Geolocation Tools
NSIDC provides software tools to extract and geolocate data in a polar stereographic projection derived from gridded passive microwave data sets at NSIDC, as well as masking tools that limit the influence of weather effects on sea ice concentrations. We also provide software and tools for geolocating and displaying EASE-Grid data sets at NSIDC.
This page provides links to software and tools for geolocating and displaying EASE-Grid and polar stereographic projection data sets available at NSIDC. All tools are available by FTP.
Table of Contents
EASE-Grid Data Tools
The software and tools are grouped into the following categories:
- Geolocation Software - Including C, FORTRAN, and IDL (Interactive Data Language) conversion software
- Geolocation Data Files - Look-up files that contain arrays with the latitude and longitude at the center of each grid cell
Geolocation Software
Tool Name | ezlhconv.c (With header file, ezlhconv.h, for data set users with knowledge of C programming) |
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Tool Type | C |
Applicable Data Sets | AMSR-E/Aqua Daily EASE-Grid Brightness Temperatures AMSR-E/Aqua Daily L3 Global Snow Water Equivalent EASE-Grids AMSR-E/Aqua 5-Day L3 Global Snow Water Equivalent EASE-Grids AMSR-E/Aqua Monthly L3 Global Snow Water Equivalent EASE-Grids AMSR-E/Aqua Daily L3 Surface Soil Moisture, Interpretive Parms, & QC EASE-Grids Nimbus-7 SMMR Pathfinder Daily EASE-Grid Brightness Temperatures DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures Global Monthly EASE-Grid Snow Water Equivalent Climatology Near-Real-Time SSM/I EASE-Grid Daily Global Ice Concentration and Snow Extent |
Description | Subroutines in these files can be called from the user's main program, to convert between latitude/longitude and row/column coordinates. |
Access | FTP |
Tool Name | ezlhconv.f (For data set users with knowledge of FORTRAN programming) |
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Tool Type | FORTRAN |
Applicable Data Sets | AMSR-E/Aqua Daily EASE-Grid Brightness Temperatures AMSR-E/Aqua Daily L3 Global Snow Water Equivalent EASE-Grids AMSR-E/Aqua 5-Day L3 Global Snow Water Equivalent EASE-Grids AMSR-E/Aqua Monthly L3 Global Snow Water Equivalent EASE-Grids AMSR-E/Aqua Daily L3 Surface Soil Moisture, Interpretive Parms, & QC EASE-Grids Nimbus-7 SMMR Pathfinder Daily EASE-Grid Brightness Temperatures DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures Global Monthly EASE-Grid Snow Water Equivalent Climatology Near-Real-Time SSM/I EASE-Grid Daily Global Ice Concentration and Snow Extent Northern Hemisphere EASE-Grid Weekly Snow Cover and Sea Ice Extent Version 3 |
Description | Subroutines in these files can be called from the user's main program, to convert between latitude/longitude and row/column coordinates. |
Access | FTP |
Geolocation Data Files
For data set users who only have the need of the latitude and longitude of the center of any cell in the grid, the following geolocation data file is available.
This section explains the file naming convention used for the following geolocation data files.
These geolocation files contain flat, binary arrays of 4-byte integers containing the latitude or longitude of the respective grid cell in hundred-thousandth degrees. The user should divide the stored integer value by 100,000. to yield decimal degrees, with 1 meter precision. The user is expected to know which byte-ordering convention is required by their system. Files are provided in PC (little-endian/LSB) byte orders.
Depending on the coverage area, which varies for different grids (such as ML, NH, SL, Sa25 and so on), scaled latitudes range from -90.00000 to 90.00000, and scaled longitudes range from -180.00000 to 180.00000 with missing data (such as corners of grids with hemispheric coverage) indicated by scaled value 14316.55765.
