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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 361 records · Page 20

Variable-length codes and the Fano metric.

It is shown that the metric proposed originally by Fano for sequential decoding is precisely the required statistic for minimum-error-probability decoding of variable-length codes. The analysis shows further that the 'natural' choice of bias in the metric is the code rate and gives insight into why the Fano metric has proved to be the best practical choice in sequential decoding. The recently devised Jelinek-Zigangirov 'stack algorithm' is shown to be a natural consequence of this interpretation of the Fano metric. Finally, it is shown that the elimination of the bias in the 'truncated' portion of the code tree gives a slight reduction in average computation at the sacrifice of increased error probability.

Massey, J. L.↗

Possible variation of the gravitational constant over the elements.

We re-examine the theory and data of the Kreuzer experiment to measure the relative difference in the gravitational constant between two elements. Significant errors appear in the statistical analysis of Kreuzer which vitiate his conclusions. The upper bound for the relative difference of F and Br from his experimental data correctly becomes .02, about 10 times the limit already set on the general variation of the gravitational constant over the elements by direct use of a Cavendish balance.

Gilvarry, J. J.↗

Identification of interplanetary tangential and rotational discontinuities.

Discontinuities in the interplanetary magnetic field detected by the Mariner 5 magnetometer have been analyzed to distinguish tangential and rotational discontinuities. The method used was based on finding the field component normal to the plane of the discontinuities that vanishes for tangential discontinuities and is nonzero for rotational discontinuities. Slightly less than one half of the 118 discontinuities analyzed could not be classified because neither the normal component nor the changes in field magnitude were statistically significant owing to errors in the field measurements and in finding the normal direction. The 44 rotational discontinuities that were finally identified did not exhibit changes in field magnitude in excess of 20%.-

Smith, E. J.↗

Evaluation of optimal control type models for the human gunner in an Anti-Aircraft Artillery (AAA) system

The selection of the structure of optimal control type models for the human gunner in an anti aircraft artillery system is considered. Several structures within the LQG framework may be formulated. Two basic types are considered: (1) kth derivative controllers; and (2) proportional integral derivative (P-I-D) controllers. It is shown that a suitable criterion for model structure determination can be based on the ensemble statistics of the tracking error. In the case when the ensemble tracking steady state error is zero, it is suggested that a P-I-D controller formulation be used in preference to the kth derivative controller.

Phatak, A. V.↗

Angular sensitivities of scintillator slab configurations for location of gamma ray bursts

Thin flat scintillator slabs are a useful means of measuring the angular location of gamma ray fluxes of astronomical interest. A statistical estimate of position error was made of two scintillator systems suitable for gamma ray burst location from a balloon or satellite platform. A single rotating scintillator with associated flux monitor is compared with a pair of stationary orthogonal scintillators. Position error for a strong burst is of the order of a few arcmin if systematic errors are ignored.

Gregory, J. C.↗

LACIE performance predictor final operational capability program description, volume 3

The requirements and processing logic for the LACIE Error Model program (LEM) are described. This program is an integral part of the Large Area Crop Inventory Experiment (LACIE) system. LEM is that portion of the LPP (LACIE Performance Predictor) which simulates the sample segment classification, strata yield estimation, and production aggregation. LEM controls repetitive Monte Carlo trials based on input error distributions to obtain statistical estimates of the wheat area, yield, and production at different levels of aggregation. LEM interfaces with the rest of the LPP through a set of data files.

Source record↗

Ice tracking techniques, implementation, performance, and applications

Present techniques of ice tracking make use both of cross-correlation and of edge tracking, the former being more successful in heavy pack ice, the latter being critical for the broken ice of the pack margins. Algorithms must assume some constraints on the spatial variations of displacements to eliminate fliers, but must avoid introducing any errors into the spatial statistics of the measured displacement field. We draw our illustrations from the implementation of an automated tracking system for kinematic analyses of ERS-1 and JERS-1 SAR imagery at the University of Alaska - the Alaska SAR Facility's Geophysical Processor System. Analyses of the ice kinematic data that might have some general interest to analysts of cloud-derived wind fields are the spatial structure of the fields, and the evaluation and variability of average deformation and its invariants: divergence, vorticity and shear. Many problems in sea ice dynamics and mechanics can be addressed with the kinematic data from SAR.

Rothrock, D. A.↗

An Analysis of the Tracking Performances of Two Straight-wing and Two Swept-wing Fighter Airplanes with Fixed Sights in a Standardized Test Maneuver

Standard air-to-air-gunnery tracking runs were conducted with F-51H, F8F-1, F-86A, and F-86E airplanes equipped with fixed gunsights. The tracking performances were documented over the normal operating range of altitude, Mach number, and normal acceleration factor for each airplane. The sources of error were studied by statistical analyses of the aim wander.

