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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

How do drought and heat affect the response of soybean seed yield to elevated O 3 ? An analysis of 15 seasons of free–air O 3 concentration enrichment studies

The coincidence of rising ozone concentrations ([O 3 ]), increasing global temperatures, and drought episodes is expected to become more intense and frequent in the future. A better understanding of the responses of crop yield to elevated [O 3 ] under different levels of drought and high temperature stress is, therefore, critical for projecting future food production potential. Using a 15-year open-air field experiment in central Illinois, we assessed the impacts of elevated [O 3 ] coupled with variation in growing season temperature and water availability on soybean seed yield. Thirteen soybean cultivars were exposed to a wide range of season-long elevated [O 3 ] in the field using free-air O 3 concentration enrichment. Elevated [O3] treatments reduced soybean seed yield from as little as 5.3% in 2005 to 35.2% in 2010. Although cultivars differed in yield response to elevated [O 3 ] (R), ranging from 17.5% to –76.4%, there was a significant negative correlation between R and O 3 dosage. Soybean cultivars showed greater seed yield losses to elevated [O 3 ] when grown at drier or hotter conditions compared to wetter or cooler years, because the hotter and drier conditions were associated with greater O 3 treatment. However, year-to-year variation in weather conditions did not influence the sensitivity of soybean seed yield to a given increase in [O 3 ]. Collectively, this study quantitatively demonstrates that, although drought conditions or warmer temperatures led to greater O 3 treatment concentrations and O 3 -induced seed yield reduction, drought and temperature stress did not alter soybean's sensitivity to O 3 . Our results have important implications for modeling the effects of rising O 3 pollution on crops and suggest that altering irrigation practices to mitigate O 3 stress may not be effective in reducing crop sensitivity to O 3 .

60 APPLIED LIFE SCIENCES↗
DOE OSTI2025

Incorporating Elevation in Traffic-Vehicle CO-Simulation: Issues, Impacts, and Solutions

Traffic-vehicle co-simulation couples microscopic traffic simulation with full-body vehicle dynamics to assess system-level impacts on mobility, energy, and safety with greater realism. Incorporating elevation is critical for accurately modeling vehicle behavior and energy use, especially for gradient-sensitive vehicles such as electric and heavy-duty trucks. However, raw elevation data often contain noise, discontinuities, and inconsistencies. While such issues may be negligible in traditional traffic simulations, they significantly affect traffic-vehicle co-simulations where vehicle dynamics are sensitive to road grade variations. This paper investigates the impact of unprocessed elevation data on vehicle behavior and energy consumption using a 42-mile simulation along Interstate 81. We propose an elevation processing workflow that can mitigate the effects stem from elevation data issues, improving the realism and stability of traffic-vehicle co-simulation. Results show that the method effectively removes noise and abrupt elevation transitions while preserving roadway geometry.

Xu, Guanhao [ORNL] (ORCID:0000000214326357)↗
DOE OSTI2024

Photosynthetic capacity in middle-aged larch and spruce acclimates independently to experimental warming and elevated CO 2

Photosynthetic acclimation to both warming and elevated CO 2 of boreal trees remains a key uncertainty in modelling the response of photosynthesis to future climates. We investigated the impact of increased growth temperature and elevated CO 2 on photosynthetic capacity (V cmax and J max ) in mature trees of two North American boreal conifers, tamarack and black spruce. We show that V cmax and J max at a standard temperature of 25°C did not change with warming, while V cmax and J max at their thermal optima (T opt ) and growth temperature (T g ) increased. Moreover, V cmax and J max at either 25°C, T opt or T g decreased with elevated CO 2 . The J max /V cmax ratio decreased with warming when assessed at both T opt and T g but did not significantly vary at 25°C. The J max /V cmax increased with elevated CO 2 at either reference temperature. We found no significant interaction between warming and elevated CO 2 on all traits. If this lack of interaction between warming and elevated CO 2 on the V cmax , J max and J max /V cmax ratio is a general trend, it would have significant implications for improving photosynthesis representation in vegetation models. However, future research is required to investigate the widespread nature of this response in a larger number of species and biomes.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1998

