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1

The Global Multi-Resolution Topography (GMRT) Synthesis  

NASA Astrophysics Data System (ADS)

Topographic maps provide a backdrop for research in nearly every earth science discipline. There is particular demand for bathymetry data in the ocean basins, where existing coverage is sparse. Ships and submersibles worldwide are rapidly acquiring large volumes of new data with modern swath mapping systems. The science community is best served by a global topography compilation that is easily accessible, up-to-date, and delivers data in the highest possible (i.e. native) resolution. To meet this need, the NSF-supported Marine Geoscience Data System (MGDS; www.marine-geo.org) has partnered with the National Geophysical Data Center (NGDC; www.ngdc.noaa.gov) to produce the Global Multi-Resolution Topography (GMRT) synthesis - a continuously updated digital elevation model that is accessible through Open Geospatial Consortium (OGC; www.opengeospatial.org) Web services. GMRT had its genesis in 1992 with the NSF RIDGE Multibeam Synthesis (RMBS); later grew to include the Antarctic Multibeam Synthesis (AMBS); expanded again to include the NSF Ridge 2000 and MARGINS programs; and finally emerged as a global compilation in 2005 with the NSF Legacy of Ocean Exploration (LOE) project. The LOE project forged a permanent partnership between MGDS and NGDC, in which swath bathymetry data sets are routinely published and exchanged via the Open Archives Initiative Protocol for Metadata Harvesting (OAI-PMH; www.openarchives.org). GMRT includes both color-shaded relief images and underlying elevation values at ten different resolutions as high as 100m. New data are edited, gridded, and tiled using tools originally developed by William Haxby at Lamont-Doherty Earth Observatory. Global and regional data sources include the NASA Shuttle Radar Topography Mission (SRTM; http://www.jpl.nasa.gov/srtm/); Smith & Sandwell Satellite Predicted Bathymetry (http://topex.ucsd.edu/marine_topo/); SCAR Subglacial Topographic Model of the Antarctic (BEDMAP; http://www.antarctica.ac.uk/bedmap/); and International Bathymetric Chart of the Arctic Ocean (IBCAO; http://www.ngdc.noaa.gov/mgg/bathymetry/arctic/). Local data sources include high-resolution bathymetry swaths and grids from over 210 research cruises, submersible dives, and related compilations to date. GMRT is accessible via a OGC Web Map Service (WMS) which offers dynamic resolution and on-the-fly map re- projection. A growing number of commercial and open-source clients support OGC protocols, including recent versions of Google Earth and Google Maps which now support WMS natively. GMRT is incorporated as a primary basemap in science Web portals and geobrowsers including EarthChem (www.earthchem.org) and GeoMapApp (www.geomapapp.org), which also serves the underlying elevation values. Future development work will include extension of GMRT to higher resolutions; addition of the International Bathymetric Chart of the Southern Ocean (IBCSO; www.ibcso.org) and the improved SRTM V2; and deployment of new OGC services including a Web Coverage Service (WCS) and Web Terrain Service (WTS).

Arko, R.; Ryan, W.; Carbotte, S.; Melkonian, A.; Coplan, J.; O'Hara, S.; Chayes, D.; Weissel, R.; Goodwillie, A.; Ferrini, V.; Stroker, K.; Virden, W.

2007-12-01

2

Next generation digital backends for the GMRT  

NASA Astrophysics Data System (ADS)

The GMRT Backend Group is in the process of developing wide-band digital backends as part of a major upgrade of the GMRT. The main requirements are for processing 400 MHz bandwidth signals from 30 antennas for interferometry and array mode operations, along with additional features like narrow band modes and RFI cancellation schemes. Both FPGA and GPU based designs have been explored and this paper presents the design and implementation details along with results from testing of prototype units. A comparison of the resources needed and performance achieved on FPGA and GPU based designs is presented, along with an extrapolation of these designs to a 30 station backend for the final GMRT system.

Ajithkumar, B.; Choudhari, S. C.; Buch, K. D.; Muley, M. V.; Shelton, G. J.; Reddy, S. H.; Kudale, S.; Roy, J.; Gupta, Y.

2013-04-01

3

SN2007bg : GMRT Radio observations  

NASA Astrophysics Data System (ADS)

The GMRT observed SN2007bg (Quimby et al. 2007, CBET #927; Prieto et al. GCN #9444; Soderberg A. M., ATel #2066) on 26th June and 1st July 2009 at 610 and 1280 MHz, respectively. The SN was not detected at 610 MHz to a three sigma upper limit of 225 microJy.

Kamble, Atish; Pal, Sabyasachi; Bhattacharya, Dipankar; Wijers, Ralph; Chandra, Ishwara

2009-07-01

4

FLAGCAL: FLAGging and CALlibration Pipeline for GMRT Data  

NASA Astrophysics Data System (ADS)

FLAGging and CALlibration (FLAGCAL) is a software pipeline developed for automatic flagging and calibration of the GMRT data. This pipeline can be used for preprocessing (before importing the data in AIPS) any other interferromteric data also (given that the data file is in FITS format and contains multiple channels & scans).There are also a few GUI based tools which can be used for quick visualization of the data.

Prasad, Jayanti; Chengalur, Jayaram

2011-12-01

5

A real-time software backend for the GMRT  

NASA Astrophysics Data System (ADS)

The new era of software signal processing has a large impact on radio astronomy instrumentation. Our design and implementation of a 32 antennae, 33 MHz, dual polarization, fully real-time software backend for the GMRT, using only off-the-shelf components, is an example of this. We have built a correlator and a beamformer, using PCI-based ADC cards and a Linux cluster of 48 nodes with dual gigabit inter-node connectivity for real-time data transfer requirements. The highly optimized compute pipeline uses cache efficient, multi-threaded parallel code, with the aid of vectorized processing. This backend allows flexibility in final time and frequency resolutions, and the ability to implement algorithms for radio frequency interference rejection. Our approach has allowed relatively rapid development of a fairly sophisticated and flexible backend receiver system for the GMRT, which will greatly enhance the productivity of the telescope. In this paper we describe some of the first lights using this software processing pipeline. We believe this is the first instance of such a real-time observatory backend for an intermediate sized array like the GMRT.

Roy, Jayanta; Gupta, Yashwant; Pen, Ue-Li; Peterson, Jeffrey B.; Kudale, Sanjay; Kodilkar, Jitendra

2010-08-01

6

Complete 150MHz GMRT source catalogue (Ghosh+, 2012)  

NASA Astrophysics Data System (ADS)

We have observed in GMRT Time Allocation Committee (GTAC) the fields: * I on 2008-01-08 for 11hrs at 153MHz, center(J2000)=05:30:00+60:00:00 * II on 2010-02-07 for 6hrs at 148MHz, center(J2000)=06:00:00+62:12:58 * III on 2010-02-08 for 6hrs at 148MHz, center(J2000)=12:36:49+62:12:58 * IV on 2005-06-15 for 13hrs at 153MHz, center(J2000)=01:36:48+41:24:23 (1 data file).

Ghosh, A.; Prasad, J.; Bharadwaj, S.; Ali, Sk. S.; Chengalur, J. N.

2013-04-01

7

Electron beam irradiation of poly(vinyl methyl ether) films: 1. Synthesis and film topography.  

PubMed

Temperature-sensitive hydrogel layers on silicon (Si) substrates were synthesized by electron beam irradiation of spin-coated poly(vinyl methyl ether) (PVME) films. The influences of the used solvent, the polymer concentration, and the spinning velocity on the homogeneity and the thickness of the PVME film were investigated. In the range of concentration c(p) = 1-15 wt% PVME in ethanol solution, homogeneous films with a thickness between d = 50 nm and 1.7 mum were obtained. The films were cross-linked by electron beam irradiation under inert atmosphere and analyzed by sol-gel-analysis. The results were compared with bulkgels formed by electron beam irradiation of PVME in the dry state. The film topography was analyzed by high-resolution field emission scanning electron microscopy and atomic force microscopy. An islandlike structure in the dry, swollen, and shrunken state of the hydrogel films was observed. PMID:15952862

Hegewald, Jan; Schmidt, Thomas; Gohs, Uwe; Günther, Margarita; Reichelt, Rudolf; Stiller, Burkhard; Arndt, Karl-Friedrich

2005-06-21

8

Multi-frequency GMRT observations of SNR G338.3-0.0  

NASA Astrophysics Data System (ADS)

In this paper we present multi-frequency radio observations of the supernova remnant (SNR) G338.3-0.0. The data were acquired in 2008 with the Giant Metrewave Radio Telescope (GMRT, India) operating in dual mode 235/610 MHz and at 1280 MHz. The instrumental capabilities of GMRT permited to spatially resolve the emission down to few arcseconds. The new images represent a significant increase in resolution and sensitivity over previously published data.

Castelletti, G.; Giacani, E.; Dubner, G.; Pramesh, R.; Joshi, B. C.

9

Rate and topography of peptidoglycan synthesis during cell division in Escherichia coli: Concept of a leading edge  

SciTech Connect

The rate at which the peptidoglycan of Escherichia coli is synthesized during the division cycle was studied with two methods. One method involved synchronization of E. coli MC4100 lysA cultures by centrifugal elutriation and subsequent pulse-labeling of the synchronously growing cultures with (meso-{sup 3}H)diaminopimelic acid (({sup 3}H)Dap). The second method was autoradiography of cells pulse-labeled with ({sup 3}H)Dap. It was found that the peptidoglycan is synthesized at a more or less exponentially increasing rate during the division cycle with a slight acceleration in this rate as the cells start to constrict. Apparently, polar cap formation requires synthesis of extra surface components, presumably to accommodate for a change in the surface-to-volume ratio. Furthermore, it was found that the pool size of Dap was constant during the division cycle. Close analysis of the topography of ({sup 3}H)Dap incorporation at the constriction site revealed that constriction proceeded by synthesis of peptidoglycan at the leading edge of the invaginating cell envelope. During constriction, no reallocation of incorporation occurred, i.e., the incorporation at the leading edge remained high throughout the process of constriction. Impairment of penicillin-binding protein 3 by mutation or by the specific {beta}-lactam antibiotic furazlocillin did not affect ({sup 3}H)Dap incorporation during initiation of constriction. However, the incorporation at the constriction site was inhibited in later stages of the constriction process. It is concluded that during division at least two peptidoglycan-synthesizing systems are operating sequentially.

Wientjes, F.B.; Nanninga, N. (Univ. of Amsterdam (Netherlands))

1989-06-01

10

GRO J1744-28: search for radio counterpart with the GMRT  

NASA Astrophysics Data System (ADS)

As a part of radio follow-up observation program on X-ray transients in low-mass X-ray binaries, we obtained a short GMRT observation on the rare bursting accretion-powered pulsar GRO J1744-28 during its recent outburst (ATel #5790, #5810, #5845, #5858, #5883, #5896, #5901). Our observation was made on 2014 February 12 in continuum mode for 2 hours. No possible radio counterpart was detected at 610 MHz for GRO J1744-28 with the GMRT up to 0.5+/-0.1 mJy level within the Chandra position error circle (ATel #5895).

Pandey-Pommier, M.; Masetti, N.; Durouchoux, P.

2014-02-01

11

Corneal topography  

Microsoft Academic Search

This paper explores the many aspects of the nature and measurement of the corneal surface. Its structure and the factors that influence it are described. The traditional techniques of keratometry are summarized and there is an emphasis on new experimental methods of determining corneal topography including moiré, holographic interferometric and profile techniques. The advantages and disadvantages of these procedures are

Thomas W. Smith

1977-01-01

12

Low Frequency Radio Observations of GRS1915+105 with GMRT  

Microsoft Academic Search

We present the first detailed low frequency radio measurements of the galactic microquasar GRS1915+105 with GMRT. Simultaneous observations were carried out at 610 and 244 MHz. Our data does not show any signature of spectral turn over even at low radio frequency of 244 MHz. We propose that while the radio emission at high radio frequencies could predominantly come from

C. H. Ishwara-Chandra; A. Pramesh Rao; Mamta Pandey; R. K. Manchanda; Philippe Durouchoux

2005-01-01

13

Discovery of three new pulsars in a 610-MHz pulsar survey with the GMRT  

NASA Astrophysics Data System (ADS)

We report on the discovery of three new pulsars in the first blind survey of the north Galactic plane (45° < l < 135° |b| < 1°) with the Giant Meterwave Radio telescope (GMRT) at an intermediate frequency of 610 MHz. The survey covered 106 deg2 with a sensitivity of roughly 1 mJy to long-period pulsars (pulsars with period longer than 1 s). The three new pulsars have periods of 318, 933 and 1056 ms. Their timing parameters and flux densities, obtained in follow-up observations with the Lovell Telescope at Jodrell Bank and the GMRT, are presented. We also report on pulse nulling behaviour in one of the newly discovered pulsars, PSR J2208+5500.

Joshi, B. C.; McLaughlin, M. A.; Lyne, A. G.; Ludovici, D. A.; Pawar, N. A.; Faulkner, A. J.; Lorimer, D. R.; Kramer, M.; Davies, M. L.

2009-09-01

14

Low Frequency Radio Observations of GRS1915+105 with GMRT  

Microsoft Academic Search

We present the first detailed low frequency radio measurements of the\\u000agalactic microquasar GRS1915+105 with GMRT. Simultaneous observations were\\u000acarried out at 610 and 244 MHz. Our data does not show any signature of\\u000aspectral turn over even at low radio frequency of 244 MHz. We propose that\\u000awhile the radio emission at high radio frequencies could predominantly come\\u000afrom

C. H. Ishwara-Chandra; A. Pramesh Rao; Mamta Pandey; R. K. Manchanda; Philippe Durouchoux

2005-01-01

15

A combined GMRT/CLFST image of IC443 at 150 MHz  

NASA Astrophysics Data System (ADS)

IC443 is a relatively large Galactic (~45 arcmin) SNR with a high radio surface brightness. It has fine scale structure down to arcsec scales, and so is difficult to image on all angular scales with a single instrument. Here observations of IC443 at 151 MHz made with both the GMRT and the CLFST are combined to give a composite image of IC443 on all scales from >45 arcmin down to ~20 arcsec.

Mitra, D.; Green, D. A.; Rao, A. Pramesh

2014-01-01

16

Search for millisecond pulsars at the GMRT and the exotic discoveries  

NASA Astrophysics Data System (ADS)

There are, arguably, no other astronomical object whose discovery and subsequent studies provides more insight in such a rich variety of physics and astrophysics than the millisecond pulsars (MSPs). MSPs are a small sub-class of pulsars, rotating with periods of only a few milliseconds and due to their extraordinary rotational stability, MSPs can be considered as astrophysical clocks. The search for such exotic objects will not only enhance the MSP population, but will also allow much wider probe to explore their evolutionary history. We have discovered six MSPs with much diverse characteristics at the positions of Fermi LAT unassociated sources using the GMRT. Being the first galactic disk millisecond pulsars discovered at the GMRT, these discoveries are very important scientific achievement from India and illustrate the importance of low-frequency search for nearby millisecond pulsars. The discovery of these precise astrophysical clocks demands much finer grid in search phase space, which is completely driven by the number crunching capability of the High Performance Compute engine. The discoveries of binary MSPs in exotic evolutionary phases demands complete 3-D search. For example, 7.5 Tflops of compute power is used for the discovery of a very compact binary MSP, a Black Widow pulsar. This pulsar eclipses for about 13% of its orbit by a very low-mass companion (0.017 M_{?}). Such Black Widow pulsars are missing link between the isolated and fully recycled pulsars, where the pulsar is ablating its companion creating significant amount of intra-binary material to obscure the pulsar emission. Radio timing ephemeris allowed us to detect the gamma-ray pulsations from this millisecond pulsar. The details of the GMRT discoveries, the interesting results from our observations and the possible scientific impact of the discoveries of such exotic systems will be illustrated in this presentation.

Bhaswati Bhattacharyya, Bhaswati

17

Low Frequency Radio Observations of GRS1915+105 with GMRT  

NASA Astrophysics Data System (ADS)

We present the first detailed low frequency radio measurements of the galactic microquasar GRS1915+105 with GMRT. Simultaneous observations were carried out at 610 and 244 MHz. Our data does not show any signature of spectral turn over even at low radio frequency of 244 MHz. We propose that while the radio emission at high radio frequencies could predominantly come from compact jets, the emission at lower frequency originates in the lobes at the end of the jet which acts like a reservoir of low energy electrons.

Ishwara-Chandra, C. H.; Pramesh Rao, A.; Pandey, Mamta; Manchanda, R. K.; Durouchoux, Philippe

2005-06-01

18

Low-frequency GMRT observations of the magnetic Bp star HR Lup (HD 133880)  

NASA Astrophysics Data System (ADS)

We present radio observations of the magnetic chemically peculiar Bp star HR Lup (HD 133880) at 647 and 277 MHz with the GMRT. At both frequencies the source is not detected but we are able to determine upper limits to the emission. The 647 MHz limits are particularly useful, with a 5? value of 0.45 mJy. Also, no large enhancements of the emission were seen. The non-detections, along with previously published higher frequency detections, provide evidence that an optically thick gyrosynchrotron model is the correct mechanism for the radio emission of HR Lup.

George, Samuel J.; Stevens, Ian R.

2012-06-01

19

GMRT discovery of a 1.69 ms radio pulsar associated with XSS J12270-4859  

NASA Astrophysics Data System (ADS)

Following the reported state change observed in the low-mass X-ray binary XSS J12270-4859 (ATel #5647; Bassa et al. 2014, arXiv:1402.0765), we were granted Director's Discretionary Time to search for radio pulsations using the GMRT. We observed at 607 MHz with the GMRT coherent phased-array mode utilizing 70% of the array resulting in a beam width of 30 arcsec. We recorded 3 scans, each of 1-hour beginning on 2014 Feb 12 at 20:46:15 UTC, producing filter-bank outputs of 512 x 0.0651 MHz sampled at 61.44 microsec.

Roy, J.; Bhattacharyya, B.; Ray, P. S.

2014-02-01

20

Five Years of Multi-frequency Monitoring of GRB030329 Afterglow Using the GMRT and WSRT  

SciTech Connect

GRB 030329 displayed one of the brightest optical afterglows ever. We have followed the radio afterglow of GRB 030329 for over 5 years using the GMRT and WSRT at low radio frequencies. This is the longest as well as the lowest frequency follow up of any GRB afterglow ever.Radio observations of a GRB afterglow provide a unique probe of the physics of the blast wave at late times, when the expansion of the fireball slows down to non-relativistic speeds. Our GMRT-WSRT observations suggest that the afterglow of GRB030329 entered the non-relativistic phase around 60 days after the burst. The estimate of the fireball energy content, {approx}10{sup 51} erg, in this near-isotropic phase is much less susceptible to the collimation-related uncertainties arising in the relativistic phase. We have also been closely monitoring the evolution of the afterglow to look for possible signatures of emission from a counter jet, but no conclusive evidence has so far been found.

Kamble, Atish; Wijers, Ralph; Rol, Evert [Astronomical Institute 'Anton Pannekoek', Kruislaan 403, 1098 SJ Amsterdam (Netherlands); Horst, A. J. van der; Kouveliotou, Chryssa [National Space Science and Technology Center, 320 Sparkman Drive, Huntsville, AL 35805 (United States); Bhattacharya, D. [Inter University Centre for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, Pune: 411 007 (India); Chandra, C. H. Ishwara [National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Pune University Campus, Pune: 411 007 (India); Resmi, L. [GRECO, Institut d'Astrophysique de Paris, 98bis, bd Arago-75014, Paris (France); Strom, R. [ASTRON, P.O. Box 2, 7990 AA Dwingeloo (Netherlands); Astronomical Institute 'Anton Pannekoek', Kruislaan 403, 1098 SJ Amsterdam (Netherlands)

2009-05-25

21

Density Isostasy and Topography  

NSDL National Science Digital Library

Density, Isostasy, and Topography Anne Egger, Stanford University The original activity Density, Isostasy, and Topography already exists within the SERC website. This page describes how this activity can be used ...

22

GMRT Observations of SNR G15.4+0.1/HESS J1818-154  

NASA Astrophysics Data System (ADS)

We report here on the first dedicated simultaneous imaging and pulsar observations towards the supernova remnant (SNR) G15.4+0.1, the possible counterpart of the very high energy (VHE) source HESS J1818-154. The observations were carried out using the Giant Metrewave Radio Telescope (GMRT) at 610 and 1400 MHz. Preliminary analysis of data suggests absence of pulsations towards the centroid of HESS J1818-154, with upper limits of 0.6 and 0.3 mJy at 610 and 1400 MHz, respectively. Analysis of data with a larger beam is in progress, which may confirm the presence of a putative pulsar and its wind nebula if it is offset from the centroid of HESS J1818-154.

Castelletti, G.; Joshi, B. C.; Surnis, M. P.; Supán, L.; Dubner, G.

2014-01-01

23

Status update on double pulsar: Multi-frequency multi-epoch observations with GMRT  

NASA Astrophysics Data System (ADS)

The double pulsar system, J0737-3039, a highly relativistic binary system with two radio pulsars (periods ˜23 ms and 2.8 s), is an excellent system to study the gravity theories, processes in pulsar magnetosphere and the effects of geodetic precession on the observed pulse emission. It is a highly relativistic binary system with two radio pulsars in a tight edge-on mildly eccentric orbit with a significant advance of angle of periastron (orbital period 2.4 hr, orbital inclination angle 87.7 deg, eccentricity 0.09). PSR J0737-3039A exhibits a double peaked profile independent of orbital phase with different spectral index for the two components, while PSR J0737-3039B exhibits a narrow profile, in two windows centered on orbital longitudes 210 and 280 deg (Lyne et al. 2004), called bright phase 1 and bright phase 2. Both profiles evolve significantly with observation frequency. The time-scale for geodetic precession is a factor of 4 shorter than that for Hulse-Taylor pulsar, PSR B1913+16, allowing these effects to be detected in a short time. Indeed, significant effects have been reported since the discovery of this system and in most recent observations with Giant Metrewave Radio Telescope (GMRT). A report on monitoring of this system at multiple frequencies and epochs with GMRT is presented and the implications of the results are discussed. An update on the current status of the research on this system is presented. In particular, the fading away of PSR J0737-3039B is reported.

Joshi, Bhal Chandra

24

OpenTopography  

NASA Astrophysics Data System (ADS)

OpenTopography is a cyberinfrastructure-based facility for online access to high-resolution topography and tools. The project is an outcome of the Geosciences Network (GEON) project, which was a research project funded several years ago in the US to investigate the use of cyberinfrastructure to support research and education in the geosciences. OpenTopography provides online access to large LiDAR point cloud datasets along with services for processing these data. Users are able to generate custom DEMs by invoking DEM services provided by OpenTopography with custom parameter values. Users can track the progress of their jobs, and a private myOpenTopo area retains job information and job outputs. Data available at OpenTopography are provided by a variety of data acquisition groups under joint agreements and memoranda of understanding (MoU). These include national facilities such as the National Center for Airborne Lidar Mapping, as well as local, state, and federal agencies. OpenTopography is also being designed as a hub for high-resolution topography resources. Datasets and services available at other locations can also be registered here, providing a "one-stop shop" for such information. We will describe the OpenTopography system architecture and its current set of features, including the service-oriented architecture, a job-tracking database, and social networking features. We will also describe several design and development activities underway to archive and publish datasets using digital object identifiers (DOIs); create a more flexible and scalable high-performance environment for processing of large datasets; extend support for satellite-based and terrestrial lidar as well as synthetic aperture radar (SAR) data; and create a "pluggable" infrastructure for third-party services. OpenTopography has successfully created a facility for sharing lidar data. In the next phase, we are developing a facility that will also enable equally easy and successful sharing of services related to these data.

Baru, C.; Arrowsmith, R.; Crosby, C.; Nandigam, V.; Phan, M.; Cowart, C.

2012-04-01

25

Improved foreground removal in GMRT 610 MHz observations towards redshifted 21-cm tomography  

NASA Astrophysics Data System (ADS)

Foreground removal is a challenge for 21-cm tomography of the high-redshift Universe. We use archival Giant Metrewave Radio Telescope (GMRT) data (obtained for completely different astronomical goals) to estimate the foregrounds at a redshift of ˜1. The statistic we use is the cross power spectrum between two frequencies separated by ?? at the angular multipole ?, or equivalently the multi-frequency angular power spectrum C?(??). An earlier measurement of C?(??) using these data had revealed the presence of oscillatory patterns along ??, which turned out to be a severe impediment for foreground removal. Using the same data, in this paper we show that it is possible to considerably reduce these oscillations by suppressing the sidelobe response of the primary antenna elements. The suppression works best at the angular multipoles ? for which there is a dense sampling of the u-v plane. For three angular multipoles ?= 1405, 1602 and 1876, this sidelobe suppression along with a low order polynomial fitting completely results in residuals of (? 0.02 mK2), consistent with the noise at the 3? level. Since the polynomial fitting is done after estimation of the power spectrum it can be ensured that the estimation of the H I signal is not biased. The corresponding 99 per cent upper limit on the H I signal is ?, where ? is the mean neutral fraction and b is the bias.

Ghosh, Abhik; Bharadwaj, Somnath; Ali, Sk. Saiyad; Chengalur, Jayaram N.

2011-12-01

26

Derivation of model topography  

NASA Technical Reports Server (NTRS)

The Fourth-Order model necessitates representation of the topography. The problem of the representation of the topography at grid points is addressed. The attempted was to derive an envelope topography. The TI is obtained by taking local mean plus one standard deviation at each grid point and sigma filtering it. The method was greatly influenced by large standard deviations at steep mountains. The O1 topography is the local mean. The S1 is obtained by Sigma filtering in both latitude and longitude the mean O1. The S2 is when the operation is applied twice and S3 thrice, the Q3 is the sigma filtered local mean of the upper third quantile of the source data.

Balgovind, R. C.

1985-01-01

27

Topography-assisted photoablation  

NASA Astrophysics Data System (ADS)

Topography assisted photoablation (TAP) is an important and logic step for future customized therapeutic photokeratectomy. Its goal is to reshape any irregular corneal surface in order to achieve an ideal sphere. Accuracy and reproducibility of the 2D and 3D topography data, strategies of data acquisition, data modification and transfer are essential elements. Accurate and appropriate subtraction methods for difference mapping are discussed. Furthermore, the properties and algorithms of the lasers' delivery systems, have to be taken into account. The overview paper describes and discusses some of the central elements of TAP.

Jean, Benedikt J.; Bende, Thomas

1999-06-01

28

Resistivity modelling with topography  

NASA Astrophysics Data System (ADS)

A major difficulty of electrical resistivity forward modelling is the singularity of the potential occurring at the source location. To avoid large numerical errors, the potential is split into a primary part containing the singularity and a secondary part. The primary potential is defined analytically for flat topography, and is classically computed numerically in the presence of topography: in that case, an accurate solution requires expensive computations. We propose to define the primary potential as the analytic solution valid for a homogeneous model and flat topography, and to modify accordingly the free surface boundary condition for the secondary potential, such that the overall potential still satisfies the Poisson equation. The modified singularity removal technique thus remains fully efficient for any acquisition geometries, without any additional numerical computation, and also applicable in the presence of a buried cavity. This approach is implemented with the generalized finite difference method developed on unstructured meshes and validated through the comparison with analytical solutions. Finally, we illustrate in simple 2-D and 3-D cases how the potential depends on the shape of the topography and on the electrode positions.

Penz, Sébastien; Chauris, Hervé; Donno, Daniela; Mehl, Caroline

2013-09-01

29

Flow Interaction with Topography  

NSDL National Science Digital Library

This module explores the fundamental concepts used to determine how air flow interacts with topography. Using the simple analogy of a marble rolling over a hill, this module examines the relationship between wind speed and static stability of the atmosphere. These results are further extended to include three-dimensional terrain barriers as well as the evolution through time of the interaction.

Spangler, Tim

1999-05-01

30

Deep GMRT 150 MHz Observations of the DEEP2 Fields: Searching for High Red-Shift Radio Galaxies Revisited  

NASA Astrophysics Data System (ADS)

High red-shift radio galaxies are best searched at low radio frequencies, due to its steep radio spectra. Here we present preliminary results from our programme to search for high red-shift radio galaxies to ˜10 to 100 times fainter than the known population till date. We have extracted ultra-steep spectrum (USS) samples from deep 150 MHz Giant Meter-wave Radio Telescope (GMRT) observations from one of the three well-studied DEEP2 fields to this effect. From correlating these radio sources with respect to the high-frequency catalogues such as VLA, FIRST and NVSS at 1.4 GHz, we find ˜100 steep spectrum (spectral index, ? > 1) radio sources, which are good candidates for high red-shift radio galaxies.

Bisoi, Susanta K.; Ishwara-Chandra, C. H.; Sirothia, S. K.; Janardhan, P.

2011-12-01

31

Investigation of the solar UV/EUV heating effect on the Jovian radiation belt by GMRT-IRTF observation  

NASA Astrophysics Data System (ADS)

Jupiter's synchrotron radiation (JSR) is the emission from relativistic electrons, and it is the most effective probe for remote sensing of Jupiter's radiation belt from the Earth. Recent intensive observations of JSR revealed short term variations of JSR with the time scale of days to weeks. Brice and McDonough (1973) proposed a scenario for the short term variations; i.e, the solar UV/EUV heating for Jupiter's upper atmosphere causes enhancement of total flux density. The purpose of this study is to investigate whether sufficient solar UV/EUV heating in Jupiter's upper atmosphere can actually causes variation in the JSR total flux and brightness distribution. Previous JSR observations using the Giant Metrewave Radio Telescope (GMRT) suggested important characteristics of short term variations; relatively low energy particles are accelerated by some acceleration processes which might be driven by solar UV/EUV heating and/or Jupiter's own magnetic activities. In order to evaluate the effect of solar UV/EUV heating on JSR variations, we made coordinated observations using the GMRT and NASA Infra-Red Telescope Facility (IRTF). By using IRTF, we can estimate the temperature of Jupiter's upper atmosphere from spectroscopic observation of H_3^+ infrared emission. Hence, we can evaluate the relationship between variations in Jupiter's upper atmosphere initiated by the solar UV/EUV heating and its linkage with the JSR. The GMRT observations were made during Nov. 6-17, 2011 at the frequency of 235/610MHz. The H_3^+ 3.953 micron line was observed using the IRTF during Nov. 7-12, 2011. During the observation period, the solar UV/EUV flux variations expected on Jupiter showed monotonic increase. A preliminary analysis of GMRT 610MHz band showed a radio flux variation similar to that in the solar UV/EUV. Radio images showed that the emission intensity increased at the outer region and the position of equatorial peak emission moved in the outward direction. If radial diffusion increases globally by the solar UV/EUV heating, it is expected that the peak intensity would increase and the peak position move inwards. However, our results are not consistent with the global enhancement of radial diffusion. In addition to that, the equatorial H_3^+ emission indicated that emission intensity decreased from the first day of observation to the last day. It is expected that equatorial temperature of Jupiter's atmosphere decreases during this observation period. Therefore, we propose that radial diffusion increased not globally but only at the outer region around L=2-3 during this period. From this hypothesis, it is expected that enhancement of radial diffusion at the outer region is caused by high latitude temperature enhancement. We discuss possible causes of the short term variations of JSR from the IRTF observation results at high latitude.

Kita, H.; Misawa, H.; Bhardwaj, A.; Tsuchiya, F.; Tao, C.; Uno, T.; Kondo, T.; Morioka, A.

2012-12-01

32

Corneal topography system  

NASA Astrophysics Data System (ADS)

A new corneal topography system is described which combines proven grid projection and stereo triangulation techniques with an innovative user interface which simplifies the data capture process. Principles of the imaging, measurement, and calibration processes used with the system are presented. The device generates a complete topographic model of the anterior corneal surface with spatial resolution of 0.2 millimeters and elevation accuracy of 2 microns. System applications include pre- and post-operative assessment of refractive surgery patients, contact lens fitting including specification of custom RGP lenses, and excimer surgery planning and simulation. The innovative features of the system are described along with preliminary results of accuracy evaluations.

Cambier, James L.; Gao, Yan

1998-03-01

33

Ocean Surface Topography from Space  

NSDL National Science Digital Library

Interactive Flash Module about Ocean Surface Topography. Module includes sea surface observations and measurements as well as visuals explanations of the alimetry instruments used to detect surface changes.

Jet Propulsion Laboratory, California Institute of Technology, NASA

34

RADAR Reveals Titan Topography  

NASA Technical Reports Server (NTRS)

The Cassini Titan RADAR Mapper is a K(sub u)-band (13.78 GHz, lambda = 2.17 cm) linear polarized RADAR instrument capable of operating in synthetic aperture (SAR), scatterometer, altimeter and radiometer modes. During the first targeted flyby of Titan on 26 October, 2004 (referred to as Ta) observations were made in all modes. Evidence for topographic relief based on the Ta altimetry and SAR data are presented here. Additional SAR and altimetry observations are planned for the T3 encounter on 15 February, 2005, but have not been carried out at this writing. Results from the T3 encounter relevant to topography will be included in our presentation. Data obtained in the Ta encounter include a SAR image swath

Kirk, R. L.; Callahan, P.; Seu, R.; Lorenz, R. D.; Paganelli, F.; Lopes, R.; Elachi, C.

