Recurring Spring Leads and Landfast Ice in the Beaufort and Chukchi Seas, 1993-2004
Summary
In the Beaufort and Chukchi Seas, the most significant sea ice anomalies have occurred in the summer ice extent (Eicken et al. 2006). In addition, there has been a considerable decline in the multiyear ice pack in this region (Eicken et al. 2006). To help understand these anomalies, this data set contains information on recurring spring leads and landfast ice extent in this area. This data set maps and documents the spatial and temporal distribution of recurring leads and landfast ice off the coast of northern Alaska in the Chukchi and Beaufort Seas (Eicken et al. 2006). The leads data span from 1993 through 2004 and are based on visible and infrared Advanced Very High Resolution Radiometer (AVHRR) data onboard the NOAA 12, 14, 15, 16, and 17 satellites. The landfast ice extent data extend from 1996 through 2004 and are based on RADARSAT-1 Synthetic Aperture Radar (SAR) imagery. The data are available in a number of formats including ArcGIS geodatabases (the geodatabases are held in Microsoft Access files (.mdb)), shapefiles (.shp), ArcGIS grids (.adf), ArcGIS grids in ArcInfo interchange format (.e00), and GeoTIFFs (.tif). Statistics are also provided in Microsoft Excel spreadsheets (.xls) and metadata in several formats including XML (.xml), SGML (.sgml), HTML (.html), and ASCII text (.txt). Quick-view browse images in JPEG (.jpg) format are provided for the shapefiles, grids, and GeoTIFFs. Data are available via FTP.
Citing These Data
The following example shows how to cite the use of this data set in a publication. For more information, see our Use and Copyright Web page.
Eicken, H., L. Shapiro, A. G. Gaylord, A. Mahoney and P. W. Cotter. 2009. Recurring spring leads and landfast ice in the Beaufort and Chukchi Seas, 1993-2004. Boulder, Colorado USA: National Snow and Ice Data Center. http://dx.doi.org/10.7265/N5SB43P0
Overview Table
| Category | Description | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Data Format | Landfast Ice Extent
Leads
|
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| Spatial Coverage and Resolution | Beaufort and Chukchi Seas:
Northernmost Latitude: 73.957687° N AVHRR data for leads: 1.1 km resolution Refer to Figure 1 for a spatial coverage map. |
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| Temporal Coverage and Resolution |
Landfast Ice Extent
1996 - 2004 for the months October - July 1993 - 2004 for the months December - June |
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| Grid/Projection Description | Albers Conical Equal Area projection using the North American Datum of 1983 (NAD 1983) SAR data: 100 m grid cell size AVHRR data: 1.1km grid cell size |
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| Tools for Accessing Data | Geographic Information System (GIS) software Image viewing software Microsoft Excel Text editor See the Tools section for more information |
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| File Naming Convention | See the File Naming Convention section for more information. | ||||||||||||
| File Size | Zipped Files range from 100 KB to 30 MB See the File Size section for information on individual files. |
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| Parameters | Landfast Ice Extent Leads |
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| Metadata access | View metadata | ||||||||||||
| Data access | Data are available via FTP |
Table of Contents
1. Contacts
2. Detailed Data Description
3. Data Access and Tools
4. Data Acquisition and Processing
5. Related Data Collections
6. References and Related Publications
7. Acknowledgements
8. Document Information
1. Contacts
Investigators
Hajo Eicken and Lewis H. Shapiro
Geophysical Institute
University of Alaska Fairbanks
Fairbanks, AK 99775-7320
USA
Allison Graves Gaylord
Nuna Technologies
Homer, AK 99603
USA
Technical Contacts
NSIDC User Services
National Snow and Ice Data Center
CIRES, 449 UCB
University of Colorado
Boulder, CO 80309-0449 USA
phone: +1 303.492.6199
fax: +1 303.492.2468
form: Contact NSIDC User Services
e-mail: nsidc@nsidc.org
2. Detailed Data Description
Background
Recurring leads in the Beaufort and Chukchi Seas signal the deformation of the ice pack and impact the ocean-atmosphere heat exchange and polar ecosystems (Eicken et al. 2006). Landfast ice lessens the impact of coastal erosion, impacts travel and hunting for the local communities, and is utilized for oil and gas development (Mahoney et al. 2007).
In Mapping and Characterization of Recurring Spring Leads and Landfast Ice in the Beaufort and Chukchi Seas, Eicken et al. (2006) say:
The Arctic sea-ice cover has undergone significant changes in the past two decades. These changes include a reduction in summer ice extent (with four consecutive record minima attained between 2001 and 2005) as well as substantial thinning of the ice pack. The western Arctic, i.e., the Chukchi and Beaufort Seas, has seen the largest anomalies in summer ice extent, as well as a substantial reduction in the amount of multiyear ice over the Beaufort and Chukchi shelves. The present project was aimed at mapping and documenting changes in the spatial and temporal distribution of spring lead systems and landfast ice extent off the coast of northern Alaska. In addition to providing baseline data against which to evaluate further changes, the work also examined present-day conditions in relation to earlier studies conducted in the 1970s as part of the Outer Continental Shelf Environmental Assessment Project and discussed the role of different forcing mechanisms in controlling spatial and temporal patterns of variability in lead distribution and landfast ice extent (Eicken et al. 2006).
Parameters
Because of the intricacies involved with identifying landfast ice extent and leads, precise definitions of both parameters are explained below.
Landfast Ice Extent
In general, landfast ice can be defined as sea ice that is mostly stationary and attached to land. For this data set, a more specific definition is used from Mahoney et al. (2005). Specifically, landfast ice is defined as ice that is contiguous with the coast and ice that lacks detectable motion for approximately 20 days.
Leads
Leads are defined as "any fracture or passage-way through sea ice which is navigable by surface vessels" (Eicken et al. 2006). This definition is expanded using Lindsay and Rothrock (1995) to include thin ice (0.15 m to 2 m thick). The definition of leads in this data set does not discriminate between open linear leads and areas covered by thin ice.
Spatial Coverage
The majority of the study area covers the Beaufort Sea and to a lesser extent the Chukchi Sea. Specifically, the study area is off the coast of northern Alaska in the Chukchi and Beaufort Seas between Wainwright bordering the Chukchi Sea and the Mackenzie River Delta in the Canadian Beaufort Sea. Figure 1 shows the spatial coverage. Leads were examined within regions 1 through 12, and landfast ice extent identified within regions 2 through 11. The spatial coordinates of the area are listed below:
Northernmost Latitude: 73.957687° N
Southernmost Latitude: 68.482036° N
Easternmost Longitude: 129.877138° W
Westernmost Longitude: 164.080843° W
 |
Figure 1. Spatial Coverage Map of the Study Area |
Spatial Resolution
The AVHRR source data for the leads have a 1.1 km resolution.
