A data processor applies transform processing to a first group of samples at a primary sampling rate, where the first group of samples is within a data window associated with at least one of the data blocks. A detector detects an estimated frequency shift between the transmitted signal and the reflected signal based on a primary peak frequency determined by the transform processing at the primary sampling rate. The data processor applies transform processing to a second group of samples at a secondary sampling rate, where the data window contains previously read samples and at least one new sample, if the estimated frequency shift falls within a target response frequency band. The detector detects an observed frequency shift between the transmitted signal and the reflected signal based on a secondary peak frequency determined by the transform processing at the secondary sampling rate. A velocity estimator for estimating a velocity of at least one of the object and the transmitter based on the estimated frequency shift, the observed frequency shift, or both.