This data set contains daily and weekly sea ice motion vectors, as well as browse images representing the weekly data. Input data sources, derived from AVHRR, AMSRE, SMMR, SSMI, and SSMI/S sensors; IABP buoys; and NCEP/NCAR Reanalysis forecasts, used to generate the daily and weekly sea ice motion estimates are also included.
Polar Pathfinder Daily 25 km EASE-Grid Sea Ice Motion Vectors, Version 4
This is the most recent version of these data.
Changes to this version include:
Data are provided in georeferenced netCDF format rather than ASCII and raw binary files
Merge 15 highest-weighted rather than 15 closest input vectors
Improved filtering of SSMI inputs
Each buoy provides one daily motion estimate instead of separate noon and midnight estimates
Monthly ice motion estimates are no longer provided
COMPREHENSIVE Level of Service
Data: Data integrity and usability verified; data customization services available for select data
Documentation: Key metadata and comprehensive user guide available
User Support: Assistance with data access and usage; guidance on use of data in tools and data customization services
|
Geographic Coverage |
- If you are not currently logged in to Earthdata, you will be prompted to do so.
- You may register for an Earthdata Login if you do not have an account.
Once you have logged in, you will be able to click and download files via a Web browser. There are also options for downloading via a command line or client. For more detailed instructions, please see Options Available for Bulk Downloading Data from HTTPS with Earthdata Login.
As a condition of using these data, you must cite the use of this data set using the following citation. For more information, see our Use and Copyright Web page.
Tschudi, M., W. N. Meier, J. S. Stewart, C. Fowler, and J. Maslanik. 2019. Polar Pathfinder Daily 25 km EASE-Grid Sea Ice Motion Vectors, Version 4. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: https://doi.org/10.5067/INAWUWO7QH7B. [Date Accessed].Data Description
Parameters
The main parameters for this data set are daily and weekly sea ice motion (cm/s). Sea ice motion is divided into along-x (u) and along-y (v) components. Error variance (for daily data) and the number of contributing files (for weekly data) are also provided.
Additionally, the input data used to calculate daily and weekly sea ice motion vectors are included in this data set. The input data consist of sea ice motion vectors derived from specific sensors (see Table 2 for more details).
File Information
Format
Daily and weekly sea ice motion are provided in georeferenced netCDF (.nc) format. Input data are also provided in netCDF (.nc) format.
PNG (.png) browse images are also included.
Daily and Weekly Sea Ice Motion File Contents
Daily and weekly sea ice motion netCDF file contents are described in Table 1 and represented in Figure 1.
Variable | Description | Units | Missing / Fill Value |
---|---|---|---|
u | Along-x component of the sea ice motion (not the eastward velocity1) | cm/s | -9999 |
v | Along-y component of the sea ice motion (not the northward velocity1) | cm/s | -9999 |
icemotion_error_estimate |
Estimated vector error obtained from the optimal interpolation process; only included in daily data files:
|
N/A | -9999 |
number_of_observations | Number of contributing daily files; only included in the weekly data files | Number of daily files | N/A |
latitude | Latitude | ° N | N/A |
longitude | Longitude | ° E | N/A |
crs | Coordinate reference system (e.g. EASE-Grid North 25 km) | N/A | N/A |
x | X coordinate | Projected meters | N/A |
y | Y coordinate | Projected meters | N/A |
time | Time of measurement | Days since 1970-01-01 (daily data files) Date range (weekly data files) |
N/A |
1See How to convert the horizontal and vertical components to east and north for more details |
.png)
Browse Image File Contents
One browse image displaying weekly sea ice motion is provided for every week of data. Figure 2 contains a sample browse image.

Input Data File Contents
Input data files are described in Table 2. All input data files contain the same variables and structure, except for the IABP buoy data. Since the buoy data are point-source data, they are stored as a list, not as a georeferenced grid. Input data fields are described in more detail in Tables 3 and 4.
