- 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.
Next: Crossover height differences Up: Results Previous: SLR residuals
Altimeter height residuals
Altimeter height residuals are a means to monitor the radial orbit error, although part of the residuals are caused by the fact that the reference surface will not be a perfect representation of the actual instantaneous mean sea level. The radial orbit error can, however, be distinguished from reference model errors in the spectrum of the height residuals. Orbit errors will be concentrated around the lower frequencies (particularly around 10-cpr), whereas reference model errors are expected to occupy the high-frequency part of the spectrum (above 10-cpr).
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:
Next: Crossover height differences Up: Results Previous: SLR residuals