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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 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Identifying and Characterizing Discrepancies Between Test and Analysis Results of Compression-Loaded Panels

Results from a study to identify and characterize discrepancies between validation tests and high-fidelity analyses of compression-loaded panels are presented. First, potential sources of the discrepancies in both the experimental method and corresponding high-fidelity analysis models were identified. Then, a series of laboratory tests and numerical simulations were conducted to quantify the discrepancies and develop test and analysis methods to account for the discrepancies. The results indicate that the discrepancies between the validation tests and high-fidelity analyses can be attributed to imperfections in the test fixture and specimen geometry; test-fixture-induced changes in specimen geometry; and test-fixture-induced friction on the loaded edges of the test specimen. The results also show that accurate predictions of the panel response can be obtained when these specimen imperfections and edge conditions are accounted for in the analysis. The errors in the tests and analyses, and the methods used to characterize these errors are presented.

Thornburgh, Robert P.↗
NASA NTRS2005

NASA's Global Precipitation Mission Ground Validation Segment

NASA is designing a Ground Validation Segment (GVS) as one of its contributions to the Global Precipitation Measurement (GPM) mission. The GPM GVS provides an independent means for evaluation, diagnosis, and ultimately improvement of the GPM spaceborne measurements and precipitation products. NASA's GPM GVS concept calls for a combination of direct observations executed within a Multidimensional Observing Volume (MOV) and model-based analyses executed by a Satellite Simulator Model (SSM). The MOV consists of ground-based instruments that measure local surface and atmospheric properties required for GPM validation. The SSM utilizes MOV measurements in a forward numerical model. The goal of the SSM forward modeling is calculation of the following properties: top-of-atmosphere microwave radiative quantities to within sensor noise of those measured by the GPM Core Satellite, precipitation quantities identical to those generated by the standard GPM precipitation retrieval algorithms, and quantitative/objective error estimates of both sets of quantities. At present, the GVS is in the early design stage and various scenarios have been generated to assess how it will be used in the GPM era. The GPM GVS will be operational in the year prior to the launch of the GPM core satellite, which has a launch date scheduled for December 2010.

GVS (GROUND VALIDATION SEGMENT)↗
NASA NTRS2004

A Behavioral Model of Landscape Change in the Amazon Basin: The Colonist Case

This paper presents the prototype of a predictive model capable of describing both magnitudes of deforestation and its spatial articulation into patterns of forest fragmentation. In a departure from other landscape models, it establishes an explicit behavioral foundation for algorithm development, predicated on notions of the peasant economy and on household production theory. It takes a 'bottom-up' approach, generating the process of land-cover change occurring at lot level together with the geography of a transportation system to describe regional landscape change. In other words, it translates the decentralized decisions of individual households into a collective, spatial impact. In so doing, the model unites the richness of survey research on farm households with the analytical rigor of spatial analysis enabled by geographic information systems (GIs). The paper describes earlier efforts at spatial modeling, provides a critique of the so-called spatially explicit model, and elaborates a behavioral foundation by considering farm practices of colonists in the Amazon basin. It then uses, insight from the behavioral statement to motivate a GIs-based model architecture. The model is implemented for a long-standing colonization frontier in the eastern sector of the basin, along the Trans-Amazon Highway in the State of Para, Brazil. Results are subjected to both sensitivity analysis and error assessment, and suggestions are made about how the model could be improved.

Walker, R. A.↗
NASA NTRS2003

Using Computational Cognitive Modeling to Diagnose Possible Sources of Aviation Error

We present a computational model of a closed-loop, pilot-aircraft-visual scene-taxiway system created to shed light on possible sources of taxi error. Creating the cognitive aspects of the model using ACT-R required us to conduct studies with subject matter experts to identify experiential adaptations pilots bring to taxiing. Five decision strategies were found, ranging from cognitively-intensive but precise, to fast, frugal but robust. We provide evidence for the model by comparing its behavior to a NASA Ames Research Center simulation of Chicago O'Hare surface operations. Decision horizons were highly variable; the model selected the most accurate strategy given time available. We found a signature in the simulation data of the use of globally robust heuristics to cope with short decision horizons as revealed by errors occurring most frequently at atypical taxiway geometries or clearance routes. These data provided empirical support for the model.

