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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

Recent Changes in the Greenland Ice Sheet as Seen from Space

Many changes in the Greenland Ice Sheet have been reported in the recent scientific literature and have been attributed to various responses of the ice sheet due to regional (and global) warming. Because melting of the ice sheet would contribute approximately 7 m to sea-level rise, the lives and habitat of hundreds of millions of people worldwide would be directly and indirectly affected if continued ice-sheet melting occurs. As mean-annual global temperatures have increased, there has been an increasing focus on studying the Greenland Ice Sheet using available satellite data, and numerous expeditions have been undertaken. Regional "clear-sky" surface temperature increases since the early 1980s in the Arctic, measured using Advanced Very High Resolution Radiometer (AVHRR) infrared data, range from 0.57+/-0.02 C to 0.72+/-0.10 C per decade. Arctic warming has important implications for ice-sheet mass balance because much of the periphery of the Greenland Ice Sheet is already near O C during the melt season, and is thus vulnerable to more extensive melting if temperatures continue to increase. An increase in melting of the ice sheet would accelerate sea-level rise, an issue of increasing concern to billions of people worldwide. The surface temperature of the ice sheet has been studied in even greater detail using Moderate-Resolution Imaging Spectroradiometer (MODIS) data in the six individual drainage basins as well as for the ice sheet as a whole. Surface temperature trends in the decade of the 2000s have not been strong, according to the MODIS measurements. In addition to surface-temperature increases over the last few decades as measured by AVHRR, other changes have been observed such as accelerated movement of many of Greenland's outlet glaciers and sudden draining of supraglacial lakes. Decreasing mass of the ice sheet since (at least) 2002 has been measured using Gravity Recovery and Climate Experiment (GRACE) data, along with an build-up of ice at the higher elevations and a decrease of ice at the lower elevations as measured using airborne Lidar and Ice, Cloud and Land Elevation Satellite (ICESat) data. The seminar will address the above issues using a variety of NASA satellite data and ground observations.

Hall, Dorothy K.↗
NASA NTRS1972

Thermally stable macromolecules.

Man-made polymers are compared with certain naturally occurring polymers which have long been used at elevated temperatures. The pyrolysis of model compounds is discussed together with aspects of thermogravimetric analysis, torsional braid analysis, and questions of chemical and radiation stability. Some structure-property relationships are examined, giving attention to asbestos, mica, graphite, and diamond. Questions of bond strengths are investigated along with the stability of ladder polymers and some fundamental concepts in the synthesis of aromatic and heteroaromatic polymers. The substances considered include aromatic single-strand polymers, heteroaromatic polymers, polymers obtained by addition polymerizations, and nonhydrogen-containing polymers. Future trends are also explored.

Pezdirtz, G. F.↗
NASA NTRS1976

Measurements of spectral and total emittance of reinforced carbon-carbon

Elevated temperature measurements of the spectral emittance of reinforced carbon-carbon (RCC) as the thermal protection material for the leading edge areas of the Space Shuttle Orbiter were carried out in situ, with environments provided by arc-heated streams of air and argon. A monochromator, infrared pyrometers, and thermocouples were used in evaluating the response of the RCC test specimens during the emittance measurements. Results indicate that the material is nongray, with lowest spectral emittance at the short wavelengths and with relatively high total emittance. The trend of the total emittance data suggests a slight decrease in total emittance with increasing temperature, although the emittance value stabilizes with continuing exposure.

