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GLAS Subsetter: Order geographic and temporal subsets of the data.
Data Set ID:
GLA09

GLAS/ICESat L2 Global Cloud Heights for Multi-layer Clouds, Version 33

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.

Level-2 cloud heights for multi-layer clouds (GLA09) contain cloud layer top and bottom height data at sampling rates of 4 sec, 1 sec, 5 Hz, and 40 Hz.

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:

For information about Version 33, see the NSIDC ICESat Description of Data Releases page.

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):
  • Clouds > Cloud Height
  • Clouds > Cloud Vertical Distribution
Platform(s) ICESAT
Sensor(s): ALTIMETERS, GLAS
Data Format(s):
  • Binary
Version: V33
Data Contributor(s): H. Zwally, Robert Schutz, Steve Palm, William Hart, Dennis Hlavka, James Spinhirne, Ellsworth Welton

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, W. Hart, D. Hlavka, S. Palm, J. Spinhirne, and E. Welton. 2011. GLAS/ICESat L2 Global Cloud Heights for Multi-layer Clouds, Version 33. [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/DATA222. [Date Accessed].
No technical references available for this data set.

FAQ

In GLA09 (GLAH09), is there a cloud bottom for every cloud top? How do you match them?

For every top of layer given, there is definitely a bottom of layer given in the same corresponding location in the vector. The tops and bottoms vectors are ordered top-down for each channel (532 nm or 1064 nm) independently. Thus, if Cld_top and Cld_bot are the 10-element arrays that hold the... read more

Since two different algorithms are used in GLA08 (GLAH08) and GLA09 (GLAH09), are the aerosol layers different between the two products?

GLA09 (GLAH09) should not contain elevated aerosol layers, only cloud heights. If the GLA09 (GLAH09) algorithm detects a layer in the data, a cloud/aerosol discrimination routine is called. If the layer is considered cloud, then it is output to GLA09 (GLAH09). If it is... read more

GLA08 and GLA09 were originally designed to use only the 532 nm profiles from GLA07; however, these two products use the 1064 nm channel data in addition to 532 nm. Where do the 1064 nm layers come from, and do the 532 nm and 1064 nm algorithms differ?

The GLAS science team added the 1064 nm-based layer detection just a few months before ICESat launched, because they discovered potentially serious problems in the 532 nm channel. The initial design of the software only used the 532 nm channel because of its superior data quality; however, when... read more

How different are the cloud layer heights in GLA09 identified by the 532 nm and 1064 nm channels?

Users may note duplication of cloud layers in GLA09, meaning that a given layer is reported twice: once from 532 nm and once from 1064 nm (assuming that both channels are operating). If this occurs, the top and bottom of the layer should be slightly different, because two completely different... read more

In GLA09 (GALH09), is there a cloud bottom for every cloud top? How do you match them?

For every top of layer given, there is definitely a bottom of layer given in the same corresponding location in the vector. The tops and bottoms vectors are ordered top-down for each channel (532 nm or 1064 nm) independently. Thus, if Cld_top and Cld_bot are the 10-element arrays that hold the... read more