Ice Surface Elevation Changes in East Antarctica from Satellite Altimetry

Estimates of the overall mass balance and seasonal and inter-annual variations in the surface mass balance are obtainable from time-series of ice surface elevations measured by satellite altimetry. Beginning in 2001, NASA's ICESat laser altimeter and lidar mission will significantly improve the range accuracy, the orbit accuracy, and the spatial coverage for measurement of ice sheet elevations (to 86 S) , as compared to previous radar altimeters designed for ocean measurements The radar altimeters on Seasat and Geosat provided ice sheet measurements to 72 S, and on ERS-1 and ERS-2 to 81 S. Although radar altimetry has significant limitations in coverage (due to loss of tracking) and accuracy over sloping surfaces, information on ice-sheet surface-elevation changes has been derived for parts of Antarctica. Recently, the accuracy of the ice measurements by Seasat (3 months of 1978) and Geosat (1985 to 1989) have been improved by new calculations of the satellite orbit heights and other altimeter corrections. Residual orbit errors and inter-satellite biases are evaluated by crossover analysis and by global adjustments to an ocean surface derived from altimeter data. The standard deviation of the orbit error is less than 9 cm, and the long-term trend in the error appears to be less than 1 cm/yr. Orbit errors can be further reduced by adjustment to the ocean surface, but false signals of several cm/yr may be also introduced by the adjustments. These false signals are caused mainly by residual errors in the altimeter corrections over the ocean, and secondary by real changes in the ocean surface elevation. Maps of ice sheet elevation changes north of 72 S are derived from Seasat-Geosat crossovers and from 4.5 years of Geosat crossovers. A notable ice thinning rate of about 50 cm/yr is found at elevations below 2200 meters between 70 and 72 S to the East of the Amery ice shelf, in both the Seasat-Geosat and Geosat-Geosat time intervals Above 2200 meters, to the ridge around 95 E, the thinning is about 10 to 20 cm/yr. For the Seasat/Geosat interval, a thickening is noted on the area East of the ridge between about 95 E and 115 E. Preliminary results from analysis of ERS-1 and ERS-2 radar altimeter data are also described.

Zwally, H. Jay↗
NASA NTRS1998

Antiproliferative effect of elevated glucose in human microvascular endothelial cells

Diabetic microangiopathy has been implicated as a fundamental feature of the pathological complications of diabetes including retinopathy, neuropathy, and diabetic foot ulceration. However, previous studies devoted to examining the deleterious effects of elevated glucose on the endothelium have been performed largely in primary cultured cells of macrovessel origin. Difficulty in the harvesting and maintenance of microvascular endothelial cells in culture have hindered the study of this relevant population. Therefore, the objective of this study was to characterize the effect of elevated glucose on the proliferation and involved signaling pathways of an immortalized human dermal microvascular endothelial cell line (HMEC-1) that possess similar characteristics to their in vivo counterparts. Human dermal microvascular endothelial cells (HMEC-1) were grown in the presence of normal (5 mM) or high D-glucose (20 mM) for 14 days. The proliferative response of HMEC-1 was compared under these conditions as well as the cAMP and PKC pathways by in vitro assays. Elevated glucose significantly inhibited (P < 0.05) HMEC-1 proliferation after 7, 10, and 14 days. This effect was not mimicked by 20 mM mannitol. The antiproliferative effect was more pronounced with longer exposure (1-14 days) to elevated glucose and was irreversible 4 days after a 10-day exposure. The antiproliferative effect was partially reversed in the presence of a PKA inhibitor, Rp-cAMP (10-50 microM), and/or a PKC inhibitor, Calphostin C (10 nM). HMEC-1 exposed to elevated glucose (20 mM) for 14 days caused an increase in cyclic AMP accumulation, PKA, and PKC activity but was not associated with the activation of downstream events such as CRE and AP-1 binding activity. These data support the hypothesis that HMEC-1 is a suitable model to study the deleterious effects of elevated glucose on microvascular endothelial cells. Continued studies with HMEC-1 may prove advantageous in delineation of the molecular pathophysiology associated with diabetic microangiopathy.

