NASA Distributed Active Archive Center (DAAC) at NSIDC

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

Data from Defense Meteorological Satellite Program (DMSP) Sensors

Total Ice-Covered Area and Extent

NSIDC distributes several data sets for ice-covered area and extent. Along with one historical data set from the Electrically Scanning Microwave Radiometer (ESMR), these data sets are derived from the Scanning Multichannel Microwave Radiometer (SMMR), the Special Sensor Microwave/Imager (SSM/I), and the Special Sensor Microwave Imager/Sounder (SSMIS). The data sets are computed using the NASA Team and Bootstrap algorithms, and are provided by the NASA Goddard Space Flight Center (GSFC). See the Sea Ice Data Frequently Asked Questions page for more information about the differences between the algorithms. This document provides information and access for each data set.

Table of Contents


Regional Graphs: Time-Series Plots

The regional graphs show monthly time-series plots of ice-covered area, 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). Region masks for this data set are available on the Polar Stereographic Data Masks and Overlays page.

Table 1 lists the Arctic regions covered by this data set along with their abbreviations found in the data files. Table 2 lists the Antarctic regions covered by this data set along with their abbreviations found in the data files.
 

Table 1. 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 2. 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

To see the time-series plots of area, area anomalies, extent, and extent anomalies for each region, click on the region names in the maps in Figures 1 and 2. To see graphs for an entire area, click on the Total Arctic or Total Antarctic links below.
 

Total Arctic

   

Total Antarctic

Figure 1. Northern Regions     Figure 2. Southern Regions
Northern sea ice regions     Antarctic sea ice regions

 


Sea of Okhotsk and Japan Bering Sea Arctic Ocean Canadian Archipelago Baffin Bay/Davis Strait/Labrador Sea Hudson Bay Gulf of St. Lawrence Kara and Barents Seas Greenland Sea Weddell Sea Indian Ocean Bellingshausen Sea Ross Sea Pacific Ocean

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

In computing the total ice-covered area and ice extent 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.

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.

NASA Team Algorithm Data Sets

Daily and monthly total ice-covered area and total sea ice extent data spanning the SSM/I-SSMIS record from October 1978 through the most recent processing date are provided by Don Cavalieri of the NASA Goddard Space Flight Center (GSFC) Oceans and Ice Branch, and are produced from the NASA Team Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS Passive Microwave Data.

Bootstrap Algorithm Data Sets

Daily and monthly total ice-covered area data and total sea ice extent spanning the SMMR and SSM/I-SSMIS record from October 1978 through the most recent processing date are provided by Joey Comiso of the NASA GSFC Oceans and Ice Branch, and are produced from the Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS data set.

File Descriptions

The following file descriptions pertain to both the NASA Team and Bootstrap algorithm data sets. Data are provided in two different temporal resolutions: daily and monthly.

Data Access

NASA Team Data are available via FTP.
Bootstrap Data are available via FTP.


Daily Data

Data Format

Data are in ASCII text format arranged in columns as described in Table 3.

Table 3. Column Descriptions for Daily 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 last 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; see Table 1 and Table 2 for a list of abbreviations for the column names for the Arctic and Antarctic regions, respectively.

File Naming Convention

There are two different types of daily files: ice covered area files and sea ice extent files. The files are named according to the following convention, and as described in Table 4:

gsfc.algorithm.daily.area.1978-yyyy.r
gsfc.algorithm.daily.extent.1978-yyyy.r

where:

Table 4. File Naming Convention for Daily Files
Variable Description
gsfc Indicates that this is GSFC data
algorithm Algorithm used to process the data (nasateam or bootstrap)
daily Indicates that this file contains daily data
area Indicates that this file contains ice covered area measurements
extent Indicates that this file contains sea ice extent measurements
yyyy 4-digit year (most recent year of processing)
r Region (n: Arctic, s: Antarctic)

Monthly Data

Data Format

Data are in ASCII text format arranged in columns as described in Table 5 and Table 6.

Monthly mean sea ice concentrations were used to derive monthly extents. Using monthly mean sea ice concentrations may provide a more accurate monthly ice extent since the effects of storms on the ice edge are less pronounced in the monthly mean sea ice data than in the daily sea ice data. However, this has not been verified by NSIDC.
 

Table 5. Column Descriptions for Monthly Area, Extent, and Anomaly Files
Column Description
Year 4-digit year
Mon 1-digit and 2-digit month
Ver Version number (pre: preliminary, v01: version 01)
Region The last columns of the Arctic and Antarctic monthly area, extent, and anomaly files list the total ice-covered area (km2), total sea ice extent (km2), and the difference from the mean, respectively. The columns are labeled by region; see Tables 2 and 3 for a list of abbreviations for the column names for the Arctic and Antarctic regions, respectively.

 

Table 6. Column Descriptions for Monthly Mean Files
Column Description
Mon 1-digit and 2-digit month
Region The last columns of the Arctic and Antarctic monthly mean files list the data (area or extent) averaged over the entire temporal coverage for each month. The columns are labeled by region; see Tables 2 and 3 for a list of abbreviations for the column names for the Arctic and Antarctic regions, respectively. See the Note below for more information on monthly mean files.

Missing Data and Monthly Anomalies

Periods for which there are no available data are described in Table 7.