2005-01-01

35

The Extended GMRT Radio Halo Survey. I. New upper limits on radio halos and mini-halos  

NASA Astrophysics Data System (ADS)

Context. A fraction of galaxy clusters host diffuse radio sources called radio halos, radio relics and mini-halos. These are associated with the relativistic electrons and magnetic fields present on ~Mpc scales in the intra-cluster medium. Aims: We aim to carry out a systematic radio survey of all luminous galaxy clusters selected from the REFLEX and eBCS X-ray catalogues with the Giant Metrewave Radio Telescope, to understand the statistical properties of the diffuse radio emission in galaxy clusters. Methods: We present the sample and first results from the Extended GMRT Radio Halo Survey (EGRHS), which is an extension of the GMRT Radio Halo Survey (GRHS, Venturi et al. 2007, 2008). Analysis of radio data at 610/ 235/ 325 MHz on 12 galaxy clusters are presented. Results: We report the detection of a newly discovered mini-halo in the cluster RX J1532.9+3021 at 610 MHz. The presence of a small-scale relic (~200 kpc) is suspected in the cluster Z348. We do not detect cluster-scale diffuse emission in 11 clusters. Robust upper limits on the detection of radio halo of size of 1 Mpc are determined. We also present upper limits on the detections of mini-halos in a sub-sample of cool-core clusters. The upper limits for radio halos and mini-halos are plotted in the radio power- X-ray luminosity plane and the correlations are discussed. Diffuse extended emission that is not related to the target clusters, but detected as by-products in the sensitive images of two of the cluster fields (A689 and RX J0439.0+0715) is also reported. Conclusions: Based on the information about the presence of radio halos (or upper limits), available on 48 clusters out of the total sample of 67 clusters (EGRHS+GRHS), we find that 23 ± 7% of the clusters host radio halos. The radio halo fraction rises to 31 ± 11%, when only the clusters with X-ray luminosities >8 × 1044 erg s-1 are considered. Mini-halos are found in ~50% of cool-core clusters. A qualitative examination of the X-ray images of the clusters with no diffuse radio emission indicates that a majority of these clusters do not show extreme dynamical disturbances and supports the idea that mergers play an important role in generating radio halos and relics. The analysis of the full sample will be presented in a future work. Appendix A is available in electronic form at http://www.aanda.org

Kale, R.; Venturi, T.; Giacintucci, S.; Dallacasa, D.; Cassano, R.; Brunetti, G.; Macario, G.; Athreya, R.

2013-09-01

36

Topography of chance  

NASA Astrophysics Data System (ADS)

We present a model of multiplicative Langevin dynamics that is based on two foundations: the Langevin equation and the notion of multiplicative evolution. The model is a nonlinear mechanism transforming a white-noise input to a dynamic-equilibrium output, using a single control: an underlying convex U-shaped potential function. The output is quantified by a stationary density which can attain a given number of shapes and a given number of randomness categories. The model generates each admissible combination of the output's shape and randomness in a universal and robust fashion. Moreover, practically all the probability distributions that are supported on the positive half-line, and that are commonly encountered and applied across the sciences, can be reverse engineered by this model. Hence, this model is a universal equilibrium mechanism, in the context of multiplicative dynamics, for the robust generation of “chance”: the model's output. In turn, the properties of the produced “chance,” the output's shape and randomness, are determined with mathematical precision by the control's landscape, its topography. Thus, a topographic map of chance is established. As a particular application, probability distributions with power-law tails are shown to be universally and robustly generated by controls on the “edge of convexity”: convex U-shaped potential functions with asymptotically linear wings.

Eliazar, Iddo I.; Cohen, Morrel H.

2013-11-01

37

Density, Isostasy, and Topography  

NSDL National Science Digital Library

Show caption HideA critical component of this activity involves sharing team data with the entire class, done the old-fashioned way on the chalkboard. Details This activity begins with an exploration of a topographic map of the earth, ending with the question: Why is the distribution of topography on the earth bimodal? The students then collect two forms of data. They measure the density of the most common rocks that make up oceanic crust (basalt), continental crust (granite), and the mantle (peridotite). They also measure the density of several different kinds of wood, and how high each kind floats in a tub of water. In each case, they work in teams of two or three and then the entire class shares their data. Based on the data from the wood, they derive an equation that relates the density of the wood to the height at which the block floats in the water - the isostasy equation. They then substitute density values for real rocks into their equation to derive thicknesses for average continental and oceanic crust, and apply their knowledge in order to draw a cross-section of the crust across South America. This activity gives students a real, hands-on and mathematical understanding of the principle of isostasy.

Egger, Anne

38

Topography of a wrinkled membrane  

NASA Astrophysics Data System (ADS)

Polymerized vesicle membranes on cooling below the transition temperature, undergo a wrinkling transition and resemble a crumpled elastic sheet or a dried prune. We examine the topography of the surface of a wrinkled vesicle using SEM and AFM measurements.

Natrajan, Vinay; Chaieb, Sahraoui

2004-03-01

39

Global Topography and Tectonic Plates  

NSDL National Science Digital Library

The goal of this activity is to investigate global topographic and tectonic features, especially the tectonic plates and their boundaries. Using a double-page size digital topographic map of the Earth that includes both land and sea floor topography, students are asked to draw plate boundaries, deduce plate motions and interactions, and explore the connections between topography and tectonic processes at the global scale.

Greene, David

40

Simultaneous Topography and Recognition Imaging  

NASA Astrophysics Data System (ADS)

Atomic force microscopy (AFM) has developed into a key technique for the investigation of biological samples. In contrast to other microscopy methods, high lateral resolution down to the nanometer scale and measurements under physiological conditions are possible. Additionally, the piconewton force sensitivity allows accurate data collection for single-molecule interactions. This chapter describes the combination of high-resolution imaging and single-molecule interaction measurements. In the so-called topography and recognition imaging (TREC) mode, the scanning AFM tip is upgraded into a molecular sensor by anchoring a ligand to the tip. Enhanced electronics, including a recently developed feedback loop, allow measurement of the sample topography while simultaneously mapping ligand-binding sites. This results in topography images recorded alongside with recognition images, thereby allowing accurate allocation of the binding sites with a lateral resolution of one to a few nanometers. TREC has been successfully used for recognition imaging on isolated proteins, native and artificial membranes, and cells.

Ebner, A.; Chtcheglova, L. A.; Preiner, J.; Tang, J.; Wildling, L.; Gruber, H. J.; Hinterdorfer, P.

41

Measured and Estimated Seafloor Topography: Land Topography from GTOPO30  

NSDL National Science Digital Library

This web site displays two "clickable" maps - one topographic, and the other a Ship Track Each of 16 regions on the maps displays measured and estimated seafloor topography. A poster of the images can be ordered for a fee. Links to related sites are also provided.

42

Noninvasive measurement of corneal topography  

Microsoft Academic Search

The authors present a brief overview of the surface to be measured (the cornea of the eye), review the current state of the technology designed to measure the corneal topography, and define the outstanding issues of current significance. The topics discussed include: eye movements; fundamental operating principles of new systems; videokeratographic systems; fundamental limitations of the operating principles; limitations of

R. A. Applegate; H. C. Howland

1995-01-01

43

Reactions of cells to topography  

Microsoft Academic Search

Though contact guidance has been known since the very early days of cell culture very little quantitative examination of the reaction of cells to topography has been made. Exceptions to this subjective approach are given prominence below. Yet if we are to understand how cells react and if we are to be able to design ideal substrata for particular cells

Adam S. G. Curtis; Chris D. W. Wilkinson

1998-01-01

44

X-ray Topography in Protein Crystals  

NASA Astrophysics Data System (ADS)

X-ray topography, especially synchrotron X-ray topography, provides a useful tool for the characterization of protein crystals in order to characterize the defects. We observed clear images of dislocations in hen-egg white lysozyme crystals. In this article we overviewed the research on crystal defects, especially dislocations of protein crystals by synchrotron X-ray topography.

Kojima, Kenichi; Tachibana, Masaru

45

Mars Gravity and Topography Interpretations  

NASA Technical Reports Server (NTRS)

New models of the topography of Mars and its gravity field from the Mars Global Surveyor mission are shedding new light on the structure of the planet and the state of isostatic compensation. Gravity field observations over the flat northern hemisphere plains show a number of anomalies at the 100 to 200 mGal level that have no apparent manifestation in the surface topography. We believe that these anomalies are probably the result of ancient impacts and represent regions of denser material buried beneath the outer depositional crust. Similar anomalies are also found in the region of the north polar ice cap even though a gravity anomaly resulting from the 3 km high icecap has not been uniquely identified. This leads us to speculate that the ice cap is largely compensated and is older than the timescale of isostatic compensation, about 10(exp 15) years.

Zuber, Maria T.; Smith, David E.; Solomon, Sean C.; Phillips, Roger J.

1999-01-01

46

Topography, Cell Response, and Nerve Regeneration  

PubMed Central

In the body, cells encounter a complex milieu of signals, including topographical cues. Imposed topography can affect cells on surfaces by promoting adhesion, spreading, alignment, morphological changes, and changes in gene expression. Neural response to topography is complex, and depends on the dimensions and shapes of physical features. Looking toward repair of nerve injuries, strategies are being explored to engineer guidance conduits with precise surface topographies. How neurons and other cell types sense and interpret topography remains to be fully elucidated. Studies reviewed here include those of topography on cellular organization and function as well as potential cellular mechanisms of response.

Hoffman-Kim, Diane; Mitchel, Jennifer A.; Bellamkonda, Ravi V.

2010-01-01

47

Ocean Surface Topography From Space  

NSDL National Science Digital Library

This site provides information on the many aspects of the study of the sea surface from space. Measuring the ocean surface topography provides information for studying global ocean circulation and the oceans heat budget. Regular scanning of the ocean surface to maintain a database of ocean surface topography can help predict short-term changes in weather and longer-term patterns of climate. Educational materials include a wide variety of games, puzzles, and facts; educational entertainment; on-line resources for educators; information about useful books; and links to lesson plans and classroom activities. There is information on obtaining a variety of visual materials on Oceanography and El Nino in both hardcopy form or PDF files. A class activities area presents plans for classroom activities in Oceans, Climate and Life from the "Visit to an Ocean Planet" CD-ROM in PDF format; shows how an El Nino works using common household items; and describes an El Nino Skit for primary grades. This area also lists on-line resources for educators, information about useful books, and links to lesson plans and classroom activities.

Kawasaki, Kristy

2002-12-13

48

Venus topography - A harmonic analysis  

NASA Technical Reports Server (NTRS)

A model of Venusian global topography has been obtained by fitting an eighteenth-degree harmonic series to Pioneer Venus orbiter radar altimeter data. The mean radius is (6051.45 + or - 0.04) km. The corresponding mean density is (5244.8 + or 0.5) kg/cu m. The center of figure is displaced from the center of mass by (0.339 + or - 0.088) km towards (6.6 + or 10.1) deg N, (148. 8 + or - 7.7) deg. The figure of Venus is distinctly triaxial, but the orientation and magnitudes of the principal topographic axes correlate rather poorly with the gravitational principal axes. However, the higher-degree harmonics of topography and gravity are significantly correlated. The topographic variance spectrum of Venus is very similar in form to those of the moon, Mars, and especially earth. It is suggested that this spectral similarity simply reflects a statistical balance between constructional and degradational geomorphic proceses. Venus and earth are particularly similar (and differ from the moon and Mars) in that the larger bodies both exhibit a significant low degree deficit (relative to the extrapolated trend of the higher harmonics).

Bills, B. G.; Kobrick, M.

1985-01-01

49

Plasma processing for nanostructured topographies  

NASA Astrophysics Data System (ADS)

Plasma and directed ion interactions with materials have been widely observed to create complex surface patterns on a micro- and nano- scale. Generally, these texturizations are byproducts of another intended application (such as a feature formation on a sputtering target) and patterning is considered inconsequential or even detrimental. This work examined the possibility of using these phenomena as primary methods for producing beneficial topographies. Specifically, investigations focused on the use of helium plasma exposure and directed ion etching to create nanostructured surfaces capable of affecting biological interactions with implanted materials. Orthogonal argon ion etching and low energy helium plasma texturization of titanium were considered for use on orthopedic and dental implants as a means of increasing osteoblast activity and bone attachment; and oblique angle etching was evaluated for its use in creating topographies with cell deterrent or anti-thrombogenic properties. In addition, the helium driven evolution of surface features on 6061 aluminum alloy was characterized with respect to ion energy and substrate temperature. These surfaces were then considered for ice phobic applications.

Riedel, Nicholas Alfred

50

The Shuttle Radar Topography Mission  

NASA Technical Reports Server (NTRS)

On February 22, 2000 Space Shuttle Endeavour landed at Kennedy Space Center, completing the highly successful 11-day flight of the Shuttle Radar Topography Mission (SRTM). Onboard were over 300 high-density tapes containing data for the highest resolution, most complete digital topographic map of Earth ever made. SRTM is a cooperative project between NASA and the National Imagery and Mapping Agency (NIMA) of the U.S. Department of Defense. The mission was designed to use a single-pass radar interferometer to produce a digital elevation model (DEM) of the Earth's land surface between about 60 deg north and 56 deg south latitude. When completed, the DEM will have 30 m pixel spacing and about 15 m vertical accuracy. Two orthorectified image mosaics (one from the ascending passes with illumination from the southeast and one from descending passes with illumination from the southwest) will also be produced.

Farr, Tom G.; Kobrick, Mike

2000-01-01

51

Venus - Global gravity and topography  

NASA Astrophysics Data System (ADS)

A new gravity field determination that has been produced combines both the Pioneer Venus Orbiter (PVO) and the Magellan Doppler radio data. Comparisons between this estimate, a spherical harmonic model of degree and order 21, and previous models show that significant improvements have been made. Results are displayed as gravity contours overlaying a topographic map. We also calculate a new spherical harmonic model of topography based on Magellan altimetry, with PVO altimetry included where gaps exist in the Magellan data. This model is also of degree and order 21, so in conjunction with the gravity model, Bouguer and isostatic anomaly maps can be produced. These results are very consistent with previous results, but reveal more spatial resolution in the higher latitudes.

McNamee, J. B.; Borderies, N. J.; Sjogren, W. L.

1993-05-01

52

Venus - Global gravity and topography  

NASA Technical Reports Server (NTRS)

A new gravity field determination that has been produced combines both the Pioneer Venus Orbiter (PVO) and the Magellan Doppler radio data. Comparisonsbetween this estimate, a spherical harmonic model of degree and order 21, and previous models show that significant improvements have been made. Results are displayed as gravity contours overlaying a topographic map. We also calculate a new spherical harmonic model of topography based on Magellan altimetry, with PVO altimetry included where gaps exist in the Magellan data. This model is also of degree and order 21, so in conjunction with the gravity model, Bouguer and isostatic anomaly maps can be produced. These results are very consistent with previous results, but reveal more spatial resolution in the higher latitudes.

Mcnamee, J. B.; Borderies, N. J.; Sjogren, W. L.

1993-01-01

53

Enhanced characterization of niobium surface topography  

NASA Astrophysics Data System (ADS)

Surface topography characterization is a continuing issue for the superconducting radio frequency (SRF) particle accelerator community. Efforts are under way to both improve surface topography and its characterization and analysis using various techniques. In measurement of topography, power spectral density (PSD) is a promising method to quantify typical surface parameters and develop scale-specific interpretations. PSD can also be used to indicate how the process modifies topography at different scales. However, generating an accurate and meaningful topographic PSD of an SRF surface requires careful analysis and optimization. In this report, niobium surfaces with different process histories are sampled with atomic force microscopy and stylus profilometry and analyzed to trace topography evolution at different scales. An optimized PSD analysis protocol to serve SRF needs is presented.

Xu, Chen; Tian, Hui; Reece, Charles E.; Kelley, Michael J.

2011-12-01

54

Topography and Landforms of Ecuador  

USGS Publications Warehouse

EXPLANATION The digital elevation model of Ecuador represented in this data set was produced from over 40 individual tiles of elevation data from the Shuttle Radar Topography Mission (SRTM). Each tile was downloaded, converted from its native Height file format (.hgt), and imported into a geographic information system (GIS) for additional processing. Processing of the data included data gap filling, mosaicking, and re-projection of the tiles to form one single seamless digital elevation model. For 11 days in February of 2000, NASA, the National Geospatial-Intelligence Agency (NGA), the German Aerospace Center (DLR), and the Italian Space Agency (ASI) flew X-band and C-band radar interferometry onboard the Space Shuttle Endeavor. The mission covered the Earth between 60?N and 57?S and will provide interferometric digital elevation models (DEMs) of approximately 80% of the Earth's land mass when processing is complete. The radar-pointing angle was approximately 55? at scene center. Ascending and descending orbital passes generated multiple interferometric data scenes for nearly all areas. Up to eight passes of data were merged to form the final processed SRTM DEMs. The effect of merging scenes averages elevation values recorded in coincident scenes and reduces, but does not completely eliminate, the amount of area with layover and terrain shadow effects. The most significant form of data processing for the Ecuador DEM was gap-filling areas where the SRTM data contained a data void. These void areas are a result of radar shadow, layover, standing water, and other effects of terrain, as well as technical radar interferometry phase unwrapping issues. To fill these gaps, topographic contours were digitized from 1:50,000 - scale topographic maps which date from the mid-late 1980's (Souris, 2001). Digital contours were gridded to form elevation models for void areas and subsequently were merged with the SRTM data through GIS and remote sensing image-processing techniques. The data contained in this publication includes a gap filled, countrywide SRTM DEM of Ecuador projected in Universal Transverse Mercator (UTM) Zone 17 North projection, Provisional South American, 1956, Ecuador datum and a non gap filled SRTM DEM of the Galapagos Islands projected in UTM Zone 15 North projection. Both the Ecuador and Galapagos Islands DEMs are available as an ESRI Grid, stored as ArcInfo Export files (.e00), and in Erdas Imagine (IMG) file formats with a 90 meter pixel resolution. Also included in this publication are high and low resolution Adobe Acrobat (PDF) files of topography and landforms maps in Ecuador. The high resolution map should be used for printing and display, while the lower resolution map can be used for quick viewing and reference purposes.

Chirico, Peter G.; Warner, Michael B.

2005-01-01

55

Maps of Mars Global Topography  

NASA Technical Reports Server (NTRS)

Maps of Mars' global topography. The projections are Mercator to 70o latitude and stereographic at the poles with the south pole at left and north pole at right. Note the elevation difference between the northern and southern hemispheres. The Tharsis volcano-tectonic province is centered near the equator in the longitude range 220o E to 300o E and contains the vast east-west trending Valles Marineris canyon system and several major volcanic shields including Olympus Mons (18o N, 225o E), Alba Patera (42o N, 252o E), Ascraeus Mons (12o N, 248o E), Pavonis Mons (0o, 247o E), and Arsia Mons (9o S, 239o E). Regions and structures discussed in the text include Solis Planum (25o S, 270o E), Lunae Planum (10o N, 290o E), and Claritas Fossae (30o S, 255o E). Major impact basins include Hellas (45o S, 70o E), Argyre (50o S, 320o E), Isidis (12o N, 88o E), and Utopia (45o N, 110o E). This analysis uses an areocentric coordinate convention with east longitude positive.

1999-01-01

56

Enhanced Characterization of Niobium Surface Topography  

SciTech Connect

Surface topography characterization is a continuing issue for the Superconducting Radio Frequency (SRF) particle accelerator community. Efforts are underway to both to improve surface topography, and its characterization and analysis using various techniques. In measurement of topography, Power Spectral Density (PSD) is a promising method to quantify typical surface parameters and develop scale-specific interpretations. PSD can also be used to indicate how chemical processes modifiesy the roughnesstopography at different scales. However, generating an accurate and meaningful topographic PSD of an SRF surface requires careful analysis and optimization. In this report, polycrystalline surfaces with different process histories are sampled with AFM and stylus/white light interferometer profilometryers and analyzed to indicate trace topography evolution at different scales. evolving during etching or polishing. Moreover, Aan optimized PSD analysis protocol will be offered to serve the SRF surface characterization needs is presented.

Chen Xu, Hui Tian, Charles Reece, Michael Kelley

2011-12-01

57

Visualization of pressure distribution by applying moire topography to free-surface water table  

NASA Astrophysics Data System (ADS)

Moire topography is applied to a free-surface water table in order to observe the pressure distribution in a gas flow. Given the water table, the time and size of a gas flow can be extended (Takasaki, 1970), while by using moire topography, the contour line map of water depth, and thus the isobaric line map for a gas flow, can be visualized (Barclay et al., 1963). The inclined grid method was developed to discriminate between the rise and fall of the water surface and to achieve high sensitivity. The switching action of an attachment jet by a control jet is used as an experimental example. Results show that the pressure visualization technique applying moire topography to a free-surface water table is adequate for observing an unsteady flow, and can give effective data for the analysis and synthesis of fluidic elements.

Yamamoto, K.; Nomoto, A.; Yamashita, H.

58

Dynamic topography over the Antarctic continent  

NASA Astrophysics Data System (ADS)

Our knowledge of dynamic topography in Antarctica remains in an infancy stage compared to other continents. We assess the space-time variability in dynamic topography in Antarctica by analysing grids of global dynamic topography from present-day to 80 Ma based on the tomographic model S40RTS. Our model reveals that the Gamburtsev Province and Dronning Maud Land, two of the major nucleation sites for the East Antarctic Ice Sheet (EAIS) were ~500 m higher 60 Ma ago. The increased elevation may have facilitated ephemeral ice cap development in the early Cenozoic. Between ca 25 and 50 Ma the northern Wilkes Subglacial Basin was ca 200 m higher than today and a major increase in regional elevation (>600 m) occurred over the last 20-15 Ma over the northern and southern Victoria Land in the Transantarctic Mountains (TAM). The most prominent signal is observed over the Ross Sea Rift (RSR) where predicted Neogene dynamic topography exceeds 1,000 m. The flow of warm mantle from the West Antarctic Rift System (WARS) may have driven these dynamic topography effects over the TAM and RSR. However, we found that these effects are comparatively less significant over the Marie Byrd Land Dome and the interior of the WARS. If these contrasting dynamic topography effects are included, then the predicted elevations of the Ross Sea Embayment ca 20 Ma ago are more similar to the interior of the WARS, with significant implications for the early development of the West Antarctic Ice Sheet

Anderson, L.; Ferraccioli, F.; Eagles, G.; Steinberger, B. M.; Ritsema, J. E.

2012-12-01

59

Corneal topography measurements for biometric applications  

NASA Astrophysics Data System (ADS)

The term biometrics is used to describe the process of analyzing biological and behavioral traits that are unique to an individual in order to confirm or determine his or her identity. Many biometric modalities are currently being researched and implemented including, fingerprints, hand and facial geometry, iris recognition, vein structure recognition, gait, voice recognition, etc... This project explores the possibility of using corneal topography measurements as a trait for biometric identification. Two new corneal topographers were developed for this study. The first was designed to function as an operator-free device that will allow a user to approach the device and have his or her corneal topography measured. Human subject topography data were collected with this device and compared to measurements made with the commercially available Keratron Piccolo topographer (Optikon, Rome, Italy). A third topographer that departs from the standard Placido disk technology allows for arbitrary pattern illumination through the use of LCD monitors. This topographer was built and tested to be used in future research studies. Topography data was collected from 59 subjects and modeled using Zernike polynomials, which provide for a simple method of compressing topography data and comparing one topographical measurement with a database for biometric identification. The data were analyzed to determine the biometric error rates associated with corneal topography measurements. Reasonably accurate results, between three to eight percent simultaneous false match and false non-match rates, were achieved.

Lewis, Nathan D.

60

Evaluation of corneal thickness and topography in normal eyes using the Orbscan corneal topography system  

Microsoft Academic Search

AIMSTo map the thickness, elevation (anterior and posterior corneal surface), and axial curvature of the cornea in normal eyes with the Orbscan corneal topography system.METHODS94 eyes of 51 normal subjects were investigated using the Orbscan corneal topography system. The anterior and posterior corneal elevation maps were classified into regular ridge, irregular ridge, incomplete ridge, island, and unclassified patterns, and the

Zuguo Liu; Andrew J Huang; Stephen C Pflugfelder

1999-01-01

61

Development of Global Bathymetry and Topography at 15 arc seconds  

NASA Astrophysics Data System (ADS)

The global bathymetry provided at approximately 1 km resolution (SRTM30_PLUS) is used in many scientific studies and is also displayed in Google Earth over most of the oceans where higher resolution data is unavailable. One problem with this compilation is that the ubiquitous abyssal hill fabric, evident in multibeam bathymetry, is poorly resolved at 1 km resolution. In an effort to better resolve seafloor features globally we are developing a 500 m global bathymetry and topography grid following the approach of Smith and Sandwell [1997] and Becker et al., [2009]. Land topography is derived from three sources: hole-filled SRTM 3-arc second topography provided by CGIAR (http://srtm.csi.cgiar.org/), ASTER GDEM (http://www.gdem.aster.ersdac.or.jp/) for latitudes where SRTM us unavailable, and the ICESAT DEM ( http://nsidc.org/data ) for Greenland and Antarctica. Topography of some larger lakes has been included. Ocean bathymetry is based on three data types coming from hundreds of sources. 1) A newly developed altimetry-derived bathymetry is used as the low-resolution (~10 km) shape of the ocean basins between latitudes +/- 81 degrees. This new model uses the latest marine gravity based on all non-repeat orbit altimeters including CryoSat and Envisat. 2) Higher resolution grids have been added from the LDEO Ridge Multibeam Synthesis Project, the JAMSTEC Data Site for Research Cruises, and the NGDC Coastal Relief Model. Arctic bathymetry is mostly from the International Bathymetric Chart of the Oceans (IBCAO) [Jakobsson et al., 2012]. 3) The best resolution comes from a reanalysis of the US multibeam data archived at the National Geophysical Data Center. The main difficulty with gridding the bathymetry data at this higher resolution is that millions of erroneous bathymetric soundings, that were previously hidden by the 1 km median filtering are visible at 500 m resolution. These outliers must be edited using both automated and manual methods. At the meeting we'll report the progress on this new global compilation.

Becker, J. J.; Sandwell, D. T.

2012-12-01

62

ENGINEERING POLYMER SURFACE CHEMISTRY AND TOPOGRAPHY VIA ADDITIVE MIGRATION AND PHYSICAL SECTIONING  

Microsoft Academic Search

This work detailed in this thesis has developed two new technologies for modifying polymer surfaces with variable chemistry and topography: 1. Surfadditive (surface-active-additive) approach for polymer surface chemistry modification during molding. This concept was demonstrated by the synthesis and application of two types of surfadditives. The first type of surfadditive is a block copolymer having the “head-neck-body” structure. The “head”

Hongyan Gu

2011-01-01

63

Mars topography harmonics and geophysical implications  

NASA Technical Reports Server (NTRS)

The paper describes an improved model of Martian global topography which has been obtained by fitting a sixteenth-degree harmonic series to occultation, radar, spectral, and photogrammetric measurements. Empirical elevation data based on photographic data are used to supplement the observations in areas without data. Values for the mean radius, the mean density, and the displacement of the center of the figure from the center of mass are presented. The reported geometric flattening is too great and the reported dynamic flattening is too small for Mars to be homogeneous and hydrostatic. Maps of the data distribution, global topography, and Bouguer gravity anomaly are interpreted in terms of a crustal thickness map which is consistent with gravity, topography, and recent preliminary Viking seismic results.

Bills, B. G.; Ferrari, A. J.

1978-01-01

64

Calculating the topography of a differentiated Vesta  

NASA Astrophysics Data System (ADS)

Previous examination of the topography of a homogenous Vesta revealed an immense, seemingly abnormal impact crater near the south pole of the asteroid. The crater appeared anomalously shallow, with an extremely tall central peak, suggesting an unusual formation or subsequent modification. Conversely, Vesta is almost certainly differentiated, and we incorporate this notion to reexamine its topography. We find that the central peak is well below the crater rim and that the overall depth of the crater increases, giving it a more ordinary profile. The large density contrast between the metallic core and the overlying silicate layers has the strongest control on the topography. As previously discussed, the location of the crater at the south pole suggests polar wander, necessitating a mechanical structure that allows reorientation of Vesta's large rotational bulge yet preserves the crater's shape, a possibly restrictive scenario. NASA's Dawn spacecraft may observe tectonics consistent with polar wander.

Kattoum, Yaser N.; Dombard, Andrew J.

2009-12-01

65

Topography of Earth's Inner Core Boundary  

NASA Astrophysics Data System (ADS)

Lateral variations in the structure and crystallization of the inner core will likely be associated with lateral variations in the topography of its boundary. Depending on liquid fraction and the ratio of solid over liquid viscosity, the process of compaction of solids and expulsion of fluids at the solidifying boundary can be dynamically unstable, resulting in small-scale corrugations of the boundary of 0.1 to 5 km height with a horizontal scale on the order of 1 to 10 km. Evidence of such ICB topography has been inferred from waveforms of PKiKP doublets (1). An additional observation consistent ICB topography includes the seismic wave diffracted around the top of the inner core (PKP-Cdiff), whose travel time agrees with that predicted by the AK135 Earth model, but whose amplitude decays more rapidly into the inner core shadow than is predicted by AK135 (2). These observations are modeled by synthesizing seismic body waves with a pseudospectral method (3) having a densified grid in the vicinity of a rough ICB. Validation of the forward modeling includes a comparison of results obtained with a boundary element method. Modeled spectra of ICB topography are used to constrain the parameters and processes that produce the topography. These include compaction length (assuming freezing upward from below), the structure of precipitated piles (assuming metallic snow falling from above), the sedimentary processes due to flow in the overlying F-layer of the outer core, and the relaxation of topography from viscous deformation of the inner core. 1. Cao, A., Y. Masson, and B. Romanowicz, PNAS, 104, 31-35, 2007. 2. Zou, Z., K. Koper, and V.F. Cormier, J. Geophys. Res., 113, 2008. doi: 10.1029/2007JB005316. 3. Furumura T., B.L.N. Kennett, and M. Furumura, Geophys. J. Int., 135, 845--860, 1998.

Cormier, V. F.; Zheng, Y.; Hernlund, J. W.

2011-12-01

66

Noninterferometric topography measurements of fast moving surfaces.  

PubMed

The topography of moving surfaces is recovered by noninterferometric measurements. The phase reconstruction is derived by measuring the intensities of a backscattered pulsed laser light and solving the transport intensity equation (TIE). The TIE is solved by expanding the phase into a series of Zernike polynomials, leading to a set of appropriate algebraic equations. This technique, which enables us to make a direct connection between experiments and the TIE, has been successfully tested in gas gun experiments. In particular, the topographies of a moving projectile and the free surface of a shocked target were recovered. PMID:21811317

Pinhasi, Shirly Vinikman; Eliezer, Shalom; Glam, Benny; Appelbaum, Gabi; Bakshi, Lior

2011-08-01

67

Effects of patterned topography on biofilm formation  

NASA Astrophysics Data System (ADS)

Bacterial biofilms are a population of bacteria attached to each other and irreversibly to a surface, enclosed in a matrix of self-secreted polymers, among others polysaccharides, proteins, DNA. Biofilms cause persisting infections associated with implanted medical devices and hospital acquired (nosocomial) infections. Catheter-associated urinary tract infections (CAUTIs) are the most common type of nosocomial infections accounting for up to 40% of all hospital acquired infections. Several different strategies, including use of antibacterial agents and genetic cues, quorum sensing, have been adopted for inhibiting biofilm formation relevant to CAUTI surfaces. Each of these methods pertains to certain types of bacteria, processes and has shortcomings. Based on eukaryotic cell topography interaction studies and Ulva linza spore studies, topographical surfaces were suggested as a benign control method for biofilm formation. However, topographies tested so far have not included a systematic variation of size across basic topography shapes. In this study patterned topography was systematically varied in size and shape according to two approaches 1) confinement and 2) wetting. For the confinement approach, using scanning electron microscopy and confocal microscopy, orienting effects of tested topography based on staphylococcus aureus (s. aureus) (SH1000) and enterobacter cloacae (e. cloacae) (ATCC 700258) bacterial models were identified on features of up to 10 times the size of the bacterium. Psuedomonas aeruginosa (p. aeruginosa) (PAO1) did not show any orientational effects, under the test conditions. Another important factor in medical biofilms is the identification and quantification of phenotypic state which has not been discussed in the literature concerning bacteria topography characterizations. This was done based on antibiotic susceptibility evaluation and also based on gene expression analysis. Although orientational effects occur, phenotypically no difference was observed between the patterned topography tested. Another potential strategy for biofilm control through patterned topography is based on the design of robust non-wetting surfaces with undercut feature geometries, characterized by 1) breakthrough pressure and 2) triple phase contact line model. It was found that height and presence of undercut had statistically significant effects, directly proportional to breakthrough pressures, whereas extent of undercut did not. A predictive triple phase contact line model was also developed. (Full text of this dissertation may be available via the University of Florida Libraries web site. Please check http://www.uflib.ufl.edu/etd.html)

Vasudevan, Ravikumar

68

On the tectonic origin of Iberian topography  

Microsoft Academic Search

The present-day topography of the Iberian peninsula can be considered as the result of the Mesozoic–Cenozoic tectonic evolution of the Iberian plate (including rifting and basin formation during the Mesozoic and compression and mountain building processes at the borders and inner part of the plate, during the Tertiary, followed by Neogene rifting on the Mediterranean side) and surface processes acting

A. M. Casas-Sainz; G. de Vicente

2009-01-01

69

The relationship between Martian gravity and topography  

Microsoft Academic Search

The relationship between gravity and topography of various regions of Mars is used to estimate their effective elastic thicknesses Te using direct measurements of line of sight velocity, rather than spherical harmonic coefficients. Estimates of Te vary from 70 km for Tharsis, 29 km for Elysium, to 14.5 km for the southern hemisphere, and show that the thickness of the

Dan McKenzie; David N. Barnett; Dah-Ning Yuan

2002-01-01

70

Carpal tunnel topography during endoscopic decompression  

Microsoft Academic Search

The safety of the endoscopic technique for carpal tunnel release remains a major concern. Serious complications such as division nerves, tendons or vessels may occur. In this study the topography of the carpal tunnel was studied in fresh cadaver hands after the introduction of the blade assembly of a one portal system. By using a plastination method, it was possible

J. Koebke; W. Schäfer; T. Aust

1999-01-01

71

EEG topography recognition by neural networks  

Microsoft Academic Search

Electroencephalography (EEG) pattern-recognition studies were carried out using EEG topography (readiness potential, or RP, spatiotemporal patterns) generated the moment before voluntary movements of muscles. RPs generated prior to pronouncing syllables and controlling a joystick were studied by experiments and simulation. The spatiotemporal patterns of RPs were measured by multichannel surface electrodes pasted on the subject's scalp. Backpropagation neural networks were

A. Hiraiwa; K. Shimohara; Y. Tokunaga

1990-01-01

72

Ocean Surface Topography from Space - Science  

NSDL National Science Digital Library

This site, from the Jet Propulsion Laboratory at the California Institute of Technology, describes the scientific applications of ocean surface topography from missions such as TOPEX/Poseidon and Jason-1. Other topics include uses of the collected data, such as evaluations of ocean circulation, tides, weather and climate patterns, and other trends.

