The capability of frequency-swept cross-borehole radar to detect an empty rectangular cylinder embedded in a dielectric medium is simulated numerically by employing the boundary element method. The frequency loci providing the strongest double dips in the received signal pattern are plotted as functions of the observation distance and the cross-sectional width. It is found that, regardless of the shape of the rectangular cross-section, the strongest double dips become double nulls in the near-field region.

A program is developed to simulate the signal received by a bistatic pulse radar for a defined scenario. The signal collected at the receiving antenna is calculated as a function of time by taking into account the vectorial aspect of the electromagnetic waves and various elements operating in the radar radiolink. The radar radiolink is designed in a modular structure for a general configuration where the transmitter, the target and the receiver are moving. Modules such as elements characterizing the antennas radiation or defining the target scattering can be inserted in accordance with the desired radar scenario. Then the developed model permits to simulate a wide range of radar scenarios where returns from targets and clutter can be individually processed and their characteristics can be investigated in time or frequency. The interest of this model is great because it permits, for a defined scenario, to generate radar data which can be used in signal processing algorithms for target detection, clutter suppression or target classification. This paper shows the implementation of the simulation program considering a concrete radar scenario. The presented scenario deals with the simulation of the sea clutter occurring in a bistatic radar radiolink over the sea surface. In this application where the sea surface is considered as the target, the electric field scattered from the sea surface is calculated by assuming that the surface is described by two independent scales of roughness.

A two-dimensional algorithm, which combines the well-known Synthetic Aperture Radar (SAR) imaging and the recently developed effective inversion method, is presented and applied to a three-dimensional configuration. During the first stage a two-dimensional image of a realistic three-dimensional buried object is obtained. In the second stage the average permittivity of the object is estimated using a two-dimensional effective inversion scheme where the geometrical information retrieved from the SAR image is employed. The algorithm is applicable in real time.

Borehole radar is known as a powerful technique for monitoring of subsurface structures such as water flow. However, conventional borehole radar systems are operated in the frequency range lower than 100 MHz and the resolution is poor to measure a surface roughness and an inner structure of subsurface fractures directly. In order to monitor the water flow, these characteristics of subsurface fractures are important. We developed a polarimetric borehole radar system using dipole antennas and axial slot antennas and have found that this system can provide more information than conventional borehole radar. However, the relationship between the characteristic of subsurface fracture and the measured polarimetric radar information has not been clear. In this paper, we simulate electromagnetic wave scattering from subsurface fractures having a rough surface by Finite-Difference Time-Domain (FDTD) technique and discuss the relationship between a surface roughness of subsurface fracture and the polarimetric information. It is found that the subsurface fracture having strong cross-polarized components can be estimated to be rough surface fracture. The full polarimetric single-hole radar measurement was carried out at the Mirror Lake site, NH, USA. In this experiment, we found that subsurface fractures can be classified into some groups by an energy scattering matrix, and found that the subsurface fracture estimated to have a rough surface corresponds to that has higher water permeability.

The use of a chirp signal is one of the methods to expand the detection range in subsurface radar. However, the presence of time-sidelobes after a conventional pulse-compression makes the detection range degraded because weak signals from underground objects are covered with a large time-sidelobe due to a ground surface reflection. In this paper, we propose a new pulse compression subsurface radar using a short chirp signal in which the echoes from the ground surface and the object are not overlapped. We show that the short chirp signal can improve the detection ability compared with a conventional chirp signal and examine the influence that the decreases of the signal duration and the compression ratio exert on the detection range. By the new pulse compression subsurface radar, the steel pipes buried down to 5 m in depth can be detected.

The development of Radar Polarimetry and Radar Interferometry is advancing rapidly. Whereas with radar polarimetry, the textural fine-structure, target orientation, symmetries and material constituents can be recovered with considerable improvement above that of standard amplitude-only radar; with radar interferometry the spatial (in depth) structure can be explored. In Polarimetric Interferometric Synthetic Aperture Radar (POL-IN-SAR) Imaging, it is possible to recover such co-registered textural and spatial information from POL-IN-SAR digital image data sets simultaneously, including the extraction of Digital Elevation Maps (DEM) from either Polarimetric (scattering matrix) or Interferometric (single platform: dual antenna) SAR systems. Simultaneous Polarimetric-plus-Interferometric SAR offers the additional benefit of obtaining co-registered textural-plus-spatial three-dimensional POL-IN-DEM information, which when applied to Repeat-Pass Image-Overlay Interferometry provides differential background validation, stress assessment and environmental stress-change information with high accuracy. Then, by either designing Multiple Dual-Polarization Antenna POL-IN-SAR systems or by applying advanced POL-IN-SAR image compression techniques, it will result in POL-arimetric TOMO-graphic (Multi-Inter-ferometric) SAR or POL-TOMO-SAR Imaging. This is of direct relevance to local-to-global environmental background validation, stress assessment and stress-change monitoring of the terrestrial and planetary covers.