NASA Discipline Cell Biology↗
NASA NTRS2004

Advances in Measuring Antarctic Sea-Ice Thickness and Ice-Sheet Elevations with ICESat Laser Altimetry

NASA's Ice, Cloud and Land Elevation Satellite (ICESat) has been measuring elevations of the Antarctic ice sheet and sea-ice freeboard elevations with unprecedented accuracy. Since February 20,2003, data has been acquired during three periods of laser operation varying from 36 to 54 days, which is less than the continuous operation of 3 to 5 years planned for the mission. The primary purpose of ICESat is to measure time-series of ice-sheet elevation changes for determination of the present-day mass balance of the ice sheets, study of associations between observed ice changes and polar climate, and estimation of the present and future contributions of the ice sheets to global sea level rise. ICESat data will continue to be acquired for approximately 33 days periods at 3 to 6 month intervals with the second of ICESat's three lasers, and eventually with the third laser. The laser footprints are about 70 m on the surface and are spaced at 172 m along-track. The on-board GPS receiver enables radial orbit determinations to an accuracy better than 5 cm. The orbital altitude is around 600 km at an inclination of 94 degrees with a 8-day repeat pattern for the calibration and validation period, followed by a 91 -day repeat period for the rest of the mission. The expected range precision of single footprint measurements was 10 cm, but the actual range precision of the data has been shown to be much better at 2 to 3 cm. The star-tracking attitude-determination system should enable footprints to be located to 6 m horizontally when attitude calibrations are completed. With the present attitude calibration, the elevation accuracy over the ice sheets ranges from about 30 cm over the low-slope areas to about 80 cm over areas with slopes of 1 to 2 degrees, which is much better than radar altimetry. After the first period of data collection, the spacecraft attitude was controlled to point the laser beam to within 50 m of reference surface tracks over the ice sheets. Detection of ice elevation changes over select areas of the ice sheet is demonstrated with using both crossover analysis and precise-repeat track analysis. Sea ice freeboard-height distributions over the Antarctic sea pack are derived over distances of 50 km and converted into maps of average freeboard thickness and sea-ice thickness.

Zwally, H. Jay↗
NASA NTRS2005

Elevation change (2000-2004) on the Malaspina Glacier, Alaska

The glaciers of the southeastern Alaska coastal region are the largest temperate glacier meltwater source on Earth and may contribute one third of the total glacier meltwater entering the global ocean. Since melt onset and refreeeze timing in this region show a tendency toward earlier onset and longer ablation seasons, accelerated glacier wastage may be occurring. In this study we focus on one of the largest temperate glacier systems on Earth, the Malaspina Glacier. This glacier, with a length of approximately 110 km and an area of approximately square 5,000 km, has the largest piedmont lobe of any temperate glacier. The entire lobe, which lies at elevations below 600 m, is within the ablation zone. We report and interpret ice elevation change between a digital elevation model (DEM) derived from the Shuttle Radar Topography Mission (SRTM C band) observations in Feb. 2000 and ICESat Laser 1-3 observations between Feb. 2003 and Nov. 2004. We use these elevation change results, along with earlier studies, to address the spatial and temporal variability in wastage of the piedmont lobe. Between 2000 and 2004 ice elevation changes of 10-30 meters occurred across the central Malaspina piedmont lobe. From 1972/73 (USGS DEM) to 1999 (SRTM corrected for estimated winter snow accumulation) Malaspina's (Agassiz, Seward Lobe, and Marvine) mean ice thinning was estimated at -47 m with maximum thinning on parts of the lobes to -160 m. The Malaspina's accumulation area is only slightly larger than its ablation area (2,575 km2 vs. 2,433 km2); unfortunately few glaciological observations are available from this source region. Snow accumulation rates have been largely inferred from low-altitude precipitation and temperature data. Comparing sequential ICESat observations in the Malaspina source region, we estimated short-term elevation increases of up to 5 meters during the winter of 2003/04.