Example file name: MLLATLSB
ggpppooo
Where:
Variable | Description |
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gg | Grid name (NL, NH, SL, SH, ML, MH, NAARI, Na25, Sa25) |
ppp | Parameter (LAT, LON) |
ooo | Byte order: LSB: Least Significant Byte/litte-endian MSB: Most Significant Byte/big-endian1 |
1As of January 2012, EASE-Grid geolocation files are no longer provided in MSB byte order. |
Tool Names | MLLATooo and MLLONooo |
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Tool Type | Geolocation Data Files |
Applicable Data Sets | AMSR-E/Aqua Daily L3 Surface Soil Moisture, Interpretive Parms, & QC EASE-Grids AMSR-E/Aqua Daily EASE-Grid Brightness Temperatures DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures Nimbus-7 SMMR Pathfinder Daily EASE-Grid Brightness Temperatures |
Description | Provides latitude and longitude for the center of any cell in the grid. For additional details, please refer to the Geolocation Data Files section of this Web page. |
Grid Name | ML |
Coverage | Global |
Resolution | 25 km |
Dimensions | 1383 x 586 pixels |
Access | FTP |
Tool Names | MHLATooo and MHLONooo |
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Tool Type | Geolocation Data Files |
Applicable Data Sets | DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures |
Description | Provides latitude and longitude for the center of any cell in the grid. For additional details, please refer to the Geolocation Data Files section of this Web page. |
Grid Name | MH |
Coverage | Global |
Resolution | 12.5 km |
Dimensions | 2766 x 1171 pixels |
Access | FTP |
Tool Names | NLLATooo and NLLONooo |
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Tool Type | Geolocation Data Files |
Applicable Data Sets | DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures Nimbus-7 SMMR Pathfinder Daily EASE-Grid Brightness Temperatures AMSR-E/Aqua Daily L3 Global Snow Water Equivalent EASE-Grids AMSR-E/Aqua 5-Day L3 Global Snow Water Equivalent EASE-Grids AMSR-E/Aqua Monthly L3 Global Snow Water Equivalent EASE-Grids Global Monthly EASE-Grid Snow Water Equivalent Climatology Near-Real-Time SSM/I EASE-Grid Daily Global Ice Concentration and Snow Extent Northern Hemisphere EASE-Grid Weekly Snow Cover and Sea Ice Extent Version 3 |
Description | Provides latitude and longitude for the center of any cell in the grid. For additional details, please refer to the Geolocation Data Files section of this Web page. |
Grid Name | NL |
Coverage | Northern Hemisphere |
Resolution | 25 km |
Dimensions | 721 x 721 pixels |
Access | FTP |
Tool Names | NHLATooo and NHLONooo |
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Tool Type | Geolocation Data Files |
Applicable Data Sets | DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures |
Description | Provides latitude and longitude for the center of any cell in the grid. For additional details, please refer to the Geolocation Data Files section of this Web page. |
Grid Name | NH |
Coverage | Northern Hemisphere |
Resolution | 12.5 km |
Dimensions | 1441 x 1441 pixels |
Access | FTP |
Tool Names | SLLATooo and SLLONooo |
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Tool Type | Geolocation Data Files |
Applicable Data Sets | AMSR-E/Aqua Daily EASE-Grid Brightness Temperatures DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures Nimbus-7 SMMR Pathfinder Daily EASE-Grid Brightness Temperatures Global Monthly EASE-Grid Snow Water Equivalent Climatology AMSR-E/Aqua Daily L3 Global Snow Water Equivalent EASE-Grids AMSR-E/Aqua 5-Day L3 Global Snow Water Equivalent EASE-Grids AMSR-E/Aqua Monthly L3 Global Snow Water Equivalent EASE-Grids Near-Real-Time SSM/I EASE-Grid Daily Global Ice Concentration and Snow Extent |
Description | Provides latitude and longitude for the center of any cell in the grid. For additional details, please refer to the Geolocation Data Files section of this Web page. |
Grid Name | SL |
Coverage | Southern Hemisphere |
Resolution | 25 km |
Dimensions | 721 x 721 pixels |
Access | FTP |
Tool Names | SHLATooo and SHLONooo |
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Tool Type | Geolocation Data Files |
Applicable Data Sets | DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures |
Description | Provides latitude and longitude for the center of any cell in the grid. For additional details, please refer to the Geolocation Data Files section of this Web page. |
Grid Name | SH |
Coverage | Southern Hemisphere |
Resolution | 12.5 km |
Dimensions | 1441 x 1441 pixels |
Access | FTP |
Tool Names | NAARILATooo and NAARILONooo |
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Tool Type | Geolocation Data Files |
Applicable Data Sets | AARI 10-Day Arctic Ocean EASE-Grid Sea Ice Observations |
Description | Provides latitude and longitude for the center of any cell in the grid. For additional details, please refer to the Geolocation Data Files section of this Web page. |
Grid Name | NAARI |
Coverage | Subset of the Northern Hemisphere |
Resolution | 25 km |
Dimensions | 721 x 721 pixels |
Access | FTP |
Tool Names | Na25LATooo and Na25LONooo |
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Tool Type | Geolocation Data Files |
Applicable Data Sets | Polar Pathfinder Daily 25 km EASE-Grid Sea Ice Motion Vectors National Ice Center Arctic Sea Ice Charts and Climatologies in Gridded Format AVHRR Polar Pathfinder Twice-Daily 25 km EASE-Grid Composites |
Description | Provides latitude and longitude for the center of any cell in the grid. For additional details, please refer to the Geolocation Data Files section of this Web page. |
Grid Name | Na252 |
Coverage | Subset of the Northern Hemisphere |
Resolution | 25 km |
Dimensions | The Na25 EASE-Grid is a subset of the 25 km Northern Hemisphere Azimuthal EASE-Grid, including the center 361 columns by 361 rows, with the North Pole at the center of the center-most grid cell. |
Access | FTP |
Tool Names | Sa25LATooo and Sa25LONooo |
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Tool Type | Geolocation Data Files |
Applicable Data Sets | Polar Pathfinder Daily 25 km EASE-Grid Sea Ice Motion Vectors National Ice Center Arctic Sea Ice Charts and Climatologies in Gridded Format AVHRR Polar Pathfinder Twice-Daily 25 km EASE-Grid Composites |
Description | Provides latitude and longitude for the center of any cell in the grid. For additional details, please refer to the Geolocation Data Files section of this Web page. |
Grid Name | Sa252 |
Coverage | Subset of the Southern Hemisphere |
Resolution | 25 km |
Dimensions | The Sa25 EASE-Grid is a subset of the 25 km Northern Hemisphere Azimuthal EASE-Grid, including the center 321 columns by 321 rows, with the North Pole at the center of the center-most grid cell. |
Access | FTP |
Additional Tools for EASE-Grid
Geolocating EASE-Grid Data in ENVI
The Geolocating EASE-Grid Data in ENVI document describes how to geolocate North, South, and Global EASE-Grid data from the DMSP SSM/I-SSMIS Pathfinder Daily EASE-Grid Brightness Temperatures product using ENVI Software.
