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At least 109 records · Page 6

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NASA NTRS2023

Wildfire-fighting Use Case Requirements to Monitor

In this technical report, we provide requirements for a wildfire-fighting use-case, towards the Safety Demonstrator 1. The use case will incorporate ground and airborne assets operating in a coordinated fashion, and will comprise five activities, from detection to the execution of the initial attack. Depending on the activity and the data involved, the requirements identified may be non-probabilistic or probabilistic. In both cases, we first identify some of the requirements we wish to monitor, and then present a formalization using the language of requirements of the NASA requirements elicitation tool FRET. To formalize probabilistic requirements, we use a novel extension to FRET’s requirements language that incorporates notions of probability, and discuss how requirements can be translated into existing probabilistic temporal logics like PCTL. We exemplify how some of the requirements presented can be monitored using the existing tools Ogma and Copilot. We close with a summary and future directions.

Requirements↗

NASA NTRS1988

Ultraviolet and radio flares from UX Arietis and HR 1099

Simultaneous observations of the RS CVn systems UX Ari and HR 1099 with the IUE satellite and the VLA are presented. Flaring activity is observed at ultraviolet wavelengths with the IUE when none is detected at radio wavelengths with the VLA. Radio flares with no detectable ultraviolet activity have also been observed. Thus, flares in the two spectral regions are either uncorrelated or weakly correlated. The flaring emission probably originates in different regions at the two wavelengths. Radio flares from RS CVn stars may originate in sources that are larger than, or comparable to, a star in size. This is in sharp contrast to compact, coherent radio flares from dwarf M stars. The ultraviolet flares from RS CVn stars probably originate in sources that are smaller than a component star.

Lang, Kenneth R.↗

NASA NTRS1989

Impact of device level faults in a digital avionic processor

This study describes an experimental analysis of the impact of gate and device-level faults in the processor of a Bendix BDX-930 flight control system. Via mixed mode simulation, faults were injected at the gate (stuck-at) and at the transistor levels and, their propagation through the chip to the output pins was measured. The results show that there is little correspondence between a stuck-at and a device-level fault model, as far as error activity or detection within a functional unit is concerned. In so far as error activity outside the injected unit and at the output pins are concerned, the stuck-at and device models track each other. The stuck-at model, however, overestimates, by over 100 percent, the probability of fault propagation to the output pins. An evaluation of the Mean Error Durations and the Mean Time Between Errors at the output pins shows that the stuck-at model significantly underestimates (by 62 percent) the impact of an internal chip fault on the output pins. Finally, the study also quantifies the impact of device fault by location, both internally and at the output pins.

Suk, Ho Kim↗

NASA NTRS1985

Reduced phenylalanine ammonia-lyase and tyrosine ammonia-lyase activities and lignin synthesis in wheat grown under low pressure sodium lamps

Wheat (Triticum aestivum L. cv Fremont) grown in hydroponic culture under 24-hour continuous irradiation at 560 to 580 micromoles per square meter per second from either metalhalide (MH), high pressure sodium (HPS), or low pressure sodium (LPS) lamps reached maturity in 70 days. Grain yields were similar under all three lamps, although LPS-grown plants lodged at maturity. Phenylalanine ammonia-lyase (PAL) and a tyrosine ammonia lyase (TAL) with lesser activity were detected in all extracts of leaf, inflorescence, and stem. Ammonia-lyase activities increased with age of the plant, and plants grown under the LPS lamp displayed PAL and TAL activities lower than wheat cultured under MH and HPS radiation. Greenhouse solar-grown wheat had the highest PAL and TAL activities. Lignin content of LPS-grown wheat was also significantly reduced from that of plants grown under MH or HPS lamps or in the greenhouse, showing a correlation with the reduced PAL and TAL activities. Ratios of far red-absorbing phytochrome to total phytochrome were similar for all three lamps, but the data do not yet warrant a conclusion about specific wavelengths missing from the LPS lamps that might have induced PAL and TAL activities in plants under the other lamps.

