We present a method for the realistic simulation of tissue backscatter in the ultrasound simulation program Field II. The method, based on an application of the Rayleigh speckle model, is implemented as an additional convolution step which appropriately scales and filters RF data to match an arbitrary backscattering coefficient spectrum. We verify that the method accurately captures the statistics and frequency-dependent behavior of diffuse tissue by simulating a standard backscattering coefficient measurement for focused transducers. We provide an example of how this method can be used to create simulation phantoms for assessing tissue detectibility in low SNR applications.