Importing Passive Microwave EASE-Grid Data into a ArcGIS
The Importing NSIDC Passive Microwave EASE-Grid Data into ArcGIS document describes how to import Passive Microwave EASE-Grid data into ArcGIS.
Polar Stereographic Data Tools
The software and tools are grouped into the following categories:
- Data Extraction Tools: The data extraction tools allow the user to extract and read the data from the data files.
- Data Display Tools: The data display tools allow the user to display data from the data files in various ways.
- Geocoordinate and Pixel-Area Tools: The Geocoordinate tools allow the user to obtain latitude/longitude coordinates from (i,j) coordinates and vice versa. The pixel-area tools allow the user to obtain the area of a given pixel.
- Masks and Overlays: NSIDC provides land, region, and ocean masks and overlays that can be applied to the polar stereographic data files.
Data Extraction Tools
Tool Name | extract.pro |
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Applicable Data Sets | DMSP SSM/I Daily Polar Gridded Brightness Temperatures Nimbus-5 ESMR Polar Gridded Brightness Temperatures Near Real-Time DMSP SSM/I Daily Polar Gridded Brightness Temperatures |
Description | IDL program that allows you to open a brightness temperature grid file and read it into an array, making it available for further manipulation in IDL or to write to hard disc. After the program has read the user-indicated time range, an array is returned with a 2-byte integer array of brightness temperatures expressed in tenths of a kelvin (0.1 K). For example, a value of 2358 translates to 235.8 K. |
Access | FTP |
Usage Example | IDL Routines for Passive Microwave Data: Usage Examples - extract.pro |
Tool Name | extract_ice.pro |
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Applicable Data Sets | Nimbus-5 ESMR Polar Gridded Sea Ice Concentrations Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Near-Real-Time DMSP SSM/I-SSMIS Daily Polar Gridded Sea Ice Concentrations |
Description | IDL program that extracts a time series of polar sea ice data. The extraction routine works on both the daily and monthly sea ice files allowing users to select and display sea ice concentrations. For monthly data, users may select which image threshold to view (0, 5, 10, or 15% ice cut off). |
Access | FTP |
Usage Example | IDL Routines for Passive Microwave Data: Usage Examples - extract_ice.pro |
Data Display Tool
Tool Name | display_onset_of_melt.pro |
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Applicable Data Sets | Snow Melt Onset Over Arctic Sea Ice from SMMR and SSM/I-SSMIS Brightness Temperatures |
Description | IDL program that allows the user to view the data in graphical form. |
Access | FTP |
Geocoordinate and Pixel-Area Tools
The geocoordinate and pixel-area tools described here provide the same functionality for all polar stereographic passive microwave data sets at NSIDC. They include Fortran routines for determining latitude and longitude from i,j coordinates and a pixel-area grid.