Laboratory, Jet P.; Nasa

73

Localized Gravity/Topography Admittances on Mars  

NASA Technical Reports Server (NTRS)

Admittances from Mars Global Surveyor (MGS) gravity and topography yield estimates of lithosphere thickness on Mars: central Tharsis > 100 km, Alba Patera = 50 km, southern highlands < 20 km (but south polar cap > 50 km). Alba Patera and Elysium Rise are similar structures.

McGovern, Patrick J.; Solomon, Sean C.; Smith, David E.; Zuber, Maria T.; Neumann, Gregory A.; Head, James W.

2000-01-01

74

Sea bottom topography imaging with SAR  

NASA Technical Reports Server (NTRS)

It is well known that under favorable meteorological and hydrodynamical conditions the bottom topography of shallow seas can be mapped with airborne or spaceborne imaging radar. This phenomenon was observed for the first time in 1969 by de Loor and co-workers in Q-band Side Looking Airborne Radar (SLAR) imagery of sandwaves in the North Sea. It is now generally accepted that the imaging mechanism consists of three steps: (1) interaction between (tidal) current and bottom topography causes spatial modulations in the surface current velocity; (2) modulations in the surface current velocity give rise to variations in the spectrum of wind-generated waves, as described by the action balance equation; and (3) variations in the wave spectrum show up as intensity modulations in radar imagery. In order to predict radar backscatter modulations caused by sandwaves, an imaging model, covering the three steps, was developed by the Dutch Sea Bottom Topography Group. This model and some model results will be shown. On 16 Aug. 1989 an experiment was performed with the polarimetric P-, L-, and C-band synthetic aperture radar (SAR) of NASA/JPL. One scene was recorded in SAR mode. On 12 Jul. 1991 another three scenes were recorded, of which one was in the ATI-mode (Along-Track Interferometer). These experiments took place in the test area of the Sea Bottom Topography Group, 30 km off the Dutch coast, where the bottom topography is dominated by sand waves. In-situ data were gathered by a ship in the test area and on 'Measuring Platform Noordwijk', 20 km from the center of the test area. The radar images made during the experiment were compared with digitized maps of the bottom. Furthermore, the profiles of radar backscatter modulation were compared with the results of the model. During the workshop some preliminary results of the ATI measurements will be shown.

Vanderkooij, M. W. A.; Wensink, G. J.; Vogelzang, J.

1992-01-01

75

A layout dependent full-chip copper electroplating topography model  

Microsoft Academic Search

In this paper, a layout dependent full-chip electroplating (ECP) topography model is developed based on the additive nature of the physics of the EP process. Two layout attributes: layout density, and feature perimeter sum are used to compute the post-ECP topography. Under a unified mechanism, two output variables representing the final topography: the array height and the step height are

Jianfeng Luo; Qing Su; Charles Chiang; Jamil Kawa

2005-01-01

76

The Belize margin revisited. 2. Origin of Holocene antecedent topography  

Microsoft Academic Search

The importance of antecedent topography in dictating Holocene facies patterns has been generally recognized. There is, however, disagreement as to origin or lithology of the antecedent topography, particularly with respect to the siliciclastic or carbonate nature of the underlying topography and structural patterns. To help resolve these problems, published and unpublished information have been compiled to produce a structural fabric

Edward G. Purdy; Eberhard Gischler; Anthony J. Lomando

2003-01-01

77

Curvature sensor for the measurement of the static corneal topography and the dynamic tear film topography in the human eye  

NASA Astrophysics Data System (ADS)

A system to measure the topography of the first optical surface of the human eye noninvasively by using a curvature sensor is described. The static corneal topography and the dynamic topography of the tear film can both be measured, and the topographies obtained are presented. The system makes possible the study of the dynamic aberrations introduced by the tear film to determine their contribution to the overall ocular aberrations in healthy eyes, eyes with corneal pathologies, and eyes wearing contact lenses.

Gruppetta, Steve; Koechlin, Laurent; Lacombe, François; Puget, Pascal

2005-10-01

78

New null screen design for corneal topography  

NASA Astrophysics Data System (ADS)

In this work we report the design of a null screen for corneal topography. Here we assume that the corneal surface is an ellipsoid with a diameter of 12 mm and a curvature radius of 7.8 mm. To avoid the difficulties in the alignment of the test system due to the face contour (eyebrows, nose, or eyelids), we design a conical null-screen with spots (similar to ellipses) drawn on it in such a way that its image, which is formed by reflection on the test surface, becomes an exact radial array of circular spots if the surface is perfect. Additionally, we performed a numerical simulation introducing Gaussian random errors in the coordinates of the centroids of the spots on the image plane, and in the coordinates of the sources (spots on the null-screen) in order to obtain the conical null-screen that reduces the error in the evaluation of the topography.

Campos-García, Manuel; Estrada-Molina, Amilcar; Díaz-Uribe, Rufino

2011-08-01

79

Diffraction imaging (topography) with monochromatic synchrotron radiation  

NASA Technical Reports Server (NTRS)

Structural information of special interest to crystal growers and device physicists is now available from high resolution monochromatic synchrotron diffraction imaging (topography). In the review, the importance of superior resolution in momentum transfer and in space is described, and illustrations are taken from a variety of crystals: gallium arsenide, cadmium telluride, mercuric iodide, bismuth silicon oxide, and lithium niobate. The identification and understanding of local variations in crystal growth processes are shown. Finally, new experimental opportunities now available for exploitation are indicated.

Steiner, Bruce; Kuriyama, Masao; Dobbyn, Ronald C.; Laor, Uri

1988-01-01

80

Topography over South America from ERS altimetry  

NASA Technical Reports Server (NTRS)

The results of the surface topography mapping of South America during the ERS-1 geodetic mission are presented. The altimeter waveforms, the range measurement, and the internal and Doppler range corrections were obtained. The atmospheric corrections and solid tides were calculated. Comparisons between Shuttle laser altimetry and ERS-1 altimetry grid showed good agreement. Satellite radar altimetry data can be used to improve the topographic knowledge of regions for which only poor elevation data currently exist.

Brenner, Anita; Frey, Herb; DiMarzio, John; Tsaoussi, Lucia

1997-01-01

81

Mercury and Vesta - Preliminary shape and topography  

NASA Astrophysics Data System (ADS)

This year two spacecraft, MESSENGER and Dawn, were placed into orbit around Mercury and the asteroid Vesta, respectively. We have been using stereophotoclinometry (SPC) to analyze MESSENGER and Dawn images both for navigation and to determine the precise shapes and topography of these bodies. Because SPC requires images at different local Sun elevations and azimuths to distinguish between albedo and topographic variations, Mercury presents the challenges of a slow spin rate and a long solar day. Vesta, on the other hand, rotates more than four times per Earth day, allowing a given area of surface to be viewed under rapidly changing illumination and topographic information to be built up rapidly. The essence of SPC is that small pieces of surface called maplets and modeled with digital elevation and albedo are illuminated and correlated with images. Hundreds of these maplets are found in each image, providing a valuable data type for spacecraft navigation. Hundreds of images go into the construction of each maplet, and the resulting multi-image stereo over a wide range of viewing conditions provides a precise determination of the maplet's body-fixed position. The construction of topography with SPC uses each pixel, allowing resolutions comparable to the images themselves. Mercury's topography varies by about 5 km above and below that of a sphere of radius 2440 km. We compare the SPC-derived shape and topography with data from MESSENGER's Mercury Laser Altimeter (MLA). Vesta, although a tenth of Mercury's size, exhibits variations in elevation between 17 km below and 12 km above the equipotential that best matches its surface. The lowest areas lie on the floor of the south polar impact crater, and the highest points lie on the crater's rim.

Gaskell, R. W.; Palmer, E. E.; Mastrodemos, N.; Barnouin, O. S.; Jorda, L.; Taylor, A. H.

2011-12-01

82

Sensory properties of menthol and smoking topography  

Microsoft Academic Search

Although there is a great deal known about menthol as a flavoring agent in foods and confections, less is known about the\\u000a particular sensory properties of menthol cigarette smoke. Similarly, although smoking topography (the unique way an individual\\u000a smokes a cigarette) has been well studied using non-menthol cigarettes, there is relatively less known about how menthol affects\\u000a smoking behavior. The

Deirdre Lawrence; Brie Cadman; Allison C Hoffman

2011-01-01

83

ATM Coastal Topography-Alabama 2001  

USGS Publications Warehouse

These remotely sensed, geographically referenced elevation measurements of Lidar-derived first surface (FS) topography were produced collaboratively by the U.S. Geological Survey (USGS), Florida Integrated Science Center (FISC), St. Petersburg, FL, and the National Aeronautics and Space Administration (NASA), Wallops Flight Facility, VA. This project provides highly detailed and accurate datasets of the Alabama coastline, acquired October 3-4, 2001. The datasets are made available for use as a management tool to research scientists and natural resource managers. An innovative scanning Lidar instrument originally developed by NASA, and known as the Airborne Topographic Mapper (ATM), was used during data acquisition. The ATM system is a scanning Lidar system that measures high-resolution topography of the land surface, and incorporates a green-wavelength laser operating at pulse rates of 2 to 10 kilohertz. Measurements from the laser ranging device are coupled with data acquired from inertial navigation system (INS) attitude sensors and differentially corrected global positioning system (GPS) receivers to measure topography of the surface at accuracies of +/-15 centimeters. The nominal ATM platform is a Twin Otter or P-3 Orion aircraft, but the instrument may be deployed on a range of light aircraft. Elevation measurements were collected over the survey area using the ATM system, and the resulting data were then processed using the Airborne Lidar Processing System (ALPS), a custom-built processing system developed in a NASA-USGS collaboration. ALPS supports the exploration and processing of Lidar data in an interactive or batch mode. Modules for pre-survey flight line definition, flight path plotting, Lidar raster and waveform investigation, and digital camera image playback have been developed. Processing algorithms have been developed to extract the range to the first and last significant return within each waveform. ALPS is routinely used to create maps that represent submerged or first surface topography.

Nayegandhi, Amar; Yates, Xan; Brock, John C.; Sallenger, A.H.; Bonisteel, Jamie M.; Klipp, Emily S.; Wright, C. Wayne

2009-01-01

84

ATM Coastal Topography-Mississippi, 2001  

USGS Publications Warehouse

These remotely sensed, geographically referenced elevation measurements of lidar-derived first-surface (FS) topography were produced collaboratively by the U.S. Geological Survey (USGS), Florida Integrated Science Center (FISC), St. Petersburg, FL, and the National Aeronautics and Space Administration (NASA), Wallops Flight Facility, VA. This project provides highly detailed and accurate datasets of the Mississippi coastline, from Lakeshore to Petit Bois Island, acquired September 9-10, 2001. The datasets are made available for use as a management tool to research scientists and natural-resource managers. An innovative scanning lidar instrument originally developed by NASA, and known as the Airborne Topographic Mapper (ATM), was used during data acquisition. The ATM system is a scanning lidar system that measures high-resolution topography of the land surface and incorporates a green-wavelength laser operating at pulse rates of 2 to 10 kilohertz. Measurements from the laser-ranging device are coupled with data acquired from inertial navigation system (INS) attitude sensors and differentially corrected global positioning system (GPS) receivers to measure topography of the surface at accuracies of +/-15 centimeters. The nominal ATM platform is a Twin Otter or P-3 Orion aircraft, but the instrument may be deployed on a range of light aircraft. Elevation measurements were collected over the survey area using the ATM system, and the resulting data were then processed using the Airborne Lidar Processing System (ALPS), a custom-built processing system developed in a NASA-USGS collaboration. ALPS supports the exploration and processing of lidar data in an interactive or batch mode. Modules for presurvey flight-line definition, flight-path plotting, lidar raster and waveform investigation, and digital camera image playback have been developed. Processing algorithms have been developed to extract the range to the first and last significant return within each waveform. ALPS is used routinely to create maps that represent submerged or first-surface topography.

Nayegandhi, Amar; Yates, Xan; Brock, John C.; Sallenger, A.H.; Klipp, Emily S.; Wright, C. Wayne

2009-01-01

85

Evolution of Neogene Dynamic Topography in Africa  

NASA Astrophysics Data System (ADS)

The characteristic basins and swells of Africa's surface topography probably reflect patterns of convective circulation in the sub-lithospheric mantle. We have interrogated drainage networks to determine the spatial and temporal pattern of convectively driven uplift. ~560 longitudinal river profiles were extracted from a digital elevation model of Africa. An inverse model is then used to minimise the misfit between observed and calculated river profiles as a function of uplift rate history. During inversion, the residual misfit decreases from ~22 to ~5. Our results suggest that Africa's topography began to grow most rapidly after ~30 Ma at peak uplift rates of 0.1-0.15 mm/yr. The algorithm resolves distinct phases of uplift which generate localized swells of high topography and relief (e.g. the Angolan Dome). Uplift rate histories are shown to vary significantly from swell to swell. The calculated magnitudes, timing, and location of uplift agree well with local independent geological constraints, such as intense volcanism at Hoggar (42-39 Ma) and Afar (31-29 Ma), uplifted marine terraces, and warped peneplains. We have also calculated solid sediment flux histories for major African deltas which have persisted through time. This onshore record provides an important indirect constraint on the history of vertical motions at the surface, and agrees well with the offshore flux record, obtained from mapping isopachs of deltaic sediments. Our modelling and reconstructed sedimentary flux histories indicate that the evolution of drainage networks may contain useful information about mantle convective processes.

Paul, Jonathan; Roberts, Gareth; White, Nicky

2013-04-01

86

Long wavelength gravity and topography anomalies  

NASA Technical Reports Server (NTRS)

It is shown that gravity and topography anomalies on the earth's surface may provide new information about deep processes occurring in the earth, such as those associated with mantle convection. Two main reasons are cited for this. The first is the steady improvement that has occurred in the resolution of the long wavelength gravity field, particularly in the wavelength range of a few hundred to a few thousand km, mainly due to increased coverage of terrestrial gravity measurements and the development of radar altimeters in orbiting satellites. The second reason is the large number of numerical and laboratory experiments of convection in the earth, including some with deformable upper and lower boundaries and temperature-dependent viscosity. The oceans are thought to hold the most promise for determining long wavelength gravity and topography anomalies, since their evolution has been relatively simple in comparison with that of the continents. It is also shown that good correlation between long wavelength gravity and topography anomalies exists over some portions of the ocean floor

Watts, A. B.; Daly, S. F.

1981-01-01

87

OpenTopography: Enabling Online Access to High-Resolution Lidar Topography Data and Processing Tools  

NASA Astrophysics Data System (ADS)

High-resolution topography data acquired with lidar (light detection and ranging) technology are revolutionizing the way we study the Earth's surface and overlying vegetation. These data, collected from airborne, tripod, or mobile-mounted scanners have emerged as a fundamental tool for research on topics ranging from earthquake hazards to hillslope processes. Lidar data provide a digital representation of the earth's surface at a resolution sufficient to appropriately capture the processes that contribute to landscape evolution. The U.S. National Science Foundation-funded OpenTopography Facility (http://www.opentopography.org) is a web-based system designed to democratize access to earth science-oriented lidar topography data. OpenTopography provides free, online access to lidar data in a number of forms, including the raw point cloud and associated geospatial-processing tools for customized analysis. The point cloud data are co-located with on-demand processing tools to generate digital elevation models, and derived products and visualizations which allow users to quickly access data in a format appropriate for their scientific application. The OpenTopography system is built using a service-oriented architecture (SOA) that leverages cyberinfrastructure resources at the San Diego Supercomputer Center at the University of California San Diego to allow users, regardless of expertise level, to access these massive lidar datasets and derived products for use in research and teaching. OpenTopography hosts over 500 billion lidar returns covering 85,000 km2. These data are all in the public domain and are provided by a variety of partners under joint agreements and memoranda of understanding with OpenTopography. Partners include national facilities such as the NSF-funded National Center for Airborne Lidar Mapping (NCALM), as well as non-governmental organizations and local, state, and federal agencies. OpenTopography has become a hub for high-resolution topography resources. Datasets hosted by other organizations, as well as lidar-specific software, can be registered into the OpenTopography catalog, providing users a "one-stop shop" for such information. With several thousand active users, OpenTopography is an excellent example of a mature Spatial Data Infrastructure system that is enabling access to challenging data for research, education and outreach. Ongoing OpenTopography design and development work includes the archive and publication of datasets using digital object identifiers (DOIs); creation of a more flexible and scalable high-performance environment for processing of large datasets; expanded support for satellite and terrestrial lidar; and creation of a "pluggable" infrastructure for third-party programs and algorithms. OpenTopography has successfully created a facility for sharing lidar data. In the project's next phase, we are working to enable equally easy and successful sharing of services for processing and analysis of these data.

Crosby, Christopher; Nandigam, Viswanath; Baru, Chaitan; Arrowsmith, J. Ramon

2013-04-01

88

Wafer topography proximity effect modeling and correction for implant layer patterning  

NASA Astrophysics Data System (ADS)

Photolithography on reflective surfaces with topography can cause overexposure in some areas in the photoresist, resulting in undesired critical dimension (CD) variations in the printed patterns. Using bottom anti-reflective coatings (BARCs) will reduce the severity of the problem. However it is not a preferred solution in some situations due to added process complexity, such as the case of implant blocking layer patterning. This topography proximity effect (TPE) has been ignored in the mask synthesis flow for the 45nm and larger nodes due to its relatively small impact to the CDs. When the device critical length reaches 32nm and lower, the variations on the implant layer caused by underlying topography becomes more and more an issue and need to be addressed properly. In order to do that, simulation with nonplanar stack is required. The available tools for photolithography simulation with wafer topography, such as Synopsys' Sentaurus Lithography (S-Litho), usually adopt a rigorous approach based on the solution of the Maxwell equations and unsuitable for full chip optical proximity correction (OPC) due to their prohibitively long runtimes. A fast method for TPE modeling is needed to make full chip TPE correction feasible. In this paper, we propose a computationally fast approximate method that captures TPE well. It enables fast model calibration and full chip implant layer mask correction, and fits in the current OPC flows easily. We validate the method's effectiveness by comparing its simulation results with those produced by Sentaurus Lithography. We also show how it helps implant layer mask synthesis that takes TPE from previous layers into consideration.

Song, Hua; Shiely, James; Su, Irene; Zhang, Lin; Lei, Wen-Kang

2009-10-01

89

The relationship between Martian gravity and topography  

NASA Astrophysics Data System (ADS)

The relationship between gravity and topography of various regions of Mars is used to estimate their effective elastic thicknesses Te using direct measurements of line of sight velocity, rather than spherical harmonic coefficients. Estimates of Te vary from 70 km for Tharsis, 29 km for Elysium, to 14.5 km for the southern hemisphere, and show that the thickness of the Martian lithosphere increases with age as the radioactive isotopes of K, Th, and U decay. A simple parameterised model of the convective thermal history is used to estimate the temperature structure of the lithosphere, and shows that the base of the elastic layer has a temperature of 300±50°C, or similar to the value for terrestrial continents. In both cases the rheology is probably affected by the presence of water. The short wavelength behaviour of the gravity field allows the density of the rocks that form the topography to be estimated, and gives values of about 3.0 Mg/m 3 for Tharsis and Elysium. This value is substantially greater than that of 2.7 Mg/m 3 obtained for Earth, and is in agreement with estimates from SNC (Shergottites-Nahklites-Chassigny) meteorites of 3.3 Mg/m 3. The density of the topography of Valles Marineris is only 2.35 Mg/m 3, and suggests that ice may be present below the surface. In the heavily bombarded southern hemisphere, isostatic compensation occurs at wavelengths as short as 700 km, which requires the effective compensation depth to be no more than 10 km. The gravity field with wavelengths greater than 1500 km may be supported dynamically, by a plume rising beneath the Tharsis region. The difference in temperature between the solidus and the present areotherm is less than 250°C, so melt generation can occur in rising plumes.

McKenzie, Dan; Barnett, David N.; Yuan, Dah-Ning

2002-01-01

90

Macromolecular Topography Leaps into the Digital Age  

NASA Technical Reports Server (NTRS)

A low-cost, real-time digital topography system is under development which will replace x-ray film and nuclear emulsion plates. The imaging system is based on an inexpensive surveillance camera that offers a 1000x1000 array of 8 im square pixels, anti-blooming circuitry, and very quick read out. Currently, the system directly converts x-rays to an image with no phosphor. The system is small and light and can be easily adapted to work with other crystallographic equipment. Preliminary images have been acquired of cubic insulin at the NSLS x26c beam line. NSLS x26c was configured for unfocused monochromatic radiation. Six reflections were collected with stills spaced from 0.002 to 0.001 degrees apart across the entire oscillation range that the reflections were in diffracting condition. All of the reflections were rotated to the vertical to reduce Lorentz and beam related effects. This particular CCD is designed for short exposure applications (much less than 1 sec) and so has a relatively high dark current leading to noisy raw images. The images are processed to remove background and other system noise with a multi-step approach including the use of wavelets, histogram, and mean window filtering. After processing, animations were constructed with the corresponding reflection profile to show the diffraction of the crystal volume vs. the oscillation angle as well as composite images showing the parts of the crystal with the strongest diffraction for each reflection. The final goal is to correlate features seen in reflection profiles captured with fine phi slicing to those seen in the topography images. With this development macromolecular topography finally comes into the digital age.

Lovelace, J.; Bellamy, H.; Snell, E. H.; Borgstahl, G.

2003-01-01

91

Seismic waveform sensitivity to global boundary topography  

NASA Astrophysics Data System (ADS)

We investigate the implications of lateral variations in the topography of global seismic discontinuities, in the framework of high-resolution forward modelling and seismic imaging. We run 3-D wave-propagation simulations accurate at periods of 10 s and longer, with Earth models including core-mantle boundary topography anomalies of ˜1000 km spatial wavelength and up to 10 km height. We obtain very different waveform signatures for PcP (reflected) and Pdiff (diffracted) phases, supporting the theoretical expectation that the latter are sensitive primarily to large-scale structure, whereas the former only to small scale, where large and small are relative to the frequency. PcP at 10 s seems to be well suited to map such a small-scale perturbation, whereas Pdiff at the same frequency carries faint signatures that do not allow any tomographic reconstruction. Only at higher frequency, the signature becomes stronger. We present a new algorithm to compute sensitivity kernels relating seismic traveltimes (measured by cross-correlation of observed and theoretical seismograms) to the topography of seismic discontinuities at any depth in the Earth using full 3-D wave propagation. Calculation of accurate finite-frequency sensitivity kernels is notoriously expensive, but we reduce computational costs drastically by limiting ourselves to spherically symmetric reference models, and exploiting the axial symmetry of the resulting propagating wavefield that collapses to a 2-D numerical domain. We compute and analyse a suite of kernels for upper and lower mantle discontinuities that can be used for finite-frequency waveform inversion. The PcP and Pdiff sensitivity footprints are in good agreement with the result obtained cross-correlating perturbed and unperturbed seismogram, validating our approach against full 3-D modelling to invert for such structures.

Colombi, Andrea; Nissen-Meyer, Tarje; Boschi, Lapo; Giardini, Domenico

2012-09-01

92

Evaluation of entire-cornea topography measurement  

NASA Astrophysics Data System (ADS)

We quantitatively evaluated a technique for combining multiple videokeratograph views of different areas of cornea. To achieve this we first simulated target reflection from analytic descriptions of various shapes believed to mimic common corneal topographies. The splicing algorithm used the simulated reflections to achieve a good quality estimation of the shapes. Actual imagery was then acquired of manufactured models of the same shapes and the splicing algorithm was found to achieve a less perfect estimation. The cause was thought mainly to be image blur due to defocus. To investigate this, blur was introduced into the reflection simulation, and the results of the splicing algorithm compared to those found from the actual imagery.

Shevlin, Fergal P.; Klein, Stanley A.; Mandell, Robert B.; Carney, Thom

2000-06-01

93

Comparison of parameters describing stratified surface topography  

NASA Astrophysics Data System (ADS)

There are a lot of methods of two-process surface topography description. Some parameters can be computed from material ratio graph. There are included in ISO standards. The methods described in ISO standards 13565-2 (Pk, Ppk, Pvk, Pmr1 and Pmr2) and 13565-3 (Pmq, Pvq and Pmq) are compared in this paper. Profiles with given values of Pmq, Pvq and Pmq parameters and wavelengths were modelled. For these profiles, material ratio curve and Pk, Ppk, Pvk, Pmr1 and Pmr2 parameters were calculated. As a result, dependencies among parameters from ISO 13565-3 and ISO 13565-2 standard were found.

Pawlus, P.; Reizer, R.; Lenart, A.

2014-03-01

94

EAARL Coastal Topography - Sandy Hook 2007  

USGS Publications Warehouse

These remotely sensed, geographically referenced elevation measurements of Lidar-derived topography were produced as a collaborative effort between the U.S. Geological Survey (USGS), Florida Integrated Science Center (FISC), St. Petersburg, FL; the National Park Service (NPS), Northeast Coastal and Barrier Network, Kingston, RI; and the National Aeronautics and Space Administration (NASA), Wallops Flight Facility, VA. This project provides highly detailed and accurate datasets of Gateway National Recreation Area's Sandy Hook Unit in New Jersey, acquired on May 16, 2007. The datasets are made available for use as a management tool to research scientists and natural resource managers. An innovative airborne Lidar instrument originally developed at the NASA Wallops Flight Facility, and known as the Experimental Advanced Airborne Research Lidar (EAARL) was used during data acquisition. The EAARL system is a raster-scanning, waveform-resolving, green-wavelength (532-nanometer) Lidar designed to map near-shore bathymetry, topography, and vegetation structure simultaneously. The EAARL sensor suite includes the raster-scanning, water-penetrating full-waveform adaptive Lidar, a down-looking red-green-blue (RGB) digital camera, a high-resolution multi-spectral color infrared (CIR) camera, two precision dual-frequency kinematic carrier-phase GPS receivers and an integrated miniature digital inertial measurement unit, which provide for submeter georeferencing of each laser sample. The nominal EAARL platform is a twin-engine Cessna 310 aircraft, but the instrument may be deployed on a range of light aircraft. A single pilot, a Lidar operator, and a data analyst constitute the crew for most survey operations. This sensor has the potential to make significant contributions in measuring sub-aerial and submarine coastal topography within cross-environmental surveys. Elevation measurements were collected over the survey area using the EAARL system, and the resulting data were then processed using the Airborne Lidar Processing System (ALPS), a custom-built processing system developed in a NASA-USGS collaboration. ALPS supports the exploration and processing of Lidar data in an interactive or batch mode. Modules for pre-survey flight line definition, flight path plotting, Lidar raster and waveform investigation, and digital camera image playback have been developed. Processing algorithms have been developed to extract the range to the first and last significant return within each waveform. ALPS is routinely used to create maps that represent submerged or first surface topography. Specialized filtering algorithms have been implemented to determine the 'bare earth' under vegetation from a point cloud of last return elevations.

Nayegandhi, Amar; Brock, John C.; Wright, C. Wayne; Stevens, Sara; Yates, Xan; Bonisteel, Jamie M.

2008-01-01

95

Measurement of the topography of human cadaver lenses using the PAR corneal topography system  

NASA Astrophysics Data System (ADS)

To measure the radius of curvature and asphericity of the anterior and posterior surfaces of crystalline lenses of human Eye-Bank eyes using the PAR Corneal Topography System. The measured values will be used in an optical model of the eye for lens refilling procedures.

Fernandez, Viviana; Manns, Fabrice; Zipper, Stanley; Sandadi, Samith; Hamaoui, Marie; Tahi, Hassan; Ho, Arthur; Parel, Jean-Marie A.

2001-06-01

96

Evaluation of facial palsy by moire topography  

NASA Astrophysics Data System (ADS)

To evaluate facial nerve function, the visual assessment method proposed by the Japan Society of Facial Research is used frequently. It is of great value clinically, but the method has several weak points concerning objective and quantitative assessment. This study uses moire topography to solve these problems. mA moire camera, FM3013, of the lattice irradiation type was used for measurement of the face. Five moire photographs were taken: at rest, wrinkling the forehead, closing the eyes lightly, blowing out the cheeks and grinning. The degree of facial palsy was determined by the Asymmetry Index (AI) as a measure of the degree of facial deviation. Total AI was expressed as the average AI based on calculations of the measurement in 5 photos. Severe paralysis is represented by an AI of more than 20%. Partial paralysis has a range of 20-8%. Nearly normal is judged to be less than 8%. Ten normal individuals are measured as control and show an AI of 3% or less. Moire topography is useful in assessing the recovery process because it has the benefit of making the site and grade of palsy easily achieved by the AI and the deviation in its patterns. The authors propose that the moire method is better for an objective and quantitative evaluation than the society's method.

Inokuchi, Ikuo; Kawakami, Shinichiro; Maeta, Manabu; Masuda, Yu

1991-08-01

97

Reduction of linewidth variation over reflective topography  

NASA Astrophysics Data System (ADS)

As device dimensions have shrunk well below the one micron level, linewidth control particularly over reflective topography has become a major problem in optical lithography. Other than reflective notching caused by light reflected into unwanted areas, thin-film interference is the major contributor to linewidth variations. Small changes in film thickness over steps cause significant changes in the amount of energy deposited into photoresist films. Various methods used to solve this problem are investigated to measure their relative effectiveness. Conventional photoresist, dyed-resist, bottom layer ARCs (antireflective coatings; both inorganic and organic), TAR (top-antireflective layer) and CEL (contrast enhancement layer) as a special case of TAR are compared for their relative effectiveness as well as their advantages and disadvantages for use in manufacturing. Simulations and functional evaluation of film thickness effects on exposure requirement and on linewidths as well as imaging over topography are used as a means of comparison. The use of TAR is a relatively new approach to solving this problem in a simple, effective manner. Material choice depends on film refractive index and ease of processing. Several TAR materials have been investigated and are discussed.

Miura, Steve S.; Lyons, Christopher F.; Brunner, Timothy A.

1992-06-01

98

Hydrothermal circulation in fault slots with topography  

NASA Astrophysics Data System (ADS)

There are numerous cases where the circulation of hydrothermal fluid is likely to be confined within a permeable fault slot. Examples are (1) the Lost City Hydrothermal Field (LCHF) at 30 N in the Atlantic, which is likely to be controlled by large E-W faults related to the Atlantis transform fault and mass wasting on the southern wall of the Atlantis Massif, and (2) large normal faults bounding the Hess Deep rift in the East Pacific, which contain intense hydrothermal metamorphic assemblages in lower crustal gabbros formed at 200-350 ° C. This type of circulation could occur anywhere where steep faults cut the oceanic crust, including large near-axis normal faults, transform faults and faults at subduction bend zones, and could be the major way in which the upper mantle and lower crust are hydrated. It is therefore important to constrain the controls on temperature conditions of alteration and hence mineral assemblages. Previous 2-D modelling of the LCHF shows that seafloor topography and permeability structure combine together to localise the field near the highest point of the Atlantis Massif. Our new models are 3-D, based on a 10km cube with seafloor topography of ~ 2km affecting both the fault slot and impermeable wall rocks. We have used Comsol multiphysics in this modelling, with a constant basal heatflow corresponding to the near conductive thermal gradient measured in IODP Hole 1309D, 5km north of the LCHF, and a constant temperature seafloor boundary condition. The wall rocks of the slot have a permeability of 10-17 m2 while permeability in the slot is varied between 10-14 and 10-15 m2. Initial conditions are a conductive thermal structure corresponding to the basal heatflow at steady state. Generic models not based on any particular known topography quickly stabilise a hydrothermal system in the fault slot with a single upflow zone close to the model edge with highest topography. In models with a depth of circulation in the fault slot of about 6 km, after an initial period of higher temperature venting which removes heat from the initial condition, venting temperature is approximately 200 ° C with a permeability of 3x10-15 m2. This falls to about 170 ° C with a permeability of 5x10-15 m2. Temperatures can be reduced by restricting the depth of hydrothermal circulation. These temperatures correspond to prehnite-chlorite assemblages seen in fault rocks at Hess Deep, but are higher than those observed at the LCHF. Work is continuing to vary permeability, fault slot geometry and topography to better match the conditions in the Atlantis Massif, and to model the effects of dyke intrusion into the fault zone as observed at Hess Deep.

Titarenko, Sofya; McCaig, Andrew

2014-05-01

99

Optic nerve head topography and static perimetry in glaucoma diagnostics  

NASA Astrophysics Data System (ADS)

Analysis of the optic nerve head topography and static perimetry, are important in glaucoma diagnostics. Topography of the optic nerve head by Topographic Scanning Systems, carries a lot of planimetric and volumetric values. In this paper, results of optic nerve head topography and static perimetry of 116 primary open angle glaucoma cases, are discussed. Estimating correlation between topographic and perimetric data, the most valuable parameter of the topographic method is carried out. Its values in different stages of glaucoma are given.

Rzendkowski, Marek; Janiec, Slawomir; Momot-Kawalska, Barbara; Blazejewska-Meller, Grazyna

1998-10-01

100

Surface topography evolution and fatigue fracture in polysilicon MEMS structures  

Microsoft Academic Search

This paper presents the results of an experimental study of the micromechanisms of surface topography evolution and fatigue fracture in polysilicon MEMS structures. The initial stages of fatigue are shown to be associated with stress-assisted surface topography evolution and the thickening of SiO2 layers that form on the unpassivated polysilicon surfaces and crack\\/notch faces. The differences in surface topography and

Seyed M. Allameh; Pranav Shrotriya; Alex Butterwick; Stuart B. Brown; Wole O. Soboyejo

2003-01-01

101

Assimilation of altimeter topography into oceanic models  

NASA Technical Reports Server (NTRS)

The primary goals of the authors are to build an intuition for assimilation techniques and to investigate the impact of variable altimeter topography on simple or complex oceanic models. In particular, applying various techniques and sensitivity studies to model and data constraints plays a key role. We are starting to use quasi-geostrophic, semigeostrophic, and primitive-equation (PE) models and to test the schemes in regions of interest to the World Ocean Circulation Experiment (WOCE), as well as in the northeast Atlantic and the Mediterranean. The impact of scatterometer wind forcing on the results is also investigated. The use of Geosat, European Remote Sensing satellite (ERS-1), and TOPEX/POSEIDON altimetry data is crucial in fine tuning the models and schemes to the selected areas of interest.

