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All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Stellar oxygen abundances. 4: Systematic effects on oxygen abundances derived from the 6300 A (O I) and 7774 A O I lines

We consider potential systematic effects on oxygen abundances derived from the 6300 A (OI) line and the 7774 A OI triplet. Our solar intensity spectra of the 7774 A triplet confirm previous results which indicate a discrepancy between the observed equivalent widths of Altrock (1968) and the values predicted by Local Thermodynamic Equilibrium (LTE) and recent NLTE models. However, this disagreement (at low micron(s)) does not seem to affect the solar O abundance as derived from flux spectra. We derive O abundances for a selection of relatively metal-rich F and G dwarfs from both the 6300 A (OI) line and 7774 A OI triplet and detail the various uncertainties which enter into the analyses. Minimizing possible systematic effects to the extent possible, we find for T(sub eff) approximately less than 6200-6300 K no systematic difference between the 6300 and 7774 A abundances. For T(sub eff) approximately greater than 6200-6300 K, however 7774 A abundances are substantially larger than the 6300 A abundances. This agreement in O abundances from the two features at cooler T(sub eff) conflicts with that of others and we suggest that the discrepancy may be due to the different model atmospheres utilized. If recently proposed, hotter T(sub eff) values for metal-poor dwarfs are correct, then there appears to be no discrepancy between the 6300 A abundances of metal-poor giants are correct, then there appears to be no discrepancy between the 6300 A abundances of metal-poor giants or dwarfs and the 7774 A abundances for dwarfs. This would seem to rule out substantial LTE departures or atmospheric inhomogeneity effects skewing metal-poor O abundances from the 7774 A triplet (for cooler stars having low metallicity anyway). Given the repeated inability of authors to reproduce each others' O abundances from the 6300 A (OI) line and the uncertainties in the solar equivalent width, we question the usual assumption that the 6300 A (OI) line and the uncertainties in the solar equivalent width, we question the usual assumption that the 6300 A (OI) abundances are more reliable than those from the permitted triplet.

King, Jeremy R.↗
NASA NTRS1996

Systematic Effects on Duration Measurements of Gamma-Ray Bursts

The parameters T(sub 90) and T(sub 50) have recently been introduced as a measurement of the duration of gamma-ray bursts. We present here a description of the method of measuring T(sub 90) and T(sub 50) and its application to gamma-ray bursts observed with the Burst and Transient Source Experiment (BATSE) onboard the Compton Gamma-Ray Observatory (CGRO). We use simulated as well as observed time profiles to address some of the possible systematic effects affecting individual T(sub 90) (T(sub 50)) measurements. We show that these systematic effects do not mimic those effects that would result from time dilation if the burst sources are at distances of several Gpc. We discuss the impact of these systematic effects on the T(sub 90) (T(sub 50)) distributions for the gamma-ray bursts observed with BATSE. We distinguish between various types of T(sub 90) (T(sub 50)) distributions, and discuss the ways in which distributions observed with different experiments can vary, even though the measurements for commonly observed bursts may be the same. We then discuss the distributions observed with BATSE and compare them to those observed with other experiments.

Koshut, Thomas M.↗
NASA NTRS1998

Galaxy Cluster Shapes and Systematic Errors in H_0 as Determined by the Sunyaev-Zel'dovich Effect

Imaging of the Sunyaev-Zeldovich (SZ) effect in galaxy clusters combined with cluster plasma x-ray diagnostics promises to measure the cosmic distance scale to high accuracy. However, projecting the inverse-Compton scattering and x-ray emission along the cluster line-of-sight will introduce systematic error's in the Hubble constant, H_0, because the true shape of the cluster is not known. In this paper we present a study of the systematic errors in the value of H_0, as determined by the x-ray and SZ properties of theoretical samples of triaxial isothermal "beta-model" clusters, caused by projection effects and observer orientation relative to the model clusters' principal axes. We calculate three estimates for H_0 for each cluster, based on their large and small apparent angular core radii, and their arithmetic mean. We average the estimates for H_0 for a sample of 25 clusters and find that the estimates have limited systematic error: the 99.7% confidence intervals for the mean estimated H_0 analyzing the clusters using either their large or mean angular core r;dius are within 14% of the "true" (assumed) value of H_0 (and enclose it), for a triaxial beta model cluster sample possessing a distribution of apparent x-ray cluster ellipticities consistent with that of observed x-ray clusters.

