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Data Set ID:
GLAH12

GLAS/ICESat L2 Antarctic and Greenland Ice Sheet Altimetry Data (HDF5), Version 34

GLAH06 is used in conjunction with GLAH05 to create the Level-2 altimetry products. Level-2 altimetry data provide surface elevations for ice sheets (GLAH12), sea ice (GLAH13), land (GLAH14), and oceans (GLAH15). Data also include the laser footprint geolocation and reflectance, as well as geodetic, instrument, and atmospheric corrections for range measurements. The Level-2 elevation products, are regional products archived at 14 orbits per granule, starting and stopping at the same demarcation (± 50° latitude) as GLAH05 and GLAH06. Each regional product is processed with algorithms specific to that surface type. Surface type masks define which data are written to each of the products. If any data within a given record fall within a specific mask, the entire record is written to the product. Masks can overlap: for example, non-land data in the sea ice region may be written to the sea ice and ocean products. This means that an algorithm may write the same data to more than one Level-2 product. In this case, different algorithms calculate the elevations in their respective products. The surface type masks are versioned and archived at NSIDC, so users can tell which data to expect in each product. Each data granule has an associated browse product.

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):
  • Glaciers/Ice Sheets > Glacier Elevation/Ice Sheet Elevation
  • Glaciers/Ice Sheets > Glacier Topography/Ice Sheet Topography
  • Glaciers/Ice Sheets > Ice Sheets
  • Sea Ice > Reflectance > Laser Reflectance
  • Glaciers/Ice Sheets > Glacier Elevation/Ice Sheet Elevation > Laser Reflectance
  • Sea Ice > Reflectance
Platform(s) ICESAT
Sensor(s): ALTIMETERS, GLAS
Data Format(s):
  • HDF
Version: V34
Data Contributor(s): David Hancock, H. Zwally, Robert Schutz, John Dimarzio

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, D. Hancock, and J. Dimarzio. 2014. GLAS/ICESat L2 Antarctic and Greenland Ice Sheet Altimetry Data (HDF5), 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/DATA209. [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 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

Does GLA14 (GLAH14) cover the ice sheets, and if so, does it use a different algorithm over ice sheets?

Yes, the land mask (and thus, GLA14) includes ice sheets, although it applies the same algorithm to compute elevation regardless of whether the surface is ice or not. You should use GLA12 for more accurate ice sheet elevations.

How To

Stepping through the HDFView User Guide with GLAS HDF5 Data
HDFView

https://support.hdfgroup.org/products/java/hdfview/

When you first open HDFView, the HDFView window appears with an empty tree and data panel.

The main window consists of six different components... read more