ICESat-2 Level-2 Products

Image: NASA Goddard Space Flight Center

Global Geolocated Photon Data (ATL03)

ATL03 provides time, latitude, longitude, and ellipsoidal height for each photon event downlinked from ATLAS. Heights are corrected for several geophysical phenomena, such as effects of the atmosphere and solid earth deformation. By design, users can easily remove each geophysical correction, if desired.

Each event is classified as either a likely signal photon or a likely background photon. To distinguish signal photons from the background, ATL03 processing generates histograms of the number of photon events as a function of height and calculates the signal-to-noise ratio for each histogram bin.

ATL03 also contains five surface masks—land, land ice, ocean, sea ice, and inland water—that collectively cover Earth's surface.

Image: NASA Goddard Space Flight Center/Kate Ramsayer.

Normalized Relative Backscatter (ATL04)

ATL04 provides along-track, normalized relative backscatter (NRB) profiles that can be used to identify atmospheric layers and their boundaries, including clouds, aerosols, and blowing snow. The profiles extend from 13.75 km above the local DEM surface to -0.25 km, and as such include the ground.

NRB profiles are generated by subtracting background photon events from raw photon counts, multiplying by the square of the range from the satellite to the return height, and normalizing by the laser energy. The profiles are also passed to and used by higher level products to characterize the atmosphere.

NRB profiles are generated from the strong beam only of each beam pair, and thus each ATL04 granule contains three atmospheric profiles. Strong beam data are downlinked after summing 400 laser pulses—about 280 m of along-track distance—are binned vertically at ~30 m.