Demey, Pierre; Menard, Yves; Pinardi, Nadia; Schroeter, J.; Verron, J.

1991-01-01

102

Forecasting Hurricane Impact on Coastal Topography  

NASA Astrophysics Data System (ADS)

Extreme storms can have a profound impact on coastal topography and thus on ecosystems and human-built structures within coastal regions. For instance, landfalls of several recent major hurricanes have caused significant changes to the U.S. coastline, particularly along the Gulf of Mexico. Some of these hurricanes (e.g., Ivan in 2004, Katrina and Rita in 2005, and Gustav and Ike in 2008) led to shoreline position changes of about 100 meters. Sand dunes, which protect the coast from waves and surge, eroded, losing several meters of elevation in the course of a single storm. Observations during these events raise the question of how storm-related changes affect the future vulnerability of a coast.

Plant, Nathaniel G.; Stockdon, Hilary F.; Sallenger, Asbury H.; Turco, Michael J.; East, Jeffery W.; Taylor, Arthur A.; Shaffer, Wilson A.

2010-02-01

103

Mean Dynamic Topography of the Arctic Ocean  

NASA Technical Reports Server (NTRS)

ICESat and Envisat altimetry data provide measurements of the instantaneous sea surface height (SSH) across the Arctic Ocean, using lead and open water elevation within the sea ice pack. First, these data were used to derive two independent mean sea surface (MSS) models by stacking and averaging along-track SSH profiles gathered between 2003 and 2009. The ICESat and Envisat MSS data were combined to construct the high-resolution ICEn MSS. Second, we estimate the 5.5-year mean dynamic topography (MDT) of the Arctic Ocean by differencing the ICEn MSS with the new GOCO02S geoid model, derived from GRACE and GOCE gravity. Using these satellite-only data we map the major features of Arctic Ocean dynamical height that are consistent with in situ observations, including the topographical highs and lows of the Beaufort and Greenland Gyres, respectively. Smaller-scale MDT structures remain largely unresolved due to uncertainties in the geoid at short wavelengths.

Farrell, Sinead Louise; Mcadoo, David C.; Laxon, Seymour W.; Zwally, H. Jay; Yi, Donghui; Ridout, Andy; Giles, Katherine

2012-01-01

104

EAARL Submarine Topography - Biscayne National Park  

USGS Publications Warehouse

Project Description This lidar-derived submarine topography map was produced as a collaborative effort between the U.S. Geological Survey (USGS) Coastal and Marine Geology Program, National Park Service (NPS) South Florida/Caribbean Network Inventory and Monitoring Program, and the National Aeronautics and Space Administration (NASA) Wallops Flight Facility. One objective of this research is to create techniques to survey coral reefs for the purposes of habitat mapping, ecological monitoring, change detection, and event assessment (for example: bleaching, hurricanes, disease outbreaks). As part of this project, data from an innovative instrument under development at the NASA Wallops Flight Facility, the NASA Experimental Airborne Advanced Research Lidar (EAARL) are being used. This sensor has the potential to make significant contributions in this realm for measuring water depth and conducting cross-environment surveys. High spectral resolution, water-column correction, and low costs were found to be key factors in providing accurate and affordable imagery to managers of coastal tropical habitats.

Brock, John C.; Wright, C. Wayne; Patterson, Matt; Nayegandhi, Amar; Patterson, Judd; Harris, Melanie S.; Mosher, Lance

2006-01-01

105

Mean dynamic topography of the Arctic Ocean  

NASA Astrophysics Data System (ADS)

ICESat and Envisat altimetry data provide measurements of the instantaneous sea surface height (SSH) across the Arctic Ocean, using lead and open water elevation within the sea ice pack. First, these data were used to derive two independent mean sea surface (MSS) models by stacking and averaging along-track SSH profiles gathered between 2003 and 2009. The ICESat and Envisat MSS data were combined to construct the high-resolution ICEn MSS. Second, we estimate the 5.5-year mean dynamic topography (MDT) of the Arctic Ocean by differencing the ICEn MSS with the new GOCO02S geoid model, derived from GRACE and GOCE gravity. Using these satellite-only data we map the major features of Arctic Ocean dynamical height that are consistent with in situ observations, including the topographical highs and lows of the Beaufort and Greenland Gyres, respectively. Smaller-scale MDT structures remain largely unresolved due to uncertainties in the geoid at short wavelengths.

Farrell, Sinéad Louise; McAdoo, David C.; Laxon, Seymour W.; Zwally, H. Jay; Yi, Donghui; Ridout, Andy; Giles, Katharine

2012-01-01

106

EAARL Topography - Dry Tortugas National Park  

USGS Publications Warehouse

Project Description This lidar-derived submarine topography map was produced as a collaborative effort between the U.S. Geological Survey (USGS) Coastal and Marine Geology Program, National Park Service (NPS) South Florida/Caribbean Network Inventory and Monitoring Program, and the National Aeronautics and Space Administration (NASA) Wallops Flight Facility. One objective of this research is to create techniques to survey coral reefs for the purposes of habitat mapping, ecological monitoring, change detection, ad event assessment (for example: bleaching, hurricanes, disease outbreaks). As part of this project, data from an innovative instrument under development at the NASA Wallops Flight Facility, the NASA Experimental Airborne Advanced Research Lidar (EAARL) are being used. This sensor has the potential to make significant contributions in this realm for measuring water depth and conducting cross-environment surveys. High spectral resolution, water-column correction, and low costs were found to be key factors in providing accurate and affordable imagery to managers of coastal tropical habitats.

Brock, John C.; Wright, C. Wayne; Patterson, Matt; Nayegandhi, Amar; Patterson, Judd

2008-01-01

107

Evolution of Neogene Dynamic Topography in Madagascar  

NASA Astrophysics Data System (ADS)

Madagascar is located on the fringes of the African superswell. Its position and the existence of a +30 mGal long wavelength free-air gravity anomaly suggest that its present-day topography is maintained by convective circulation of the sub-lithospheric mantle. Residual depth anomalies of oceanic crust encompassing the island imply that Madagascar straddles a dynamic topographic gradient. In June-July 2012, we examined geologic evidence for Neogene uplift around the Malagasy coastline. Uplifted coral reef deposits, fossil beach rock, and terraces demonstrate that the northern and southern coasts are probably being uplifted at a rate of ~0.2 mm/yr. Rates of uplift clearly vary around the coastline. Inland, extensive peneplains occur at elevations of 1 - 2 km. These peneplains are underlain by 10 - 20 m thick laterite deposits, and there is abundant evidence for rapid erosion (e.g. lavaka). Basaltic volcanism also occurred during Neogene times. These field observations can be combined with an analysis of drainage networks to determine the spatial and temporal pattern of convectively driven uplift. ~100 longitudinal river profiles were extracted from a digital elevation model of Madagascar. An inverse model is then used to minimize the misfit between observed and calculated river profiles as a function of uplift rate history. During inversion, the residual misfit decreases from ~20 to ~4. Our results suggest that youthful and rapid uplift of 1-2 km occurred at rates of 0.2-0.4 mm/yr during the last ?15 Myr. The algorithm resolves distinct phases of uplift which generate localized swells of high topography and relief (e.g. the Hauts Plateaux). Our field observations and modeling indicate that the evolution of drainage networks may contain useful information about mantle convective processes.

Paul, J. D.; Roberts, G.; White, N. J.

2012-12-01

108

Seismological Modeling of Inner Core Boundary Topography  

NASA Astrophysics Data System (ADS)

Earth's solid inner core is created by the slow freezing of a well-mixed, vigorously convecting, iron-rich outer core. The structure near inner core boundary (ICB) has a significant effect on core dynamics including the mechanisms behind the growth of inner core and the compositional convection driving the geodynamo. A dynamically unstable process of compaction of solids and expulsion of fluids at a solidifying boundary can produce small-scale corrugations of the inner core boundary with heights on the order of 1km, consistent with a number of previous observations of body waves interacting with the ICB. We determine topographic models of a rough ICB that match the observed PKiKP and PKP-Cdiff waveforms. In order to constrain parameters of the modeled topography, the observations are compared with synthetic seismograms generated using a boundary element method that exploits a dense discretization along the surface of the ICB. This method of modeling is more computationally efficient and flexible than finite difference methods previously used in these studies, which in turn allows us to make our calculations more accurate. The implementation of the modeling procedure starts by setting up boundary element method for a two-layered homogeneous interior and exterior of ICB system and later adds the real Earth's radial inhomogeneity to the exterior where propagation of rays are calculated using ray theory. An initial test is carried out to identify the parametric limits of models where ICB topography begins to impose observable effects to the PKiKP coda at approximately 50° great circle distance.

de Silva, S. M.; Cormier, V. F.; Zheng, Y.; Hernlund, J. W.

2013-12-01

109

Bedrock topography beneath the Red Lake peatlands  

SciTech Connect

Detailed hydrologic investigations of peat landforms in the Red Lake Peatlands have revealed that groundwater flow is significantly related to the type of landform and vegetation community present at a given site. Hydrogeologic modeling of shallow groundwater systems suggests that bedrock topography is an important, perhaps the vital, boundary condition controlling groundwater flow. Determination of depth to bedrock beneath different peat landforms is necessary to test the hydrogeologic models and obtain a better understanding of the processes which produce them. Direct determination of bedrock depth in peatlands is hampered by the difficult conditions and high costs of boring. In addition, environmental impacts from boring activities would probably be substantial in these sensitive ecosystems. Shallow seismic methods appear to be the most promising approach to obtain the necessary data. Unfortunately the 2+ meters of peat covering Lake Agassiz sediments overlying the bedrock is not only a poor substrate for geophone emplacement, but is a strong attenuator of seismic waves. These difficulties have been overcome by constructing a tool which allows the geophones to be emplaced beneath the peat and into the top of the sediments. The shotgun cartridge source is also located beneath the peat. This combination results in very good seismic records, far better than those possible with surface sources and geophones. The results from a preliminary survey along a 600m line show that there are significant variations in bedrock topography below the peat. In a distance of less than 500m, depth to bedrock changes by about 30%, from about 55m to about 40m. This is similar to variations indicated by the models.

Miller, P.; Shaw, G.H. (Union Coll., Schenectady, NY (United States). Geology Dept.); Glaser, P. (Univ. of Minnesota, Minneapolis, MN (United States). Limnological Research Center); Siegel, D. (Syracuse Univ., NY (United States). Dept. of Geology)

1992-01-01

110

The Role of Topography in Glacial Inception  

NASA Astrophysics Data System (ADS)

We test the influence of model topography on glacial inception using a coupled atmosphere-slab ocean version of NCAR’s Community Climate System Model (CCSM3). Simulations employ a modern orbital configuration and greenhouse gas concentrations representing both recent (year 1990) and hypothetically lower present-day values in accordance with Ruddiman’s Early Anthropogenic Hypothesis (240 ppm CO2 and 450 ppb CH4). The model is run at two different resolutions: a relatively coarse horizontal configuration (T42, approximately 2.8 degrees) and comparatively fine resolution (T85, approximately 1.4 degrees). Although under contemporary greenhouse forcing the extent of permanent boreal snow cover in the two model configurations is similar, imposing lower concentrations of CO2 and CH4 generates much more extensive glacial inception in the T85 experiment (150% increase) than in the T42 version (80% increase). Furthermore, the spatial patterns of glacial inception differ considerably. Only the T85 resolution produces widespread permanent snow cover over the Rocky Mountains and on Baffin Island, consistent with geologic evidence for ice sheet nucleation in northeastern Canada. Although much of the enhanced sensitivity in the higher-resolution simulations is directly attributable to the colder and wetter conditions around elevated topography, some of the response also appears to be driven dynamically and remotely as a function of the simulated elevation of Greenland. The colder conditions over and downstream of the Greenland Ice Sheet in the modern T85 simulation promote a smaller cooling locally under lowered greenhouse forcing that seems to activate a wave-1 dynamical response in the atmospheric pressure field. The resulting circulation anomalies favor stronger upslope wind flow from the Pacific Ocean over the northern Rocky Mountains, enhancing the regional development of a permanent snow pack. Although these experiments are driven by greenhouse forcing rather than historical orbital variations, we believe that our findings apply to the general mechanisms of glacial inception.

Vavrus, S. J.; Philippon-Berthier, G.; Kutzbach, J. E.; Ruddiman, W. F.

2009-12-01

111

Destabilization of barotropic flows small-scale topography  

NASA Astrophysics Data System (ADS)

The stability of a barotropic zonal jet aligned with zonal topography on the beta-plane is investigated. The topography is assumed to be spatially periodic, with a period much smaller than the width of the jet. The problem is examined both by linear normal-mode analysis and by direct numerical simulations.

Benilov, E. S.; Nycander, J.; Dritschel, D. G.

2004-10-01

112

Bottom Topography as a Control Variable in an Ocean Model  

Microsoft Academic Search

The possibility of using topography in a state estimation context as a control parameter is explored in a linear barotropic shallow water model. Along with its adjoint, the model is used to systematically assess the influence of the depth field on the modeled circulation in a steady state. Sensitivity of the flow field to the topography is greater in a

Martin Losch; Carl Wunsch

2003-01-01

113

Accuracy and resolution of shuttle radar topography mission data  

Microsoft Academic Search

We assess the accuracy and resolution of topography data provided by the Shuttle Radar Topography Mission (SRTM) through spectral comparisons with the National Elevation Dataset (NED) and a high-resolution laser data set of the 1999 Hector Mine earthquake rupture. We find that SRTM and the NED are coherent for wavelengths greater than 200 m, however the spatial resolution of the

Bridget Smith; David Sandwell

2003-01-01

114

Numerical wind analysis on complex topography using multiscale simulation model  

Microsoft Academic Search

We calculate the wind flow around the complex terrain to examine the environmental flow by the topography effect around the urban area. In Japan, comparatively many cities face the mountain and\\/or the ocean. In such cities, cold air may blow from the mountain and\\/or the ocean, and the wind from the mountainous topography affects the cities environment. To examine the

Takeshi Sugimura; Keiko Takahashi; Makoto Iida

2009-01-01

115

Stratified Quasi-geostrophic Flow Over Rough Topography  

NASA Astrophysics Data System (ADS)

Averaged equations describing large-scale, quasi-geostrophic flow over small-scale, one-dimensional topography are derived, and some of their solutions are examined. In the scaling regime considered, the interior dynamics is governed by the usual lin- earized potential-vorticity equation, while a new bottom boundary condition is found as a result of the topography. This boundary condition is nonlinear and depends ex- plicitly on the topography height through a linear transform of its correlation function. Linear waves are easily found as solutions of the averaged equations. In the particular case of vanishing interior potential vorticity -- the case of surface quasi-geostrophic dynamics -- nonlinear waves (both periodic and solitary) can also be found explic- itly: they satisfy a nonlinear pseudo-differential equation which reduces to the Peierls­ Nabarro equation for sinusoidal topography. A modification of Eady's model of baro- clinic instability which takes into account small-scale topography is also discussed.

Vanneste, J.

116

Synthetic river valleys: Creating prescribed topography for form–process inquiry and river rehabilitation design  

NASA Astrophysics Data System (ADS)

The synthesis of artificial landforms is complementary to geomorphic analysis because it affords a reflection on both the characteristics and intrinsic formative processes of real world conditions. Moreover, the applied terminus of geomorphic theory is commonly manifested in the engineering and rehabilitation of riverine landforms where the goal is to create specific processes associated with specific morphology. To date, the synthesis of river topography has been explored outside of geomorphology through artistic renderings, computer science applications, and river rehabilitation design; while within geomorphology it has been explored using morphodynamic modeling, such as one-dimensional simulation of river reach profiles, two-dimensional simulation of river networks, and three-dimensional simulation of subreach scale river morphology. To date, no approach allows geomorphologists, engineers, or river rehabilitation practitioners to create landforms of prescribed conditions. In this paper a method for creating topography of synthetic river valleys is introduced that utilizes a theoretical framework that draws from fluvial geomorphology, computer science, and geometric modeling. Such a method would be valuable to geomorphologists in understanding form–process linkages as well as to engineers and river rehabilitation practitioners in developing design surfaces that can be rapidly iterated. The method introduced herein relies on the discretization of river valley topography into geometric elements associated with overlapping and orthogonal two-dimensional planes such as the planform, profile, and cross section that are represented by mathematical functions, termed geometric element equations. Topographic surfaces can be parameterized independently or dependently using a geomorphic covariance structure between the spatial series of geometric element equations. To illustrate the approach and overall model flexibility examples are provided that are associated with mountain, lowland, and hybrid synthetic river valleys. To conclude, recommended advances such as multithread channels are discussed along with potential applications.

Brown, R. A.; Pasternack, G. B.; Wallender, W. W.

2014-06-01

117

Stereo Pair: Inverted Topography, Patagonia, Argentina  

NASA Technical Reports Server (NTRS)

The Meseta de Somuncura is a broad plateau capped by basalt. Near its western edge is evidence of multiple volcanic events and a complex erosion history. Most notable are the long, narrow-, and winding lava flows that run across most of the right side of the image. These formed from low-viscosity lava that flowed down gullies over fairly flat terrain. Later, erosion of the landscape continued and the solidified flows were more resistant than the older surrounding rocks. Consequently, the flows became the ridges we see here. This natural process of converting gullies to ridges is called topographic inversion. See image PIA02755 (upper left corner) for a good example of topographic inversion in its earlier stages.

Other features seen here include numerous and varied closed depressions. The regional drainage is not well integrated, and drainage ends up in salty lakes (blue if shallow, black if deep). Wind streaks indicate that winds blow toward the east (right) and blow salt grains off the lakebeds when dry. The bowtie pattern in the upper left has resulted from differing grazing practices among fenced fields.

This cross-eyed stereoscopic image pair was generated using topographic data from the Shuttle Radar Topography Mission, combined with an enhanced Landsat 7satellite color image. The topography data are used to create two differing perspectives of a single image, one perspective for each eye. In doing so, each point in the image is shifted slightly, depending on its elevation. When stereoscopically merged, the result is a vertically exaggerated view of the Earth's surface in its full three dimensions.

Landsat satellites have provided visible light and infrared images of the Earth continuously since 1972. SRTM topographic data match the 30-meter (99-foot) spatial resolution of most Landsat images and provide a valuable complement for studying the historic and growing Landsat data archive. The Landsat 7 Thematic Mapper image used here was provided to the SRTM project by the United States Geological Survey, Earth Resources Observation Systems (EROS) Data Center,Sioux Falls, South Dakota.

Elevation data used in this image was acquired by the Shuttle Radar Topography Mission (SRTM) aboard the Space Shuttle Endeavour, launched on February 11,2000. SRTM used the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. SRTM was designed to collect three-dimensional measurements of the Earth's surface. To collect the 3-D data, engineers added a 60-meter-long (200-foot) mast, installed additional C-band and X-band antennas, and improved tracking and navigation devices. The mission is a cooperative project between the National Aeronautics and Space Administration (NASA), the National Imagery and Mapping Agency (NIMA) of the U.S. Department of Defense (DoD), and the German and Italian space agencies. It is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA, for NASA's Earth Science Enterprise,Washington, DC.

Size: 21.5 kilometers (13.4 miles) x 27.2 kilometers (16.9 miles) Location: 41.6 deg. South lat., 67.9 deg. West lon. Orientation: North toward upper left Image Data: Landsat bands 1,4,7 in blue, green, red Date Acquired: February 19, 2000 (SRTM), January 22, 2000 (Landsat)

2000-01-01

118

Topography and Volcanoes on Io (color)  

NASA Technical Reports Server (NTRS)

The images used to create this enhanced color composite of Io were acquired by NASA's Galileo spacecraft during its seventh orbit (G7) of Jupiter. Low sun angles near the terminator (day-night boundary near the left side of the image) offer lighting conditions which emphasize the topography or relief on the volcanic satellite. The topography appears very flat near the active volcanic centers such as Loki Patera (the large dark horse-shoe shaped feature near the terminator) while a variety of mountains and plateaus exist elsewhere. The big reddish-orange ring in the lower right is formed by material deposited from the eruption of Pele, Io's largest volcanic plume.

North is to the top of this picture which merges images obtained with the clear, red, green, and violet filters of the solid state imaging (CCD) system on NASA's Galileo spacecraft. The resolution is 6.1 kilometers per picture element. The images were taken on April 4th, 1997 at a range of 600,000 kilometers.

The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is an operating division of California Institute of Technology (Caltech).

Concurrent results from Galileo's exploration of Io appear in the October 15th, 1997 issue of Geophysical Research Letters. The papers are: Temperature and Area Constraints of the South Volund Volcano on Io from the NIMS and SSI Instruments during the Galileo G1 Orbit, by A.G. Davies, A.S. McEwen, R. Lopes-Gautier, L. Keszthelyi, R.W. Carlson and W.D. Smythe. High-temperature hot spots on Io as seen by the Galileo Solid-State Imaging (SSI) experiment, by A. McEwen, D. Simonelli, D. Senske, K. Klassen, L. Keszthelyi, T. Johnson, P. Geissler, M. Carr, and M. Belton. Io: Galileo evidence for major variations in regolith properties, by D. Simonelli, J. Veverka, and A. McEwen.

This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://galileo.jpl.nasa.gov. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo

1997-01-01

119

New Global Bathymetry and Topography Model Grids  

NASA Astrophysics Data System (ADS)

A new version of the "Smith and Sandwell" global marine topography model is available in two formats. A one-arc-minute Mercator projected grid covering latitudes to +/- 80.738 degrees is available in the "img" file format. Also available is a 30-arc-second version in latitude and longitude coordinates from pole to pole, supplied as tiles covering the same areas as the SRTM30 land topography data set. The new effort follows the Smith and Sandwell recipe, using publicly available and quality controlled single- and multi-beam echo soundings where possible and filling the gaps in the oceans with estimates derived from marine gravity anomalies observed by satellite altimetry. The altimeter data have been reprocessed to reduce the noise level and improve the spatial resolution [see Sandwell and Smith, this meeting]. The echo soundings database has grown enormously with new infusions of data from the U.S. Naval Oceanographic Office (NAVO), the National Geospatial-intelligence Agency (NGA), hydrographic offices around the world volunteering through the International Hydrographic Organization (IHO), and many other agencies and academic sources worldwide. These new data contributions have filled many holes: 50% of ocean grid points are within 8 km of a sounding point, 75% are within 24 km, and 90% are within 57 km. However, in the remote ocean basins some gaps still remain: 5% of the ocean grid points are more than 85 km from the nearest sounding control, and 1% are more than 173 km away. Both versions of the grid include a companion grid of source file numbers, so that control points may be mapped and traced to sources. We have compared the new model to multi-beam data not used in the compilation and find that 50% of differences are less than 25 m, 95% of differences are less than 130 m, but a few large differences remain in areas of poor sounding control and large-amplitude gravity anomalies. Land values in the solution are taken from SRTM30v2, GTOPO30 and ICESAT data. GEBCO has agreed to adopt this model and begin updating it in 2009. Ongoing tasks include building an uncertainty model and including information from the latest IBCAO map of the Arctic Ocean.

Smith, W. H.; Sandwell, D. T.; Marks, K. M.

2008-12-01

120

Basins of attraction on random topography.  

PubMed

We investigate the consequences of fluid flowing on a continuous surface upon the geometric and statistical distribution of the flow. We find that the ability of a surface to collect water by its mere geometrical shape is proportional to the curvature of the contour line divided by the local slope. Consequently, rivers tend to lie in locations of high curvature and flat slopes. Gaussian surfaces are introduced as a model of random topography. For Gaussian surfaces the relation between convergence and slope is obtained analytically. The convergence of flow lines correlates positively with drainage area, so that lower slopes are associated with larger basins. As a consequence, we explain the observed relation between the local slope of a landscape and the area of the drainage basin geometrically. To some extent, the slope-area relation comes about not because of fluvial erosion of the landscape, but because of the way rivers choose their path. Our results are supported by numerically generated surfaces as well as by real landscapes. PMID:11308547

Schorghofer, N; Rothman, D H

2001-02-01

121

Basal topography of Kronebreen, NW Svalbard  

NASA Astrophysics Data System (ADS)

Kronebreen is a tidewater outlet glacier draining the icefield Holtedahlfonna, in the Kongsfjord area of NW Svalbard. Like most glaciers in Svalbard, Kronebreen has been in retreat since the first front positions were recorded, with the exception of a brief advance during the surge of the neighboring glacier Kongsvegen around 1948. Kronebreen is one of the fastest non-surging glaciers in Svalbard, with average annual velocities near the calving front of around 450 m/yr. It has not been possible until recently to calculate ice fluxes, however, since the bottom topography of Kronebreen has been unknown. In 2009, ice thickness data were obtained using low frequency radar from helicopter over the heavily crevassed Kronebreen. These new thickness data are combined with surface elevation maps, older ice depth data, and fjord bathymetry data to create an expanded bed map of the Kongsfjord area. Velocity data of Kronebreen derived from feature tracking of high-res visible imagery is also combined with thickness data to calculate estimates of flux throughout the glacier. Analysis of this new data will give a better understanding of Kronebreen's retreat history, its mass balance and flux into Kongsfjord, and help in making predictions of when and how quickly further glacier retreat may occur.

O'Sadnick, M.; Kohler, J.; Langley, K.; Kehrl, L. M.; Berthier, E.

2010-12-01

122

Predicting maximum lake depth from surrounding topography.  

PubMed

Information about lake morphometry (e.g., depth, volume, size, etc.) aids understanding of the physical and ecological dynamics of lakes, yet is often not readily available. The data needed to calculate measures of lake morphometry, particularly lake depth, are usually collected on a lake-by-lake basis and are difficult to obtain across broad regions. To span the gap between studies of individual lakes where detailed data exist and regional studies where access to useful data on lake depth is unavailable, we developed a method to predict maximum lake depth from the slope of the topography surrounding a lake. We use the National Elevation Dataset and the National Hydrography Dataset - Plus to estimate the percent slope of surrounding lakes and use this information to predict maximum lake depth. We also use field measured maximum lake depths from the US EPA's National Lakes Assessment to empirically adjust and cross-validate our predictions. We were able to predict maximum depth for ?28,000 lakes in the Northeastern United States with an average cross-validated RMSE of 5.95 m and 5.09 m and average correlation of 0.82 and 0.69 for Hydrological Unit Code Regions 01 and 02, respectively. The depth predictions and the scripts are openly available as supplements to this manuscript. PMID:21984945

Hollister, Jeffrey W; Milstead, W Bryan; Urrutia, M Andrea

2011-01-01

123

Inversion of topography in Martian highland terrains  

SciTech Connect

Ring furrows are flat-floored trenches, circulate in plan view, forming rings 7 to 50 km in diameter. Typically, ring furrows, which are 0.5 km deep and 2 to 10 km wide, surround a central, flat-topped, circular mesa or plateau. The central plateau is about the same elevation or lower than the plain outside the ring. Ring furrows are unique features of the dissected martian uplands. Related landforms range from ring furrows with fractured central plateaus to circular mesas without encircling moats. Ring furrows are superposed on many types of materials, but they are most common cratered plateau-type materials that are interpreted as volcanic flow material overlying ancient cratered terrain. The ring shape and size suggest that they are related to craters partially buried by lava flows. Ring furrows were formed by preferential removal of exposed rims of partially buried craters. Evidence of overland flow of water is lacking except within the channels. Ground ice decay and sapping followed by fluvial erosion are responsible for removal of the less resistant rim materials. Thus, differential erosion has caused a reversal of topography in which the originally elevated rim is reduced to negative relief.

De Hon, R.A.

1985-01-01

124

The Cortical Topography of Local Sleep  

PubMed Central

In a recent series of experiments, we demonstrated that a visuomotor adaptation task, 12 hours of left arm immobilization, and rapid transcranial magnetic stimulation (rTMS) during waking can each induce local changes in the topography of electroencephalographic (EEG) slow wave activity (SWA) during subsequent non-rapid eye movement (NREM) sleep. However, the poor spatial resolution of EEG and the difficulty of relating scalp potentials to the activity of the underlying cortex limited the interpretation of these results. In order to better understand local cortical regulation of sleep, we used source modeling to show that plastic changes in specific cortical areas during waking produce correlated changes in SWA during sleep in those same areas. We found that implicit learning of a visuomotor adaptation task induced an increase in SWA in right premotor and sensorimotor cortices when compared to a motor control. These same areas have previously been shown to be selectively involved in the performance of this task. We also found that arm immobilization resulted in a decrease in SWA in sensorimotor cortex. Inducing cortical potentiation with repetitive transcranial magnetic stimulation (rTMS) caused an increase in SWA in the targeted area and a decrease in SWA in the contralateral cortex. Finally, we report the first evidence that these modulations in SWA may be related to the dynamics of individual slow waves. We conclude that there is a local, plasticity dependent component to sleep regulation and confirm previous inferences made from the scalp data.

Murphy, Michael; Huber, Reto; Esser, Steve; Riedner, Brady A.; Massimini, Marcello; Ferrarelli, Fabio; Ghilardi, M. Felice; Tononi, Giulio

2011-01-01

125

Shape, topography, gravity anomalies and tidal deformation of Titan  

NASA Astrophysics Data System (ADS)

Gravity measurements and elevation data from the Cassini mission have been used to create shape, global topography and gravity anomaly models of Titan that enable an improved understanding of its outer ice I shell structure. We provide constraints on the averaged ice shell thickness and its long-wavelength lateral variations, as well as the density of the subsurface ocean using gravity anomalies, the tidal Love number k2 measurement and long-wavelength topography. We found that Titan’s surface topography is consistent with an approximate isostatically compensated ice shell of variable thickness, likely in a thermally conductive or in a subcritical convective state, overlying a relatively dense subsurface ocean.

Mitri, Giuseppe; Meriggiola, Rachele; Hayes, Alex; Lefevre, Axel; Tobie, Gabriel; Genova, Antonio; Lunine, Jonathan I.; Zebker, Howard

2014-07-01

126

SRTM Anaglyph: Inverted Topography, Patagonia, Argentina  

NASA Technical Reports Server (NTRS)

The Meseta de Somuncura is a broad plateau capped by basalt. Near its western edge is evidence of multiple volcanic events and a complex erosion history. Most notable are the long, narrow, and winding lava flows that run across most of the right side of the image. These formed from low-viscosity lava that flowed down gullies over fairly flat terrain. Later, erosion of the landscape continued, and the solidified flows were more resistant than the older surrounding rocks. Consequently, the flows became the ridges we see here. This natural process of converting gullies to ridges is called topographic inversion. See image PIA02755 (upper left corner) for a good example of topographic inversion in its earlier stages.

Other features seen here include numerous and varied closed depressions. The regional drainage is not well integrated, but instead the drainage ends up in salty lakes (dark water, some with bright shores). Wind streaks indicate that winds blow toward the east (right) and blow salt grains off the lake beds when dry. The bowtie pattern in the upper left has resulted from differing grazing practices among fenced fields.

This anaglyph was generated by first draping a Landsat Thematic Mapper image over a topographic map from the Shuttle Radar Topography Mission, then producing the two differing perspectives, one for each eye. When viewed through special glasses, the result is a vertically exaggerated view of the Earth's surface in its full three dimensions. Anaglyph glasses cover the left eye with a red filter and the right eye with a blue filter.

Landsat satellites have provided visible light and infrared images of the Earth continuously since 1972. SRTM topographic data match the 30-meter (99-foot) spatial resolution of most Landsat images and provide a valuable complement for studying the historic and growing Landsat data archive. The Landsat 7 Thematic Mapper image used here was provided to the SRTM project by the United States Geological Survey, Earth Resources Observation Systems (EROS) Data Center,Sioux Falls, South Dakota.

Elevation data used in this image was acquired by the Shuttle Radar Topography Mission (SRTM) aboard the Space Shuttle Endeavour, launched on February 11,2000. SRTM used the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. SRTM was designed to collect three-dimensional measurements of the Earth's surface. To collect the 3-D data, engineers added a 60-meter-long (200-foot) mast, installed additional C-band and X-band antennas, and improved tracking and navigation devices. The mission is a cooperative project between the National Aeronautics and Space Administration (NASA), the National Imagery and Mapping Agency (NIMA) of the U.S. Department of Defense (DoD), and the German and Italian space agencies. It is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA, for NASA's Earth Science Enterprise,Washington, DC.

Size: 21.5 kilometers (13.4 miles) x 27.2 kilometers (16.9 miles) Location: 41.6 deg. South lat., 67.9 deg. West lon. Orientation: North toward upper left Image Data: Landsat band 7 (short infrared) Date Acquired: February 19, 2000 (SRTM), January 22, 2000 (Landsat)

2000-01-01

127

Science in Motion: Isolated Araneiform Topography  

NASA Technical Reports Server (NTRS)

[figure removed for brevity, see original site] Figure 1

Have you ever found that to describe something you had to go to the dictionary and search for just the right word?

The south polar terrain is so full of unearthly features that we had to visit Mr. Webster to find a suitable term. 'Araneiform' means 'spider-like'. These are channels that are carved in the surface by carbon dioxide gas. We do not have this process on Earth.

The channels are somewhat radially organized (figure 1) and widen and deepen as they converge. In the past we've just refered to them as 'spiders.' 'Isolated araneiform topography' means that our features look like spiders that are not in contact with each other.

Observation Geometry Image PSP_003087_0930 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on 24-Mar-2007. The complete image is centered at -87.1 degrees latitude, 126.3 degrees East longitude. The range to the target site was 244.4 km (152.8 miles). At this distance the image scale is 24.5 cm/pixel (with 1 x 1 binning) so objects 73 cm across are resolved. The image shown here has been map-projected to 25 cm/pixel . The image was taken at a local Mars time of 08:22 PM and the scene is illuminated from the west with a solar incidence angle of 81 degrees, thus the sun was about 9 degrees above the horizon. At a solar longitude of 206.4 degrees, the season on Mars is Northern Autumn.

