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The ELDORA ASTRAIA airborne Doppler weather radar: goals, design, and first field tests
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| Pengarang | : | - |
| Nama Majalah/Jurnal | : | Proceedings of the IEEE |
| Volume / Edisi | : | 82-12, DECEMBER (No. 12) |
| Halaman | : | 1873-1890 |
| Abstrak | : | Describes the development and first operation of a innovative research tool for observing atmospheric storms: an airborne X-band Doppler radar. The radar has been built jointly by the National Center for Atmospheric Research (NCAR) in Boulder, CO and the Centre de Recherches en Physique de l'Environnement Terrestre et Planetaire (CRPE) in Paris, France. The radar is called ELDORA/ASTRAIA for Electra Doppler Radar/Analyse Stereoscopique par Radar Aeroporte sur Electra. The radar is designed to provide high-resolution measurements of the air motion and rainfall characteristics of very large storms: storms which are frequently too large and/or too remote to be adequately observed by ground-based radars. This paper includes discussions of the scientific impetus and design criteria as well as the engineering solutions to these design needs. The design options and tradeoffs of the resulting capabilities are discussed. The paper concludes with an evaluation of the performance of the system at its first field test, conducted as a part of the international global warming experiment in the equatorial Pacific Ocean known as the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE). This evaluation illustrates that the major design goals for the radar - collection of relatively noise-free velocity and reflectivity data using a rapid scanning radar - have been adequately met. Future options for further improvements to the radar are discussed. |
Design of a bistatic dual-Doppler radar for retrieving vector winds using one transmitter and a remote low-gain passive receiver
| Pengarang | : | Wurman, J. |
| Nama Majalah/Jurnal | : | Proceedings of the IEEE |
| Volume / Edisi | : | 82-12, DECEMBER (No. 12) |
| Halaman | : | 1861-1872 |
| Abstrak | : | A bistatic dual-Doppler network consisting of an existing single transmitting pencil-beam weather radar and a remotely located, nontransmitting, passive bistatic receiver with a low-gain antenna was constructed and tested during 1993. High-quality dual Doppler vector winds were retrieved from this system. The windfields were compared with those collected with a traditional two-transmitter dual-Doppler system. Several interesting engineering challenges relating to frequency and timing synchronization were resolved in order to retrieve successfully Doppler velocities at a remote bistatic site. Frequency synchronization was achieved by using extremely stable local oscillators, linked by both Global Positioning Satellite (GPS) signals and transmitter sidelobe coupling. Both methods provided the necessary one part in 10/sup 9/ coherence necessary for calculating accurate Doppler velocities. Timing/gating synchronization with submicrosecond accuracy was achieved by using local oscillators at each site linked with GPS and sidelobe coupling. The successful testing of this system demonstrates that inexpensive and practical bistatic multiple-Doppler networks can be deployed. These systems can provide three-dimensional vector winds for a number of purposes in research, aviation, media, weather prediction, education, meteorological modeling and severe weather detection. |
Airborne scatterometers: investigating ocean backscatter under low- and high-wind conditions
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | Proceedings of the IEEE |
| Volume / Edisi | : | 82-12, DECEMBER (No. 12) |
| Halaman | : | 1835-1860 |
| Abstrak | : | Attempting to understand and predict weather on a local and global basis has challenged both the scientific and engineering communities. One key parameter in understanding the weather is the ocean surface wind vector because of its role in the energy exchange at the air-sea surface. scatterometers, radars that measure the reflectivity of a target offer a tool with which to remotely monitor these winds from tower-, aircraft-, and satellite-based platforms. This paper introduces three current airborne scatterometer systems, and presents data collected by these instruments under low-, moderate-, and high-wind conditions. The paper focuses on airborne scatterometers because of their ability to resolve submesoscale variations in wind fields. Discrepancies between existing theory and the observations are noted and the concerns in measuring low-wind speeds discussed. Finally, the application of using this technology for estimating the surface-wind vector during a hurricane is demonstrated. |
Environmental characterization with magnetics and STOLS
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | Proceedings of the IEEE |
| Volume / Edisi | : | 82-12, DECEMBER (No. 12) |
| Halaman | : | 1823-1834 |
