An instrument (100) is provided according to an embodiment of the invention. The instrument (100) includes an interface (101) configured to receive a Doppler measurement signal and a processing system (112) coupled to the interface (101) and receiving the Doppler measurement signal. The processing system (112) is configured to generate a two-sided velocity spectrum including a plurality of discrete frequency bins from the Doppler measurement signal, with the two-sided velocity spectrum distinguishing spectral elements, and process one or more velocity spectrum bin pairs against a plurality of local gate thresholds, with the one or more velocity spectrum bin pairs being substantially symmetrically located about one or more carrier wave bins and wherein each velocity spectrum bin pair is processed against a corresponding local gate threshold of the plurality of local gate thresholds.