We have built a pulse-compressed high-resolution radar for surveying polar ice caps and ice sheet. In experiments with this instrument at the Agassiz ice cap, radio echoes from the bedrock and internal layers measured with high resolution. The resolution of the radar in ice is about 1 meter. The greatest depth from which signals from bedrock were received was more than 400 meters and that from which signals from internal ice were received was about 200 meters. Such performances are suitable for generating data that can be used for detailed comparison between ice core analysis and radar data. This radar is expected to be an effective tool for revealing the three-dimensional extension of event-layer in the ice core and to give information about the scattering mechanism of internal echoes.

A Frequency Modulated Continuous Wave (FMCW) radar using only in-phase channel is advantageous for automotive applications. In this radar, it is necessary to search the pairs of beat frequencies in an up-chirp mode and a down-chirp mode to measure the distances and the velocity of multiple targets similarly to a FMCW radar with both of in-phase and quadrature-phase channel. However the number of combinations to search the pairs is larger than that for the FMCW radar with both of in-phase and quadrature-phase channel. Therefore, false targets by mistaking the combination of these pairs increase. In this paper, we propose a novel measurement algorithm to reduce the false targets. We extract only the beat frequencies of the relatively moving targets using the differential frequency power spectrum of the up-chirp mode and the down-chirp mode. We can reduce the number of selected incorrect pairs by separating the stationary targets and the moving targets. We have conducted some simulations to confirm the capability of the proposed measurement algorithm. It was shown that the false target appearance probability is reduced without significant deterioration of the target detection probability.

The application of subsurface radar using electromagnetic waves in the VHF band is wide and includes surveying voids under the ground and archaeological prospecting. To achieve a wider application range, the survey depth must be deeper. In this paper, a method of pulse compression using a chirp signal as one of the methods to fulfill this requirement is described, and its advantages and problems are discussed. First, a delay correlation method is proposed as a processing method of pulse compression. It converts RF band chirp signal directly into a pulse. Moreover, the method improves the S/N ratio by over 40 dB compared with conventional pulse radar. Therefore, it has the same detection ability as conventional pulse radar even though it uses less transmitting power. Next, the influences of RF amplifier saturation and underground propagation characteristics on the chirp signal are discussed; both are shown to have little influence on the detection ability of the method.

Meteor storms and showers are now considered as potential hazard in the space environment. Radar observations of meteors has an advantage of a much higher sensitivity over optical observations. The MU radar of Kyoto University, Japan has a unique capability of very fast beam steerability as well as a high sensitivity to the echoes from ionization around the meteors. We developed a special observation scheme which enables us to determine the orbit of individual meteors. The direction of the target is determined by comparing the echo intensity at three adjacent beams. The Doppler pulse compression technique is applied to improve the signal-to-noise ratio of the echoes from the very fast target, and also to determine the range accurately. The developed scheme was applied to the observation made during the Leonid meteor storm on November 18, 1998 (JST). Estimated orbital distribution seems to suggest that the very weak meteors detected by the MU radar are dominated by sporadic meteors rather than the stream meteors associated with the Leonids storm.

An algorithm that detects the surface echo peak position in a radar echo range profile has been developed for the TRMM Precipitation Radar (PR). The purpose of the surface echo peak detection is to determine the range window in which "over-sample" data are collected. The surface echo position in the range profile is variable due to the systematic change of satellite geodetic altitude and surface topography. The dynamic control of the over-sample range window using the surface detection algorithm contributes significantly to the reduction of PR data rate that should be sent to the ground station. The algorithm employs an α-β tracking filter and has three functions; surface tracking, lock-off detection and tracking loop initialization. After the launch of the TRMM satellite, a series of initial check-out of the PR was conducted. The performance of the algorithm was evaluated through the initial check-out and two-years operation of the PR. The results indicate that the algorithm is working as expected and basically meets the specification; however, it is found that some functions such as the tracking loop initialization algorithm need to be improved.

A Rayleigh lidar (laser radar) system was developed and is now working well for temperature observations of the middle atmosphere at Poker Flat Research Range near Fairbanks, Alaska (65.1 N, 147.5 W). A comparison of lidar data and balloon sonde data showed good agreement in overlapped altitudes. The atmospheric fluctuations are detected in the temperature profiles obtained by the Rayleigh lidar and these are useful for the study of gravity waves. A Rayleigh Doppler lidar for wind measurements of the middle atmosphere is under the phase of development. The expected accuracy in measurements of horizontal winds up to an altitude of 60 km is smaller than 6 m/s in 2 hours observation. The system will be operated at Poker Flat after the completion of development. The combination of these lidars and radars installed at Poker Flat, give us chances of simultaneous observations of the structure and dynamics of the atmosphere in broad range of altitudes. Here, we give descriptions of the Rayleigh lidar and the Rayleigh Doppler lidar for the observations of the Arctic middle atmosphere at Poker Flat.

