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At least 1,117 records · Page 62
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Sea ice lead dynamics from ERS-1 SAR

The use of ERS-1 SAR (Synthetic Aperture Radar) images to measure ice lead changes and ice deformation, and thus to determine their relationships and compare them to theory, is reported. ERS-1 SAR data collected at the Alaska (U.S.) SAR facility are processed into low resolution geocoded images which are used as input to the Geophysical Processor System (GPS). The GPS uses cross correlation and edge detection on sequential pairs of images to track a regular 5 km array of grid points. The result for each sequential image pair is a field of ice displacement that contains, on average, more than 200 vectors. The GPS also classifies all the pixels of the images into one of four ice types based on the normalized backscatter coefficients and a seasonal look-up table. This allows all pixels to be labeled as either multiyear ice or as the first year ice and open water that comprise leads.

Stern, Harry L.↗
NASA NTRS2005

Numerical Simulations of Plasma Based Flow Control Applications

A mathematical model was developed to simulate flow control applications using plasma actuators. The effects of the plasma actuators on the external flow are incorporated into Navier Stokes computations as a body force vector. In order to compute this body force vector, the model solves two additional equations: one for the electric field due to the applied AC voltage at the electrodes and the other for the charge density representing the ionized air. The model is calibrated against an experiment having plasma-driven flow in a quiescent environment and is then applied to simulate a low pressure turbine flow with large flow separation. The effects of the plasma actuator on control of flow separation are demonstrated numerically.

Suzen, Y. B.↗
NASA NTRS2020

Identify the Limits of Geometric Optics Ray Tracing by Numerically Solving the Vector Kirchhoff Integral

The properties of a pencil of light as defined approximately in the geometric optics ray tracing method are investigated. The vector Kirchhoff integral is utilized to accurately compute the electromagnetic near field in and around the pencil of light with various beam base sizes, shapes, propagation directions and medium refractive indices. If a pencil of light has geometric mean cross section size of the order p times the wavelength, it can propagate independently to a distance p2 times the wavelength, where most of the beam energy diffuses out of the beam region. This is consistent with a statement that van de Hulst made in a classical text on light scattering. The electromagnetic near fields in the pencil of light are not uniform, have complicated patterns within short distances from the beam base, and the fields tend to converge to Fraunhofer diffraction fields far away from the base.

Far field diffraction↗
NASA NTRS1983

Electric field measurements at the magnetopause. I Observation of large convective velocities at rotational magnetopause discontinuities

Large convective electric fields of the order of 10 mV/m (sometimes as high as 22 mV/m) are observed at rotational magnetopause discontinuities. These observations were made with the long cylindrical (179-m base line) probes carried on the ISEE 1 satellite. These electric field observations yield convective velocity magnitudes (equal to the cross product of the vector E and the vector B, the latter divided by the square of the magnitude of B) of the order of 150 km/s. In this format for the convective velocity magnitudes, some of these observations are similar to the high speed plasma velocity observations that were made at the magnetopause with the plasma experiment carried on the ISEE 1 satellite. It is shown that, for many of these magnetopause crossings, there exists a special moving coordinate system where the observed electric fields vanish. Such a unique reference system is often used in theoretical studies of magnetic discontinuities. This special coordinate system does not move at the local plasma velocity but moves instead at a velocity intermediate between the convective velocity and the local Alfven velocity. It is used here as a diagnostic tool for the experimental investigation of rotational discontinuities at the magnetopause.

Aggson, T. L.↗
NASA NTRS1981

Magnetic field observations on DE-A and -B

Magnetic field observations are conducted on each of the DE-A and -B satellites by a triaxial fluxgate magnetometer. In the basic mode the instrumental resolution is + or - 1.5 nT; in addition, the DE-A magnetometer has two modes of higher resolution: + or - 0.25 nT and + or - 20 pT. The sampling rate is 16 vector samples per second in all modes. The experiment objectives include observations of field-aligned currents, magnetospheric equatorial currents, and ULF waves. These observations, taking full advantage of the specifically selected orbits of the two spacecraft and of the unique combination of instruments, are performed to achieve a better understanding of the electrodynamic coupling within the atmosphere-ionosphere-magnetosphere system and of wave-particle interactions which contribute to the coupling processes.

Farthing, W. H.↗
NASA NTRS1978

The ISEE-C vector helium magnetometer

The ISEE-C magnetometer will make continuous observations of the interplanetary magnetic field near 1 AU. This paper describes the scientific objectives of the magnetometer experiment and gives attention to instrument design (sensor, electronics, and operating principles). A functional block diagram of the system is presented and attention is given to minor modifications required by the ISEE mission (the magnetometer is essentially one that served as the spare unit for the Pioneer 10 and 11 missions to Jupiter).

