ICESat-2 ATL12 Ocean Surface Height and ATL19 Gridded Dynamic Ocean Topography

The Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) measures ocean surface heights using a pulsed, photon-counting laser altimeter. The data from ICESat-2 ATL03 consist of a point cloud of returned photon heights at typical rates over the ocean of one to four measured surface heights per meter. Our primary processing for the ATL12 Ocean Surface Height product consists of surface finding and deconvolution of the instrument impulse response to yield surface height histograms with their first four moments over ocean segment lengths of a few hundred meters to 7 km. ATL12 also includes spatial series of surface photons heights averaged in 10-m along track bins, and these data are used to characterize surface waves, calculate the horizontal correlation length scale, degrees-of-freedom, sea surface height (SSH) uncertainty, and the correlation of photon return rate and surface height that constitutes the EM sea state bias (SSB) in the mean SSH. The ATL19/23 gridded product is intended to provide users with a realization of dynamic ocean topography (DOT) mapped over the world ocean over 1-month (ATL19) and 3-month (ATL23) intervals and 1/4° (mid-latitude grid) or 25-km (polar grids) bins of the ATL12 ocean surface height. The basic product includes simple averages and averages weighted by the estimated degrees of freedom for each beam ocean segment. The simple and degree-of-freedom weighted average grid or latitude-longitude positions of all the beam ocean segments in a grid cell are also output, as are the simple and degree-of-freedom weighted averages of other key variables necessary to interpret DOT, such as the geoid and the sea state bias.