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Interpolation
The antenna offsets are derived from the Antenna Slow table together
with other position values. Namely the 5 following elements have to be
computed:
- lambda offset from reference position,
- beta offset,
- azimuth,
- elevation,
- local sidereal time.
All these elements are available in the ANTSLOW table, at a
typical sampling rate of 1 Hz. Since the spectra dumps can be produced at
different time sampling (no assumption is made on the rate or its
variations), each spectrum positions are interpolated from the
ANT table thanks to their respective Modified Julian
Day values
 |
(3.1) |
where
is the spectrum MJD value, and
is the MJD value
of the
trace in the ANTSLOW table.
is computed
thanks to a dichotomic search in the table such as
 |
(3.2) |
being the interpolation fraction between the
and
trace, the positions are interpolated by
![\begin{displaymath}
\ensuremath{l_{S}} = \ensuremath{l_{A}}(j) + f \times \ensu...
...left[ \ensuremath{l_{A}}(j+1)-\ensuremath{l_{A}}(j) \right] },
\end{displaymath}](img29.png) |
(3.3) |
where
and
are the spectrum and antenna lambda offsets
respectively. Same formula applies for the beta, azimuth, and elevation
values.
If
is found beyond the ANTSLOW table limits, the
boundary values are applied without extrapolation. However, this is not
expected to happen since such spectra should be rejected since they are out
of the on-track range.
Next: Wobbler switching
Up: Antenna offsets
Previous: Projection system
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Gildas manager
2023-06-01