Geocoordinate Tools
The following geocoordinate tools are available:
- locate.for
- mapll.for and mapxy.for
- psn06lats_v3.dat and pss06lats_v3.dat
- psn06lons_v3.dat and pss06lons_v3.dat
- psn12lats_v3.dat and pss12lats_v3.dat
- psn12lats_v3.dat and pss12lons_v3.dat
- psn25lats_v3.dat and pss25lats_v3.dat
- psn25lons_v3.dat and pss25lons_v3.dat
Tool Name | locate.for |
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Applicable Data Sets | DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures Nimbus-5 ESMR Polar Gridded Sea Ice Concentrations Nimbus-5 ESMR Polar Gridded Brightness Temperatures Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS Near Real-Time DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures Snow Melt Onset Over Arctic Sea Ice from SMMR and SSM/I-SSMIS Brightness Temperatures AMSR-E/Aqua Daily L3 6.25 km 89 GHz Brightness Temperature Polar Grids AMSR-E/Aqua Daily L3 12.5 km Brightness Temperature, Sea Ice Concentration, & Snow Depth Polar Grids AMSR-E/Aqua Daily L3 25 km Brightness Temperature & Sea Ice Concentration Polar Grids |
Description | Fortran executable that allows the user to enter an (i, j) coordinate, obtain the corresponding latitude/longitude coordinate, and vice versa. This executable must be run with the subroutines mapll.for and mapxy.for. |
Access | Brightness Temperature Data Sets: FTP Sea Ice Data Sets: FTP |
Tool Name | mapll.for and mapxy.for |
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Applicable Data Sets | DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures Nimbus-5 ESMR Polar Gridded Sea Ice Concentrations Nimbus-5 ESMR Polar Gridded Brightness Temperatures Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS Near Real-Time DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures Snow Melt Onset Over Arctic Sea Ice from SMMR and SSM/I-SSMIS Brightness Temperatures AMSR-E/Aqua Daily L3 6.25 km 89 GHz Brightness Temperature Polar Grids AMSR-E/Aqua Daily L3 12.5 km Brightness Temperature, Sea Ice Concentration, & Snow Depth Polar Grids AMSR-E/Aqua Daily L3 25 km Brightness Temperature & Sea Ice Concentration Polar Grids |
Description | Subroutines that are associated with the Fortran executable, locate.for. These programs need to be compiled but are not run explicitly. They are called by locate.for; thus, the user should compile these programs with locate.for, and then use locate to do the conversions. |
Access | Brightness Temperature Data Sets: FTP Sea Ice Data Sets: FTP |
Tool Name | psn06lats_v3.dat and pss06lats_v3.dat (Note on Versions)1 |
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Applicable Data Sets | AMSR-E/Aqua Daily L3 6.25 km 89 GHz Brightness Temperature Polar Grids |
Description | Grids that determine the latitude of a given pixel for the 6.25 km grids for either hemisphere (psn for the Northern Hemisphere and pss for the Southern Hemisphere). These latitude grids are in binary format and are stored as 4-byte integers (little endian) scaled by 100,000 (divide the stored value by 100,000 to get decimal degrees). Each array location (i, j) contains the latitude value at the center of the corresponding data grid cells. psn06lats_v3.dat: 1216 columns x 1792 rows, range = [31.011, 89.959] pss06lats_v3.dat: 1264 columns x 1328 rows, range = [-39.264, -89.959] |
Access | FTP |
Tool Name | psn06lons_v3.dat and pss06lons_v3.dat (Note on Versions)1 |
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Applicable Data Sets | AMSR-E/Aqua Daily L3 6.25 km 89 GHz Brightness Temperature Polar Grids |
Description | Grids that determine the longitude of a given pixel for the 6.25 km grids for either hemisphere (psn for the Northern Hemisphere and pss for the Southern Hemispere). These longitude grids are in binary format and are stored as 4-byte integers (little endian) scaled by 100,000 (divide the stored value by 100,000 to get decimal degrees). Each array location (i, j) contains the longitude value at the center of the corresponding data grid cells. An East-longitude convention is used; therefore, positive longitude values are to the east of Greenwich, England. psn06lons_v3.dat: 1216 columns x 1792 rows, range = [-180.000, 179.953] pss06lons_v3.dat: 1264 columns x 1328 rows, range = [-179.955, 179.955] |
Access | FTP |
Tool Name | psn12lats_v3.dat and pss12lats_v3.dat (Note on Versions)1 |
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Applicable Data Sets | DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures Near Real-Time DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures AMSR-E/Aqua Daily L3 12.5 km Brightness Temperature, Sea Ice Concentration, & Snow Depth Polar Grids |
Description | Grids that determine the latitude of a given pixel for the 12.5 km grids for either hemisphere (psn for the Northern Hemisphere and pss for the Southern Hemisphere). These latitude grids are in binary format and are stored as 4-byte integers (little endian) scaled by 100,000 (divide the stored value by 100,000 to get decimal degrees). Each array location (i, j) contains the latitude value at the center of the corresponding data grid cells. psn12lats_v3.dat: 608 columns x 896 rows, range = [31.041, 89.918] pss12lats_v3.dat: 632 columns x 664 rows, range = [-39.297, -89.918] |