The RADARSAT-1 SAR source data for the landfast ice extent have a 100 m resolution.
Projection
The data in this data set have been geolocated (geolocation error less than three km) and reprojected into an Albers Conical Equal Area projection with a 100 m grid cell size for SAR data and 1.1 km grid cell size for AVHRR data using the North American Datum of 1983 (NAD 1983). Following are the detailed projection and datum parameters:
| Map Projection Name: | Albers Conical Equal Area |
|---|---|
| Standard Parallel: | 55.000000 |
| Standard Parallel: | 65.000000 |
| Longitude of Central Meridian: | -154.000000 |
| Latitude of Projection Origin: | 50.000000 |
| False Easting: | 0.000000 |
| False Northing: | 0.000000 |
| Planar Coordinate Information | |
| Planar Distance Units: | Meters |
| Coordinate Encoding Method: | Coordinate pair |
| Coordinate Representation | |
| Abscissa Resolution: | 0.002048 |
| Ordinate Resolution: | 0.002048 |
| Geodetic Model | |
| Horizontal Datum Name: | North American Datum of 1983 |
| Ellipsoid Name: | Geodetic Reference System 80 |
| Semi-major Axis: | 6378137.000000 |
| Denominator of Flattening Ratio: | 298.257222 |
Temporal Coverage
Landfast Ice Extent
The landfast ice extent data span 1996 to 2004. RADARSAT-1 SAR images are acquired for the months October through July approximately every 10 days.
Leads
The lead data span 1993 to 2004. AVHRR images are acquired for the months December through June at irregular intervals. During certain years, some months (October to December) may be omitted if clouds obstructed the visible AVHRR imagery.
Data Format
This data set is distributed in a number of formats. Most files are compressed into zip files to conserve space and to bundle like files. To more easily describe the different formats and how they interrelate, the Data Format section is organized in the same way that the files are organized into directories on the FTP site. For example, on the FTP site, the data are divided into three main directories: one for landfast ice extent data, one for lead data, and one for supplemental information. Here, and in other sections of this document, the content is broken down in the same way. Follow the links below to navigate the Data Format section. For more information about the directory structure, see the Directory Structure section of this document.
The file extensions of all of the formats in this data set are listed in Table 1.
Landfast Ice Extent
The landfast ice extent data are grouped into the following four categories:
- Annual Geodatabase Files
- RADARSAT-1 SAR Imagery (Source Data)
- XML Metadata Templates
- Monthly Averages
Annual Geodatabase Files
The annual geodatabase files are GIS vectorized outlines of the seaward landfast ice edge (SLIE) for each annual ice season (for example, the 1996/1997 ice season) from the source RADARSAT-1 SAR imagery. The files are in ArcGIS geodatabase format (the geodatabases are held in Microsoft Access files (.mdb)) and have been compressed into zip files (.zip). All files reside in the landfast1996-2004/annual_geodb directory.
RADARSAT-1 SAR Imagery (Source Data)
ArcGIS Grids, shapefiles, and GeoTIFF Mosaics
These images are provided in three formats: ArcGIS grids in ArcInfo interchange format (.e00), shapefiles (.shp), and GeoTIFF mosaics (.tif). Low resolution browse images of each of these is provided in JPEG format (.jpg). The GeoTIFFs do not have the geographic information embedded in the file. This information is included in a .aux file associated with each GeoTIFF. The GeoTIFFs also have associated metadata in a .tif.xml file. Also included with each shapefile and grid are metadata files provided in a number of formats: SGML (.sgml), ASCII text (.txt), XML (.xml) and HTML (.html). Most files have been compressed together in zip files to conserve space and to bundle like files. All files reside in the landfast1996-2004/data/yyyy/mmm directories.
Note: The Canadian Space Agency holds the intellectual property and copyright permissions for the RADARSAT-1 SAR images.
Binarized GeoTIFF
The images of the landfast ice extent have also been binarized and converted to GeoTIFF format (.tif). In the images, the landfast ice extent is represented in white and the coast and open ocean are black. These GeoTIFF files do not have the geographic information embedded within the file. Instead, they are distributed with their associated world file (.tfw) which contains the geographic information. All files reside in the landfast1996-2004/data/binarized_geotiffs directory.
XML Metadata Templates
The XML metadata templates for the landfast ice extent data are four, FGDC-compliant metadata files in XML format (.xml) that provide an XML template of the metadata for four different types of landfast data files. The XML files reside in the landfast1996-2004/metadata_templates directory and are explained in Table 2.
| XML File | Description |
|---|---|
| monthyavg_slie_shape_templ.xml | XML template for the landfast monthly averaged shapefiles (max_mmshape.zip files in the landfast1996-2004/monthly_averages directory) |
| radarsat_template.xml | XML template for the RADARSAT GeoTIFF mosaics (rYY_ddd_dddmos.zip files in the landfast1996-2004/data/YYYY/mmm directories) |
| monthlyavg_slie_grid_templ.xml | XML template for the landfast ArcGIS monthly averaged grid files (monthly_stats_grids.zip files in the landfast1996-2004/monthly_averages/ directory) |
| slie_grid_template.xml | XML template for the landfast binarized GeoTIFFs in ArcInfo Interchange format (rYY_ddd_ddd.zip files in the landfast1996-2004/data/YYYY/mmm directories) |
Note: These XML metadata templates differ slightly from the metadata provided with the data. The abstract, supplemental information, and processing description are worded differently, but all other content is the same.
Monthly Averages
The monthly averages files provide mean, median, maximum, and minimum averages of landfast ice extent for each month derived from the RADARSAT-1 SAR imagery. The data are provided in ArcGIS grids (.adf), shapefiles (.shp), ArcGIS geodatabases (the geodatabases are held in Microsoft Access files (.mdb)), and GeoTIFF files (.tif). Most files are zipped together by month and data format (grid, shapefile, geodatabase, or GeoTIFF) and have the .zip file extension. All ancillary and auxiliary files needed to open the shapefiles and grids such as .prj or .dbf are included in the zip files. The GeoTIFFs do not have the geographic information embedded in the file. This information is included in a .aux file associated with each GeoTIFF. Browse images in JPEG format (.jpg) of the mean, median, maximum, and minimum monthly shapefiles and the monthly GeoTIFFS are available unzipped for quick viewing. All files reside in the landfast1996-2004/monthly_averages directory on the FTP site.
