Photon Correlation Techniques for Wind-Tunnel Anemometry

The experience gained at the Royal Aircraft Establishment in laser anemometry techniques, using a photon correlator, is reviewed. The theory of operation of the equipment is summarized for both laminar and turbulent flows, and methods of data-reduction are discussed, with particular reference to the optical criteria which should be met. Flow seeding requirements are considered and a practical system described. The results of a number of experiments on subsonic and supersonic airflows, both laminar and turbulent, are presented.     

Comet West 1976 VI: Photopolarimetry by the Helios 2 Zodiacal Light Experiment

Shortly after it passed through perihelion on February 25, 1976 Comet West was observed by the Helios Zodiacal Light Experiment. Broadband photopolarimetric measurements of the head and of the tail were performed in three wavelength bands (U, B, V). The phase angles encountered range from 67° to 85°. The polarization measurements indicated wavelength independent linear polarization. The maximum degree of polarization in the visual channel was found to be .28 at a phase angle of 83°.     

Estimating Noise Variances by Using Multiple Observers

Unknown variances of the noises that excite a time-invariant, linear dynamic system and/or in the observation of its output can be estimated by use of multiple observers. One observer is needed, in general, for each unknown variance. Each observer is time invariant and has different gains from the others. It is shown that each unknown variance is a linear combination of the variances of the residuals of the observers. The required estimates of the noise variances are obtained by using the measured variances of the residuals. The method presented in this paper is illustrated by an application to determining noise parameters in a ring laser gyro.     

High resolution measurements of nightside ion troughs at venus: Evidence of electrodynamic perturbations

The Bennett rf ion mass spectrometer (OIMS) on the Pioneer Venus Orbiter was particularly designed to provide variable temporal resolution for measurements of thermal ion composition and density. An Explore-Adapt mode is used to obtain priority for measurement of most prominent ion species, and in a 2/16 configuration, the two dominant ions within the available range of 16 species are selectively sampled at the highest rate of 0.2 sec/sample. The high resolution measurements are combined with independent observations from the magnetic field (OMAG), neutral mass spectrometer (ONMS), and electron temperature (OETP) experiments to investigate sharply structured troughs in the low altitude nightside ion concentrations. The results indicate a close correlation between the structure in the ion distributions and the structured configuration of the magnetic field which is draped about the planet. In the regions of the ion depletions, sharp fluctuations in electron temperature and anomalous increases in the density of neutral gases indicate that the ion depletion may be associated either with dynamic perturbation in the ion and neutral flows, and/or local joule heating. The configuration of the ion flow/magnetic field draping and consequent electric fields for these events must be analyzed in detail to understand the relationships.     

A proposed Comet Nucleus Penetrator for the Comet Rendezvous Asteroid Flyby mission

Among the major objectives of NASA's program of space exploration is a better understanding of the origin and evolution of the solar system. Crucial to this objective is the study of comets, which are thought to be the most primitive, pristine bodies remaining in the solar system. The importance of the study of comets has led NASA to plan a mission to rendezvous with comet Tempel 2 in 1997. Critical to the understanding of comets will be measurements of the nucleus material to determine its elemental and isotopic composition, its mechanical properties, and its thermal state and properties. This paper describes a proposal for a Comet Nucleus Penetrator to accomplish these measurement goals. The Comet Nucleus Penetrator will implant instruments into the comet's nucleus beneath a probable volatile-depleted surface mantle into material more representative of the bulk composition of the nucleus.     

A Statistical Glint/Radar Cross Section Target Model

We review the details of the glint (angular scintillation) problem in electromagnetic scattering. These results are employed to develop a statistical glint and radar cross section (RCS) target model featuring the correct glint probability density function, the correct time correlations of RCS and glint, and the correct cross correlation between RCS and glint. This model is suitable for simulation applications, and an implementation scheme for a glint/RCS signal generator is included.     

Asynchronous Performance of Slitted Rotor Reluctance Machines: Saturation Effects

Analytical investigation based on limiting nonlinear theory presented here for the asychronous performance of a slitted solid iron rotor reluctance machine include the effect of rotor iron saturation. Characteristic curves depicting nondimensional expressions developed for the rotor impedance factor and the power factor enable a visualization of the effects of 1) ratio of depth of saliency to depth of penetration, 2) slit number and depth, and 3) effective resistivities and saturation flux densities of different regions of the rotor on rotor parameter variations. Further predicted values are compared with experimental values and conclusions are drawn.