Frandsen, A. M. A.↗
NASA NTRS1978

Effectiveness of basic display augmentation in vehicular control by visual field cues

The paper investigates the effectiveness of different basic display augmentation concepts - fixed reticle, velocity vector, and predicted future vehicle path - for RPVs controlled by a vehicle-mounted TV camera. The task is lateral manual control of a low flying RPV along a straight reference line in the presence of random side gusts. The man-machine system and the visual interface are modeled as a linear time-invariant system. Minimization of a quadratic performance criterion is assumed to underlie the control strategy of a well-trained human operator. The solution for the optimal feedback matrix enables the explicit computation of the variances of lateral deviation and directional error of the vehicle and of the control force that are used as performance measures.

Grunwald, A. J.↗
NASA NTRS1985

Inviscid analysis of advanced turboprop propeller flow fields

A three-dimensional Euler code, previously developed for high speed propellers, was rewritten and vectorized for the Cray computer. Calculations were compared with previous results and measurements. The new code requires less memory and is more than two times faster than its predecessor. The new boundary conditions produced more accurate results and improved stability. The accuracy and stability characteristics also resulted in reduced manual intervention required to obtain solutions. The code is a useful tool for examining the fluid dynamics and performance of propellers.

Barton, J. M.↗
NASA NTRS2001

Magnetic Characteristics of Active Region Heating Observed with TRACE, SOHO/EIT, and Yohkoh/SXT

Over the past several years, we have reported results from studies that have compared the magnetic structure and heating of the transition region and corona (both in active regions and in the quiet Sun) by combining X-ray and EUV images from Yohkoh and Solar and Heliospheric Observatory (SOHO) with photospheric magnetograms from ground-based observatories. Our findings have led us to the hypothesis that most heating throughout the corona is driven from near and below the base of the corona by eruptive microflares occurring in compact low-lying "core magnetic fields (i.e., fields rooted along and closely enveloping polarity inversion lines in the photospheric magnetic flux). We now extend these studies, comparing sequences of UV images from Transition Region and Coronal Explorer (TRACE) with longitudinal magnetograms from Kitt Peak and vector magnetograms from MUSIC. These comparisons confirm the previous results regarding the importance of core-field activity to active region heating. Activity in fields associated with satellite polarity inclusions and/or magnetically sheared configurations is especially prominent. This work is funded by NASA's Office of Space Science through the Sun-Earth Connection Guest Investigator Program and the Solar Physics Supporting Research and Technology Program.

Porter, J. G.↗
NASA NTRSDate not supplied

Enabling Intelligent Data Downlink Prioritization of In-Situ Observations through Generalizable and Computationally Inexpensive Anomaly Detection

High-fidelity measurements of magnetic fields and other observed properties, such as energetic particle fluxes, are a necessary component to our understanding of the highly dynamic near-Earth space environment. As our desire to study smaller-scale phenomena such as shocks and dipolorizations has increased, we have been driven to take and telemeter measurements at higher cadences. Unfortunately, many missions are unable to downlink all their captured data due to the well-known data transmission bottleneck at the DSN. These missions must then prioritize their high-cadence data such that the most scientifically useful intervals are transmitted. One simple prioritization technique uses the spacecraft position to telemeter data from only the region of interest. Although easy to implement, this method does not leverage the available scientific data and can omit intervals of useful scientific data when they lie outside the region of interest. The Magnetospheric Multiscale Mission (MMS) uses mission-specific parameterization of several data products to automatically prioritize scientifically useful intervals. Then, MMS verifies the automatically selected intervals by having a domain expert manually select intervals for downlink. The overall complexity required by this technique make it prohibitive for deployment on low-cost platforms (i.e., CubeSats) or on future missions featuring large constellations of satellites such as the Geospace Dynamics Constellation (GDC). We present preliminary results for a simple, generic, and data-driven method of downlink prioritization for magnetic field (and other) measurements. Specifically, Principal Components Analysis (PCA) and One-Class Support Vector Machines (OC-SVMs) are used to detect intervals containing anomalous activity, which can then be prioritized for subsequent downlink. The computational simplicity of this algorithm makes it an excellent candidate for implementation on spaceflight hardware, as well as provide generalizability to a broad range of missions and data products. Initial analysis of this technique has been performed using magnetic field measurements from the Magnetospheric Multiscale Mission and CASSIOP, where it automatically identified scientifically interesting intervals containing Alfvén waves and EMIC activity.

