  We analyze more than 5000 days of high-quality Sun-as-a-star, radial velocity
GOLF and photometric VIRGO/SPM helioseismic observations to extract precise
estimates of the visibilities of the low-degree p modes and the m-height ratios
of the l=2 and 3 multiplets in the solar acoustic spectrum. The mode
visibilities are shown to be larger during the GOLF red-wing configuration than
during the blue-wing configuration, and to decrease as the wavelength of the
VIRGO/SPM channels increases. We also show that the mode visibilities are
independent of the solar activity cycle and remain constant overall with time,
but that nevertheless they follow short-term fluctuations on a time scale of a
few months. The l=1 mode visibility also increases significantly toward the end
of the year 1999. Comparisons with theoretical predictions are provided. Even
though there is qualitative agreement, some significant discrepancies appear,
especially for the l=3 modes. The limb darkening alone cannot explain the
relative visibilities of modes. These precise estimates should be used as
references for the extraction of the p-mode parameters for any future
investigation using the GOLF and VIRGO/SPM observations.