CONTROL, LATERAL↗

Metrology: Calibration and measurement processes guidelines

The guide is intended as a resource to aid engineers and systems contracts in the design, implementation, and operation of metrology, calibration, and measurement systems, and to assist NASA personnel in the uniform evaluation of such systems supplied or operated by contractors. Methodologies and techniques acceptable in fulfilling metrology quality requirements for NASA programs are outlined. The measurement process is covered from a high level through more detailed discussions of key elements within the process, Emphasis is given to the flowdown of project requirements to measurement system requirements, then through the activities that will provide measurements with defined quality. In addition, innovations and techniques for error analysis, development of statistical measurement process control, optimization of calibration recall systems, and evaluation of measurement uncertainty are presented.

Castrup, Howard T.↗

Calibration of TOPEX/POSEIDON at Platform Harvest

We present estimates for the mean bias of the TOPEX/POSEIDON NASA altimeter (ALT) and the Centre National d'Etudes Spatiales altimeter (SSALT) using in-situ data gathered at Platform Harvest during the first 36 cycles of the mission. Data for 21 overflights of the ALT and six overflights of the SSALT have been analyzed. The analysis includes an independent assessment of in-situ measurements of sea level, the radial component of the orbit, wet tropospheric path delay, and ionospheric path delay. (The sign convention used is such that, to correct the geophysical data record values for sea level, add the bias algebraically. Unless otherwise stated, the uncertainty in a given parameter is depicted by +/- sigma(sub x), where sigma(sub x) is the sample standard deviation of x about the mean.) Tide gauges at Harvest provide estimates of sea level with an uncertainty of +/- 1.5 cm. The uncertainty in the radial component of the orbit is estimated to be +/- 1.3 cm. In-situ measurements of tropopsheric path delay at Harvest compare to within +/- 1.3 cm of the TOPEX/POSEIDON microwave radiometer, and in-situ measurements of the ionospheric path delay compare to within -0.4 +/- 0.7 cm of the dual-frequency ALT and 1.1 +/- 0.6 cm of Doppler orbitography and radiopositioning integrated by satellite. We obtain mean bias estimates of -14.5 +/- 2.9 cm for the ALT and +0.9 +/- 3.1 cm for the SSALT (where the uncertainties are based on the standard deviation of the estimated mean (sigma(sub bar x/y), which is derived from sample statistics and estimates for errors that cannot be observed). These results are consistent with independent estimates for the relative bias between the two altimeters. A linear regression applied to the complete set of data shows that there is a discernable secular trend in the time series for the ALT bias estimates. A preliminary analysis of data obtained through cycle 48 suggests that the apparent secular drift may be the result of a poorly sampled annual signal.

Christensen, E. J.↗

Magnetospheric Image Unfolding

The Grant was a three year grant funded under the Space Physics Supporting Research and Technology and Suborbital Program. Our objective was to develop automated techniques needed to unfold or "invert" global images of the magnetospheric ion populations obtained by the new magnetospheric imaging techniques (ENA, EUV) in anticipation of future missions such as the Magnetospheric Imager and, now, IMAGE. Our focus on the present three year grant is to determine the degree to which such images can quantitatively constrain the global electromagnetic properties of the magnetosphere. In a previous three year grant period we successfully automated a forward modeling inversion algorithm, demonstrated that these inversions are robust in the face of realistic instrumental considerations such as counting statistics and backgrounds, applied error analysis techniques to the extracted parameters using variational procedures, implemented very realistic magnetospheric test images to test the inversion algorithms using the Rice University Magnetospheric Specification Model, and began the process of generating parametric models with the flexibility to handle the realistic magnetospheric images (e.g. Roelof et al, 1992; 1993). Our plan for the present 3 year grant period was to complete the development of the inversion tools needed to handle realistic magnetospheric images, assess the degree to which global electrodynamics is quantitatively constrained by ENA images of the magnetosphere, and bring the inversion of EUV images up to the maturity that we will have achieved for the ENA imaging. Below the accomplishments of our three year effort are present followed by a list of our presentations and publications. The accomplishments of all three years are presented here, and thus some of these items appeared on interim progress reports.

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Development and Characterization of a Low-Pressure Calibration System for Hypersonic Wind Tunnels

Minimization of uncertainty is essential for accurate ESP measurements at very low free-stream static pressures found in hypersonic wind tunnels. Statistical characterization of environmental error sources requires a well defined and controlled calibration method. A calibration system has been constructed and environmental control software developed to control experimentation to eliminate human induced error sources. The initial stability study of the calibration system shows a high degree of measurement accuracy and precision in temperature and pressure control. Control manometer drift and reference pressure instabilities induce uncertainty into the repeatability of voltage responses measured from the PSI System 8400 between calibrations. Methods of improving repeatability are possible through software programming and further experimentation.

Green, Del L.↗

The Application of Lidar to Synthetic Vision System Integrity

One goal in the development of a Synthetic Vision System (SVS) is to create a system that can be certified by the Federal Aviation Administration (FAA) for use at various flight criticality levels. As part of NASA s Aviation Safety Program, Ohio University and NASA Langley have been involved in the research and development of real-time terrain database integrity monitors for SVS. Integrity monitors based on a consistency check with onboard sensors may be required if the inherent terrain database integrity is not sufficient for a particular operation. Sensors such as the radar altimeter and weather radar, which are available on most commercial aircraft, are currently being investigated for use in a real-time terrain database integrity monitor. This paper introduces the concept of using a Light Detection And Ranging (LiDAR) sensor as part of a real-time terrain database integrity monitor. A LiDAR system consists of a scanning laser ranger, an inertial measurement unit (IMU), and a Global Positioning System (GPS) receiver. Information from these three sensors can be combined to generate synthesized terrain models (profiles), which can then be compared to the stored SVS terrain model. This paper discusses an initial performance evaluation of the LiDAR-based terrain database integrity monitor using LiDAR data collected over Reno, Nevada. The paper will address the consistency checking mechanism and test statistic, sensitivity to position errors, and a comparison of the LiDAR-based integrity monitor to a radar altimeter-based integrity monitor.

