Application of multispectral radar and LANDSAT imagery to geologic mapping in death valley

Side-Looking Airborne Radar (SLAR) images, acquired by JPL and Strategic Air Command Systems, and visible and near-infrared LANDSAT imagery were applied to studies of the Quaternary alluvial and evaporite deposits in Death Valley, California. Unprocessed radar imagery revealed considerable variation in microwave backscatter, generally correlated with surface roughness. For Death Valley, LANDSAT imagery is of limited value in discriminating the Quaternary units except for alluvial units distinguishable by presence or absence of desert varnish or evaporite units whose extremely rough surfaces are strongly shadowed. In contrast, radar returns are most strongly dependent on surface roughness, a property more strongly correlated with surficial geology than is surface chemistry

Imaging Radar Observations Of Normal Faults In Tibet

NASA/JPL has an ongoing program to study land processes that will lead to a better understanding of the geologic evolution of the continents and the history of global climate change. Northwestern China and Tibet are key areas for these investigations because arid regions such as these retain the record of climate change and a wide variety of large-scale structures are present throughout the area as a result of the continuing collision between the Indian and Asian plates. During the Shuttle Imaging Radar Missions (SIR-A and SIR-B) a number of image swaths were acquired over the People's Republic of China that show interesting landforms indicative of climate change and large-scale faulting in the arid regions of Tibet and northwestern China. One of the 50-km wide swaths (data-take 32-33) passed from northeastern India, through Lhasa and southern Tibet, to the Karakorum Himalaya and beyond. This swath provides a view of several active faults related to the collision between India and Asia, in particular, normal faults in the Yangbajain Valley, northeast of Lhasa. The scarps are oriented N12°E±16° and most of them dip to the west, which is generally within a few degrees of being parallel to the illumination direction of SIR-A. Since conventional interpretation of the interaction of radar signals with steep scarps predicts that they will not be visible if the illumination azimuth is nearly parallel to the scarp strike because of a lack of the "highlighting" that occurs when a scarp face is oriented normal to the incoming illumination, it is surprising they show up in such light tones on the SIR-A image. The most likely reason for the high radar returns from the scarp faces is that their surfaces are rougher than the smooth, grass-covered valley floor. Height, slope-angle, and surface-roughness measurements were obtained on several scarps and we found that scarps which were visible on the SIR-A image are higher than 5 m and are rough at the decimeter to meter scale. This result is significant since orbital radar sensors can obtain high-resolution images of large areas that are difficult to access, and it appears that they may provide an efficient means with which to survey large areas, extrapolate local observations, and derive quantitative estimates of rates of tectonic processes

Binary evolution with LOFT

This is a White Paper in support of the mission concept of the Large Observatory for X-ray Timing (LOFT), proposed as a medium-sized ESA mission. We discuss the potential of LOFT for the study of very faint X-ray binaries, orbital period distribution of black hole X-ray binaries and neutron star spin up. For a summary, we refer to the paper.Comment: White Paper in Support of the Mission Concept of the Large Observatory for X-ray Timing. (v2 few typos corrected

Spaceborne radar observations: A guide for Magellan radar-image analysis

Geologic analyses of spaceborne radar images of Earth are reviewed and summarized with respect to detecting, mapping, and interpreting impact craters, volcanic landforms, eolian and subsurface features, and tectonic landforms. Interpretations are illustrated mostly with Seasat synthetic aperture radar and shuttle-imaging-radar images. Analogies are drawn for the potential interpretation of radar images of Venus, with emphasis on the effects of variation in Magellan look angle with Venusian latitude. In each landform category, differences in feature perception and interpretive capability are related to variations in imaging geometry, spatial resolution, and wavelength of the imaging radar systems. Impact craters and other radially symmetrical features may show apparent bilateral symmetry parallel to the illumination vector at low look angles. The styles of eruption and the emplacement of major and minor volcanic constructs can be interpreted from morphological features observed in images. Radar responses that are governed by small-scale surface roughness may serve to distinguish flow types, but do not provide unambiguous information. Imaging of sand dunes is rigorously constrained by specific angular relations between the illumination vector and the orientation and angle of repose of the dune faces, but is independent of radar wavelength. With a single look angle, conditions that enable shallow subsurface imaging to occur do not provide the information necessary to determine whether the radar has recorded surface or subsurface features. The topographic linearity of many tectonic landforms is enhanced on images at regional and local scales, but the detection of structural detail is a strong function of illumination direction. Nontopographic tectonic lineaments may appear in response to contrasts in small-surface roughness or dielectric constant. The breakpoint for rough surfaces will vary by about 25 percent through the Magellan viewing geometries from low to high Venusian latitudes. Examples of anomalies and system artifacts that can affect image interpretation are described

