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NASA NTRS1990

Empirical modeling of ion composition in the middle and topside ionosphere

The paper reviews the efforts to represent the global and temporal variations of the ionospheric ion composition in the altitude range from 100 km to 1000 km. The ground and space data sets that have been collected for the ion densities over the past decades are listed. Empirical models are discussed including models for the densities and compositions of O(+), H(+), He(+), O(2+), and NO(+) ions, and for the characteristic transition heights from light ions to atomic oxygen ions and from atomic oxygen ions to molecular ions. The status of the ion composition model in the International Reference Ionosphere (IRI) is reviewed, and shortcomings are pointed out. Possible improvements of IRI with the help of recent modeling studies are summarized.

Bilitza, Dieter↗

NASA NTRS1991

Bioregenerative life support - The initial CELSS reference configuration

The next major step in the development of an operational Controlled Ecological Life-Support System (CELSS) is the creation of a human-rated ground-based demonstrator able to constitute a CELSS's proof-of-concept. The reference configuration recently devised for such a ground facility by NASA will furnish a common reference to all investigators in the field, thereby facilitating performance comparisons among candidate subsystems and clarifying system-level modeling. A detailed NASA reference CELSS flowcharting is presented.

Rummel, John D.↗

NASA NTRS2019

A Joint Analysis of GPS Displacement and GRACE Geopotential Data for Simultaneous Estimation of Geocenter Motion and Gravitational Field

Gravitational potential data from GRACE are being used to study mass redistribution within and between the atmosphere, hydrosphere, cryosphere, and solid Earth. The GRACE data are made available in a reference frame with its origin at the center of mass of the Earth system (geocenter) while many other geophysical models and data sets refer to a reference frame attached to the Earth's surface. Changes in the offset between these reference frames (geocenter motion) must be accounted for when GRACE data are used to quantify surface mass changes. In this study, we developed a technique for co‐estimation of geocenter motion and gravitational potential field seamlessly from degree 1 to 90 by simultaneously inverting a set of globally‐distributed GPS displacement time series and the temporally‐varying GRACE gravity data. We found that the effect of geocenter motion was evident particularly in the GPS time series of horizontal displacements. Our estimates of geocenter motion are most consistent with the Satellite Laser Ranging (SLR) results within 1 mm in X and Z components and a submillimeter in Y component, when compared to monthly variability averaged over the period of 2003–2016. The overall magnitude of the degree‐1 (l = 1) surface mass load is estimated to be ~3 cm in equivalent water height annually migrating south‐westward from Europe (December–January) to the South Pacific (June–July). Our results also show that dense GPS network data improve water storage recovery in major river basins in the United States and Europe by contributing significantly to the recovery of higher‐degree (l ≥ ~20) geopotential coefficients.

Razeghi, Mahdiyeh↗

NASA NTRS1966

Altitude determination by Kalman filtering Third quarterly progress report

Mathematical background for dynamic, geometric, and statistical analyses and transformations for inertial attitude reference determination by Kalman filtering

KALMAN-SCHMIDT FILTER↗

NASA NTRS1989

A comparison of two trusses for the space station structure

The structural performance of two truss configurations, the orthogonal tetrahedral and a Warren-type, are compared using finite element models representing the November Reference Phase 1 Space Station. The truss torsional stiffness properties and fundamental torsion frequency are determined using cantilever truss-beam models. Frequencies, mode shapes, transient response, and truss strut compressive loads are compared for the two space station models. The performance benefit resulting from using a high modulus truss strut is also presented. Finally, assembly and logistics characteristics of the two truss configurations are evaluated.

Sutter, Thomas R.↗

NASA NTRS1989

The analysis and modeling of dilatational terms in compressible turbulence

It is shown that the dilatational terms that need to be modeled in compressible turbulence include not only the pressure-dilatation term but also another term - the compressible dissipation. The nature of these dilatational terms in homogeneous turbulence is explored by asymptotic analysis of the compressible Navier-Stokes equations. A non-dimensional parameter which characterizes some compressible effects in moderate Mach number, homogeneous turbulence is identified. Direct numerical simulations (DNS) of isotropic, compressible turbulence are performed, and their results are found to be in agreement with the theoretical analysis. A model for the compressible dissipation is proposed; the model is based on the asymptotic analysis and the direct numerical simulations. This model is calibrated with reference to the DNS results regarding the influence of compressibility on the decay rate of isotropic turbulence. An application of the proposed model to the compressible mixing layer has shown that the model is able to predict the dramatically reduced growth rate of the compressible mixing layer.