Access | Brightness Temperature Data Sets: FTP Sea Ice Data Sets: FTP |
Tool Name | psn12lons_v3.dat and pss12lons_v3.dat (Note on Versions)1 |
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Applicable Data Sets | DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures Near Real-Time DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures AMSR-E/Aqua Daily L3 12.5 km Brightness Temperature, Sea Ice Concentration, & Snow Depth Polar Grids |
Description | Grids that determine the longitude of a given pixel for the 12.5 km grids for either hemisphere (psn for the Northern Hemisphere and pss for the Southern Hemisphere). These longitude grids are in binary format and are stored as 4-byte integers (little endian) scaled by 100,000 (divide the stored value by 100,000 to get decimal degrees). Each array location (i, j) contains the longitude value at the center of the corresponding data grid cells. An East-longitude convention is used; therefore, positive longitude values are to the east of Greenwich, England. psn12lons_v3.dat: 608 columns x 896 rows, range = [-180.000, 179.907] pss12lons_v3.dat: 632 columns x 664 rows, range = [-179.909, 179.909] |
Access | Brightness Temperature Data Sets: FTP Sea Ice Data Sets: FTP |
Tool Name | psn25lats_v3.dat and pss25lats_v3.dat (Note on Versions)1 |
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Applicable Data Sets | DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures Nimbus-5 ESMR Polar Gridded Sea Ice Concentrations Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS Passive Microwave Data Nimbus-5 ESMR Polar Gridded Brightness Temperatures Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS Near Real-Time DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures Near-Real-Time DMSP SSM/I-SSMIS Daily Polar Gridded Sea Ice Concentrations Snow Melt Onset Over Arctic Sea Ice from SMMR and SSM/I-SSMIS Brightness Temperatures AMSR-E/Aqua Daily L3 25 km Brightness Temperature & Sea Ice Concentration Polar Grids |
Description | Grids that determine the latitude of a given pixel for the 25 km grids for either hemisphere (psn for the Northern Hemisphere and pss for the Southern Hemisphere). These latitude grids are in binary format and are stored as 4-byte integers (little endian) scaled by 100,000 (divide the stored value by 100,000 to get decimal degrees). Each array location (i, j) contains the latitude value at the center of the corresponding data grid cells. psn25lats_v3.dat: 304 columns x 448 rows, range = [31.102, 89.836] pss25lats_v3.dat: 316 columns x 332 rows, range = [-39.364, -89.836] |
Access | Brightness Temperature Data Sets: FTP Sea Ice Data Sets: FTP |
Tool Name | psn25lons_v3.dat and pss25lons_v3.dat (Note on Versions)1 |
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Applicable Data Sets | DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures Nimbus-5 ESMR Polar Gridded Sea Ice Concentrations Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS Passive Microwave Data Nimbus-5 ESMR Polar Gridded Brightness Temperatures Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS Near Real-Time DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures Near-Real-Time DMSP SSM/I-SSMIS Daily Polar Gridded Sea Ice Concentrations Snow Melt Onset Over Arctic Sea Ice from SMMR and SSM/I-SSMIS Brightness Temperatures AMSR-E/Aqua Daily L3 25 km Brightness Temperature & Sea Ice Concentration Polar Grids |
Description | Grids that determine the longitude of a given pixel for the 25 km grids for either hemisphere (psn for the Northern Hemisphere and pss for the Southern Hemisphere). These longitude grids are in binary format and are stored as 4-byte integers (little endian) scaled by 100,000 (divide the stored value by 100,000 to get decimal degrees). Each array location (i, j) contains the longitude value at the center of the corresponding data grid cells. An East-longitude convention is used; therefore, positive longitude values are to the east of Greenwich, England. psn25lons_v3.dat: 304 columns x 448 rows, range = [-180.000, 179.814] pss25lons_v3.dat: 316 columns x 332 rows, range = [-179.818, 179.818] |
Access | Brightness Temperature Data Sets: FTP Sea Ice Data Sets: FTP |
Pixel-Area Grids
The following pixel-area tools are availabe:
- psn06area_v3.dat and pss06area_v3.dat
- psn12area_v3.dat and pss12area_v3.dat
- psn25area_v3.dat and pss25area_v3.dat
Please note that the data ranges given here are latitude and longitude values for the center of each grid cell. The range covered by the full grid extends to the pole (90 degrees latitude) and all longitudes (0 to 360 degrees longitude). Also note that corrected grids for the northern hemisphere were created June 22, 1999 and should replace the three psn25*.dat files that were distributed prior to this date.
To determine the lat/lon values of corresponding (i,j) data grid cells:
- Read in the array as long (4-byte) integers.