Source | Spatial Resolution |
---|---|
AVHRR | 50km |
AMSR-E | 37.5 km |
SMMR | 75 km |
SSM/I | 75 km |
SSMIS | 75 km |
National Center for Environmental Prediction (NCEP) / National Center for Atmospheric Research (NCAR) Reanalysis U-wind and V-wind data | 50 km |
International Arctic Buoy Program (IABP) buoys | Point source, locations indexed to 25 km EASE-Grid |
Variable
|
Description
|
Units
|
||||
---|---|---|---|---|---|---|
U | Along-x component of the sea ice motion (not the eastward velocity); scaled by a factor of 10 | cm/s | ||||
V | Along-y component of the sea ice motion (not the northward velocity); scaled by a factor of 10 | cm/s | ||||
AMSRE_quality_info1 | Correlation coefficient; ranges from 0.0 - 1.0 | N/A | ||||
S*_source2 | Indicates the input source channel (S* = SMMR, SSMI, or SSMIS)
|
N/A | ||||
number_of_AVHRR_observations3 | The number of vectors averaged together at a given location, includes up to four passes and two channels (infrared and visible) | N/A | ||||
Wind_Source4 | Indicates that the input source for this data set was the NCEP/NCAR U-wind and V-wind data set | N/A | ||||
Latitude
|
Latitude
|
° N
|
||||
Longitude
|
Longitude
|
° E
|
||||
CRS | Coordinate reference system (e.g. EASE-Grid North 25 km) | N/A | ||||
X |
Projected x coordinate
|
Projected meters
|
||||
Y |
Projected y coordinate
|
Projected meters
|
||||
Time | Time of measurement | Julian day | ||||
1only appears in the AMSRE input data files 2only appears in the SMMR, SSMI, and SSMI/S input data files 3only appears in the AVHRR input data files 4only appears in the NCEP/NCAR input data files |
Variable | Description | Units |
---|---|---|
U | Along-x component of the sea ice motion (not the eastward velocity); scaled by a factor of 10 | cm/s |
V | Along-y component of the sea ice motion (not the northward velocity); scaled by a factor of 10 | cm/s |
observation_date | Day of observation | Days since 1970-01-01 |
buoy_ID | IABP buoy number | N/A |
X | Projected x coordinate on the 25 km EASE-Grid | Projected meters |
Y | Projected y coordinate on the 25 km EASE-Grid | Projected meters |
Directory Structure
Data are available for download via HTTPS; the link is accessible through the "Download Data" tab.
Within the file directory, data are sorted by hemisphere. There are two main subdirectories: north and
south
. Within these subdirectories, folders are subdivided by data type. Table 5 provides a listing of the subfolders.
Data Subdirectory
|
Description
|
---|---|
/north/browse/ |
Contains the browse images of all of the weekly sea ice motion values. Within this directory, the data are divided by year. |
/north/daily/ |
Contains the daily sea ice motion data files.
|
/north/input_sources/ |
Contains the input data files. Within this directory, the data are subdivided into folders based on input data source (see Table 2 for more details):
|
/north/weekly/ |
Contains the weekly sea ice motion data files. |
Daily and Weekly Sea Ice Motion File Naming Convention
The daily and weekly data files are named according to the following convention and as described in Table 6:icemotion_<daily|weekly>_hh_rrrr_<start-date>_<end-date>_v##.nc
Example:icemotion_daily_sh_25km_19781101_19781231_v4.1.nc
icemotion_weekly_sh_25km_19790101_19791231_v4.1.nc
Variable | Description |
---|---|
<daily|weekly> | Indicates whether the file contains daily or weekly sea ice motion values |
hh | Hemisphere (nh = Northern, sh = Southern) |
rrrr | Resolution of input data in km (e.g. 50 km) |
<start-date> | First day of data represented in the file, written in yyyymmdd (4-digit year, 2-digit month, 2-digit day) format |
<end-date> | Last day of data represented in the file, written in yyyymmdd (4-digit year, 2-digit month, 2-digit day) format |
v## | Version number |
Browse Image File Naming Convention
The browse images are named according to the following convention and as described in Table 7:icemotion_weekly_hh_rrrr_<start-date>_<end-date>_v##.png
Example:icemotion_weekly_nh_25km_20000101_20000108_v4.1.png
Variable | Description |
---|---|
hh | Hemisphere (nh = Northern, sh = Southern) |
rrrr | Resolution of input data in km (e.g. 50 km)3 |
<start-date> | First day of the week that the image represents, written in yyyymmdd (4-digit year, 2-digit month, 2-digit day) format |