Sarkar, S.↗

NASA NTRS1991

The analysis and modelling of dilatational terms in compressible turbulence

Sarkar, S.↗

NASA NTRS1991

Experimental flutter boundaries with unsteady pressure distributions for the NACA 0012 Benchmark Model

The Structural Dynamics Div. at NASA-Langley has started a wind tunnel activity referred to as the Benchmark Models Program. The objective is to acquire test data that will be useful for developing and evaluating aeroelastic type Computational Fluid Dynamics codes currently in use or under development. The progress is described which was achieved in testing the first model in the Benchmark Models Program. Experimental flutter boundaries are presented for a rigid semispan model (NACA 0012 airfoil section) mounted on a flexible mount system. Also, steady and unsteady pressure measurements taken at the flutter condition are presented. The pressure data were acquired over the entire model chord located at the 60 pct. span station.

Rivera, Jose A., Jr.↗

NASA NTRS1990

Spacecraft software training needs assessment research, appendices

The appendices to the previously reported study are presented: statistical data from task rating worksheets; SSD references; survey forms; fourth generation language, a powerful, long-term solution to maintenance cost; task list; methodology; SwRI's instructional systems development model; relevant research; and references.

Ratcliff, Shirley↗

NASA NTRS1981

Predicted magnitudes and colors from cool-star model atmospheres

An intercomparison of model stellar atmospheres and observations of real stars can lead to a better understanding of the relationship between the physical properties of stars and their observed radiative flux. In this spirit we have determined wide-band and narrow-band magnitudes and colors for a subset of models of K and M giant and supergiant stars selected from the grid of 40 models by Johnson, Bernat and Krupp (1980) (hereafter referred to as JBK). The 24 models selected have effective temperatures of 4000, 3800, 3600, 3400, 3200, 3000, 2750 and 2500 K and log g = 0, 1 or 2. Emergent energy fluxes (erg/ sq cm s A) were calculated at 9140 wavelengths for each model. These computed flux curves were folded through the transmission functions of Wing's 8-color system (Wing, 1971; White and Wing, 1978) and through Johnson's (1965) wide-band (BVRIJKLM) system. The calibration of the resultant magnitudes was made by using the absolute calibration of the flux curve of Vega by Schild, et al. (1971).

Johnson, H. R.↗

NASA NTRS1991

Experimental flutter boundaries with unsteady pressure distributions for the NACA 0012 Benchmark Model

The Structural Dynamics Division at NASA Langley Research Center has started a wind tunnel activity referred to as the Benchmark Models Program. The primary objective of the program is to acquire test data that will be useful for developing and evaluating aeroelastic type CFD codes currently in use of under development. This paper describes the progress achieved in testing the first model in the Benchmark Models Program. Experimental flutter boundaries are presented for a rigid semispan model (NACA 0012 airfoil section) mounted on a flexible mount system. Also, steady and unsteady pressure measurements taken at the flutter condition are presented. The pressure data were acquired over the entire model chord located at the 60 percent span station.

Rivera, Jose A.↗

NASA NTRS2020

A Machine Learning-Based Cloud Detection and Thermodynamic Phase Classification Algorithm using Passive Spectral Observations

We trained two Random Forest (RF) machine-learning models for cloud mask and cloud thermodynamic phase detection using spectral observations from VIIRS on Suomi NPP (SNPP). Observations from CALIOP were carefully selected to provide reference labels. The two RF models were trained for all-day and daytime-only conditions using a 4-year collocated VIIRS/CALIOP dataset from 2013 to 2016. Due to the orbit difference, the collocated CALIOP and SNPP VIIRS training samples cover a broad viewing zenith angle range, which is a great benefit to overall model performance. The all-day model uses 3 VIIRS infrared (IR) bands (8.6,11, and 12 μm) and the daytime model uses 5 Near-IR (NIR) and Shortwave-IR (SWIR) bands (0.86, 1.24, 1.38, 1.64 and 2.25 μm) together with the 3 IR bands to detect clear, liquid water, and ice cloud pixels. Up to 7 surface types, namely, ocean/water, forest, cropland, grassland, snow/ice, barren/desert, and shrubland, were considered separately to enhance performance for both models. Detection of cloudy pixels and thermodynamic phase with the two RF models were compared against collocated CALIOP products from 2017. It is shown that, with a conservative screening process that excludes the most challenging cloudy pixels for passive remote sensing, the two RF models have high accuracy rates in comparison with the CALIOP reference for both cloud detection and thermodynamic phase. Other existing SNPP VIIRS and Aqua MODIS cloud mask and phase products are also evaluated, with results showing that the two RF models and the MODIS MYD06 optical property phase product are the top 3 algorithms with respect to lidar observations during the daytime. During the nighttime, the RF all-day model works best for both cloud detection and phase, in particular for pixels over snow/ice surfaces. The present RF models can be extended to other similar passive instruments if training samples can be collected from CALIOP or other lidars. However, the quality of reference labels and potential sampling issues that may impact model performance would need further attention.