Low-loss criterion and effective area considerations for photonic crystal fibers

We study the class of endlessly single-mode all-silica photonic crystal fibers with a triangular air-hole cladding. We consider the sensibility to longitudinal nonuniformities and the consequences and limitations for realizing low-loss large-mode area photonic crystal fibers. We also discuss the dominating scattering mechanism and experimentally we confirm that both macro and micro-bending can be the limiting factor.Comment: Accepted for Journal of Optics A - Pure and Applied Optic

Estimating the Permanent Loss of Groundwater Storage in the Southern San Joaquin Valley, California

In the San Joaquin Valley, California, recent droughts starting in 2007 have increased the pumping of groundwater, leading to widespread subsidence. In the southern portion of the San Joaquin Valley, vertical subsidence as high as 85 cm has been observed between June 2007 and December 2010 using Interferometric Synthetic Aperture Radar (InSAR). This study seeks to map regions where inelastic (not recoverable) deformation occurred during the study period, resulting in permanent compaction and loss of groundwater storage. We estimated the amount of permanent compaction by incorporating multiple data sets: the total deformation derived from InSAR, estimated skeletal-specific storage and hydraulic parameters, geologic information, and measured water levels during our study period. We used two approaches, one that we consider to provide an estimate of the lowest possible amount of inelastic deformation, and one that provides a more reasonable estimate. These two approaches resulted in a spatial distribution of values for the percentage of the total deformation that was inelastic, with the former estimating a spatially averaged value of 54%, and the latter a spatially averaged value of 98%. The former corresponds to the permanent loss of 4.14*108 m3 of groundwater storage, or roughly 5% of the volume of groundwater used over the study time period; the latter corresponds to the loss of 7.48*108 m3 of groundwater storage, or roughly 9% of the volume of groundwater used. This study demonstrates that a data-driven approach can be used effectively to estimate the permanent loss of groundwater storage

Imaging Radar Observations Of Normal Faults In Tibet

NASA/JPL has an ongoing program to study land processes that will lead to a better understanding of the geologic evolution of the continents and the history of global climate change. Northwestern China and Tibet are key areas for these investigations because arid regions such as these retain the record of climate change and a wide variety of large-scale structures are present throughout the area as a result of the continuing collision between the Indian and Asian plates. During the Shuttle Imaging Radar Missions (SIR-A and SIR-B) a number of image swaths were acquired over the People's Republic of China that show interesting landforms indicative of climate change and large-scale faulting in the arid regions of Tibet and northwestern China. One of the 50-km wide swaths (data-take 32-33) passed from northeastern India, through Lhasa and southern Tibet, to the Karakorum Himalaya and beyond. This swath provides a view of several active faults related to the collision between India and Asia, in particular, normal faults in the Yangbajain Valley, northeast of Lhasa. The scarps are oriented N12°E±16° and most of them dip to the west, which is generally within a few degrees of being parallel to the illumination direction of SIR-A. Since conventional interpretation of the interaction of radar signals with steep scarps predicts that they will not be visible if the illumination azimuth is nearly parallel to the scarp strike because of a lack of the "highlighting" that occurs when a scarp face is oriented normal to the incoming illumination, it is surprising they show up in such light tones on the SIR-A image. The most likely reason for the high radar returns from the scarp faces is that their surfaces are rougher than the smooth, grass-covered valley floor. Height, slope-angle, and surface-roughness measurements were obtained on several scarps and we found that scarps which were visible on the SIR-A image are higher than 5 m and are rough at the decimeter to meter scale. This result is significant since orbital radar sensors can obtain high-resolution images of large areas that are difficult to access, and it appears that they may provide an efficient means with which to survey large areas, extrapolate local observations, and derive quantitative estimates of rates of tectonic processes