Search NASA⌕ Search

SEARCH · Search NASA

Results for “subsurface reflectivity imaging”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Evidence for highly reflecting materials on the surface and subsurface of Venus

Radar images at a 12.5-centimeter wavelength made with the Goldstone radar interferometer in 1980 and 1986, together with lunar radar images and recent Venera 15 and 16 data, indicate that material on the surface and subsurface of Venus has a Fresnel reflectivity in excess of 50 percent. Such high reflectivities have been reported on the surface in mountainous regions. Material of high reflectivity may also underlie lower reflectivity surficial materials of the plains regions, where it has been excavated by impact cratering in some areas.

Jurgens, R. F.↗
NASA NTRS1973

The Apollo 17 Lunar Sounder

The Apollo Lunar Sounder Experiment, a coherent radar operated from lunar orbit during the Apollo 17 mission, has scientific objectives of mapping lunar subsurface structure, surface profiling, surface imaging, and galactic noise measurement. Representative results from each of the four disciplines are presented. Subsurface reflections have been interpreted in both optically and digitally processed data. Images and profiles yield detailed selenomorphological information. The preliminary galactic noise results are consistent with earlier measurements by other workers.

Phillips, R. J.↗
NASA NTRS1973

The Apollo 17 Lunar Sounder.

The Apollo Lunar Sounder Experiment (ALSE) was a three-frequency wide-band coherent radar system operated from lunar orbit during the Apollo 17 mission. The scientific objectives of the experiment include the mapping of subsurface structure, surface profiling, surface imaging, and galactic noise measurement. Examples of subsurface reflections are discussed, giving attention to VHF sounding, HF2 sounding, and HF1 sounding. Examples of imagery and profiles are also considered, taking into account various craters and profile high points.

Phillips, R. J.↗
NASA NTRS2009

Mid-Infrared Reflectance Imaging of Thermal-Barrier Coatings

An apparatus for mid-infrared reflectance imaging has been developed as means of inspecting for subsurface damage in thermal-barrier coatings (TBCs). The apparatus is designed, more specifically, for imaging the progression of buried delamination cracks in plasma-sprayed yttria-stabilized zirconia coatings on turbine-engine components. Progression of TBC delamination occurs by the formation of buried cracks that grow and then link together to produce eventual TBC spallation. The mid-infrared reflectance imaging system described here makes it possible to see delamination progression that is invisible to the unaided eye, and therefore give sufficiently advanced warning before delamination progression adversely affects engine performance and safety. The apparatus (see figure) includes a commercial mid-infrared camera that contains a liquid-nitrogen-cooled focal plane indium antimonide photodetector array, and imaging is restricted by a narrow bandpass centered at wavelength of 4 microns. This narrow wavelength range centered at 4 microns was chosen because (1) it enables avoidance of interfering absorptions by atmospheric OH and CO2 at 3 and 4.25 microns, respectively; and (2) the coating material exhibits maximum transparency in this wavelength range. Delamination contrast is produced in the midinfrared reflectance images because the introduction of cracks into the TBC creates an internal TBC/air-gap interface with a high diffuse reflectivity of 0.81, resulting in substantially higher reflectance of mid-infrared radiation in regions that contain buried delamination cracks. The camera is positioned a short distance (.12 cm) from the specimen. The mid-infrared illumination is generated by a 50-watt silicon carbide source positioned to the side of the mid-infrared camera, and the illumination is collimated and reflected onto the specimen by a 6.35-cm-diameter off-axis paraboloidal mirror. Because the collected images are of a steady-state reflected intensity (in contrast to the transient thermal response observed in infrared thermography), collection times can be lengthened to whatever extent needed to achieve desired signal-to-noise ratios. Each image is digitized, and the resulting data are processed in several steps to obtain a true mid-infrared reflectance image. The raw image includes thermal radiation emitted by the specimen in addition to the desired reflected radiation. The thermal-radiation contribution is eliminated by subtracting the image obtained with the illumination off from the image obtained with the illumination on. A flat-field correction is then made to remove the effects of non-uniformities in the illumination level and pixel-to-pixel variations in sensitivity. This correction is performed by normalizing to an image of a standard object that has a known reflectance at a wavelength of 4 microns. After correction, each pixel value is proportional to the reflectance (at a wavelength of 4-microns) at the corresponding location on the specimen. Mid-infrared reflectance imaging of specimens that were thermally cyc led for different numbers of cycles was performed and demonstrated t hat mid-infrared reflectance imaging was able to monitor the gradual delamination progression that occurs with continued thermal cycling . Reproducible values were obtained for the reflectance associated w ith an attached and fully delaminated TBC, so that intermediate refle ctance values could be interpreted to successfully predict the numbe r of thermal cycles to failure.

