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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS2010

Assessment of the Jason-2 Extension to the TOPEX/Poseidon, Jason-l Sea-Surface Height Time Series for Global Mean Sea Level Monitoring

The Jason-2 (OSTM) follow-on mission to Jason-I provides for the continuation of global and regional mean sea level estimates along the ground-track of the initial phase of the TOPEX/Poseidon mission. During the first several months, Jason-I and Jason-2 flew in formation separated by only 55 seconds, enabling the isolation of intermission instrument biases through direct collinear differencing of near simultaneous observations. The Jason-2 Ku-band range bias with respect to Jason-I is estimated to be -84 +/- 9 mm, based on the orbit altitudes provided on the Geophysical Data Records. Modest improved agreement is achieved with the GSFC replacement orbits, which further enables the isolation of subtle 1 cm) instrument-dependent range correction biases. Inter-mission bias estimates are confirmed with an independent assessment from comparisons to a 64-station tide-gauge network, also providing an estimate of the stability of the 17-year time series to be less than 0.1 mm/yr +/- 0.4 mm/yr. The global mean sea level derived from the multi-mission altimeter sea-surface height record from January 1993 through September 2009 is 3.3 +/- 0.4 mm/yr. Recent trends over the period from 2004 through 2008 are smaller and estimated to be 2.0 +/- 0.4 mm/yr.

Beckley, B. D.↗
NASA NTRS1971

The stopping rate of negative cosmic-ray muons near sea level

A production rate of 0.065 + or - 0.003 Ar-37 atom/kg min of K-39 at 2-mwe depth below sea level was measured by sweeping argon from potassium solutions. This rate is unaffected by surrounding the solution by paraffin and is attributed to negative muon captures and the electromagnetic interaction of fast muons, and not to nucleonic cosmic ray component. The Ar-37 yield from K-39 by the stopping of negative muons in a muon beam of a synchrocyclotron was measured to be 8.5 + or - 1.7%. The stopping rate of negative cosmic ray muons at 2-mwe depth below sea level from these measurements and an estimated 17% electromagnetic production is 0.63 + or - 0.13 muon(-)/kg min. Previous measurements on the muon stopping rate vary by a factor of 5. Our value is slightly higher but is consistent with two previous high values. The sensitivity of the Ar-37 radiochemical method for the detection of muons is considerably higher than that of the previous radiochemical methods and could be used to measure the negative muon capture rates at greater depths.

Spannagel, G.↗
NASA NTRS1932

The Effect of Valve Timing Upon the Performance of a Supercharged Engine at Altitude and an Unsupercharged Engine at Sea Level

This investigation was conducted to determine the comparative effects of valve timing on the performance of an unsupercharged engine at sea level and a supercharged engine at altitude. The tests were conducted on the NACA universal test engine. The timing of the four valve events was varied over a wide range; the engine speeds were varied between 1,050 and 1,500 r.p.m.; the compression ratios were varied between 4.35:1 and 7.35:1. The conditions of exhaust pressure and carburetor pressure of a supercharged engine were simulated for altitudes between 0 and 18,000 feet. The results show that optimum valve timing for a supercharged engine at an altitude of 18,000 feet differs slightly from that for an unsupercharged engine at sea level. A small increase in power is obtained by using the optimum timing for 18,000 feet for altitudes above 5,000 feet. The timing of the intake opening and exhaust closing becomes more critical as the compression ratio is increased.

Schey, Oscar W↗
NASA NTRS2018

Increased Snowfall over the Antarctic Ice Sheet Mitigated Twentieth-Century Sea-Level Rise

Changes in accumulated snowfall over the Antarctic Ice Sheet have an immediate and time-delayed impact on global mean sea level. The immediate impact is due to the instantaneous change in freshwater storage over the ice sheet, whereas the time-delayed impact acts in opposition through enhanced ice dynamic flux into the ocean. Here, we reconstruct 200 years of Antarctic-wide snow accumulation by synthesizing a newly compiled database of ice core records using reanalysis derived spatial coherence patterns. The results reveal that increased snow accumulation mitigated twentieth-century sea-level rise by approximately 10 millimeters since 1901, with rates increasing from 1.1 mm per decade between 1901 and 2000 to 2.5 mm per decade after 1979. Reconstructed accumulation trends are highly variable in both sign and magnitude at the regional scale, and linked to the trend towards a positive Southern Annular Mode since 1957. Because the observed Southern Annular Mode trend is accompanied by a decrease in Antarctic Ice Sheet accumulation, changes in the strength and location of the circumpolar westerlies cannot explain the reconstructed increase, which may instead be related to stratospheric ozone depletion. However, our results indicate that a warming atmosphere cannot be excluded as a dominant force in the underlying increase.