Pilots↗
NASA NTRS2006

Track Level Compensation Look-up Table Improves Antenna Pointing Precision

The pointing accuracy of the NASA Deep Space Network antennas is significantly impacted by the unevenness of the antenna azimuth track. The track unevenness causes repeatable antenna rotations, and repeatable pointing errors. The paper presents the improvement of the pointing accuracy of the antennas by implementing the track-level-compensation look-up table. The table consists of three axis rotations of the alidade as a function of the azimuth position. The paper presents the development of the table, based on the measurements of the inclinometer tilts, processing the measurement data, and determination of the three-axis alidade rotations from the tilt data. It also presents the determination of the elevation and cross-elevation errors of the antenna as a function of the alidade rotations. The pointing accuracy of the antenna with and without a table was measured using various radio beam pointing techniques. The pointing error decreased when the table was used, from 1.5 mdeg to 1.2 mdeg in elevation, and from 20.4 mdeg to 2.2 mdeg in cross-elevation.

Rotation↗
NASA NTRS2010

Methodology for the Assessment of 3D Conduction Effects in an Aerothermal Wind Tunnel Test

This slide presentation reviews a method for the assessment of three-dimensional conduction effects during test in a Aerothermal Wind Tunnel. The test objectives were to duplicate and extend tests that were performed during the 1960's on thermal conduction on proturberance on a flat plate. Slides review the 1D versus 3D conduction data reduction error, the analysis process, CFD-based analysis, loose coupling method that simulates a wind tunnel test run, verification of the CFD solution, Grid convergence, Mach number trend, size trends, and a Sumary of the CFD conduction analysis. Other slides show comparisons to pretest CFD at Mach 1.5 and 2.16 and the geometries of the models and grids.

Oliver, Anthony Brandon↗
NASA NTRS2010

CPO Prediction: Accuracy Assessment and Impact on UT1 Intensive Results

The UT1 Intensive results heavily depend on the celestial pole offset (CPO) model used during data processing. Since accurate CPO values are available with a delay of two to four weeks, CPO predictions are necessarily applied to the UT1 Intensive data analysis, and errors in the predictions can influence the operational UT1 accuracy. In this paper we assess the real accuracy of CPO prediction using the actual IERS and PUL predictions made in 2007-2009. Also, results of operational processing were analyzed to investigate the actual impact of EOP prediction errors on the rapid UT1 results. It was found that the impact of CPO prediction errors is at a level of several microseconds, whereas the impact of the inaccuracy in the polar motion prediction may be about one order of magnitude larger for ultra-rapid UT1 results. The situation can be amended if the IERS Rapid solution will be updated more frequently.

Malkin, Zinovy↗
NASA NTRS2012

An Overview of Atmospheric Composition OSSE Activities at NASA's Global Modeling and Assimilation Office

A model-based Observing System Simulation Experiment (OSSE) is a framework for numerical experimentation in which observables are simulated from fields generated by an earth system model, including a parameterized description of observational error characteristics. Simulated observations can be used for sampling studies, quantifying errors in analysis or retrieval algorithms, and ultimately being a planning tool for designing new observing missions. While this framework has traditionally been used to assess the impact of observations on numerical weather prediction, it has a much broader applicability, in particular to aerosols and chemical constituents. In this talk we will give a general overview of Observing System Simulation Experiments (OSSE) activities at NASA's Global Modeling and Assimilation Office, with focus on its emerging atmospheric composition component.

daSilva, Arlinda↗
NASA NTRS2015

Formal Assurance Arguments: A Solution In Search of a Problem?

An assurance case comprises evidence and argument showing how that evidence supports assurance claims (e.g., about safety or security). It is unsurprising that some computer scientists have proposed formalizing assurance arguments: most associate formality with rigor. But while engineers can sometimes prove that source code refines a formal specification, it is not clear that formalization will improve assurance arguments or that this benefit is worth its cost. For example, formalization might reduce the benefits of argumentation by limiting the audience to people who can read formal logic. In this paper, we present (1) a systematic survey of the literature surrounding formal assurance arguments, (2) an analysis of errors that formalism can help to eliminate, (3) a discussion of existing evidence, and (4) suggestions for experimental work to definitively answer the question.

Graydon, Patrick J.↗
NASA NTRS2018

Navigation Requirements Development and Performance Assessment of a Martian Ascent Vehicle

To support development of Martian Ascent Vehicles, analysis tools are needed to support the development of Guidance, Navigation, and Control requirements. This paper presents a focused approach to Navigation analysis to capture development of requirements on initial state knowledge and inertial sensor capabilities. A simulation and analysis framework was used to assess the capability of a range of sensors to operate inertially along a range of launch trajectories. The baseline Martian Ascent Vehicle was used as the input for optimizing a set of trajectories from each launch site. These trajectories were used to perform Monte Carlo analysis dispersing error sensor terms and their effects on integrated vehicle performance. Additionally, this paper provides insight into the use of optical navigation techniques to assess state determination and the potential to use observations of local extraplanetary bodies to estimate state. This paper provides an initial level of performance assessment of navigation components to support continued requirements development of a Martian Ascent Vehicle with applications to both crew and sample return missions.