Triticum/enzymology/growth & development/metabolis↗

NASA NTRS2009

Enceladus: An Active Cryovolcanic Satellite

Enceladus is one of the most remarkable satellites in the solar system, as revealed by Cassini's detection of active plumes erupting from warm fractures near its south pole. This discovery makes Enceladus the only icy satellite known to exhibit ongoing internally driven geological activity. The activity is presumably powered by tidal heating maintained by Enceladus 2:1 mean-motion resonance with Dione, but many questions remain. For instance, it appears difficult or impossible to maintain the currently observed radiated power (probably at least 6 GW) in steady state. It is also not clear how Enceladus first entered its current self-maintaining warm and dissipative state initial heating from non-tidal sources is probably required. There are also many unanswered questions about Enceladus interior. The silicate fraction inferred from its density of 1.68 g per cubic centimeter is probably differentiated into a core, though we have only indirect evidence for differentiation. Above the core there is probably a global or regional water layer, inferred from several models of tidal heating, and an ice shell thick enough to support the ~1 kilometer amplitude topography seen on Enceladus. It is possible that dissipation is largely localized beneath the south polar region. Enceladus surface geology, ranging from moderately cratered terrain to the virtually crater-free active south polar region, is highly diverse, tectonically complex, and remarkably symmetrical about the rotation axis and the direction to Saturn. South polar activity is concentrated along the four tiger stripe fractures, which radiate heat at temperatures up to at least 167 K and are the source of multiple plumes ejecting ~200 kilograms per second of H2O vapor along with significant N2 (or C2H4), CO2, CH4, NH3, and higher-mass hydrocarbons. The escaping gas maintains Saturn's neutral gas torus, and the plumes also eject a large number of micron-sized H2O ice grains that populate Saturn's E-ring. The mechanism that powers the plumes is not well understood, and whether liquid water is involved is a subject of active debate (but likely nonetheless). Enceladus provides a promising potential habitat for life in the outer solar system, and the active plumes allow the unique opportunity for direct sampling of that zone. Enceladus is thus a prime target for Cassini's continued exploration of the Saturn system, and will be a tempting target for future missions.

Spencer, J. R.↗

NASA NTRS1972

Iridium and tantalum foils for spaceflight neutron dosimetry.

Description of a two-foil system of iridium and tantalum which can measure thermal and intermediate energy neutrons at flux densities of 1 neutron/sq cm-sec over a ten-day lunar mission (1,000,000 neutrons/sq cm). The foils are chemically inert and nontoxic, weigh less than 1 g each, and require only routine gamma pulse height analysis for activation measurement. Detection of fluences below 1,000,000 neutrons/sq cm are achieved for counts of foil activity made as late as two months following neutron exposure. Tantalum foils flown in Apollo 11 indicated a mean dose equivalent to the astronauts of less than 16 mrem from thermal plus intermediate energy neutrons, while nuclear emulsion track analysis indicated approximately 17 mrem from neutrons of energy greater than 0.6 MeV. Iridium foils flown on Apollo 12 indicated dose equivalents of 1.8 to 2.8 mrem from thermal neutrons, excluding tissue thermalized SNAP-27 neutrons.

English, R. A.↗

NASA NTRSDate not supplied

Shock Capturing via Limiting for High-Order Methods including Discontinuous Galerkin

High-order methods, such as discontinuous Galerkin (DG), spectral, and flux reconstruction (FR), are prone to generating unwanted oscillations near shocks and discontinuities. Conventional limiting techniques, while effective in suppressing oscillations near shocks, often compromise accuracy near extrema, where the solution is only first-order accurate. This paper introduces a novel limiting technique for these high-order schemes, aimed at effectively managing shocks while preserving accuracy. The key idea is to expand the standard monotonicity limits to provide “room” near smooth extrema, ensuring that limiting has no effect and thus preserving accuracy. Near a discontinuity, these expanded limits effectively reduce to the original monotonicity limits, suppressing oscillations. Additional motivation is drawn from a formula for the derivative of Radau polynomials, which depicts the behavior of oscillations resulting from discontinuities. This behavior leads to a simplification by applying the limits to the sum of magnitudes of all modes, linear and higher degree. Unlike typical approaches, which rely on successful detection to activate limiting, our limiter depends continuously on the data, there by avoiding potential issues if detection fails. To reduce computing time, efficient criteria for detecting smooth regions where limiting is unnecessary are presented. Combined with detection, the continuous dependence on the data is lost, but the method is more economical. A notable characteristic of the entire process is its simplicity in both concept and implementation. Numerical tests for advection and Euler equations are conducted to demonstrate the effectiveness of the proposed method.

