This paper proposes an automated 3D visualization method of embedded tubes applicable to the scanned result of pulse-radar Non-Destructive Testing (NDT). The proposed method consists of three stages. First, our method defines the processing region which includes a pattern generated by a tube. This region is determined by referring to the composition of a received wave. Second, after expert knowledge of a tube is translated into fuzzy inference rules, the positions of embedded tubes are identified by inferring them. Third, 3D links of the identified positions are formed to visualize the continuous shape of the tubes. Consequently, the tubes are extracted, and their 3D shapes are visualized. The experimental result on the specimens shows that our method was able to find all tubes that exist in the radiograph and the schematic. Our method could thus provide the internal information of concrete with sufficient accuracy required in the practical construction work.

Polarimetric SAR interferometry has been successful and attractive for forest parameters (tree height and canopy extinction) estimation. In this paper, we propose to use the ESPRIT algorithm to extract the interferometric phase of local scatterers with polarimetric and interferometric SAR data. Two or three local scattering waves can be extracted at each image patch when a fully polarimetric data set (HH, HV, VV) is available. Furthermore, the ESPRIT can estimate two dominant local scattering centers when only a dual polarimetric data set (e.g., VV and VH) is provided. In order to demonstrate effectiveness the proposed technqiue, we examined the relation between local scattering centers extracted by this method and complex coherence of the coherent scattering model for vegetation cover. The results show that the three-wave estimation can be more accurate than the two-wave case. The extracted interferometric phases with full and dual polarization data sets correspond to effective ground and canopy scattering centers. In this investigation, SIR-C/X-SAR data of the Tien Shan flight-pass are used.

In this paper, a new method is proposed for supervised classification of ground cover types by using polarimetric synthetic aperture radar (SAR) data. The concept of similarity parameter between two scattering matrices is introduced for characterizing target scattering mechanism. Four similarity parameters of each pixel in image are used for classification. They are the similarity parameters between a pixel and a plane, a dihedral, a helix and a wire. The total received power of each pixel is also used since the similarity parameter is independent of the spans of target scattering matrices. The supervised classification is carried out based on the principal component analysis. This analysis is applied to each data set in image in the feature space for getting the corresponding feature transform vector. The inner product of two vectors is used as a distance measure in classification. The classification result of the new scheme is shown and it is compared to the results of principal component analysis with other decomposition coefficients, to demonstrate the effectiveness of the similarity parameters.

The radar cross section (RCS) of a dielectric-coated cylindrical cavity was measured and the measurements were compared with those calculated according to the iterative physical optics (IPO). The IPO analysis used the equivalent-impedance boundary condition (EIBC) based on transmission-line theory which takes into account the thickness of the coating. It was consequently found that this condition is much more effective than the ordinary-impedance boundary condition based on the intrinsic impedance of the material.

This paper introduces an automatic and multi-instrument snowfall observation system and proposes techniques that could be used in the estimation of snowfall characteristics. The instruments used in this study include two microwave radars, an optical lidar, a CCD camera based imaging system and high-accuracy electrical balances for reference data. The emphasis has been on obtaining good temporal resolution and synchronization accuracy of separate datasets. In most research done so far, this has not been a principal point, either because only very long snowfall events have been measured, or wide area estimates were desired, or due to limitations in manual sampling methods and other technical issues. The measurements were also contained in a small area to make sure that all instruments record data from the same target. One radar and the optical lidar recorded an atmospheric profile up to 6000 m, while the other radar, the imaging system and the two balances recorded snowfall on the ground level. The combination of optical, microwave and direct visual observations of snowfall show that a change in cloud conditions can result in snowfall having different characteristics. The lidar backscatter was used as main indicator of transitions in cloud conditions. A direct visual evaluation of snowflake size distribution using a CCD camera shows that it is extremely helpful in order to interpret radar data. The camera observed velocity distribution showed no large variations between snowfall events, however, it could be useful in detecting graupel and hail precipitations which have much faster terminal velocities. This paper will conclude with a discussion on further elaborating the use of lidar and visual data to complement radar observations of snowfall.