2007-01-01

128

X-ray topography of a lysozyme crystal  

SciTech Connect

X-ray topography methods were employed to identify defects in lysozyme crystals. White-beam and monochromatic topographs of lysozyme crystals obtained at the National Synchrotron Light Source are presented.

Stojanoff,V.; Siddons, D.

1996-01-01

129

EAARL coastal topography--North Shore, Lake Pontchartrain, Louisiana, 2010  

USGS Publications Warehouse

This DVD contains lidar-derived coastal topography GIS datasets of a portion of the north shore of Lake Pontchartrain, Louisiana. These datasets were acquired on February 28, March 1, and March 5, 2010.

Bonisteel-Cormier, J.M.; Nayegandhi, Amar; Fredericks, Xan; Wright, C.W.; Brock, J.C.; Nagle, D.B.; Vivekanandan, Saisudha; Barras, J.A.

2012-01-01

130

Calculation of irrotational wind pattern with application to Cleveland topography  

NASA Technical Reports Server (NTRS)

Small perturbation theory is applied to compute the deflection of the wind blowing across land that has an irregular topography. As an illustration, the method is applied first to the flow around a single hill of Gaussian profile. Then calculations are made for the irregular topography on the east side of Cleveland where the elevation changes by several hundred feet. It was found that the topography produced small wind deflections that would not be of practical importance in air pollution dispersion studies. The calculations were for a neutrally stable atmosphere. Although they are not investigated here, other factors such as thermal stratification of the atmosphere, diurnal variations, and convection currents resulting from the proximity of Lake Erie and the city heat island effect are expected to be more significant than the influence of topography.

Siegel, R.

1972-01-01

131

Role of Topography in Geodetic Gravity Field Modelling.  

National Technical Information Service (NTIS)

Masses associated with the topography, bathymetry, and its isostatic compensation are a dominant source of gravity field variations, especially at shorter wavelengths. On global scales the topographic/isostatic effects are also significant, except for the...

R. Forsberg M. G. Sideris

1989-01-01

132

Stereo Topography and Subsurface Thermal Profiles on Icy Satellites  

NASA Astrophysics Data System (ADS)

Stereo topography is used in combination with numerical modeling to study the subsurface structure and thermal history of icy satellites of Jupiter and Saturn, with important implications for past and perhaps current habitability.

Phillips, C. B.

2014-02-01

133

Engineering microscale topographies to control the cell-substrate interface  

PubMed Central

Cells in their in vivo microenvironment constantly encounter and respond to a multitude of signals. While the role of biochemical signals has long been appreciated, the importance of biophysical signals has only recently been investigated. Biophysical cues are presented in different forms including topography and mechanical stiffness imparted by the extracellular matrix and adjoining cells. Microfabrication technologies have allowed for the generation of biomaterials with microscale topographies to study the effect of biophysical cues on cellular function at the cell–substrate interface. Topographies of different geometries and with varying microscale dimensions have been used to better understand cell adhesion, migration, and differentiation at the cellular and sub-cellular scales. Furthermore, quantification of cell-generated forces has been illustrated with micropillar topographies to shed light on the process of mechanotransduction. In this review, we highlight recent advances made in these areas and how they have been utilized for neural, cardiac, and musculoskeletal tissue engineering application.

Nikkhah, Mehdi; Edalat, Faramarz; Manoucheri, Sam; Khademhosseini, Ali

2013-01-01

134

Osteoblast Mechanoresponses on Ti with Different Surface Topographies  

Microsoft Academic Search

During implant healing, mechanical force is transmitted to osteogenic cells via implant surfaces with various topographies. This study tested a hypothesis that osteoblasts respond to mechanical stimulation differently on titanium with different surface topographies. Rat bone-marrow-derived osteoblastic cells were cultured on titanium disks with machined or acid-etched surfaces. A loading session consisted of a 3-minute application of a 10- or

N. Sato; K. Kubo; M. Yamada; N. Hori; T. Suzuki; H. Maeda; T. Ogawa

2009-01-01

135

Three-dimensional inversion of CSAMT data including topography  

NASA Astrophysics Data System (ADS)

CSAMT is widely used in geothermal prospecting, mineral and petroleum exploration, environmental geophysics and geological engineering. However, few data are collected on the flat surface in the field CSAMT work. Most of CSAMT data are collected in the presence of strong topography either at the source position or in the survey area. Large interpretation errors may occur in CSAMT surveys if field distortions caused by the surface topography are not considered. Therefore, the CSAMT inversion should consider the topographic effect. In this work we develop a 3D inversion algorithm for inverting CSAMT data with topography using conjugate gradient inversion method. In the 3D forward problem, the total electric and magnetic fields is separated into their primary and secondary components to calculate the response from the 3D model with irregular topography. 3D rectangular grid with stair-stepped ground-air interface is used to approximate topography. The primary electric and magnetic field can be calculated by one-dimensional modeling, using the altitude of the highest point of the topography as the altitude of the flat surface. The secondary electric and magnetic field can be calculated using the staggered-grid finite difference method. Then, the apparent resistivity and phase response can be obtained by Cagniard equation. In the 3D inversion problem, conjugate gradient method is used to invert the CSAMT apparent resistivity and phase data including topography. The background resistivity is a constant value and the anomalous resistivity is used as the inversion parameter. Only the anomalous resistivity under the surface topography is updated in the inversion. Results from the synthetic tests show the validity and stability of the inversion algorithm.

Lin, C.; Tan, H.; Tong, T.; Zeng, W.

2013-12-01

136

Influence of surface topography on elastically backscattered electrons  

NASA Astrophysics Data System (ADS)

A Monte Carlo simulation, taking into account of the detailed surface roughness of a realistic solid sample, has been performed to study the surface topography influence on elastic peak intensity. To describe quantitatively the surface topography effect, here we introduce surface roughness parameter (SRP) according to the ratio of elastic peak intensities between a rough surface and an ideal planar surface. Simulation results for Al sample have shown that SRP varies with surface roughness particularly at large incidence/emission angles.

Ding, X.; Da, B.; Gong, J. B.; Mao, S. F.; Ding, Z. J.

2014-04-01

137

Phase contrast in Simultaneous Topography and Recognition imaging.  

PubMed

The operation of a force microscope in Simultaneous Topography and Recognition (TREC) imaging mode is analyzed by means of numerical simulations. Both topography and recognition signals are analyzed by using a worm-like chain force as the specific interaction between the functionalized tip probe and the sample. The special feedback mechanism in this mode is shown to couple the phase signal to the presence of molecular recognition interactions even in absence of dissipation. PMID:19523768

Fuss, M C; Sahagún, E; Köber, M; Briones, F; Luna, M; Sáenz, J J

2009-08-01

138

X ray topography study of gallium phosphate crystals and resonators  

Microsoft Academic Search

Using the synchrotron radiation delivered by the DCI storage ring at LURE (Orsay, France), the X-ray topography technique was used to study the crystalline perfection of GaPO4 samples grown under different conditions. The growth of gallium phosphate on a berlinite seed is analyzed by X-ray section topography. The results obtained demonstrate the feasibility of gallium phosphate epitaxy on large berlinite

B. Capelle; A. Zarka; J. Schwartzel; J. Detaint; Y. Zheng; A. Ibanez; E. Philippot

1993-01-01

139

Evolution of Topography in Glaciated Mountain Ranges  

NASA Technical Reports Server (NTRS)

This thesis examines the response of alpine landscapes to the onset of glaciation. The basic approach is to compare fluvial and glacial laudscapes, since it is the change from the former to the latter that accompanies climatic cooling. This allows a detailed evaluation of hypotheses relating climate change to tectonic processes in glaciated mountain belts. Fieldwork was carried out in the eastern Sierra Nevada, California, and the Sangre de Cristo Range, Colorado, alongside digital elevation model analyses in the western US, the Southern Alps of New Zealand, and the Himalaya of northwestern Pakistan. hypothesis is overstated in its appeal to glacial erosion as a major source of relief production and subsequent peak uplift. Glaciers in the eastern Sierra Nevada and the western Sangre de Cristos have redistributed relief, but have produced only modest relief by enlarging drainage basins at the expense of low-relief topography. Glaciers have lowered valley floors and ridgelines by similar amounts, limiting the amount of "missing mass' that can be generated, and causing a decrease in drainage basin relief. The principal response of glaciated landscapes to rapid rock uplift is the development of towering cirque headwalls. This represents considerable relief production, but is not caused by glacial erosion alone. Large valley glaciers can maintain their low gradient regardless of uplift rate, which supports the "glacial buzzsaw" hypothesis. However, the inability of glaciers to erode steep hillslopes as rapidly can cause mean elevations to rise. Cosmogenic isotope dating is used to show that (i) where plucking is active, the last major glaciation removed sufficient material to reset the cosmogenic clock; and (ii) former glacial valley floors now stranded near the crest of the Sierra Nevada are at varying stages of abandonment, suggesting a cycle of drainage reorganiszation and relief inversion due to glacial erosion similar to that observed in river networks. Glaciated landscapes are quite distinct from their fluvial counterparts in both landforms and processes. Given the scarcity of purely fluvial, active mountain ranges, it is essential that glacial erosion be considered amongst the processes sculpting active orogenic belts.

Brocklehurst, Simon H.

2002-01-01

140

Overland Tsunami Flow through Complex Topography  

NASA Astrophysics Data System (ADS)

As seen in numerous Japanese eyewitness videos that captured the tsunami inundation on March 11th 2011, flow interaction with the built environment is extremely complex. In addition to the entrainment of sediment and large discrete objects such as cars and ships, tsunami energy amplification due to topographic focusing was widely observed. In coastal towns and cities, this topographic focusing was due to large structures which channelled the flow to either side, often through roadways or other low-obstruction pathways. Structures in the "line-of-fire" of this channelized flow were often found to have been inflicted with relatively greater levels of damage, while the opposite was true for structures in the flow-shadow of large buildings. In this presentation, we attempt to quantify the hydrodynamic variability of flow through complex topography, such as a city layout. Understanding this variability is of particular relevance to on-going engineering efforts to develop standards for tsunami design of coastal structures. A novel set of large-scale experimental data will be introduced and used to validate a depth-integrated model. The experiment was performed in the Tsunami Wave Basin at Oregon State University. Transient long wave flooding in a 1/50 scale model of the town of Seaside, Oregon was tested. Data from the experiment, including water elevations and co-located flow speeds, are used to confirm the simulated dynamics in the numerical model. The model is shown to be capable of accurately reproducing the instantaneous wave elevation, velocity, and momentum flux of a long wave flooding a town. It is found that the numerical prediction is sensitive to the value of the bottom roughness coefficient. The model is then extended to look at the hydrodynamics in more detail and for other cases. Predicted momentum flux values from with structures resolved, with-out structures resolved, and with spatially variable bottom roughness will be discussed. It is found that localized maximum momentum flux values can be two orders of magnitude greater than the alongshore-transect mean. A method to calculate statistical variability of hydrodynamic flow properties, such as might be used in a risk-based analysis, will be discussed.

Lynett, P. J.; Cox, D. T.; Park, H.; Wiebe, D. M.

2012-12-01

141

Destabilization of barotropic flows by small-scale topography  

NASA Astrophysics Data System (ADS)

We investigate the stability of a zonal jet aligned with zonal topography, on the barotropic beta-plane. The topography is assumed to be spatially periodic, with the period being much smaller than the width of the jet. The problem is examined by means of linear normal-mode analysis and direct numerical simulation of the nonlinear governing equation. The following results have been obtained: If topography is sufficiently weak, the growth rate of the most unstable normal mode has two maxima. The long-wave maximum occurs at wavelengths comparable to the width of the jet and is described by Benilov's (2000) asymptotic theory. The short-wave maximum is associated with topography. Each short-wave mode has two localisation points, which coincide with topographic crests located on opposite slopes of the jet. The mode localised near the lines of maximum shear of the jet, has the largest growth rate. For strong topography, only the short-wave maximum is present, and long-wave disturbances are stable. The long-term evolution of unstable jets has been examined through direct numerical simulation. Three scenarios have been found: (i) If topography is weak and does not stabilise long-wave normal modes, the evolution of the flow is similar to that in the case of a flat bottom, i.e. the jet begins to meander and breaks up into separate vortices. (ii) For strong topography, long-wave disturbances are stable, and short-wave disturbances are confined to two narrow strips near the lines of maximum shear. This comes as a surprise, as there are plenty of normal modes localised elsewhere, with growth rates only marginally smaller than that of the fastest growing mode. The strips rapidly become nonlinear and turbulent, and the potential vorticity within them homogenises. Eventually, after a long period of "quasistability", the strips widen, begin to interact, and meander, and the jet breaks up into turbulence-filled vortices.

Benilov, E.; Nycander, J.; Dritschel, D. G.

2003-04-01

142

Predicting surface dynamic topographies of stagnant lid planetary bodies  

NASA Astrophysics Data System (ADS)

Although planetary mantles are viscoelastic media, numerical models of thermal convection in a viscoelastic spherical shell are still very challenging. Here, we examine the validity of simplified mechanical and rheological frameworks classically used to approximate viscoelastic dynamic topography. We compare three simplified approaches to a linear Maxwell viscoelastic shell with a pseudo upper free-surface, considered as the reference model. A viscous model with a free-slip boundary condition at the surface correctly reproduces the final relaxed shape of the viscoelastic body but it cannot reproduce the time evolution of the viscoelastic topography. Nevertheless, characterizing the topography development is important since it can represent a significant fraction of the history for planets having a thick and rigid lithosphere (e.g. Mars). A viscous model with a pseudo free-surface, despite its time-dependency, also systematically fails to describe correctly these transient stages. An elastic filtering of the instantaneous viscous topography is required to capture the essence of the time evolution of the topography. We show that a single effective elastic thickness is needed to correctly reproduce the constant transient viscoelastic topography obtained when the lithosphere corresponds to a step-like viscosity variation, while a time-dependence of the effective elastic thickness must be considered to take account of realistic temperature-dependent viscosity variations in the lithosphere. In this case, the appropriate thickness of the elastic shell can be evaluated, at a given instant, with a simple procedure based on the local Maxwell time. Furthermore, if the elastic filtering is performed using the thin elastic shell formulation, an unrealistic degree-dependence of the thickness of the elastic shell is needed to correctly approximate the viscoelastic topography. We show that a model that fully couples a viscous body to an elastic shell of finite thickness estimated using the local Maxwell time gives the best approximation of the viscoelastic deformation, whatever the degree of the load and the time of loading.

Dumoulin, C.; ?adek, O.; Choblet, G.

2013-12-01

143

Corneal topography from spectral optical coherence tomography (sOCT)  

PubMed Central

We present a method to obtain accurate corneal topography from a spectral optical coherence tomography (sOCT) system. The method includes calibration of the device, compensation of the fan (or field) distortion introduced by the scanning architecture, and image processing analysis for volumetric data extraction, segmentation and fitting. We present examples of three-dimensional (3-D) surface topography measurements on spherical and aspheric lenses, as well as on 10 human corneas in vivo. Results of sOCT surface topography (with and without fan-distortion correction) were compared with non-contact profilometry (taken as reference) on a spherical lens, and with non-contact profilometry and state-of-the art commercial corneal topography instruments on aspheric lenses and on subjects. Corneal elevation maps from all instruments were fitted by quadric surfaces (as well as by tenth-order Zernike polynomials) using custom routines. We found that the discrepancy in the estimated radius of curvature from nominal values in artificial corneas decreased from 4.6% (without fan distortion correction) to 1.6% (after fan distortion correction), and the difference in the asphericity decreased from 130% to 5%. In human corneas, the estimated corneal radius of curvature was not statistically significantly different across instruments. However, a Bland-Altman analysis showed consistent differences in the estimated asphericity and corneal shape between sOCT topographies without fan distortion correction and the rest of the measurements.

Ortiz, Sergio; Siedlecki, Damian; Perez-Merino, Pablo; Chia, Noelia; de Castro, Alberto; Szkulmowski, Maciej; Wojtkowski, Maciej; Marcos, Susana

2011-01-01

144

Controls on (anomalous) topography in rifted margin settings  

NASA Astrophysics Data System (ADS)

Contrasting end members of volcanic and non-volcanic passive margin formation show a large variability in basin shape and structure, subsidence history, and associated topographic evolution of the onshore rifted margins. The large range of structural style and associated topography of these systems imply a strong variability in the underlying thermo-mechanical conditions at the time of rifting. Rift - passive margin styles ranging from narrow to ultra wide are explained using forward numerical models with varying rheological structure, with strong crust lithosphere leading to narrow rift formation associated with highly elevated rift shoulders and conversely weak crust lithosphere resulting in highly stretched wide rifted conjugate margins and little flank morphology. In some cases rifted margins appear to indicate the formation of anomalous post rift topography. A number of mechanisms including small-scale convective removal of the lower lithosphere, lithosphere counter-flow, and dynamic topography, have been invoked to explain the anomalous topography. Forward numerical models are used to predict the magnitude and characteristic topography associated with each of these mechanisms and to evaluate their potential for explaining these apparent anomalous characteristics of rifts and rifted margins.

Huismans, Ritske S.

2014-05-01

145

Gravity, Topography and the Early Evolution of the Moon  

NASA Astrophysics Data System (ADS)

The early evolution of terrestrial planets was characterized processes that shaped interiors and surfaces such as differentiation, magmatism, tectonism and impact bombardment. The Moon preserves well the record of these early processes, and due to proximity to Earth this record can be studied in unprecedented detail. Observations of the Lunar Orbiter Laser Altimeter (LOLA), an instrument on the Lunar Reconnaissance Orbiter, has collected over 5.6 billion measurements of lunar topography and has yielded the most accurate global topography model for any planet. LOLA topography enables significant advances in the quantitative characterization of planetary surfaces. Topography combined with high-resolution gravity measurements from the Gravity Recovery and Interior Laboratory (GRAIL) mission, provides the opportunity to map the lunar interior from crust to core. Spherical harmonic models of topography to degree 720 and gravity to degree 420 allow estimates of crustal thickness, density and porosity, as well as insights into the structure of the lithosphere and in particular the compensation states of major impact basins and their relationships to mare volcanism. Of great interest is the role of impact bombardment in early evolution, from the size-frequency distribution to refine relative ages, to the role of impacts in melting and re-distributing the crust. Understanding gained from the Moon can analyzed in the context of observations from other terrestrial planets to provide a holistic view of early planetary evolution.

Zuber, M. T.

2012-12-01

146

Toroidal vortices over isolated topography in geophysical flows  

NASA Astrophysics Data System (ADS)

This work deals with a model of a topographically trapped vortex appearing over isolated topography in a geophysical flow. The main feature of the study is that we pay special attention to the vertical structure of a topographically trapped vortex. The model considered allows one to study the vertical motion which is known not to be negligible in many cases. Given topography in the form of an isolated cylinder, and radial symmetry and stationarity of a uniform flow, in the linear approximation, we formulate a boundary value problem that determines all the components of the velocity field through a six-order differential operator, and nonincreasing boundary conditions at the center of the topography, and at infinity. The eigenvalues of the boundary value problem correspond to bifurcation points, in which the flow becomes unstable, hence non-negligible vertical velocities occur. We formulate a condition for the boundary value problem to have a discrete spectrum of these bifurcation points, and hence to be solvable. Conducting a series of test calculations, we show that the resulting vortex lies in the vicinity of topography, and can attain the distance up to half of the topography characteristic radius.

Koshel, Konstantin V.; Ryzhov, Evgeny A.; Zyryanov, Valery N.

2014-06-01

147

The influence of surface topography on Kelvin probe force microscopy.  

PubMed

Long-range electrostatic forces govern the imaging mechanism in electrostatic force microscopy as well as in Kelvin probe force microscopy. To improve the analysis of such images, simulations of the electrostatic field distribution have been performed in the past using a flat surface and a cone-shaped tip. However, the electrostatic field distribution between a tip and a sample depends strongly on the surface topography, which has been neglected in previous studies. It is therefore of general importance to study the influence of sample topography features on Kelvin probe force microscopy images, which we address here by performing finite element simulations. We show how the surface potential measurement is influenced by surface steps and surface grooves, considering potential variations in the form of a potential peak and a potential step. The influence of the topography on the measurement of the surface potential is found to be rather small compared to a typical experimental resolution. Surprisingly, in the case of a coinciding topography and potential step an improvement of the potential profile due to the inclusion of the topography is observed. Finally, based on the obtained results, suggestions for the realization of KPFM measurement are given. PMID:19934483

Sadewasser, S; Leendertz, C; Streicher, F; Lux-Steiner, M Ch

2009-12-16

148

Linear baroclinic instability in the presence of large scale topography  

NASA Technical Reports Server (NTRS)

The effect of a planetary-scale, wavenumber 2 topography on baroclinically active disturbances is investigated for a channel domain in a two-layer, quasi-geostrophic context. When the lower-layer zonal velocity is nonzero, the topography influences the disturbances by forcing a stationary wave, and the topography and the forced wave influence the growth rates and the spatial structures of the time-dependent solutions. The case of zero zonal velocity in the lower layer was also investigated, for which no forced wave exists. Asymptotic forms of the equations, valid when the topographic effect (governed by the ratio of the nondimensional topographic height to the rotational Froude number) is small, are used to obtain both the stationary and time-dependent solutions. The latter are also obtained using a numerical approach, in which is determined the eigenvalues and eigenfunctions of a matrix representing the dynamical equations. Agreement is good between the two approaches. Recent laboratory experiments with a baroclinic annulus in which there is a false bottom with wavenumber 2 topography, are used to select governing parameters. The simultaneous presence of a stationary forced wave of wavenumber 2 and a time-dependent baroclinic wave of wavenumber 4, which has wavenumber 2 and 6 sidebands due to the topography, yields a flow field that exhibits some principal features of the laboratory experiments. The position of the forced wave and the location of an excursion in latitude of the storm track show qualitative resemblance to those features observed in the atmosphere.

Reynolds, Nathaniel Dunton

1987-01-01

149

Efficient simulation and optimization of wafer topographies in double patterning  

NASA Astrophysics Data System (ADS)

As the technology marches towards the 32nm node and beyond in semiconductor manufacturing, double patterning and double exposure techniques are currently regarded as the potential candidates to produce lines and spaces (L&S) and contact holes (C/H), respectively. In this paper, the Waveguide method, a rigorous electromagnetic field (EMF) solver, is employed to investigate the impact of wafer topographies on two specific double patterning techniques. At first, the topography effects induced by the first patterning on the second lithography process in a lithography-etch-lithographyetch (LELE) process are demonstrated. A new methodology of the bottom anti-reflective coating (BARC) optimization is proposed to reduce the impact of wafer topography on resist profiles. Additionally, an optical proximity correction (OPC) of the second lithography mask is demonstrated to compensate the wafer topography induced asymmetric deformations of line ends. Rigorous EMF simulations of lithographic exposures are also applied to investigate wafer topography effects in a freezing process. The difference between the optical properties of the frozen (first) resist and the second resist potentially causes linewidth variations. Quantitative criteria for tolerable refractive index and extinction differences between the two resist materials are given. The described studies can be used for the optimizations of topographic waferstacks, the OPC of the second litho mask, and for the development of resist materials with appropriate optical properties.

Shao, Feng; Evanschitzky, Peter; Fühner, Tim; Erdmann, Andreas

2009-03-01

150

Surface topography-connections between lubrication and failure initiation  

NASA Technical Reports Server (NTRS)

The characteristics of the initial surface topography is intimately connected to the machining process by which it is produced. Both processes create a near surface region of residual stresses, microstructure and hardness that is different from the bulk. The material properties in this rather undefined region can significantly influence the mode of failure, such as wear, scuffing or fatigue, as well as the degree of failure resistance for a given material. Under full film elastohydrodynamic (EHD) conditions, where shear is accomodated within a relatively thick lubricant film, the normal and shear stresses are distributed uniformly over the near surface region, and the surface topography has little influence on the lubrication or failure process. Under more typical conditions where surface roughness and lubricant film thickness are of the same order of magnitude, the surface topography not only emerges as an important parameter in failure initiation, but it also becomes intimately involved in the lubrication process itself.

Wedeven, L. D.

1983-01-01

151

Implications of MOLA Global Roughness, Statistics, and Topography  

NASA Technical Reports Server (NTRS)

New insights are emerging as the ongoing high-quality measurements of the Martian surface topography by Mars Orbiter Laser Altimeter (MOLA) on board the Mars Global Surveyor (MGS) spacecraft increase in coverage, resolution, and diversity. For the first time, a global characterization of the statistical properties of topography is possible. The data were collected during the aerobreaking hiatus, science phasing, and mapping orbits of MGS, and have a resolution of 300-400 m along track, a range resolution of 37.5 cm, a range precision of 1-10 m for surface slopes up to 30 deg., and an absolute accuracy of topography of 13 m. The spacecraft's orbit inclination dictates that nadir observations have latitude coverage of about 87.1S to 87.1N; the addition of observations obtained during a period of off-nadir pointing over the north pole extended coverage to 90N. Additional information is contained in the original extended abstract.

Aharonson, O.; Zuber, M. T.; Neumann, G. A.

1999-01-01

152

SPC Shape and Topography of Vesta from DAWN Imaging Data  

NASA Astrophysics Data System (ADS)

The DAWN spacecraft has now left Vesta, leaving a legacy of more than 16000 clear filter images of the asteroid. During the last month of Dawn's stay at Vesta, the sun slowly crept northward, enabling the spacecraft to view topography closer to the north pole. We have used these images with our stereophotoclinometry (SPC) software to construct topography for most of Vesta's surface to 50 meter resolution, and below about 60 degrees south to 20 meter resolution. We present this topography as a 1/64 degree gridded map (about 70 m resolution), as a stereographic projection of the south polar region at 25 m resolution and as a global shape model with 1.57 million vectors. In addition, we present solutions for the s/c position and camera pointing at all imaging times during DAWN's entire stay at Vesta.

Gaskell, Robert W.

2012-10-01

153

Direct measurement of carbon contamination topography on patterned EUV masks  

NASA Astrophysics Data System (ADS)

In our previous work, various techniques were used to confirm the contamination deposits on the sidewall of extreme ultraviolet (EUV) mask absorbers [1-2]. In order to further understand the effects of contamination topography on mask absorbing features, direct measurements of contaminated features is needed. In this work, we investigated the contamination topography using cross-section transmission electron microscope (TEM) image analysis on four different masks. TEM specimens of contaminated features from silicon and ruthenium capped EUV masks were prepared using a focused ion beam (FIB). We conducted the contamination experiment with three different exposure sources including EUV, out-of-band, and electron induced processes. Thickness measurements from each contamination experiment were provided. Shadowing effect and geometric analysis on the contamination topography is also discussed.

Fan, Yu-Jen; Murray, Thomas; Goodwin, Frank; Ashworth, Dominic; Denbeaux, Gregory

2014-04-01

154

Influence of nanophase titania topography on bacterial attachment and metabolism  

PubMed Central

Surfaces with nanophase compared to conventional (or nanometer smooth) topographies are known to have different properties of area, charge, and reactivity. Previously published research indicates that the attachment of certain bacteria (such as Pseudomonas fluorescens 5RL) is higher on surfaces with nanophase compared to conventional topographies, however, their effect on bacterial metabolism is unclear. Results presented here show that the adhesion of Pseudomonas fluorescens 5RL and Pseudomonas putida TVA8 was higher on nanophase than conventional titania. Importantly, in terms of metabolism, bacteria attached to the nanophase surfaces had higher bioluminescence rates than on the conventional surfaces under all nutrient conditions. Thus, the results from this study show greater select bacterial metabolism on nanometer than conventional topographies, critical results with strong consequences for the design of improved biosensors for bacteria detection.

Park, Margaret R; Banks, Michelle K; Applegate, Bruce; Webster, Thomas J

2008-01-01

155

The global topography of Mars and implications for surface evolution  

NASA Technical Reports Server (NTRS)

Elevations measured by the Mars Orbiter Laser Altimeter have yielded a high-accuracy global map of the topography of Mars. Dominant features include the low northern hemisphere, the Tharsis province, and the Hellas impact basin. The northern hemisphere depression is primarily a long-wavelength effect that has been shaped by an internal mechanism. The topography of Tharsis consists of two broad rises. Material excavated from Hellas contributes to the high elevation of the southern hemisphere and to the scarp along the hemispheric boundary. The present topography has three major drainage centers, with the northern lowlands being the largest. The two polar cap volumes yield an upper limit of the present surface water inventory of 3.2 to 4.7 million cubic kilometers.

Smith, D. E.; Zuber, M. T.; Solomon, S. C.; Phillips, R. J.; Head, J. W.; Garvin, J. B.; Banerdt, W. B.; Muhleman, D. O.; Pettengill, G. H.; Neumann, G. A.; Lemoine, F. G.; Abshire, J. B.; Aharonson, O.; Brown, C. D.; Hauck, S. A.; Ivanov, A. B.; McGovern, P. J.; Zwally, H. J.; Duxbury, T. C.

1999-01-01

156

Numerical investigation of MASW applications in presence of surface topography  

NASA Astrophysics Data System (ADS)

In the applications of multichannel analysis of surface waves (MASW), dispersion curves are usually picked in an energy tracing manner on dispersion images. They are compared with the theoretical dispersion curves based on a horizontally layered earth model during the subsequent inversion for shear-wave velocities. Surface topography can strongly influence energy distribution on a dispersion image. In theory, static correction should be applied to seismic records before generating dispersion images if there are any elevation variations along a two-dimensional (2D) survey line. The out-of-plane noise from side areas of a survey line in three dimensions (3D) can also contaminate the recorded wavefield. We synthesize the seismograms through finite-difference modeling for 12 types of 2D earth models that represent the basic elements of topography along a survey line. The dispersion images are compared with the corresponding theoretical dispersion curves that are calculated by ignoring the topography of the models. The comparison shows that errors of the picked Rayleigh-wave phase velocities can be constrained within 4% if a slope angle of the topography is less than about 10°. For steeper topography, errors of the picked phase velocities are greater than 4% and static correction are recommended before the dispersion analysis. In the 3D case, we investigate a set of 3D levee-shaped earth models to evaluate the errors caused by the out-of-plane noise from the edge of an embankment. The analysis suggests that the distance between the edge of an embankment and a MASW survey line should be at least 1/10 of the dominant Rayleigh-wave wavelength so that energy distortion on dispersion images due to topography are less significant than that caused by other noises.

Zeng, Chong; Xia, Jianghai; Miller, Richard D.; Tsoflias, Georgios P.; Wang, Zhejiang

2012-09-01

157

Efficient inversion for CMB topography: benchmarks and preliminary maps  

NASA Astrophysics Data System (ADS)

We map lateral topography variations of global seismic discontinuities focusing on the core-mantle boundary (CMB), in the framework of high-resolution forward modeling and seismic imaging. We present a method to compute sensitivity kernels relating seismic travel times (measured by cross-correlation of observed and theoretical seismograms) to the topography of seismic discontinuities at any depth in the Earth using full 3D wave propagation. Calculation of accurate finite-frequency sensitivity kernels is notoriously expensive, but we reduce computational costs drastically by limiting ourselves to spherically symmetric reference models, and exploiting the axial symmetry of the resulting propagating wave-field that collapses to a 2D numerical domain. We compute and analyze a suite of kernels for CMB sensitive phases that can be used for finite frequency waveform inversion. We benchmark and tune our methodology inverting cross-correlation travel-times of PcP, various PKP branches, Pdiff and ScS computed with 3-D wave-propagation with ground-truth Earth models including realistic CMB topography. Finally, we present CMB topography maps derived from two different datasets that we inverted using our technique. One includes ~50000 cross-correlated travel-time measurement for SKSac, and ScS phases while the other consists of ~220000 ISC manually picked travel-time for PKIKP and PcP phases. Prior to interpretation, we analyze the coverage using the approximate Hessian to discriminate well-constrained areas from less determined locations. Although with different amplitudes, our new CMB models reveal a low-elevation ring around the Pacific similar to other studies. While this is a pilot study extending topography inversions to full-wave based imaging mainly showing consistency with previous findings, we expect to further enhance these studies for a new generation of CMB topography models by combining various datasets and joint inversion with mantle structure.

Colombi, A.; Nissen-Meyer, T.; Boschi, L.

2012-12-01

158

Mercury's Thermal Evolution, Dynamical Topography and Geoid  

NASA Astrophysics Data System (ADS)

Among the terrestrial planets Mercury is not only the smallest, but also the densest (after correction for self-compression). To explain Mercury's high density it is considered likely that the planet's mantle was removed during a giant impact event, when proto-Mercury was already differentiated into an iron core and a silicate mantle. Beside the damage to the planet's mantle the vaporization would cause a significant loss of volatile elements, leaving the remaining planet molten and dominated by extremely refractory material.Since the arrival of a spacecraft at the enigmatic planet is not to be expected before 2011 (Messenger) or 2019 (BepiColombo) we might already prepare ourselves for the upcoming results and perform tests that allow some anticipation of the measured data. The hermean mantle is modelled as an internally and bottom heated, isochemical fluid in a spherical shell. The principle of this convection model is widely accepted and is used for various models of thermal evolution of terrestrial planets, e.g., the Earth, Mars or the Moon. We are solving the hydrodynamical equations, derived from the conservation of mass, momentum and energy. A program originally written by S. Zhang is used to solve the temperature field which employs a combination of a spectral and a finite difference method. Beside the large core as a heat source 'from below' the decay of radioactive isotopes provides internal heating of the hermean mantle. The viscosity of the mantel material depends exponentially on the inverse temperature. The model results show the typical behaviour of a one-plate-planet, meaning the surface is not broken into several tectonic plates but the outside is a single rigid shell. The thermal evolution is generally charaterized by the growth of a massive lithosphere on top of the convecting mantle. The lower mantle and core cool comparatively little and stay at temperatures between 1900K and 2000K until about 2.0Ga after the simulation was started. The stagnant lid comprises roughly half the mantle after only 0.5Ga. Since the rigid lithosphere does not take part in the convection anymore, the heat coming from the interior (due to the cooling of the large core) can only be transported through the lithosphere by thermal conduction. This is a significantly less effective mechanism of heat transport than convection and hence the lithosphere forms an insulating layer. As a result, the interior is kept relatively warm.Because the mantle is relatively shallow compared to the planet's radius, and additionally the thick stagnant lid is formed relatively rapid, the convection is confined to a layer of only about 200km to 300km. Convection structures are therefore relatively small structured. The flow patterns in the early evolution show that mantle convection is characterized by numerous upwelling plumes, which are fed by the heat flow from the cooling core. These upwellings are relatively stable regarding their spatial position. As the core cools down the temperature anomalies become colder and less pronounced but not less numerous. In our calculations, a region of partial melt in the mantle forms immediately after the start of the model at a depths of roughly 220km. While in the entire lower mantle the temperature exceeds the solidus, the highest melt degrees can be found in the upwelling plumes. The partial molten region persists a significant time (up to 2.5Ga). How long the partial molten zone actually survives depends strongly on the initial conditions of the model. For instance, an outer layer with a reduced thermal conductivity would keep the lower mantle significantly warmer and a molten layer survives longer. The hot upwellings cause a surface deformation (dynamical topography) which itself causes a gravity anomaly. Due to the weak constraints of important parameters (e.g. sulfur content of the core, mantle rheology, amount and distribution of radiogenic heat sources, planetary contraction, thermal conductivity, etc) numerous models are required to understand the importance and influence of the mentioned variables.