numerical methods↗

NASA NTRSDate not supplied

Shock Capturing via Limiting for High-Order Methods including Discontinuous Galerkin

numerical methods↗

NASA NTRS2012

Onboard Science and Applications Algorithm for Hyperspectral Data Reduction

An onboard processing mission concept is under development for a possible Direct Broadcast capability for the HyspIRI mission, a Hyperspectral remote sensing mission under consideration for launch in the next decade. The concept would intelligently spectrally and spatially subsample the data as well as generate science products onboard to enable return of key rapid response science and applications information despite limited downlink bandwidth. This rapid data delivery concept focuses on wildfires and volcanoes as primary applications, but also has applications to vegetation, coastal flooding, dust, and snow/ice applications. Operationally, the HyspIRI team would define a set of spatial regions of interest where specific algorithms would be executed. For example, known coastal areas would have certain products or bands downlinked, ocean areas might have other bands downlinked, and during fire seasons other areas would be processed for active fire detections. Ground operations would automatically generate the mission plans specifying the highest priority tasks executable within onboard computation, setup, and data downlink constraints. The spectral bands of the TIR (thermal infrared) instrument can accurately detect the thermal signature of fires and send down alerts, as well as the thermal and VSWIR (visible to short-wave infrared) data corresponding to the active fires. Active volcanism also produces a distinctive thermal signature that can be detected onboard to enable spatial subsampling. Onboard algorithms and ground-based algorithms suitable for onboard deployment are mature. On HyspIRI, the algorithm would perform a table-driven temperature inversion from several spectral TIR bands, and then trigger downlink of the entire spectrum for each of the hot pixels identified. Ocean and coastal applications include sea surface temperature (using a small spectral subset of TIR data, but requiring considerable ancillary data), and ocean color applications to track biological activity such as harmful algal blooms. Measuring surface water extent to track flooding is another rapid response product leveraging VSWIR spectral information.

Chien, Steve A.↗

NASA NTRS2013

Detection Thresholds of Falling Snow From Satellite-Borne Active and Passive Sensors

There is an increased interest in detecting and estimating the amount of falling snow reaching the Earths surface in order to fully capture the global atmospheric water cycle. An initial step toward global spaceborne falling snow algorithms for current and future missions includes determining the thresholds of detection for various active and passive sensor channel configurations and falling snow events over land surfaces and lakes. In this paper, cloud resolving model simulations of lake effect and synoptic snow events were used to determine the minimum amount of snow (threshold) that could be detected by the following instruments: the W-band radar of CloudSat, Global Precipitation Measurement (GPM) Dual-Frequency Precipitation Radar (DPR)Ku- and Ka-bands, and the GPM Microwave Imager. Eleven different nonspherical snowflake shapes were used in the analysis. Notable results include the following: 1) The W-band radar has detection thresholds more than an order of magnitude lower than the future GPM radars; 2) the cloud structure macrophysics influences the thresholds of detection for passive channels (e.g., snow events with larger ice water paths and thicker clouds are easier to detect); 3) the snowflake microphysics (mainly shape and density)plays a large role in the detection threshold for active and passive instruments; 4) with reasonable assumptions, the passive 166-GHz channel has detection threshold values comparable to those of the GPM DPR Ku- and Ka-band radars with approximately 0.05 g *m(exp -3) detected at the surface, or an approximately 0.5-1.0-mm * h(exp -1) melted snow rate. This paper provides information on the light snowfall events missed by the sensors and not captured in global estimates.

remote sensing↗

NASA NTRS2012

Detection of Spectral Evolution in the Bursts Emitted During the 2008-2009 Active Episode of SGR J1550 - 5418

In early October 2008, the Soft Gamma Repeater SGRJ1550 - 5418 (1E1547.0 - 5408, AXJ155052 - 5418, PSR J1550 - 5418) became active, emitting a series of bursts which triggered the Fermi Gamma-ray Burst Monitor (GBM) after which a second especially intense activity period commenced in 2009 January and a third, less active period was detected in 2009 March-April. Here we analyze the GBM data of all the bursts from the first and last active episodes. We performed temporal and spectral analysis for all events and found that their temporal characteristics are very similar to the ones of other SGR bursts, as well the ones reported for the bursts of the main episode (average burst durations 170ms). In addition, we used our sample of bursts to quantify the systematic uncertainties of the GBM location algorithm for soft gamma-ray transients to less than or equal to 8 degrees. Our spectral analysis indicates significant spectral evolution between the first and last set of events. Although the 2008 October events are best fit with a single blackbody function, for the 2009 bursts an Optically Thin Thermal Bremsstrahlung (OTTB) is clearly preferred. We attribute this evolution to changes in the magnetic field topology of the source, possibly due to effects following the very energetic main bursting episode.