Edlridge, Jeffrey I.↗
NASA NTRS2003

Numerical Simulations of Silverpit Crater Collapse

The Silverpit crater is a recently discovered, 60-65 Myr old complex crater, which lies buried beneath the North Sea, about 150 km east of Britain. High-resolution images of Silverpit's subsurface structure, provided by three-dimensional seismic reflection data, reveal an inner-crater morphology similar to that expected for a 5-8 km diameter terrestrial crater. The crater walls show evidence of terrace-style slumping and there is a distinct central uplift, which may have produced a central peak in the pristine crater morphology. However, Silverpit is not a typical 5-km diameter terrestrial crater, because it exhibits multiple, concentric rings outside the main cavity. External concentric rings are normally associated with much larger impact structures, for example Chicxulub on Earth, or Orientale on the Moon. Furthermore, external rings associated with large impacts on the terrestrial planets and moons are widely-spaced, predominantly inwardly-facing, asymmetric scarps. However, the seismic data show that the external rings at Silverpit represent closely-spaced, concentric faultbound graben, with both inwardly and outwardly facing fault-scarps. This type of multi-ring structure directly analogous to the Valhalla-type multi-ring basins found on the icy satellites. Thus, the presence and style of the multiple rings at Silverpit is surprising given both the size of the crater and its planetary setting. A further curiosity of the Silverpit structure is that the external concentric rings appear to be extensional features on the West side of the crater and compressional features on the East side. The crater also lies in a local depression, thought to be created by postimpact movement of a salt layer buried beneath the crater.

Collins, G. S.↗
NASA NTRS2003

Numerical Simulations of Silverpit Crater Collapse

The Silverpit crater is a recently discovered, 60-65 Myr old complex crater, which lies buried beneath the North Sea, about 150 km east of Britain. High-resolution images of Silverpit's subsurface structure, provided by three-dimensional seismic reflection data, reveal an inner-crater morphology similar to that expected for a 5-8 km diameter terrestrial crater. The crater walls show evidence of terracestyle slumping and there is a distinct central uplift, which may have produced a central peak in the pristine crater morphology. However, Silverpit is not a typical 5-km diameter terrestrial crater, because it exhibits multiple, concentric rings outside the main cavity. External concentric rings are normally associated with much larger impact structures, for example Chicxulub on Earth, or Orientale on the Moon. Furthermore, external rings associated with large impacts on the terrestrial planets and moons are widely-spaced, predominantly inwardly-facing, asymmetric scarps. However, the seismic data show that the external rings at Silverpit represent closely-spaced, concentric fault-bound graben, with both inwardly and outwardly facing faults-carps. This type of multi-ring structure is directly analogous to the Valhalla-type multi-ring basins found on the icy satellites. Thus, the presence and style of the multiple rings at Silverpit is surprising given both the size of the crater and its planetary setting.

Collins, G. S.↗
NASA NTRS2014

Estimating Major Ion and Nutrient Concentrations in Mangrove Estuaries in Everglades National Park Using Leaf and Satellite Reflectance

Coastal mangrove ecosystems are under duress worldwide because of urban development, sea-level rise, and climate change, processes that are capable of changing the salinity and nutrient concentration of the water utilized by the mangroves. This study correlates long-term water chemistry in mangrove environments, located in Everglades National Park,with mangrove spectral reflectance measurements made at both the leaf and canopy scales. Spectral reflectance measurements were collected using a handheld spectrometer for leaf-level measurements and Landsat 5TMdata for regional coverage. Leaf-level reflectance data were collected from three mangrove species (i.e., red, black and white mangroves) across two regions; a tall mangrove (approximately 18m) and dwarf mangrove (1- 2 m) region. The reflectance data were then used to calculate a wide variety of biophysical reflectance indices (e.g., NDVI, EVI, SAVI) to determine signs of stress. Discrete, quarterly water samples from the surface water, groundwater, and pore water (20 and 85 cm depths) and daily autonomous surface water samples were collected at each site and analyzed for major anions (Cl(−) and SO(2(-)/4)), cations (Na(+), K(+), Mg(sup 2(+)), and Ca(sup 2(+)), total nitrogen (TN) and total phosphorus (TP).Mangrove sites that exhibited the highest salinity and ionic concentrations in the surface and subsurface water also had the lowest near-infrared reflectance at both the leaf and satellite levels. Seasonal reflectance responses were measured in the near-infrared (NIR) wavelengths at both the leaf and canopy scales and were strongly correlated with nutrient and ionic concentrations in the surface and subsurface water, even though there was no significant separability between the three mangrove species. Study sites that experienced the greatest variability in surface and subsurface water ionic concentrations also exhibited the greatest fluctuations in NIR spectral reflectance. Landsat 5TM images were able to detect tall and dwarf mangroves by the differences in spectral indices (e.g., NDVI, NDWI, and EVI) because of the variability in the background conditions amongst the environments. In addition, Landsat 5TM images spanning 16 years (1993- 2009) were successfully used to estimate the seasonal variability in ionic concentrations in the surface water across the Florida Coastal mangrove ecotone. This study has shown that water chemistry can be estimated indirectly by measuring the change in spectral response at the leaf- or satellite-scale. Furthermore, the results of this research may be extrapolated to similar coastal mangrove systems throughout the Caribbean and world-wide wherever red, black, and white mangroves occur.