Anzalone, Evan J.↗
NASA NTRS2020

Validation of Carbon Trace Gas Profile Retrievals from the NOAA-Unique Combined Atmospheric Processing System for the Cross-Track Infrared Sounder

This paper provides an overview of the validation of National Oceanic and Atmospheric Administration (NOAA) operational retrievals of atmospheric carbon trace gas profiles, specifically carbon monoxide (CO), methane (CH4) and carbon dioxide (CO2), from the NOAA-Unique Combined Atmospheric Processing System (NUCAPS), a NOAA enterprise algorithm that retrieves atmospheric profile environmental data records (EDRs) under global non-precipitating (clear to partly cloudy) conditions. Vertical information about atmospheric trace gases is obtained from the Cross-track Infrared Sounder (CrIS), an infrared Fourier transform spectrometer that measures high resolution Earth radiance spectra from NOAA operational low earth orbit (LEO) satellites, including the Suomi National Polar-orbiting Partnership (SNPP) and follow-on Joint Polar Satellite System (JPSS) series beginning with NOAA-20. The NUCAPS CO, CH4, and CO2 profile EDRs are rigorously validated in this paper using well-established independent truth datasets, namely total column data from ground-based Total Carbon Column Observing Network (TCCON) sites, and in situ vertical profile data obtained from aircraft and balloon platforms via the NASA Atmospheric Tomography (ATom) mission and NOAA AirCore sampler, respectively. Statistical analyses using these datasets demonstrate that the NUCAPS carbon gas profile EDRs generally meet JPSS Level 1 global performance requirements, with the absolute accuracy and precision of CO 5% and 15%, respectively, in layers where CrIS has vertical sensitivity; CH4 and CO2 product accuracies are both found to be within ±1%, with precisions of ≈1.5% and ⪅0.5%, respectively, throughout the tropospheric column.

satellite cal/val; error analysis; greenhouse gase↗
NASA NTRS2020

Underlying Fundamentals of Kalman Filtering for River Network Modeling

The grand challenge of producing hydrometeorological estimates every time and everywhere has motivated the fusion of sparse observations with dense numerical models, with a particular interest on discharge in river modeling. Ensemble methods are largely preferred as they enable the estimation of error properties, but at the expense of computational load and generally with underestimations. These imperfect stochastic estimates motivate the use of correction methods, that is, error localization and inflation, although the physical justifications for their optimality are limited. The purpose of this study is to use one of the simplest forms of data assimilation when applied to river modeling and reveal the underlying mechanisms impacting its performance. Our framework based on assimilating daily averaged in situ discharge measurements to correct daily averaged runoff was tested over a 4-yr case study of two rivers in Texas. Results show that under optimal conditions of inflation and localization, discharge simulations are consistently improved such that the mean values of Nash–Sutcliffe efficiency are enhanced from211.32 to 0.55 at observed gauges and from212.24 to21.10 at validation gauges. Yet, parameters controlling the inflation and the localization have a large impact on the performance. Further investigations of these sensitivities showed that optimal inflation occurs when compensating exactly for discrepancies in the magnitude of errors while optimal localization matches the distance traveled during one assimilation window. These results may be applicable to more advanced data assimilation methods as well as for larger applications motivated by upcoming river-observing satellite missions, such as NASA’s Surface Water and Ocean Topography mission.

Streamflow↗
NASA NTRS2020

SNPP and NOAA-20 VIIRS On-Orbit Geolocation Trending and Improvements

Two Visible Infrared Imaging Radiometer Suite (VIIRS) sensors have been in operations for more than 8.5 and 2.5 years since they were launched in October 2011 on SNPP satellite and in November 2017 on NOAA-20 satellite, respectively. These are two satellites in the Join Polar Satellite System (JPSS) constellation, of which Suomi National Polar-orbiting Partnership (SNPP) is a risk reduction satellite and NOAA-20 is the first of four JPSS satellites(JPSS-1 became NOAA-20 after launch). Accurate geolocation is a critical element in data calibration for accurate retrieval of global biogeophysical parameters. In this paper, we describe the latest trends in the continuously improved geolocation accuracy in VIIRS Collection-1 (C1) and C2 re-processing. We implemented a VIIRS instrument geometric model update (VIGMU)for both sensors that correct for geolocation error oscilations in the scan direction. We borrowed code from Moderate Resolution Imaging Spectroradiometer (MODIS) geolocation software to correct for time-dependent pointing variations, that are particularly acute in NOAA-20 VIIRS, and some pointing anomalies in SNPP VIIRS. We developed a Kalman Filter using gyrodata to correct for attitude errors due to the degradation of the star trackers performance from the SNPP satellite. We also present an improved ground control point matching (CPM) tool, in which the ground control point (GCP) chips library is refreshed using recently launched Landsat-8 images.