Grinberg, I. M.↗
NASA NTRS2022

CO Chondrite Parent Body Processing as Recorded by Noble Gases

**Introduction:** CO carbonaceous chondrites are among the most primitive meteorites, of which some experienced mild degrees of thermal alteration (up to 500 °C) in their parent asteroid. Previous studies on aqueously altered CM, CY and CR chondrites have shown that the noble gases preserved in those meteorites can be used to assess the extent of parent body processing. This is mostly due to an Ar-rich carrier phase being susceptible to aqueous alteration. In this study, we follow up on these findings by investigating the effects of mild thermal alteration on the noble gas content of CO chondrites. They are subclassified from petrologic subtype 3.0 (e.g., Yamato-81025) to 3.8 (e.g., Isna) according to the degree of thermal alteration experienced. Understanding these effects does not only help to distinguish the most primitive samples from the severely altered ones, but also adds to the picture of the primordial volatile composition and distribution, as preserved in the most primitive material which accreted from the solar nebula at different heliocentric distances. Additionally, we search for pairing among samples, as part of an ongoing survey of Antarctic CO chondrites. **Experimental:** Noble gas measurements were conducted on aliquots of ~20-25 mg from 16 different samples of varying petrologic subtype from 3.0 to 3.8. The gas extraction occurred in one temperature step at ~1700 °C, followed by separation into three fractions, He-Ne, Ar, and Kr-Xe, measured successively in a custom-built mass spectrometer. For each sample, complete gas extraction was verified by a re-extraction step at ~1750 °C. Details on the sample preparation and measurement protocols can be found in. **Results and Discussion:** In most cases, the gas concentrations for all five noble gases decrease with increasing petrologic subtype, and the trend is most pronounced for Ne. An exception is e.g. CO3.0 Colony, which is strongly terrestrially weathered. CO3.8 Isna shows an unusually short expo-sure time to cosmic rays (~0.15 Ma), which may be explained by a direct injection into a mean orbital resonance shortly after collision. The currently ill-defined Ar-rich carrier phase, found only in the least aqueously altered CM and CR samples, is still abundantly present in the predominately anhydrous CO chondrites, indicating that this component is less susceptible to moderately elevated temperatures. No CO chondrites examined so far contain solar wind, supporting the hypothesis that CO chondrites originate from the asteroidal interior. It thus remains enigmatic which material could account for the surface layer.

Noble gas↗
NASA NTRS1972

Atmospheric pressure, density, temperature and wind variations between 50 and 200 km

Data on atmospheric pressure, density, temperature and winds between 50 and 200 km were collected from sources including Meteorological Rocket Network data, ROBIN falling sphere data, grenade release and pitot tube data, meteor winds, chemical release winds, satellite data, and others. These data were analyzed by a daily difference method and results on the distribution statistics, magnitude, and spatial structure of the irregular atmospheric variations are presented. Time structures of the irregular variations were determined by the analysis of residuals from harmonic analysis of time series data. The observed height variations of irregular winds and densities are found to be in accord with a theoretical relation between these two quantities. The latitude variations (at 50 - 60 km height) show an increasing trend with latitude. A possible explanation of the unusually large irregular wind magnitudes of the White Sands MRN data is given in terms of mountain wave generation by the Sierra Nevada range about 1000 km west of White Sands. An analytical method is developed which, based on an analogy of the irregular motion field with axisymmetric turbulence, allows measured or model correlation or structure functions to be used to evaluate the effective frequency spectra of scalar and vector quantities of a spacecraft moving at any speed and at any trajectory elevation angle.

Justus, C. G.↗
NASA NTRS1989

In situ observations of BrO over Antarctica - ER-2 aircraft results from 54 deg S to 72 deg S latitude

Bromine monoxide was observed in situ during nine flights of the NASA ER-2 aircraft from Punta Arenas, Chile (54 deg S latitude), to 72 deg S latitude over the Palmer Peninsula, Antarctica. The first flight for the BrO detection system was on August 28. The distribution of BrO inside the chemically perturbed region defined by greatly elevated ClO abundances was different from that found just outside. Inside, the BrO mixing ratio was 6.1 + or - 1.1 pptv above the 440 K potential temperature surface, 4.7 + or - 2.0 pptv between the 400 and 440 K surfaces, and less than 4 pptv below the 400 K surface. At high latitudes outside the chemically perturbed region, the BrO mixing ratio was 5.4 + or - 1.4 pptv near the 450 K surface, but decreased to 2.9 + or - 1.2 pptv at the 420 K surface. The abundance of BrO showed no discernible temporal trend during the course of the nine flights. Away from the south polar region, at latitudes between 47 deg S and 37 deg N and potential temperatures between 435 and 500 K (18.5- to 20.7-km altitude), the BrO mixing ratio was 0.5-3.0 pptv.