Ziethe, Ruth; Benkhoff, Johannes

159

Geoid, topography, and convection-driven crustal deformation on Venus  

NASA Technical Reports Server (NTRS)

High-resolution Magellan images and altimetry of Venus reveal a wide range of styles and scales of surface deformation that cannot readily be explained within the classical terrestrial plate tectonic paradigm. The high correlation of long-wavelength topography and gravity and the large apparent depths of compensation suggest that Venus lacks an upper-mantle low-viscosity zone. A key difference between Earth and Venus may be the degree of coupling between the convecting mantle and the overlying lithosphere. Mantle flow should then have recognizable signatures in the relationships between surface topography, crustal deformation, and the observed gravity field.

Simons, Mark; Hager, Bradford H.; Solomon, Sean C.

1992-01-01

160

Topography Influence on the Lake Equations in Bounded Domains  

NASA Astrophysics Data System (ADS)

We investigate the influence of the topography on the lake equations which describe the two-dimensional horizontal velocity of a three-dimensional incompressible flow. We show that the lake equations are structurally stable under Hausdorff approximations of the fluid domain and L p perturbations of the depth. As a byproduct, we obtain the existence of a weak solution to the lake equations in the case of singular domains and rough bottoms. Our result thus extends earlier works by Bresch and Métivier treating the lake equations with a fixed topography and by Gérard-Varet and Lacave treating the Euler equations in singular domains.

Lacave, Christophe; Nguyen, Toan T.; Pausader, Benoit

2014-06-01

161

Switchable micropatterned surface topographies mediated by reversible shape memory.  

PubMed

Reversibly switching topography on micrometer length scales greatly expands the functionality of stimuli-responsive substrates. Here we report the first usage of reversible shape memory for the actuation of two-way transitions between microscopically patterned substrates, resulting in corresponding modulations of the wetting properties. Reversible switching of the surface topography is achieved through partial melting and recrystallization of a semi-crystalline polyester embossed with microscopic features. This behavior is monitored with atomic force microscopy (AFM) and contact angle measurements. We demonstrate that the magnitude of the contact angle variations depends on the embossment pattern. PMID:24824729

Turner, Sara A; Zhou, Jing; Sheiko, Sergei S; Ashby, Valerie Sheares

2014-06-11

162

Modeling the lithography of ion implantation resists on topography  

NASA Astrophysics Data System (ADS)

With emerging technologies, such as fin-based field-effect transistors (finFETs), the structures, which define the functionality of a device, have added one dimension in the patterning and are now three-dimensional. Lithography for CMOS patterning becomes more complicated for finFETs given the three-dimensional substrate structure, and the resist modeling targeting this issue is yet to be fully investigated. Here, we present lithographic simulations on topography relevant for finFET devices compatible with nodes down to 10 nm. We investigate the influence of different materials and of the additional optical complexity due to the topography and density of the gates and fins.

Winroth, Gustaf; Vaglio Pret, Alessandro; Ercken, Monique; Robinson, Stewart A.; Biafore, John J.

2014-03-01

163

Sound propagation over uneven ground and irregular topography  

NASA Technical Reports Server (NTRS)

The goal of this research is to develop theoretical, computational, and experimental techniques for predicting the effects of irregular topography on long range sound propagation in the atmosphere. Irregular topography is understood to imply a ground surface that is not idealizable as being perfectly flat or that is no idealizable as having a constant specific acoustic impedance. The focus is on circumstances where the propagation is similar to what might be expected for noise from low-altitude air vehicles flying over suburban or rural terrain, such that rays from the source arrive at angles close to grazing incidence.

Berthelot, Yves H.; Pierce, Allan D.; Main, Geoffrey L.; Zhou, Ji-Xun; Kearns, James A.

1988-01-01

164

Dynamic topography in subduction zones: insights from laboratory models  

NASA Astrophysics Data System (ADS)

The topography in subduction zones can exhibit very complex patterns due to the variety of forces operating this setting. If we can deduce the theoretical isostatic value from density structure of the lithosphere, the effect of flexural bending and the dynamic component of topography are difficult to quantify. In this work, we attempt to measure and analyze the topography of the overriding plate during subduction compared to a pure shortening setting. We use analog models where the lithospheres are modeled by thin-sheet layers of silicone putty lying on low-viscosity syrup (asthenosphere). The model is shorten by a piston pushing an oceanic plate while a continental plate including a weak zone to localize the deformation is fixed. In one type of experiments, the oceanic plate bends and subducts underneath the continental one; in a second type the two plates are in contact without any trench, and thus simply shorten. The topography evolution is monitored with a laser-scanner. In the shortening model, the elevation increases progressively, especially in the weak zone, and is consistent with expected isostatic values. In the subduction model, the topography is characterized, from the piston to the back-wall, by a low elevation of the dense oceanic plate, a flexural bulge, the trench forming a deep depression, the highly elevated weak zone, and the continental upper plate of intermediate elevation. The topography of the upper plate is consistent with isostatic values for very early stages, but exhibits lower elevations than expected for later stages. For a same amount of shortening of the continental plate, the thickening is the same and the plate should have the same elevation in both types of models. However, comparing the topography at 20, 29 and 39% of shortening, we found that the weak zone is 0.4 to 0.6 mm lower when there is an active subduction. Theses values correspond to 2.6 to 4 km in nature. Although theses values are high, there are of the same order as dynamic topography and could represent the dynamic effect of the slab sinking into the asthenosphere and lowering the elevation of the upper plate.

Bajolet, Flora; Faccenna, Claudio; Funiciello, Francesca

2014-05-01

165

The interaction of marine fouling organisms with topography of varied scale and geometry: a review.  

PubMed

Many studies have examined the effects of surface topography on the settlement behaviour of marine organisms and this article reviews these investigations with more emphasis on the effects of topography scale. It has been observed that macro topographies (1-100 mm) are generally favoured by marine fouling taxa and are unsuitable for antifouling applications. This is because macro topographies are usually large enough to fit fouling organisms and provide refuge from dangers in the marine environment. Micro topographies had only limited success at reducing fouling from a wide range of marine taxa. The antifouling performance of micro topographies (1 to ?1000 ?m) is dependent on the properties of topography features in terms of symmetry, isotropy, width, length, height/depth, separation distance and average roughness. In terms of the antifouling performance of micro topography, topography geometry may only be of secondary importance in comparison to the size of features itself. It is also noted that hydrodynamic stresses also contribute to the settlement trends of foulers on textured surfaces. Future studies on antifouling topographies should be directed to hierarchical topographies because the mixed topography scales might potentially reduce fouling by both micro and macro organisms. Patterned nano-topographies (1- ?1000 nm) should also be explored because the antifouling mechanisms of these topographies are not yet clear. PMID:24706140

Myan, Felicia Wong Yen; Walker, James; Paramor, Odette

2013-12-01

166

Mars Mantle (MOHO) Topography with Mantle Elevation Texture Map  

NSDL National Science Digital Library

This site from NASA features a rotating animation of Mars using data from Mars Orbiting Laser Altimeter (MOLA). The topography is colored to indicate elevation. Additionally, an image highlighting the mantle is colored to indicate its elevation. A flat version of this same dataset is also available.

Studio, Nasa/goddard S.; Nasa

167

Corneal topography of photorefractive keratectomy versus laser in situ keratomileusis  

Microsoft Academic Search

ObjectiveThis study aimed to compare qualitative patterns of corneal topography early in the postoperative course after excimer laser photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) when used for the treatment of myopia of 6.0 to 15.0 diopters.

Peter S Hersh; Kevin S Scher; Rashna Irani

1998-01-01

168

Global Topography of Titan from Cassini RADAR Data (Invited)  

NASA Astrophysics Data System (ADS)

Cassini RADAR data are used to construct a global, albeit sparsely-sampled, topography map, and to generate a hypsometric profile to compare with other planetary bodies. Titan’s hypsogram is unimodal and strikingly narrow compared with the terrestrial planets. To investigate topographic extremes, a novel variant on the classic hypsogram is introduced, with a logarithmic abscissa to highlight mountainous terrain. In such a plot, the top of the terrestrial hypsogram is quite distinct from those of Mars and Venus due to the ‘glacial buzz-saw’ that clips terrestrial topography above the snowline. In contrast to the positive skew seen in other hypsograms, with a long tail of positive relief due to mountains, there is an indication (weak, given the limited data for Titan so far) that the Titan hypsogram appears slightly negatively skewed, suggesting a significant population of unfilled depressions. Limited data permit only a simplistic comparison of Titan topography with other icy satellites but we find that the standard deviation of terrain height (albeit at different scales) is similar to those of Ganymede and Europa. The topography of terrestrial planets is sampled with the same coverage that we have for Titan to gauge what as-yet-undiscovered topographic surprises may yet be hidden by Titan’s haze.

Lorenz, R. D.; Cassini RADAR Team

2010-12-01

169

Effects of Landscape Pattern and Topography on Emissions and Transport  

Microsoft Academic Search

Landscape pattern (land use and natural patchiness) and complex topography strongly influence re- gional variation in emissions of trace gases and pollutants, as well as atmospheric transport processes. This leads to small-scale variation in the amount of (biogenic) emission, atmospheric deposition and in local concentrations of atmospheric consitutents. This chapter addresses the most important processes that control trace gas emission

Franz X. Meixner; Werner Eugster

1999-01-01

170

THE SURFACE WATER AND OCEAN TOPOGRAPHY (SWOT) MISSION  

Microsoft Academic Search

Satellite altimetry has revolutionized the study of the global oceans for the past two decades by providing unprecedented observations of the ocean surface topography at scales larger than about 200 km and made significant advances in our understanding of global ocean circulation and sea level change. However, the coarse cross-track sampling and measurement precision have prevented resolving scales shorter than

Douglas Alsdorf; Erensto Rodriguez; Rosemary Morrow; Nelly Mognard; Juliette Lambin; Parag Vaze; Thierry Lafon

171

Hydrodynamical Model of Topography Elevations at Mid-Ocean Ridges  

Microsoft Academic Search

Ridge crest depth variations recently have been recognized as an important features of spreading process. The goal of our investigation is an accounting the development of topography elevations at the ocean floor related to dynamical effect of mantle advection beneath the mid-ocean ridges. Hydrodynamical model is to be elaborated to calculate time-dependent behavior of ocean floor deformations. The mantle is

Vladimir M. Cherniavski; Elena I. Suetnova

1996-01-01

172

Analysis of Multiple Manding Topographies during Functional Communication Training  

ERIC Educational Resources Information Center

We evaluated the effects of reinforcing multiple manding topographies during functional communication training (FCT) to decrease problem behavior for three preschool-age children. During Phase 1, a functional analysis identified conditions that maintained problem behavior for each child. During Phase 2, the children's parents taught them to…

Harding, Jay W.; Wacker, David P.; Berg, Wendy K.; Winborn-Kemmerer, Lisa; Lee, John F.; Ibrahimovic, Muska

2009-01-01

173

Eye Shape and Retinal Topography in Owls (Aves: Strigiformes)  

Microsoft Academic Search

The eyes of vertebrates show adaptations to the visual environments in which they evolve. For example, eye shape is associated with activity pattern, while retinal topography is related to the symmetry or ‘openness’ of the habitat of a species. Although these relationships are well documented in many vertebrates including birds, the extent to which they hold true for species within

Thomas J. Lisney; Andrew N. Iwaniuk; Mischa V. Bandet; Douglas R. Wylie

2012-01-01

174

Topography Estimation With Interferometric Synthetic Aperture Radar Using Fringe Detection  

Microsoft Academic Search

We present new methods for using SAR interferometry data to estimate surface topography. To begin an expression is given to relate the elevation of a ground point to the phase difference of SAR images received from two spatially separated antennas. An iterative algorithm is developed, which solves for the position and elevation of each point in the image simultaneously. One

Qian Lin; John F. Vesecky; Howard A. Zebker

1991-01-01

175

A BISTATIC ALTIMETRY MISSION FOR OCEAN TOPOGRAPHY MAPPING  

Microsoft Academic Search

Through a feasibility study funded by the European Space Agency (ESA), the authors analysed the possibility of using the innovative concepts of bistatic altimetry to enhance the spatial sampling of topography measurements over the oceans. Purpose of this paper is thus to review the major results of the mission design, focusing on the spacecraft configuration, mission analysis and the descripition

C. Zelli; M. Martin-Neira; G. Alberti; F. Impagnatiello; M. Matteoni

2010-01-01

176

High spatial resolution radar altimetry for global Earth topography mapping  

Microsoft Academic Search

This paper summarises the work performed by Alenia Aerospazio in the design of new radar altimeter systems suitable for high spatial resolution Earth topography observation. The instrument concept proposed is based on the application of synthetic aperture processing and interferometric techniques to a conventional Ku band pulse limited system. The major design features and expected performance are briefly presented

G. Angino; F. Impagnatiello; C. Zelli

1997-01-01

177

Examining topography and stream discharge at Sherburne National Wildlife Refuge  

NSDL National Science Digital Library

In this inquiry based geologic field lab students will be estimating and measuring stream flow. Students will also map out a full scale live topography map of a dry streambed to help them estimate flow discharge. Students will use their journals to record their hypothesis, lab report questions, graphed data and evidence to backs up their observations.

Todd Koenig Zimmerman High School ISD 728 Zimmerman, MN I will be using a modified concept of the contour mapping exercise we did at St. Thomas and the Hydrology flow lab we preformed at Coon Creek.

178

Seismic wave simulation in the presence of real volcano topography  

Microsoft Academic Search

We use a finite-difference method on a 3-D staggered grid to simulate seismic wave propagation in the presence of strong topographic variations. An application to Merapi volcano, Indonesia, is presented. In order to focus on the effect of topography on the seismic wave field, calculations are performed for a rather simple model with an isotropic point source and a homogeneous

J. Ripperger; H. Igel; J. Wasserman

2003-01-01

179

Synchrotron Radiation X Ray Topography Study of Lateral Field Resonators.  

National Technical Information Service (NTIS)

Using synchrotron radiation, plano-convex AT resonators excited by a lateral field were studied by the X-ray topography technique. Different overtones and anharmonics of the three types of the thickness modes were observed. The study showed that it is pos...

B. Capelle, J. Detaint, J. Schwartzel, Y. Zheng, A. Zarka

1992-01-01

180

Residual topography and lithospheric structure of the Antarctic continent  

NASA Astrophysics Data System (ADS)

Antarctica has been the subject of considerable interest in the past few years, following the International Polar Year. The structure of its crust at a continental scale is however still known with large uncertainty. A new Moho depth map for the Antarctic continent has been recently assembled (AntMoho), merging copious information from geophysical and geological studies selected from the literature. A large volume of old and new data has been analyzed: mostly seismic experiments, as well as receiver functions and geological studies, ranging from DSS profiles acquired by Soviet Union field experiments, to recent seismic receiver function studies. AntMoho has a reference lateral resolution of 1 degree. We compare this new model to other available for the whole continent (Bassin et al., 2000; Block et al., 2009) and study the possible geodynamic consequences calculating the residual topography. Residual topography is obtained by removing the isostatic contribution of the crust from the observed topography. Long-wavelength residual topography is interpreted as dynamic response to large scale mantle convection and density contrasts. Our calculations show that significantly different inferences on lithospheric structure and mantle dynamics may result from the variance in Moho depth recorded in the different models. A better knowledge of Moho depth and, more generally, crustal structure for Antarctica at a continent scale is a goal with likely consequences for better understanding of the complex dynamic processes acting at a regional scale.

Molinari, I.; Baranov, A.; Danesi, S.; Morelli, A.

2012-12-01

181

Bed Topography of River Bends with Suspended Sediment Transport.  

National Technical Information Service (NTIS)

The objective of the investigation is the prediction of the bed topography in river bends with suspended sediment transport. To reduce the complexity of the problem some constraints to the scope of the investigation are made. Rivers of constant width are ...

A. M. Talmon

1992-01-01

182

Dental topography of platyrrhines and prosimians: convergence and contrasts.  

PubMed

Dental topographic analysis is the quantitative assessment of shape of three-dimensional models of tooth crowns and component features. Molar topographic curvature, relief, and complexity correlate with aspects of feeding behavior in certain living primates, and have been employed to investigate dietary ecology in extant and extinct primate species. This study investigates whether dental topography correlates with diet among a diverse sample of living platyrrhines, and compares platyrrhine topography with that of prosimians. We sampled 111 lower second molars of 11 platyrrhine genera and 121 of 20 prosimian genera. For each tooth we calculated Dirichlet normal energy (DNE), relief index (RFI), and orientation patch count (OPCR), quantifying surface curvature, relief, and complexity respectively. Shearing ratios and quotients were also measured. Statistical analyses partitioned effects of diet and taxon on topography in platyrrhines alone and relative to prosimians. Discriminant function analyses assessed predictive diet models. Results indicate that platyrrhine dental topography correlates to dietary preference, and platyrrhine-only predictive models yield high rates of accuracy. The same is true for prosimians. Topographic variance is broadly similar among platyrrhines and prosimians. One exception is that platyrrhines display higher average relief and lower relief variance, possibly related to lower relative molar size and functional links between relief and tooth longevity distinct from curvature or complexity. Explicitly incorporating phylogenetic distance matrices into statistical analyses of the combined platyrrhine-prosimian sample results in loss of significance of dietary effects for OPCR and SQ, while greatly increasing dietary significance of RFI. PMID:24318939

Winchester, Julia M; Boyer, Doug M; St Clair, Elizabeth M; Gosselin-Ildari, Ashley D; Cooke, Siobhán B; Ledogar, Justin A

2014-01-01

183

EAARL coastal topography-Virginia, post-Nor'Ida, 2009  

USGS Publications Warehouse

This DVD contains lidar-derived first-surface (FS) and bare-earth (BE) topography GIS datasets of a portion of the Virginia coastline beachface. These datasets were acquired post-Nor'Ida on November 27, 2009, November 29, 2009, and December 1, 2009.

Bonisteel-Cormier, J.M.; Nayegandhi, Amar; Fredericks, Xan; Klipp, E.S.; Nagle, D.B.; Vivekanandan, Saisudha; Wright, C.W.; Sallenger, A.H.; Brock, J.C.

2011-01-01

184

Attitude sensor calibration for the ocean topography experiment satellite  

Microsoft Academic Search

A ground-based software system to calibrate the attitude control sensors for the Ocean Topography Experiment (TOPEX) spacecraft is described. The algorithm determines sensor misalignment, bias and scale factor errors from gyro, sun sensor and star tracker measurements. The inherent yaw slew motion of the spacecraft during normal mission mode is exploited to make the error parameters observable. A two loop

Scott Davis; John Lai

1993-01-01

185

EAARL topography-Potato Creek watershed, Georgia, 2010  

USGS Publications Warehouse

This DVD contains lidar-derived first-surface (FS) and bare-earth (BE) topography GIS datasets of a portion of the Potato Creek watershed in the Apalachicola-Chattahoochee-Flint River basin, Georgia. These datasets were acquired on February 27, 2010.

Bonisteel-Cormier, J.M.; Nayegandhi, Amar; Fredericks, Xan; Jones, J.W.; Wright, C.W.; Brock, J.C.; Nagle, D.B.

2011-01-01

186

Martian wrinkle ridge topography: Evidence for subsurface faults from MOLA  

Microsoft Academic Search

Mars Orbiter Laser Altimeter (MOLA) topography shows distinct elevation offsets across wrinkle ridges that can be explained simply by subsurface thrust faults. MOLA has provided the first reliable topographic data of wrinkle ridges to test models for their origin; although previous work has shown that wrinkle ridges result from compressional folding and faulting of near-surface units, the role of thrust

M. P. Golombek; F. S. Anderson; M. T. Zuber

2001-01-01

187

Unbounded, Exact Solution for 3-D Topography Driven Groundwater Flow  

NASA Astrophysics Data System (ADS)

An exact analytical solution is presented for saturated groundwater flow to provide improved understanding of the renewal rate of deep and shallow groundwater and the long-term management of groundwater resources. The solution is derived under the assumptions that the hydraulic potential of the groundwater surface follows the topography and imposes a steady boundary condition for driving the groundwater flow. This assumption is justified in most areas of humid climate. The solution is applicable on a wide range of spatial scales and accounts for decaying permeability with depth, stratified aquifers as well as anisotropy. The flow problem is solved by representing the topography with a three-dimensional spectral scaling solution based on harmonic functions that are independent in x- and y-directions. In most areas the Fourier-series, representing the topography, give a nearly perfect image of the ground surface elevation. The topography is found to be fractal and this imposes a fractal nature of the groundwater flow that is altered by the additional geometrical scales. The groundwater flow solution, based on the Fourier-spectrum, depends on the decay with depth and anisotropy in hydraulic conductivity and stratifications due to quaternary deposits, layered sediments etc. Prior analytical solutions are limited to either two-dimensional flows or harmonic functions uniform in the x- and y- directions, hence making them unable to predict three-dimensional subsurface flows beneath a realistic landscape. However, the most important advantage of this new method is the ability to analyse the impact of different geometrical scales on the groundwater flow. Analyses indicate that in a homogeneous subsurface, shallow groundwater flows would be approximately equally controlled by all scales of topography. Although shorter topographical wavelengths control the surface water flux, their impact decreases faster with depth in relation to longer wavelengths. This induces an increasing importance of large-scale topography with depth. However, the hydraulic conductivity tends to decay with depth and this counteracts the effect of the large-scale topography on the groundwater flow more effectively than the smaller landscape scales. For the depth-dependent hydraulic conductivity applicable to the Fennoscandian bedrock, we find a depth-limitation of the flow cells that tends to reduce the importance of the larger wavelengths on the fluxes at all depths.

Marklund, L.; Wörman, A.

2007-12-01

188

Causes and Consequences of Time-Varying Dynamic Topography  

NASA Astrophysics Data System (ADS)

Convective circulation of the Earth's mantle maintains plate motion but we know little about the spatial and temporal details of this circulation. Accurate maps of the spatial and temporal pattern of dynamic topography will profoundly affect our understanding the the relationship between surface geology and deep Earth processes. A major difficulty is the 'tyranny of isostasy'. In other words, dynamic topography is difficult to measure because crustal and lithospheric thickness and density changes are the dominant control of surface elevation. Some progress can be made along continental margins by measuring residual depth anomalies of the oldest oceanic floor on newly available seismic reflection and wide-angle profiles. These estimates of dynamic topography have amplitudes of ±1 km and wavelengths of 102-104 km. They mostly, but not always, correlate with long wavelength free-air gravity anomalies. Correlation with seismic tomographic images is much poorer. The distribution of dynamic topography throughout the rest of the oceanic realm can be supplemented by using ship-track data in regions with sparse sedimentary cover and by exploiting the mid-oceanic ridge system. On the continents, it is more difficult to measure dynamic topography with the same accuracy since the density structure of continental lithosphere is so variable but progress can be made on three fronts. First, long-wavelength gravity anomalies which straddle continental margins are an obvious and important guide. Secondly, stratal geometries across continental shelves contain information about positive and negative surface elevation changes. In several cases, 2- and 3-D seismic surveys calibrated by boreholes can be used to constrain spatial and temporal patterns of dynamic topography. In the North Atlantic Ocean, examples of buried ephemeral landscapes suggest that dynamic topography can grow and decay on timescales as short as a few million years. Recognition of positive and negative vertical motions, which cannot be accounted for by global eustasy, is encouraging and suggests that we are on the verge of creating global dynamic topographic maps which can be used to test predictive global models.

White, Nicky

2013-04-01

189

Impact of lithosphere rheology on the dynamic topography  

NASA Astrophysics Data System (ADS)

Dynamic topography is a key observable signature of the Earth's and planetary (e.g. Venus) mantle dynamics. In general view, it reflects complex mantle flow patterns, and hence is supposed to correlate at different extent with seismic tomography, SKS fast orientations, geodetic velocity fields and geoid anomalies. However, identification of dynamic topography had no systematic success, specifically in the Earth's continents. Here we argue that lithosphere rheology, in particular, rheological stratification of continents, results in modulation of dynamic topography, converting commonly expected long-wavelength/small amplitude undulations into short-wavelength surface undulations with wide amplitude spectrum, superimposed onto "tectonic" topography. These ideas are explored in 3D using unprecedentedly high resolution numerical experiments (grid step size 2-3 km for 1500x1500x600 km computational area) incorporating realistic rheologically stratified lithosphere. Such high resolution is actually needed to resolve small-scale crustal faulting and inter-layer coupling/uncoupling that shape surface topography. The results reveal strikingly discordant, counterintuitive features of 3D dynamic topography, going far beyond the inferences from previous models. In particular, even weak anisotropic tectonic stress field results both in large-scale small-amplitude dynamic topography and in strongly anisotropic short-wavelength (at least in one direction) dynamic topography with wide amplitude range (from 100 to 2000-3000 m), including basins and ranges and large-scale linear normal and strike-slip faults. Even very slightly pre-stressed strong lithosphere yields and localizes deformation much easier , than un-prestressed one, in response to plume impact and mantle flow. The results shed new light on the importance of lithosphere rheology and active role of lithosphere in mantle-lithosphere interactions as well as on the role of mantle flow and far-field stresses in tectonic-scale deformation. We show, for example, that crustal fault patterns initiated by plume impact are rapidly re-organized in sub-linear rifts and spreading centers, which orientation is largely dictated (e.g., perpendicular to) by the direction of the tectonic far-field stress field, as well as the plume-head material soon starts to flow along the sub-linear rifted shear zones in crustal and mantle lithosphere further amplifying their development. The final surface deformation and mantle flow patterns rapidly loose the initial axisymmetric character and take elongated sub-linear shapes whereas brittle deformation at surface is amplified and stabilized by coherent flow of mantle/plume-head material from below. These "tectonically" looking dynamic topography patterns are quite different from those expected from conventional models as well as from those directly observed, for example, on Venus where plume-lithosphere interactions produce only axisymmetric coronae domal-shaped features with radiating extensional rifts, suggesting that the Venusian lithosphere is rheologically too weak , and its crust is too thin, to produce any significant impact on the dynamic topography.

Burov, Evgueni; Gerya, Taras; Koptev, Alexander

2014-05-01

190

Seismic waveform inversion for core-mantle boundary topography  

NASA Astrophysics Data System (ADS)

The topography of the core-mantle boundary (CMB) is directly linked to the dynamics of both the mantle and the outer core, although it is poorly constrained and understood. Recent studies have produced topography models with mutual agreement up to degree 2. A broad-band waveform inversion strategy is introduced and applied here, with relatively low computational cost and based on a first-order Born approximation. Its performance is validated using synthetic waveforms calculated in theoretical earth models that include different topography patterns with varying lateral wavelengths, from 600 to 2500 km, and magnitudes (˜10 km peak-to-peak). The source-receiver geometry focuses mainly on the Pdiff, PKP, PcP and ScS phases. The results show that PKP branches, PcP and ScS generally perform well and in a similar fashion, while Pdiff yields unsatisfactory results. We investigate also how 3-D mantle correction influences the output models, and find that despite the disturbance introduced, the models recovered do not appear to be biased, provided that the 3-D model is correct. Using cross-correlated traveltimes, we derive new topography models from both P and S waves. The static corrections used to remove the mantle effect are likely to affect the inversion, compromising the agreement between models derived from P and S data. By modelling traveltime residuals starting from sensitivity kernels, we show how the simultaneous use of volumetric and boundary kernels can reduce the bias coming from mantle structures. The joint inversion approach should be the only reliable method to invert for CMB topography using absolute cross-correlation traveltimes.

Colombi, Andrea; Nissen-Meyer, Tarje; Boschi, Lapo; Giardini, Domenico

2014-07-01

191

Patterns of glacial erosion affected by initial topography  

NASA Astrophysics Data System (ADS)

Spatial and temporal variations in glacial erosion patterns are generally difficult to unravel on longer timescales. Methods constraining glacial erosion rates have proven very dependent on the timescales on which they work, and long-term measures are often accompanied with a lack of temporal detail. In addition, numerical approaches simulating glacial erosion are often forced to choose between either spatial or temporal resolution due to extensive computational costs. The linking of observations and numerical modeling results is complicated further by the fact that the initial pre-glacial landscape is often poorly constrained. This poses significant challenges when considering the topographic control there exists on ice flow and glacier sliding. Here we investigate the effect of the initial pre-glacial topography on patterns of glacial erosion using numerical modeling. We investigate 1) characteristic glacial sliding patterns when simulating glacial conditions in high-resolution landscapes for a number of characteristic natural settings including wedge-type topography and plateau-type topography, and 2) high-resolution long-term patterns of glacial erosion for characteristic landscapes. In order to accomplish this latter part, we use spatially constricted generic models, designed to capture the long-term evolution of glacial landscapes over multiple glacial-interglacial cycles at high spatial resolution. Studies examining glacial erosion processes often use either an existing present-day landscape or a reconstructed fluvial steady-state configuration. However, it is important to investigate the effect of initial pre-glacial topography on patterns of glacial erosion, as fluvial steady state is not often found to occur. Glacial erosion patterns therefore need to be understood in the context of the pre-existing topography when trying to link observations of glacial erosion rates and long-term landscape evolution.

Kathrine Pedersen, Vivi; Huismans, Ritske

2013-04-01

192

Seismic waveform inversion for core-mantle boundary topography  

NASA Astrophysics Data System (ADS)

The topography of the core-mantle boundary (CMB) is directly linked to the dynamics of both the mantle and the outer core, although it is poorly constrained and understood. Recent studies have produced topography models with mutual agreement up to degree 2. A broad-band waveform inversion strategy is introduced and applied here, with relatively low computational cost and based on a first-order Born approximation. Its performance is validated using synthetic waveforms calculated in theoretical earth models that include different topography patterns with varying lateral wavelengths, from 600 to 2500 km, and magnitudes (˜10 km peak-to-peak). The source-receiver geometry focuses mainly on the Pdiff, PKP, PcP and ScS phases. The results show that PKP branches, PcP and ScS generally perform well and in a similar fashion, while Pdiff yields unsatisfactory results. We investigate also how 3-D mantle correction influences the output models, and find that despite the disturbance introduced, the models recovered do not appear to be biased, provided that the 3-D model is correct. Using cross-correlated traveltimes, we derive new topography models from both P and S waves. The static corrections used to remove the mantle effect are likely to affect the inversion, compromising the agreement between models derived from P and S data. By modelling traveltime residuals starting from sensitivity kernels, we show how the simultaneous use of volumetric and boundary kernels can reduce the bias coming from mantle structures. The joint inversion approach should be the only reliable method to invert for CMB topography using absolute cross-correlation traveltimes.

Colombi, Andrea; Nissen-Meyer, Tarje; Boschi, Lapo; Giardini, Domenico

2014-04-01

193

Effects of dynamic topography on Australian Paleogeography in the Cenozoic  

NASA Astrophysics Data System (ADS)

We have investigated the effects of dynamic topography combined with eustatic sea level variations on Australian paleogeography for the Late Cretaceous to present. Using an analytical flow model (Steinberger et al., 2001, doi: 10.1016/S0012-821X(01)00229-1 with the surface plate velocity field as boundary condition, we advect density anomalies converted from tomographic velocity anomalies (SMEAN tomographic model; Becker &Boschi, 2002, doi: 10.1029/2001GC000168) back through time. For each time step, we compute dynamic topography with a free upper boundary. This approach allows us to evaluate the spatio-temporal effects of large scale mantle convection patterns on surface processes like continental flooding and sediment deposition. The Australian continent, especially the southern Australian margin, provides a unique example for an extensive region that has been stable and fairly isolated from plate boundary processes like flexure or rift shoulder uplift for the time between 70 Ma to the present. This makes it ideal to investigate the effects of dynamic topography. Late Cretaceous and Cenozoic sedimentary deposits along the southern Australian margin indicate transgressive/regressive phases of limited extent, which can not be explained by eustatic sea level fluctuations alone. By using common estimates for the eustatic sea level in conjunction with our dynamic topography model, we have been able to reconstruct the position of the Australian paleo-shorelines, flooding patterns and water depths. We find a good agreement of our computed paleogeography with published stratigraphic data for Tertiary brown coal deposits along the southern Australian seabord (Gippsland, Murray, Otway and Bremer Basins) and stratigraphic sequences in the Murray Basin region, along the NW Australian margin and in the Eromanga Basin. Despite minor spatial discrepancies between the current model output and geological data which yet remain unresolved, our approach and modular workflow set up provides an important stepping stone to understand the influence of deep Earth processes and their impact on sediment deposition and other geomorphological processes. Due to the usage of non-proprietary data formats and open-source software it is possible to easily change the dynamic topography model input and extend the computations to incorporate the effects of sedimentation history and isostasy. We expect a further convergence of predicted paleogeography from dynamic topography models with increasing accuracy and resolution of tomographic models.

Heine, C.; M{Ü}Ller, R.; Steinberger, B.