| Abstrak | : | The application of techniques utilizing total field magnetic anomaly measurements can contribute significantly to the environmental characterization of lands contaminated with hazardous, toxic, or radioactive wastes. By addressing the correlated problem of detection and characterization of HTRW waste containers, predominantly made of ferromagnetic materials, high-density magnetics systems can be used to characterize a wide range of buried hazardous materials. Ferromagnetic materials such as iron and steel, induce an observable secondary magnetic field which can be measured and modeled to yield estimates of location, depth, and mass of the ferromagnetic objects. As a passive geophysical technique magnetics is logistically tractable, allowing for development of systems which acquire high density data over large areas. The STOL magnetics detection system was developed for this purpose, and is outfitted with seven total field magnetometers which are integrated with a differential GPS to provide 20 Hz magnetic-field measurements positioned with nominal absolute position accuracy of 30 cm. Processing of magnetic data requires the removal of the Earth's primary field and the interpolation onto a mesh. Image processing techniques are applied to enhance and segment the data for anomaly delineation. Isolated anomalies are modeled under the point dipole assumption to produce estimates of object position, depth, and mass. |
Ground penetrating radar as a subsurface environmental sensing tool
| Pengarang | : | Sumadjudin, Bambang,Setiawan, Budi ,Sujatmoko, Kris |
| Nama Majalah/Jurnal | : | Proceedings of the IEEE |
| Volume / Edisi | : | 82-12, DECEMBER (No. 12) |
| Halaman | : | 1802-1822 |
| Abstrak | : | Ground penetrating radar (GPR) is considered as an environmental tool. The basic concepts involved in GPR are introduced briefly including the antennas, propagation, target scattering, and mapping. Target identification is important when using GPR since the scatterer can only be observed by evacuation. This is discussed in terms of mapping and complex natural resonances. GPR has been used and is being considered as a tool for the detection of a wide variety of subterranean features. A very brief description of the various applications of GPR is presented. In terms of environmental sensing, it has been applied to detect buried tanks, landfill debris, water levels, and contaminated fluids. The detection of various military devices also represent a serious environmental concern including landmines and unexploded ordnance. There are also possible applications involving the detection of buried utilities highway voids, grave sites. It has been used for examining archeological sites. The above list is far from complete because of the ever-expanding use of GPR. |
ESTAR: a synthetic aperture microwave radiometer for remote sensing applications
| Pengarang | : | Vine, D.M. Le |
| Nama Majalah/Jurnal | : | Proceedings of the IEEE |
| Volume / Edisi | : | 82-12, DECEMBER (No. 12) |
| Halaman | : | 1787-1801 |
| Abstrak | : | ESTAR represents a new technology being developed for passive microwave remote sensing of the environment from space. The instrument employs an interferometric technique called aperture synthesis in which the coherent product from pairs of antennas is measured as a function of pair spacing. Substantial reductions in the antenna aperture needed for a given spatial resolution can be achieved with this technique. As a result, aperture synthesis could lead to practical passive microwave remote sensing instruments in space to measure parameters such as soil moisture and ocean salinity which require observations at long wavelengths and, therefore, large antennas. ESTAR is an L-band, aircraft built as part of research to develop this technique ESTAR is a hybrid real-and-synthetic aperture radiometer which employs stick antennas to achieve resolution along track and uses aperture synthesis to achieve resolution across track. Experiments to validate the instrument's ability to measure soil moisture have recently been conducted at the USDA watersheds at Walnut Gulch in Arizona and the Little Washita River in Oklahoma. The results of both experiments indicate that a valid image reconstruction and calibration have been obtained for this remote sensing technique. |
Mapping the world's topography using radar interferometry: the TOPSAT mission
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | Proceedings of the IEEE |
| Volume / Edisi | : | 82-12, DECEMBER (No. 12) |
| Halaman | : | 1774-1786 |