Sauber, J.↗
NASA NTRS1999

"Ultra"-Fast Fracture Strength of Advanced Structural Ceramic Materials Studied at Elevated Temperatures

The accurate determination of inert strength is important in reliable life prediction of structural ceramic components. At ambient temperature, the inert strength of a brittle material is typically regarded as free of the effects of slow crack growth due to stress corrosion. Therefore, the inert strength can be determined either by eliminating active species, especially moisture, with an appropriate inert medium, or by using a very high test rate. However, at elevated temperatures, the concept or definition of the inert strength of brittle ceramic materials is not clear, since temperature itself is a degrading environment, resulting in strength degradation through slow crack growth and/or creep. Since the mechanism to control strength is rate-dependent viscous flow, the only conceivable way to determine the inert strength at elevated temperatures is to utilize a very fast test rate that either minimizes the time for or eliminates slow crack growth. Few experimental studies have measured the elevated-temperature, inert (or "ultra"-fast fracture) strength of advanced ceramics. At the NASA Lewis Research Center, an experimental study was initiated to better understand the "ultra"-fast fracture strength behavior of advanced ceramics at elevated temperatures. Fourteen advanced ceramics - one alumina, eleven silicon nitrides, and two silicon carbides - have been tested using constant stress-rate (dynamic fatigue) testing in flexure with a series of stress rates including the "ultra"-fast stress rate of 33 000 MPa/sec with digitally controlled test frames. The results for these 14 advanced ceramics indicate that, notwithstanding possible changes in flaw populations as well as flaw configurations because of elevated temperatures, the strength at 33 000 MPa/sec approached the room-temperature strength or reached a higher value than that determined at the conventional test rate of 30 MPa/sec. On the basis of the experimental data, it can be stated that the elevated-temperature, inert strength of an advanced ceramic material can be defined as the strength where no slow crack growth takes place at the temperature.

Choi, Sung R.↗
NASA NTRS2011

Modeling of Firn Compaction for Estimating Ice-Sheet Mass Change from Observed Ice-Sheet Elevation Change

Changes in ice-sheet surface elevation are caused by a combination of ice-dynamic imbalance, ablation, temporal variations in accumulation rate, firn compaction and underlying bedrock motion. Thus, deriving the rate of ice-sheet mass change from measured surface elevation change requires information on the rate of firn compaction and bedrock motion, which do not involve changes in mass, and requires an appropriate firn density to associate with elevation changes induced by recent accumulation rate variability. We use a 25 year record of surface temperature and a parameterization for accumulation change as a function of temperature to drive a firn compaction model. We apply this formulation to ICESat measurements of surface elevation change at three locations on the Greenland ice sheet in order to separate the accumulation-driven changes from the ice-dynamic/ablation-driven changes, and thus to derive the corresponding mass change. Our calculated densities for the accumulation-driven changes range from 410 to 610 kg/cu m, which along with 900 kg/cu m for the dynamic/ablation-driven changes gives average densities ranging from 680 to 790 kg/cu m. We show that using an average (or "effective") density to convert elevation change to mass change is not valid where the accumulation and the dynamic elevation changes are of opposite sign.

Li, Jun↗
NASA NTRS2012

Comparison of Surface Elevation Changes of the Greenland and Antarctic Ice Sheets from Radar and Laser Altimetry

