New-generation altimeters incorporate the so-called SAR Altimetry mode (currently known as Delay-Doppler processing mode). This technique exploits coherent processing of groups of transmitted pulses. It is not a pulse-limited transmission like classical radar altimeters, but beam-limited. Thus, the full Doppler bandwidth is exploited to make the most efficient use of the power reflected from the surface.
Delay-Doppler/SAR altimeters “look” at each resolved along-track cell as the radar passes overhead for as long as that particular cell is illuminated. Each cell is viewed over a larger fraction of the antenna beam than the pulse-limited; hence more data is gathered, which leads to substantial benefits (e.g. having a much better signal-to-noise ratio, SNR).
The Delay-Doppler/SAR altimetry processes the data such that they could be seen as having been acquired from a synthetic aperture antenna. This along track processing increases resolution and offers a multilook processing with the two independent dimensions: along-track and across-track (range).