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NSIDC distributes several products for ice-covered area and extent. These products are derived from different original data (ESMR, SMMR, and/or SSM/I data) and use different algorithms (NASA Team or Bootstrap). Some products are produced at NSIDC; some products are provided by the NASA Goddard Space Flight Center (GSFC). See the Sea Ice Products Frequently Asked Questions page for more information about the differences between the algorithms and products. See the descriptions on this page for information about each product, and to access the data on NSIDC's FTP site. Click one of the links below to jump to a description:
Regional Graphs |
The NSIDC SSM/I and GSFC products are updated regularly. The processing dates for these products are:
| Source | Algorithm | Dates |
| NSIDC | NASA Team | July 1987 through December 2005 |
| Bootstrap | July 1987 through December 2005 | |
| GSFC | NASA Team | October 1978 through December 2004 |
| Bootstrap | October 1978 through December 2004 |
Click on the region names in the maps below to see graphs of area, area anomalies, extent, and extent anomalies for each region, or click on the Total Arctic or Total Antarctic links to see graphs for an entire area.
North |
South |
NSIDC computes daily and monthly total sea ice extent and ice-covered areas, to support investigations of interannual variability and trends in sea ice cover. These summaries are derived from NSIDC's DMSP SSM/I Daily and Monthly Polar Gridded Sea Ice Concentrations, and will be updated as data become available (see Processing Dates).
Daily Summaries
| Bootstrap algorithm | FTP Data |
| NASA Team algorithm | FTP Data |
File names are as follows:
nsidc.bootstrap.extent.1987-yyyy.n
nsidc.bootstrap.extent.1987-yyyy.s
nsidc.nasateam.extent.1987-yyyy.n
nsidc.nasateam.extent.1987-yyyy.s
where:
yyyy is the most recent year of processing,
the n file extension represents the Arctic, and
the s file extension represents the Antarctic.
Data are in ASCII text format, with columns for daily file name, total ice-covered area (km2), total number of pixels with at least 15% ice, and total ice extent (km2). The "browse" directory contains graphs of ice extent, area, and anomalies in GIF and Portable Network Graphics (PNG) image formats. These are the same graphs as shown when following links to regional summaries in the above map.
In computing total ice-covered area and ice extent, pixels must have an ice concentration of 15% or greater to be included; thus, total ice extent is computed by summing the total number of pixels with at least 15% ice concentration multiplied by the area per pixel. Total ice-covered area is defined as the area of each pixel with at least 15% ice concentration, multiplied by the ice fraction in the pixel (0.15-1.00). Total sea ice extent and area in the Arctic and Antarctic are computed for each day that contains data.
Monthly Summaries
Monthly mean ice extent and area are also provided. Monthly mean ice concentration files were used to generate the data for each region. A land mask was extended by two pixels and applied to the ice concentration data. Sea ice concentrations at the pole are assumed to be 100%, even though the SSM/I instrument does not view the poles. Values of ice extent and area will differ from those in Daily and Monthly Total Sea Ice Extent and Total Ice-Covered Area from GSFC since an expanded land mask was used to eliminate false ice along the coasts.
| Bootstrap algorithm | FTP Data |
| NASA Team algorithm | FTP Data |
File names are as follows:
nsidc.bootstap.month.area.1987-yyyy.n
nsidc.bootstap.month.area.1987-yyyy.s
nsidc.bootstap.month.extent.1987-yyyy.n
nsidc.bootstap.month.extent.1987-yyyy.s
nsidc.nasateam.month.area.1987-yyyy.n
nsidc.nasateam.month.area.1987-yyyy.s
nsidc.nasateam.month.extent.1987-yyyy.n
nsidc.nasateam.month.extent.1987-yyyy.s
where:
yyyy is the most recent year of processing,
the n file extension represents the Arctic, and
the s file extension represents the Antarctic.
Monthly Anomalies
Monthly anomalies of ice extent and ice-covered area are calculated for each hemisphere. These anomalies show the deviations from the mean monthly values averaged over the entire time series. Anomalies are computed from the monthly mean values for July 1987 through the most recent processing date (see Processing Dates).
| Bootstrap algorithm | FTP Data |
| NASA Team algorithm | FTP Data |
File names are as follows:
nsidc.bootstrap.area.anomalies.1987-yyyy.n
nsidc.bootstrap.area.anomalies.1987-yyyy.s
nsidc.bootstrap.extent.anomalies.1987-yyyy.n
nsidc.bootstrap.extent.anomalies.1987-yyyy.s
nsidc.nasateam.area.anomalies.1987-yyyy.n
nsidc.nasateam.area.anomalies.1987-yyyy.s
nsidc.nasateam.extent.anomalies.1987-yyyy.n
nsidc.nasateam.extent.anomalies.1987-yyyy.s
where:
yyyy is the most recent year of processing,
the n file extension represents the Arctic, and
the s file extension represents the Antarctic.
Data are in ASCII text format. Columns represent year-month, ice-covered area anomaly (km2), and ice extent anomaly (km2).
Daily and monthly total sea ice extent and total ice-covered area data spanning the SMMR-SSM/I record through the most recent processing date (see Processing Dates), were provided by Don Cavalieri of the NASA Goddard Space Flight Center, Oceans and Ice Branch, and produced from the Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data. In computing the total ice-covered area and ice extent, pixels must have an ice concentration of 15% or greater to be included; thus, total ice extent is computed by summing the number of pixels with at least 15% ice concentration multiplied by the area per pixel. Total ice-covered area is defined as the area of each pixel with at least 15% ice concentration multiplied by the ice fraction in the pixel (0.15-1.00). Sea ice concentrations at the pole are assumed to be 100%, even though the SMMR and SSM/I instruments do not view the poles.
