Arctic Sea Ice Freeboard and Thickness

Summary

This data set provides measurements of sea ice freeboard and sea ice thickness for the Arctic region. The data were acquired from the Ice, Cloud, and land Elevation Satellite (ICESat) Geoscience Laser Altimeter System (GLAS) instrument, the Special Sensor Microwave/Imager (SSM/I), and climatologies of snow and drift of ice. The data span six GLAS campaigns, laser 3D through 3I, from 21 October 2005 to 05 November 2007. Data parameters include sea ice freeboard and thickness measured in meters derived from GLAS Release 28 data. The data are provided in three formats: ASCII track data derived from binary track data, binary gridded polar stereographic data derived from ASCII gridded polar stereographic files, and Portable Network Graphic (PNG) image files. Also included are mask files used in preparation of the image files, a Mapx grid definition file, and grid cell center latitude and longitude files. The ASCII track data vectors of position and ice thickness have a resolution of about 170 meters in the along-track direction. The binary gridded polar stereographic data have a resolution of 25 km. The data set is approximately 940 megabytes. The data are available via FTP.

Citing These Data

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.

The following example shows how to cite the use of this data set in a publication. List the principal investigators, year of data set release, data set title and version number, dates of the data you used (for example, March to June 2004), publisher: NSIDC, and digital media.

Yi, Donghui and Jay Zwally. 2010. Arctic Sea Ice Freeboard and Thickness. Boulder, Colorado USA: National Snow and Ice Data Center. Digital media.

Overview Table
 

Category Description
Data format Space delimited ASCII text
Binary gridded 32-byte little-endian
Spatial coverage and resolution Spatial Coverage: Arctic Region
Southernmost Latitude: 65° N
Northernmost Latitude: 86° N
Westernmost Longitude: 180° W
Easternmost Longitude: 180° E

Spatial resolution: The centers of 70 m spots illuminated by the laser on the earth's surface are separated in the along-track direction by 170 m.
Temporal coverage and resolution Laser 3D  2005-10-21 to 2005-11-24
Laser 3E  2006-02-22 to 2006-03-27
Laser 3F  2006-05-24 to 2006-06-26
Laser 3G  2006-10-25 to 2006-11-27
Laser 3H  2007-03-12 to 2007-04-14
Laser 3I    2007-10-02 to 2007-11-05

A Release Schedule lists the temporal coverage of each ICESat/GLAS product.

Data are sampled 40 times per second, captured during 14.8 orbits per day.
Tools for accessing data ASCII data: any Web browser, plain text display or spreadsheet software.
Binary gridded data: ENVI, ArcGIS, other similar software packages.
Grid/projection description Binary gridded data are in polar stereographic projection.

ASCII track data are provided with latitude and longitude for each data point and are not projected.

Geoid models:
EGM96 global gravity field model is used below 64° N.
ArcGP is used north of 64° N.
File naming convention ASCII files: laser3h1341001.txt

Binary gridded data:
laser3d_freeboard_mskd.img
laser3d_freeboard_mskd.img.hdr
laser3d_freeboard_mskd.png
laser3d_thickness_mskd.img
laser3d_thickness_mskd.img.hdr
laser3d_thickness_mskd.png

Mask:
gsfc_25n.msk
gsfc_25n.msk.hdr

Mapx grid definition file:
PS25km_north.gpd

Grid cell center lat / long files:
PS25km_north_lon.img
PS25km_north_lon.img.hdr
PS25km_north_lat.img
PS25km_north_lat.img.hdr
File size ASCII files range from approximately 2 KB to 1 MB.

Binary gridded files:
ENVI header files (.hdr) are 749 bytes each.
Image files (.img) are 532 KB each.
Portable Network Graphics files (.png) range from approximately 31 KB to 42 KB.

Mapx grid definition file: 1 KB.

Grid cell center lat / long image files are 532 KB each.
Grid cell center lat / long files ENVI header files are 1 KB each.

Mask file is 133 KB.
Mask file ENVI header is 1KB.
Parameter(s) Sea ice freeboard in meters
Sea ice thickness in meters
Metadata Access View Metadata
Procedures for obtaining data Available via FTP.