Brune, W. H.↗
NASA NTRS2014

Secular Climate Change on Mars: An Update Using One Mars Year of MSL Pressure Data

The South Polar Residual Cap (SPRC) on Mars is an icy reservoir of CO2. If all the CO2 trapped in the SPRC were released to the atmosphere the mean annual global surface pressure would rise by approximately 20 Pa. Repeated MOC and HiRISE imaging of scarp retreat within the SPRC led to suggestions that the SPRC is losing mass. Estimates for the loss rate vary between 0. 5 Pa per Mars Decade to 13 Pa per Mars Decade. Assuming 80% of this loss goes directly into the atmosphere, an estimate based on some modeling (Haberle and Kahre, 2010), and that the loss is monotonic, the global annual mean surface pressure should have increased between approximately 1-20 Pa since the Viking mission (approximately 20 Mars years ago). Surface pressure measurements by the Phoenix Lander only 2.5 Mars years ago were found to be consistent with these loss rates. Last year at this meeting we compared surface pressure data from the MSL mission through sol 360 with that from Viking Lander 2 (VL-2) for the same period to determine if the trend continues. The results were ambiguous. This year we have a full Mars year of MSL data to work with. Using the Ames GCM to compensate for dynamics and environmental differences, our analysis suggests that the mean annual pressure has decreased by approximately 8 Pa since Viking. This result implies that the SPRC has gained (not lost) mass since Viking. However, the estimated uncertainties in our analysis are easily at the 10 Pa level and possibly higher. Chief among these are the hydrostatic adjustment of surface pressure from grid point elevations to actual elevations and the simulated regional environmental conditions at the lander sites. For these reasons, the most reasonable conclusion is that there is no significant difference in the size of the atmosphere between now and Viking. This implies, but does not demand, that the mass of the SPRC has not changed since Viking. Of course, year-to-year variations are possible as implied by the Phoenix data. Given that there has been no unusual behavior in the climate system as observed by a variety of spacecraft at Mars since Phoenix, its seems more likely that the Phoenix data simply did not have a long enough record to accurately determine annual mean pressure changes as Haberle and Kahre (2010) cautioned. In the absence of a strong signal in the MSL data, we conclude that if the SPRC is loosing mass it is not going into the atmosphere reservoir.

Phoenix data↗
NASA NTRS2016

Antarctic Sea-Ice Freeboard and Estimated Thickness from NASA's ICESat and IceBridge Observations

ICESat completed 18 observational campaigns during its lifetime from 2003 to 2009. Data from all of the 18 campaign periods are used in this study. Most of the operational periods were between 34 and 38 days long. Because of laser failure and orbit transition from 8-day to 91-day orbit, there were four periods lasting 57, 16, 23, and 12 days. IceBridge data from 2009, 2010, and 2011 are used in this study. Since 2009, there are 19 Airborne Topographic Mapper (ATM) campaigns, and eight Land, Vegetation, and Ice Sensor (LVIS) campaigns over the Antarctic sea ice. Freeboard heights are derived from ICESat, ATM and LVIS elevation and waveform data. With nominal densities of snow, water, and sea ice, combined with snow depth data from AMSR-E/AMSR2 passive microwave observation over the southern ocean, sea-ice thickness is derived from the freeboard. Combined with AMSR-E/AMSR2 ice concentration, sea-ice area and volume are also calculated. During the 2003-2009 period, sea-ice freeboard and thickness distributions show clear seasonal variations that reflect the yearly cycle of the growth and decay of the Antarctic pack ice. We found no significant trend of thickness or area for the Antarctic sea ice during the ICESat period. IceBridge sea ice freeboard and thickness data from 2009 to 2011 over the Weddell Sea and Amundsen and Bellingshausen Seas are compared with the ICESat results.

