to Table 6 and Table 7 for a list of abbreviations for the column names for the Arctic and Antarctic regions.

Table 6 lists the Arctic regions covered by this data set along with their abbreviations found in the data files. Table 7 lists the Antarctic regions covered by this data set along with their abbreviations found in the data files.

Table 6. Arctic Regions and Abbreviations
Arctic Region Abbreviation in Data Files
Total Arctic TotalArc
Seas of Okhotsk & Japan Okhotsk
Bering Sea Bering
Hudson Bay Hudson
Baffin Bay Baffin
Greenland Sea Grnland
Kara and Barents Seas BarKara
Arctic Ocean ArctOcn
Canadian Archipelago CanArch
Gulf of St. Lawrence StLawr
Table 7. Antarctic Regions and Abbreviations
Antarctic Region Abbreviation in Data Files
Total Antarctic TotalAnt
Weddell Sea Weddell
Indian Ocean Indian
Pacific Ocean Pacific
Ross Sea Ross
Bellingshausen and Amundsen Seas BellAm

Merged ESMR-SMMR-SSMI Sea Ice Extent ASCII Text File Column Header Names

Data are in ASCII text format arranged in columns as described in Table 8 and Table 9 for the daily and monthly data.

Column No. Description
Table 8. Column Descriptions for Merged Daily Data Files
1 4-digit year
2 1-digit and 2-digit month
3 1-digit and 2-digit day of month
4 1-digit to 3-digit day of year
5 Observed/interpolated sea ice extent (106 km2)

Column Description
Table 9 Column Descriptions for Merged Monthly Data Files
Year 4-digit year
Months (remaining 12 columns) 3-character month abbreviation
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File Size
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Volume
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Spatial Coverage

N: -39.23, S: -90, E: 180, W: -180
N: 90, S: 30.98, E: 180, W: -180

Spatial Resolution

25 km x 25 km

Projection Description

Polar Stereo

Grid Description

For the Northern Hemisphere, the grid size is 304 x 448 pixels.

For the Southern Hemisphere, the grid size is 316 x 332 pixels.

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Temporal Coverage

26 October 1978 to 31 December 2013

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Parameter or Variable

Sea Ice Extent
Sea Ice Concentration

total ice-covered area (km2)
total sea ice extent (km2)

Parameter Description

Ice Persistence

Land is set to a value of 254 and coastlines to a value of 253.

Monthly Climatology of Sea Ice Concentration

97 means 97 percent sea ice concentration.

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Software and Tools

Map Tool

To see the time-series plots of an area, area anomalies, extent, and extent anomalies for each region, click on the colored region area in the maps in Figures 1 and 2. Do not click on the region name because the link won't work then.

To see graphs for an entire area, click on the Total Arctic or Total Antarctic links.

Example
Figure 1. Arctic Region Areas
Figure 2. Antarctica Region Areas
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Software and Tools
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Quality Assessment
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Data Acquisition and Processing

Theory of Measurements

There is a circular section over the Northern Hemisphere pole known as the "pole hole," which is never measured due to orbit inclination. For the purposes of ice extent, pixels under the pole hole are always considered to be at least 15 percent. For total ice-covered area, the pixels under the pole hole are not used. The Southern Hemisphere also has a pole hole, but it does not affect this sea ice data set because there is only land under this hole. For SMMR, the hole is 611 km in radius and is located poleward of 84.5 degrees North. For SSM/I and SSMIS, the hole is 311 km in radius and is located poleward of 87.2 degrees North. Note: The difference in pole hole areas between SMMR and SSM/I-SSMIS results in a discontinuity in the Northern Hemisphere ice-covered area time series across the instrument transitions.

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Data Acquisition Methods
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Derivation Techniques and Algorithms

Processing Steps

Total Ice-Covered Areas and Sea Ice Extent Data

In computing the total ice-covered area and ice extent data with both the NASA Team and Bootstrap Algorithms, pixels must have an ice concentration of 15 percent or greater to be included. Total ice-covered area is defined as the area of each pixel with at least 15 percent ice concentration multiplied by the ice fraction in the pixel (0.15 to 1.00). Total ice extent is computed by summing the number of pixels with at least 15 percent ice concentration multiplied by the area per pixel; thus, the entire area of any pixel with at least 15 percent ice concentration is considered to contribute to the total ice extent. Anomalies are the difference between the current time period's average value and the long-term average.  A positive anomaly indicates that the current period has greater extent or area than the average

Ice Persistence Data

Individual ocean pixels containing a minimum of 15 percent ice cover are summed throughout the time series. The maximum ice persistence value is 100 percent. Each pixel represents the percentage of years for which ice was present during that month. Only the NASA Team Algorithm is used to compute these data.

Monthly Climatology of Sea Ice Concentration

A threshold of 15 percent concentration is applied to the monthly climatology fields. Only the NASA Team Algorithm is used to compute these data.

Version History

Version No. Date Description
Table 10. Version Histroy Information
1 28 July 2014 Reprocessing is complete and updated data are now available through 31 December 2013 for all Sea Ice Trends and Sea Ice Trends and Climatologies from SMMR and SSM/I-SSMIS data sets.
1 04 September 2013 Reprocessing is complete and updated data are now available through 31 December 2012 for all Sea Ice Trends and Sea Ice Trends and Climatologies from SMMR and SSM/I-SSMIS data sets. With this update, the following changes have been implemented:
Total Ice-Covered Area and Extent

The cutoff value which defines a region as ice-covered or not ice-covered has been adjusted from 14.8 percent to 15 percent to more closely match the methodology used to calculate other sea ice extent and area products at NSIDC.

Ice Persistence and Monthly Climatology of Sea Ice Concentration (Monthly Means)
  • Includes the new 15 percent cutoff value described above.
  • To prevent inconsistencies between different algorithms, these parameters are now calculated exclusively using the NASA team algorithm.
Monthly Ocean Masks and Maximum Extent Masks

The ocean mask files and maximum extent mask files have been temporarily removed as they are not the masks used in the production of these data sets. NSIDC is currently standardizing masks across all sea ice products and will distribute the replacement masks as soon as they are available.

This most recent reprocessing also rectifies two previous releases of these data sets that contained erroneous data. In January/February of 2012, and May of 2013, the products were to have contained data from 2007 to 2010 and from 2010 to 2011, respectively. However, the climatology products contained data only through 2007. We recommend replacing previously downloaded 2010 and 2011 climatology data files with the climatology files that now extend through 2012. The Total Ice-Covered Area and Extent data set did contain post-2007 data, but reprocessed data utilizing the new methodology are available in the 2012 release.

Missing Data and Monthly Anomalies

Periods for which there are no available data are described in Table 11.

Monthly anomalies of ice-covered area and ice extent are calculated from monthly mean ice concentrations throughout the period of study. These anomalies show the deviations from the mean monthly values averaged over the entire time series.

Table 11. Missing Data
Time Periods Data Type Description
October 1978, December 1987 Sea ice Sea ice data are missing for most days, so monthly values are not calculated for these months.
January 1988 Sea ice January 1988 is missing data for the first half of the month. A value is given for this month, but the value may not represent true monthly mean since the sea ice data are incomplete.
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Sensor or Instrument Description
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References and Related Publications

Document Information

DOCUMENT CREATION DATE

DOCUMENT REVISION DATE

No technical references available for this data set.

How To

How to import the sea ice trends data into ArcGIS

The following are instructions describing how to import "Sea Ice Trends and Climatologies from SMMR and SSM/I-SSMIS" binary files into ArcGIS. These instructions were tested with ArcInfo 10.0.

1. Rename the Data File.

In order to be able to import a... read more