<end-date> | Last day of the week that the image represents, written in yyyymmdd (4-digit year, 2-digit month, 2-digit day) format |
v## | Version number |
Input Data File Naming Convention
The input data files are named according to the following convention and as described in Table 8:im_from_<source>_hh_rrrr_<start-date>_<end-date>_v##.nc
Example:im_from_amsre_nh_37.5km_20020619_20021231_v4.1.nc
im_from_avhrr_nh_50km_19810724_19811231_v4.1.nc
im_from_buoy_nh_list_198790101_19791231_v4.1.nc
im_from_smmr_nh_75km_19781025_19781231_v4.1.nc
im_from_smmi_nh_75km_19870821_19871231_v4.1.nc
im_from_smmis_nh_75km_20070101_20071231_v4.1.nc
im_from_wind_nh_50km_19781025_19781231_v4.1.nc
Variable | Description |
---|---|
im_from | Indicates that the file contains sea ice motion estimates used as input for the daily sea ice motion calculations |
<source> | Input data source (amsre, smmr, ssmi, ssmis, buoy1, or wind2) |
hh | Hemisphere (nh = Northern, sh = Southern) |
rrrr | Resolution of input data, in km (e.g. 50 km)3 |
<start-date> | First day of data represented in the file, written in yyyymmdd (4-digit year, 2-digit month, 2-digit day) format |
<end-date> | Last day of data represented in the file, written in yyyymmdd (4-digit year, 2-digit month, 2-digit day) format |
v## | Version number |
1Available for Northern Hemisphere only
2Indicates that the data come from the NCEP/NCAR Reanalysis U-wind and V-wind at 10 m data set 3The resolution is described as "list" for point-source data
|
File Size
Daily sea ice motion files range from approximately 18.0 - 22.0 MB.
Weekly sea ice motion files range from approximately 3.0 - 4.0 MB.
Input data files range from approximately 0.2 - 8.0 MB.
Browse images are approximately 0.5 - 1.5 MB.
Spatial Information
Coverage
Daily and weekly sea ice motion data are confined to the poles in the Northern and Southern Hemisphere, as represented in Figure 3.

Resolution
The final daily and weekly sea ice motion data are provided at a resolution of 25 km. Input data have different spatial resolutions (see Table 2).
Geolocation
Daily and weekly sea ice motion data are georeferenced to the Northern and Southern 25 km original EASE-Grid projections. More details on these projections and grids are provided in the tables below. More details on EASE-Grid can be found on the EASE Grids website.
Geographic coordinate system | N/A |
---|---|
Projected coordinate system | NSIDC EASE-Grid North |
Longitude of true origin | 0 |
Latitude of true origin | 90 |
Scale factor at longitude of true origin | N/A |
Datum | N/A |
Ellipsoid/spheroid | International 1924 Authalic Sphere |
Units | meter |
False easting | 0 |
False northing | 0 |
EPSG code | 3408 |
PROJ4 string |
+proj=laea +lat_0=90 +lon_0=0 +x_0=0 +y_0=0 +a=6371228 +b=6371228 +units=m +no_defs
|
Reference | http://epsg.io/3408 |
Grid cell size (x, y pixel dimensions) | 25067.5 projected meters (x) 25067.5 projected meters (y) |
---|---|
Number of rows | 361 |
Number of columns | 361 |
Geolocated lower left point in grid | 29.71270° S, 45.00000° W |
Nominal gridded resolution | 25 km by 25 km |
Grid rotation | N/A |
ulxmap – x-axis map coordinate of the outer edge of the upper-left pixel | -4524683.8 m |
ulymap – y-axis map coordinate of the outer edge of the upper-left pixel | +4524683.8 m |
Geographic coordinate system | N/A |
---|---|
Projected coordinate system | NSIDC EASE-Grid South |
Longitude of true origin | 0 |
Latitude of true origin | 90 |
Scale factor at longitude of true origin | N/A |
Datum | N/A |
Ellipsoid/spheroid | International 1924 Authalic Sphere |
Units | Meter |
False easting | 0 |
False northing | 0 |
EPSG code | 3409 |
PROJ4 string |
+proj=laea +lat_0=-90 +lon_0=0 +x_0=0 +y_0=0 +a=6371228 +b=6371228 +units=m +no_defs
|
Reference | http://epsg.io/3409 |
Grid cell size (x, y pixel dimensions) | 25067.5 projected meters (x) 25067.5 projected meters (y) |
---|---|
Number of rows | 321 |
Number of columns | 321 |
Geolocated lower left point in grid | 36.95776° S, 135.00000° W |
Nominal gridded resolution | 25 km by 25 km |
Grid rotation | N/A |
ulxmap – x-axis map coordinate of the outer edge of the upper-left pixel | -4023333.8 m |
ulymap – y-axis map coordinate of the outer edge of the upper-left pixel | +4023333.8 m |
Temporal Information
Coverage and Resolution
The temporal coverage and resolution vary by data type and sensor. See Table 13 for more details.
