A method of processing acoustic or electromagnetic signals recorded by a receiver, said acoustic or electromagnetic signals being representative of acoustic or electromagnetic waves reflected by a medium to be studied after reflection off said medium of acoustic or electromagnetic waves transmitted by a transmitter to illuminate the medium to be studied, characterised in that the method comprises the following steps: - the successive transmission, by the transmitter, of first and second waves in response to the successive application to the transmitter of first and second electrical excitation signals in first and second separate frequency bands contained in a range of excitation frequencies of the transmitter, the frequency band of each of the first and second electrical excitation signals, as measured based on a bandwidth at -6 dB, being less than a quarter of the frequency range of the transmitter, - the reception, by the receiver, of respective first and second acoustic or electromagnetic echoes due to the respective reflections of the first and second waves at the interface of a target object contained in the medium to be studied, and the conversion of the first and second acoustic or electromagnetic echoes into respective first and second electrical reception signals, - the pre-processing of the first and second electrical reception signals to obtain pre-processed signals, the pre-processing consisting in: o a digitization of the first and second electrical reception signals to obtain first and second digital signals, o at least one mixing of the first and second digital signals to obtain first and second mixed signals, the mixing frequency of the first digital signal being different from the mixing frequency of the second digital signal, o at least one low-pass filtering of the first and second mixed signals to obtain first and second filtered signals, the cut-off frequency of the low-pass filter, as measured based on a bandwidth at -6 dB, being less than an eighth of the frequency range of the transmitter, o at least one decimation of the first and second filtered signals to obtain first and second decimated signals characterized by a flow rate of demodulated and decimated complex samples less than half the frequency range of the transmitter. - the successive transmission, by the transmitter, of first and second waves in response to the successive application to the transmitter of first and second electrical excitation signals in first and second separate frequency bands contained in a range of excitation frequencies of the transmitter, the frequency band of each of the first and second electrical excitation signals, as measured based on a bandwidth at -6 dB, being less than a quarter of the frequency range of the transmitter, - the reception, by the receiver, of respective first and second acoustic or electromagnetic echoes due to the respective reflections of the first and second waves at the interface of a target object contained in the medium to be studied, and the conversion of the first and second acoustic or electromagnetic echoes into respective first and second electrical reception signals, - the pre-processing of the first and second electrical reception signals to obtain pre-processed signals, the pre-processing consisting in: o a digitization of the first and second electrical reception signals to obtain first and second digital signals, o at least one mixing of the first and second digital signals to obtain first and second mixed signals, the mixing frequency of the first digital signal being different from the mixing frequency of the second digital signal, o at least one low-pass filtering of the first and second mixed signals to obtain first and second filtered signals, the cut-off frequency of the low-pass filter, as measured based on a bandwidth at -6 dB, being less than an eighth of the frequency range of the transmitter, o at least one decimation of the first and second filtered signals to obtain first and second decimated signals characterized by a flow rate of demodulated and decimated complex samples less than half the frequency range of the transmitter. o a digitization of the first and second electrical reception signals to obtain first and second digital signals, o at least one mixing of the first and second digital signals to obtain first and second mixed signals, the mixing frequency of the first digital signal being different from the mixing frequency of the second digital signal, o at least one low-pass filtering of the first and second mixed signals to obtain first and second filtered signals, the cut-off frequency of the low-pass filter, as measured based on a bandwidth at -6 dB, being less than an eighth of the frequency range of the transmitter, o at least one decimation of the first and second filtered signals to obtain first and second decimated signals characterized by a flow rate of demodulated and decimated complex samples less than half the frequency range of the transmitter.