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Data Set ID: 

ATLAS/ICESat-2 L3A Ocean Surface Height, Version 4

This data set (ATL12) contains along-track sea surface heights at variable length scales over cloud-free regions. Estimates of height distributions, surface roughness, surface slope, and apparent reflectance 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.

There is a more recent version of these data.

Version Summary: 

Changes for this version include:

  • Implemented the usage of the ATL03 orbit and pointing flag (podppd_flag) to only process data with podppd_flag=0. This is done to avoid putting out bad sea surface heights when the underlying pointing and position data are bad.
  • Updated the moving average process to consider photons with signal confidence 3 and 4 to be consistent with the ATBD.
  • Aligned the atmosphere data (layer_flag) collected only for the strong beams by segment_id for the processing of weak beam data.
  • Changed from surface finding based on the distribution of photon heights to surface finding based on the photon height anomaly relative to a moving bin average of high confidence photon heights. This is done to exclude subsurface returns under the crests of surface waves that otherwise fall inside the histogram of true surface heights. Added control variables (Table 5 of ATBD) conf_lim, the limiting confidence level to be included in the moving bin average, nphoton, the number of photons either side of a central photon to be included in the moving bin average, e.g., for nphoton=10, a 21 point average is used.
  • Computed nharms harmonic coefficients, a, and SNR, snr, of along-track heights. These are added features to characterize the surface wave environment in each ocean segment as harmonic coefficients versus wave numbers, wn, in the along-track direction (wave direction is not accounted for at this time).
  • Computed correlation length scale from 10-m bin averaged heights, l_scale, the corresponding degrees of freedom, np_effect, and resultant uncertainty, h_uncrtn, in the estimated sea surface heights. This is to provide an uncertainty estimate for average height over an ocean segment that accounts for the lack of statistical independence between photon heights over surface waves.
  • Updated to process only data with quality_ph equal to zero to avoid outputting surface heights based on poor quality photon heights as determined in ATL03.

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

See All Level of Service Details

Data Format(s):
  • HDF5
Spatial Coverage:
N: 90, 
S: -90, 
E: 180, 
W: -180
Spatial Resolution:
  • Varies
Temporal Coverage:
  • 13 October 2018
Temporal Resolution91 dayMetadata XML:View Metadata Record
Data Contributor(s):James Morison, David Hancock, Suzanne Dickinson, John Robbins, Leeann Roberts, et al

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.

Morison, J. H., D. Hancock, S. Dickinson, J. Robbins, L. Roberts, R. Kwok, S. P. Palm, B. Smith, M. F. Jasinski, and the ICESat-2 Science Team. 2021. ATLAS/ICESat-2 L3A Ocean Surface Height, Version 4. [Indicate subset used]. Boulder, Colorado USA. NASA National Snow and Ice Data Center Distributed Active Archive Center. doi: [Date Accessed].

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How To

Programmatic Data Access Guide
Data from the NASA National Snow and Ice Data Center Distributed Active Archive Center (NSIDC DAAC) can be accessed directly from our HTTPS file system or through our Application Programming Interface (API). Our API offers you the ability to order data using specific temporal and spatial filters... read more
ICESat, IceBridge, and ICESat-2: A primer on data access across the three missions
This guide will provide an overview of the altimetry measurements and data sets across the missions, as well as a guide for accessing the data through NASA Earthdata Search and programmatically using an Application Programming Interface (API). Overview The NASA ICESat, Operation IceBridge, and... read more
Explore, Access, and Customize ICESat-2 data at the NASA NSIDC DAAC
This webinar introduces the ICESat-2 mission and shows you how to explore, access and customize ICESat-2 data with the OpenAltimetry application, using NSIDC DAAC tools, and shows you how to subset, reformat and analyze the data using Python. This webinar was originally presented on July 23, 2019... read more
Search, order, and customize NSIDC DAAC data with NASA Earthdata Search
NASA Earthdata Search is a map-based interface where a user can search for Earth science data, filter results based on spatial and temporal constraints, and order data with customizations including re-formatting, re-projecting, and spatial and parameter subsetting. Thousands of Earth science data... read more
Filter and order from a data set web page
Many NSIDC data set web pages provide the ability to search and filter data with spatial and temporal contstraints using a map-based interface. This article outlines how to order NSIDC DAAC data using advanced searching and filtering.  Step 1: Go to a data set web page This article will use the... read more
How do I convert an HDF5/HDF-EOS5 file into binary format?
To convert HDF5 files into binary format you will need to use the h5dump utility, which is part of the HDF5 distribution available from the HDF Group. How you install HDF5 depends on your operating system. Full instructions for installing and using h5dump on Mac/Unix and... read more


What subsetting and reformatting services are available for ICESat-2 data?
The following table describes the subsetting and reformatting services that are currently available for ICESat-2 data via the NASA Earthdata Search tool, along with ... read more