Antarctic↗
NASA NTRS2018

Increased snowfall over the Antarctic Ice Sheet mitigated twentieth-century sea-level rise

Changes in accumulated snowfall over the Antarctic Ice Sheet have an immediate and time-delayed impact on global mean sea level. The immediate impact is due to the instantaneous change in freshwater storage over the ice sheet, whereas the time-delayed impact acts in opposition through enhanced ice-dynamic flux into the ocean1. Here, we reconstruct 200 years of Antarctic-wide snow accumulation by synthesizing a newly compiled database of ice core records2 using reanalysis-derived spatial coherence patterns. The results reveal that increased snow accumulation mitigated twentieth-century sea-level rise by ~10 mm since 1901, with rates increasing from 1.1 mm decade−1 between 1901 and 2000 to 2.5 mm decade−1 after 1979. Reconstructed accumulation trends are highly variable in both sign and magnitude at the regional scale, and linked to the trend towards a positive Southern Annular Mode since 19573. Because the observed Southern Annular Mode trend is accompanied by a decrease in Antarctic Ice Sheet accumulation, changes in the strength and location of the circumpolar westerlies cannot explain the reconstructed increase, which may instead be related to stratospheric ozone depletion4. However, our results indicate that a warming atmosphere cannot be excluded as a dominant force in the underlying increase.

B Medley↗
NASA NTRS1981

Global analysis of January and July sea level pressure

A global analysis of monthly mean sea level pressure for January and July over a 16 year period (1961 through 1976) is presented. For both hemispheres, the summer circulation is characterized by continental lows and oceanic highs. The prominent features of the Northern Hemispheric winter circulation, forced by diabatic heat sources and orography, are Aleutian low, Icelandic low and Siberian high. The interannual variability is small over the tropics and large over the extratropics. Maximum variability occurs over the locations of Icelandic and Aleutian lows in the Northern Hemispheric winter. The locations and intensities of the Southern Hemispheric subtropical highs, which occur over the oceans, are remarkably similar in January and July and show small interannual variability. The north Atlantic and south Atlantic subtropical highs attain their maximum intensity at the same time, during July.

Godbole, R. V.↗
NASA NTRS1990

Sea level oscillations observed with Geosat along the two shear fronts of the Pacific north equatorial countercurrent

Geosat data are processed and analyzed into sea-level variations over the tropical Pacific Ocean during the first 26 months of the Exact Repeat Mission from November 15, 1986 to January 15, 1989. The resolution is 1 deg latitude and longitude and 10 days. The frequency and wavenumber spectra of these sea-level variations show much more energy in the northeastern than in the western or southern Pacific. Energy highs of 8000 sq cm per (cycle per day) per (cycle per deg longitude) are clearly identified along 5 deg N for periods of 28-40 days and wavelengths of 1000-2200 km (band 1), and along 12 deg N for periods of 50-90 days and wavelengths of 630-950 km (band 2).

Perigaud, Claire↗
NASA NTRS2019

Improved Earth Oblateness Rate Reveals Increased Ice Sheet Losses and Mass-Driven Sea Level Rise

Satellite laser ranging (SLR) observations are routinely applied toward the estimation of dynamic oblateness, C(sub 20), which is the largest globally integrated component of Earth's time-variable gravity field. Since 2002, GRACE and GRACE Follow-On have revolutionized the recovery of higher spatial resolution features of global time-variable gravity, with SLR continuing to provide the most reliable estimates of C (sub 20).We quantify the effect of various SLR processing strategies on estimating C(sub 20) and demonstrate better signal recovery with the inclusion of GRACE-derived low-degree gravity information in the forward model. This improved SLR product modifies the Antarctic and Greenland Ice Sheet mass trends by -15.4 and -3.5 Gt/year, respectively, as compared to CSR TN11, and improves global mean sea level budget closure by modifying sea level rise by +0.08 mm/year. We recommend that this new C(sub 20) product be applied to RL06 GRACE data products for enhanced accuracy and scientific interpretation.