Table of Contents

  1. Contacts and Acknowledgments
  2. Detailed Data Description
  3. Data Access and Tools
  4. Data Acquisition and Processing
  5. References and Related Publications
  6. Document Information

1. Contacts and Acknowledgments

Investigator(s)

Donghui Yi
Stinger Ghaffarian Technologies, Inc.
Cryospheric Sciences Branch
NASA Goddard Space Flight Center
Greenbelt, MD 20771 USA

Technical Contact

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

Format

ASCII

Each space delimited ASCII vector data file contains file headers followed by columns for latitude, longitude, freeboard, and thickness.

Longitude in WGS 84 degrees in the approximate range of 0 to 360.
Freeboard in meters above local sea level at the time of the measurement.
Thickness in meters.

Freeboard = 0 means the sea ice surface is at sea level. The average of the lowest 1percent reference elevation is used as reference sea level, so about 0.5 percent of the data are below sea level, that is, negative freeboard. Freeboard values less than zero are set to zero.

Note: Thickness values of -999 indicate that a thickness value could not be calculated and should be treated as missing data.

Binary

The freeboard and thickness binary gridded files are 304 columns x 448 rows containing little-endian floating-point values in meters. The grid is the 25 km polar stereographic grid used for SSM/I processing.

File and Directory Structure

Data are available on the FTP site in the following directory:

ftp://sidads.colorado.edu/pub/DATASETS/NSIDC0393_GLAS_SI_Freeboard_v01

File Naming Convention

ASCII File Names

ASCII files are named according to the following convention and as described in Table 1:

Example file name: laser3i1343001.txt

laserLPTTTTCCC.txt

Table 1.Valid Values for the ASCII File Name Variables
Variable Description
laserLP GLAS Laser Period used to collect data. LP = 3d, 3e, 3f, 3g, 3h, or 3i
TTTT Laser track number: 0001 through 0432, or 1282 through 1354
CCC Cycle of Reference Orbit: 001, 002, or 003
.txt Identifies the file as ASCII data

Binary File Names

Binary gridded files are named according to the following convention and as described in Table 2:

Example file name: laser3d_freeboard_mskd.img

Example file name: laser3d_freeboard_mskd.img.hdr

laserLP_nnnnnnnnn.mskd.zzz

Table 2. Valid Values for the Binary Grid File Name Variables
Variable Description
laserLP GLAS Laser Period used to collect data. LP = 3d, 3e, 3f, 3g, 3h, or 3i
_nnnnnnnnn Indicating 'freeboard' or 'thickness'
_mskd Indicating masked image
.zzz Identifies file type: .img (image), .img.hdr (header), or .png (Portable Network Graphics)

Grid Cell Center Latitude and Longitude Files

The grid cell center files provide the latitude and longitude for the center of each grid cell as a little-endian floating-point number. The files are named according to the following convention, and as described in Table 3.

Example file name: PS25km_north_lon.img

PS25km_north_mmm.zzz

Table 3. Valid Values for the Grid Cell Center File Name Variables
Variable Description
PS Polar Stereographic
25km 25 kilometer grid
_north northern hemisphere
mmm latitude (lat) or longitude (lon)
.zzz Identifies file type: .img (image), img.hdr (header)

Mask File

The mask file consists of values 0 = water, 1 = land. The file is named gsfc_25n.msk. The corresponding header file is gsfc_25n.msk.hdr.

File Size

ASCII File Size

ASCII file sizes range from 2 K to 1 MB

Binary File Size

The .hdr files are each 749 bytes.
The .img files are each 532 KB.
The .png files range from 31 KB to 44 KB.

Spatial Coverage

Arctic region

Southernmost Latitude: 65° N
Northernmost Latitude: 86° N
Westernmost Longitude: 180° W
Easternmost Longitude: 180° E

Note: The ASCII data are reported with longitude of 0 degrees to 360 degrees.

