Altimeter measurements are deduced from the waveforms, i.e. the radar echoes (see How altimetry works for Further details).

Altimetric range

The range is the distance from the satellite’s centre of mass to the surface of the Earth, as measured by the altimeter. Thus, the altimeter measurements are referred as ‘range’ or ‘altimeter range’, not height. This is the principal measurement made by the radar altimeters. The range is estimated from the echo waveforms as part of the processing known as retracking. This measurement is not the altitude, it is still only a measurement of distance.

If the altimeter is a two-frequency instrument, there will be a range computed for both frequencies. However, the Ku band range is used for most applications.

Significant Wave Height

Significant wave height is computed from the slope of the return radar pulse (the gradient of the leading edge of the radar echo, known as the leading-edge slope), after reflection on the surface.
If the altimeter is a dual-frequency instrument, there will be a Significant Wave Height computed for both frequencies.

Backscatter coefficient (Sigma-naught)

The backscatter coefficient, sigma0, is computed from the power of the altimeter’s return pulse.
If the altimeter is a dual-frequency instrument, there will be a backscatter coefficient computed for both frequencies.

Wind speed

The backscatter coefficient can be related to wind speed. Empirical models have established a relationship between the wind speed, the sea surface backscatter coefficient and significant wave height. Wind speed is calculated from the mathematical relationship with the Ku-band backscatter coefficient and the significant wave height. The wind speed model function is evaluated for 10 metres above the sea surface and is considered to be accurate to 2 m/s