The sea surface height relative to the geoid (the mean ocean surface of the Earth if the ocean is at rest) is derived from TOPEX/Poseidon, Envisat, Jason-1, and OSTM/Jason-2 altimetry measurements. Altimetry is a technique for measuring height. Satellite altimetry measures the time taken by a radar pulse to travel from the satellite antenna to the surface and back to the satellite receiver. Combined with precise satellite location data, altimetry measurements yield sea-surface heights. This AVISO dataset was created by binning and averaging monthly values on 1 degree grids.
AVISO stands for "Archiving, Validation and Interpretation of Satellite Oceanographic data".
National Center for Atmospheric Research Staff (Eds). Last modified 02 Jul 2016. "The Climate Data Guide: AVISO: Satellite derived Sea Surface Height above Geoid." Retrieved from https://climatedataguide.ucar.edu/climate-data/aviso-satellite-derived-sea-surface-height-above-geoid.