Spatial Resolution

The resolution of the gridded data is 25 km. Vectors have a resolution of about 170 meters in the along-track direction, or the distance between the centers of adjacent GLAS footprints. Several kilometers typically separate the ICESat GLAS data tracks.

Projection

Two geoid models are used in this study. North of 64° N, the Arctic Gravity Project (ArcGP) latitude limit, the ArcGP geoid is used. The Earth Gravitational Model 1996 (EGM96) geoid is used below 64° N. The difference, D, between ICESat measured sea level and the geoid was used to create a 5 km D-grid for each period. The mean of the 5 km D-grids was used as an improved geoid.

Temporal Coverage

Release 28 Laser Identifier 3D: 21 Oct 2005 to 24 Nov 2005
Release 28 Laser Identifier 3E: 22 Feb 2006 to 27 Mar 2006
Release 28 Laser Identifier 3F: 24 May 2006 to 26 Jun 2006
Release 28 Laser Identifier 3G: 25 Oct 2006 to 27 Nov 2006
Release 28 Laser Identifier 3H: 12 Mar 2007 to 14 Apr 2007
Release 28 Laser Identifier 3I:  02 Oct 2007 to 05 Nov 2007

A Release Schedule lists the temporal coverage of each ICESat/GLAS product.

Temporal Resolution

Each ICESat campaign period, 3D through 3I, represents one Arctic-wide ice thickness assessment. Thus the temporal resolution for this data set is approximately two to three times per year.

Parameter or Variable

The parameters of this data set are sea ice freeboard, and sea ice thickness.

Parameter Description

Sea ice freeboard is the height in meters of the sea ice above the water level. Thickness is the thickness in meters of the sea ice.

In the ASCII files, the thickness value -999 indicates missing values, possibly due to failure of the thickness algorithm for certain corresponding freeboard measurements.

The binary gridded *.img and *.png files have been masked. Table 4 shows the mask color value assignments to surface features.

Table 4. Binary Image File and PNG File Values
.img File Value .png File Value Surface Feature
-4 gray = 128 land south of 65° N
-3 gray = 164 land at or north of 65° N
-2 gray = 64 water south of 65° N
-1 gray = 96 water at or north of 65° N
greater than or equal to 0 full color (rainbow) applied across parameter value range sea ice freeboard or thickness measurements in meters

Sample Data Record

ASCII

The following sample of the laser3d0001002.txt ASCII file shows header information, and the first four records of Latitude, Longitude, Freeboard and Thickness values.

Binary

The following sample shows the laser3d_freeboard_mskd.img masked binary gridded image.

 laser3d_freeboard.img binary gridded image

The following sample shows the laser3d_freeboard_mskd.png masked binary gridded image.

 laser3d_freeboard_masked.jpg masked binary gridded image

Error Sources

Table 5 summarizes the GLAS single-shot error budget for elevation measurements (Zwally et al. 2002).

Table 5. GLAS Single-shot Error Budget for ICESat Elevation Measurements
Error Source Error Limit
Precision orbit determination (POD) 5 cm
Precision attitude determination (PAD) 7.5 cm
Atmospheric delay 2 cm
Atmospheric forward scattering 2 cm
Other (tides, etc.) 1 cm
RSS 13.8 cm

For further discussion on error sources, see Zwally et al. 2002, and also refer to the Error Sources section of the NSIDC GLAS/ICESat L1 and L2 Global Altimetry Data Web page.

Quality Assessment

For further discussion on quality assessment of GLAS products, refer to the Quality Assessment section of the NSIDC GLAS/ICESat L1 and L2 Global Altimetry Data Web page.

3. Data Access and Tools

Data Access

Data are available via FTP.

Volume

ASCII

The total volume for the ASCII track data files is approximately 932 megabytes.

Binary

The total volume for the binary gridded image, header and masked image files is approximately eight megabytes.

Software and Tools

ASCII

The ASCII track data may be displayed with any Web browser or plain text display software.

Binary

The binary gridded data may be displayed using ENVI, ArcGIS, or other similar software packages.

Related Data Collections

4. Data Acquisition and Processing

Theory of Measurements

Two geoid models are used in this study. The ArcGP geoid is used north of 64° N since that is the ArcGP latitude limit. The EGM96 geoid is used below 64° N.