Note: Some GeoTIFF images may appear black when viewed. Landfast ice pixels were assigned a value of 1 and non-landfast ice pixels were assigned a value of 0, so the images appear black when viewed on a scale of 0 to 255. Rescale or threshold the image to view it properly.
Leads
Annual Geodatabase Files
The annual geodatabase files are GIS vectorized lead outlines in ArcGIS geodatabase format (the geodatabases are held in Microsoft Access files (.mdb)) created from the source AVHRR imagery. The geodatabases organize the lead data by ice season. All files reside in the lead1993-2004/annual_geodb directory.
AVHRR Imagery (Source Data)
ArcGIS Grids, Shapefiles, and GeoTIFF Files
Data derived from the source AVHRR imagery are provided in three formats. This includes the AVHRR image in an ArcGIS grid in ESRI ArcInfo interchange format (.e00), shapefiles (.shp), and GeoTIFF format (.tif) with a land mask overlaid. Low resolution browse images of each of these is provided in JPEG format (.jpg). The GeoTIFFs do not have the geographic information embedded in the file. This information is included in a .aux file included with each GeoTIFF. The GeoTIFFs also have associated metadata in a .tif.xml file. Also included with each shapefile and grid are metadata files provided in a number of formats: SGML (.sgml), ASCII text (.txt), XML (.xml) and HTML (.html). All files have been bundled together in zip files and reside in the lead1993-2004/data/YYYY/mmm directories.
Binarized Data
The images of the leads have also been binarized and converted to GeoTIFF format (.tif). In these GeoTIFF files, the geographic information has been embedded within the file (no extra metadata file is needed). Areas that are black are leads and areas that are white are ice and land mask. See the Processing Steps section of this document for information on how these files were created. All files reside in the lead1993-2004/data/binarized_data directory.
XML Metadata Templates
The XML metadata templates for the leads data are FGDC-compliant metadata files in XML format (.xml) that provide an XML template of the metadata for three different types of lead data files. The XML files reside in the leads1993-2004/metadata_templates directory and are explained in Table 3.
| XML File | Description |
|---|---|
| avhrr_template.xml | XML template for the AVHRR imagery GeoTIFFS (cYYdddmos.zip files in the leads1993-2004/data/YYYY/mmm directories) |
| leads_grid_template.xml | XML template for the AVHRR imagery ArcGIS grids (cYYdddgrid.zip files in the leads1993-2004/data/YYYY/mmm directories) |
| leads_shape_template.xml | XML template for the AVHRR imagery shapefiles (cYYdddshape.zip files in the leads1993-2004/data/YYYY/mmm directories) |
Note: Some file naming convention information in the metadata files is inaccurate; follow the naming conventions provided in the File Naming Convention section of this document.
Stacked Leads
The stacked leads files represent the sum of all binarized lead images for each month in the study area and are provided in GeoTIFF format (.tif). In these GeoTIFF files, the geographic information has been embedded within the file (no extra metadata file is needed). The pixel value represents the number of images in which a lead was observed at that location during a particular month from 1993 to 2004. These were converted to probabilities by dividing by the total number of images stacked for each month (Eicken et al. 2006). The darker the area the higher the lead occurrence frequency. The white along the bottom of the image is the Alaskan coast mask. All files reside in the lead1993-2004/stacked_leads directory.
Summary Statistics
Two Microsoft Excel spreadsheets (.xls) are provided with this data set: mean.xls and lead_fraction.xls. The statistics in these files include calculations of total and mean lead fraction; the geographic location, area, perimeter, and major/minor dimensions of individual leads; and derived statistics including lead number densities and size distributions for each ice season. All files reside in the lead1993-2004/summary_statistics directory.
Supplemental Information
Two supplemental documents supplied as Microsoft Excel files provide a catalog of the file names of the original AVHRR and RADARSAT-1 SAR scenes. The AVHRR files are cataloged in avhrr_catalog.xls and the RADARSAT-1 SAR files are cataloged in sar_catalog.xls.
Directory Structure
The data files in this data set are available via FTP. This section describes the directory structure of the FTP site. The top level of the directory structure, G02173, is divided into three main directories. Two for the parameters (landfast ice extent and leads) and a third directory for supplemental information. Landfast ice extent data reside in the landfast1996-2004 directory, lead data reside in the lead1993-2004 directory, and the supplemental information resides in the data_catalogs directory. The landfast and lead directories are further broken down into subdirectories. Figure 2 shows the top level directory structure. Table 4 describes the landfast1996-2004 directory, and Table 5 describes the lead1993-2004 directory.
 |
| Figure 2. Top Level Directory Structure This image shows the G02173 directory expanded to first- and second-level subdirectories. |
Landfast Ice Extent
| Directory Name | Definition |
|---|---|
| landfast1996-2004 | Contains data files pertaining to landfast ice. This directory contains four subdirectories: annual_geodb, data, metadata_templates, and monthly_averages. |
| annual_geodb | Contains the ArcGIS geodatabases with vectorized outlines of the landfast ice extent for each annual ice season. |
| data | Contains the RADARSAT-1 SAR grids, shapefiles, GeoTIFF mosaics, and binarized GeoTIFF images. This directory is further broken down into subdirectories, one for each year that data was collected (1996-2004) labeled as the 4-digit year (YYYY) and a directory called binarized_geotiffs. The year directories are subdivided into directories labeled by the 3-character month abbreviation (mmm) and contain the RADARSAT-1 SAR grids, shapefiles, and GeoTIFF mosaics. The binarized_geotiffs directory contains the binarized RADARSAT-1 SAR GeoTIFFs. See Figure 3. |
| metadata_templates | Contains the XML files with FGDC-compliant metadata templates. |
| monthly_averages | Contains the statistics for the landfast data including mean, median, maximum, and minimum averages for each month. |
 |
| Figure 3. Landfast Directory Structure |
Leads
| Directory Name | Definition |
|---|---|
| lead1993-2004 | Contains data files pertaining to leads in sea ice. This directory contains five subdirectories: annual_geodb, data, metadata_templates, stacked_leads, and summary_statistics. |
| annual_geodb | Contains GIS vectorized lead outlines for each ice season. |
| data | Contains the original AVHRR grids, shapefiles, GeoTIFF images, and binarized GeoTIFF images. This directory is further broken down into subdirectories, one for each year that data was collected (1993-2004) labeled as the 4-digit year (YYYY) and a directory called binarized_data. The year directories are subdivided into directories labeled by the 3-character month abbreviation (mmm) and contain the original AVHRR grids, shapefiles, and GeoTIFF images. The binarized_data directory contains the binarized AVHRR GeoTIFFs. See Figure 4. |
| metadata_templates | Contains the XML files with FGDC-compliant metadata templates. |
| stacked_leads | Contains the stacked leads for each month in the study area. |
| summary_statistics | Contains the mean and areal fraction of leads statistics. |
 |
| Figure 4. Leads Directory Structure |
File Naming Convention
This section explains the file naming conventions. To access the different sections, follow the links below:
Landfast Ice Extent
Annual Geodatabase Files
The annual geodatabase files containing the vectorized landfast data have been compressed into zip files. All files reside in the landfast1996-2004/annual_geodb directory. The zip files are named according to the following convention:
Zipped File: YYYY-YY_vector_geodb.zip
Once unzipped, the files are named as follows. Table 6 describes the file naming convention variables for both the zipped and unzipped files.