A primary purpose of satellite altimeter measurements is determination of the mass balances of the Greenland and Antarctic ice sheets and changes with time by measurement of changes in the surface elevations. Since the early 1990's, important measurements for this purpose have been made by radar altimeters on ERS-l and 2, Envisat, and CryoSat and a laser altimeter on ICESat. One principal factor limiting direct comparisons between radar and laser measurements is the variable penetration depth of the radar signal and the corresponding location of the effective depth of the radar-measured elevation beneath the surface, in contrast to the laser-measured surface elevation. Although the radar penetration depth varies significantly both spatially and temporally, empirical corrections have been developed to account for this effect. Another limiting factor in direct comparisons is caused by differences in the size of the laser and radar footprints and their respective horizontal locations on the surface. Nevertheless, derived changes in elevation, dHldt, and time-series of elevation, H(t), have been shown to be comparable. For comparisons at different times, corrections for elevation changes caused by variations in the rate offrrn compaction have also been developed. Comparisons between the H(t) and the average dH/dt at some specific locations, such as the Vostok region of East Antarctic, show good agreement among results from ERS-l and 2, Envisat, and ICESat. However, Greenland maps of dHidt from Envisat and ICESat for the same time periods (2003-2008) show some areas of significant differences as well as areas of good agreement. Possible causes of residual differences are investigated and described.

Zwally, H. Jay↗
NASA NTRS2021

Using Remote Sensing to Monitor the Spring Phenology of Acadia National Park Across Elevational Gradients

Greenup dates and their responses to elevation and temperature variations across the mountains of Acadia National Park are monitored using remote sensing data, including Landsat 8 surface reflectances (at a 30-m spatial resolution) and VIIRS reflectances adjusted to a nadir view (gridded at a 500-m spatial resolution), during the 2013–2016 growing seasons. The 30-m resolution provides a better scale for studying the phenology variation across elevational gradients than the 500-m resolution, as greenup dates monitored at 30-m scale have better agreement with leaf-out dates recorded in the field alongside the north–south-oriented hiking trails on three of the park’s tallest mountains (466 m, 418 m, and 380 m), and can provide landcover-specific analysis. The spring phenology responses to temperature and elevation vary among different spatial scales. Greenup dates of Acadia National Park monitored at 30-m scale show a weak advancing trend with higher spring temperature, while greenup dates monitored at 500 m show a weak delaying trend. The species mix within landcover at 30-m scale could weaken the advancing trend detected at field observation level. The landcover mix and elevation variation within 500-m scale could alter the spring phenology response to spring temperature variation. Greenup dates monitored at both 30-m and 500-m scales vary among different elevational zones, aspects, landcovers, and years. However, the relationship between greenup dates and elevation is rather weak.

Yan Liu↗
DOE OSTI2025

Groundwater table elevation and temperature from 2015 to 2024 at the Lower Montane site in the East River Watershed, Colorado.

This groundwater level elevation and temperature data package is aimed at improving the predictive understanding of hydro-biogeochemical processes at the lower montane site in the East River Watershed, Colorado. The dataset is obtained using pressure transducers placed in shallow wells in the floodplain. This dataset contains data from wells with Location ID's ER-DOW (alias DO1West), ER-DOE (alias DO2East), ER-MBA1 (alias M1Bend1), ER-MBA2 (alias M1Bend2), ER-UPW (alias UP1West), ER-UPM (alias UP2), ER-UPE (alias UP3East). Another dataset contains the data from wells with Location ID's ER-CPA1 to ER-CPA6. Each file contains the water level elevation and the water temperature. Water level elevation has been obtained using the barometric pressure from the pressure transducer (Hobos sensor) in the well, barometric pressure from a sensor in air located at the same site (lower montane), depth from top-of-casing (TOC) to sensor measurement point, and TOC elevation. Data have been checked with a few measurements of water table depths. A real-time kinematic (RTK) global positioning system (GPS) has been used to survey the TOC (data in file Well_Location.csv). The water level elevation is given in UTM13N Geoid2012AB. While depth to water level is not present in the data files, it can be easily calculated with the TOC and distance to ground provided in the GPS coordinate file. The dataset quality is discussed in Collection/Analysis section of the methods. Time-series of measurements were initially added to the archive for the period 2015 to 2019, and later updated with time-series until 2024 (end of data collection). The dataset contains 8 *.csv data files, and 3 *.csv metadata files. Feel free to contact the author with any questions or collaboration interests. The publication year was updated from "2020" to "2025" to reflect the revised version of this dataset.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Groundwater table elevation and temperature from 2015 to 2024 across Meander C at the Lower Montane site in the East River Watershed, Colorado.