Daily Summaries
| FTP Data |
File names are as follows:
gsfc.nasateam.area.1978-yyyy.n
gsfc.nasateam.area.1978-yyyy.s
gsfc.nasateam.extent.1978-yyyy.n
gsfc.nasateam.extent.1978-yyyy.s
where:
yyyy is the most recent year of processing,
the n file extension represents the Arctic, and
the s file extension represents the Antarctic.
Data are in ASCII text format, with columns for year, day, and total ice extent by region (in km2). Daily ice-covered area file columns represent year, day, and total ice-covered area (in km2) by region.
Monthly Summaries
Mean monthly values are computed by averaging the daily values in each month. Sea ice data are missing for some days in October 1978, December 1987, and January 1988; therefore, in these months, mean monthly values are given, but the values do not represent "true" monthly means since the sea ice data are incomplete.
| FTP Data |
File names are as follows:
gsfc.nasateam.month.area.1978-yyyy.n
gsfc.nasateam.month.area.1978-yyyy.s
gsfc.nasateam.month.extent.1978-yyyy.n
gsfc.nasateam.month.extent.1978-yyyy.s
where:
yyyy is the most recent year of processing,
the n file extension represents the Arctic, and
the s file extension represents the Antarctic.
Data are in ASCII text format. Columns include year, month, and total ice extent or ice-covered area (in km2) by region.
Daily Summaries
Daily and monthly total sea ice extent and ice covered area data, spanning the SMMR-SSM/I record through the most recent processing date (see Processing Dates), were provided by Joey Comiso of the NASA Goddard Space Flight Center, Oceans and Ice Branch and produced from the Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I data set. Data are provided as ASCII text tables. In computing the total ice-covered area and ice extent, pixels must have an ice concentration of 15% or greater to be included; thus, total ice-covered area is defined as the area of each pixel with at least 15% ice concentration multiplied by the ice fraction in the pixel (0.15-1.00). Total ice extent is computed by summing the number of pixels with at least 15% ice concentration multiplied by the area per pixel. Sea ice concentrations at the pole are assumed to be 100%, even though the SMMR and SSM/I instruments do not view the poles.
| FTP Data |
gsfc.bootstrap.area.1978-yyyy.n
gsfc.bootstrap.area.1978-yyyy.s
gsfc.bootstrap.extent.1978-yyyy.n
gsfc.bootstrap.extent.1978-yyyy.s
where:
yyyy is the most recent year of processing,
the n file extension represents the Arctic, and
the s file extension represents the Antarctic.
Data are in ASCII text format, with columns for year, day, and total ice extent by region (in km2). Daily ice-covered area file columns represent year, day, and total ice-covered area (in km2) by region.
Monthly Summaries
Monthly mean sea ice concentrations were used to derive monthly extents, rather than averaging daily data. According to Comiso, 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. This has not been verified by NSIDC.
| FTP Data |
gsfc.bootstrap.month.area.1978-yyyy.n
gsfc.bootstrap.month.area.1978-yyyy.s
gsfc.bootstrap.month.extent.1978-yyyy.n
gsfc.bootstrap.month.extent.1978-yyyy.s
where:
yyyy is the most recent year of processing,
the n file extension represents the Arctic, and
the s file extension represents the Antarctic.
Data are in ASCII text format. Columns include year, month, and total ice extent or ice-covered area (in km2) by region.
Monthly Anomalies
Monthly anomalies of ice extent and ice-covered area 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 (November 1978 through the most recent processing date; see Processing Dates).
| FTP Data |
gsfc.bootstrap.area.anomalies.1987-yyyy.n
gsfc.bootstrap.area.anomalies.1987-yyyy.s
gsfc.bootstrap.extent.anomalies.1987-yyyy.n
gsfc.bootstrap.extent.anomalies.1987-yyyy.s
where:
yyyy is the most recent year of processing,
the n file extension represents the Arctic, and
the s file extension represents the Antarctic.
Data are in ASCII text format. Columns represent year-month, ice-covered area anomaly (km2), and ice extent anomaly (km2).
Daily and monthly sea ice extent summaries from 01 January 1972 to 31 December 2002 are provided for the Northern Hemisphere and 01 January 1 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 sea ice concentrations were derived using the NASA Team algorithm. The temporal data gap in the satellite-derived sets were filled in 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" between the three satellite-based products and eliminate biases between the products from the three sensors. See Cavalieri, Parkinson, and Vinnikov (2003) or visit the National Ice Center Web site for more information.
| FTP Data |
gsfc.nasateam.extent.1972-2002.n
gsfc.nasateam.extent.1973-2002.s
gsfc.nasateam.month.extent.1972-2002.n
gsfc.nasateam.month.extent.1973-2002.s
where:
the n file extension represents the Arctic, and
the s file extension represents the Antarctic.
Data are in ASCII text format. Columns in daily files are year (yyyy), month (mm), day (dd), Julian day (ddd), and observed/interpolated sea ice extent (106 km2).
References:
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), 1970, doi: 10.1029/2003GL018031.
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.
Ropelewski, C.F. 1983. Spatial and temporal variations
in Antarctic sea ice (1973-82). Journal of Climate and Applied
Meteorology 22: 470-473.
http://www.natice.noaa.gov/PUB/Archive/antarctic/