von Kienlin, Andreas↗

NASA NTRS1975

Application of the Nimbus 5 ESMR to rainfall detection over land surfaces

The ability of the Nimbus 5 Electrically Scanning Microwave Radiometer (ESMR) to detect rainfall over land surfaces was evaluated. The ESMR brightness temperatures (Tb sub B) were compared with rainfall reports from climatological stations for a limited number of rain events over portions of the U.S. The greatly varying emissivity of land surfaces precludes detection of actively raining areas. Theoretical calculations using a ten-layer atmospheric model showed this to be an expected result. Detection of rain which had fallen was deemed feasible over certain types of land surfaces by comparing the Tb sub B fields before and after the rain fell. This procedure is reliable only over relatively smooth terrain having a substantial fraction of bare soil, such as exists in major agricultural regions during the dormant or early growing seasons. Soil moisture budgets were computed at selected sites to show how the observed emissivity responded to changes in the moisture content of the upper soil zone.

Meneely, J. M.↗

NASA NTRS1999

Rapid direct methods for enumeration of specific, active bacteria in water and biofilms

Conventional methods for detecting indicator and pathogenic bacteria in water may underestimate the actual population due to sublethal environmental injury, inability of the target bacteria to take up nutrients and other physiological factors which reduce bacterial culturability. Rapid and direct methods are needed to more accurately detect and enumerate active bacteria. Such a methodological advance would provide greater sensitivity in assessing the microbiological safety of water and food. The principle goal of this presentation is to describe novel approaches we have formulated for the rapid and simultaneous detection of bacteria plus the determination of their physiological activity in water and other environmental samples. The present version of our method involves the concentration of organisms by membrane filtration or immunomagnetic separation and combines an intracellular fluorochrome (CTC) for assessment of respiratory activity plus fluorescent-labelled antibody detection of specific bacteria. This approach has also been successfully used to demonstrate spatial and temporal heterogeneities of physiological activities in biofilms when coupled with cryosectioning. Candidate physiological stains include those capable of determining respiratory activity, membrane potential, membrane integrity, growth rate and cellular enzymatic activities. Results obtained thus far indicate that immunomagnetic separation can provide a high degree of sensitivity in the recovery of seeded target bacteria (Escherichia coli O157:H7) in water and hamburger. The captured and stained target bacteria are then enumerated by either conventional fluorescence microscopy or ChemScan(R), a new instrument that is very sensitive and rapid. The ChemScan(R) laser scanning instrument (Chemunex, Paris, France) provides the detection of individual fluorescently labelled bacterial cells using three emission channels in less than 5 min. A high degree of correlation has been demonstrated between results obtained with the ChemScan and traditional plate counts of mixed natural bacterial populations in water. The continuing evolution of these methods will be valuable in the rapid and accurate analysis of environmental samples.

Review, Tutorial↗

NASA NTRS2023

Potentially Underestimated Gas Flaring Activities—A New Approach to Detect Combustion Using Machine Learning and NASA’s Black Marble Product Suite

Monitoring changes in greenhouse gas (GHG) emission is critical for assessing climate mitigation efforts towards the Paris Agreement goal. A crucial aspect of science-based GHG monitoring is to provide objective information for quality assurance and uncertainty assessment of the reported emissions. Emission estimates from combustion events (gas flaring and biomass burning) are often calculated based on activity data (AD) from satellite observations, such as those detected from the visible infrared imaging radiometer suite (VIIRS) onboard the Suomi-NPP and NOAA-20 satellites. These estimates are often incorporated into carbon models for calculating emissions and removals. Consequently, errors and uncertainties associated with AD propagate into these models and impact emission estimates. Deriving uncertainty of AD is therefore crucial for transparency of emission estimates but remains a challenge due to the lack of evaluation data or alternate estimates. This work proposes a new approach using machine learning (ML) for combustion detection from NASA's Black Marble product suite and explores the assessment of potential uncertainties through comparison with existing detections. We jointly characterize combustion using thermal and light emission signals, with the latter improving detection of probable weaker combustion with less distinct thermal signatures. Being methodologically independent, the differences in ML-derived estimates with existing approaches can indicate the potential uncertainties in detection. The approach was applied to detect gas flares over the Eagle Ford Shale, Texas. We analyzed the spatio-temporal variations in detections and found that approximately 79.04% and 72.14% of the light emission-based detections are missed by ML-derived detections from VIIRS thermal bands and existing datasets, respectively. This improvement in combustion detection and scope for uncertainty assessment is essential for comprehensive monitoring of resulting emissions and we discuss the steps for extending this globally.