2006-12-01

194

Spatial and Temporal variability in Dynamic Topography in East Antarctica  

NASA Astrophysics Data System (ADS)

Recent aerogeophysical exploration has provided novel views of the Gamburtsev Subglacial Mountains and the Wilkes and Aurora subglacial basins in East Antarctica. Reconstructing the evolution of East Antarctic topography through time is a critical next step for developing new coupled climate and ice sheet models (e.g. http://www.antscape.org/). Insights into tectonic and isostatic components driving the uplift of the Gamburtsevs have emerged from geophysical investigations and modeling (Ferraccioli et al., 2011, Nature). However, our knowledge of the larger-scale consequences of dynamic topography in East Antarctica remains poor compared to other continents. Seismic tomographic models provide a tool to derive large-scale models of convection in the Earth's mantle, which can then be used to reconstruct dynamic topography through time. By analyzing grids of global dynamic topography from present-day to 100 Ma based on the tomographic models S40RTS & S20RTS (Ritsema et al. 1999, 2011) we assess for the first time the potential space-time variability in dynamic topography in East Antarctica. We acknowledge that there are significant limitations when compared to similar studies over other continents, such as the relatively poor seismic resolution of the lithosphere and asthenosphere beneath East Antarctica and the lack of geological and geophysical data to constrain surface movements through time. However, currently available global datasets do reveal several new insights. Our models reveal that at ca 65 Ma the Gamburtsev Province and Dronning Maud Land regions were elevated. This was followed by at least 500 m of subsidence throughout the Cenozoic. The increased regional elevation likely facilitated ephemeral ice cap development in the early Cenozoic, which was followed by ice cap coalescence to form the East Antarctic Ice Sheet at ca 34 Ma. In contrast, a major and more rapid increase in elevation (up to 1,000 m) is observed over the Transantarctic Mountains (TAM) and the adjacent Wilkes Subglacial Basin, in particular over the last 15 Ma. Neogene dynamic topography in the TAM region may be related to the flow of warm mantle from the West Antarctic Rift System and/or the Balleny plume.

Anderson, L.; Ferraccioli, F.; Eagles, G.; Steinberger, B.; Ritsema, J.

2012-04-01

195

On the R- approximations of the Earth's surface topography  

NASA Astrophysics Data System (ADS)

The determination of a function describing the Earth's surface topography on a generally irregular grid is important for the interpretation of gravity data, calculation of the corrections for the topography and construction of maps of plumb line deviations. Thus, we have the problem of describing a surface D, or more specifically, the problem of constructing an approximation of a surface D that will be used in the calculation of the function (the derivative of the potential with respect to the coordinate ). We can write where are the observation points. If the model of the plane Earth is adopted, the surface D may be represented by a function of two variables , parametrizing points on an equipotential surface. Then, the correction for topographic masses (the gravity reduction) is calculated by the approximate formula , (1) where, in the case of a detailed survey, the plane must be such that (a) approximate formula (1) (ensuring a required accuracy) can be used for all , where is a finite simply connected area in the plane and (b) for all . (2) The main computational procedure consists of the construction of an analytical approximation of the function (3) From its values given on a set of points ; this approximation should be valid on the entire integration domain. The analytical approximation can be constructed by the R-approximation method, which is a variant of the linear integral representation method based upon the Radon-transform. The values used for the construction of the analytical approximation are given, first, immediately at the observation points; second, on a certain set of points of topographic maps on an adequate scale (for example, it is desirable to use topographic maps on a 1:10 000 scale in the case of a detailed gravity survey on a scale 1:25 000); third, on a certain set of characteristic points of the relief (these values must be measured during gravity surveys). The method proposed in this topic for the Earth's topography description with the help of R-approximations is effective for solving various geophysical, geomorphological, an geodetic problems. Using this method, the values of the function describing the topography can be determined on an arbitrary grid. Therefore, the preliminary regularization of initial data, their ordering, and so on, are not required. A smoother topography is reconstructed to within a few centimeters, whereas mountainous topography is reconstructed less accurately (1-3 sm with a height contrast of about 1000 m).

Stepanova, I. E.

2010-05-01

196

Fractal mapping of digitized images - Application to the topography of Arizona and comparisons with synthetic images  

Microsoft Academic Search

The concept of fractal mapping is introduced and applied to digitized topography of Arizona. It is shown that the fractal statistics satisfy the topography of the state to a good approximation. The fractal dimensions and roughness amplitudes from subregions are used to construct maps of these quantities. It is found that the fractal dimension of actual two-dimensional topography is not

J. Huang; D. L. Turcotte

1989-01-01

197

A theory of the imaging mechanism of underwater bottom topography by real and synthetic aperture radar  

Microsoft Academic Search

A simple theoretical model of the imaging mechanism of underwater bottom topography in tidal channels by real and by synthetic aperture radar (SAR) is presented. The imaging is attributed to surface effects induced by current variations over bottom topography. The current modulates the short-scale surface roughness, which in turn gives rise to changes in radar reflectivity. The bottom topography-current interaction

Werner Alpers; Ingo Hennings

1984-01-01

198

Nanometrology of surface topography: Application to the research in development of a new mass standard  

Microsoft Academic Search

Surface topography metrology has a great success in a variety of applications at micron-scale, for instance lubrication of automobile engines. In extension, surface metrology may be carried out for nano-regime applications, such as topography analysis of MEMS components, thin films and integrated circuits. Studies on nanometrology of surface topography may help improve the quality of human life in health, environment

T. Y. Lin; G. S. Peng

1998-01-01

199

Iceland, the Farallon slab, and dynamic topography of the North Atlantic  

Microsoft Academic Search

Upwelling or downwelling flow in Earth's mantle is thought to elevate or depress Earth's surface on a continental scale. Direct observation of this ''dynamic topography'' on the seafloor, however, has remained elusive because it is obscured by isostatically sup- ported topography caused by near-surface density variations. We calculate the nonisostatic topography of the North Atlantic by correcting seafloor depths for

Clinton P. Conrad; Carolina Lithgow-Bertelloni; Keith E. Louden

2004-01-01

200

Mapping Damping Ratio From ICESat-derived Surface Topography Over The Antarctic Ice Sheet  

Microsoft Academic Search

The Ice, Cloud, and land Elevation Satellite (ICESat) has acquired detailed surface topography (to ±86° latitude) that allows the investigation of the relation between surface and bedrock undulations from ice sheet margins to regions further inland, where accurate surface topography was not previously available. Using ICESat data combined with bedrock topography from BEDMAP along Antarctic ice-sheet flowlines, we perform power-spectral

W. Wang; J. Li; J. H. Zwally

2005-01-01

201

Keratometry and corneal topography using multiple delay element OCT  

NASA Astrophysics Data System (ADS)

We have presented previously a novel method for the evaluation of the surface shape of an object, with immediate application to measurement of cornea shape. This method uses single shot C-scans obtained by using a multiple delay element (MDE) in the reference path of an OCT system. A calibrated MDE-OCT system can be used to measure the elevation of points on the cornea, in contrast to existing methods which are based on measurement of the cornea slope. The associated algorithm for extracting corneal topography data points from the MDE-OCT C-Scan image will be presented, data points which can then be used to calculate the Zernike coefficients for the cornea shape. The differences between the existing systems and the MDE-OCT method for keratometry and corneal topography are discussed.

Plesea, Lucian; Podoleanu, Adrian G.

2008-03-01

202

On the detection of underwater bottom topography by imaging radars  

NASA Technical Reports Server (NTRS)

A theoretical model which explains basic properties of radar imaging of underwater bottom topography in tidal channels is presented. The surface roughness modulation is described by weak hydrodynamic interaction theory in the relaxation time approximation. In contrast to previous theories on short wave modulation by long ocean waves, a different approximation is used to describe short wave modulation by tidal flow over underwater bottom topography. The modulation depth is proportional to the relaxation time of the Bragg waves. The large modulation of radar reflectivity observed in SEASAT-SAR imagery of sand banks in the Southern Bight of the North Sea are explained by assuming that the relaxation time of 34 cm Bragg waves is of the order of 30-40 seconds.

Alpers, W.

1984-01-01

203

Method and Apparatus for Creating a Topography at a Surface  

DOEpatents

Methods and apparatus whereby an optical interferometer is utilized to monitor and provide feedback control to an integrated energetic particle column, to create desired topographies, including the depth, shape and/or roughness of features, at a surface of a specimen. Energetic particle columns can direct energetic species including, ions, photons and/or neutral particles to a surface to create features having in-plane dimensions on the order of 1 micron, and a height or depth on the order of 1 nanometer. Energetic processes can include subtractive processes such as sputtering, ablation, focused ion beam milling and, additive processes, such as energetic beam induced chemical vapor deposition. The integration of interferometric methods with processing by energetic species offers the ability to create desired topographies at surfaces, including planar and curved shapes.

Adams, David P. (Albuquerque, NM); Sinclair, Michael B. (Albuquerque, NM); Mayer, Thomas M. (Albuquerque, NM); Vasile, Michael J. (Albuquerque, NM); Sweatt, William C. (Albuquerque, NM)

2008-11-11

204

AFM dissipation topography of soliton superstructures in adsorbed overlayers  

NASA Astrophysics Data System (ADS)

In the atomic force microscope, the nanoscale force topography of even complex surface superstructures is extracted by the changing vibration frequency of a scanning tip. An alternative dissipation topography with similar or even better contrast has been demonstrated recently by mapping the (x,y) -dependent tip damping but the detailed damping mechanism is still unknown. Here we identify two different tip dissipation mechanisms: local mechanical softness and hysteresis. Motivated by recent data, we describe both of them in a one-dimensional model of Moiré superstructures of incommensurate overlayers. Local softness at “soliton” defects yields a dissipation contrast that can be much larger than the corresponding density or corrugation contrast. At realistically low vibration frequencies, however, a much stronger and more effective dissipation is caused by the tip-induced nonlinear jumping of the soliton, naturally developing bistability and hysteresis. Signatures of this mechanism are proposed for experimental identification.

Negri, Carlotta; Manini, Nicola; Vanossi, Andrea; Santoro, Giuseppe E.; Tosatti, Erio

2010-01-01

205

Irregular topography at the Earth's inner core boundary  

PubMed Central

Compressional seismic wave reflected off the Earth’s inner core boundary (ICB) from earthquakes occurring in the Banda Sea and recorded at the Hi-net stations in Japan exhibits significant variations in travel time (from -2 to 2.5 s) and amplitude (with a factor of more than 4) across the seismic array. Such variations indicate that Earth’s ICB is irregular, with a combination of at least two scales of topography: a height variation of 14 km changing within a lateral distance of no more than 6 km, and a height variation of 4–8 km with a lateral length scale of 2–4 km. The characteristics of the ICB topography indicate that small-scale variations of temperature and/or core composition exist near the ICB, and/or the ICB topographic surface is being deformed by small-scale forces out of its thermocompositional equilibrium position and is metastable.

Dai, Zhiyang; Wang, Wei; Wen, Lianxing

2012-01-01

206

Topography, relief, climate and glaciers: a global prespective  

NASA Astrophysics Data System (ADS)

The examination of the relationship between Earth's topography and present and past climate (i.e. long-term elevation of glaciers Equilibrium Line Altitude) reveals that the elevation of mountain ranges may be limited or controlled by glaciations. This is of prime importance, because glacial condition would lead to a limit the mountain development, hence the accumulation of gravitational energy and prevent the development of further glacial conditions as well as setting the erosion in (peri)glacial environments. This study examines the relationships between topography and the global Equilibrium Line Altitude of alpine glaciers around the world (long term snowline, i.e. the altitude where the ice mass balance is null). Two main observations can be drawn: 1) The distance between the (averaged and maximum) topography, and the ELA decreases pole ward the poles, and even become reversed (mean elevation above to ELA) at high latitude. Correlatively, the elevation of very large portion of land at mid-latitude cannot be related to glaciations, simply because it was never glaciated (large distance between topography and long-term mean ELA). The maximum distance between the ELA and the topography is greater close to the equator and decreases poleward. In absence of glacial and periglacial erosion, this trend cannot have its origin in glacial and periglacial processes. Moreover, the ELA elevation shows a significant (1000 - 1500m) depression in the intertropical zone. This depression of the ELA is not reflected at all in the topography. 2) The distribution of relief on Earth, if normalized by the mean elevation of mountain ranges (as a proxy for available space to create relief) shows a latitudinal band of greater relief between 40° and 60° (or between ELA of 500m to 2500m a.s.l.). This mid-latitude relatively greater relief challenges the straightforward relationship between glaciations, erosion and topography. Oppositely, it suggests that glacier may be more efficient agent in temperate area, with important amplitude between glacial and interglacial climate. This is consistent with the view of a very variable glacier erodibility that can erode and protect the landscape, as well as with studies documenting a bimodal location of the preferred glacial erosion, at relatively high elevation (around the long-term ELA), and at much lower elevation (close to the glacial maximum lower reaches), thanks to efficient water lubrication of the glacier bases that greatly enhance the sliding velocity. These findings show that the relation between the mountain topography and the long term snowline is not as straightforward as previously proposed. Beside the role of tectonic forcing highlighted by several authors, the importance of the glacial erosion appears to be crucial at mid latitude, but more complex at both high and low latitude. Moreover, the relief at mid latitude appears to be higher, hence suggesting a positive correlation between relief and topographic control of glacier on the landscape.

Champagnac, Jean-Daniel; Valla, Pierre; Herman, fred

2014-05-01

207

Three-dimensional measurement and characterization of grinding tool topography  

NASA Astrophysics Data System (ADS)

A comprehensive 3-dimensional measurement and characterization method for grinding tool topography was developed. A stylus instrument (SOMICRONIC, France) was used to measure the surface of a metal-bonded diamond grinding tool. The sampled data was input the software SurfStand developed by Centre for Precision Technology (CPT) for reconstruction and further characterization of the surface. Roughness parameters pertaining to the general surface and specific feature parameters relating to the grinding grits, such as height and angle peak curvature have been calculated. The methodology of measurement has been compared with that using an optical microscope. The comparison shows that the three-dimensional characterization has distinct advantages for grinding tool topography assessment. It is precise, convenient and comprehensive so it is suitable for precision measurement and analysis where an understanding of the grinding tool and its cutting ability are required.

Cui, Changcai; Blunt, Liam; Jiang, Xiangqian; Xu, Xipeng; Huang, Hui; Ye, Ruifang

2013-01-01

208

Intraocular lens power calculations using corneal topography after photorefractive keratectomy  

Microsoft Academic Search

PURPOSE: To report two patients (two eyes) with previous photorefractive keratectomy, who subsequently underwent cataract extraction years later.DESIGN: Case reports.METHODS: Corneal topography was used to determine corneal power used in intraocular lens power calculations.RESULTS: In two eyes of two patients, intraocular lens calculations after photorefractive keratectomy were inadequate, which resulted in a hyperopic postoperative refractive error requiring implantation of a

John G Ladas; Brian S Boxer Wachler; John D Hunkeler; Daniel S Durrie

2001-01-01

209

Unraveling topography around subduction zones from laboratory models  

NASA Astrophysics Data System (ADS)

The relief around subduction zones results from the interplay of dynamic processes that may locally exceed the (iso)static contributions. The viscous dissipation of the energy in and around subduction zones is capable of generating kilometer scale vertical ground movements. In order to evaluate dynamic topography in a self-consistent subduction system, we carried out a set of laboratory experiments, wherein the lithosphere and mantle are simulated by means of Newtonian viscous materials, namely silicone putty and glucose syrup. Models are kept in their most simple form and are made of negative buoyancy plates, of variable width and thickness, freely plunging into the syrup. The surface of the model and the top of the slab are scanned in three dimensions. A forebulge systematically emerges from the bending of the viscous plate, adjacent to the trench. With a large wavelength, dynamic pressure offsets the foreside and backside of the slab by ~ 500 m on average. The suction, that accompanies the vertical descent of the slab depresses the surface on both sides. At a distance equal to the half-width of the slab, the topographic depression amounts to ~ 500 m on average and becomes negligible at a distance that equals the width of the slab. In order to explore the impact of slab rollback on the topography, the trailing edge of the plates is alternatively fixed to (fixed mode) and freed from (free mode) the end wall of the tank. Both the pressure and suction components of the topography are ~ 30% lower in the free mode, indicating that slab rollback fosters the dynamic subsidence of upper plates. Our models are compatible with first order observations of the topography around the East Scotia, Tonga, Kermadec and Banda subduction zones, which exhibit anomalous depths of nearly 1 km as compared to adjacent sea floor of comparable age.

Husson, Laurent; Guillaume, Benjamin; Funiciello, Francesca; Faccenna, Claudio; Royden, Leigh H.

2012-03-01

210

Electronic cigarettes: abuse liability, topography and subjective effects  

PubMed Central

Objective To review the available evidence evaluating the abuse liability, topography, subjective effects, craving and withdrawal suppression associated with e-cigarette use in order to identify information gaps and provide recommendations for future research. Methods Literature searches were conducted between October 2012 and January 2014 using five electronic databases. Studies were included in this review if they were peer-reviewed scientific journal articles evaluating clinical laboratory studies, national surveys or content analyses. Results A total of 15 peer-reviewed articles regarding behavioural use and effects of e-cigarettes published between 2010 and 2014 were included in this review. Abuse liability studies are limited in their generalisability. Topography (consumption behaviour) studies found that, compared with traditional cigarettes, e-cigarette average puff duration was significantly longer, and e-cigarette use required stronger suction. Data on e-cigarette subjective effects (such as anxiety, restlessness, concentration, alertness and satisfaction) and withdrawal suppression are limited and inconsistent. In general, study data should be interpreted with caution, given limitations associated with comparisons of novel and usual products, as well as the possible effects associated with subjects’ previous experience/inexperience with e-cigarettes. Conclusions Currently, very limited information is available on abuse liability, topography and subjective effects of e-cigarettes. Opportunities to examine extended e-cigarette use in a variety of settings with experienced e-cigarette users would help to more fully assess topography as well as behavioural and subjective outcomes. In addition, assessment of ‘real-world’ use, including amount and timing of use and responses to use, would clarify behavioural profiles and potential adverse health effects.

Evans, Sarah E; Hoffman, Allison C

2014-01-01

211

Bridges of the sella turcica - anatomy and topography.  

PubMed

This paper presents anatomy and topography of the inconstant osseous bridges that may occur in the sella turcica region. The interclinoid bridge and the caroticoclinoid bridge can be formed in consequence of abnormal ossification of the dural folds or disturbances in development of the sphenoid bone. Their presence may be of clinical importance because of potential influence on the neurovascular structures passing in the vicinity of the clinoid processes of the sphenoid bone. PMID:24852690

Skrzat, Janusz; Mroz, Izabela; Marchewka, Justyna

2012-01-01

212

MOLA Topography of the Crustal Dichotomy Boundary Zone, Mars  

NASA Technical Reports Server (NTRS)

Mars Orbiter Laser Altimeter (MOLA) profiles frequently cross the crustal dichotomy boundary where the transition zone (TZ) between cratered highland terrain (CT) and lowland smooth plains (SP) is marked by mesas and knobby terrain. The detailed topographic character of the boundary zone is longitudinally variable, as is the geomorphology of the TZ. Some portions of the boundary are associated with an outer ring of the Utopia impact basin; MOLA topography is consistent with this. The regional character of the boundary topography is a 2-4 km step function from nearly flat SP to almost as flat CT. This rise has a regional slope of 1-2 degrees, 50-100 times that of the Cr and SP away from TZ, which suggests a significant change in crustal properties (thickness, composition or both) across the TZ. The overall topography is very similar to that at some passive continent-oceanic crustal margins on the Earth, with the seafloor allowed to adjust upward after removal of the overlying water. A possible temporal constraint on the CT/SP elevation difference comes from two MOLA profiles which pass through two large (150 km diameter) craters located at the boundary in Aeolis. The N and S rims of the more degraded crater are at the same elevation; north of the N rim the topography drops by greater than 2 km to the floor of the TZ. This crater predates the elevation offset between CT and TZ floor. The better preserved crater (Gale) has a N rim 2 km lower than its S rim, and appears to have been emplaced on a pre-existing regional slope of about I degree. Gale probably post- dates the elevation difference between CT and TZ floor. Based on the stratigraphy of the units in which these craters are found, the elevation difference appears to have been in place in the Mid to Late Noachian.

Frey, Herbert V.; E. H., Susan; H., James

1998-01-01

213

ATM Coastal Topography-Texas, 2001: UTM Zone 15  

USGS Publications Warehouse

These remotely sensed, geographically referenced elevation measurements of lidar-derived first-surface (FS) topography were produced collaboratively by the U.S. Geological Survey (USGS), Florida Integrated Science Center (FISC), St. Petersburg, FL, and the National Aeronautics and Space Administration (NASA), Wallops Flight Facility, VA. This project provides highly detailed and accurate datasets of a portion of the Texas coastline within UTM zone 15, from Matagorda Peninsula to Galveston Island, acquired October 12-13, 2001. The datasets are made available for use as a management tool to research scientists and natural-resource managers. An innovative scanning lidar instrument originally developed by NASA, and known as the Airborne Topographic Mapper (ATM), was used during data acquisition. The ATM system is a scanning lidar system that measures high-resolution topography of the land surface and incorporates a green-wavelength laser operating at pulse rates of 2 to 10 kilohertz. Measurements from the laser-ranging device are coupled with data acquired from inertial navigation system (INS) attitude sensors and differentially corrected global positioning system (GPS) receivers to measure topography of the surface at accuracies of +/-15 centimeters. The nominal ATM platform is a Twin Otter or P-3 Orion aircraft, but the instrument may be deployed on a range of light aircraft. Elevation measurements were collected over the survey area using the ATM system, and the resulting data were then processed using the Airborne Lidar Processing System (ALPS), a custom-built processing system developed in a NASA-USGS collaboration. ALPS supports the exploration and processing of lidar data in an interactive or batch mode. Modules for presurvey flight-line definition, flight-path plotting, lidar raster and waveform investigation, and digital camera image playback have been developed. Processing algorithms have been developed to extract the range to the first and last significant return within each waveform. ALPS is used routinely to create maps that represent submerged or first-surface topography.

Klipp, Emily S.; Nayegandhi, Amar; Brock, John C.; Sallenger, A.H.; Bonisteel, Jamie M.; Yates, Xan; Wright, C. Wayne

2009-01-01

214

ATM Coastal Topography-Florida 2001: Western Panhandle  

USGS Publications Warehouse

These remotely sensed, geographically referenced elevation measurements of Lidar-derived first surface (FS) topography were produced collaboratively by the U.S. Geological Survey (USGS), Florida Integrated Science Center (FISC), St. Petersburg, FL, and the National Aeronautics and Space Administration (NASA), Wallops Flight Facility, VA. This project provides highly detailed and accurate datasets of the western Florida panhandle coastline, acquired October 2-4 and 7-10, 2001. The datasets are made available for use as a management tool to research scientists and natural resource managers. An innovative scanning Lidar instrument originally developed by NASA, and known as the Airborne Topographic Mapper (ATM), was used during data acquisition. The ATM system is a scanning Lidar system that measures high-resolution topography of the land surface and incorporates a green-wavelength laser operating at pulse rates of 2 to 10 kilohertz. Measurements from the laser-ranging device are coupled with data acquired from inertial navigation system (INS) attitude sensors and differentially corrected global positioning system (GPS) receivers to measure topography of the surface at accuracies of +/-15 centimeters. The nominal ATM platform is a Twin Otter or P-3 Orion aircraft, but the instrument may be deployed on a range of light aircraft. Elevation measurements were collected over the survey area using the ATM system, and the resulting data were then processed using the Airborne Lidar Processing System (ALPS), a custom-built processing system developed in a NASA-USGS collaboration. ALPS supports the exploration and processing of Lidar data in an interactive or batch mode. Modules for presurvey flight line definition, flight path plotting, Lidar raster and waveform investigation, and digital camera image playback have been developed. Processing algorithms have been developed to extract the range to the first and last significant return within each waveform. ALPS is routinely used to create maps that represent submerged or first surface topography.

Yates, Xan; Nayegandhi, Amar; Brock, John C.; Sallenger, A.H.; Bonisteel, Jamie M.; Klipp, Emily S.; Wright, C. Wayne

2009-01-01

215

ATM Coastal Topography-Florida 2001: Eastern Panhandle  

USGS Publications Warehouse

These remotely sensed, geographically referenced elevation measurements of Lidar-derived first surface (FS) topography were produced collaboratively by the U.S. Geological Survey (USGS), Florida Integrated Science Center (FISC), St. Petersburg, FL, and the National Aeronautics and Space Administration (NASA), Wallops Flight Facility, VA. This project provides highly detailed and accurate datasets of the eastern Florida panhandle coastline, acquired October 2, 2001. The datasets are made available for use as a management tool to research scientists and natural resource managers. An innovative scanning Lidar instrument originally developed by NASA, and known as the Airborne Topographic Mapper (ATM), was used during data acquisition. The ATM system is a scanning Lidar system that measures high-resolution topography of the land surface and incorporates a green-wavelength laser operating at pulse rates of 2 to 10 kilohertz. Measurements from the laser-ranging device are coupled with data acquired from inertial navigation system (INS) attitude sensors and differentially corrected global positioning system (GPS) receivers to measure topography of the surface at accuracies of +/-15 centimeters. The nominal ATM platform is a Twin Otter or P-3 Orion aircraft, but the instrument may be deployed on a range of light aircraft. Elevation measurements were collected over the survey area using the ATM system, and the resulting data were then processed using the Airborne Lidar Processing System (ALPS), a custom-built processing system developed in a NASA-USGS collaboration. ALPS supports the exploration and processing of Lidar data in an interactive or batch mode. Modules for presurvey flight line definition, flight path plotting, Lidar raster and waveform investigation, and digital camera image playback have been developed. Processing algorithms have been developed to extract the range to the first and last significant return within each waveform. ALPS is routinely used to create maps that represent submerged or first surface topography.

Yates, Xan; Nayegandhi, Amar; Brock, John C.; Sallenger, A.H.; Bonisteel, Jamie M.; Klipp, Emily S.; Wright, C. Wayne

2009-01-01

216

How to handle topography in practical geoid determination: three examples  

Microsoft Academic Search

.  ?Three different methods of handling topography in geoid determination were investigated. The first two methods employ the\\u000a residual terrain model (RTM) remove–restore technique, yielding the quasigeoid, whereas the third method uses the classical\\u000a Helmert condensation method, yielding the geoid. All three methods were used with the geopotential model Earth Gravity Model\\u000a (1996) (EGM96) as a reference, and the results were

O. C. D. Omang; R. Forsberg

2000-01-01

217

Ocean Surface Topography From Space (TOPEX/Poseidon Missions)  

NSDL National Science Digital Library

A joint US and France project, the TOPEX-Poseidon satellites continuously measure sea surface height. The oceans store and transport solar heat, helping to keep Earth's climate in balance. The overall shape of the oceans' "hills" and "valleys" is called ocean surface topography, or OST. Precise knowledge of OST is essential to predict the effects of catastrophic storms. Educational resources available for all ages and backgrounds. Outstanding animation of OTS also included.

2010-08-11

218

Topography of Equatorial Mercury from MESSENGER Flybys 1 and 2  

Microsoft Academic Search

During the first flyby of Mercury by the MESSENGER spacecraft on January 14, 2008, the Mercury Laser Altimeter (MLA) obtained a 3200-kilometer-long profile that spanned approximately 20% of the near- equatorial region of the planet. Topography along that profile is characterized by a 5.2-kilometer dynamic range and approximately 1-kilometer root-mean-square roughness. Sampled craters are shallower than their counterparts on the

M. T. Zuber; D. E. Smith; S. C. Solomon; R. J. Phillips; S. J. Peale; J. W. Head; S. A. Hauck; R. L. McNutt; J. Oberst; G. A. Neumann; F. G. Lemoine; X. Sun; O. Barmouin-Jha; C. L. Johnson

2008-01-01

219

ATM Coastal Topography-Texas, 2001: UTM Zone 14  

USGS Publications Warehouse

These remotely sensed, geographically referenced elevation measurements of lidar-derived first-surface (FS) topography were produced collaboratively by the U.S. Geological Survey (USGS), Florida Integrated Science Center (FISC), St. Petersburg, FL, and the National Aeronautics and Space Administration (NASA), Wallops Flight Facility, VA. This project provides highly detailed and accurate datasets of a portion of the Texas coastline within UTM zone 14, acquired October 12-13, 2001. The datasets are made available for use as a management tool to research scientists and natural-resource managers. An innovative scanning lidar instrument originally developed by NASA, and known as the Airborne Topographic Mapper (ATM), was used during data acquisition. The ATM system is a scanning lidar system that measures high-resolution topography of the land surface and incorporates a green-wavelength laser operating at pulse rates of 2 to 10 kilohertz. Measurements from the laser-ranging device are coupled with data acquired from inertial navigation system (INS) attitude sensors and differentially corrected global positioning system (GPS) receivers to measure topography of the surface at accuracies of +/-15 centimeters. The nominal ATM platform is a Twin Otter or P-3 Orion aircraft, but the instrument may be deployed on a range of light aircraft. Elevation measurements were collected over the survey area using the ATM system, and the resulting data were then processed using the Airborne Lidar Processing System (ALPS), a custom-built processing system developed in a NASA-USGS collaboration. ALPS supports the exploration and processing of lidar data in an interactive or batch mode. Modules for presurvey flight-line definition, flight-path plotting, lidar raster and waveform investigation, and digital camera image playback have been developed. Processing algorithms have been developed to extract the range to the first and last significant return within each waveform. ALPS is used routinely to create maps that represent submerged or first-surface topography.

Klipp, Emily S.; Nayegandhi, Amar; Brock, John C.; Sallenger, A.H.; Bonisteel, Jamie M.; Yates, Xan; Wright, C. Wayne

2009-01-01

220

Design consideration and performance analysis of OCT-based topography  

NASA Astrophysics Data System (ADS)

We report a study on design consideration and performance analysis of OCT-based topography by tracking of maximum intensity at each layer's interface. We demonstrate that, for a given stabilized OCT system, a high precision and accuracy of OCT-based layers and thickness topography in the order of tens nanometer can be achieved by using a technique of maximum amplitude tracking. The submicron precision was obtained by over sampling through the FFT of the acquired spectral fringes but was eventually limited by the system stability. Furthermore, we report characterization of a precision, repeatability, and accuracy of the surfaces, sub-surfaces, and thickness topography using our optimized FD-OCT system. We verified that for a given stability of our OCT system, precision of the detected position of signal's peak of down to 20 nm was obtained. In addition, we quantified the degradation of the precision caused by sensitivity fall-off over depth of FD-OCT. The measured precision is about 20 nm at about 0.1 mm depth, and degrades to about 80 nm at 1 mm depth, a position of about 10 dB sensitivity fall-off. The measured repeatability of thickness measurements over depth was approximately 0.04 micron. Finally, the accuracy of the system was verified by comparing with a digital micrometer gauging.

Meemon, Panomsak; Yao, Jianing; Rolland, Jannick P.

2014-03-01

221

Influence of grain topography on near infrared hyperspectral images.  

PubMed

Near infrared hyperspectral imaging (NIR-HSI) allows spatially resolved spectral information to be collected without sample destruction. Although NIR-HSI is suitable for a broad range of samples, sizes and shapes, topography of a sample affects the quality of near infrared (NIR) measurements. Single whole kernels of three cereals (barley, wheat and sorghum), with varying topographic complexity, were examined using NIR-HSI. The influence of topography (sample shape and texture) on spectral variation was examined using principal component analysis (PCA) and classification gradients. The greatest source of variation for all three grain types, despite spectral preprocessing with standard normal variate (SNV) transformation, was kernel curvature. Only 1.29% (PC5), 0.59% (PC6) and 1.36% (PC5) of the spectral variation within the respective barley, wheat and sorghum image datasets was explained within the principal component (PC) associated with the chemical change of interest (loss of kernel viability). The prior PCs explained an accumulated total of 91.18%, 89.43% and 84.39% of spectral variance, and all were influenced by kernel topography. Variation in sample shape and texture relative to the chemical change of interest is an important consideration prior to the analysis of NIR-HSI data for non-flat objects. PMID:22284484

Manley, Marena; McGoverin, Cushla M; Engelbrecht, Paulina; Geladi, Paul

2012-01-30

222

Anomalous topography on the continental shelf around Hudson Canyon  

USGS Publications Warehouse

Recent seismic-reflection data show that the topography on the Continental Shelf around Hudson Canyon is composed of a series of depressions having variable spacings (< 100 m to 2 km), depths (1-10 m), outlines, and bottom configurations that give the sea floor an anomalous "jagged" appearance in profile. The acoustic and sedimentary characteristics, the proximity to relict shores, and the areal distribution indicate that this rough topography is an erosional surface formed on Upper Pleistocene silty sands about 13,000 to 15,000 years ago by processes related to Hudson Canyon. The pronounced southward extension of the surface, in particular, may reflect a former increase in the longshore-current erosion capacity caused by the loss of sediments over the canyon. Modern erosion or nondeposition of sediments has prevented the ubiquitous sand sheet on the Middle Atlantic shelf from covering the surface. The "anomalous" topography may, in fact, be characteristic of areas near other submarine canyons that interrupt or have interrupted the longshore drift of sediments. ?? 1979.

Knebel, H. J.

1979-01-01

223

The application of confocal technology based on polycapillary X-ray optics in surface topography  

NASA Astrophysics Data System (ADS)

A confocal micro-X-ray fluorescence (MXRF) technology based on polycapillary X-ray optics was proposed for determining surface topography. This confocal topography method involves elemental sensitivity and can be used to classify the objects according to their elemental composition while obtaining their surface topography. To improve the spatial resolution of this confocal topography technology, the center of the confocal micro-volume was overlapped with the output focal spot of the polycapillary X-ray, focusing the lens in the excitation channel. The input focal spot of the X-ray lens parallel to the detection channel was used to determine the surface position of the sample. The corresponding surface adaptive algorithm was designed to obtain the surface topography. The surface topography of a ceramic chip was obtained. This confocal MXRF surface topography method could find application in the materials sciences.

