Does NSIDC have tools to extract and geolocate polar stereographic data?

NSIDC provides software tools to extract and geolocate data in a polar stereographic projection derived from passive microwave instruments, as well as masking tools that limit the influence of weather effects on sea ice concentrations. All tools are available by FTP. The tools work with the polar stereographic gridded passive microwave data sets at NSIDC.

Types of tools include:

  1. Data extraction tools
  2. Geocoordinate tools
  3. Masks & overlays

Data Extraction Tools

The following data extraction tools allow you to extract and read the data from the data files.

extract.pro

An 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

Applicable Data Sets

IDL Routines for Passive Microwave Data: Usage Example - extract.pro

Items in bold indicate user input. 

IDL> extract,array

% Compiled module: EXTRACT.Enter the processing type(1 = near-real-time)(2 = polar grids from hard drive)

: 1

Enter start and end dates for animation (yyyymmdd, e.g., 19950610).

Start Date: 20010404End Date: 20010404

Enter the channel to be extracted1 2 3 4 5 6 7--- --- --- --- --- --- ---19V 19H 22V 37V 37H 85V 85HEnter position of parameter (1-7)

: 2

Enter the hemisphere(1 = northern)(2 = southern)

: 1

Enter the full name of the directory that the Tb files are in.(Note: must correctly use upper and lower case letters.)

: /usr2/projects/tb_tools/usr2/projects/tb_tools/NRTSI_SSMIF13_20010404_N.19H

% Loaded DLM: HDF.

IDL> 

extract_


extract_ice.pro

An 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).

Applicable Data Sets

Access: FTP

IDL Routines for Passive Microwave Data: Usage Example - extract_ice.pro

Items in bold indicate user input. 

IDL> extract_ice,array

% Compiled module: EXTRACT_ICE.Enter the processing type (1 = near-real-time)(2 = polar grids)

: 1

Enter start and end dates (yyyymmdd, e.g., 19950610).

Start Date: 20010404End Date: 20010404

Enter the hemisphere (1 = northern)(2 = southern)

: 1

Enter the full name of the directory that the sea ice files are in.(Note: must correctly use upper and lower case letters.)

: /usr2/projects/tb_tools

Enter the satellite number (e.g., 8, 11, or 13)

: 13

/usr2/projects/tb_tools/NRTSI_SSMIF13_20010404_N.BIN/usr2/projects/tb_tools/NRTSI_SSMIF13_20010404_N.BIN

IDL> 


Geocoordinate Tools

For data set users who need the latitude and longitude of the center of any cell in the grid, the following geocoordinate tools are available.

Tool Name Polar Stereographic Ancillary Grid Information
Applicable Data Sets
Description Polar stereographic grids provide arrays of the latitude or longitude, in degrees, at grid cell centers for the 6.25km, 12.5km, and 25km grids for the Northern and Southern Hemispheres.
Access Via HTTPS
Tool Name locate.for
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 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 Via GitHub
Tool Name mapll.for and mapxy.for
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
AMSR-E/AMSR2 Daily L3 6.25 km 89 GHz Brightness Temperature Polar Grids
AMSR-E/AMSR2 Unified L3 Daily 25 km Brightness Temperatures & 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 Via GitHub

 

Land Masks

NSIDC provides masks and overlays to supply users with many options for concealing unwanted regions or overlaying coastlines and latitude/longitude grids. The land masks are useful for concealing the land of the Northern and Southern Hemispheres prior to processing of the data. The files are divided into two categories: Northern Hemisphere and Southern Hemisphere.

Note on Land Masks

Several versions of the land masks have been developed, though NSIDC only distrubutes the most current masks.

Beginning with the SMMR era, the first masks NSIDC developed were landmask.ntb and landmask.stb. Other masks were later added for use with SSM/I F8 data. The last set of masks to be added to the series are those beginning with gsfc, which were originally developed for use with SSM/I F11 and F13. However, all of the masks provided here will work across all platforms (SMMR and SSM/I).

The relatively slight differences in numbers of SSM/I-grid pixels masked as land can introduce discrepancies in analyses of time series spanning the SMMR and SSM/I period. One method of addressing this issue is to generate a composite mask in which all pixels mapped as land in any of the masks are coded as land pixels in the composite mask. Use of such a composite mask improves the consistency of the SMMR and SSM/I record at the expense of masking additional ocean areas as land. A composite of the CIA World Data Bank I and II (GSFC-1 and JPL-1) has been produced by J. Maslanik at NSIDC.

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. 

Tool Name amsr_gsfc_6n.hdf and amsr_nic_6s.hdf
Applicable Data Sets AMSR-E/Aqua Daily L3 6.25 km 89 GHz Brightness Temperature Polar Grids
AMSR-E/AMSR2 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
Values are 0 (water), 3 (coast), 216 (land)
amsr_nic_6s.hdf: 1264 columns x 1328 rows
Values are 0 (water), 1 (land), 2 (coast)

Access FTP
Tool Name amsr_gsfc_12n.hdf and amsr_nic_12s.hdf
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
Values are 0 (water) and 1 (land).
amsr_nic_12s.hdf: 632 columns x 664 rows
Values are 0 (water), 1 (land), and 2 (coast).

Access FTP
Tool Name amsr_gsfc_25n.hdf and amsr_nic_25s.hdf
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
Values are 0 (water) and 1 (land).
amsr_nic_25s.hdf: 316 columns x 332 rows
Values are 0 (water), 1 (land) and 2 (coast).

Access FTP
Tool Name gsfc_12n.msk and gsfc_12s.msk
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
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
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 pole_n.msk
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.

Tool Name coast_12n.msk and coast_12s.msk
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
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
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
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
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
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
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. (See user guide references for NSIDC-0192.)

region_n.msk: 448 rows x 304 columns
region_s.msk: 316 rows x 332 columns

Regions are assigned different byte values as follows:
 
Pixel Value Arctic Region Antarctic Region

1

Non-regional ocean  

2

Sea of Okhotsk and Japan Weddell Sea

3

Bering Sea Indian Ocean

4

Hudson Bay Pacific Ocean

5

Baffin Bay/Davis Strait/Labrador Sea Ross Sea

6

Greenland Sea Bellingshausen Amundsen Sea

7

Kara and Barents Seas  

8

Arctic Ocean  

9

Canadian Archipelago  

10

Gulf of St. Lawrence  

11

Land Land

12

Coast Coast

0

Lakes, extended coast  
Access FTP