Antarctic↗
NASA NTRS2020

The Role of Declining Snow Cover in the Desiccation of the Great Salt Lake, Utah, using MODIS Data

The Great Salt Lake (GSL) in Utah has been shrinking since the middle of the 19th Century, leading to decreased area and volume, and increased salinity. We use satellite data products from the Terra and Aqua MODerate-resolution Imaging Spectroradiometer (MODIS) and the Landsat-7 and -8 satellites, along with meteorological and streamflow data, and modeled data products to study the relationship between changing snow-cover conditions and the decline of the GSL since 2000 in the context of the historical record of lake levels. The GSL basin includes much of the snow-dominated Wasatch and Uinta mountain ranges to the east of the lake. Snowmelt feeds the Bear, Jordan, and Weber rivers which are the three main rivers that flow into the lake. Snowmelt-timing maps, derived from a new MODIS standard snow-cover product, MOD10A1F, show that snow melted ~9.5 days earlier in the GSL basin during the study period, extending from 2000 – 2018. Air temperatures derived from 26 meteorological stations and surface temperatures measured by the Aqua MODIS land-surface temperature (LST) products, MYD21A1D and MYD21A1N, show trends of increasing temperature of ~0.94°C (a=0.05), and ~2.18°C, respectively, with most of the LST trends in the GSL basin being statistically significant (a=0.05). Increasing air temperatures in the basin have led to less precipitation falling as snow, lower snow depth (by ~34.5 mm (=0.01)) and snow-water equivalent (0.02 mm (a=0.01)), and earlier snowmelt. Also during the study period, Global Land surface Evaporation Amsterdam Model data show evaporation increasing by ~3.2 mm/yr, with trends in much of the basin being statistically significant (a=0.05). Trends calculated from the various products are generally in agreement indicating higher temperatures, greater evaporation, less snowfall and snow-on-the ground, and earlier snowmelt. Earlier snowmelt contributes to increasing evaporative loss from water flowing toward the lake. Furthermore, a lower mountain snowpack and less precipitation falling as snow (versus rain) is associated with lower stream discharge even if overall precipitation stays the same. The surface-water temperature of the GSL also increased over the study period by ~ 0.69°C, according to the MODIS LST data products, and the surface-water elevation of the lake dropped by ~1.7 m between 2000 and 2018 based on United States Geological Survey measurements, and the areal extent of the lake decreased by ~901 km2 as measured using Landsat imagery. Desiccation of the lake is associated with deleterious effects on wildlife, recreational activities, and some local industries. And, importantly, an expanding lake bed can also fuel dust storms that promote dangerous air quality along the Wasatch Front. This work elucidates the key role that satellite remote sensing can play in documenting earlier snowmelt and other changes in the GSL basin that influence the ongoing decline of the Great Salt Lake.

Dorothy K Hall↗
NASA NTRS2000

Evaluating Ultraviolet Radiation Exposures Determined from TOMS Satellite Data at Sites of Amphibian Declines in Central and South America

Many amphibian species have experienced substantial population declines, or have disappeared altogether, during the last several decades at a number of amphibian census sites in Central and South America. This study addresses the use of satellite-derived trends in solar ultraviolet-B (UV-B; 280-320 nm) radiation exposures at these sites over the last two decades, and is intended to demonstrate a role for satellite observations in determining whether UV-B radiation is a contributing factor in amphibian declines. UV-B radiation levels at the Earth's surface were derived from the Total Ozone Mapping Spectrometer (TOMS) satellite data, typically acquired daily since 1979. These data were used to calculate the daily erythemal (sunburning) UV-B, or UV-B(sub ery), exposures at the latitude, longitude, and elevation of each of 20 census sites. The annually averaged UV-B(sub ery) dose, as well as the maximum values, have been increasing in both Central and South America, with higher levels received at the Central American sites. The annually averaged UV-B(sub ery) exposures increased significantly from 1979-1998 at all 11 Central American sites examined (r(exp 2) = 0.60 - 0.79; P<=0.015), with smaller but significant increases at five of the nine South American sites (r(exp 2) = 0.24-0.42; P<=0.05). The contribution of the highest UV-B(sub ery) exposure levels (>= 6750 J/sq m*d) to the annual UV-B(sub ery) total has increased from approx. 5% to approx. 15% in Central America over the 19 year period, but actual daily exposures for each species are unknown. Synergy among UV-B radiation and other factors, especially those associated with alterations of water chemistry (e.g., acidification) in aqueous habitats is discussed. These findings justify further research concerning whether UV-B(sub ery) radiation plays a role in amphibian population declines and extinctions.