Unzipped File: YYYY-YY_Vector_GeoDB.mdb
Where:
| Variable | Description |
|---|---|
| YYYY | 4-digit year of the start of the data |
| YY | 2-digit year of the end of the data |
| vector_geodb/Vector_GeoDB | Identifies this as a vectorized geodatabase file |
| .zip | Identifies that this file has been zipped |
| .mdb | Identifies this file as an ArcGIS geodatabase file - the geodatabases are held in Microsoft Access files. |
RADARSAT-1 SAR Imagery (Source Data)
ArcGIS Grids, shapefiles, and GeoTIFF Mosaics
The RADARSAT-1 SAR ArcGIS grids, shapefiles and GeoTIFF mosaics have been compressed into zip files. The zip files, along with quick-view browse images in JPEG format (.jpg), reside in the landfast1996_2004/data/YYYY/mmm directories. The zip files are named according to the following convention:
Zipped File: rYY_ddd_dddtype.zip
Once unzipped, the files are named as follows. Table 7 describes the file naming convention variables for both the zipped and unzipped files.
Unzipped Files: rYY_ddd_dddtype.xxx
Where:
| Variable | Description |
|---|---|
| r | Identifies this as RADARSAT-1 SAR data |
| YY | 2-digit year |
| ddd | 3-digit day of year, the first ddd is the start day and the last ddd is the stop day of the data |
| type | File format or type
none: ArcGIS grid |
| .zip | Identifies that this file has been zipped |
| .xxx | File extensions inside each type of zip file Grids: .e00, .rrd, .html, .txt, .sgml, .jpg |
Note: A .rrd file does not exist in every zip file. The .rrd file is simply a pyramid file that draws the files more quickly and is not required. Upon opening the files in any ESRI software, a user will be prompted to create pyramids to enhance draw speeds for future use.
Quick-View Browse Images:
The quick-view browse images provide a way to quickly view a thumbnail of the contents of the zip files for the grids, shapefiles, and mosaics without having to unzip the files. These thumbnails also reside in the zip files. Table 8 provides a description of the quick-view browse images. Note: Not all files have a quick-view browse image.
| File Name | Description |
|---|---|
| rYY_ddd_dddmos.jpg | JPEG quick-view browse image for the AVHRR GeoTIFFS |
| rYY_ddd_dddshape.jpg | JPEG quick-view browse image for the shapefiles |
| rYY_ddd_ddd.jpg | JPEG quick-view browse image of the grid files |
Binarized GeoTIFFs
The binarized landfast ice extent GeoTIFF images are compressed into zip files by ice season. All files reside in the landfast1996-2004/data/binarized_geotiffs directory. The zip files are named according to the following convention:
Zipped File: rYYYY_YY_slie.zip
These zip files contain GeoTIFFs (.tif) and metadata in their associated world file (.tfw). The world files reside in a directory called TFW. Note: You can ignore all files and directories that begin with ._ as they are just a byproduct of processing. Once unzipped, the files are named as follows. Table 9 describes the file naming convention variables for both the zipped and unzipped files.
Unzipped Files:
Files in the top level directory are named according to the following convention:
rYYYYddd-ddd_slie.tif
Files in the TFWs directory are named as follows:
rYYYYddd-ddd_slie.tfw
| Variable | Description |
|---|---|
| r | Identifies this as RADARSAT-1 SAR data |
| YYYY | 4-digit start year of data |
| YY | 2-digit end year |
| ddd | 3-digit day of year, the first ddd is the start day and the last ddd is the stop day of the data |
| slie | Identifies this file as containing SLIE data |
| .zip | Identifies that this file has been zipped |
| .tif | Identifies this as a GeoTIFF file |
| .tfw | Identifies this as a World file |
XML Metadata Templates
There are four landfast metadata templates that reside in the landfast1996-2004/metadata_templates directory with the following names:
- monthlyavg_slie_grid_templ.xml
- monthyavg_slie_shape_templ.xml
- RADARSAT-1_template.xml
- slie_grid_template.xml
Monthly Averages
The monthly averages are divided into four categories by format and all files reside in the landfast1996-2004/monthly_averages directory.
ArcGIS grids
The monthly averages ArcGIS grid files containing landfast data have been compressed into zip files. The zip files are named according to the following convention:
Zipped file: monthly_stat_grids.zip
These zip files contain an ArcInfo workspace containing 10 ArcGIS grids, one for each month that data was obtained (October through July). For more information on ArcGIS grids, visit the ESRI ArcGIS Desktop Help: About the ESRI Grid Format Web page. Once unzipped, you will see a number of files in the top level directory, a directory called info, and 10 coverage directories of the form stat_MM (one for each ArcGIS grid). This structure must be preserved so that ArcGIS can open the files properly. See Figure 5 for a screenshot of an unzipped file. Unzipped files are named according to the convention below. Table 11 describes the file naming convention variables for both the zipped and unzipped files.
Unzipped files:
Files in the top level directory are named according to the following convention:
- stat_MM.xxx
Files in the info directory:
- arc.dir
- arcXXXX.dat
- arcXXXX.nit
- arcPPPPr.001
Files in coverage directories (stat_MM):
- dblbnd.adf
- hdr.adf
- log
- metadata.xml
- prj.adf
- sta.adf
- vat.adf
- w001001.adf
- w001001x.adf
Where:
| Variable | Description |
|---|---|
| monthly | Identifies these file as containing monthly averaged data |
| stat | Statistic in this file (maximum/max, mean, median, or minimum/min) |
| MM | 2-digit month |
| grids | Identifies this as an ArcGIS grid file |
| arc | Identifies this as an ArcGIS info file |
| XXXX | ArcGIS index for shapefile (0000 to 0029) |
| PPPP | ArcGIS index for shapefile (0002, 0005, 0008, 0011, 0014, 0017, 0020, 0023, 0026, and 0029) |
| .zip | Identifies that this file has been zipped |
| .adf | ArcGIS grid files that reside in the coverage directories (stat_MM) |
| .xxx | File extension (.rrd, .aux, .html, .jpg, .txt, .xml) See Table 1 for a description of the file extensions |
 |
| Figure 5. Screenshot of the Contents of monthly_maximum_grids.zip |
Shapefiles
The monthly averages shapefiles containing landfast data have been compressed into zip files. The zip files are named according to the following convention:
Zipped file: stat_MMshape.zip
These zip files contain multiple files of varying formats. Once unzipped, the files are named as follows. Table 10 describes the file naming convention variables for both the zipped and unzipped files.
