Method of determining impulse responses from a medium in relation to the transmission of waves between different points

A method of determining impulse responses of a medium in relation to the transmission of waves between different points, method comprising:

• (a) at least one step of emission in the course of which waves are emitted into the medium by generating signals ei(t) on the basis of a number N of emission points belonging to the medium, where N is an integer at least equal to 2 and i is an index lying between 1 and N which designates one of said N emission points,
• (b) at least one step of reception in the course of which signals rj(t) are picked up from said waves after transmission in said medium, at a number M of reception points belonging to the medium, where M is a non-zero natural integer and j is an index lying between 1 and M which designates one of said M reception points,
• (c) and at least one step of determination of said impulse responses hij(t) between each emission point i and each reception point j on the basis of the signals emitted ei(t) and picked up rj(t),
• wherein during the course of step (a), said N emission points are made to simultaneously emit the signals ei(t), these signals ei(t) having a duration T and each being a sum of n substantially monochromatic elementary signals, of like amplitude and of respective frequencies f0,i+k.δf, where f0,i is a predetermined eigenfrequency at the point i, k is an integer lying between 0 and n, n is an integer at least equal to 2 and δf is a predetermined frequency interval, the respective eigenfrequencies f0,i at the various points i being distinct and lying in a frequency band of width δf,
• and wherein during the course of step (c), each impulse response hij(t) is calculated on the basis of a signal of correlation between the signal ei(t) emitted at the point i and the signal rj(t) picked up at the point j.