Data
|
Source
|
Start Date
|
End Date
|
Resolution
|
---|---|---|---|---|
Daily Sea
Ice Motions
|
Interpolated from input data |
01 November 1978
|
31
December 2018
|
Daily
|
Weekly Sea
Ice Motions
|
Averaged from Daily Sea Ice Motions
|
05 November 1978
|
31 December 2018
|
Weekly
|
Input Data
|
AMSR-E
|
19 June 2002
|
08 August 2011
|
Data are available every day for any given grid cell.
|
AVHRR
|
24 July 1981
|
31 December 2000 |
Four satellite passes are used each day when available.
|
|
IABP buoys
|
18 January 1979
|
31
December 2018
|
The 12:00 Greenwich Mean Time (GMT) buoy positions
were used to compute 24-hour mean velocities. |
|
NCEP-NCAR U-wind and V-wind
|
25 October 1978
|
31
December 2018
|
Data are available every day for any given grid cell.
|
|
SMMR
|
25 October 1978
|
08 July 1987
|
Data are available every other day for any given grid cell. See the SMMR 48 Hour Temporal Resolution Consequences for more information.
|
|
SSM/I
|
09 July 1987
|
31 December 2006
|
Data are available every day for any given grid cell.
|
|
SSMIS
|
01 January 2007
|
31
December 2018
|
Data are available every day for any given grid cell.
|
Data Acquisition and Processing
Background
Sea ice movement is measured using imagery acquired by frequent, repeat coverage by remote sensing instruments. Ice motion computed from satellite imagery represents the displacement between two images with the same spatial coverage taken at different acquisition times. Researchers identify a feature, such as an ice floe, on two registered images and measure its pixel displacement. Ice velocity vectors are computed based on the pixel resolution and the time span between images.
A more automated method is to measure the correlation of groups of pixels between image pairs. A small target area in one image is correlated with several areas of the same size in a search region of the second image. The displacement of the ice is then defined by the location in the second image where the correlation coefficient is the highest. This is the spatial correlation method used to produce sea ice motion vectors for this data set.
The approach used for this data set is generally valid over short distances away from the ice edge in areas where ice conditions are relatively stable from day to day. Spatial correlation methods cannot find matches between images where a complete knowledge of ice dynamics is needed, e.g. in areas where ice is deforming or in the ice margins near the open ocean where the spatial or spectral characteristics of the ice within a pixel are changing rapidly (Emery, Fowler, and Maslanik 1995).
Acquisition
AVHRR Input Data
This input data derived sea ice motion vectors from AVHRR channel 2 (visible band) and channel 4 (infrared) Global Area Coverage (GAC) images. These images have a 50 km gridded resolution, are available for nearly two decades, provide an intermediate spatial resolution between passive microwave and buoys, and have a finer time sampling than microwave data.
Beginning with Version 3 of this data set, misregistered AVHRR estimates were removed.
For more information on AVHRR input data, please refer to: AVHRR Polar Pathfinder Twice-Daily 5 km EASE-Grid Composites.
Buoy Input Data
This input data derived sea ice motion vectors from International Arctic Buoy Program (IABP) C buoy position data. IABP provides buoy location information through satellite tracking of buoys placed on sea ice. Several buoy locations are determined each day and corresponding sea ice motions are calculated. Sea ice motion estimates from buoys are very accurate, but they are limited since the numbers and locations of buoys are driven by cost and logistics. In addition, buoys have not been placed on ice in the Eastern Arctic.
IABP buoy locations are generally provided every 12 hours: at noon and at midnight Greenwich Mean Time (GMT). This sea ice motion product uses 24-hour motion estimates from the IABP. For example, the IABP motion estimate for a buoy at noon on 01 January 2010 is derived by taking the difference of the buoy's location at noon on 02 January 2010 and its location at noon on 01 January 2010 and then dividing by 24 hours. The intervening midnight location value is not factored into the noon-to-noon 24-hour motion estimate. Similarly, the IABP motion estimate for midnight is calculated the same way, ignoring the intervening noon location information. Therefore, each buoy generally has two independent, 24-hour motion estimates: one for midnight and one for noon. Beginning with Version 4 of this data set, the noon-time and midnight buoy vectors were averaged together to provide one buoy-derived sea ice motion per day.