Sulkanen, Martin E.↗
NASA NTRS2006

The Origin of Systematic Errors in the GCM Simulation of ITCZ Precipitation over Oceans

This study provides explanations for some of the experimental findings of Chao (2000) and Chao and Chen (2001) concerning the mechanisms responsible for the ITCZ in an aqua-planet model. These explanations are then applied to explain the origin of some of the systematic errors in the GCM simulation of ITCZ precipitatin over oceans. The ITCZ systematic errors are highly sensitive to model physics and by extension model horizontal resolution. The findings in this study along with those of Chao (2000) and Chao and Chen (2001, 2004) contribute to building a theoretical foundation for ITCZ study. A few possible methods of alleviating the systematic errors in the GCM simulaiton of ITCZ are discussed. This study uses a recent version of the Goddard Modeling and Assimilation Office's Goddard Earth Observing System (GEOS-5) GCM.

Chao, Winston C.↗
NASA NTRS2013

Effects of Systematic and Random Errors on the Retrieval of Particle Microphysical Properties from Multiwavelength Lidar Measurements Using Inversion with Regularization

In this work we study the effects of systematic and random errors on the inversion of multiwavelength (MW) lidar data using the well-known regularization technique to obtain vertically resolved aerosol microphysical properties. The software implementation used here was developed at the Physics Instrumentation Center (PIC) in Troitsk (Russia) in conjunction with the NASA/Goddard Space Flight Center. Its applicability to Raman lidar systems based on backscattering measurements at three wavelengths (355, 532 and 1064 nm) and extinction measurements at two wavelengths (355 and 532 nm) has been demonstrated widely. The systematic error sensitivity is quantified by first determining the retrieved parameters for a given set of optical input data consistent with three different sets of aerosol physical parameters. Then each optical input is perturbed by varying amounts and the inversion is repeated. Using bimodal aerosol size distributions, we find a generally linear dependence of the retrieved errors in the microphysical properties on the induced systematic errors in the optical data. For the retrievals of effective radius, number/surface/volume concentrations and fine-mode radius and volume, we find that these results are not significantly affected by the range of the constraints used in inversions. But significant sensitivity was found to the allowed range of the imaginary part of the particle refractive index. Our results also indicate that there exists an additive property for the deviations induced by the biases present in the individual optical data. This property permits the results here to be used to predict deviations in retrieved parameters when multiple input optical data are biased simultaneously as well as to study the influence of random errors on the retrievals. The above results are applied to questions regarding lidar design, in particular for the spaceborne multiwavelength lidar under consideration for the upcoming ACE mission.

vertical profiles↗
NASA NTRS2015

The Ocean Colour Climate Change Initiative: II. Spatial and Temporal Homogeneity of Satellite Data Retrieval Due to Systematic Effects in Atmospheric Correction Processors

The established procedure to access the quality of atmospheric correction processors and their underlying algorithms is the comparison of satellite data products with related in-situ measurements. Although this approach addresses the accuracy of derived geophysical properties in a straight forward fashion, it is also limited in its ability to catch systematic sensor and processor dependent behaviour of satellite products along the scan-line, which might impair the usefulness of the data in spatial analyses. The Ocean Colour Climate Change Initiative (OC-CCI) aims to create an ocean colour dataset on a global scale to meet the demands of the ecosystem modelling community. The need for products with increasing spatial and temporal resolution that also show as little systematic and random errors as possible, increases. Due to cloud cover, even temporal means can be influenced by along-scanline artefacts if the observations are not balanced and effects cannot be cancelled out mutually. These effects can arise from a multitude of results which are not easily separated, if at all. Among the sources of artefacts, there are some sensor-specific calibration issues which should lead to similar responses in all processors, as well as processor-specific features which correspond with the individual choices in the algorithms. A set of methods is proposed and applied to MERIS data over two regions of interest in the North Atlantic and the South Pacific Gyre. The normalised water leaving reflectance products of four atmospheric correction processors, which have also been evaluated in match-up analysis, is analysed in order to find and interpret systematic effects across track. These results are summed up with a semi-objective ranking and are used as a complement to the match-up analysis in the decision for the best Atmospheric Correction (AC) processor. Although the need for discussion remains concerning the absolutes by which to judge an AC processor, this example demonstrates clearly, that relying on the match-up analysis alone can lead to misjudgement.