Unzipped files: stat_MMshape.xxx
Where:
| Variable | Description |
|---|---|
| stat | Statistic in this file (max, mean, median, or min) |
| MM | 2-digit month |
| shape | Identifies this as an shapefile |
| .zip | Identifies that this file has been zipped |
| .xxx | File extension (.shp, .dbf, .shx, .sbx, .sbn, .shp.xml, .prj, .jpg, .aux, .txt, .html, .xml) See Table 1 for a description of file extensions |
ArcGIS Geodatabases
The monthly averages ArcGIS geodatabases containing landfast data have been compressed into zip files. The zip files are named according to the following convention:
Zipped file: slie_monthly_stat.zip
Once unzipped, the files are named as follows. Table 12 describes the file naming convention variables for both the zipped and unzipped files.
Unzipped file: SLIE_Monthly_stat.mdb
Where:
| Variable | Description |
|---|---|
| slie_monthly/SLIE_Monthly | Identifies this as a file containing derived monthly SLIE data |
| stat | Statistic in this file (Maximum/maximum, Mean/mean, Median,/median, or Minimum/minimum) |
| .zip | Identifies that this file has been zipped |
| .mdb | Identifies this as an ArcGIS geodatabase file - the geodatabases are held in Microsoft Access files. |
GeoTIFFs
The monthly averages GeoTIFF files containing landfast data have been compressed into zip files. The zip files are named according to the following convention:
Zipped file: monthly_stat_geotiffs.zip
These zip files contain GeoTIFF images and their associated .aux file. Once unzipped, the files are named as follows. Table 13 describes the file naming convention variables for both the zipped and unzipped files.
Unzipped files:
- stat_MM.xxx
Where:
| Variable | Description |
|---|---|
| monthly | Identifies these file as containing monthly averaged data |
| stat | Statistic in this file (max, mean, med, or min) |
| geotiffs | Identifies this as a Geotiff file |
| MM | 2-digit month |
| .zip | Identifies that this file has been zipped |
| .xxx | File extension (.tif, .aux, or .rrd) See Table 1 for a description of the file extensions |
Note: A .rrd file does not exist in every zip file. The .rrd file is simply a pyramid file that draws the files more quickly and is not required. Upon opening the files in any ESRI software, a user will be prompted to create pyramids to enhance draw speeds for future use.
Leads
Annual Geodatabase Files
The annual geodatabase files containing the vectorized lead data have been compressed into zip files. All files reside in the lead1993-2004/annual_geodb directory. The zip files are named according to the following convention:
Zipped File: leads_YYYY-YY_vector_geodb.zip
Once unzipped, the files are named as follows. Table 14 describes the file naming convention variables for both the zipped and unzipped files.
Unzipped File: Leads_YYYY-YY_Vector_GeoDB.mdb
Where:
| Variable | Description |
|---|---|
| leads/Leads | Identifies this file as containing lead data |
| YYYY | 4-digit year of the start of the data |
| YY | 2-digit year of the end of the data |
| vector_geodb/Vector_GeoDB | Identifies this as a vectorized geodatabase file |
| .zip | Identifies that this file has been zipped |
| .mdb | Identifies this file as an ArcGIS geodatabase file - the geodatabases are held in Microsoft Access files. |
AVHRR Imagery (Source Data)
ArcGIS Grids, shapefiles, and GeoTIFF files
The AVHRR source data imagery have been compressed into zip files. All files reside in the lead1993-2004/data/YYYY/mmm directories. The zip files, along with quick-view browse images in JPEG format (.jpg), reside in leads1993_2004/data/YYYY/mmm. Note: Some months may not contain data for a specific year due to the cloud coverage. The zip files are named according to the following convention:
Zipped file: cYYdddtype.zip
Once unzipped, the files are named as follows. Table 15 describes the file naming convention variables for both the zipped and unzipped files.
Unzipped file: cYYdddtype.xxx
Where:
| Variable | Description |
|---|---|
| c | Channel
v: visible, AVHRR channel 1 |
| YY | 2-digit year |
| ddd | 3-digit day of year |
| type | File format or type
grid: ArcGIS grid file |
| .zip | Identifies that this file has been zipped |
| .xxx | File extension inside of each type of zip file Grids: .e00, .html, .txt, .sgml, .jpg |
Quick-View Browse Images:
The quick-view browse images provide a way to quickly view a thumbnail of the contents of the zip files without having to unzip the files. These thumbnails also reside in the zip files but have a slightly different file name. See Table 16 for a complete description of the quick-view browse images.
| File Name | Description | Name in Zip File |
|---|---|---|
| cYYddd_tha.jpg | JPEG quick-view browse image for the AVHRR GeoTIFFS | cYYddd.jpg |
| cYYddd_thb.jpg | JPEG quick-view browse image for the shapefiles | cYYdddshape.jpg |
| cYYdddgrid or cYYddd.jpg | JPEG quick-view browse image of the grid files | cYYdddgrid.jpg |
Binarized Data
There are two binarized AVHRR source imagery files: one for the visible channel and one for the thermal channel. All files reside in the lead1993-2004/data/binarized_data directory. The files have been compressed into zip files and are named according to the following convention:
Zipped files:
- AVHRR_Thermal.zip
- AVHRR_Visible.zip
Once unzipped, the files are named as follows. Table 17 describes the file naming convention variables for both the zipped and unzipped files.