Mangroves↗
NASA NTRS1992

The Quickest, Lowest-cost Lunar Resource Assessment Program: Integrated High-tech Earth-based Astronomy

Science and technology applications for the Moon have not fully kept pace with technical advancements in sensor development and analytical information extraction capabilities. Appropriate unanswered questions for the Moon abound, but until recently there has been little motivation to link sophisticated technical capabilities with specific measurement and analysis projects. Over the last decade enormous technical progress has been made in the development of (1) CCD photometric array detectors; (2) visible to near-infrared imaging spectrometers; (3)infrared spectroscopy; (4) high-resolution dual-polarization radar imaging at 3.5, 12, and 70 cm; and equally important (5) data analysis and information extraction techniques using compact powerful computers. Parts of each of these have been tested separately, but there has been no programmatic effort to develop and optimize instruments to meet lunar science and resource assessment needs (e.g., specific wavelength range, resolution, etc.) nor to coordinate activities so that the symbiotic relation between different kinds of data can be fully realized. No single type of remotely acquired data completely characterizes the lunar environment, but there has been little opportunity for integration of diverse advanced sensor data for the Moon. Two examples of technology concepts for lunar measurements are given. Using VIS/near-IR spectroscopy, the mineral composition of surface material can be derived from visible and near-infrared radiation reflected from the surface. The surface and subsurface scattering properties of the Moon can be analyzed using radar backscattering imaging.

Pieters, Carle M.↗
NASA NTRS2004

Potential of Radar Imaging and Sounding Methods in Mapping Heavily Eroded Impact Craters: Mapping Some Structural Elements of the Hico Crater, TX

Shuttle Radar Topography Mission (SRTM) and Ground Penetrating Radar (GPR) data collected over an area north of the town of Hico, central Texas, have been used to map disturbances in the surface topography and subsurface stratigraphy. The Radar topography results confirm the presence of multiple rings suggestive of an impact crater. Correlation between the orbital SRTM and on-the-ground GPR field data are affected by different biases related to variations in terrain and vegetation cover. Nevertheless, the correspondence of the two data sets supports the earlier conclusions that a complex, multiple ring impact structure is reflected in the topography of this area. The SRTM data reveal three previously unrecognized rings; with the outermost ring some 5-6 km in diameter. The crater appears to be significantly larger than the size (2.5 km diameter) previously inferred on the basis of aerial images. In addition, the GPR data suggest the presence of subsurface faulting that spatially coincides with the two inner rings of the crater. This suggests that the topographic rings are structurally controlled by faulting.

Heggy, E.↗
NASA NTRS2021

The Science Case for Spacecraft Exploration of the Uranian Satellites: Candidate Ocean Worlds in an Ice Giant System

The 27 satellites of Uranus are enigmatic, with dark surfaces coated by material that could be rich in organics. Voyager 2 imaged the southern hemispheres of Uranus’s five largest “classical” moons—Miranda, Ariel, Umbriel, Titania, and Oberon, as well as the largest ring moon, Puck—but their northern hemispheres were largely unobservable at the time of the flyby and were not imaged. Additionally, no spatially resolved data sets exist for the other 21 known moons, and their surface properties are essentially unknown. Because Voyager 2 was not equipped with a near-infrared mapping spectrometer, our knowledge of the Uranian moons’ surface compositions, and the processes that modify them, is limited to disk-integrated data sets collected by ground- and space-based telescopes. Nevertheless, images collected by the Imaging Science System on Voyager 2 and reflectance spectra collected by telescope facilities indicate that the five classical moons are candidate ocean worlds that might currently have, or had, liquid subsurface layers beneath their icy surfaces. To determine whether these moons are ocean worlds, and to investigate Uranus’s ring moons and irregular satellites, close-up observations and measurements made by instruments on board a Uranus orbiter are needed.