Elevations varying more than plus-or-minus 4 meters are not used. This condition filters out some land, island, and iceberg data. These conditions are the same as in Zwally et al. 2008.

ICESat measures a surface elevation profile referenced to an ellipsoid. Due to the limited accuracy of the geoids and ocean tide models, and poor knowledge of the dynamic topography, sea-ice surface elevation referenced to a geoid cannot be regarded as sea-ice freeboard. The information needed to calculate sea-ice freeboard is the elevation difference between the top of the snow surface, local sea levels, and snow height and density above the snow/ice interface. If the elevation difference is known, even if the absolute elevations are biased, the sea-ice freeboard can be determined. Thus, the knowledge of relative elevation is crucial while absolute elevation is less important. This is the underlying concept in the derivation of freeboard.

In this study, constant densities of ρW = 1023.9 kg m-3 and ρI = 915.1 kg m-3 are used to calculate sea ice thickness from the freeboard. There is no spatial variation of now density ρS. Snow density, including the time variation, is based on Kwok 2008. The range of the snow density is 0.16 to 0.40.

Refer to the Processing Steps section below for details on the application of theory of measurements.

Sensor or Instrument Description

The data for this data set were acquired with the GLAS instrument onboard the Ice, Cloud, and land Elevation satellite (ICESat), from the SSM/I instrument on board the Defense Meteorological Satellite Program (DMSP), and from weather stations on the sea ice.

Data Acquisition Methods

Freeboard is measured from ICESat elevation profiles (Zwally et al. 2008). Snow depth is interpolated, both spatially and temporally, from climatology snow depth in situ measurements (Warren et al. 1999). Thickness is estimated from ICESat freeboard and climatology snow depth. SSM/I daily ice concentration data (Gloersen et al. 1992) from January 2003 to October 2008 are used to determine sea ice boundaries.

Derivation Techniques and Algorithms

The grids of sea ice freeboard and thickness were derived from the corresponding ICESat point measurements of freeboard and thickness using the following steps:

  1. Freeboard/thickness values are estimated for each valid ICESat sea ice observation during the laser period.
     
  2. The latitude/longitude of each freeboard/thickness observation is mapped into a column/row for a particular cell of the 25 km resolution 304 by 448 Polar Stereographic grid.
     
  3. All the freeboard/thickness observations that fall into the same Polar Stereographic grid cell are averaged together resulting in a single freeboard/thickness value pair for each cell. This resampling algorithm is commonly referred to as "drop in the bucket" resampling. The cell will be empty if there is no data in that cell.
     
  4. The daily SSM/I Goddard Space Flight Center (GSFC) sea ice concentration values for each cell in the Polar Stereographic grid for the laser periods are averaged together for each ICESat campaign. Those cells that do not have a sea ice concentration value, which are cells that fall within the pole hole poleward of 84.5° N, are assigned values. Values from cells across eight equiangular sectors, nearest to the estimation point, are formed into a weighted average. The weight, w, is based on distance, d, from the estimation point to the nearest cell value in a particular sector, via the following relation in Equation 1 which is described in Table 6:

    Pulse Broadening Parameter (Equation 1)

    Where:

    Table 6. Cell Value Weighted Average Equation Description
    Variable Description
    w Weight
    d Distance
    r Maximum radius from which to draw samples. To interpolate values across the polar region, r was set to 420 km.

     
  5. Assign 0 to freeboard/thickness grid cells where mean ice concentration is less than 20 percent. For freeboard/thickness grid cells having no value and ice concentration greater than or equal to 20 percent, interpolate values.
     

Processing Steps

Sea ice freeboard and thickness are calculated from ICESat GLAS ground tracks using the following steps.

  1. Elevation data filtering. Before calculating the sea-ice freeboard and thickness, the following conditions were applied to filter out data contaminated by clouds, saturation, and land or islands.
     