Unzipped file: cYYddd.tif
Where:
| Variable | Description |
|---|---|
| AVHRR | Identifies that this file contains AVHRR data |
| Thermal | Identifies that this file contains AVHRR thermal channel (channel 4) data |
| Visible | Identifies that this file contains AVHRR visible channel (channel 1) data |
| c | AVHRR channel used
v: visible (channel 1) |
| YY | 2-digit year |
| ddd | 3-digit day of year |
| .zip | Identifies that this file has been zipped |
| .tif | Identifies this as a GeoTIFF file |
XML Metadata Templates
There are three lead metadata templates that reside in the leads1993-2004/metadata_templates directory. They have the following names:
- avhrr_template.xml
- leads_grid_template.xml
- leads_shape_template.xml
Stacked Leads
The stacked lead files reside in the lead1993-2004/stacked_leads directory. They are named according to the following convention and as described in Table 18:
stacked_leads_mmm.tif
Where:
| Variable | Description |
|---|---|
| stacked_leads | Identifies this file as containing stacked lead data |
| mmm | 3-character month abbreviation |
| .tif | Identifies this as a GeoTIFF file |
Summary Statistics
There are two files containing statistics about the lead data. They reside in the lead1993-2004/summary_statistics directory.
- lead_fraction.xls
- means.xls
File Size
Landfast Ice Extent
The file sizes for each type of landfast ice extent data file is shown in Table 19.
| File Type | Size |
|---|---|
| Annual Geodatabase Files | Zipped: 16.9 - 22.7 MB per file Unzipped: 64.6 - 85.9 MB per file |
| RADARSAT-1 SAR Imagery | Zipped: 100 KB - 29.1 MB per file Unzipped: 1 KB - 30.2 MB per file |
| Metadata Templates | 22.9KB - 128 KB per file (files are not zipped) |
| Monthly Averages | Zipped: 610 KB - 7.58 MB per file Unzipped: 1 KB - 29 MB per file |
Leads
The file sizes for each type of lead data file is shown in Table 20.
| File Type | Size |
|---|---|
| Annual Geodatabase Files | Zipped: 1.23 MB - 8.62 MB per file
Unzipped: 7.1 MB - 40.3 MB per file |
| AVHRR Imagery | Zipped: 37.7 KB - 1.55 MB per file
Unzipped: 3 KB - 2 MB per file |
| Metadata Templates | 15.8 KB - 18.8 KB per file (files are not zipped) |
| Stacked Leads | 426 KB per file (files are not zipped) |
| Summary Statistics | 436 KB - 532 KB per file (files are not zipped) |
Sample Data Record
This section shows examples of the data files in this data set.
Landfast Ice Extent
Annual Geodatabases
 |
| Figure 6. Screenshot of 1996-97_Vector_GeoDB.mdb Shows the geodatabase for the 1996/1997 ice season in ArcGIS. |
 |
| Figure 7. Screenshot of the r96_289_312shape Layer
and Attribute Table Shows the shape layer for 15 Oct - 07 Nov 1996 in ArcGIS. Click image for a high resolution version. |
RADARSAT-1 SAR Imagery (Source Data)
 |
| Figure 8. Example of RADARSAT-1 SAR Image Mosaic GeoTIFF Image is for 16 March - 18 March 2000 (r00_076_078mos.tif). |
Monthly Averages
 |
| Figure 9. Example of a Monthly Averaged Minimum GeoTIFF Image is for the month of January from 1996 to 2004 (Min_01.tif from monthly_minimum_geotiffs.zip). |
Leads
AVHRR Imagery (Source Data)
 |
| Figure 10. AVHRR GeoTIFF File This is an example of a visible band AVHRR GeoTIFF file for 14 June 1996 (v96166.tif from v96166.zip). The associated .tfw world file contains the projection information for each corresponding GeoTIFF file. The Alaskan coast is shown in white due to a land mask that was applied. |
 |
| Figure 11. Binarized Lead Binarized lead image for 14 June 1996 (v96166grid.e00). |
Stacked Leads
Figure 12 is an example of a stacked leads image for the month of June from 1993 to 2004. The darker the area the higher the lead occurrence frequency. The white along the bottom of the image is the Alaskan coast mask.
 |
| Figure 12. Example of Stacked Leads Image is for the month of June from 1993 to 2004 (stacked_leads_jun.tif). |
Summary Statistics
 |
| Figure 13. Beginning Portion of lead_fraction.xls |
 |
| Figure 14. Beginning Portion of means.xls |
3.Data Access and Tools
Data Access
Data are available via FTP. See the Directory Structure section of this document for a description of the organization of the FTP directory.
Software and Tools
Tools that work with this data are Geographic Information System (GIS) software, image viewing software, Microsoft Excel, and text editors. Zipped files can be unzipped with WinZip or other similar compression software.
Note to WinZip Users: In some versions of WinZip (WinZip 9.x or lower), the WinZip window does not preserve the directory structure of the zipped file. To see the directory structure, extract the files from WinZip to your computer, or obtain WinZip 10.x and higher which does preserve the directory structure within the WinZip window.
4. Data Acquisition and Processing
Sensor or Instrument Description
Landfast Ice Extent
The instrument used to acquire the landfast ice extent images was the Synthetic Aperture Radar (SAR) onboard RADARSAT-1. It was launched on 04 November 1995 into a sun synchronous orbit and measured horizontally polarized (HH) C-band microwave radiation at 5.3 GHz to obtain data of the surface of the Earth.
Leads
The instruments used to acquire the leads data were the Advanced Very High Resolution Radiometers (AVHRR) on the NOAA 12, 14, 15, 16, and 17 satellites. The AVHRR sensor is a broad-band, 5- or 6-channel scanning radiometer (NOAA 12 and 14 - 5 channels; NOAA 15, 16, and 17 - 6 channels). It takes measurements in the visible, near-infrared, and thermal infrared portions of the electromagnetic spectrum.
Data Acquisition Methods
The original AVHRR data used to derive the leads were acquired from the Geographic Information Network of Alaska (GINA) at the University of Alaska Fairbanks (UAF). Full resolution (100 meter) RADARSAT-1 SAR data used to derive the landfast ice extent were acquired from the Alaska Satellite Facility (ASF) via the Electronic Data Gateway (EDG). The original RADARSAT-1 SAR data are courtesy of the Canadian Space Agency.
Data Processing Steps
The data processing section is divided into two sections: landfast ice extent and leads. Most of the content below came from Mapping and Characterization of Recurring Spring Leads and Landfast Ice in the Beaufort and Chukchi Seas (Eicken et al. 2006).
Landfast Ice Extent
The landfast ice extent was determined by the distance between
land (the Alaskan coast) and the SLIE that is derived
from RADARSAT-1 SAR data from 1996 through 2004. Off
the northern coast of Alaska, landfast ice extent starts advancing between October
and November and then breaks up by July. The landfast ice extent exists
for a majority of the year, and then the coastal area becomes ice-free for a
couple of months (August and September). For the landfast ice extent region in this
study, there are approximately 1,000 SAR scenes that were originally analyzed.
