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Abstract
The area of an altimeter footprint is determined by which reflections from the ocean surface arrive back at the radar antenna simultaneously rather than by which part of the ocean surface is simultaneously illuminated. In the presence of waves, the footprint area can be defined from the area of the surface from which returns are arriving at a given instant or as the region encompassing returns at a given instant. This distinction occurs because the effective half power pulse width for SEASAT, GEOSAT, and TOPEX is only 0.47 m. In the presence of realistic magnitude waves, only part of the surface of each major wave is illuminated at a given time. The area from which returns are arriving is important since it is used for normalizing the radar backscatter to determine the relative radar cross‐section. The area of the region encompassing returns is important for determining sea level. This paper presents an equation for the altimeter footprint for sea level measurements based on the half‐power width of the effective altimeter pulse and the half‐power width of a δ‐function pulse reflected from a Gaussian sea.