A multi-range resolution radar using sideband spectrum energy is investigated. The basic system consists of a sharpening processor and least-error energy shaping filters. First, the sharpening processor makes long flat pulses sharpened. Next, the least-error shaping filters compress the input pulse into the desired pulse width. Then the output pulse width can become narrower than the reciprocal of the input bandwidth, because the least-error shaping filters make the equivalent bandwidth expanded by the enhancement of the sideband spectrum energy and the suppression of the main spectrum. The transmitted signals with simple phase modulation are studied to obtain the multi-range resolution where the pulse is compressed into a pulse with the same bandwidth and another pulse width equal to the reciprocal of the input bandwidth. The peak-to-sidelobe ratio after the pulse compression and the improvement factor of the output signal-to-noise ratio are measured. Further, the experimental results are shown to verify our proposed technique.

We observed the log normal, log-Weibull and K-distributed sea-clutter from high sea state 7 with an X-band radar for grazing angles between 3.1 and 17.5. To determine the sea-clutter amplitude statistics, we introduced the Akaike Information Criterion (AIC), which is more rigorous fit of the distribution to the data than the least-squares method.

The concept of the equi-phase curve is introduced for the cross-polarized channel case. It is proved that the equi-phase curves are a series of half circles on the Poincare sphere, and that all these curves have two common ends. Based on the introduced concept, this letter demonstrates the distribution of the received voltage's phases on the Poincare sphere. In addition, it is shown theoretically that the cross-polarized phase of the off-diagonal elements of a scattering matrix is unstable for most natural targets. Therefore, the cross-polarized phase information cannot be used for extracting target characteristics in polarimetric radar remote sensing.

A 5.3-GHz klystron has been recently designed and fabricated. In many countries, the transmitting frequency of 5.6 GHz (5,600 to 5,650 MHz) is commonly used for C-band meteorological radars. However, 5.3 GHz is generally used in Japan. To detect low-level wind shears by a Doppler radar, it is essential to use a MOPA (Master Oscillator and Power Amplifier) that generates stable coherent microwaves. The klystron is most suitable for this purpose. However, there are no commercially available klystrons in C-band that operate at 5.3 GHz. We developed a klystron for this band, making use of a simulation technique originally devised for S- and X-bands. The klystron operates at frequencies between 5,250 and 5,350 MHz. The typical operating parameters are a peak output power of 200 kW, a pulse width of 1 µs, and an RF duty cycle of 0.002. The klystron, including the electromagnet for focusing the magnetic field, is approximately 67 cm long with a diameter of 40 cm and a weight of 162 kg. Phase modulation is suppressed below 20% of the phase change required for the minimum resolution of Doppler velocity measurement by the radar for which this klystron is employed. The klystron shows favorable performance for Doppler radars operated in major airports in Japan.

A novel power spectral density accumulation (PSDA) method for estimating the bandwidth of the clutter spectra is proposed, based on a priori knowledge of the shape of the clutter spectra. The comparison of the complexity and the performance between the PSDA method and the general ones is presented. It is shown that the PSDA method is effective for the short-time clutter data in the practical application.

A stabilized local oscillator is one of the key components for any radar system, especially for a Doppler radar in detecting slowly moving targets. Based on hybrid semiconductor/superconductor circuitry, the HTS local oscillator produces stable, low noise performance superior to that achieved with conventional technology. The device combines a high Q HTS sapphire cavity resonator (f=5.6 GHz) with a C-band low noise GsAs HEMT amplifier. The phase noise of the oscillator, measured by a HP 3048A noise measurement system, is -134 dBc/Hz at 10 kHz offset at 77 K.

The periodicity of a target scattering matrix is studied when the target is rotated about the sight line of a monostatic radar. Except for the periodicity and invariance of the scattering matrix diag(a,a), it is proved that only helixes have the quasi-invariance, and that only N-targets have the quasi-periodicity, demonstrating that a target with some angle rotation symmetry also has the scattering matrix form diag(a,a). From this result, we conclude that it is impossible to extract the shape characteristics of a complex target from its scattering matrix or its Kennaugh matrix.

In this paper, we examine the polarimetric characteristics and the potential of the coherent decomposition in polarimetric synthetic aperture radar (SAR) interferometry. Coherent scattering decomposition based on the coherence optimization can separate effective phase center of different scattering mechanisms and can be used to generate canopy digital elevation model (DEM). This decomposition is applied to a simplified stochastic scattering model such as forest canopy. However, since the polarimetric characteristics are not well understood when the decomposition is carried out, we investigate its characteristics and potential using polarimetric entropy-alpha and three-component scattering matrix decomposition. The results show that the first and third components correspond to the lower and upper layer, respectively, in ideal case. In this investigation, SIR-C/X-SAR data of the Tien Shan flight-pass are used.