Because
one SAR scene does not cover the entire study area, three or four scenes were
combined or mosaiced to cover the entire landfast ice extent study area (subregions
2-11). Refer to Figure 1. However, due to orbital constraints of the RADARSAT-1 satellite, the scenes were not acquired
at the same time, each mosaic typically spans two to three days. Complete mosaics
were produced approximately every 10 days. Sets of three consecutive RADARSAT-1 SAR
mosaics, spanning a period of approximately 20 days, were then used to identify
landfast ice extent. Figure 15 shows an example of a RADARSAT-1 SAR mosaic comprised of five
individual SAR scenes.
 |
| Figure 15. Example of RADARSAT-1 SAR Mosaic Covering the Entire
Study Area This mosaic is comprised of five individual SAR scenes for 01 December through 04 December 1996 (r96_336_340mos.tif from r96_336_340mos.zip). Image courtesy of the Canadian Space Agency. |
Figure 16 shows three mosaics around Barrow, Alaska. The green line depicts the Alaskan shoreline and the red line shows the SLIE based on all three mosaics.
 |
| Figure 16. Three Consecutive RADARSAT-1 SAR Mosaics These images are sub-regions of three consecutive RADARSAT SAR mosaics focused on Barrow, AK (dates are noted in each image). Images courtesy of Andrew Mahoney. |
These RADARSAT-1 SAR images were processed into GeoTIFF format in the Alaska Statewide Albers equal-area conical map projection using Advanced Product Development SAR tools from ASF. An IDL script was then used to mosaic individual scenes together to cover the whole area.
To determine the regions of ice that met the landfast ice definition criteria in each set of three mosaics, a combination of automated and manual techniques was employed. As well as visual comparison of all three mosaics, a composite image was produced based upon the magnitude of the net difference in vector backscatter gradient between the mosaics. This gradient difference highlighted regions of change or motion and helped reduce the subjectivity of the analysis. In addition to not showing movement in three successive mosaics, the ice had to have a low gradient difference value in order to be considered landfast ice. Further details of this process are described by Mahoney et al. (2005) and Eicken et al. (2006).
Leads
The leads were derived from AVHRR data from 1993 through 2004. The AVHRR images were acquired from the UAF HRPT receiving station, with data from recent years augmented by NOAA Gilmore Creek receiving station during periods where the UAF station was down. At least one AVHRR image was analyzed and used each day during the period when leads in the Beaufort and Chukchi Seas are most prominent, which is from early December to late June. Both visible and infrared AVHRR images were used; visible images were used when sunlight was available and infrared (IR) images were used during dark months in Alaska. In months with some sunlight, both types of AVHRR images were used. AVHRR
In visible AVHRR data, land is white (due to a land mask that was applied), sea ice is gray, and leads are black. Refer to Figure 17. In IR AVHRR imagery, land is black (due to a land mask that was applied), sea ice is gray, and leads are shown in white.
 |
| Figure 17. AVHRR Visible Band Image for 04 May 2004 (v04125.tif from v04125.zip) Leads appear dark, ice and landfast ice appear grayish, and the Alaskan coast is white. Click for a high resolution version. |
Approximately 2,000 AVHRR images were analyzed and visually examined. Each scene covers more than one subregion.
If clouds were misidentified as leads or if an AVHRR image was mostly cloud
covered over the study region, the images were either corrected by removing
cloud covered sectors from the image or eliminated, meaning some months may not contain data for a specific year
due to the cloud coverage. This resulted in a total
of 385 AVHRR images in this data set. Figures 18 and 19 show the number of AVHRR
images by region and month. Since most AVHRR scenes cover more than one subregion,
Figure 18 illustrates that data coverage is slightly better in the middle of
the study area. Figure 19 shows that the months were consistently sampled and
that there are fewer cloud-free scenes during the transition months of December
and June.
 |
| Figure 18. Number of AVHRR Scenes Analyzed per Subregion During the Study Period (1993-2004) |
 |
| Figure 19. Number of AVHRR Scenes Analyzed Per Month from 1993-2004 |
Recurring lead patterns and features are identified and named. The way to distinguish whether a pattern or feature is persistent over time was to look for evidence of differential ice motion between AVHRR scenes, and to quantify the persistent occurrence of leads for each grid cell over a given time period.
AVHRR data were geolocated, calibrated, and reprojected in GeoTIFF format in the Alaska Statewide Albers equal-area conical map projection using TeraScan software. A coast mask was applied in ENVI. "The fraction of leads within each pixel was determined based on the brightness temperatures or reflectances of open water and the surrounding thick ice, as described by Lindsay and Rothrock (1995)" (Eicken et al., 2006). The data were corrected for regional differences in surface temperature and reflectance, as well as thin cloud cover, by determining the fraction of leads within a moving 50 by 50 pixel (55 km x 55 km) square window, with the fraction of thick ice based on the upper and lower quartile reflectance and brightness temperature, respectively. For a few cases of more expansive stretches of open water, manual adjustments of open water extent were made. The resulting image indicates the fraction of open water in each pixel. Each image is then classified, such that any pixel containing 25 percent or more open water or thin ice is designated as lead and any pixel containing less than 25 percent open water or thin is classified as ice. The resulting image is a binary image, containing only leads and ice with the land mask assigned the same value as ice. This information was then brought into NIH Image for derivation of lead location, shape and size statistics, open water fractions, and other information for the different study subregions. Stacked leads (monthly lead probabilities) were also produced based on the binarized leads. These stacked leads represent the sum of all lead images for each month in the study area. The darker the area the higher the lead occurrence frequency. The white along the bottom of the image is the Alaskan coast mask.
Error Sources
Landfast Ice Extent
The SLIE is located to within 500 m (geolocation accuracy). The timing of the SLIE is approximately +/- 5 days due to the time interval between mosaics. Radiometric errors are not a significant source of errors for landfast ice edge derivation because of the combination of spatial gradient and manual delineation approaches employed (Mahoney et al. 2006). One source of error is the ambiguous signature between open water and thin ice in the RADARSAT-1 data (Kwok and Cunningham 1994).
Leads
Geolocation errors for leads were determined to be less than 3 km and generally within 1.2 km (Eicken et al., 2006). Radiometric errors impact the detectability of leads, along with limitations imposed by sensor resolution (Eicken et al., 2006). These error sources impact number densities and the lower end of lead size distributions, but are not as relevant for other derived quantities.
Quality Assessment
Note: NSIDC did not perform a quality assessment of the data.
Landfast Ice Extent
The manual process for identifying landfast ice extent has subjectivity. However, this subjectivity was reduced by using a gradient difference. Refer to the landfast ice extent Data Processing section of this document for more information on the gradient difference.