- Divide these values by 100,000. The resulting array gives the lat/lon values for the data grid cells in decimal degree
Tool Name | psn06area_v3.dat and pss06area_v3.dat (Note on Versions)1 |
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Applicable Data Sets | AMSR-E/Aqua Daily L3 6.25 km 89 GHz Brightness Temperature Polar Grids |
Description | Grids that determine the area of a given pixel for the 6.25 km grids for either hemisphere (psn for the Northern Hemisphere and pss for the Southern Hemisphere). The arrays are in binary format and are stored as 4-byte integers scaled by 1000 (divide by 1000 to get square km). psn06lons_v3.dat: 1216 columns x 1792 rows pss06lons_v3.dat: 1264 columns x 1328 rows |
Access | FTP |
Tool Name | psn12area_v3.dat and pss12area_v3.dat (Note on Versions)1 |
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Applicable Data Sets | DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures Near Real-Time DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures AMSR-E/Aqua Daily L3 12.5 km Brightness Temperature, Sea Ice Concentration, & Snow Depth Polar Grids |
Description | Grids that determine the area of a given pixel for the 12.5 km grids for either hemisphere (psn for the Northern Hemisphere and pss for the Southern Hemisphere). The arrays are in binary format and are stored as 4-byte integers scaled by 1000 (divide by 1000 to get square km). psn12area_v3.dat: 608 columns x 896 rows pss12area_v3.dat: 632 columns x 664 rows |
Access | Brightness Temperature Data Sets: FTP Sea Ice Data Sets: FTP |
Tool Name | psn25area_v3.dat and pss25area_v3.dat (Note on Versions)1 |
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Applicable Data Sets | DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures Nimbus-5 ESMR Polar Gridded Sea Ice Concentrations Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS Passive Microwave Data Nimbus-5 ESMR Polar Gridded Brightness Temperatures Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS Near Real-Time DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures Near-Real-Time DMSP SSM/I-SSMIS Daily Polar Gridded Sea Ice Concentrations Snow Melt Onset Over Arctic Sea Ice from SMMR and SSM/I-SSMIS Brightness Temperatures AMSR-E/Aqua Daily L3 25 km Brightness Temperature & Sea Ice Concentration Polar Grids |
Description | Grids that determine the area of a given pixel for the 25 km grids for either hemisphere (psn for the Northern Hemisphere and pss for the Southern Hemisphere). The arrays are in binary format and are stored as 4-byte integers scaled by 1000 (divide by 1000 to get square km). psn25area_v3.dat: 304 columns x 448 rows pss25area_v3.dat: 316 columns x 332 rows |
Access | Brightness Temperature Data Sets: FTP Sea Ice Data Sets: FTP |
1 Version 3 (V3) pixel area files, developed by the NASA National Snow and Ice Data Center Distributed Active Archive Center (NSIDC DAAC), provide a more accurate mapping of area for the polar stereographic grid. V3 and V2 area files differ by a maximum of approximately 0.5 sq km per grid cell at the corners of the grid. The effect on total extent and total area estimates is, at most, 10,000 sq km (approximately ~0.1%).
Masks and Overlays
The masks and overlays provided here supply the user with many options for concealing unwanted regions or overlaying coastlines and latitude/longitude grids; they are divided into the following categories:
Land Masks
Another issue is the effect of contamination of coastal ocean pixels by their proximity to land. Such proximity can modify the brightness temperatures of coastal ocean pixels, producing false ice concentration values along some coasts. These pixel mixing errors are considered in the summer 1996 issue of NSIDC Notes (Issue no. 18). Maslanik et al. (1996) discuss the effects of such land contamination in introducing differences between SMMR and SSM/I time series, and they describe the use of a modified land mask where land areas are extended to mask substantial contamination. The Snow Melt Onset Over Arctic Sea Ice from SMMR and SSM/I Brightness Temperatures land mask (n3blcmsk.hdf) alleviates this problem whereby ocean pixels adjacent to land or one pixel removed from land are designated as land-contaminated.
The land masks that are availabe are the following:
- amsr_gsfc_6n.hdf and amsr_nic_6s.hdf
- amsr_gsfc_12n.hdf and amsr_nic_12s.hdf
- amsr_gsfc_25n.hdf and amsr_nic_25s.hdf
- gsfc_12n.msk and gsfc_12s.msk
- gsfc_25n.msk and gsfc_25s.msk
- landmask.ntb and landmask.stb
- n3blcmsk.hdf
- pole_n.msk
Tool Name | amsr_gsfc_6n.hdf and amsr_nic_6s.hdf |
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Applicable Data Sets | AMSR-E/Aqua Daily L3 6.25 km 89 GHz Brightness Temperature Polar Grids |
Description | 6.25 km AMSR-E land mask for the Northern Hemisphere (amsr_gsfc_6n.hdf) and the Southern Hemisphere (amsr_nic_6s.hdf). The North land mask has not been updated since 1997. The South land mask includes an updated ice shelf definition created by the National Ice Center Science Department in June 2011 and an updated shoreline developed from ENVISAT and RADARSAT imagery from October 2009 to April 2010.
A 1-byte integer array is included in each HDF file. amsr_gsfc_6n.hdf: 1216 columns x 1792 rows |
Access | FTP |
Tool Name | amsr_gsfc_12n.hdf and amsr_nic_12s.hdf |
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Applicable Data Sets | AMSR-E/Aqua Daily L3 12.5 km Brightness Temperature, Sea Ice Concentration, & Snow Depth Polar Grids |
Description | 12.5 km AMSR-E land mask for the Northern Hemisphere (amsr_gsfc_12n.hdf) and the Southern Hemisphere (amsr_nic_12s.hdf). The North land mask is identical to gsfc_12n.msk and was last updated in 1997. The South land mask includes an updated ice shelf definition created by the National Ice Center Science Department in June 2011 and an updated shoreline developed from ENVISAT and RADARSAT imagery from October 2009 to April 2010.
