A simplified ZoomFFT algorithm in digital sonar

DEMON and LOFAR have been proved the powerful mean in underwater acoustic signal processing,espe-cially in weak signal detection and target noise classification.Sometimes one need to know the fine structure of frequencyspectrum of received signal.It is necessary to take a very long data to get high frequency resolution.This is not alwayspossible due to the hardware and software limitation.ZoomFFT is one of the trade-off consideration for solving highfrequency resolution problem,if we are only focus on some special frequency bins.Previous discussions mainly bifurcate into two different representations,the Complex Modulation⁴ and Cascade FFT^5,6.The former one traditionallyneeds some kind of special treatment,e.g.the complex modulation,Lowpass filtering,down——sampling.While the latterachieves the same result by two successive FFT,with necessary modifications in phase and amplitude,thus is feasiblefor real-time implementation.Based on some theoretical analysis,a relationship between the Complex Modulation andCascade FFT has been described in this paper.In addition,the selection of parameters such as sample rate,overlapfactor has been discussed.Finally,the algorithm is presented and some simulation results are illustrated.