Spatio-spectral densities of VEGA dispersed fringes in 3T mode (left) with CLIMB used as IR group delay tracking and in 4T mode (right) with MIRC used as IR group delay tracking. Axes correspond to the (u, v) coordinates defined in Eq. (6): u is the horizontal direction, v the vertical one. The three (respectively sic) high-frequency fringe signals are clearly separated in this 2D spectral density for the 3T (respectively 4T) mode.