Ocean Colour↗
NASA NTRS2017

Correlations Among Microstructure, Morphology, Chemistry, and Isotopic Systematics of Hibonite in CM Chondrites

Introduction: Hibonite is a primary refractory phase occurring in many CAIs, typically with spinel and perovskite. Our microstructural studies of CAIs from carbonaceous chondrites reveal a range of stacking defect densities and correlated non-stoichiometry in hibonite. We also conducted a series of annealing experiments, demonstrating that the Mg-Al substitution stabilized the formation of defect-structured hibonite. Here, we continue a detailed TEM analysis of hibonite-bearing inclusions from CM chondrites that have been well-characterized isotopically. We examine possible correlations of microstructure, morphology, mineralogy, and chemical and isotopic systematics of CM hibonites in order to better understand the formation history of hibonite in the early solar nebula. Methods: Fifteen hibonite-bearing inclusions from the Paris CM chondrite were analyzed using a JEOL 7600F SEM and a JEOL 8530F electron microprobe. In addition to three hibonite-bearing inclusions from the Murchison CM chondrite previously reported, we selected three inclusions from Paris, Pmt1-6, 1-9, and 1-10, representing a range of 26Al/27Al ratios and minor element concentrations for a detailed TEM study. We extracted TEM sections from hibonite grains using a FEI Quanta 3D field emission gun SEM/FIB. The sections were then examined using a JEOL 2500SE field-emission scanning TEM equipped with a Thermo-Noran thin window EDX spectrometer. Results and Discussion: A total of six hibonite-bearing inclusions, including two platy hibonite crystals (PLACs) and four spinel-hibonite inclusions (SHIBs), were studied. There are notable differences in chemical and isotopic compositions between the inclusions (Table 1), indicative of their different formation environment or timing. Our TEM observations show perfectly-ordered, stoichiometric hibonite crystals without stacking defects in two PLACs, 2-7-1 and 2-8-2, and in three SHIBs, Pmt1-6, 1-9, and 1-10. In contrast, SHIB 1-9-5 hibonite grains contain a low density of stacking defects linked to an increase in MgO contents, indicating complex, disordered intergrowths of stoichiometric and MgO-enriched hibonites. From the data collected to date, we find no clear correlation between the microstructures of hibonite and its morphological and mineralogical types that reflect distinct chemical and isotopic systematics [6-8,10]. Interestingly, the presence of no or few stacking defects in hibonite from the PLACs and SHIBs are in contrast to our experimental studies that produced very high densities of stacking defects in hibonite [3-5]. Unlike our experi-ments, electron microprobe data from the PLACs and SHIBs hibonite grains show a strong correlation between (Ti4++Si4+) and Mg2+ cations, suggesting that coupled substitutions of (Ti4++Mg2+) and (Si4++Mg2+) for 2Al3+ inhibit the formation of defect-structured hibonite. However, our experimental studies suggest that kinetics (e.g., cooling rate) or other thermal effects also exert a strong control on the microstructures and chemical compositions of hibonite. In Pmt1-6, elongated perovskite grains present at the hibonite grain boundaries display (121) twinning, indicative of a fast cooling (>50degC/min) after high-temperature events. Therefore, the nebular microstructural characteristics of hibonite, at least in this inclusion, would not have destroyed by subsequent high-temperature annealing. Conclusions: Our TEM observations thus far show no clear correlation in microstructures, morphological and mineralogical characteristics, and chemical and isotopic systematics of hibonites from CM chondrites. The observed variation in stacking defect densities in the hibonites may be controlled by thermal processes in the early solar nebula. A detailed TEM analysis of additional CM hibonite samples is underway to evaluate this hypothesis.

Han, J.↗
NASA NTRS2019

Systematic Error Cancellation for a Four-Port Interferometric Polarimeter

The Primordial Inflation Explorer (PIXIE) is an Explorer-class mission concept to measure the gravitational-wave signature of primordial inflation through its distinctive imprint on the linear polarization of thecosmic microwave background (CMB). Its optical system couples a polarizing Fourier transform spectrometerto the sky to measure the differential signal between orthogonal linear polarization states from two co-pointedbeams on the sky. The double differential nature of the four-port measurement mitigates beam-related systematic errors common to the two-port systems used in most CMB measurements. Systematic errors coupling unpolarized temperature gradients to a false polarized signal cancel to first order for any individual detector. Thiscommon-mode cancellation is performed optically, prior to detection, and does not depend on the instrumentcalibration. Systematic errors coupling temperature to polarization cancel to second order when comparing signals from independent detectors. We describe the polarized beam patterns for PIXIE and assess the systematicerror for measurements of CMB polarization.

