Recently, non-line-of-sight (NLOS) detection based on time of flight (TOF) has been investigated. In order to simulate the NLOS location of a hidden object, we derive the signal scattered by the object and build a model of photon flight based on photon scattering and propagation. To improve the authenticity of the model, the bidirectional reflectance distribution function (BRDF) is used to characterize the scattering process. The Gauss filter is proposed to extract the TOF of the scattering sources of interest without a priori information or manual judgment of the useful scattered signal by filtering the disturbance out of the histogram. The hidden object can then be located by TOF processing. Compared with previous work using a fitting algorithm, the Gauss filtering approach preserves more waveform information and presents improved positioning accuracy and robustness under the influence of noise, which is demonstrated in both simulation and experiment. It is possible to locate a NLOS object automatically through filtering identification of the object signal. The simplicity, high efficiency, and automation of this algorithm make it applicable for tracking a hidden moving object.

In this paper, the ultrasonic frequency coordination relation has been re-designed in the high-dimensional space by the principle of Kernel function nonlinear mapping. The relative deviation of ultrasonic frequency coordination relation from the original formula has been obtained by analyzing I.C.Chang theoretical model and P.A.Gass revised theoretical model concretely, theraby indicating the inadequacy of the two theoretical models; Using the principle of the nonlinear mapping to map the original data samples into a high dimensional kernel space, in other words, translating the nonlinear problem into a linear problem can clarify the relationships not only between ultrasonic frequency and incident angle but also between ultrasonic frequency and optical wavelength, leading to an appropriate kernel function and the improved coordination of the ultrasonic frequency relation.

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