SNPP↗
NASA NTRS2023

The Gmao Hybrid 4d-Envar Observing System Simulation Experiment Framework.

This work describes the extension of the Global Modeling and Assimilation Office (GMAO) Observing System Simulation Experiment (OSSE) framework to use a hybrid 4D-EnVar scheme instead of 3D-Var. The original 3D-Var and hybrid 4D-EnVar OSSEs use the same version of the data assimilation system (DAS) so that a direct comparison is possible in terms of the validation with respect to their corresponding real cases. Rather than quantifying the differences between the two data assimilation methodologies, a short inter-comparison of upgrading from a 3D- to a 4D-OSSE is provided to highlight aspects where this change matters to the OSSE community and to identify features of data assimilation that can only be explored in a four-dimensional OSSE framework. A short validation of the hybrid 4D-EnVar OSSE shows that conclusions from previous assessments of the 3D-Var OSSE in its ability to mimic the behavior of the real system still hold with the same caveats. Furthermore, some aspects of the ensemble configuration and behavior are discussed along with forecast sensitivity to observation impacts (FSOI). Estimates of error standard deviations are shown to be smaller in the hybrid 4D-EnVar OSSE but with little impact on the character of the error. A discussion on future work directions focuses on exploring the four-dimensional aspect such as the error distribution within the assimilation window or four-dimensional handling of high-temporal density observations.

Data assimilation↗
NASA NTRSDate not supplied

Comparison of Detector Based and Source Based Absolute Radiance Standards

A detailed comparison of two separate radiometric calibration standards was conducted with analysis of error sources for each. One is a detector based standard, with radiance traceable to fundamental units using the electrical substitution method. The other is based on a calibrated field emission lamp (FEL) generating blackbody radiation. This study was motivated by the discontinuance of the FEL lamps by the manufacturer and a desire to calibrate sensors using non-blackbody spectral profiles. Three spectrometers were calibrated simultaneously by both methods to separate spectrometer artifacts from differences in the radiometric standards and error in the irradiance to radiance conversion procedure needed for the FEL. Conducting this study now is important to provide continuity between the extensive prior FEL based calibration database with a replacement method while calibrated FEL lamps are still available. This also begins a longer term repeatability study of the spectrometers used in this work for evaluation as calibrated transfer standards, usable with both monochromatic and broad spectrum radiance sources. Eliminating the tie to the FEL blackbody spectrum with a detector based standard allows for flexibility in the illumination source. In particular, for Earth science sensors intended for use with sunlit scenes, augmenting traditional tungsten halogen lighting with blue and ultraviolet light emitting diodes allows for a better match to the solar spectrum during laboratory testing.

radiometry↗
NASA NTRSDate not supplied

Comparison of Detector Based and Source Based Absolute Radiance Standards

A detailed comparison of two separate radiometric calibration standards was conducted with analysis of error sources for each. One is a detector based standard, with radiance traceable to fundamental units using the electrical substitution method. The other is based on a calibrated field emission lamp (FEL) generating blackbody radiation. This study was motivated by the discontinuance of the FEL lamps by the manufacturer and a desire to calibrate sensors using non-blackbody spectral profiles. Three spectrometers were calibrated simultaneously by both methods to separate spectrometer artifacts from differences in the radiometric standards and error in the irradiance to radiance conversion procedure needed for the FEL. Conducting this study now is important to provide continuity between the extensive prior FEL based calibration database with a replacement method while calibrated FEL lamps are still available. This also begins a longer term repeatability study of the spectrometers used in this work for evaluation as calibrated transfer standards, usable with both monochromatic and broad spectrum radiance sources. Eliminating the tie to the FEL blackbody spectrum with a detector based standard allows for flexibility in the illumination source. In particular, for Earth science sensors intended for use with sunlit scenes, augmenting traditional tungsten halogen lighting with blue and ultraviolet light emitting diodes allows for a better match to the solar spectrum during laboratory testing.

radiometry↗