Matthew G. Finley↗
NASA NTRSDate not supplied

Enabling Intelligent Data Downlink Prioritization of In-Situ Observations through Generalizable and Computationally Inexpensive Anomaly Detection

High-fidelity measurements of magnetic fields and other observed properties, such as energetic particle fluxes, are a necessary component to our understanding of the highly dynamic near-Earth space environment. As our desire to study smaller-scale phenomena such as shocks and dipolorizations has increased, we have been driven to take and telemeter measurements at higher cadences. Unfortunately, many missions are unable to downlink all their captured data due to the well-known data transmission bottleneck at the DSN. These missions must then prioritize their high-cadence data such that the most scientifically useful intervals are transmitted. One simple prioritization technique uses the spacecraft position to telemeter data from only the region of interest. Although easy to implement, this method does not leverage the available scientific data and can omit intervals of useful scientific data when they lie outside the region of interest. The Magnetospheric Multiscale Mission (MMS) uses mission-specific parameterization of several data products to automatically prioritize scientifically useful intervals. Then, MMS verifies the automatically selected intervals by having a domain expert manually select intervals for downlink. The overall complexity required by this technique make it prohibitive for deployment on low-cost platforms (i.e., CubeSats) or on future missions featuring large constellations of satellites such as the Geospace Dynamics Constellation (GDC). We present preliminary results for a simple, generic, and data-driven method of downlink prioritization for magnetic field (and other) measurements. Specifically, Principal Components Analysis (PCA) and One-Class Support Vector Machines (OC-SVMs) are used to detect intervals containing anomalous activity, which can then be prioritized for subsequent downlink. The computational simplicity of this algorithm makes it an excellent candidate for implementation on spaceflight hardware, as well as provide generalizability to a broad range of missions and data products. Initial analysis of this technique has been performed using magnetic field measurements from the Magnetospheric Multiscale Mission and CASSIOP, where it automatically identified scientifically interesting intervals containing Alfvén waves and EMIC activity.

Matthew G. Finley↗
NASA NTRS1976

An iterative algorithm for objective wind field analysis

Three different algorithms for objective wind field analysis were tested on the same set of initial conditions: Dickerson-Sasaki's 'strong constraint' algorithm, a fixed-vorticity algorithm, and a newly proposed fixed-station-velocity algorithm. The three methods are compared with respect to the degree of minimization of wind divergence and the accuracy of wind data at a measured station. The first two techniques, though they reduce wind divergence, produce wind vectors substantially different from the observed values. The proposed iterative scheme is similar to Endlich's (1967) procedure for treating a macroscale wind field, and minimizes divergence while retaining the observed wind vectors.

Liu, C. Y.↗
NASA NTRS1993

Field by field hybrid upwind splitting methods

A new and general approach to upwind splitting is presented. The design principle combines the robustness of flux vector splitting schemes in the capture of nonlinear waves and the accuracy of some flux difference splitting schemes in the resolution of linear waves. The new schemes are derived following a general hybridization technique performed directly at the basic level of the field by field decomposition involved in FDS methods. The scheme does not use a spatial switch to be tuned up according to the local smoothness of the approximate solution.

Coquel, Frederic↗
NASA NTRS1994

Measurement Capabilities of Single-Pulse Planar Doppler Velocimetry

Preliminary investigations are described of a method that is capable of measuring instantaneous, 3-D, velocity vectors everywhere in a light sheet generated by a pulsed laser. The technique, here called Planar Doppler Velocimetry (PDV), is a variation of a new concept for velocity measurements that was called Doppler Global Velocimetry (DGV) in its original disclosure. The concept relies on the use of a narrowband laser and measurements of the Doppler shift of scattered light from particles moving with a flow. The Doppler shift is recorded as a variation in transmission through a sharp-edged spectral filter provided by iodine vapor in a cell. Entire fields of velocity can be determined by using a solid-state camera to record the intensity variations throughout the field of view. However, the implementation of DGV has been centered principally on the use of high power, continuous-wave, ion lasers and measurement times that are determined by the 30-ms framing times of standard video cameras. Hence, they provide velocity fields that are averaged in time at least over that period. On the other hand, the PDV concept described in this presentation incorporates a high energy, repetitively pulsed, Nd-YAG laser that is injection-seeded to make it narrowband and then frequency-doubled to provide light at frequencies absorbed by the iodine vapor. The duration of each pulse is less than 10 nanoseconds. When used in combination with nonstandard, scientific quality, solid state cameras, a sequence of images can be obtained that provides instantaneous velocity vectors everywhere in the field of view. The investigations described in this paper include an accurate characterization of the iodine cell spectral behavior and its influence on the PDV measurements, a derivation of the PDV signal analysis requirements, and the unique aspects of the pulsed laser behavior related to this application. In addition, PDV measurements are to be demonstrated using data from a rotating wheel target and from the flow of a subsonic jet. Initially, single optical fiber light collection and photomultiplier detectors will be substituted for solid state cameras. Those results will allow the determination of the fundamental limitations of the PDV technique without the complications of image acquisition and processing. They will then be used to provide an analysis of the measurement capabilities of PDV both in small aerodynamic research wind tunnels and in large wind tunnels designed for production airframe and propulsion testing. Future plans include the implementation of solid state cameras and the development of the required image acquisition and processing software. Eventually, the PDV technique will be applied to an aerodynamic research program related to transonic wing flutter.