MF (medium frequency) radars (MFR) are powerful tools for understanding the upper atmosphere, by measuring horizontal wind velocity and electron density. This article introduces three MFR systems, two in Japan, Yamagawa (31.20N, 130.62E) and Wakkanai (45.36N, 141.81E) radars, and one at Poker Flat, Alaska (65.1N, 147.5W). Experimental techniques, and their observed results are briefly shown. Horizontal wind velocity was observed by those MFRs, in height ranges of 60-100 km (day) and 80-100 km (night) at Yamagawa and Wakkanai, while the data coverage is unusually low, >54 km (day) and >68 km (night), at Poker Flat. Comparison of MFR winds with temperature observed by a collocated Rayleigh lidar at Poker Flat shows consistency of those two instrument results in terms of atmospheric wave theory, implying validity of MFR data at such low altitudes. Electron density results at Poker Flat agree reasonably with International Reference Ionosphere model values at 74-84 km, and agree well with variation of cosmic noise absorption by the Poker Flat imaging riometer, suggesting valid electron density estimation by MFR at least below 80-85 km.

This paper presents a three-dimensional polarimetric detection result of targets buried in snowpack by synthetic aperture FM-CW radar system. Since the FM-CW radar is suitable for short range sensing and can be equipped with fully polarimetric capability, we further extended it to a polarimetric three-dimensional SAR system. A field experiment was carried out to image and detect targets in a natural snowpack of 280 cm deep. The polarimetric detection and identification schemes are the polarimetric filtering, three-component decomposition, and the power polarization anisotropy coefficient. These approaches to acquired data show the usefulness of three-dimensional polarimetric FM-CW SAR system.

In order to observe temporal distribution of sea clutter, radar echoes were taken from high sea state 7 at a fixed azimuth angle of 317. It is shown that the sea-clutter amplitudes obey the Weibull distribution at a grazing angle of 3.9, and obey both the Weibull distribution and K-distribution at grazing angles of 7.5 and 61.4. As the grazing angle increases, the shape parameters of Weibull distribution and K-distribution increase with both the distributions themselves tending to be closer to the Rayleigh distribution.

Speckle statistically brings series connections of dark pixels, which can be observed as dark line features in synthetic aperture radar (SAR) images. The dark lines have no physical meaning. In this paper, line features of that kind in high-resolution SAR images whose intensity obeys a K-distribution are studied. It is stochastically explained that the dark line features in 1-look K-distributed images can be observed more distinctly than those in exponential distributed images. It is further revealed that such line features are detectable enough, even if the K-distributed images are multilooked. The experiments on simulated images as well as on actual SAR images confirm the explanation.

An airborne cloud profiling radar (SPIDER) which has several unique features has been developed at CRL. In this paper, the objectives and design considerations are outlined, and the system is described. The features of SPIDER are summarized below. (1) A W-band frequency (95 GHz) is used to provide very high sensitivity to small cloud particles. (2) The radar is carried by a jet aircraft that can fly high above most clouds. (3) Full-polarimetric and Doppler capabilities are incorporated in the unit. (4) Almost all radar operational parameters are under software control, and most processing is in real time. (5) The design gives consideration to the study of cloud radiation and microphysics. The system has been completed and is still undergoing performance testing. The functions and performance of the SPIDER system are currently fulfilling the intentions of its design. Several interesting cloud features that had not been seen with previous instruments have already been observed.

A novel method is proposed to retrieve image sequences with the goal of forecasting complex and time-varying natural patterns. To that end, we introduce a framework called Memory-Based Forecasting; it provides forecast information based on the temporal development of past retrieved sequences. This paper targets the radar echo patterns in weather radar images, and aims to realize an image retrieval method that supports weather forecasters in predicting local precipitation. To characterize the radar echo patterns, an appearance-based representation of the echo pattern, and its velocity field are employed. Temporal texture features are introduced to represent local pattern features including non-rigid complex motion. Furthermore, the temporal development of a sequence is represented as paths in eigenspaces of the image features, and a normalized distance between two sequences in the eigenspace is proposed as a dissimilarity measure that is used in retrieving similar sequences. Several experiments confirm the good performance of the proposed retrieval scheme, and indicate the predictability of the image sequence.

In phased array antennas, the number of radiator rows is one of the important factors to minimizing both cost and weight. Therefore, the antenna tilt angles having relation with the element spacing are among the important design parameters. In this paper, the optimum tilt angles for several types of dipole planar arrays are investigated theoretically. To obtain optimum tilt angles, the directivity equation including phase shift factors for planar arrays are calculated.

This paper analyzes the effective radiation efficiency of a ground-penetrating radar (GPR) consisting of two resistor-loaded bow-tie antennas covered with a ferrite-coated conducting cavity by using finite-difference time-domain (FDTD) method. The GPR is located above a lossless or lossy ground surface. The relation between the radiation powers into the ground and air, dissipated powers at the loaded resistors and ferrite absorber, and the reflected power due to impedance mismatching, is clarified numerically.