This paper gives an overview of recent progress in radar polarimetry and radar polarimetric interferometry. Both techniques are of special importance for the inversion of physical scatterer parameters from radar remote sensing data. A unified treatment of polarisation effects in radar polarimetry and polarimetric interferometry based on eigenvalue processing is addressed providing a link between signal processing techniques and coherent electromagnetic models for random media scattering. In this context, the main applications of polarimetry in radar remote sensing such as single and multi-frequency polarimetric classification, the estimation of surface roughness and moisture content and vegetation structure estimation are reviewed.

Synthetic aperture radar interferometry have been established in the past two decades, and used extensively for many applications including topographic mapping of terrain and surface deformation. Vegetation analysis is also a growing area of its application. In this paper, we propose an polarimetric SAR interferometry technique for interferometric phase extraction of each local scatterer. The estimated position of local scattering centers has an important information for effective tree height estimation of forest. The proposed method formulated for local scattering center extraction is based on the ESPRIT algorithm which is known for high-resolution capability of closely located incident waves. The method shows high-resolution performance when local scattered waves are uncorrelated and have different polarization characteristics. Using the method, the number of dominant local scattering centers and interferometric phases in each image pixel can be estimated directly. Validity of the algorithm is demonstrated by using examples derived from SIR-C data.

In order to assess the possible impacts of meteors with spacecraft, which is among major hazard in the space environment, it is essential to establish an accurate statistics of their mass and velocity. We developed a radar-optical combined system for detecting faint meteors consisting of a powerful VHF Doppler radar and an ICCD video camera. The Doppler pulse compression scheme is used to enhance the S/N ratio of the radar echoes with very large Doppler shifts, as well as to determine their range with a resolution of 200 m. A very high sensitivity of more than 14 magnitude and 9 magnitude for radar and optical sensors, respectively, has been obtained. Instantaneous direction of meteor body observed by the radar is determined with the interferometry technique. We examined the optimum way of the receiving antenna arrangements, and also of the signal processing. Its absolute accuracy was confirmed by the optical observations with background stars as a reference. By combining the impinging velocity of meteor bodies derived by the radar with the absolute visual magnitude determined by the video camera simultaneously, the mass of each meteor body was estimated. The developed observation system will be used to create a valuable data base of the mass and velocity information of faint meteors, on which very little is known so far. The data base is expected to play a vital role in our understanding of the space environment needed for designing large space structures.

Complex-valued region-based-coupling image clustering (continuous soft segmentation) neural networks are proposed for interferometric radar image processing. They deal with the amplitude and phase information of radar data as a combined complex-amplitude image. Thereby, not only the reflectance but also the distance (optical length) are consistently taken into account for the clustering process. A continuous complex-valued label is employed whose structure is the same as that of input raw data and estimation image. Experiments demonstrate successfully the clustering operations for interferometric synthetic aperture radar (InSAR) images. The method is applicable also to future radar systems for image acquisition in, e.g., invisible fire smoke places and intelligent transportation systems by generating a processed image more recognizable by human and automatic recognition machine.

The boundary integral equation (BIE) on interior walls with surface impedance conditions is implemented to the iterative physical optics method and how to treat the singularities involved in the BIE of an impedance cavity is described. Singular integrals over a rectangular region can be represented by simple elementary functions.

A novel millimeter-wave slotted waveguide array antenna is developed for automotive radar systems. An antenna structure suitable for mass-production is proposed in this paper. The waveguide is composed of two parts; an upper plate and a bottom plate. It is not necessary to contact each other closely because they are divided at the center of the broad wall of the waveguide where the electric current is small. In addition, grating lobes are suppressed by using a cylindrical cavity around each slot and by controlling the slot arrangement without using dielectric material in the waveguide. We have fabricated the proposed antenna by metal injection molding. The measured antenna efficiency results in 55%, which is quite high in comparison with any other conventional low cost millimeter-wave antenna. This efficiency is almost the same as that of the antenna fabricated by precision metal machining. In this paper, it is confirmed that the proposed antenna could be manufactured with low cost.

For the microwave level meter based on the FM-CW radar, we analyze the spectrum correlation of beat signals and propose a measurement algorithm using the fact that there exists a peak in the spectrum correlation of beat signals when range difference is sufficiently small. This algorithm can compensate the nonlinear effect of VCO frequency sweep, making it possible to determine the range difference in a precise manner even using a practical VCO. We present some experimental results to show the validity of this algorithm.