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The Arecibo Observatory first opened in 1963 and has been a marvel of engineering ever since (Figure 1). It has been a monumental instrument for scientific research in the fields of astronomy, planetary radar, ionospheric probing and high-frequency (HF) heating modification, and optical probing of the atmosphere. [ABSTRACT FROM AUTHOR]

In this paper, a detailed comparative performance analysis of the two-color satellite laser ranging (SLR) systems of the Transportable Integrated Geodetic Observatory (TIGO) is presented. The study is based on four years of continuous measurement data and a comparison of two different layouts of the laser system. The focus lies on a quantitative analysis of measurement precision, range accuracy, and data production for the two laser system layouts. Main findings include a significant gain in temporal stability due to removal of active elements in the oscillator, an improvement of range measurement accuracy by a factor of 2, and an important increase in data productivity. The analysis presented here provides a valuable input for the design of future SLR systems, as well as related topics such as time transfer applications and optical communications to satellites. [ABSTRACT FROM PUBLISHER]

Design of a folded reflectarray antenna (FRA) by phase only control to provide a cosecan squared beam pattern in elevation and a pencil-beam pattern in azimuth to detect objects on the ground, e.g., on runways. A very compact folded reflectarray antenna was fabricated and its radiation pattern over frequency was simulated. During the design process a conical horn was developed, which illuminates the array, with symmetrical radiation pattern for all planes and for a frequency range of 76 to 81 GHz. As the FRA consists of a single layer substrate this kind of antenna could be a candidate for low-cost production in FOD detection on airports in the future. [ABSTRACT FROM PUBLISHER]

The Scanning Synthetic Aperture Radar (ScanSAR) is very useful for Earth observation because of its wider imaging swath and shorter revisit time. However, ScanSAR is sometimes affected by the following three artifacts: 1) scalloping, which often appears as repeating weak azimuth stripes at both edges of the focused burst image; 2) azimuth ambiguity (i.e., a form of ghosting that appears over the adjacent uniform area when the pulse repetition frequency is below the Doppler bandwidth); and 3) radiometric discontinuity (i.e., banding) between two adjacent scans. This paper proposes three methods to correct these artifacts, which are, specifically, the proposal for scalloping correction using Amazon Rainforest data, band limitation, and the correction for the inter SCAN banding using the dynamic gain correction algorithm. Several corrected sample data sets of the Phased-Array L-band SAR onboard the Advanced Land-Observing Satellite are presented to demonstrate the validity of the proposed methods. [ABSTRACT FROM AUTHOR]

In this paper, a novel hybrid tracking method for mobile active phased-array antenna systems is developed. The proposed technique consists of a mechanical stabilization loop and a direction-of-arrival (DOA) estimation algorithm, which is based on electronic beamforming. Compared with other tracking methods, the proposed method requires only one low-cost yaw rate sensor. The method utilizes electronic feedback from the phased-array antenna to compensate for the low-cost sensor irregularities. The effectiveness of the proposed tracking method is demonstrated by measured performance of a fast-moving ultra- low-profile phased-array satellite terminal, which uses the proposed approach. The field test results confirm that the hybrid tracking mechanism can nullify the base vehicle yaw disturbances up to 60°/s and 85°/s² and keep the azimuth angle error at less than the permissible bound of [-1°, + 10°. Although performance of the proposed tracking system is verified in the context of a mobile satellite television reception system, the basic principles can be applied to any tracking system that employs phased-array antennas. The mobile satellite Internet terminal is an important example. [ABSTRACT FROM AUTHOR]

A shaped-beam reflectarray based on patches, aperture-coupled to delay lines is demonstrated for local multipoint distribution system (LMDS) central station antennas, in the 10.10-10.70 GHz band. The antenna must cover a 60°-sector in azimuth with a squared cosecant pattern in elevation. The design process consists of two steps. First, a phase-only pattern synthesis technique is applied to obtain the required phase-shift distribution on the reflectarray surface which generates the shaped pattern. The second stage consists of determining the length of the delay lines, aperture-coupled to the square patches, in order to achieve the phase distribution synthesized in the previous step. Two reflectarray antennas have been designed, one for vertical (V) and the other for horizontal (H) polarization. A breadboard for V-polarization has been manufactured and tested in an anechoic chamber, showing a good agreement between theoretical and measured radiation patterns. [ABSTRACT FROM AUTHOR]

A high-resolution measurement system for the characterization of the delay and angle-of-arrival properties of all significant multipath components on mobile radio channels is presented. The system uses complex impulse response data obtained from a novel 3-D tilted cross switched antenna array as input to an improved version of 3-D Unitary ESPRIT. Results from simulations and measurements show that the approach is capable of accurately characterizing the delay and angle-of-arrival characteristics of the dominant multipath components at moderate urban speeds along a trajectory in mobile propagation environments with high resolution in both azimuth and elevation. [ABSTRACT FROM PUBLISHER]

