However, with short duration pulses that transport little energy, the range of the instrument can again be affected. To limit this problem, “pulse-coherent” profilers use sequences of coded pulses. For sinusoidal signal carrier frequency fc, it is possible to modulate the phase for a duration T with help from a pseudo-random binary sequence b(t) of N bits, which has good autocorrelation properties. A change of one bit is generated by applying a jump in phase of π to the carrier. The signal therefore takes the following form: