Shouhei Kidera

Accurate UWB Radar Three-Dimensional Imaging Algorithm for a Complex Boundary Without Range Point Connections

Ultrawide-band pulse radars have immeasurable potential for a high-range-resolution imaging in the near field and can be used for noncontact measurement of industrial products with specular or precision surfaces, such as reflector antenna or aircraft fuselage, or identifying and locating the human body in security systems. In our previous work, we developed a stable and high-speed 3-D imaging algorithm, Envelope, which is based on the principle that a target boundary can be expressed as inner or outer envelopes of spheres, which are determined using antenna location and observed ranges. Although Envelope produces a high-resolution image for a simple shape target that may include edges, it requires an exact connection for observed ranges to maintain the imaging quality. For complex shapes or multiple targets, this connection becomes a difficult task because each antenna receives multiple echoes from many scattering points on the target surface. This paper proposes a novel imaging algorithm without range point connection to accomplish high-quality and flexible 3-D imaging for various target shapes. The algorithm uses an accurate estimation for the direction of arrival using signal amplitudes and realizes direct mapping from observed ranges to target points. Several comparative studies of conventional algorithms clarify that our proposed method accomplishes accurate and reliable 3-D imaging even for complex or multiple boundaries.

High-Resolution and Real-Time Three-Dimensional Imaging Algorithm With Envelopes of Spheres for UWB Radars

Ultrawideband pulse radars have a great potential for high-range resolution in near field imaging and can be used for noncontact measuring in precision or specular products such as reflector antennas and aircraft fuselages. We have already proposed a high-speed 3-D imaging algorithm, SEABED, which is based on a reversible transform, which is the boundary scattering transform, between the received signals and the target shape. However, the estimated image with SEABED is unstable with random noise because it utilizes a derivative of the received data. In this paper, we propose a robust 3-D imaging algorithm with an envelope of spheres that completely resolves the instability due to derivative operations. Moreover, to enhance the resolution of estimated images, this method is combined with a direct waveform compensation method that does not sacrifice high-speed calculation. Numerical simulations and an experiment confirm that the proposed method can realize fast, robust, and high-resolution 3-D imaging for arbitrary targets.

A robust and fast imaging algorithm with an envelope of circles for UWB pulse radars

Target shape estimation with UWB pulse radars is a promising imaging technique for household robots. We have already proposed a fast imaging algorithm, SEABED, that is based on a reversible transform BST (Boundary Scattering Transform) between the received signals and the target shape. However, the target image obtained by SEABED deteriorates in a noisy environment because it utilizes a derivative of received data. In this paper, we propose a robust imaging method with an envelope of circles. We clarify by numerical simulation that the proposed method can realize a level of robust and fast imaging that cannot be achieved by the original SEABED.

Extended Imaging Algorithm Based on Aperture Synthesis With Double-Scattered Waves for UWB Radars

Ultrawideband (UWB) pulse radar with high range resolution is suitable for near-field sensing. Applications of UWB pulse radar include human body identification in blurry vision for security or rescue purposes and accurate spatial measurements for industrial products such as a reflector antenna. The synthetic aperture radar is still promising for these applications because it creates an accurate image even for near-field targets in free space. However, for complex-shaped or multiple objects, this algorithm suffers from increased shadow region because it employs only a single-scattered signal for imaging. To resolve this difficulty, this paper proposes a novel imaging algorithm based on aperture synthesis for double-scattered signals. In general, double-scattered waves include independent information on target points, which are not obtained by a single-scattered wave. Based on this principle, the proposed method effectively synthesizes the double-scattered signals and enhances the reconstructible range of a target shape, part of which becomes a shadow in the former approach. In order to enhance accuracy, a false image suppression approach based on the Fresnel zone theory is also incorporated in the proposed method. The results from numerical simulations and an experiment verify that our method significantly enhances the visible range of target surfaces without either a priori knowledge of target shapes or preliminary observation of their surroundings.

High-Resolution 3-D Imaging Algorithm With an Envelope of Modified Spheres for UWB Through-the-Wall Radars

Through-the-wall imaging techniques with ultrawideband (UWB) radars are promising candidates for non-destructive testing and reliable human detection, especially in disaster areas, where victims are buried under collapsed walls. These applications require high-resolution target imaging to identify the object shape, such as a human body. We have already proposed a high-quality 3-dimensional (3-D) imaging algorithm in the form of envelope that is aimed at near field sensing for non-contact measurement or target identification for robots. Envelope achieves real-time accurate 3-D imaging with group mapping from multiple observed ranges to target points, and offers a reliable image even in noisy situations. However, this method does not maintain its quality for through-the-wall imaging because an observed range shift due to wall penetration causes a serious distortion in the image. This paper presents a high-resolution 3-D imaging algorithm by modifying the original envelope, and which gives a more accurate object shape behind a wall. Furthermore, to enhance the resolution of the estimated images, this method is combined with a direct waveform compensation method, known as spectrum offset correction. Numerical simulations and an experiment verify that our proposed method achieves high-resolution 3-D imaging for through-the-wall radar applications.

Super-Resolution UWB Radar Imaging Algorithm Based on Extended Capon With Reference Signal Optimization

Near field radar employing ultrawideband (UWB) signals with its high range resolution has great promise for various sensing applications. It enables non-contact measurement of precision devices with specular surfaces like an aircraft fuselage and wing, or a robotic sensor that can identify a human body in invisible situations. As one of the most promising radar algorithms, the range points migration (RPM) was proposed. This achieves fast and accurate surface extraction, even for complex-shaped objects, by eliminating the difficulty of connecting range points. However, in the case of a more complex shape whose variation scale is less than a pulsewidth, it still suffers from image distortion caused by multiple interference signals with different waveforms. As a substantial solution, this paper proposes a novel range extraction algorithm by extending the Capon method, known as frequency domain interferometry (FDI). This algorithm combines reference signal optimization with the original Capon method to enhance the accuracy and resolution for an observed range into which a deformed waveform model is introduced. The results obtained from numerical simulations and an experiment with bi-static extension of the RPM prove that super-resolution UWB radar imaging is accomplished by the combination between the RPM and the extended Capon methods, even for an extremely complex-surface target including edges.

Fast and Accurate 3-D Imaging Algorithm with Linear Array Antennas for UWB Pulse Radars

Pulse radars with UWB signals are promising as a high-resolution imaging technique that can be used for the non-destructive measurement of surface details in industrial products such as antennas and aircraft. We have already proposed a fast 3-D imaging algorithm, SEABED, that utilizes a reversible transform between the time delay and the target boundary. However, data acquisition is time-consuming when obtaining an accurate image because it assumes a mono-static radar with 2-D scanning of an antenna. In this paper, we utilize linear array antennas and propose a fast and accurate imaging algorithm. We extend the reversible transform for mono-static radars to apply to bi-static radars to reduce the data acquisition time. The effectiveness of the proposed method is verified with numerical simulations and experiments.

An Accurate Imaging Algorithm with Scattered Waveform Estimation for UWB Pulse Radars

SUMMARY UWB pulse radars that offer target shape estimation are promising as imaging techniques for household or rescue robots. We have already proposed an efficient algorithm for a shape estimation method SEABED which is a fast algorithm based on a reversible transform. SEABED extracts quasi wavefronts from received signals with the filter that matches the transmitted waveform. However, the scattered waveform is, in general, different from the transmitted one depending on the shape of targets. This difference causes estimation errors in SEABED. In this paper, we propose an accurate algorithm for a polygonal-target based on scattered waveform estimation. The proposed method is presented first, followed by

A High-Resolution Imaging Algorithm without Derivatives Based on Waveform Estimation for UWB Radars

UWB pulse radars enable us to measure a target location with high range-resolution, and so are applicable for measurement systems for robots and automobile. We have already proposed a robust and fast imaging algorithm with an envelope of circles, which is suitable for these applications. In this method, we determine time delays from received signals with the matched filter for a transmitted waveform. However, scattered waveforms are different from transmitted one depending on the target shape. Therefore, the resolution of the target edges deteriorates due to these waveform distortions. In this paper, a high-resolution imaging algorithm for convex targets is proposed by iteration of the shape and waveform estimation. We show application examples with numerical simulations and experiments, and confirm its capability to detect edges of an object.

An experimental study on a fast imaging algorithm for UWB pulse radar systems

In this paper, we have applied SEABED algorithm to experimental data. The random components in the received signal degrade the estimated image. Two kinds of smoothing method to solve this problem have been investigated. One of them directly utilizes the 2nd order derivative, which cannot improve the image accuracy. The proposed smoothing method utilizes the upper bound of the 2nd order derivative instead of the 2nd order derivative itself. The proposed smoothing method has been confirmed to significantly improve the image, which corresponds to the gain of 5 dB in S/N. In the future study, it is important to extend the proposed smoothing method in order to get rid of the required condition of target shape