A 1-byte integer array is included in each HDF file. amsr_gsfc_12n.hdf: 608 columns x 896 rows |
Access | FTP |
Tool Name | amsr_gsfc_25n.hdf and amsr_nic_25s.hdf |
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Applicable Data Sets | AMSR-E/Aqua Daily L3 25 km Brightness Temperature & Sea Ice Concentration Polar Grids |
Description | 25 km AMSR-E land mask for the Northern Hemisphere (amsr_gsfc_25n.hdf) and the Southern Hemisphere (amsr_nic_25s.hdf). The North land mask is identical to gsfc_25n.msk and was last updated in 1997. The South land mask includes an updated ice shelf definition created by the National Ice Center Science Department in June 2011 and an updated shoreline developed from ENVISAT and RADARSAT imagery from October 2009 to April 2010.
A 1-byte integer array is included in each HDF file. amsr_gsfc_25n.hdf: 304 columns x 448 rows |
Access | FTP |
Tool Name | gsfc_12n.msk and gsfc_12s.msk |
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Applicable Data Sets | DMSP SSM/I Daily Polar Gridded Brightness Temperatures Near Real-Time DMSP SSM/I Daily Polar Gridded Brightness Temperatures |
Description | 12.5 km land and coast mask for both hemispheres (n: Northern Hemisphere, s: Southern Hemisphere). A 1-byte integer array is included in each file. Values are 0 or 1, where 1 is the mask. gsfc_12n.msk: 608 columns x 896 rows gsfc_12s.msk: 632 columns x 664 rows |
Access | FTP |
Tool Name | gsfc_25n.msk and gsfc_25s.msk |
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Applicable Data Sets | DMSP SSM/I Daily Polar Gridded Brightness Temperatures Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data Nimbus-5 ESMR Polar Gridded Brightness Temperatures Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Near Real-Time DMSP SSM/I Daily Polar Gridded Brightness Temperatures Near Real-Time DMSP SSM/I Daily Polar Gridded Sea Ice Concentrations |
Description | 25 km land and coast mask for both hemispheres (n: Northern Hemisphere, s: Southern Hemisphere). A 1-byte integer array is included in each file. Values are 0 or 1, where 1 is the mask. gsfc_25n.msk: 304 columns x 448 rows gsfc_25s.msk: 316 columns x 332 rows |
Access | Brightness Temperature Data Sets: FTP Sea Ice Data Sets: FTP |
Tool Name | landmask.ntb and landmask.stb |
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Applicable Data Sets | Nimbus-5 ESMR Polar Gridded Brightness Temperatures |
Description | Northern (ntb) and Southern (stb) Hemisphere land mask at a 25 km resolution. Note: These have been superseded by the gsfc_25n.msk and gsfc_25s.msk but may be more appropriate for the ESMR data sets. landmask.ntb: 304 columns x 448 rows landmask.stb: 316 columns x 332 rows |
Access | FTP |
Tool Name | n3blcmsk.hdf |
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Applicable Data Sets | Snow Melt Onset Over Arctic Sea Ice from SMMR and SSM/I Brightness Temperatures |
Description | Northernth Hemisphere, 25 km land mask. Ocean pixels adjacent to land or one pixel removed from land are designated as land-contaminated. 304 columns x 448 rows |
Access | FTP |
Tool Name | pole_n.msk |
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Applicable Data Sets | Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Near Real-Time DMSP SSM/I Daily Polar Gridded Sea Ice Concentrations |
Description | Circular mask that symmetrically covers the observed maximum extent of the missing data (resulting from the orbit inclination and instrument swath) near the North Pole. This is a 1-byte array with no header. The area of the SSM/I hole has a value of 1. The additional area of the SMMR hole (a ring around the SSM/I hole) has a value of 2. All other pixels have a value of 0. pole_n.msk: 304 columns x 448 rows |
Access | FTP |
Land Overlays
The land overlays are useful for overlaying coast line and latitude/longitude grids on top of images and processed data. The files are broken down into two categories: Northern Hemisphere and Southern Hemisphere.