    1. Gain limit. An upper limit of detector gain is applied to filter out stronger atmospheric attenuated waveforms. The upper limit for the laser periods are: 50 counts for L1, L2, L2A,L2B,L3A, and L3B; 80 counts for L3C,L3D,L3E,L3F,L3G,L3H, and L3I; 120 counts for L2C,L3J, and L3K (Yi et al. 2011).
       
    2. Pulse broadening limit. Define a pulse-broadening parameter, S. See Equation 2 which is described in Table 7.

      Pulse Broadening Parameter (Equation 2)

      Where:

      Table 7. Pulse-Broadening Parameter Equation Description
      Variable Description
      S Measure of the broadening of the transmitted pulse associated with surface topography and the undesirable effects of saturation and atmospheric forward scattering
      c Speed of light
      σR Echo waveform 1-sigma pulse width
      σT Transmitted waveform 1-sigma pulse width

      Heavily saturated waveforms and forward scattering waveforms have broadened pulse widths, so data with S larger than 0.8 m are discarded.
       
    3. Reflectivity limit. Heavily saturated waveforms also tend to have very high apparent reflectivity, and forward scattering waveforms tend to have low reflectivity. Therefore, data with reflectivity smaller than 0.05 or larger than 0.9 are discarded.
       
    4. Elevation limit. Elevation varying more than plus or minus four meters are not used. This condition filters out some land, island, and iceberg data. These conditions are the same as in Zwally et al. 2008.

  2. Geoid. Two geoid models are used in this study. The ArcGP geoid is used north of 64° N since that is the ArcGP latitude limit. The EGM96 is used below 64° N.

    The difference, D, between ICESat measured sea level and the geoid was used to create a 5 km D-grid for each period. The mean of the 5 km D-grids was used as an improved geoid.
     
  3. Saturation correction and Inverse Barometer correction are applied as shown in Equation 3 and explained in Table 8. Both corrections are the same as in Zwally et al. 2008. Sea surface response to atmospheric pressure loading, the inverse barometer effect, is computed using the method described in the Aviso and Physical Oceanography Distributed Active Archive Center (PODAAC) User Handbook (Picot et al. 2003).

    ΔHib = 9.948 × (Patm - P) (Equation 3)

    Where:

    Table 8. Inverse Barometer Effect Equation Description
    Variable Description
    ΔHib Inverse barometer correction
    Patm Surface atmospheric pressure
    P Time varying mean of the global surface atmospheric pressure over the oceans

    ΔHib is applied to the ICESat elevation at the same time as the saturation correction. The surface atmospheric pressures used here are from the National Center for Environmental Protection (NCEP) (Stackpole 1994). The mean global surface atmospheric pressures over the ocean are from Collecte Localisation Satellites (Dorandeu and Le Traon 1999).
     
  4. SSMI daily ice con. To avoid open ocean in low ice concentration areas, freeboard = 0 is assigned to areas where ice concentration less than 20 percent. This is an empirical limit to balance the sea ice filtered out and the freeboard contamination introduced by open ocean water waves.
     
  5. Elevation. The ICESat measured surface elevation, Hie, the i_elev in product GLA06, is referenced to the TOPEX/POSEIDON ellipsoid. ICESat surface elevations have instrument corrections, dry and wet troposphere corrections, and tidal corrections applied. Elevation, h, is defined in Equation 4 and described in Table 9.

    h = Hie + ΔHib + ΔHsat - hg (Equation 4)

    Where:

    Table 9. Elevation Equation Description
    Variable Description
    h Elevation above the geoid
    Hie ICESat measured surface elevation
    ΔHib Inverse barometer correction
    ΔHsat Saturation correction
    hg Geoid height
     
  6. Calculate 50 km running mean (hm) of elevation h. ICESat measures a surface elevation profile referenced to an ellipsoid. Due to the limited accuracy of the geoids and ocean tide models, and poor knowledge of the dynamic topography, sea-ice surface elevation referenced to a geoid cannot be regarded as sea-ice freeboard. The information needed to calculate sea-ice freeboard is the elevation difference between the top of the snow surface on the sea ice and local sea levels. If the elevation difference is known, even if the absolute elevations are biased, the sea-ice freeboard can be determined. Thus, the knowledge of relative elevation is crucial while absolute elevation is less important. Here we describe an algorithm to determine relative elevation and use this relative elevation to estimate sea-ice freeboard. By determining local ocean level and using only the relative elevation, the influences of the longer wavelength (greater than 50 km) factors such as geoid error, long wavelength laser pointing error and tidal error, which affect the absolute elevation, are removed from the freeboard calculation.
     