Richard J. Cartwright↗
NASA NTRS2024

Dielectric Permittivity Measurements of Geologic Samples at Venus Surface Temperatures

Synthetic-aperture radar (SAR) and radar sounding are two powerful remote sensing techniques used to examine the surface and subsurface of planets. Their value is critical in the case of Venus due to this planet’s global and visually opaque cloud layer. The recently selected VERITAS and EnVision orbital missions, slated to study the planet in the early 2030’s, employ radar instruments to image the surface (VERITAS and EnVision) and probe the subsurface (EnVision). For both techniques, the complex dielectric permittivity of the surface and subsurface materials control radar backscatter intensity and penetration depth. Since the 1970’s, many studies have characterized the dielectric permittivity of geologic materials collected both on Earth and on the Moon to constrain the radar reflectivity and transparency at a variety of radar frequencies [e.g., 1]. Two consistent findings from those studies are that complex permittivity depends on both the density (or porosity) and the composition of the material. Denser materials and more metal-rich compositions tend to have higher permittivity values and to incur greater propagation path loss. Water content also elevates permittivity of otherwise dry rocks/soils/regolith [e.g., 2]. However, permittivity is independent of frequency for the 0.5-18 GHz range, within which SAR imaging commonly lies. The one aspect poorly explored thus far is the effect of elevated temperatures on dielectric permittivity. Previous work suggests that increased lattice vibrations and flow of free electrons associated with an increase in temperature elevate both the real (reflectivity) and imaginary (path loss) parts of the complex permittivity. We are currently conducting a 3-year campaign to measure the complex dielectric permittivity of Venusrelevant geologic materials at Venus surface temperatures (380°C - 460°C) and with frequencies relevant to VERITAS, EnVision, and Magellan imaging synthetic aperture radars.

M Barmatz↗
NASA NTRS1985

Microwave hydrology: A trilogy

Microwave hydrology, as the term in construed in this trilogy, deals with the investigation of important hydrological features on the Earth's surface as they are remotely, and passively, sensed by orbiting microwave receivers. Microwave wavelengths penetrate clouds, foliage, ground cover, and soil, in varying degrees, and reveal the occurrence of standing liquid water on and beneath the surface. The manifestation of liquid water appearing on or near the surface is reported by a microwave receiver as a signal with a low flux level, or, equivalently, a cold temperature. Actually, the surface of the liquid water reflects the low flux level from the cosmic background into the input terminals of the receiver. This trilogy describes and shows by microwave flux images: the hydrological features that sustain Lake Baykal as an extraordinary freshwater resource; manifestations of subsurface water in Iran; and the major water features of the Congo Basin, a rain forest.

Stacey, J. M.↗
NASA NTRS1974

The Apollo Lunar Sounder radar system

The objectives of the Apollo 17 Lunar Sounder Experiment (ALSE) were to detect subsurface geologic structures, to generate a continuous lunar profile, and to image the moon at radar wavelengths. A three-wavelength synthetic-aperture radar (SAR) operating at 60, 20, and 2 m wavelengths was designed to attain these objectives. The design choices reflected a balance of scientific requirements versus Apollo mission and hardware constraints. The radar data from the lunar mission were recorded on photographic film in a conventional SAR format, and were returned to earth for processing. A combination of optical and digital processing and exploitation techniques was applied to the scientific interpretation of the data. Some preliminary results from the lunar mission have been obtained.

