A method for using reflections of wave energy from one or more reflecting objects to characterize certain properties of these objects through the spectral characteristics of the reflections from them, the method comprising the steps of: generating for transmission a repeating sequence (150, 160, 170) of N constant-frequency pulses of width t seconds at interpulse intervals of T seconds, with each pulse in the sequence (150, 160, 170) having a particular constant phase according to a quadratic phase sequence, which phase is applied to each pulse in a first sense of modulation; modulating the phase of echo energy received from one or more objects reflecting the transmitted repeating sequence (150, 160, 170) of N constant-frequency pulses during each receiving subinterval (152, 162, 172) by the identical quadratic phase sequence used for the transmitted repeating sequence of N constant-frequency pulses, with a second sense of modulation opposite to the first sense of modulation, so that the net phase modulation applied to echo energy reflected from a particular reflecting object at a particular range r, measured in discrete units of T of round-trip echo time, is a difference between the phase of the transmitted pulses at the time of their transmission and the phase applied to the received echo energy from range r, in either sense of the difference; and producing from the modulated received echo energy N unique and discrete frequency translations of the received echo energy as a function of range r of the reflecting objects, of magnitude equal to multiples of 1 / NT Hz, which frequency translations preserve the spectrum of the received echo energy, forming in combination a composite signal frequency spectrum. generating for transmission a repeating sequence (150, 160, 170) of N constant-frequency pulses of width t seconds at interpulse intervals of T seconds, with each pulse in the sequence (150, 160, 170) having a particular constant phase according to a quadratic phase sequence, which phase is applied to each pulse in a first sense of modulation; modulating the phase of echo energy received from one or more objects reflecting the transmitted repeating sequence (150, 160, 170) of N constant-frequency pulses during each receiving subinterval (152, 162, 172) by the identical quadratic phase sequence used for the transmitted repeating sequence of N constant-frequency pulses, with a second sense of modulation opposite to the first sense of modulation, so that the net phase modulation applied to echo energy reflected from a particular reflecting object at a particular range r, measured in discrete units of T of round-trip echo time, is a difference between the phase of the transmitted pulses at the time of their transmission and the phase applied to the received echo energy from range r, in either sense of the difference; and producing from the modulated received echo energy N unique and discrete frequency translations of the received echo energy as a function of range r of the reflecting objects, of magnitude equal to multiples of 1 / NT Hz, which frequency translations preserve the spectrum of the received echo energy, forming in combination a composite signal frequency spectrum.