Method for obtaining the profile of a surface moving in relation to the system

A method for obtaining a profile of an outer surface (22) of a medium (21) having a median plane (23) comprising the following steps:

• obtaining two time signals A and B (1002) for, at each instant, a same geometrical target on a readout line of the outer surface (22), from a measurement system (1) having a relative speed V in a direction U with respect to the outer surface (22) having the median plane (23), each signal being the result of electromagnetic interferences between an incident wave and the incident wave backscattered by the outer surface (22) along the readout line of at least one electromagnetic wave that is Gaussian, coherent, directional along at least one path (11, 12) and focused at a geometrical point (d1, d2) on the at least one path (11, 12), the two geometrical points d1 and d2 being situated on either side of the median plane (23) and, the distance between the two geometrical points d1 and d2 being greater than a greatest of the Rayleigh lengths of each electromagnetic wave, with respect to the normal to the median plane (23), and the angle of incidence (θ1, θ2) of the electromagnetic wave along each path (11, 12) on the outer surface (22) being greater than one degree in a plane defined by a normal to the median plane (23) and the direction U;
• determining at least one Doppler frequency (2001) associated with each time signal A and B;
• sampling each time signal A and B (2002) at a frequency greater than 2 times the at least one Doppler frequency to obtain a payload signal;
• determining an envelope (2004) of the payload signal of each signal A and B;
• performing a relative combination between the envelopes of each signal A and B (3001) to obtain a monotonic and bijective function F;
• and
• determining the profile of the outer surface (3002) using a calibration of the function F.