The following is a list of the quality checks performed on the landfast ice (Mahoney et al. 2005):
- Data were checked for adequate coverage over the study area (subregions 2-11).
- Images with a large geolocation error were identified and either corrected or disregarded.
- The geolocation accuracy could create collocation errors of up to 10 pixels or 1 km between parts of two mosaics.
Leads
The following checks were performed on the AVHRR data:
- Manually examined all scenes and excluded images or image sections with any trace of cloud cover or ambiguous lead/cloud features to keep the potential source of error due to clouds and fog to a minimum.
- Classified lead/ice images were compared to ship-based observations of lead fractions in May and June of 2004 and found to be in reasonable agreement with a deviation of two and one percentage-point, respectively.
5. Related Data Collections at NSIDC
Divine, D. V., and C. Dick. 2007. March through August Ice Edge Positions in the Nordic Seas, 1750-2002. Boulder, Colorado USA: National Snow and Ice Data Center. Digital media. http://nsidc.org/data/g02169.html.
National Ice Center. 2006. National Ice Center Arctic Sea Ice Charts and Climatologies in Gridded Format. Edited and compiled by F. Fetterer and C. Fowler. Boulder, Colorado USA: National Snow and Ice Data Center. Digital media. http://nsidc.org/data/g02172.html.
NSIDC/WDC for Glaciology, Boulder, compiler. 2005. The Dehn Collection of Arctic Sea Ice Charts, 1953-1986. Boulder, CO : National Snow and Ice Data Center. Digital media. http://nsidc.org/data/g01111.html.
6. References and Related Publications
For a more in depth description of the purpose and aim of this project and its data, download Mapping and Characterization of Recurring Spring Leads and Landfast Ice in the Beaufort and Chukchi Seas Final Report (Eicken et al. 2006).
Eicken, H., L. Shapiro, A. G. Gaylord, A. Mahoney, and P. Cotter. 2006. Mapping and Characterization of Recurring Spring Leads and Landfast Ice in the Beaufort and Chukchi Seas. Final Report, Minerals Management Service OCS Study MMS 2005-068.
Eicken, H., R. Gradinger, A. Graves, A. Mahoney, I. Rigor, and H. Melling. 2005. Sediment Transport by Sea Ice in the Chukchi and Beaufort Seas: Increasing Importance Due to Changing Ice Conditions? Deep-Sea Research II 52: 3281-3302.
Fett, R. W., R. E. Englebretson, and S. D. Burk. 1997. Technologies for Analyzing Lead Condition in Visible, Infrared and Microwave Satellite Imagery. Journal of Geophysical Research 102: 13657-13671.
Key, J. R., R. Stone, J. A. Maslanik, and E. Ellefsen. 1993. The Detectability of Sea-Ice Leads in Satellite Data as a Function of Atmospheric Conditions and Measurement Scale, Annals of Glaciology 17: 227-232.
Kwok, R. and G. F. Cunningham. 1994. Use of Time Series SAR Data to Resolve Ice Type Ambiguities in Newly Opened Leads. IGARSS'94: International Geoscience and Remote Sensing Symposium. Surface and Atmospheric Remote Sensing: Technologies, Data Analysis, and Interpretation: 1024-1026.
Lindsay, R. W. and D. A. Rothrock. 1995. Arctic Sea Ice Leads from Advanced Very High Resolution Radiometer Images. Journal of Geophysical Research 100: 4533-4544.
Mahoney, A. 2006. "Alaska Landfast Sea Ice Dynamics." Ph.D. Thesis, University of Alaska Fairbanks, Fairbanks, AK, August 2006.
Mahoney, A., H. Eicken, L. Shapiro, and A. Graves. 2005. Defining and Locating the Seaward Landfast Ice Edge in Northern Alaska. In: 18th International Conference on Port and Ocean Engineering under Arctic Conditions, J.P. Dempsey (Editor). POAC '05 Proceedings Volume 3, Potsdam, NY, June 26-30, 2005.
Mahoney, A., H. Eicken, A. G. Gaylord, and L. Shapiro. 2007. Alaska Landfast Sea Ice: Links with Bathymetry and Atmospheric Circulation. Journal of Geophysical Research 112, C02001.
Stroeve, J., M. Serreze, S. Drobot, S. Gearheard, M. Holland, J. Maslanik, W. Meier, and T. Scambos. 2008. Arctic Sea Ice Extent Plummets in 2007. EOS, 89(2), 8 January.
7. Acknowledgements
We would like to acknowledge the work of Andrew Mahoney (Doctoral degree student who worked on the data analysis and processing of the data) and Patrick W. Cotter (research technician who provided project support).
Distribution of the data set from NSIDC is supported by funding from NOAA's National Environmental Satellite, Data, and Information Service (NESDIS) and the National Geophysical Data Center (NGDC).
8. Document Information
Glossary
Table 21 lists the acronyms used in this document.
| Acronym | Description |
|---|---|
| ASCII | American Standard Code for Information Interchange |
| ASF | Alaska Satellite Facility |
| AVHRR | Advanced Very High Resolution Radiometer |
| EDG | Electronic Data Gateway |
| FGDC | Federal Geographic Data Committee |
| FTP | File Transfer Protocol |
| GeoTIFF | Geographic Tagged Image File Format |
| GINA | Geographic Information Network of Alaska |
| GIS | Geographic Information System |
| HTML | HyperText Markup Language |
| IDL | Interactive Data Language |
| JPEG | Joint Photographic Experts Group |
| MMS | Minerals Management Service |
| NAD | North American Datum |
| NIH | National Institutes of Health |
| NGDC | National Geophysical Data Center |
| NSIDC | National Snow and Ice Data Center |
| NOAA | National Oceanic and Atmospheric Administration |
| RADARSAT-1 | RADAR SATellite-1 |
| SAR | Synthetic Aperture Radar |
| SGML | Standard Generalized Markup Language |
| SLIE | Seaward Landfast Ice Edge |
| XML | eXtensible Markup Language |
Document Authors
A. Windnagel, L. Ballagh, and D. Miller prepared this document based on correspondence with H. Eicken, A. Gaylord, A. Mahoney, and F. Fetterer. Eicken et al. (2006), Mahoney et al. (2005), and Mahoney et al. (2007) provided most of the background content upon which this document is based.
Document Creation Date
June 2009
Document Revision Date
August 2012: A. Windnagel clarified that a .mdb file is a Microsoft Access database file which is the format used for ArcGIS geodatabases.
Document URL
http://nsidc.org/data/docs/noaa/g02173_ak_landfast_and_leads/index.html
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