- A mean height residual of 39.3 cm is found, which is compatible with the -41.5 cm radar altimeter bias determined from the ``Venice calibration'' [Francis et al., 1993].
- A 1-cpr signal is extracted from the height residuals by means of complex demodulation.
- The cosine part of the signal (,
*u*being the argument of latitude) shows a remarkable modulation which is most likely due to aliasing of reference model errors into the 1-cpr component. - The sine part of the signal () has a rather erratic modulation and seems to be mainly due to drag model errors.

From analyses of the altimeter residuals it appeared that the origin of the MSS93A model is offset from the actual orbital reference frame imposed by the SLR station coordinates. From a harmonic analysis of the altimeter height residuals it was found that, in order to match both origins, the MSS93A model has to be translated along a vector cm, yielding a reduction of the standard deviation of the altimeter height residuals from 23.6 to 19.6 cm. A similar result was found with altimeter height residuals based on the D-PAF orbit.

**Figure 5:**
(top left) Residuals of the altimeter height normal points with
respect to the MSS93A mean sea surface model with application of the
DUT JGM-2
orbits and origin correction.
(top right) Periodogram of the altimeter residuals.
(left centre) Amplitudes of the sine and cosine part of the 1-cpr
signal in the residuals, obtained through complex demodulation.
(bottom left) Altimeter residuals after demodulation.
(bottom right) Histogram of the demodulated signal.

Figure 5 gives a detailed analysis of the remaining altimeter height residuals with respect to the MSS93A mean sea surface model after implementation of the estimated offset:

Thu 16 Feb 1995