This new book provides a broad perspective of spectral estimation techniques and their implementation. It concerned with spectral estimation of discretespace sequences derived by sampling continuous-space signals. Among its key features, the book: • Emphasizes the behavior of each spectral estimator for short data records. • Provides 35 computer programs, including fast algorithms. • Provides the theoretical background and review material in linear systems, Fourier transforms matrix algebra, random processes, and statics. • Summarizes classical spectral estimation as it is practiced today. • Covers Prony's method, parametric methods, the minimum variance method, eigenanalysis-based estimators, multichannel methods, and twodimensional methods. • Includes problems. • Contains appendices that cover Sunspot Numbers, Complex Test Data, Temperature Data, and Program Conversion for Complex-to-Real Case. Of Special Interest A disk is included that has a double-sides 360kB format readable by any personal computer with an MS-DOS 2 or 3 operating system, such as the IBM XT or AT.

A water-filled impedance tube capable of improved measurement accuracy and precision is reported. The measurement instrument employs a variation of the standardized two-sensor transfer function technique. Performance improvements were achieved through minimization of elastic waveguide effects and through the use of sound-hard wall-mounted acoustic pressure sensors. Acoustic propagation inside the water-filled impedance tube was found to be well described by a plane wave model, which is a necessary condition for the technique. Measurements of the impedance of a pressure-release terminated transmission line, and the reflection coefficient from a water/air interface, were used to verify the system.

Recent experiments confirm the production of sound by breaking waves at lower frequencies (30 to 500 Hz) with a dipole characteristic. The noise produced has a broadband characteristic associated with the impact and subsequent sounds that have discrete spectral characteristics. Breaking waves are known to produce bubble plumes and bubble clouds; the dynamic evolution of which provides a mechanism for sound production. Since the initial plume and cloud have appreaciable void fractions, compressible resonant oscillations of these structures as a whole or in parts are possible. These bubble plumes would act as compact acoustic monopole sources of sound and due to the pressure release surface would have an effective dipole characteristic. Sufficient energy exists in the initial breaking vorticity and turbulence to excite these regions and to explain measured source levels. These effects have been simulated with a tipping trough experiment that demonstrates the production of low-frequency sound from salt and fresh water tipping trough events. These experimental results are shown to be consistent with the theory of sound radiation from the collective oscillations of bubble plumes.

This article is a U.S. government work, and is not subject to copyright in the United States. CrossMark a r t i c l e i n f o b s t r a c tDesert Research and Technology Studies (Desert RATS) is a multi-year series of hardware and operations tests carried out annually in the high desert of Arizona on the San Francisco Volcanic Field. These activities are designed to exercise planetary surface hardware and operations in conditions where long-distance, multi-day roving is achievable, and they allow NASA to evaluate different mission concepts and approaches in an environment less costly and more forgiving than space. The results from the RATS tests allow selection of potential operational approaches to planetary surface exploration prior to making commitments to specific flight and mission hardware development. In previous RATS operations, the Science Support Room has operated largely in an advisory role, an approach that was driven by the need to provide a loose science mission framework that would underpin the engineering tests. However, the extensive nature of the traverse operations for 2010 expanded the role of the science operations and tested specific operational approaches. Science mission operations approaches from the Apollo and Mars-Phoenix missions were merged to become the baseline for this test. Six days of traverse operations were conducted during each week of the 2-week test, with three traverse days each week conducted with voice and data communications continuously available, and three traverse days conducted with only two 1-hour communications periods per day. Within this framework, the team evaluated integrated science operations management using real-time, tactical science operations to oversee daily crew activities, and strategic level evaluations of science data and daily traverse results during a post-traverse planning shift. During continuous communications, both tactical and strategic teams were employed. On days when communications were reduced to only two communications periods per day, only a strategic team was employed. The Science Operations Team found that, if communications are good and down-linking of science data is ensured, high quality science returns is possible regardless of communications. What is absent from reduced communications is the scientific interaction between the crew on the planet and the scientists on the ground. These scientific interactions were a critical part of the science process and significantly improved mission science return over reduced communications conditions. The test also showed that the quality of science return is not measurable by simple numerical quantities but is, in fact, based on strongly non-quantifiable factors, such as the interactions between the crew and the Science Operations Teams. Although the metric evaluation data suggested some trends, there was not sufficient granularity in the data or specificity in the metrics to allow those trends to be understood on numerical data alone.Published by Elsevier Ltd. on behalf of IAA.

Experimental measurements of signal coherence and array signal gain are presented for both deep- and shallow-water sound channels. The signal gain is related to the transverse horizontal coherence length through relationships from the statistical theory of antennas. Signal gain measurements in the transverse direction are proffered as a practical measure of coherence length for both broadband and narrow-band signals. With this technique, measurements at frequencies near 400 Hz are presented and show for the deep-water cases that lengths on the order of 100 wavelengths can be achieved to ranges of 500 km; while in the variable downward refraction conditions of shallow-water waveguides with sand-silt bottoms, lengths on the order of 30 wavelengths to ranges of 45 km are realized. The measurement of broadband and narrow-band coherence is discussed with emphasis on the role of partly coherent noise backgrounds, multipath interference effects, and averaging constraints. Experimental results are interpreted with deep-ocean coherence models consistent with sound scattering from the ocean volume and Gaussian coherence function for the shallow-water waveguide.