Middleton, Elizabeth M.↗
NASA NTRS2010

An Investigation of Widespread Ozone Damage to the Soybean Crop in the Upper Midwest Determined From Ground-Based and Satellite Measurements

Elevated concentrations of ground-level ozone (O3) are frequently measured over farmland regions in many parts of the world. While numerous experimental studies show that O3 can significantly decrease crop productivity, independent verifications of yield losses at current ambient O3 concentrations in rural locations are sparse. In this study, soybean crop yield data during a 5-year period over the Midwest of the United States were combined with ground and satellite O3 measurements to provide evidence that yield losses on the order of 10% could be estimated through the use of a multiple linear regression model. Yield loss trends based on both conventional ground-based instrumentation and satellite-derived tropospheric O3 measurements were statistically significant and were consistent with results obtained from open-top chamber experiments and an open-air experimental facility (SoyFACE, Soybean Free Air Concentration Enrichment) in central Illinois. Our analysis suggests that such losses are a relatively new phenomenon due to the increase in background tropospheric O3 levels over recent decades. Extrapolation of these findings supports previous studies that estimate the global economic loss to the farming community of more than $10 billion annually.

Fishman, Jack↗
NASA NTRS2011

Integration of In-Flight and Post-Flight Water Monitoring Resources in Addressing the U.S. Water Processor Assembly Total Organic Carbon (TOC) Anomaly

Beginning in June of 2010, the total organic carbon (TOC) concentration in the U.S. Water Processor Assembly (WPA) product water started to increase. A surprisingly consistent upward TOC trend was observed through weekly ISS total organic carbon analyzer (TOCA) monitoring. As TOC is a general organic compound indicator, return of water archive samples was needed to make better-informed crew health decisions on the specific compounds of concern and to aid in WPA troubleshooting. TOCA-measured TOC was more than halfway to the health-based screening limit of 3,000 g/L before archive samples were returned. Archive samples were returned on 22 Soyuz in September 2010 and on ULF5 in November of 2010. The samples were subjected to extensive analysis. Although TOC was confirmed to be elevated, somewhat surprisingly, none of the typical target compounds were detected at high levels. After some solid detective work, it was confirmed that the TOC was associated with a compound known as dimethylsilanediol (DMSD). DMSD is believed to be a breakdown product of siloxanes which are thought to be ubiquitous in the ISS atmosphere. A toxicological limit was set for DMSD and a forward plan was developed for conducting operations in the context of understanding the composition of the TOC measured in flight. This required careful consideration of existing ISS flight rules, coordination with ISS stakeholders, and development of a novel approach for the blending of inflight TOCA data with archive results to protect crew health. Among other challenges, team members had to determine how to utilize TOCA readings when making decisions about crew consumption of WPA water. This involved balancing very real concerns associated with the assumption that TOC would continue to be comprised of only DMSD. Demonstrated teamwork, multidisciplinary awareness, and innovative problem-solving were required to respond effectively to this anomaly.