Kogut, Alan J.↗
NASA NTRS2021

JWST Noise Floor. II. Systematic Error Sources in JWST NIRCam Time Series

The James Webb Space Telescope (JWST) holds great promise for characterizing atmospheres of transiting exoplanets, potentially providing insights into Earth-sized planets within the habitable zones of M-dwarf host stars if photon-limited performance can be achieved. Here, we discuss the systematic error sources that are expected to be present in grism time-series observations with the NIRCam instrument. We find that pointing jitter and high-gain antenna moves in addition to the detectors' subpixel crosshatch patterns will produce relatively small variations (less than 6 parts per million, ppm). The time-dependent aperture losses due to thermal instabilities in the optics can also be kept to below 2 ppm. To achieve these low noise values, it is important to employ a sufficiently large (more than 1farcs1) extraction aperture. Persistence due to charge-trapping will have a minor (less than 3 ppm) effect on the time series 20 minutes into an exposure and is expected to play a much smaller role than it does for the Hubble Space Telescope WFC3 detectors. We expect detector temperature fluctuations to contribute less than 3 ppm. In total, our estimated noise floor from known systematic error sources is only 9 ppm per visit. We urge caution, however, because unknown systematic error sources could be present in flight and will only be measurable on astrophysical sources such as quiescent stars. We find that reciprocity failure may introduce a perennial instrument offset at the 40 ppm level, so corrections may be needed when a multi-instrument multi-observatory spectrum is stitched together over wide wavelength ranges.

Everett Schlawin↗
NASA NTRSDate not supplied

An Investigation Into Possible Systematic Effects on Neutron Star Radius Estimates using NICER-like Synthetic Data

Neutron star cores contain the densest matter in the observable universe. The state of this matter is of interest in numerous fields, but laboratory experiments cannot explore this matter. Although the composition of the matter would be of great interest, macroscopic observables such as the neutron star mass-radius relation depend primarily on the equation of state (EOS). As a result, precise and reliable radius measurements would be valuable in constraining the EOS. However, most attempts at radius measurements are susceptible to systematic errors, meaning the inferred radius can be significantly biased even though the fit to the data appears to be statistically good. Previous studies suggested that radii inferred using X-ray data provided by NASA’s NICER mission may be more immune from such systematic errors. This is in part because, compared with previous measurements that obtained averaged spectra and fluxes, NICER observes millisecond pulsars by timing the photons so precisely, it is possible to obtain the spectrum as a function of rotational phase and see variations such as heated regions on the star rotate into and out of view hundreds of times per second. This extra information seems promising to break degeneracies and mitigate systematic errors, but a more in-depth study is necessary. We report the first steps of that study, in which we generate NICER-like synthetic data and determine the quality of fit and bias in radius obtained when we fit the data using a model different from the model used to generate the data.

Isiah Holt↗
NASA NTRSDate not supplied

Comparing and Automatically Optimizing the Performance of Systematic Error Correctors for TESS Light Curves

Accurate and precise removal of systematic errors from TESS light curves (lcs) is critical for exoplanet, stellar, and asteroseismology studies•Various approaches exist to correct for systematics while preserving intrinsic stellar variability (Luger et al. 2016, 2018; Hedges et al. 2021; Smith et al. 2012; Stumpe et al. 2014; Aigrain et al. 2017)•However, no comprehensive analyseshave been carried out to properly compare these approaches and determine their validity on different target types in both an individual and statistical manner•Current correctors have been usually demonstrated on their own and on limited sets of hand-picked targets•To apply these corrections more generally, it is important to compare multiple correctors on larger samples•We are particularly interested in the ability to remove scattered light contaminationfrom the Earth and the Moon, which is a key systematic for TESS

David Rapetti↗
NASA NTRS2023

Wildfire Adaptation in the Russian Arctic: A Systematic Policy Review

A scientific consensus acknowledges that climate change has increased wildfire activity in the Russian Arctic, a trend projected to continue in response to further warming. Regional governments across Russia have started to design and develop adaptation policies and plans (i.e. outputs) to this end. Our comprehensive understanding on the state of wildfire adaptation in policy is limited. In this article we systematically review policies and plans developed to adapt to wildfires in the Russian Arctic. Using systematic approaches, we identify 12 wildfire adaptation outputs adopted between 2008 and 2020. Our findings indicate that wildfire adaptation outputs are aimed at reducing the risk of wildfires and improve wildland fire response, implemented through legislative and regulatory mechanisms, developed at the regional level, adopted in response to national mandates, and mainstreamed into existing forest management policies. Although there is evidence of wildfire adaptation planning occurring in the Russian Arctic, we find that the nature and extent of wildfire adaptation outputs are not sufficient to address the seriousness and severity of climate change, with key shortcomings found in relation to the scientific, human, and management characteristics. We argue that expanding the profile of climate change research in the Russian Arctic and improving the dialogue among researchers, local and Indigenous peoples, and decision-makers are critical for providing useful recommendations for policy makers to accelerate wildfire adaptation in the Russian Arctic.