  7. Calculate relative elevation: The relative elevation is calculated using Equation 5 and as described in Table 10.

    hr = h - hm (Equation 5)

    Where:

    Table 10. Relative Elevation Equation Description
    Variable Description
    hr Relative elevation
    h Elevation above geoid
    hm 50 km running mean of elevation h

  8. Sea level, hs, at any given point is determined by averaging the lowest one percent of the hr values within 50 km of that point. The one percent value was selected empirically. It provides enough points in calculating mean sea level to reduce measurement noise, and also minimizes the influence of thinner ice on the calculation. This value may be optimized further as we learn more about the distribution of leads in the Arctic. In extreme cases when there is no open water within the 100-km range, hs will measure the height of thin ice, thus underestimating freeboard.
     
  9. hd(D). The difference between ICESat measured sea level and the geoid used is shown in Equation 6 as described in Table 11.

    hd = hm - hs (Equation 6)

    Where:

    Table 11. Difference Between ICESat Measured Sea Level and the Geoid Used Equation Description
    Variable Description
    hd Difference between the ICESat measured sea level and the geoid used
    hm 50 km running mean of elevation h
    hs Sea level

  10. Freeboard height, F, at a given point is calculated as shown in Equation 7 and described in Table 12.

    F = hr - hs (Equation 7)

    Where:

    Table 12. Freeboard Height Equation Description
    Variable Description
    F Freeboard height
    hr Relative elevation
    hs Sea level

    To have a valid F at a point, there must be enough valid elevation measurements available within 50 km of that point. In this study, a point is discarded if less than 50 percent (300 points) of the total 600 points are available.
     
  11. Sea-ice thickness, according to Archimedes buoyancy principle, is shown in Equation 8 and described in Table 13.

    T = ρW F - ρW - ρS TS (Equation 8)


    ρW - ρI ρW - ρI

    Where:

    Table 13. Sea-ice Thickness Equation Description
    Variable Description
    T Sea ice thickness
    F Freeboard height
    TS Snow depth
    ρW Water density
    ρS Snow density
    ρI Sea ice density

    In this study, constant densities of ρW = 1023.9 kg m-3 and ρI = 915.1 kg m-3 are used to calculate sea ice thickness from the freeboard. There is no spatial variation of ρS. Snow density, including time variation, is based on Kwok 2008.

    Since snow depths and densities available for converting freeboard to thickness are at 25 by 25 km grid scale, these gridded values reflect grid scale mean snow depth and density over the arctic but do not have the small scale variation that can be directly used to do the ICESat shot to shot freeboard/thickness conversion. Snow depth and density must be modeled to apply them to the individual measurements. The following method is used to do the freeboard/thickness conversion at a point.

    Due to the dynamic nature of arctic sea ice, snow falls are not always accumulated on the top of sea ice. They may fall on leads or open water. So the snow depth varies from one footprint to another. Here a snow accumulation factor was defined as Fx (= 0.4, 0.4, 0.6, 0.1 for FM, MA, MJ, and ON), shown below with dates and lasers:

    Fx = 0.4 February to March (FM) Laser 3E
    Fx = 0.4 March to April (MA) Laser 3H
    Fx = 0.6 May to June (MJ) Laser 3F
    Fx = 0.1 October to November (ON) Laser 3D, 3G, 3I

    It was assumed when freeboard is larger than Fx, snow is fully accumulated on sea ice; when freeboard is less than Fx, snow accumulation on sea ice is proportional to the ratio δ=Fi/Fx. The following five conditions are applied when converting Fi to Ti:

