A high-resolution imaging algorithm without derivatives based on waveform estimation for UWB pulse radars

UWB pulse radars are promising as high-resolution imaging techniques, which are required for target positioning systems of rescue robots moving in a dark smoke, for example. It can be also applied to a non-destructive measurement for industrial products (e.g. antennas and vehicles), in order to detect small surface defects. These applications require a fast, robust, and high-resolution imaging algorithm. We have already proposed a robust and fast imaging algorithm with an envelope of circles. This method utilizes the principle that the target boundaries are expressed as the envelopes of circles with the radius corresponding to the time delays. Our method can realize robust imaging even in a noisy environment. However, the error of the estimated image is at least about 1/10 of the center wavelength of the pulse because the image is distorted especially around sharp edges. This is because we assume that the scattered waveform is the same as the transmitted one. In this paper, we utilize the shape estimation method together with a waveform estimation in order to enhance the resolution of the image. An imaging algorithm based on this idea has been published. However, the earlier study utilizes a parametric approach and can be applied only to a simple polygon. In this paper, we extend this idea to general convex targets including smooth curves and edges. Numerical simulations and experiments show that the proposed method accomplishes a high-resolution imaging.