gas flaring↗

NASA NTRS1991

Charged particle activation studies on the surface of LDEF spacecraft

High energy proton induced nuclear reaction products are examined using seven elements, namely: Al, Si, Ni, Co, Zr, Ta, and W. Activities were detected due to Na-22 from Al, Co-56 from Ni, Co-58 from Cu, and Y-88 from Zr targets. No induced activity was observed in Si, Ta, and W, most probably due to the long cooling times. Only Zr sample contained a weak Be-7 peak, although Ta and W were also located at the leading edge of the spacecraft. Gamma rays of individual isotopes were measured using high resolution Ge(Li) solid state detector coupled to 4096 multichannel analyzer. Activities were calculated for Co-56 (846 keV) and Co-57 (122 and 136 keV's) at the time of the entry of the spacecraft and found to be 0.014 + or - c/sec g, 0.018 + or - 0.002 c/sec g, and 0.0024 + or - 0.0007 c/sec g, respectively.

Olmez, Ilhan↗

NASA NTRS2003

Dual reporter transgene driven by 2.3Col1a1 promoter is active in differentiated osteoblasts

AIM: As quantitative and spatial analyses of promoter reporter constructs are not easily performed in intact bone, we designed a reporter gene specific to bone, which could be analyzed both visually and quantitatively by using chloramphenicol acetyltransferase (CAT) and a cyan version of green fluorescent protein (GFPcyan), driven by a 2.3-kb fragment of the rat collagen promoter (Col2.3). METHODS: The construct Col2.3CATiresGFPcyan was used for generating transgenic mice. Quantitative measurement of promoter activity was performed by CAT analysis of different tissues derived from transgenic animals; localization was performed by visualized GFP in frozen bone sections. To assess transgene expression during in vitro differentiation, marrow stromal cell and neonatal calvarial osteoblast cultures were analyzed for CAT and GFP activity. RESULTS: In mice, CAT activity was detected in the calvaria, long bone, teeth, and tendon, whereas histology showed that GFP expression was limited to osteoblasts and osteocytes. In cell culture, increased activity of CAT correlated with increased differentiation, and GFP activity was restricted to mineralized nodules. CONCLUSION: The concept of a dual reporter allows a simultaneous visual and quantitative analysis of transgene activity in bone.

Non-NASA Center↗

NASA NTRS1983

UHF and S-band radar observations of electrically active storm cells

The UHF-band and S-band research radars of NASA Goddard's atmospheric sciences research facility at Wallop's Island, Virginia are used to study the correlation between the location of radar-detected electrical activity in a storm cell and its precipitation reflectivity structure. The technique used to make the measurements is discussed and some typical results are presented. The existence of a bimodal distribution of lightning activity as a function of altitude is reported and supported by the data. The vertical structure of the electrical activity may be evidence of K and/or J processes. The technique used is very valuable, and provides high-resolution radar data of both reflectivities and flash density.

Gerlach, J. C.↗

NASA NTRS1988

Simultaneous S- and X-band uplink-downlink performance at DSS 13

The Deep Space Station 13 26-meter antenna with the second generation S/X feedcone was tested to determine the dual S- and X-band (2.1 to 2.3 GHz and 7.1 to 8.5 GHz) transmit and receive performance. Measurements were conducted using the 20 kW transmitters at S- and X-band while simultaneously receiving S- and X-band. This system proved to be very quiet compared with the other DSN antennas. Under normal tracking configurations, no noise burst or intermodulation product (IMP) activity was detectable to the -175 dBm level. To prove the instrumentation's ability to detect such phenomena, an IMP generator was introduced onto the system with positive, verifiable results. The IMP occurred at the -162 dBm level, accompanied by moderate noise burst activity, and was readily repeatable. The measurement also showed the possible need for additional fourth channel filtering in the system to reduce the effect of the transmitter power on the low noise amplifiers.

Freiley, A. J.↗