McKenzie, Robert L.↗
NASA NTRS2014

CM5, a Pre-Swarm Comprehensive Geomagnetic Field Model Derived from Over 12 Yr of CHAMP, Orsted, SAC-C and Observatory Data

A comprehensive magnetic field model named CM5 has been derived from CHAMP, Ørsted and SAC-C satellite and observatory hourly-means data from 2000 August to 2013 January using the Swarm Level-2 Comprehensive Inversion (CI) algorithm. Swarm is a recently launched constellation of three satellites to map the Earth's magnetic field. The CI technique includes several interesting features such as the bias mitigation scheme known as Selective Infinite Variance Weighting (SIVW), a new treatment for attitude error in satellite vector measurements, and the inclusion of 3-D conductivity for ionospheric induction. SIVW has allowed for a much improved lithospheric field recovery over CM4 by exploiting CHAMP along-track difference data yielding resolution levels up to spherical harmonic degree 107, and has allowed for the successful extraction of the oceanic M2 tidal magnetic field from quiet, nightside data. The 3-D induction now captures anomalous Solar-quiet features in coastal observatory daily records. CM5 provides a satisfactory, continuous description of the major magnetic fields in the near-Earth region over this time span, and its lithospheric, ionospheric and oceanic M2 tidal constituents may be used as validation tools for future Swarm Level-2 products coming from the CI algorithm and other dedicated product algorithms.

modelling and interpretation↗
NASA NTRS1974

Magnetic field of Jupiter and its interaction with the solar wind

Jupiter's magnetic field and its interaction with the magnetized solar wind were observed with the Pioneer 10 vector helium magnetometer. The magnetic dipole is directed opposite to that of the earth with an inclination of 15 deg lying in a system III meridian of 230 deg. The dipole is offset about 0.1 Jupiter radius north of the equatorial plane and about 0.2 Jupiter radius toward longitude 170 deg. There is severe stretching of the planetary field parallel to the equator throughout the outer magnetosphere, accompanied by a systematic departure from meridian planes. The field configuration implies substantial plasma effects inside the magnetosphere, such as thermal pressure, centrifugal forces, and differential rotation.

Smith, E. J.↗
NASA NTRS1977

Evaluation of STOL navigation avionics

Research projects, including work on a vector magnetometer for aircraft attitude measurement, are summarized. The earth's electric field phenomena was investigated in its application to aircraft control and navigation. Research on electronic aircraft cabin noise suppression is reviewed and strapdown inertial reference unit technical support is outlined.

Dunn, W. R., Jr.↗
NASA NTRS1979

Covariance analyses of satellite-derived mesoscale wind fields

Statistical structure functions have been computed independently for nine satellite-derived mesoscale wind fields that were obtained on two different days. Small cumulus clouds were tracked at 5 min intervals, but since these clouds occurred primarily in the warm sectors of midlatitude cyclones the results cannot be considered representative of the circulations within cyclones in general. The field structure varied considerably with time and was especially affected if mesoscale features were observed. The wind fields on the 2 days studied were highly anisotropic with large gradients in structure occurring approximately normal to the mean flow. Structure function calculations for the combined set of satellite winds were used to estimate random error present in the fields. It is concluded for these data that the random error in vector winds derived from cumulus cloud tracking using high-frequency satellite data is less than 1.75 m/s. Spatial correlation functions were also computed for the nine data sets. Normalized correlation functions were considerably different for u and v components and decreased rapidly as data point separation increased for both components. The correlation functions for transverse and longitudinal components decreased less rapidly as data point separation increased.

Maddox, R. A.↗