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Data Set ID:
GLA13

GLAS/ICESat L2 Sea Ice Altimetry Data, Version 34

The Geoscience Laser Altimeter System (GLAS) instrument on the Ice, Cloud, and Land Elevation Satellite (ICESat) provides global measurements of polar ice sheet elevation to discern changes in ice volume (mass balance) over time. Secondary objectives of GLAS are to measure sea ice roughness and thickness, cloud and atmospheric properties, land topography, vegetation canopy heights, ocean surface topography, and surface reflectivity.

GLAS has a 1064 nm laser channel for surface altimetry and dense cloud heights, and a 532 nm lidar channel for the vertical distribution of clouds and aerosols.

This level-2 altimetry product (GLA13) provides surface elevations for sea ice. Data also include the laser footprint gelocation and reflectance, as well as geodetic, instrument, and atmospheric corrections for range measurements.

Each data granule has an associated browse product that users can quickly view to determine the general quality of the data in the granule. Browse products consist of image plots of key parameters and statistics. Data are in scaled integer binary format, big-endian (Unix) byte order, and are available via FTP.

Version Summary:

Release 34 incorporates fixes for several data issues that were determined to exist in the GLAS Release 33 data products.

Geographic Coverage

Spatial Coverage:
  • N: 86, S: -86, E: 180, W: -180

Spatial Resolution:
  • 60 m to 70 m x 60 m to 70 m
Temporal Coverage:
  • 20 February 2003 to 11 October 2009
Temporal Resolution: 1288 minute
Parameter(s):
  • Sea Ice > Ice Roughness
  • Sea Ice > Reflectance > Laser Reflectance
  • Sea Ice > Sea Ice Elevation
Platform(s) ICESAT
Sensor(s): ALTIMETERS, GLAS
Data Format(s):
  • Binary
Version: V34
Data Contributor(s): H. Zwally, Robert Schutz, Charles Bentley, Jack Bufton, Thomas Herring, Jean-Bernard Minster, James Spinhirne, Robert Thomas

Data Citation

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.

Zwally, H. J., R. Schutz, C. Bentley, J. Bufton, T. Herring, J. Minster, J. Spinhirne, and T. Ross. 2014. GLAS/ICESat L2 Sea Ice Altimetry Data, Version 34. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: http://dx.doi.org/10.5067/ICESAT/GLAS/DATA226. [Date Accessed].
No technical references available for this data set.

FAQ

Are the altimetry data already adjusted to the Geoid, or only to the Ellipsoid?

The elevation data is relative to the ellipsoid.
The data also have a parameter indicating the geoid height which is the height of the geoid above the ellipsoid for the first and last shot in the record.

In preliminary data from laser #1, why does the "i_surfType" record indicate surface classifications that are simultaneously land, sea ice, ocean, and ice sheet?

This is not an error. The masks for these surfaces purposely overlap in order to not miss any data; the masks are used to determine which data goes in GLA12-15 (the regional products). Most of the ice sheets are considered both ice sheet and land.

In the GLAS altimetry products is there an indicator to the presence of clouds?

Yes, it is an element of: GLA06 (GLAH06), GLA12 (GLAH12), GLA13 (GLAH13), GLA14 (GLAH14), GLA15 (GLAH15)

The Multiple Scattering Warning Flag, i_cld1_mswf (cld1_mswf_flg) is based on the total... read more

What is the basic difference between a standard and alternate fit and when would you normally choose one over the other?

The standard fit is optimized for "ice sheet-like" returns. The majority of these are single-peaked, narrow waveforms. The standard fit allows for only two peaks. Alternate fitting is meant to capture up to six peaks. More peaks are necessary for more complex waveforms over land, vegetated... read more

In GLA13 (GLAH13), values of "surfType" all indicate combinations of surface types, with no values for pure sea ice or pure land. Is this correct?

Yes, surface type flags are never purely sea ice; ocean is always combined with sea ice. Since GLA13 is a sea ice product, if the sea ice bit is not turned on in "surfType," it will not be in the product. This explains why there are no "pure land" returns. Also, the mask resolution is sufficient... read more

How To

How do you compute sea ice freeboard using GLA13 (GLAH13) data?

"Freeboard" is a measure of the height of sea ice above the ocean surface. The geoid height field ("i_gdHt") cannot be effectively used as a proxy for sea level in order to estimate freeboard, because current models of the Earth's geoid are too coarse to account for the local variations in geoid... read more