For more information the buoy input data, please refer to: International Arctic Buoy Program Air Droppable RAMS (ADRAMS) Buoy.
NCEP/NCAR Wind Input Data
This input data derived sea ice motion vectors from the NCEP/NCAR Reanalysis wind data set. The data, called U-wind and V-wind at 10 m, are available from the NOAA Earth System Research Laboratory (ESRL) Physical Sciences Division (PSD).
For more information on the NCEP/NCAR input data, please refer to Kistler et al. (2000).
Passive Microwave Input Data
The passive microwave input data come from four different instruments: SMMR, SSM/I, SSMIS, and AMSR-E. All the source data are available for download from the National Snow and Ice Data Center Distributed Active Archive Center (NSIDC DAAC). The SMMR input data are derived from the NIMBUS-7 SMMR Pathfinder Brightness Temperatures data set. Due to satellite limitations, full Arctic coverage is only available every two days with SMMR; see the SMMR 48 Hour Temporal Resolution Consequences discussion for more information. The SSM/I and SSMIS input data both come from DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures, while the AMSR-E input data come from the AMSR-E/Aqua L2A Global Swath Spatially-Resampled Brightness Temperatures. Passive microwave inputs also include the Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS Passive Microwave Data data set, which is used to distinguish ice-covered and ice-free ocean.
Table 14 lists the channels used by each passive microwave sensor to derive input sea ice motion vectors. In general, the passive microwave sensors provide all-sky coverage, whereas the AVHRR visible and infrared channels are limited by cloud cover. For more information on the passive microwave instruments, please refer to:
Instrument
|
Channel Frequency
|
Resolution
|
---|---|---|
AMSR-E
|
89 GHz vertical
|
12.5 km
|
SMMR
|
37 GHz vertical and horizontal
|
25 km
|
SSM/I
|
37 GHz vertical and horizontal
85 GHz vertical and horizontal |
25 km
12.5 km |
SSMIS
|
37 GHz vertical and horizontal
91 GHz vertical and horizontal |
25 km
12.5 km |
Processing
The following steps were used to create this sea ice motion product.
-
Compute the Sea Ice Motion Fields
A sea ice mask, derived from Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS Passive Microwave Data using a threshold of 15%, is used to restrict all independent sea ice motion estimates to ice-covered ocean. Detailed information about the methods used to compute sea ice motion for each input data source can be found on the Measuring Sea Ice Motion web page.
-
Grid the Input Data to the 25 km EASE-Grid
Each of the input sea ice motion estimates are mapped to the output grid (e.g. Northern Hemisphere 25 km EASE-Grid). -
Merge the Sea Ice Motion Fields
Input sea ice motion estimates are combined to produce the daily sea ice motion product. Daily sea ice motion is a source- and distance-weighted average of the 15 highest-weighted input sea ice motion vectors. Each input data set is weighted according to the expected accuracy of the source data. For example, estimates derived from nearby buoys are weighted higher than NCEP/NCAR-derived estimates. Note that where data are sparse, the input data will be widely separated; when data are dense, only the very nearest estimates are considered. If the input sea ice motion estimates vary significantly from each other, this method can result in daily sea ice motion vectors that do not vary smoothly from one grid cell to the next. -
Calculate Daily Error Values
The input vectors from the individual input sources (NCEP/NCAR, SSM/I, SSMIS, SMMR, AMSR-E, and AVHRR) are weighted separately based upon cross-correlations with buoy vectors. The optimal interpolation uses these weights, along with their distances from the location being estimated, to obtain the final error variance. If the closest input vector was greater than 1250 km, then a value of 1000 is added to this variable. Because interpolation was applied to a surface map from passive microwave data, coastlines may contain false ice. In this case, the third variable was assigned a negative value to allow users to remove these vectors near coastlines (within 25 km). For example, a value of -1035 indicates all of the following conditions: the vector was near a coastline, the nearest sampled vector was further than 1250 km, and the vector had a standard deviation (σ) of 3.5 and an estimated error variance (σ2) of 12.25. -
Compute Weekly Fields
Weekly sea ice motion was computed from the daily gridded sea ice motion data for both the northern and southern polar regions. Weekly sea ice motion is an average of all the daily sea ice motions calculated for that week. At least four out of seven days were needed to compute the weekly mean.