    1. If Fi < 0, set Fi = 0
    2. if Fi < Fx, set δ=Fi/Fx and if Fi ³ Fx, set δ=1
    3. Ts=δ Ts', Ts' is snow depth of 25×25 km grids, Ts is snow depth used in the conversion
    4. if Ts > Fi, set Ts=Fi
    5. if Ci < 20%, set Fi=0,  Ci is bilaterally interpolated ice concentration at a point from SSM/I ice concentration

    Where:


    Table 14. Snow Accumulation Factor Description
    Variable Description
    Fi freeboard
    Fx snow accumulation factor
    d ratio Fi/Fx
    Ts snow depth
    Ci bilaterally interpolated ice concentration at a point from SSMI ice concentration
    Ti sea ice thickness

5. References and Related Publications

Dorandeu, J. and P. Y. Le Traon. 1999. Effects of Global Mean Atmospheric Pressure Variations on Mean Sea Level Changes from TOPEX/POSEIDON. Journal of Atmospheric and Oceanic Technology, 16(9): 1279-1283.

Gloersen, P., W. J. Campbell, D. J. Cavalieri, J. C. Comiso, C. L. Parkinson, and H. J. Zwally. 1992. Arctic and Antarctic Sea Ice, 1978-1987: Satellite Passive-Microwave Observations and Analysis. NASA SP-511, 290 pp.

Kwok, R., and G. F. Cunningham. 2008. ICESat Over Arctic Sea Ice: Estimation of Snow Depth and Ice Thickness. Journal of Geophysical Research 113(C08010), doi: 10.1029/2008JC004753.

Picot, N., K. Case, S. Desai, and P. Vincent. 2003. AVISO and PODAAC User Handbook, IGDR and GDR Jason Products. SMM-MU-M5-OP-13184-CN (AVISO), JPL D-21352 (PO.DAAC).

Stackpole, J. D. 1994. The WTO Format for the Storage of Weather Product Information and the Exchange of Weather Product Message in Gridded Binary Form. NOAA Office Note 388.

Warren, S. G., I. G. Rigor, N. Untersteiner, V. F. Radionov, N. N. Bryazgin, Y. I. Aleksandrov, and R. Colony. 1999. Snow Depth on Arctic Sea Ice. Journal of Climate 12: 1814 - 1829.

Yi, Donghui, H. Jay Zwally, and John W. Robbins. 2011. ICESat observations of seasonal and interannual variations of sea-ice freeboard and estimated thickness in the Weddell Sea (2003-2009). Annals of Glaciology, 52(57):43-51.

Zwally, H. J., D. Yi, R. Kwok, and Y. Zhao. 2008. ICESat Measurements of Sea Ice Freeboard and Estimates of Sea Ice Thickness in the Weddell Sea. Journal of Geophysical Research 113(C02S15), doi: 10.1029/2007JC004284.

Zwally, H. J., B. Schutz, W. Abdalati, et al. 2002. ICESat's Laser Measurements of Polar Ice, Atmosphere, Ocean, and Land. Journal of Geodynamics 34(3-4): 405-445.

6. Document Information

Acronyms

The acronyms used in this document are listed in Table 13.

Table 13. Acronyms and Abbreviations
Acronym Description
ArcGP Arctic Gravity Project
ASCII American Standard Code for Information Interchange
CIRES Cooperative Institute for Research in Environmental Science
DMSP Defense Meteorological Satellite Program
EGM96 Earth Gravitational Model 1996
ENVI Environment for Visualizing Images
FTP File Transfer Protocol
GLAS Geoscience Laser Altimeter System
GSFC Goddard Space Flight Center
ICESat Ice, Cloud, and land Elevation Satellite
NCEP National Center for Environmental Protection
NSIDC National Snow and Ice Data Center
PNG Portable Network Graphics
PAD Precision Attitude Determination
POD Precision Orbit Determination
PODAAC Physical Oceanography Distributed Active Archive Center
SSM/I Special Sensor Microwave/Imager
URL Uniform Resource Locator
WGS 84 World Geodetic System 1984

Document Creation Date

September 2010

Document URL

http://nsidc.org/data/docs/daac/nsidc0393_arctic_seaice_freeboard/index.html