A system for coherence imaging may receive ultrasound signals each having a respective delay associated with a respective ultrasonic transducer element in an ultrasonic transducer array. The system may obtain an approximation of the auto-correlation of ultrasound signals without any auto-correlation calculation, and determine the output image based on the approximation. In approximating the auto-correlation, the system may group the ultrasound signals into multiple portions, each corresponding to a respective sub-aperture of a plurality of sub-apertures of the ultrasonic transducer array. The system may determine a coherent sum of signals for each sub-aperture, perform a square operation or magnitude square operation over the coherent sum to obtain resulting data, normalize the resulting data, and sum the resulting data for all of the sub-apertures to generate the output image. A sub-aperture in the plurality of sub-apertures may overlap with another sub-aperture.