The identification of the Jovian frequency spectrum obtained by Schmider et al. (1990, 1991) is proposed from Doppler shift observations of the solar sodium D line reflected by the planet, as a signature of Jovian global-pressure modes. The spectrum, derived from 4 nights of observations, presents high-amplitude peaks whose origin in undoubtedly not noise, but it suffers from the daily interruption in the observations. Echelle diagram analysis has allowed the determination of a regular pattern, corresponding to the regularity indicated by the asymptotic theory (Tassoul 1980) revised for Jovian seismology (Provost et al., in preparation). The observed equidistance is not a direct measurement of the characteristic frequency, but is closely related to it. As expected two frequencies dominate the spectrum: the rotational frequencies of the earth and of Jupiter. However, it has been possible to construct an echelle diagram based on a frequency which satisfies three criteria. The physical implications of the low value of the characteristic frequency and of the large amplitudes of detected oscillations are discussed.