Loomis, B. D.↗
NASA NTRS1993

Absolute spectrum and charge ratio of cosmic ray muons in the energy region from 0.2 GeV to 100 GeV at 600 m above sea level

We have determined the momentum spectrum and charge ratio of muons in the region from 250 MeV/c to 100 GeV/c using a superconducting magnetic spectrometer. The absolute differential spectrum of muons obtained in this experiment at 600 m above sea level is in good agreement with the previous measurements at sea level. The differential spectrum can be represented by a power law with a varying index, which is consistent with zero below 450 MeV/c and steepens to a value of -2.7 +/- 0.1 between 20 and 100 GeV/c. The integral f1ux of muons measured in this experiment span a very large range of momentum and is in excellent agreement with the earlier results. The positive to negative muon ratio appears to be constant in the entire momentum range covered in this experiment within the errors and the mean value is 1.220 +/- 0.044. The absolute momentum spectrum and the charge ratio measured in this experiment are also consistent with the theoretical expectations. This is the only experiment which covers a wide range of nearly three decades in momentum from a very low momentum.

De Pascale, M. P.↗
NASA NTRSDate not supplied

Using Earth Observations to Analyze Shoreline Changes and Understand the Effects of Sea Level Rise in Southern Puerto Rico

This summer, the Jobos Bay National Estuarine Research Reserve (JBNERR) partnered with NASA DEVELOP to evaluate water quality, mangrove forest extent, sea level rise, and land cover changes in Jobos Bay. DEVELOP is a national capacity building program that connects satellite data with early career scientists and decision makers. Through ten-week feasibility studies, DEVELOP partners with organizations that have the power to enact policy within their communities. Jobos Bay, in the southeast coast of Puerto Rico, has experienced intense hurricane seasons with increased seasonal storm surge, near-shore land use changes, and strong variations in precipitation and runoff. Through proposals, bi-weekly meetings, and frequent email communication, this cross-sector initiative provided valuable results for management decisions within the reserve. Using satellite observations to measure land use change, the team found that 17% of the reserve has shifted from land to water along the coast since 1997. Using Sentinel-2 the team was able to visualize turbidity, chlorophyll-a, and colored dissolved organic matter (CDOM) for Jobos Bay. While some large events such as Hurricane Maria were reflected in the turbidity analysis, chlorophyll-a and CDOM visualizations were limited by the influence of shallow-water bottom reflectance, particularly around reefs and within the Bay. The team also found that Jobos Bay lost 4.9 square kilometers of mangrove habitat over the past decade, calculated using Landsat 7 and 8 within Google Earth Engine. The results from this study will inform JBNERR and its community members on the regional impacts of sea level rise as well as serve as a baseline for future conservation efforts and research in the estuary.

Olivia Spencer↗
NASA NTRS1990

Uprated OMS Engine Status-Sea Level Testing Results

The current Space Shuttle Orbital Maneuvering Engine (OME) is pressure fed, utilizing storable propellants. Performance uprating of this engine, through the use of a gas generator driven turbopump to increase operating pressure, is being pursued by the NASA Johnson Space Center (JSC). Component level design, fabrication, and test activities for this engine system have been on-going since 1984. More recently, a complete engine designated the Integrated Component Test Bed (ICTB), was tested at sea level conditions by Aerojet. A description of the test hardware and results of the sea level test program are presented. These results, which include the test condition operating envelope and projected performance at altitude conditions, confirm the capability of the selected Uprated OME (UOME) configuration to meet or exceed performance and operational requirements. Engine flexibility, demonstrated through testing at two different operational mixture ratios, along with a summary of projected Space Shuttle performance enhancements using the UOME, are discussed. Planned future activities, including ICTB tests at simulated altitude conditions, and recommendations for further engine development, are also discussed.

Bertolino, J. D.↗
NASA NTRS1989

Pulse compression and sea level tracking in satellite altimetry

An account is given of the pulse-compression technique, in which a radar altimeter transmits a relatively long pulse and processes the returned signal in a way equivalent to transmitting a very short one and measuring the returned power in a sequence of range gates. The effective short pulse enhances the range resolution that would be obtained from the actual long pulse. Pulse compression and sea-level tracking are important to the overall error budget for altimetric estimates of sea level. Attention is presently given to the high degree of accuracy required for the NASA TOPEX altimeter scheduled for launch in mid-1992.