This groundwater level elevation and temperature data package is aimed at improving the predictive understanding of hydro-biogeochemical processes at the lower montane site in the East River Watershed, Colorado. The dataset is obtained using pressure transducers placed in shallow wells in the floodplain. This dataset contains data from wells ER-CPA1 to ER-CPA6. Another dataset contains the data from wells at nearby Locations. Each file contains the water level elevation and the water temperature. Water level elevation has been obtained using the barometric pressure from the pressure transducer (Hobos sensor) in the well, barometric pressure from a sensor in air located at the same site (lower montane), depth from top-of-casing (TOC) to sensor measurement point, and TOC elevation. Data have been checked with a few measurements of water table depths. A real-time kinematic (RTK) global positioning system (GPS) has been used to survey the TOC (data in file Well_Location.csv). The water level elevation is given in UTM13N Geoid2012AB. While depth to water level is not present in the data files, it can be easily calculated with the TOC and distance to ground provided in the GPS coordinate file. The dataset quality is discussed in Collection/Analysis section of the methods. Time-series of measurements were initially added to the archive for the period 2015 to 2019, and later updated with time-series until 2024 (end of data collection). The dataset contains 7 *.csv data files, and 3 *.csv metadata files. Feel free to contact the author with any questions or collaboration interests. The publication year was updated from "2020" to "2025" to reflect the revised version of this dataset.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS2013

Sensitivity of Downward Longwave Surface Radiation to Moisture and Cloud Changes in a High-elevation Region

Several studies have suggested enhanced rates of warming in high-elevation regions since the latter half of the twentieth century. One of the potential reasons why enhanced rates of warming might occur at high elevations is the nonlinear relationship between downward longwave radiation (DLR) and specific humidity (q). Using ground-based observations at a high-elevation site in southwestern Colorado and coincident satellite-borne cloud retrievals, the sensitivity of DLR to changes in q and cloud properties is examined and quantified using a neural network method. It is also used to explore how the sensitivity of DLR to q (dDLR/dq) is affected by cloud properties. When binned by season, dDLR/dq is maximum in winter and minimum in summer for both clear and cloudy skies. However, the cloudy-sky sensitivities are smaller, primarily because (1) for both clear and cloudy skies dDLR/dq is proportional to 1/q, for q>0.5 g/kg, and (2) the seasonal values of q are on average larger in the cloudy-sky cases than in clear-sky cases. For a given value of q, dDLR/dq is slightly reduced in the presence of clouds and this reduction increases as q increases. In addition, DLR is found to be more sensitive to changes in cloud fraction when cloud fraction is large. In the limit of overcast skies, DLR sensitivity to optical thickness decreases as clouds become more opaque. These results are based on only one high-elevation site, so the conclusions here need to be tested at other high-elevation locations.

cloud physics↗
NASA NTRS2024

Short-Term Elevated Temperature Mechanical Performance and Microstructure of A Niobium-Zirconium Alloy Produced via Laser Powder Bed Fusion In-Situ Alloying

Nb-1Zr is a readily fabricable, dispersion-strengthened niobium alloy with improved elevated temperature properties compared to commercially pure niobium. This low to moderate strength niobium alloy is desirable in thermal management systems for fission power and propulsion applications; however, pre-alloyed spherical feedstock for powder-based additive manufacturing processes is generally unavailable. Laser powder bed fusion (L-PBF) in-situ alloying of a Nb-1Zr chemistry was performed using a high-purity niobium feedstock coated with 1 wt% of zirconium-based ceramic compound nano-powders: ZrO 2 , ZrC, and ZrH 2 . The additively manufactured material was mechanically tested at elevated temperatures within a controlled environment in the as-built condition. For comparison, traditionally manufactured wrought feedstock was also tested within an identical environment. Examination of the materials’ microstructure and short-term elevated temperature mechanical response determined: in-situ alloying of spherical Nb powder feedstock with Zr-based ceramic nanoparticles can be successfully implemented; the ZrO 2 addition offered the greatest elevated temperature stability and strength but exhibited brittle behavior; the ZrC addition achieved a balance of room temperature ductility and elevated temperature strength; and the ZrH 2 -modified material had the lowest as-built interstitial content and showed high ductility with mechanical performance most similar to wrought Nb-1Zr.