Straub, John E., II↗
NASA NTRS1997

Combustion Noise at Elevated Pressures in a Liquid-Fueled Premixed Combustor

Noise generated in gas turbine combustors can exist in several forms-broadband noise, sharp resonant peaks, and regular or intermittent nonlinear pulsing. In the present study, dynamic pressure measurements were made in several JP-5-fueled combustor configurations, at various mean pressures and temperatures. The fluctuating pressure was measured at mean pressures from 6 to 14 atm and inlet temperatures from 550 K to 850 K. The goal of the present work was to study the effect of changes in mean flow conditions on combustor noise: both broadband noise and sharp tones were considered. In general, the shape of the broadband noise spectrum was consistent from one configuration to another. The shape of the spectrum was influenced by the acoustic filtering of the combustion zone. This filtering ensured the basic consistency of the spectra. In general, the trends in broadband noise observed at low mean pressures were also seen at high mean pressures; that is, the total sound level decreased with both increasing equivalence ratio and increasing inlet temperature. The combustor configurations without a central pilot experienced higher broadband noise levels and were more susceptible to narrow peak resonances than configurations with a central pilot. The sharp peaks were more sensitive to the mean flow than was the broadband noise, and the effects were not always the same. In some situations, increasing the equivalence ratio made the sharp peaks grow, while at other conditions, increasing the equivalence ratio made the sharp peaks shrink. Thus, it was difficult to predict when resonances would occur; however, they were reproducible. Acoustic coupling between the upstream and downstream regions of the combustor may play a role in the sharp-peaked oscillations. Noise was also observed near lean blow out. As with other types of noise, lean blow out noise was affected by the combustion chamber acoustics, which apparently maintains the fluctuations at a uniform frequency. However, the actual conditions when this type of noise was experienced appeared to simply follow the lean blow out limit as it varied with mean temperature and pressure.

Darling, Douglas↗
NASA NTRS1994

A 12,000-year record of vertical deformation across the Yellowstone caldera margin: The shorelines of Yellowstone Lake

The 600 ka Yellowstone caldera exhibits several signs of unrest, the most evident of which is historic ground deformation including both uplift and subsidence. We document deformation in the area of the southern caldera across approximately 12,000 years using the postglactic shoreline terraces of Yellowstone Lake. Raised shoreline elevations were interpreted from 230 leveling profiles surveyed across flights of terraces, with an accuracy of +/- 0.5 m. Of about 11 recognizable terraces, the five most continuous raised shorelines were correlated around the lake basin to reveal deformation patterns. Net deformation over the past approximatley 3 kyr has been dominantly up within the caldera interior and slightly down along the caldera rim, relative to the extracaldera region. This uplift is roughly similar to the historic pattern and may largely represent the effects of the most recent inflation episode. Subtraction of the total estimated magnitude of inflation in this epsiode suggests that the overall trend of postglacial deformation has been subsidence. The cause of this trend is undetermined but is most likely related to the effects of regional extension and long-term cooling within the Yellowstone caldera.

Locke, William W.↗
NASA NTRS2002

Lidar Observations of Tropospheric Aerosols Over Northeastern South Africa During the ARREX and SAFARI-2000 Dry Season Experiments

During the ARREX-1999 and SAFARI-2000 Dry Season experiments a micropulse lidar (523 nm) instrument was operated at the Skukuza Airport in northeastern South Africa. The Mar was collocated with a diverse array of passive radiometric equipment. For SAFARI-2000 the processed Mar data yields a daytime time-series of layer mean/derived aerosol optical properties, including extinction-to-backscatter ratios and vertical extinction cross-section profile. Combined with 523 run aerosol optical depth and spectral Angstrom exponent calculations from available CIMEL sun-photometer data and normalized broadband flux measurements the temporal evolution of the near surface aerosol layer optical properties is analyzed for climatological trends. For the densest smoke/haze events the extinction-to-backscatter ratio is found to be between 60-80/sr, and corresponding Angstrom exponent calculations near and above 1.75. The optical characteristics of an evolving smoke event from SAFARI-2000 are extensively detailed. The advecting smoke was embedded within two distinct stratified thermodynamic layers, causing the particulate mass to advect over the instrument array in an incoherent manner on the afternoon of its occurrence. Surface broadband flux forcing due to the smoke is calculated, as is the evolution in the vertical aerosol extinction profile as measured by the Han Finally, observations of persistent elevated aerosol during ARREX-1999 are presented and discussed. The lack of corroborating observations the following year makes these observation; both unique and noteworthy in the scope of regional aerosol transport over southern Africa.