Weekly means for each year begin on 01 January for consistency. The last day of each year (or last two days if in a leap year) were excluded. In other words, the first week is always 01 January through 07 January and the last week of a year is either 24 December through 30 December or 23 December through 29 December (if in a leap year). -
Encode Data and Associated Metadata in netCDF Files
Beginning with Version 4, data are provided in netCDF format.
Quality, Errors, and Limitations
Quality Assessment - Input Data
The Measuring Sea Ice Motion web page provides information on the accuracy of sea ice motion estimates calculated from each input sensor.
Beginning with Version 3 of this data set, IABP buoy sea ice motion estimates above 70 cm/s were deemed physically unrealistic; thus, velocities that exceed this threshold were excluded from this data set. In addition, beginning with Version 4 of this data set, buoys which were outside the mask of valid sea ice motion (away from the coast, where sea ice concentration was greater than 15%) were excluded.
Quality Assessment - Daily and Weekly Sea Ice Motion Product
The icemotion_error_variance (daily data) and number_of_observations (weekly data) fields both provide a means of characterizing data quality. For the daily files, the error variance can indicate a "near coastline" check. For the weekly data, the more days that contributed to calculating the sea ice motion vector in a given grid cell, the higher the data quality.
Missing Data
Beginning with Version 3 of this data set, there are some missing data in the Southern Hemisphere because there was not enough data from SSMI and AVHRR sensors to yield sea ice motion vectors. Missing data fields are left blank.
Limitations
The passive-microwave-derived sea ice motion estimates are based on changes in brightness temperature over consecutive days. The methods used to generate these input vectors requires fairly large areas of open ocean. As a result, ice motion cannot be calculated in regions of mixed land and ocean coverage, such as the Canadian Archipelago. The absence of sea ice motion estimates in such locations does not imply the absence of ice in these locations.
Version History
Version
|
Date
|
Description of Changes
|
---|---|---|
V4.1 | April 2019 | |
V4
|
March 2019
|
|
V3
|
February 2016
|
|
V2
|
Sep 2013
|
|
V1
|
May 2003
|
Original version of data.
Note: V1 is not indicated in Version 1 file names |
Related Data Sets
AMSR-E/Aqua L2A Global Swath Spatially-Resampled Brightness Temperatures
AVHRR Polar Pathfinder Twice-Daily 5 km EASE-Grid Composites
AVHRR Polar Pathfinder Twice-Daily 25 km EASE-Grid Composites
DMSP SSM/I-SSMIS Daily Polar Gridded Brightness Temperatures
NIMBUS-7 SMMR Pathfinder Brightness Temperatures
Related Websites
SMMR and SSM/I-SSMIS | Overview
Contacts and Acknowledgments
Mark Tschudi
University of Colorado
Colorado Center for Astrodynamics Research (CCAR)
Department of Aerospace Engineering Sciences
University of Colorado, Boulder
431 UCB
Boulder, Colorado USA 80309-0431
Walter N. Meier
University of Colorado Boulder
449 UCB
Boulder, CO 80309-0449
J. Scott Stewart
University of Colorado Boulder
Boulder, CO 80309-0449
Chuck Fowler
University of Colorado Boulder
Boulder, CO 80309
Jim Maslanik
University of Colorado Boulder
Boulder, CO 80309
References
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Cavalieri, D., C. Parkinson, P. Gloersen, and H. J. Zwally. 1996, updated yearly. Sea Ice Concentrations from Nimbus-7 SMMR and DMSP SSM/I-SSMIS Passive Microwave Data, Version 1. [indicate subset used]. Boulder, Colorado USA: NASA DAAC at the National Snow and Ice Data Center. doi:10.5067/8GQ8LZQVL0VL.
Cracknell, A. 1997. The Advanced Very High Resolution Radiometer. London: Taylor and Francis.
Emery, W., C. Fowler, and J. Maslanik. 1995. Satellite Remote Sensing of Ice Motion, in Oceanographic Applications of Remote Sensing, ed. Motoyoshi Ikeda and Frederic W. Dobson. CRC Press, Boca Raton.
Haumann, F. Alexander, Nicolas Gruber, Matthias Münnich, Ivy Frenger and Stefan Kern. 2016. Sea-ice transport driving Southern Ocean salinity and its recent trends. Nature 537:89-92. doi:10.1038/nature19101.
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Kidwell, K. 1995. NOAA Polar Orbiter Data User's Guide. U.S. Dept. of Commerce, National Oceanic and Atmospheric Administration, NESDIS.
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