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Data Set ID: 

ATLAS/ICESat-2 L3A Sea Ice Freeboard, Version 5

This data set (ATL10) contains estimates of sea ice freeboard, calculated using three different approaches. Sea ice leads used to establish the reference sea surface and descriptive statistics used in the height estimates are also provided. The data were acquired by the Advanced Topographic Laser Altimeter System (ATLAS) instrument on board the Ice, Cloud and land Elevation Satellite-2 (ICESat-2) observatory.

This is the most recent version of these data.

Version Summary: 

Changes for this version include:

  • The ATL10 QA check for insufficient output failure was updated. The code now checks for the number of valid freeboard ice segments and number of valid, un-interpolated, reference surfaces. Previously, the total number of freeboard ice segments written (valid and invalid) were counted, and the number of reference surfaces was not considered. A new controllable parameter, min_refsurf_count, was added to control the minimum reference surface count threshold (l3a_fb_cont_mod).
  • The description of the reference surface interpolation flag has been updated to match the procedure in the atlas_l3a_fb code A controllable parameter used in the reference surface interpolation flag was also added to replace a hard coded value (max pad time).
  • The height segment inverted barometer variable was moved to the geophysical group from the height segments group (it was already in the geophysical group in ATL07).
  • The computation of the reference surface height has been updated to better match the description in the ATBD (essentially a minor bug fix).
  • The MMS, Geoid, and the two free-to-mean parameters have been calculated at the reference surface-scale (e.g. 10 km, weighted by lead group size) and added to ATL10.
  • The along track distance has been calculated at the beam reference surface and lead group scale.
  • The reference surface time and location has been updated to be set to the center of the reference surface. Previously, the location was found by simply averaging data from all the segments within the 10 km sections which caused some odd behavior (skewed locations towards the sides of the sections). The reference surface lat/lon/time is now determined using interpolation. For reference surfaces set where there are no sea ice segments for a given beam, a filling procedure is used to estimate the reference surface lat/lon. The filling procedure uses a distance routine to find the lat/lon for a point a given distance from a known point, in a known direction.
  • The new PODPPD flag, and updated segment_type flag, are read from ATL07 and used in filtering which sea ice segments are used in freeboard processing. Now, if there is a calibration scan maneuver occurring, the freeboard segment in ATL10 is invalidated. A new pointing angle variable is also calculated (from the co_elev variables) and is used to further filter the freeboard segments (currently default of 1 degree from nadir).
  • An error in the computation of reference surface sigma values let to missing sigma variables for individual freeboard segments. The error was corrected by simply interpolating from nearby reference surface sigma values. Future work will look to update this approach. Note: The missing reference surface sigmas were only present for reference surfaces with an interpolation flag value of 3. Reference surfaces where the height is interpolated also uses an interpolated sigma value. The value of sigma for an interpolated reference surface may be re-visited in the future.
  • Modified the integration test scripts to generate browse products and check for the presence of default 1 and default 2 plots.
  • The ATLAS browse plot for ATL10 reference surface and freeboard heights has been corrected.
  • New parameters of mean ocean sea level pressure dynamic inverted barometer effect from ATL07 and written to ATL10. The new parameters are: /ancillary_data/freeboard_estimation/mean_ocean_slp: Mean ocean sea level pressure computed in ATL07 and /gtx/freeboard_beam_segment/geophysical/height_segment_dynib: Dynamic inverted barometer effect computed in ATL07.These are not currently applied to the heights but could be in future releases.

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

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Data Format(s):
  • HDF5
Spatial Coverage:
N: 90, 
S: -90, 
E: 180, 
W: -180
Spatial Resolution:
  • Varies
Temporal Coverage:
  • 14 October 2018
Temporal Resolution91 dayMetadata XML:View Metadata Record
Data Contributor(s):Ron Kwok, Alek Petty, Glenn Cunningham, Thorsten Markus, David Hancock, Alvaro Ivanoff, Jesse Wimert, Marco Bagnardi, Nathan Kurtz

Geographic Coverage

Other Access Options

Other Access Options


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.

Kwok, R., A. A. Petty, G. Cunningham, T. Markus, D. Hancock, A. Ivanoff, J. Wimert, M. Bagnardi, N. Kurtz, and the ICESat-2 Science Team. 2021. ATLAS/ICESat-2 L3A Sea Ice Freeboard, Version 5. [Indicate subset used]. Boulder, Colorado USA. NSIDC: National Snow and Ice Data Center. doi: [Date Accessed].

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