The land overlays that are availabe are the following:
- coast_12n.msk and coast_12s.msk
- coast_25n.msk and coast_25s.msk
- ltln_12n.msk and ltln_12s.msk
- ltln_25n.msk and ltln_25s.msk
Tool Name | coast_12n.msk and coast_12s.msk |
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Applicable Data Sets | DMSP SSM/I Daily Polar Gridded Brightness Temperatures Near Real-Time DMSP SSM/I Daily Polar Gridded Brightness Temperatures |
Description | 12.5 km coastline grid overlay for both hemispheres (n: Northern Hemisphere, s: Southern Hemisphere). Format is 1-byte integer arrays. Values are 0 or 1, where 1 is the mask. coast_12n.msk: 608 columns x 896 rows coast_12s.msk: 632 columns x 664 rows |
Access | FTP |
Tool Name | coast_25n.msk and coast_25s.msk |
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Applicable Data Sets | DMSP SSM/I Daily Polar Gridded Brightness Temperatures Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data Nimbus-5 ESMR Polar Gridded Brightness Temperatures Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Near Real-Time DMSP SSM/I Daily Polar Gridded Brightness Temperatures Near Real-Time DMSP SSM/I Daily Polar Gridded Sea Ice Concentrations |
Description | 25 km coastline grid overlay for both hemispheres (n: Northern Hemisphere, s: Southern Hemisphere). Format is 1-byte integer arrays. Values are 0 or 1, where 1 is the mask. coast_25n.msk: 304 columns x 448 rows coast_25s.msk: 316 columns x 332 rows |
Access | Brightness Temperature Data Sets: FTP Sea Ice Data Sets: FTP |
Tool Name | ltln_12n.msk and ltln_12s.msk |
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Applicable Data Sets | DMSP SSM/I Daily Polar Gridded Brightness Temperatures Near Real-Time DMSP SSM/I Daily Polar Gridded Brightness Temperatures |
Description | 12.5 km latitude/longitude grid overlay for both hemispheres (n: Northern Hemisphere, s: Southern Hemisphere). Format is 1-byte integer arrays. Values are 0 or 1, where 1 is the mask. ltln_12n.msk: 608 columns x 896 rows ltln_12s.msk: 632 columns x 664 rows |
Access | FTP |
Tool Name | ltln_25n.msk and ltln_25s.msk |
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Applicable Data Sets | DMSP SSM/I Daily Polar Gridded Brightness Temperatures Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data Nimbus-5 ESMR Polar Gridded Brightness Temperatures Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Near Real-Time DMSP SSM/I Daily Polar Gridded Brightness Temperatures Near Real-Time DMSP SSM/I Daily Polar Gridded Sea Ice Concentrations |
Description | 25 km latitude/longitude grid overlay for both hemispheres (n: Northern Hemisphere, s: Southern Hemisphere). Format is 1-byte integer arrays. Values are 0 or 1, where 1 is the mask. ltln_25n.msk: 304 columns x 448 rows ltln_25s.msk: 316 columns x 332 rows |
Access | Brightness Temperature Data Sets: FTP Sea Ice Data Sets: FTP |
Missing Data Mask
The circular section over the Northern Hemisphere pole (known as the pole hole) is never measured due to orbit inclination. The following mask is available for the pole hole region not covered by the SMMR and SSM/I instruments.
Tool Name | pole_n.msk |
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Applicable Data Sets | Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Near Real-Time DMSP SSM/I Daily Polar Gridded Sea Ice Concentrations |
Description | Circular mask that symmetrically covers the observed maximum extent of the missing data (resulting from the orbit inclination and instrument swath) near the North Pole. This is a 1-byte array with no header. The area of the SSM/I hole has a value of 1. The additional area of the SMMR hole (a ring around the SSM/I hole) has a value of 2. All other pixels have a value of 0. pole_n.msk: 304 columns x 448 rows |
Access | FTP |
Region Masks
The region masks are smaller areas than the land masks although they can be used as land masks using the pixel value of 11.
Tool Name | region_n.msk and region_s.msk | ||||||||||||||||||||||||||||||||||||||||||
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Applicable Data Sets | Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data Bootstrap Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Near Real-Time DMSP SSM/I Daily Polar Gridded Sea Ice Concentrations Sea Ice Trends and Climatologies from SMMR and SSM/I-SSMIS |
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Description | Region masks for the Northern (n) and Southern (s) Hemisperes. The files contain a 300-byte header, followed by a two-dimensional byte array stored by rows in column order. Regions are assigned different pixel values as shown in the following table. 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_n.msk: 448 rows x 304 columns region_s.msk: 316 rows x 332 columns Regions are assigned different byte values as follows:
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Access | FTP |
Ocean Masks
Tool Name | For a full list of ocean masks and maximum extent masks, refer to the Monthly Ocean Masks and Maximum Extent Masks Web page. |
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Applicable Data Sets | Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data Sea Ice Trends and Climatologies from SMMR and SSM/I |
Description | Monthly Ocean Masks and Maximum Extent Masks are available for the Northern (n) and Southern (s) Hemispheres. For more information and a description of the files, refer to the Monthly Ocean Masks and Maximum Extent Masks Web page. |
Access | See the Data Access section of the Monthly Ocean Masks and Maximum Extent Masks Web page for FTP access. |