Chelton, Dudley B.↗
NASA NTRS1999

Detecting 1mm/Year Signals in Altimetric Global Sea Level: Effect of Atmospheric Water Vapor and Precipitation

Several research efforts exist to use Topography Experiment (TOPEX)/ Projet d'Observatorie de Surveillance et d'Etudes Integrees de la Dynamique des Oceans (Poseidon) (T/P) to detect changes in global sea level possibly associated with climate change. This requires much better than 1 mm/yr accuracy, something that none of the instruments in T/P [or the European Remote Sensing (ERS-2) satellite, or the U.S. Navy's Geosat Follow-On (GFO) satellite] were designed for. This work focuses on the ability of the T/P microwave radiometer (TMR) to retrieve the path delay due to atmospheric water vapor along the altimeter's path with accuracy in the time changes below 1 mm/yr on global average. In collaboration with Stephen Keihm of JPL and Christopher Ruf of Pennsylvania State University, we compared TMR path delay (PD) estimates with atmospheric precipitable water (PW) from the Special Sensor Microwave Imager (SSMI) aboard the Defense Meteorological Satellite Program (DMSP) series of satellites for 1992-1998 to selected radiosondes, and we also looked at the brightness temperatures measured by TMR in the lowest 1% of the histogram. The conclusion is that TMR had a slow instrumental drift, associated with the 18-GHz channel, which causes an approximate underestimation of water vapor at a rate equivalent to 1.2 mm/yr in path delay between 1992 and 1996; this effect stopped and no drift is detected in 1997. The same study concluded that there is no detectable scale error (one which is proportional to measured vapor) in TMR. In related work, carried out with graduate student Damien Cailliau, we investigated the relative abilities of TMR, SSMI and the UP dual-frequency radar altimeter to detect rain, relative to a climatology of shipborne observations. Rain is a crucial but poorly measured variable in studies of the climate system, and a dedicated mission, Tropical Rainfall Measuring Mission (TRMM), was recently launched to measure it. However, the climatologies built over the past 10 years used passive radiometers, such as SSMI, or infrared observation from National Oceanic and Atmospheric Administration (NOAA) geostationary satellites. We concluded that the dual-frequency altimeter does an excellent job at retrieving rain on scales much smaller than the passive radiometer, and a better job at retrieving total precipitation (rain as well as snow) at high latitudes. This work improves the sea level observations by allowing better flagging of observations contaminated by rain, and more importantly, provides an alternative way to measure rainfall over the oceans.

Zlotnicki, Victor↗
NASA NTRS2021

Jobos Bay Water Resources: Using Earth Observations to Analyze Shoreline Changes and Understand the Effects of Sea Level Rise in Southern Puerto Rico

Jobos Bay is located on the southern coast of Puerto Rico, which is known for intense hurricane seasons and increased seasonal storm surge. Scientists at Jobos Bay National Estuarine Research Reserve (JBNERR) are concerned that sea level rise will exacerbate coastal damage from these weather events. Using NASA Earth observations, our team analyzed coastal change, land use land cover change (LULC), mangrove forest extent, and water quality of Jobos Bay. Using Google Earth Engine, we evaluated coastal change and mangrove forest habitat within the study region by classifying NASA Earth observation imagery. We created historic LULC composite images to observe how land use changes over time and improve understanding of urbanization in the watershed. Leveraging previous water quality studies, our team compared water quality datasets generated by the Optical Reef and Coastal Area Assessment (ORCAA) tool to in situ sensors provided by JBNERR partners to understand the overall quality of water in the study area with respect to turbidity, chlorophyll-a, sea surface temperature, and colored dissolved organic matter (CDOM) concentrations. We discovered that 17% of the reserve has shifted from land to water since 1997 and lost 4.85 square kilometers of mangrove habitat over the past decade. Results from this study will inform the scientists of JBNERR and community members of the regional impacts of sea level rise. Being the first comprehensive study done in the estuary in nearly a decade, this serves as a baseline for future conservation efforts and research in the estuary.

Olivia Spencer↗