Ion-acoustic wave simultaneously observed by the LFR and TDS receivers: (a) Potentials V₁₂ (black), V₁₃ (red), and V₂₃ (blue) from LFR; (b) Potentials V₁₃ (black), V₂₁ (red), and V₂ (blue) from TDS; (c) E_y computed from the LFR (black) and TDS receivers (red); (d) E_z computed from the LFR (black) and TDS receivers (red); (e) Power spectra of E from LFR (black) and TDS (red). The blue vertical line indicates the ion plasma frequency f_pi calculated from n_e, SC.