Wildfire↗
NASA NTRS1972

Performance evaluation of a class of systematic, rate (M-1)/M, convolutional codes

The implementation and performance evaluation are described for a class of rate (M-1)/M, systematic, convolutional codes being decoded with a simple majority logic decoder. The encoding logic appends one parity bit for each PCM telemetry word. It is shown that over the critical range of received PCM telemetry signal-to-noise ratios, this coding procedure produces a net coding gain of from 1.5 to 2.5 db relative to an equal power transmission of uncoded PCM telemetry. Being a low-redundancy systematic code, it is possible to process this data without convolutional decoding with a small rate loss penalty of about 0.5 db.

Greene, E. P.↗
NASA NTRS1972

Rb-Sr systematics for chemically defined Apollo 14 breccias.

The Rb and Sr systematics were determined for eight lithic fragments from the coarse fines of Apollo 11, Apollo 12, and Apollo 14; for bulk soils from Luna 16, Apollo 14, and Apollo 15 and for 'whole rocks' from Apollo 14 and the Apollo 15 anorthosite 15415. The objective of the studies was to identify important lunar rock types by their major and trace element chemistry and utilize Rb and Sr systematics to obtain a chronology for events which establish or modify rock chemical composition.

Nyquist, L. E.↗
NASA NTRS1974

Systematic monitoring and evaluation of M7 scanner performance and data quality

An investigation was conducted to provide the information required to maintain data quality of the Michigan M7 Multispectral scanner by systematic checks on specific system performance characteristics. Data processing techniques which use calibration data gathered routinely every mission have been developed to assess current data quality. Significant changes from past data quality are thus identified and attempts made to discover their causes. Procedures for systematic monitoring of scanner data quality are discussed. In the solar reflective region, calculations of Noise Equivalent Change in Radiance on a permission basis are compared to theoretical tape-recorder limits to provide an estimate of overall scanner performance. M7 signal/noise characteristics are examined.

Stewart, S.↗
NASA NTRS1977

The Apollo 17 'melt sheet' - Chemistry, age and Rb/Sr systematics

Major, minor, and trace-element compositions, age data, and Rb/Sr systematics of Apollo 17 boulders have been compiled, and additional analyses performed on a norite breccia clast (77215) included in the Apollo 17, Station 7 boulder. The Apollo 17 boulders are found to be identical or nearly so in major, minor, and trace-element composition, suggesting that they all originated as an impact melt analogous to melt sheets found in larger terrestrial craters. The matrix dates (Ar-40/Ar-39) and Rb/Sr systematics available suggest that this impact melt formed by a single impact about 4 billion years ago. This impact excavated, shocked, brecciated, and melted norites, norite cumulates, and possibly anorthositic gabbros and dunites about 4.4 billion years old. The impact was likely a major one, possibly the Serenitatis basin-forming event.

Winzer, S. R.↗
NASA NTRS1978

Influence of systematic radiation differences on the dynamics of a model atmosphere

Numerical experiments were run on the Goddard Laboratory for Atmospheric Sciences (GLAS) nine-level GCM using two different long-wave radiation routines - the Hogan routine and the Wu-Kaplan routine - to determine whether systematic radiation difference is important in the modeling of the general circulation of the atmosphere. The climatologies produced from GCM runs using the different radiation routines were compared for both winter and summer. Systematic differences were found in the mean zonal temperatures, in the location and shape of the zonal west wind maximum, in the strength of the Hadley and Ferrel cells, in the cloud and precipitation distributions, and in the mass distributions. On the basis of comparisons with observations, it was found that the Wu-Kaplan routine had a positive impact or at least made improvements in the right direction in most respects.

Wu, M.-L. C.↗
NASA NTRS1985

Systematic and random variations in Thematic Mapper digital radiance data

Studies are reported of the systematic and random variations in digital radiance data obtained by the Landsat-4 and Landsat-5 Thematic Mappers over an agricultural crop area which was apparently uniform and cloud-free. Systematic variations appeared to be time-dependent and bandpass-dependent. The predominant effect seemed to be random variations, which appeared to be in keeping with those expected from prior investigations. It is suggested that uncorrected variations will provide a limitation on the nonphotointerpretative analysis of images.

Duggin, M. J.↗