The GOLF experiment on board SOHO is designed to measure global oscillation
s of the disk-integrated sunlight with high sensitivity and with long term
stability. The GOLF data is thus ideally suited for both the study of the p
-mode spectrum and to address the search for gravity modes. Due to their oc
casional malfunction the project decided to stop the rotating polarizing el
ements at an optimum place in order to maintain a precise sequence of measu
rements with the highest possible duty cycle. This action means that subseq
uently GOLF only measures two monochromatic intensities I-b(+) and I-b(-) o
n the blue wing of the sodium doublet. In this work we investigate the natu
re of these signals separately and in combinations. Our method is to study
the temporal relative phase relations between the low degree (l less than o
r equal to 3) p-mode signals derived from data sets obtained from simultane
ous observations, both from other SOHO instruments (GOLF and SOI) and from
Mark-I, the Tenerife station of the ground-based BISON network. It is found
that these signals are "almost" pure velocity signals. A simple model indi
cates that a contamination of a pure intensity-like signal of 14% amplitude
would fully explain the true nature of the current GOLF signal. Moreover,
it is found that the ratios, defined for other instruments (Mark-I, SOI and
, by extension BiSON and WS), also have exactly the same nature as the GOLF
ratio.