In addition, monthly anamoly files are provided via FTP. 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 7. 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.

File Naming Convention

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. The files are named according to the following convention, and as described in Table 8:

gsfc.algorithm.month.area.1978-yyyy.r
gsfc.algorithm.month.extent.1978-yyyy.r
gsfc.algorithm.month.anomaly.area.1978-yyyy.r
gsfc.algorithm.month.anomaly.extent.1978-yyyy.r
gsfc.algorithm.month.mean.area.1978-yyyy.r
gsfc.algorithm.month.mean.extent.1978-yyyy.r

where:
 

Table 8. File Naming Convention for Monthly Files
Variable Description
gsfc Indicates that this is GSFC data
algorithm Algorithm used to process the data (nasateam or bootstrap)
month Indicates that this file contains monthly averaged data
area Indicates that this file contains ice covered area measurements
extent Indicates that this file contains sea ice extent measurements
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
mean Indicates that this file contains monthly data averaged over the entire temporal coverage for each month
yyyy 4-digit year (most recent year of processing)
r Region (n: Arctic, s: Antarctic)


Merged ESMR, SMMR, and SSM/I-SSMIS Sea Ice Extent

Daily and monthly sea ice extent summaries from 01 January 1972 to 31 December 2002 are provided for the Northern Hemisphere and 01 January 1973 to 31 December 2002 for the Southern Hemisphere.

ESMR sea ice extent values were derived from single channel brightness temperatures using a simple linear algorithm. The SMMR and SSM/I-SSMIS sea ice concentrations were derived using the NASA Team algorithm.

The temporal data gap in the satellite-derived sets were filled with supplemental data sources. In the Northern Hemisphere, the U.S. National Ice Center sea ice climatologies (Dedrick et al. 2001) were used, which were based on weekly operational sea ice charts. In the Southern Hemisphere, a weekly sea ice extent time series (Ropelewski 1983) from the U.S. National Ice Center was used. These supplemental data sets were also used to match or calibrate the three satellite-based data sets and eliminate biases between the data sets from the three sensors. See Cavalieri, Parkinson, and Vinnikov (2003) or visit the National Ice Center Web site for more information.

Note: Since supplemental data are used to create this data set, it should not be combined with the SMMR and SSM/I-SSMIS data sets described above.

Data Access

Data are available via FTP.

Data Format

Data are provided in two different temporal resolutions: daily and monthly. Data are in ASCII text format arranged in columns as described in Table 9 and Table 10 for the daily and monthly data, respectively.
 

Table 9. Column Descriptions for Merged Daily Data Files
Column No. Description
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)

 

Table 10. Column Descriptions for Merged Monthly Data Files
Column Description
Year 4-digit year
Months (last 12 columns) 3-character month abbreviation

File Naming Convention

Files are named according to the following convention, and as described in Table 11:

Daily Files: gsfc.nasateam.extent.1972-yyyy.r
Monthly Files: gsfc.nasateam.month.extent.1972-yyyy.r

where:
 

Table 11. File Naming Convention of Merged 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)
yyyy 4-digit year (most recent year of processing)
r Region (n: Arctic, s: Antarctic)


References

Comiso J. C. and F. Nishio. 2008. Trends in the Sea Ice Cover Using Enhanced and Compatible AMSR-E, SSM/I, and SMMR Data. Journal of Geophysical Research 113(C02S07), doi:10.1029/2007JC004257.

Cavalieri, D. J., and C. L. Parkinson. 2008. Antarctic Sea Ice Variability and Trends, 1979–2006. J. Geophys. Res. 113(C07004). doi:10.1029/2007JC004564.

Cavalieri, D. J., C. L. Parkinson, and K. Y. Vinnikov. 2003. 30-Year Satellite Record Reveals Contrasting Arctic and Antarctic Decadal Sea Ice Variability. Geophysical Research Letters 30(18), doi:10.1029/2003GL018031.

Comiso, J. C. et al. 1997. Passive Microwave Algorithms for Sea Ice Concentration: A Comparison of Two Techniques. Remote Sensing of the Environment 60(3).

Dedrick, K. R., K. Partington, M. Van Woert, C. A. Bertoia, and D. Benner. 2001. U.S. National/Navy Ice Center Digital Sea Ice Data and Climatology. Canadian Journal of Remote Sensing 27: 457-475.

Parkinson C. L. and J. C. Comiso. 2008. Antarctic Sea Ice Parameters from AMSR-E Data Using Two Techniques and Comparisons with Sea Ice from SSM/I. Journal of Geophysical Research 113(C02S06), doi:10.1029/2007JC004253.

Parkinson, C. L. and Cavalieri, D. J. 2012. Antarctic Sea Ice Variability and Trends, 1979–2010. The Cryosphere Discuss. 6:931-956. doi:10.5194/tcd-6-931-2012.

Parkinson, C. L., D. J. Cavalieri, P. Gloersen, H. J. Zwally, and J. C. Comiso.1999. Arctic Sea Ice Extents, Areas, and Trends. 1978–1996. J. Geophys. Res.104(C9):20837–20856. doi:10.1029/1999JC900082.

Ropelewski, C. F. 1983. Spatial and Temporal Variations in Antarctic Sea Ice (1973-82). Journal of Climate and Applied Meteorology 22: 470-473.