Niobium Alloy↗
NASA NTRS1984

An interactive technique to generate digital elevation data using a vidicon camera

A technique is proposed for the semi-automatic digitization of topographic maps using a vidicon camera interfaced with a mini-computer system. The required input is a black and white map that shows only contour lines and corresponding elevation values such as the advance prints of 7.5 minute USGS topographic sheets. A set of image processing algorithms is implemented on an image of the contour map acquired by a vidicon camera. The system developed performs extraction of contour lines, tagging elevation values and subsequent interpolation of elevations to produce, in 5 sec. x 5 sec. intervals of latitude and longitude, digital elevation matrices. The interpolation of elevations for non-contour points is achieved using a steepest descent algorithm. A communications capability allows the final data to be transferred over telephone lines to an off-site unit such as the floppy disk or a micro-computer.

Sircar, J. K.↗
NASA NTRS1986

Automated matching of pairs of SIR-B images for elevation mapping

During the SIR-B mission in October 1984, a significant number of overlapping synthetic aperture radar (SAR) images of various ground areas was collected. This has offered the first opportunity to perform stereo analyses on images from space that cover large ground areas to determine elevation information. This paper presents the preliminary results of an investigation to obtain elevation data from stereo pairs of SIR-B images. First, the accuracy with which elevation information can be derived from SIR-B image pairs is evaluated theoretically. It is shown that elevation accuracy is a function of the slant range resolution, the incidence angles with which the stereo pair is obtained, the accuracies in spacecraft state estimation, and determination of corresponding pixels in the stereo pair. Next, a hierarchical method is developed to match the corresponding pixels. This method involves iterative removal of local distortions and correlations of pairs of local neighborhoods in the two images. Since it is necessary to perform the matching at every pixel in the image, it is very computationally intensive. Therefore, it has been implemented on the Massively Parallel Processor (MPP) at the Goddard Space Flight Center (GSFC). The MPP's speed permits two iterations of this technique to operate on a pair of 512 x 512 images within 7 s. Results of applying this algorithm of SIR-B images of Mount Shasta, CA, are shown. The matching algorithm performs well in regions of the image with significant features. An approximate elevation image derived from the matching process corresponds to published topographic map data, except for certain obvious discontinuities.

Ramapriyan, H. K.↗
NASA NTRS1989

Evaluation of a strain-gage load calibration on a low-aspect-ratio wing structure at elevated temperature

The environmental aspect of elevated temperature and its relationship to the science of strain gage calibrations of aircraft structures are addressed. A section of a wing designed for a high-speed aircraft structure was used to study this problem. This structure was instrumented with strain gages calibrated at both elevated and room temperatures. Load equations derived from a high-temperature load calibration were compared with equations derived from an identical load calibration at room temperature. The implications of the high temperature load calibration were studied from the viewpoint of applicability and necessity. Load equations derived from the room temperature load calibration resulted in generally lower equation standard errors than equations derived from the elevated temperature load calibration. A distributed load was applied to the structure at elevated temperature and strain gage outputs were measured. This applied load was then calculated using equations derived from both the room temperature and elevated temperature calibration data. It was found that no significant differences between the two equation systems existed in terms of computing this applied distributed load, as long as the thermal shifts resulting from thermal stresses could be identified. This identification requires a heating of the structure. Therefore, it is concluded that for this structure, a high temperature load calibration is not required. However, a heating of the structure is required to determine thermal shifts.

Reardon, Lawrence F.↗