Campbell, Jacob L.↗

A New Eddy Dissipation Rate Formulation for the Terminal Area PBL Prediction System(TAPPS)

The TAPPS employs the MASS model to produce mesoscale atmospheric simulations in support of the Wake Vortex project at Dallas Fort-Worth International Airport (DFW). A post-processing scheme uses the simulated three-dimensional atmospheric characteristics in the planetary boundary layer (PBL) to calculate the turbulence quantities most important to the dissipation of vortices: turbulent kinetic energy and eddy dissipation rate. TAPPS will ultimately be employed to enhance terminal area productivity by providing weather forecasts for the Aircraft Vortex Spacing System (AVOSS). The post-processing scheme utilizes experimental data and similarity theory to determine the turbulence quantities from the simulated horizontal wind field and stability characteristics of the atmosphere. Characteristic PBL quantities important to these calculations are determined based on formulations from the Blackadar PBL parameterization, which is regularly employed in the MASS model to account for PBL processes in mesoscale simulations. The TAPPS forecasts are verified against high-resolution observations of the horizontal winds at DFW. Statistical assessments of the error in the wind forecasts suggest that TAPPS captures the essential features of the horizontal winds with considerable skill. Additionally, the turbulence quantities produced by the post-processor are shown to compare favorably with corresponding tower observations.

Charney, Joseph J.↗

Interplanetary optical navigation 101

The JPL Navigation and Mission Design Section has two related tasks: Mission Design: calculate a nominal trajectory which meets the diverse needs of the scientists on a particular mission. Locate deterministic maneuvers required to fly the nominal trajectory, while locating statistical maneuvers which correct errors in the actual trajectory. Navigation estimates the flight path of a spacecraft (orbit determination) using three fundamental data sets: ground based astrometric data; radio metric tracking data (Doppler, range).

mission design↗

Identifying Optimal Temporal Scale for the Correlation of AOD and Ground Measurements of PM2.5 to Improve the Model Performance in a Real-time Air Quality Estimation System

Aerosol optical depth (AOD), an indirect estimate of particle matter using satellite observations, has shown great promise in improving estimates of PM 2.5 air quality surface. Currently, few studies have been conducted to explore the optimal way to apply AOD data to improve the model accuracy of PM 2.5 surface estimation in a real-time air quality system. We believe that two major aspects may be worthy of consideration in that area: 1) the approach to integrate satellite measurements with ground measurements in the pollution estimation, and 2) identification of an optimal temporal scale to calculate the correlation of AOD and ground measurements. This paper is focused on the second aspect on the identifying the optimal temporal scale to correlate AOD with PM2.5. Five following different temporal scales were chosen to evaluate their impact on the model performance: 1) within the last 3 days, 2) within the last 10 days, 3) within the last 30 days, 4) within the last 90 days, and 5) the time period with the highest correlation in a year. The model performance is evaluated for its accuracy, bias, and errors based on the following selected statistics: the Mean Bias, the Normalized Mean Bias, the Root Mean Square Error, Normalized Mean Error, and the Index of Agreement. This research shows that the model with the temporal scale of within the last 30 days displays the best model performance in this study area using 2004 and 2005 data sets.

Li, Hui↗

Far-Ultraviolet Observations of Comet C 2012 S1 (ISON) From Fortis

We have used the unique far-UV imaging capability offered by a sounding-rocket-borne instrument to acquire observations of C/2012 S1 (ISON) when its angular separation with respect to the Sun was 26 deg.3 on 2013 November 20.49. At the time of observation, the comet's heliocentric distance and velocity relative to the Sun were r h = 0.43 au and r (sub h) = 62.7 km s)exp. -1). Images dominated by C Iota Lambda 1657 and H Iota Lambda 1216 were acquired over a 10(exp. 6) x 10(exp. 6) km(exp. 2) region. The water production rate implied by the Ly Alpha observations is constrained to be Q H2O is much greater than 8 x 10(exp. 29) s(exp. -1) while the neutral carbon production rate was Q(sub c) is much greater than 4 x 10(exp. 28) s(exp. -1). The radial profile of C I was consistent with it being a dissociation product of a parent molecule with a lifetime T is approx. 5 x 10(exp. 4) s, favoring a parent other than CO. We constrain the Q(sub co) production rate to 5(+1.5)(-7.5), 10(exp. 28) s(exp. -1) with 1 sigma errors derived from photon statistics. The upper limit on the Q (sub CO)/Q(sub H2O) is 6%.

sounding rocket↗