The performance of a fingerprint matching system is affected by the nonlinear deformation introduced in the fingerprint impression during image acquisition. This nonlinear deformation causes fingerprint features such as minutiae points and ridge curves to be distorted in a complex manner. A technique is presented to estimate the nonlinear distortion in fingerprint pairs based on ridge curve correspondences. The nonlinear distortion, represented using the thin-plate spline (TPS) function, aids in the estimation of an "average" deformation model for a specific finger when several impressions of that finger are available. The estimated average deformation is then utilized to distort the template fingerprint prior to matching it with an input fingerprint. The proposed deformation model based on ridge curves leads to a better alignment of two fingerprint images compared to a deformation model based on minutiae patterns. An index of deformation is proposed for selecting the "optimal" deformation model arising from multiple impressions associated with a finger. Results based on experimental data consisting of 1,600 fingerprints corresponding to 50 different fingers collected over a period of two weeks show that incorporating the proposed deformation model results in an improvement in the matching performance. [ABSTRACT FROM AUTHOR]

This paper is concerned with the performance evaluation of fingerprint verification systems. After an initial classification of biometric testing initiatives, we explore both the theoretical and practical issues related to performance evaluation by presenting the outcome of the recent Fingerprint Verification Competition (FVC2004). FVC2004 was organized by the authors of this work for the purpose of assessing the state-of-the-art in this challenging pattern recognition application and making available a new common benchmark for an unambiguous comparison of fingerprint-based biometric systems. FVC2004 is an independent, strongly supervised evaluation performed at the evaluators' site on evaluators' hardware. This allowed the test to be completely controlled and the computation times of different algorithms to be fairly compared. The experience and feedback received from previous, similar competitions (FVC2000 and FVC2002) allowed us to improve the organization and methodology of FVC2004 and to capture the attention of a significantly higher number of academic and commercial organizations (67 algorithms were submitted for FVC2004). A new, "Light" competition category was included to estimate the loss of matching performance caused by imposing computational constraints. This paper discusses data collection and testing protocols, and includes a detailed analysis of the results. We introduce a simple but effective method for comparing algorithms at the score level, allowing us to isolate difficult cases (images) and to study error correlations and algorithm "fusion." The huge amount of information obtained, including a structured classification of the submitted algorithms on the basis of their features, makes it possible to better understand how current fingerprint recognition systems work and to delineate useful research directions for the future. [ABSTRACT FROM AUTHOR]

We study the impact of the geometry of the (planar) antenna array on the accuracy of the estimated direction(s) of arrivals of an emitting source. We develop explicit Cramer-Rao bounds (CRBs) of the azimuth and elevation angles that show a simple structure. In particular, for a fixed elevation angle, the CRBs are cosine functions of the source azimuth, and so, regardless of the array geometry. The amplitude and extremes of these functions depend on the array geometry. Hence, the array configuration can be chosen in order to ensure a desired (an)isotropic behavior. To do so, we propose a pragmatic methodology that also takes into account the array ambiguity problem. The array design problem is simplified by limiting the array search within a family of V-shaped. arrays that are advantageously characterized by a single parameter, the angle between the two branches. A performance measure is proposed, then analytically expressed, to assess the array directivity and gain with respect to the more standardly used uniform circular array. [ABSTRACT FROM AUTHOR]

Design advantages of square- and rectangular-loop antennas make these types of antennas attractive for use in mobile devices to improve their communication capabilities. However, modified characteristics of such antennas require additional analysis to evaluate interaction with antennas of other types and other components of mobile devices and human organisms. In this paper, the azimuth and radial field components of a rectangular-loop antenna in near and far fields are calculated and the results are compared to the elementary circular-loop antenna's field. It is demonsträted that loop dimensions and shape substantially affect its field magnitude, especially in the near field. [ABSTRACT FROM AUTHOR]

Reports a spatio-temporal channel characterization of a suburban non line-of-sight microcellular environment in which azimuth-delay profiles obtained by the experiment are compared with ray-tracing simulation. Description of the environment under consideration; Extraction of spatio-temporal channel parameters.

Presents empirical results characterizing the joint statistical properties of the local azimuth spread (AS), the local delay spread (DS) and the shadow fading component. Description of the measurement system and the investigated environments; Outline of the applied signal model; Spatial auto-correlation function of the AS, DS and shadow fading.

Presents a study which compared the second azimuthal harmonics of ocean surface brightness predicted by the second order small approximation (SSA) to an empirical model based on WindRAD experiments. SSA and directional spectrum models; Explanation on WindRAD empirical model; Results of the study; Conclusions.

This paper focuses on the bistatic synthetic aperture radar (BiSAR) signal processing in the spaceborne/airborne configuration. Due to the extreme differences in platform velocities and slant ranges, the airborne system operates in the inverse sliding spotlight mode, while the spaceborne system works in the sliding spotlight mode to achieve a tradeoff between the azimuth scene size and azimuth resolution. Such a mode is generally called double sliding spotlight mode. In this configuration, the echoed signal has two characteristics. Firstly, both transmitter and receiver have very short synthetic aperture times. Secondly, the airborne platform operates with wide squint difference, while the spaceborne platform works in the small squint case. According to these two features, we use different Taylor expansions to address the slant range histories of transmitter and receiver. Based on the presented model, a two-dimensional space-variant bistatic point target reference spectrum (BPTRS) is derived. Furthermore, we linearize the BPTRS to derive the transfer function of the baseband scene. From the transfer function, the signal features of the spaceborne/airborne configuration become very clear. Using the transfer function, the two-dimensional inverse scaled Fourier transform (ISFT) is used to focus the bistatic signal in the spaceborne/airborne configuration. [ABSTRACT FROM PUBLISHER]