| Abstrak | : | Global-scale topographic data are of fundamental importance to many Earth science studies, and obtaining these data is a priority for the Earth science community. Several groups have considered the requirements for such a data set, and a consensus assessment is that many critical studies would be enabled by the availability of a digital global topographic model with accuracies of 2 and 30 m in the vertical and horizontal directions, respectively. Radar interferometric techniques have been used to produce digital elevation models at these accuracies and are technologically feasible as the centerpiece of a spaceborne satellite mission designed to map the world's land masses, which we denote TOPSAT. A radar interferometer is formed by combining the radar echoes received at a pair of antennas displaced across-track, and specialized data processing results in the elevation data. Two alternative implementations, one using a 2 cm-/spl lambda/ radar, and one using a 24 cm-/spl lambda/ radar, are technologically feasible. The former requires an interferometer baseline length of about 15 m to achieve the required accuracy, and this could be built on a single spacecraft with a long extendible boom. The latter necessitates a kilometers long baseline, and would thus be best implemented using two spacecraft flying in formation. Measurement errors are dominated by phase noise, due largely to signal-to-noise ratio considerations, and attitude errors in determining the baseline orientation. For the 2-m accuracy required by TOPSAT, the orientation must be known to 1 arc-second. For the single-spacecraft approach, where attitude would be determined by star tracking systems, this performance is just beyond the several arc-second range of existing instruments. For the dual-spacecraft systems, though, differential global positioning satellite measurements possess sufficient accuracy. Studies indicate that similar performance can be realized with either system. |
Multivariate Polynomial Interpolation in Newton Forms
| Pengarang | : | Richard D. Neidinger |
| Nama Majalah/Jurnal | : | Siam Review |
| Volume / Edisi | : | 61 (No. 2) |
| Halaman | : | 361-381 |
| Abstrak | : | Techniques of univariate Newton interpolating polynomials are extended to multivariate data points by different generalizations and practical algorithms. The Newton basis format, with divided-difference algorithm for coefficients, generalizes in a straightforward way when interpolating at nodes on a grid within certain regions. While this idea, known as the tensor product case, has been around for over a century, this exposition uses modern multi-index notation to provide generality, concise algorithms, and rigor, appropriate as a topic in introductory numerical analysis. Node configurations where the tensor product case applies are called lower sets, and they include -dimensional rectangles (boxes) and triangles (corners), the latter having unique interpolation over polynomials of fixed degree. Arbitrary distinct nodes do not ensure unique interpolating polynomials but, when possible, a different basis generalization, which we call Newton--Sauer, results in a nice triangular linear system for the coefficients. For the right number of distinct nodes, an algorithm based on Gaussian elimination produces either this Newton--Sauer basis or a polynomial that is zero on all nodes, showing that unique interpolation is impossible. The algorithm may also be used on any distinct nodes to produce a polynomial subspace of minimal degree where unique interpolation is possible. A variation of this algorithm using matrix block operations produces another basis generalization that we call Newton--Olver, which exactly agrees with the classic one for a corner of nodes and computes an interpolating polynomial using formulas similar to divided differences. |
Case for First Courses on Finite Markov Chain Modeling to Include Sojourn Time Cycle Chart
| Pengarang | : | Samuel Awoniyi |
| Nama Majalah/Jurnal | : | Siam Review |
| Volume / Edisi | : | 61 (No. 2) |
| Halaman | : | 347-360 |
| Abstrak | : | This education article presents a case for first courses on Markov chain modeling to include the topic “sojourn time cycle chart" (STC chart). This article does so through a teaching module that consists of (i) hypothetical examples illustrating the application-motivated concept of STC chart, and (ii) a network-based procedure for computing sojourn times of finite Markov chains inside subsets of their states. The sojourn time computation procedure is a simplified version of computations that already exist in several journal articles, and it applies to discrete-time Markov chain (DTMC), continuous-time Markov chain (CTMC) in rate form, and CTMC in time form. The only requirement for success in the computations is that Markov chain balance equations have a unique solution. |
Bounds on the Singular Values of Matrices with Displacement Structure
| Pengarang | : | - |
| Nama Majalah/Jurnal | : | Siam Review |
| Volume / Edisi | : | 61 (No. 2) |
| Halaman | : | 319-344 |
| Abstrak | : | Matrices with displacement structure, such as Pick, Vandermonde, and Hankel matrices, appear in a diverse range of applications. In this paper, we use an extremal problem involving rational functions to derive explicit bounds on the singular values of such matrices. For example, we show that the th singular value of a real positive definite Hankel matrix, , is bounded by with explicitly given constants and , where is the spectral norm. This means that a real positive definite Hankel matrix can be approximated, up to an accuracy of with , by a rank matrix. Analogous results are obtained for Pick, Cauchy, real Vandermonde, Lo?wner, and certain Krylov matrices. |