Porcello, L. J.↗
NASA NTRS2001

Estimating Expressed Temperature and Fractional Area of Hot Lava at the Kilauea Vent with AVIRIS Spectral Measurements

Imaging spectroscopy offers a framework based in physics and chemistry for scientific investigation of a wide range of phenomena of interest in the Earth environment. In the scientific discipline of volcanology knowledge of lava temperature and distribution at the surface provides insight into the volcano status and subsurface processes. A remote sensing strategy to measure surface lava temperatures and distribution would support volcanology research. Hot targets such as molten lava emit spectral radiance as a function of temperature. A figure shows a series of Planck functions calculated radiance spectra for hot targets at different temperatures. A maximum Lambertian solar reflected radiance spectrum is shown as well. While similar in form, each hot target spectrum has a unique spectral shape and is distinct from the solar reflected radiance spectrum. Based on this temperature-dependent signature, imaging spectroscopy provides an innovative approach for the remote-sensing-based measurement of lava temperature. A natural site for investigation of the measurement of lava temperature is the Big Island of Hawaii where molten lava from the Kilauea vent is present at the surface. In the past, Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data sets have been used for the analysis of hot volcanic targets and hot burning fires. The research presented here builds upon and extends this earlier work. The year 2000 Hawaii AVIRIS data set has been analyzed to derive lava temperatures taking into account factors of fractional fill, solar reflected radiance, and atmospheric attenuation of the surface emitted radiance. The measurements, analyses, and current results for this research are presented here.

Green, Robert O.↗
NASA NTRS2004

Searching for Terrain Softening near Mercury's North Pole

In 1999, following the initial discovery of radar bright craters near both poles of Mercury measured the depth-todiameter (d/D) ratios of 170 impact craters in Mariner 10 images covering four different regions on Mercury s surface. Rapid softening of crater structure, indicated by lower d/D ratios, could indicate the possibility of subsurface water ice in Mercury's terrain originating from an internal source in the planet. Their study included 3 specific radar bright craters suggested to contain ice. They concluded that no terrain softening was apparent, and a rapidly emplaced exogenic water source was the most likely source for the proposed ice in these craters. Recent radar observations of the Mercurian North pole have pinpointed many additional radar bright areas with a resolution 10x better than previous radar measurements, and which correlate with craters imaged by Mariner 10. These craters are correlated with regions that are permanently shaded from direct sunlight, and are consistent with observations of clean water ice. We have expanded the initial study by Barlow et al. to include d/D measurements of 12 craters newly identified as radar bright at latitudes poleward of +80o. The radar reflectivity resemblances to Mars south polar cap and echoes from three icy Galilean satellites suggest that these craters too may have polar ice on Mercury. The effect of subsurface H20 on impact craters is a decrease in its d/D ratio, and softening of crater rims over a period of time. The study of Barlow et al., focused on determining the d/D ratios of 170 impact craters in the Borealis (north polar), Tolstoj (equatorial), Kuiper (equatorial), and Bach (south polar) quadrangles. This work focuses on the newly discovered radar bright craters, investigating their d/D ratios as an expansion of the earlier work..We compare our results to the statistical results from Barlow et al. here. With the upcoming Messenger spacecraft mission to Mercury, this is an especially timely study whose result could potentially help the Messenger team as they develop a mission strategy.

Cobian, P. S.↗
NASA NTRS1994

Polar volatiles on Mercury and the Moon

The possibility that condensed volatiles might be stable in the permanently shadowed polar regions of the Moon and Mercury has been anticipated in a number of theoretical studies. In 1992, VLA-Goldstone and Arecibo observations revealed the presence of bright, depolarized radar features near the poles of Mercury that have been widely interpreted as evidence for the presence of polar ice deposits. Recently acquired high-resolution Arecibo radar images show that the anomalous radar features are concentrated in crater-sized regions whose locations can be made to coincide exactly with the locations of known impact craters in the Mariner-10 images. These new Arecibo images provide an unusual opportunity to learn more about the distribution and history of Mercury's polar ice deposits. We have constructed a thermal model that can predict surface and subsurface temperatures within impact craters on Mercury and the Moon. Included in the calculations are the effects of 1-dimensional subsurface heat conduction, direct sunlight, multiply reflected sunlight within the crater, and re-radiated infrared radiation within the crater. We also use realistic crater topographic profiles for larger flat-floored craters as well as smaller spherical bowl-shaped craters.

Paige, D. A.↗
NASA NTRS2019

PERISCOPE: PERIapsis Subsurface Cave OPtical Explorer

In this NIAC report we present a new technique enabling a practical option for mapping these structures at a relatively low cost: Photon Time-of-Flight (PTOF) imaging. Consider a scene with a surface that is in a camera's line of sight, with unknown geometry beyond the line of sight. PTOF works by directing laser pulses onto the visible surface and detecting the returned light after it reflects off the visible surface, onto the hidden surfaces, and back to the detector. An algorithm then reconstructs a 3d model of the hidden surface. The information gained has a wide variety of applications across NASA, the scientific community, the burgeoning commercial space industry, and in commercial and industrial use here on Earth.

Exploration↗