Campbell, James R.↗
NASA NTRSDate not supplied

The Effects of Freestream Turbulence on Wing-Gust Interactions

There is a growing interest in the experimental study of discrete vertical gusts motivated by the proliferation of small Uncrewed Air Systems. However, gusts are not the only unsteady flow disturbances that these vehicles are expected to encounter. Freestream turbulence is also a serious consideration. Previous work has indicated that freestream turbulence has significant effects on the flow around airfoils, so this work investigates the interaction of these two unsteady flow disturbances. Airfoils are pitched to mimic the flow angle change caused by a gust at different levels of incoming freestream turbulence. The lift generated during the gust encounters with elevated incoming freestream turbulence show that the effects on the performance of the airfoil are dependent on the turbulence intensity. Low turbulence intensity has beneficial effects, delaying stall and increasing the maximum lift, whereas higher freestream turbulence intensity delays stall without a corresponding increase in the maximum lift. A preliminary investigation of 15-trial ensemble-averaged flow fields suggests that freestream turbulence dominates the flow, but the flow features associated with the dynamic lift seen in the "clean" case are still somewhat present. However, lift curves and flow fields from individual trials indicates that the turbulence increases the unsteadiness in the interaction, but the general trends are dominated by the gust interaction. Further work is still needed to better determine the flow physics of these interactions and the interplay between repeatable and stochastic flow phenomena.

Unsteady Aerodynamics↗
NASA NTRS2022

Haiti Agriculture: Utilizing NASA Earth Observations to Evaluate the Success of Reforestation Practices in Haiti

Haiti is one of the world’s most deforested and environmentally degraded countries. Over the past 30 years, the Haiti Reforestation Partnership (HRP) has provided resources, education, and expertise to support reforestation work in Haiti. The HRP has planted over 15 million trees through their partnership with Comprehensive Development Program (CODEP). However, they have yet to conduct a comprehensive analysis of forest stand survival. The NASA DEVELOP team partnered with the HRP to aid their future silvicultural decisions using satellite imagery. Through the creation of the Monitoring of Vegetation Presence (MVP) tool in Google Earth Engine, the team produced a time series showing trends in enhanced vegetation index (EVI) from 1984 to 2021, as well as a habitat suitability map using a general model for all tree species. These provided the partner with visuals to communicate their reforestation efforts and guidance on where to apply their future efforts. The team utilized Landsat 5 Thematic Mapper (TM), Landsat 7 Enhanced Thematic Mapper Plus (ETM+), Landsat 8 Operational Land Imager (OLI), Landsat 9 OLI-2 and Sentinel-2 Multispectral Instrument (MSI) vegetation indices as indicators of stand success over time. The team also incorporated WorldClim bioclimatic variables such as precipitation and temperature, Centre National de L’Information Geo-Spatiale (CNIGS) Airborne Lidar elevation, and ancillary datasets areas suitable for future reforestation efforts. Overall, the time series showed that the demonstration forest increased in EVI at a greater rate than the surrounding area and the habitat model suggested there are 49,000 hectares of suitable habitat for planting using slope, aspect and temperature as predictor variables.

Kelli Roberts↗
NASA NTRS2004

Evaluation of High Temperature Knitted Spring Tubes for Structural Seal Applications

Control surface seals are crucial to current and future space vehicles, as they are used to seal the gaps surrounding body flaps, elevons, and other actuated exterior surfaces. During reentry, leakage of high temperature gases through these gaps could damage underlying lower temperature structures such as rudder drive motors and mechanical actuators, resulting in impaired vehicle control. To be effective, control surface seals must shield lower temperature structures from heat transfer by maintaining sufficient resiliency to remain in contact with opposing sealing surfaces through multiple compression cycles. The current seal exhibits significant loss of resiliency after a few compression cycles at elevated temperatures (i.e., 1900 F) and therefore would be inadequate for advanced space vehicles. This seal utilizes a knitted Inconel X-750 spring tube as its primary resilient element. As part of a larger effort to enhance seal resiliency, researchers at the NASA Glenn Research Center performed high temperature compression testing (up to 2000 F) on candidate spring tube designs employing material substitutions and modified geometries. These tests demonstrated significant improvements in spring tube resiliency (5.5x better at 1750 F) through direct substitution of heat treated Rene 41 alloy in the baseline knit design. The impact of geometry modification was minor within the range of parameters tested, however trends did suggest that moderate resiliency improvements could be obtained by optimizing the current spring tube geometry.

Taylor, Shawn C.↗