cloud detection↗

NASA NTRS1994

The use of stellite scatterometer winds to drive a primitive equation model of the Indian Ocean: The impact of bandlike sampling

The aim of this study is to evaluate the impact of the bandlike sampling of spaceborne scatterometers on the ability of scatterometer winds to successfully force the mean flow and seasonal cycle of an ocean model in the context of equatorial and tropical dynamics. The equatorial ocean is simulated with a four-layer, primitive equation, reduced gravity model of the Indian Ocean. The variable wind stress used in this study is derived from one year (1988) of 6-hour analyses of the 10-m wind vector over the Indian Ocean performed at the European Centre for Medium-Range Weather Forecasts (ECMWF). It is applied as a forcing at every grid point of the model to drive a reference circulation. Scatterometer winds are simulated from ECMWF winds, using the nominal configurations and orbital parameters of the European Remote Sensing 1 (ERS-1) and NASA Scatterometer (NSCAT) missions. The model is forced in real time under swaths with the raw scatterometer winds of ERS-1 and NSCAT, with a persistence condition (i.e., the wind is kept constsnt until the next passage of the satellite provides a new value). The circulation obtained for each of the scatterometer experiments is compared with the reference circulation. The seasonal circulation of the Indian Ocean with NSCAT winds is very similar to the reference. The perturbations introduced by the bandlike sampling and the persistance condition have an impact similar to that of a small uncorrelated noise added to the reference forcing. The persistence condition for ERS-1 does not give results which are as good as those obtained for NSCAT.

Barnier, Bernard↗

NASA NTRS1982

The Mars reference atmosphere

A nominal atmospheric model of Mars is presented, with detailed consideration being given to the various sources of variability in the Martian atmosphere. A basic model for the midlatitude summer is outlined for the northern and southern hemispheres. Attention is given to meteorological variability due to winds, diurnal and seasonal pressure variations, temperature changes, and the effects of dust opacity, particularly on temperature stratification. Viking lander IR thermal mapper data are examined in terms of diurnal and latitudinal temperature variations, and cloud and haze formation and locations are discussed. Mass spectrometry of the atmosphere is used to describe the molecular abundances, and water vapor measurements are reviewed. Finally, radio occultation, UV airglow, and mass spectrometry of the Martian upper atmosphere are investigated, along with the temperature structure of the upper atmosphere.

Kliore, A.↗

NASA NTRS1989

A probabilistic approach to crack instability

A probabilistic model of brittle fracture is examined with reference to two-dimensional problems. The model is illustrated by using experimental data obtained for 25 macroscopically identical specimens made of short-fiber-reinforced composites. It is shown that the model proposed here provides a predictive formalism for the probability distributions of critical crack depth, critical loads, and crack arrest depths. It also provides similarity criteria for small-scale testing.

Chudnovsky, A.↗

NASA NTRS1994

A Compositional Relevance Model for Adaptive Information Retrieval

There is a growing need for rapid and effective access to information in large electronic documentation systems. Access can be facilitated if information relevant in the current problem solving context can be automatically supplied to the user. This includes information relevant to particular user profiles, tasks being performed, and problems being solved. However most of this knowledge on contextual relevance is not found within the contents of documents, and current hypermedia tools do not provide any easy mechanism to let users add this knowledge to their documents. We propose a compositional relevance network to automatically acquire the context in which previous information was found relevant. The model records information on the relevance of references based on user feedback for specific queries and contexts. It also generalizes such information to derive relevant references for similar queries and contexts. This model lets users filter information by context of relevance, build personalized views of documents over time, and share their views with other users. It also applies to any type of multimedia information. Compared to other approaches, it is less costly and doesn't require any a priori statistical computation, nor an extended training period. It is currently being implemented into the Computer Integrated Documentation system which enables integration of various technical documents in a hypertext framework.

Mathe, Nathalie↗

NASA NTRS2017

The Design of the Reference Orbit for NISAR, the NASA-ISRO Synthetic Aperture Radar Mission

The NISAR mission plans to use a 12-day-repeating sun-synchronous orbit for repeat-pass interferometry at multiple time scales using SAR data. For the interferometry to work the radar measurements must be made from within a critical baseline, which happens if all of the orbits are maintained to be within a fixed tube around a reference orbit. This paper describes the choice of dynamical models used in defining such a reference orbit, the perturbative effects of dynamics not considered in the repeat orbit, and the process of designing the orbit to repeat. We also describe our method for sharing the repeat orbit among multiple mission participants who use different models and software.

Hatch, Sara J.↗

NASA NTRS2017

The Design of the Reference Orbit for NISAR, the NASA-ISRO Synthetic Aperture Radar Mission

Hatch, Sara J.↗