Zhao, Guangcui; Sun, Tianxi; Liu, Zhiguo; Yuan, Hao; Li, Yude; Liu, Hehe; Zhao, Weigang; Zhang, Ruixia; Min, Qin; Peng, Song

2013-09-01

224

The role of topography in geodetic gravity field modelling  

NASA Astrophysics Data System (ADS)

Masses associated with the topography, bathymetry, and its isostatic compensation are a dominant source of gravity field variations, especially at shorter wavelengths. On global scales the topographic/isostatic effects are also significant, except for the lowest harmonics. In practice, though, global effects need not be taken into account as such effects are included in the coefficients of the geopotential reference fields. On local scales, the short-wavelength gravity variations due to the topography may, in rugged terrain, be an order of magnitude larger than other effects. In such cases, explicit or implicit terrain reduction procedures are mandatory in order to obtain good prediction results. Such effects may be computed by space-domain integration or by fast Fourier transformation (FFT) methods. Numerical examples are given for areas of the Canadian Rockies. In principle, good knowledge of the topographic densities is required to produce the smoothest residual field. Densities may be determined from sample measurements or by gravimetric means, but both are somewhat troublesome methods in practice. The use of a standard density, e.g., 2.67 g/cu cm, may often yield satisfactory results and may be put within a consistent theoretical framework. The independence of density assumptions is the key point of the classical Molodensky approach to the geodetic boundary value problem. The Molodensky solutions take into account that land gravity field observations are done on a non-level surface. Molodensky's problem may be solved by integral expansions or more effective FFT methods, but the solution should not be intermixed with the use of terrain reductions. The methods are actually complimentary and may both be required in order to obtain the smoothest possible signal, least prone to aliasing and other effects coming from sparse data coverage, typical of rugged topography.

Forsberg, R.; Sideris, M. G.

1989-06-01

225

Management intensity and topography determined plant diversity in vineyards.  

PubMed

Vineyards are amongst the most intensive forms of agriculture often resulting in simplified landscapes where semi-natural vegetation is restricted to small scattered patches. However, a tendency toward a more sustainable management is stimulating research on biodiversity in these poorly investigated agro-ecosystems. The main aim of this study was to test the effect on plant diversity of management intensity and topography in vineyards located in a homogenous intensive hilly landscape. Specifically, this study evaluated the role of slope, mowing and herbicide treatments frequency, and nitrogen supply in shaping plant diversity and composition of life-history traits. The study was carried out in 25 vineyards located in the area of the Conegliano-Valdobbiadene DOCG (Veneto, NE Italy). In each vineyard, 10 plots were placed and the abundance of all vascular plants was recorded in each plot. Linear multiple regression was used to test the effect of management and topography on plant diversity. Management intensity and topography were both relevant drivers of plant species diversity patterns in our vineyards. The two most important factors were slope and mowing frequency that respectively yielded positive and negative effects on plant diversity. A significant interaction between these two factors was also demonstrated, warning against the detrimental effects of increasing mowing intensity on steep slope where plant communities are more diverse. The response of plant communities to mowing frequency is mediated by a process of selection of resistant growth forms, such in the case of rosulate and reptant species. The other two management-related factors tested in this study, number of herbicide treatments and N fertilization, were less influential. In general, our study corroborates the idea that some simple changes in farming activities, which are compatible with grape production, should be encouraged for improving the natural and cultural value of the landscape by maintaining and improving wild plant diversity. PMID:24098435

Nascimbene, Juri; Marini, Lorenzo; Ivan, Diego; Zottini, Michela

2013-01-01

226

Topography and biological noise determine acoustic detectability on coral reefs  

NASA Astrophysics Data System (ADS)

Acoustic telemetry is an increasingly common tool for studying the movement patterns, behavior and site fidelity of marine organisms, but to accurately interpret acoustic data, the variability, periodicity and range of detectability between acoustic tags and receivers must be understood. The relative and interactive effects of topography with biological and environmental noise have not been quantified on coral reefs. We conduct two long-term range tests (1- and 4-month duration) on two different reef types in the central Red Sea to determine the relative effect of distance, depth, topography, time of day, wind, lunar phase, sea surface temperature and thermocline on detection probability. Detectability, as expected, declines with increasing distance between tags and receivers, and we find average detection ranges of 530 and 120 m, using V16 and V13 tags, respectively, but the topography of the reef can significantly modify this relationship, reducing the range by ~70 %, even when tags and receivers are in line-of-sight. Analyses that assume a relationship between distance and detections must therefore be used with care. Nighttime detection range was consistently reduced in both locations, and detections varied by lunar phase in the 4-month test, suggesting a strong influence of biological noise (reducing detection probability up to 30 %), notably more influential than other environmental noises, including wind-driven noise, which is normally considered important in open-water environments. Analysis of detections should be corrected in consideration of the diel patterns we find, and range tests or sentinel tags should be used for more than 1 month to quantify potential changes due to lunar phase. Some studies assume that the most usual factor limiting detection range is weather-related noise; this cannot be extrapolated to coral reefs.

Cagua, E. F.; Berumen, M. L.; Tyler, E. H. M.

2013-12-01

227

EAARL Coastal Topography-Pearl River Delta 2008: Bare Earth  

USGS Publications Warehouse

These remotely sensed, geographically referenced elevation measurements of Lidar-derived bare earth (BE) topography were produced as a collaborative effort between the U.S. Geological Survey (USGS), Florida Integrated Science Center (FISC), St. Petersburg, FL; the University of New Orleans (UNO), Pontchartrain Institute for Environmental Sciences (PIES), New Orleans, LA; and the National Aeronautics and Space Administration (NASA), Wallops Flight Facility, VA. This project provides highly detailed and accurate datasets of a portion of the Pearl River Delta in Louisiana and Mississippi, acquired March 9-11, 2008. The datasets are made available for use as a management tool to research scientists and natural resource managers. An innovative airborne Lidar instrument originally developed at the NASA Wallops Flight Facility, and known as the Experimental Advanced Airborne Research Lidar (EAARL), was used during data acquisition. The EAARL system is a raster-scanning, waveform-resolving, green-wavelength (532-nanometer) Lidar designed to map near-shore bathymetry, topography, and vegetation structure simultaneously. The EAARL sensor suite includes the raster-scanning, water-penetrating full-waveform adaptive Lidar, a down-looking red-green-blue (RGB) digital camera, a high-resolution multi-spectral color infrared (CIR) camera, two precision dual-frequency kinematic carrier-phase GPS receivers, and an integrated miniature digital inertial measurement unit, which provide for submeter georeferencing of each laser sample. The nominal EAARL platform is a twin-engine Cessna 310 aircraft, but the instrument may be deployed on a range of light aircraft. A single pilot, a Lidar operator, and a data analyst constitute the crew for most survey operations. This sensor has the potential to make significant contributions in measuring sub-aerial and submarine coastal topography within cross-environmental surveys. Elevation measurements were collected over the survey area using the EAARL system, and the resulting data were then processed using the Airborne Lidar Processing System (ALPS), a custom-built processing system developed in a NASA-USGS collaboration. ALPS supports the exploration and processing of Lidar data in an interactive or batch mode. Modules for presurvey flight line definition, flight path plotting, Lidar raster and waveform investigation, and digital camera image playback have been developed. Processing algorithms have been developed to extract the range to the first and last significant return within each waveform. ALPS is used routinely to create maps that represent submerged or first surface topography. Specialized filtering algorithms have been implemented to determine the 'bare earth' under vegetation from a point cloud of last return elevations.

Nayegandhi, Amar; Brock, John C.; Wright, C. Wayne; Miner, Michael D.; Yates, Xan; Bonisteel, Jamie M.

2009-01-01

228

EAARL Coastal Topography-Chandeleur Islands, Louisiana, 2010: Bare Earth  

USGS Publications Warehouse

These remotely sensed, geographically referenced elevation measurements of lidar-derived bare-earth (BE) and submerged topography datasets were produced collaboratively by the U.S. Geological Survey (USGS), St. Petersburg Coastal and Marine Science Center, St. Petersburg, FL, and the National Aeronautics and Space Administration (NASA), Wallops Flight Facility, VA. This project provides highly detailed and accurate datasets of a portion of the Chandeleur Islands, acquired March 3, 2010. The datasets are made available for use as a management tool to research scientists and natural-resource managers. An innovative airborne lidar instrument originally developed at the NASA Wallops Flight Facility, and known as the Experimental Advanced Airborne Research Lidar (EAARL), was used during data acquisition. The EAARL system is a raster-scanning, waveform-resolving, green-wavelength (532-nanometer) lidar designed to map near-shore bathymetry, topography, and vegetation structure simultaneously. The EAARL sensor suite includes the raster-scanning, water-penetrating full-waveform adaptive lidar, a down-looking red-green-blue (RGB) digital camera, a high-resolution multispectral color-infrared (CIR) camera, two precision dual-frequency kinematic carrier-phase GPS receivers, and an integrated miniature digital inertial measurement unit, which provide for sub-meter georeferencing of each laser sample. The nominal EAARL platform is a twin-engine Cessna 310 aircraft, but the instrument may be deployed on a range of light aircraft. A single pilot, a lidar operator, and a data analyst constitute the crew for most survey operations. This sensor has the potential to make significant contributions in measuring sub-aerial and submarine coastal topography within cross-environmental surveys. Elevation measurements were collected over the survey area using the EAARL system, and the resulting data were then processed using the Airborne Lidar Processing System (ALPS), a custom-built processing system developed in a NASA-USGS collaboration. ALPS supports the exploration and processing of lidar data in an interactive or batch mode. Modules for presurvey flight-line definition, flight-path plotting, lidar raster and waveform investigation, and digital camera image playback have been developed. Processing algorithms have been developed to extract the range to the first and last significant return within each waveform. ALPS is used routinely to create maps that represent submerged or sub-aerial topography. Specialized filtering algorithms have been implemented to determine the 'bare earth' under vegetation from a point cloud of last return elevations. For more information about similar projects, please visit the Decision Support for Coastal Science and Management website.

Nayegandhi, Amar; Bonisteel-Cormier, Jamie M.; Brock, John C.; Sallenger, A.H.; Wright, C. Wayne; Nagle, David B.; Vivekanandan, Saisudha; Yates, Xan; Klipp, Emily S.

2010-01-01

229

EAARL Coastal Topography - Northeast Barrier Islands 2007: Bare Earth  

USGS Publications Warehouse

These remotely sensed, geographically referenced elevation measurements of Lidar-derived bare earth (BE) topography were produced collaboratively by the U.S. Geological Survey (USGS), Florida Integrated Science Center (FISC), St. Petersburg, FL, and the National Aeronautics and Space Administration (NASA), Wallops Flight Facility, VA. This project provides highly detailed and accurate datasets of the northeast coastal barrier islands in New York and New Jersey, acquired April 29-30 and May 15-16, 2007. The datasets are made available for use as a management tool to research scientists and natural resource managers. An innovative airborne Lidar instrument originally developed at the NASA Wallops Flight Facility, and known as the Experimental Advanced Airborne Research Lidar (EAARL), was used during data acquisition. The EAARL system is a raster-scanning, waveform-resolving, green-wavelength (532-nanometer) Lidar designed to map near-shore bathymetry, topography, and vegetation structure simultaneously. The EAARL sensor suite includes the raster-scanning, water-penetrating full-waveform adaptive Lidar, a down-looking red-green-blue (RGB) digital camera, a high-resolution multi-spectral color infrared (CIR) camera, two precision dual-frequency kinematic carrier-phase GPS receivers and an integrated miniature digital inertial measurement unit, which provide for submeter georeferencing of each laser sample. The nominal EAARL platform is a twin-engine Cessna 310 aircraft, but the instrument may be deployed on a range of light aircraft. A single pilot, a Lidar operator, and a data analyst constitute the crew for most survey operations. This sensor has the potential to make significant contributions in measuring sub-aerial and submarine coastal topography within cross-environmental surveys. Elevation measurements were collected over the survey area using the EAARL system, and the resulting data were then processed using the Airborne Lidar Processing System (ALPS), a custom-built processing system developed in a NASA-USGS collaboration. ALPS supports the exploration and processing of Lidar data in an interactive or batch mode. Modules for presurvey flight line definition, flight path plotting, Lidar raster and waveform investigation, and digital camera image playback have been developed. Processing algorithms have been developed to extract the range to the first and last significant return within each waveform. ALPS is routinely used to create maps that represent submerged or first surface topography. Specialized filtering algorithms have been implemented to determine the 'bare earth' under vegetation from a point cloud of last return elevations.

Nayegandhi, Amar; Brock, John C.; Sallenger, A. H.; Wright, C. Wayne; Yates, Xan; Bonisteel, Jamie M.

2008-01-01

230

EAARL Coastal Topography - Northern Gulf of Mexico, 2007: Bare Earth  

USGS Publications Warehouse

These remotely sensed, geographically referenced elevation measurements of Lidar-derived bare earth (BE) topography were produced as a collaborative effort between the U.S. Geological Survey (USGS), Florida Integrated Science Center (FISC), St. Petersburg, FL; the National Park Service (NPS), Gulf Coast Network, Lafayette, LA; and the National Aeronautics and Space Administration (NASA), Wallops Flight Facility, VA. The purpose of this project is to provide highly detailed and accurate datasets of select barrier islands and peninsular regions of Louisiana, Mississippi, Alabama, and Florida, acquired on June 27-30, 2007. The datasets are made available for use as a management tool to research scientists and natural resource managers. An innovative airborne Lidar instrument originally developed at the NASA Wallops Flight Facility, and known as the Experimental Advanced Airborne Research Lidar (EAARL), was used during data acquisition. The EAARL system is a raster-scanning, waveform-resolving, green-wavelength (532-nanometer) Lidar designed to map near-shore bathymetry, topography, and vegetation structure simultaneously. The EAARL sensor suite includes the raster-scanning, water-penetrating full-waveform adaptive Lidar, a down-looking red-green-blue (RGB) digital camera, a high-resolution multi-spectral color infrared (CIR) camera, two precision dual-frequency kinematic carrier-phase GPS receivers, and an integrated miniature digital inertial measurement unit which provide for submeter georeferencing of each laser sample. The nominal EAARL platform is a twin-engine Cessna 310 aircraft, but the instrument may be deployed on a range of light aircraft. A single pilot, a Lidar operator, and a data analyst constitute the crew for most survey operations. This sensor has the potential to make significant contributions in measuring sub-aerial and submarine coastal topography within cross-environmental surveys. Elevation measurements were collected over the survey area using the EAARL system and the resulting data were then processed using the Airborne Lidar Processing System (ALPS), a custom-built processing system developed in a NASA-USGS collaboration. ALPS supports the exploration and processing of Lidar data in an interactive or batch mode. Modules for presurvey flight line definition, flight path plotting, Lidar raster and waveform investigation, and digital camera image playback have been developed. Processing algorithms have been developed to extract the range to the first and last significant return within each waveform. ALPS is used routinely to create maps that represent submerged or sub-aerial topography. Specialized filtering algorithms have been implemented to determine the 'bare earth' under vegetation from a point cloud of last return elevations.

Smith, Kathryn E. L.; Nayegandhi, Amar; Wright, C. Wayne; Bonisteel, Jamie M.; Brock, John C.

2009-01-01

231

Topography of borosilicate glass reacting interface under aqueous corrosion  

NASA Astrophysics Data System (ADS)

Molecular dynamics simulations were performed to calculate the structure of a Na-borosilicate glass. The topography of an initial flat surface of this glass caused by the instantaneous release of atoms weakly bonded to the silicate network was studied, giving the minimum roughness of the surface. The resulting profiles were compared to experimental data obtained by atom probe tomography on a complex nuclear glass, after having verified that simulations are valid for the complex glass. As experimental profiles are much thicker, these comparisons support the concept that interdiffusion is a key mechanism controlling the long-term corrosion rate of nuclear glasses.

Delaye, J. M.; Kerrache, A.; Gin, S.

2013-11-01

232

Reconstruction of the corneal topography from lateral-shearing interferograms  

NASA Astrophysics Data System (ADS)

The paper presents an approach for measurements of the corneal topography by use of lateral-shearing interferometry. In shearing interferometry the wavefront reflected from the object is split in two wavefronts. The introduction of lateral shift and superposition of the wavefronts produces interference pattern. We used phase shifting algorithm to obtain the phase differences of the wavefront reflected from the cornea. The measurements of the phase differences are carried out in two orthogonal directions. The phase of the wavefront is reconstructed by use of algorithm for the large grid based on the discrete integration. The computer-generated interferograms are used to test the procedure and to estimate its accuracy.

Licznerski, Tomasz J.; Kasprzak, Henryk T.

1999-07-01

233

Estimating Titan Surface Topography from Cassini Synthetic Aperture RADAR Data  

NASA Astrophysics Data System (ADS)

One of the more vexing dilemmas for RADAR remote sensing is the necessity to choose between altimetry and SAR imaging of a surface. Coincident surface height estimates are very useful in aiding the analysis of the unique surface features observed in the SAR imagery of Titan. Radar altimetry is optimally obtained from nadir observations, whereas SAR requires off-nadir observation in order to construct an image. Co-located nadir altimetry and SAR only occur when observations taken at different times happen to overlap. Stereo techniques can also be used to estimate topography in SAR images, but they also require multiple overlapping observations. Here we discuss a technique, SARTopo, for obtaining 10 km horizontal resolution and 75 m vertical resolution surface height estimates along each SAR swath. The height estimates comprise 1-3 cuts in each SAR pass that are 10 km wide by thousands of km long and extend along the entire long dimension of the SAR image strips. Because we obtain co-located topography along each SAR pass rather than only in regions with overlapping observations, the new technique extends the area over which we have colocated topography and SAR imagery by a couple orders of magnitude. The method is based upon Amplitude Monopulse Comparison, a technique for resolving RADAR targets developed prior to the advent of SAR. The technique requires: 1) accurate spacecraft pointing, 2) accurate spacecraft ephemeris, 3) precise knowledge of the antenna pattern of the RADAR, and 4) downlinked echo data covering the entire antenna footprint. The fourth requirement is met through synergy with Cassini SAR coverage requirements. Cassini SAR commanding and pointing is designed to utilize as much of the antenna footprint as possible in order to maximize cross-track coverage. We describe the technique and present the results for several SAR passes. We validate the technique through comparison with known features such as mountain ranges and dry lakes, and by comparison with colocated nadir altimetry and SAR stereo. In particular, we examine a strip of nadir altimetry obtained along a 1000 km strip observed by SAR a month earlier. The SARTopo height track is within 5-10 km of the nadir altimetry track for a 200 km long section. In this area, the two independent techniques agree closely. Furthermore the region contains prominent high spatial resolution topography, so it provides an excellent test of the resolution and accuracy of both techniques. SARTopo heights are also co-located and agree well with SAR stereo observations. The research described here was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.

Stiles, B. W.; Hensley, S.; Gim, Y.; Kirk, R. L.; Zebker, H. A.; Janssen, M. A.; Johnson, W. T.; West, R. D.

2007-12-01

234

Gravity Field, Topography, and Interior Structure of Amalthea  

NASA Astrophysics Data System (ADS)

A close Galileo flyby of Jupiter's inner moon Amalthea (JV) occurred on 5 November 2002. The final aimpoint was selected by the Galileo Radio Science Team on 5 July 2002. The closest approach distance for the selected aimpoint was 221 km from the center of mass, the latitude was - 45.23 Deg and the west longitude was 266.41 Deg (IAU/IAG/COSPAR cartographic coordinate system). In order to achieve an acceptable impact probability (0.15%), and yet fly close to Amalthea, the trajectory was selected from a class of trajectories running parallel to Amalthea's long axis. The Deep Space Network (DSN) had the capability to generate continuous coherent radio Doppler data during the flyby. Such data can be inverted to obtain information on Amalthea's gravity field. Amalthea is irregular and neither a triaxial ellipsoid nor an equilibrium body. It has a volume of about 2.4 x 106 km3, and its best-fit ellipsoid has dimensions 131x73x67 km. Its mass can be determined from the 2002 flyby, and in combination with the volume, a density can be obtained accurate to about 5%, where the error is dominated by the volume uncertainty. Similarly, gravity coefficients (Cnm Snm) can be detected up to fourth degree and order, and the second degree field (quadrupole) can be measured. Topography data are available from Voyager imaging and from images taken with Galileo's solid state imaging system at various times between February and June 1997. By combining the gravity and topography data, new information can be obtained on Amalthea's interior. For example if the gravity coefficients agree with those calculated from the topography, assuming constant density, we can conclude that Amalthea is homogeneous. On the other hand, if the gravity coefficients are smaller than predicted from topography, we can conclude that there is a concentration of mass toward Amalthea's center. We are presenting preliminary pre-publication results at the Fall meeting. This work was sponsored by the Galileo Project and was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. G.S., P.C.T., and W.B.M. acknowledge support by grants from NASA under the Planetary Geology and Geophysics program. G.W. is a visiting PhD student at JPL, May 2002 - May 2003, and acknowledges support from the Austrian Ministry for Technology and a Zonta - Amelia Earhart fellowship.

Anderson, J. D.; Anabtawi, A.; Jacobson, R. A.; Johnson, T. V.; Lau, E. L.; Moore, W. B.; Schubert, G.; Taylor, A. H.; Thomas, P. C.; Weinwurm, G.

2002-12-01

235

Global digital topography mapping using a scanning radar altimeter  

NASA Technical Reports Server (NTRS)

The conceptual design of a Scanning Radar Altimeter system capable of collecting less than 300-m spatial and less than 3-m height resolution digital topography data for the entire globe, from an orbital platform, is presented. A 37-GHz frequency SRA system is used to achieve the requisite resolution while reducing antenna length in the along-track dimension. Near-global coverage in a short time period is obtained by scanning the antenna beam cross-track, in a swath of about 100 km. Attention is given to the algorithm that will be used to retrieve pixel height from the return waveform.

Elachi, C.; Im, K. E.; Li, F.; Rodriguez, E.

1987-01-01

236

EAARL Topography - Natchez Trace Parkway 2007: First Surface  

USGS Publications Warehouse

These remotely sensed, geographically referenced elevation measurements of Lidar-derived first surface (FS) topography were produced as a collaborative effort between the U.S. Geological Survey (USGS), Florida Integrated Science Center (FISC), St. Petersburg, FL; the National Park Service (NPS), Gulf Coast Network, Lafayette, LA; and the National Aeronautics and Space Administration (NASA), Wallops Flight Facility, VA. This project provides highly detailed and accurate datasets of a portion of the Natchez Trace Parkway in Mississippi, acquired on September 14, 2007. The datasets are made available for use as a management tool to research scientists and natural resource managers. An innovative airborne Lidar instrument originally developed at the NASA Wallops Flight Facility, and known as the Experimental Advanced Airborne Research Lidar (EAARL), was used during data acquisition. The EAARL system is a raster-scanning, waveform-resolving, green-wavelength (532-nanometer) Lidar designed to map near-shore bathymetry, topography, and vegetation structure simultaneously. The EAARL sensor suite includes the raster-scanning, water-penetrating full-waveform adaptive Lidar, a down-looking red-green-blue (RGB) digital camera, a high-resolution multi-spectral color infrared (CIR) camera, two precision dual-frequency kinematic carrier-phase GPS receivers, and an integrated miniature digital inertial measurement unit, which provide for submeter georeferencing of each laser sample. The nominal EAARL platform is a twin-engine Cessna 310 aircraft, but the instrument may be deployed on a range of light aircraft. A single pilot, a Lidar operator, and a data analyst constitute the crew for most survey operations. This sensor has the potential to make significant contributions in measuring sub-aerial and submarine coastal topography within cross-environmental surveys. Elevation measurements were collected over the survey area using the EAARL system, and the resulting data were then processed using the Airborne Lidar Processing System (ALPS), a custom-built processing system developed in a NASA-USGS collaboration. ALPS supports the exploration and processing of Lidar data in an interactive or batch mode. Modules for presurvey flight line definition, flight path plotting, Lidar raster and waveform investigation, and digital camera image playback have been developed. Processing algorithms have been developed to extract the range to the first and last significant return within each waveform. ALPS is used routinely to create maps that represent submerged or first surface topography. Specialized filtering algorithms have been implemented to determine the 'bare earth' under vegetation from a point cloud of last return elevations.

Nayegandhi, Amar; Brock, John C.; Wright, C. Wayne; Segura, Martha; Yates, Xan

2008-01-01

237

EAARL Coastal Topography--Cape Canaveral, Florida, 2009: First Surface  

USGS Publications Warehouse

These remotely sensed, geographically referenced elevation measurements of lidar-derived first-surface (FS) topography datasets were produced collaboratively by the U.S. Geological Survey (USGS), St. Petersburg Coastal and Marine Science Center, St. Petersburg, FL, and the National Aeronautics and Space Administration (NASA), Kennedy Space Center, FL. This project provides highly detailed and accurate datasets of a portion of the eastern Florida coastline beachface, acquired on May 28, 2009. The datasets are made available for use as a management tool to research scientists and natural-resource managers. An innovative airborne lidar instrument originally developed at the NASA Wallops Flight Facility, and known as the Experimental Advanced Airborne Research Lidar (EAARL), was used during data acquisition. The EAARL system is a raster-scanning, waveform-resolving, green-wavelength (532-nanometer) lidar designed to map near-shore bathymetry, topography, and vegetation structure simultaneously. The EAARL sensor suite includes the raster-scanning, water-penetrating full-waveform adaptive lidar, a down-looking red-green-blue (RGB) digital camera, a high-resolution multispectral color-infrared (CIR) camera, two precision dual-frequency kinematic carrier-phase GPS receivers, and an integrated miniature digital inertial measurement unit, which provide for sub-meter georeferencing of each laser sample. The nominal EAARL platform is a twin-engine aircraft, but the instrument was deployed on a Pilatus PC-6. A single pilot, a lidar operator, and a data analyst constitute the crew for most survey operations. This sensor has the potential to make significant contributions in measuring sub-aerial and submarine coastal topography within cross-environmental surveys. Elevation measurements were collected over the survey area using the EAARL system, and the resulting data were then processed using the Airborne Lidar Processing System (ALPS), a custom-built processing system developed in a NASA-USGS collaboration. ALPS supports the exploration and processing of lidar data in an interactive or batch mode. Modules for presurvey flight-line definition, flight-path plotting, lidar raster and waveform investigation, and digital camera image playback have been developed. Processing algorithms have been developed to extract the range to the first and last significant return within each waveform. ALPS is used routinely to create maps that represent submerged or sub-aerial topography. Specialized filtering algorithms have been implemented to determine the "bare earth" under vegetation from a point cloud of last return elevations.

Bonisteel-Cormier, J.M.; Nayegandhi, Amar; Plant, Nathaniel; Wright, C.W.; Nagle, D.B.; Serafin, K.S.; Klipp, E.S.

2011-01-01

238

EAARL Coastal Topography-Pearl River Delta 2008: First Surface  

USGS Publications Warehouse

These remotely sensed, geographically referenced elevation measurements of Lidar-derived first surface (FS) topography were produced as a collaborative effort between the U.S. Geological Survey (USGS), Florida Integrated Science Center (FISC), St. Petersburg, FL; the University of New Orleans (UNO), Pontchartrain Institute for Environmental Sciences (PIES), New Orleans, LA; and the National Aeronautics and Space Administration (NASA), Wallops Flight Facility, VA. This project provides highly detailed and accurate datasets of a portion of the Pearl River Delta in Louisiana and Mississippi, acquired March 9-11, 2008. The datasets are made available for use as a management tool to research scientists and natural resource managers. An innovative airborne Lidar instrument originally developed at the NASA Wallops Flight Facility, and known as the Experimental Advanced Airborne Research Lidar (EAARL), was used during data acquisition. The EAARL system is a raster-scanning, waveform-resolving, green-wavelength (532-nanometer) Lidar designed to map near-shore bathymetry, topography, and vegetation structure simultaneously. The EAARL sensor suite includes the raster-scanning, water-penetrating full-waveform adaptive Lidar, a down-looking red-green-blue (RGB) digital camera, a high-resolution multi-spectral color infrared (CIR) camera, two precision dual-frequency kinematic carrier-phase GPS receivers, and an integrated miniature digital inertial measurement unit, which provide for submeter georeferencing of each laser sample. The nominal EAARL platform is a twin-engine Cessna 310 aircraft, but the instrument may be deployed on a range of light aircraft. A single pilot, a Lidar operator, and a data analyst constitute the crew for most survey operations. This sensor has the potential to make significant contributions in measuring sub-aerial and submarine coastal topography within cross-environmental surveys. Elevation measurements were collected over the survey area using the EAARL system, and the resulting data were then processed using the Airborne Lidar Processing System (ALPS), a custom-built processing system developed in a NASA-USGS collaboration. ALPS supports the exploration and processing of Lidar data in an interactive or batch mode. Modules for presurvey flight line definition, flight path plotting, Lidar raster and waveform investigation, and digital camera image playback have been developed. Processing algorithms have been developed to extract the range to the first and last significant return within each waveform. ALPS is used routinely to create maps that represent submerged or first surface topography. Specialized filtering algorithms have been implemented to determine the 'bare earth' under vegetation from a point cloud of last return elevations.

Nayegandhi, Amar; Brock, John C.; Wright, C. Wayne; Miner, Michael D.; Michael D.; Yates, Xan; Bonisteel, Jamie M.

2009-01-01

239

EAARL Coastal Topography - Northeast Barrier Islands 2007: First Surface  

USGS Publications Warehouse

These remotely sensed, geographically referenced elevation measurements of Lidar-derived first surface (FS) topography were produced collaboratively by the U.S. Geological Survey (USGS), Florida Integrated Science Center (FISC), St. Petersburg, FL, and the National Aeronautics and Space Administration (NASA), Wallops Flight Facility, VA. This project provides highly detailed and accurate datasets of the northeast coastal barrier islands in New York and New Jersey, acquired April 29-30 and May 15-16, 2007. The datasets are made available for use as a management tool to research scientists and natural resource managers. An innovative airborne Lidar instrument originally developed at the NASA Wallops Flight Facility, and known as the Experimental Advanced Airborne Research Lidar (EAARL), was used during data acquisition. The EAARL system is a raster-scanning, waveform-resolving, green-wavelength (532-nanometer) Lidar designed to map near-shore bathymetry, topography, and vegetation structure simultaneously. The EAARL sensor suite includes the raster-scanning, water-penetrating full-waveform adaptive Lidar, a down-looking red-green-blue (RGB) digital camera, a high-resolution multi-spectral color infrared (CIR) camera, two precision dual-frequency kinematic carrier-phase GPS receivers, and an integrated miniature digital inertial measurement unit, which provide for submeter georeferencing of each laser sample. The nominal EAARL platform is a twin-engine Cessna 310 aircraft, but the instrument may be deployed on a range of light aircraft. A single pilot, a Lidar operator, and a data analyst constitute the crew for most survey operations. This sensor has the potential to make significant contributions in measuring sub-aerial and submarine coastal topography within cross-environmental surveys. Elevation measurements were collected over the survey area using the EAARL system, and the resulting data were then processed using the Airborne Lidar Processing System (ALPS), a custom-built processing system developed in a NASA-USGS collaboration. ALPS supports the exploration and processing of Lidar data in an interactive or batch mode. Modules for presurvey flight line definition, flight path plotting, Lidar raster and waveform investigation, and digital camera image playback have been developed. Processing algorithms have been developed to extract the range to the first and last significant return within each waveform. ALPS is routinely used to create maps that represent submerged or first surface topography. Specialized filtering algorithms have been implemented to determine the 'bare earth' under vegetation from a point cloud of last return elevations.

Nayegandhi, Amar; Brock, John C.; Sallenger, A. H.; Wright, C. Wayne; Yates, Xan; Bonisteel, Jamie M.

2009-01-01

240

Topex orbit sustenance maneuver design. [Ocean Topography Experiment spacecraft  

NASA Technical Reports Server (NTRS)

A trade-off analysis between maneuver period, execution errors, and orbit determination uncertainties is carried out for the Ocean Topography Experiment spacecraft for a given nodal equatorial constraint. Semimajor axis and eccentricity are controlled with minimum impulse using the linear theory of optimal transfer between close coplanar near-circular orbits. Ellipses of equal minimum and average maneuver periods are presented in the (3 execution error, 3 orbit determination uncertainty) space for different nodal equatorial constraints enabling the determination of the appropriate combination of execution errors and orbit determination uncertainties that guarantees a mission required minimum maneuver period for a given nodal deadband.

Kechichian, J. A.

1982-01-01

241

EAARL Topography - Jean Lafitte National Historical Park and Preserve 2006  

USGS Publications Warehouse

These remotely sensed, geographically referenced elevation measurements of Lidar-derived first surface (FS) and bare earth (BE) topography were produced as a collaborative effort between the U.S. Geological Survey (USGS), Florida Integrated Science Center (FISC), St. Petersburg, FL; the National Park Service (NPS), Gulf Coast Network, Lafayette, LA; and the National Aeronautics and Space Administration (NASA), Wallops Flight Facility, VA. This project provides highly detailed and accurate datasets of the Jean Lafitte National Historical Park and Preserve in Louisiana, acquired on September 22, 2006. The datasets are made available for use as a management tool to research scientists and natural resource managers. An innovative airborne Lidar instrument originally developed at the NASA Wallops Flight Facility, and known as the Experimental Advanced Airborne Research Lidar (EAARL), was used during data acquisition. The EAARL system is a raster-scanning, waveform-resolving, green-wavelength (532-nanometer) Lidar designed to map near-shore bathymetry, topography, and vegetation structure simultaneously. The EAARL sensor suite includes the raster-scanning, water-penetrating full-waveform adaptive Lidar, a down-looking red-green-blue (RGB) digital camera, a high-resolution multi-spectral color infrared (CIR) camera, two precision dual-frequency kinematic carrier-phase GPS receivers, and an integrated miniature digital inertial measurement unit, which provide for submeter georeferencing of each laser sample. The nominal EAARL platform is a twin-engine Cessna 310 aircraft, but the instrument may be deployed on a range of light aircraft. A single pilot, a Lidar operator, and a data analyst constitute the crew for most survey operations. This sensor has the potential to make significant contributions in measuring sub-aerial and submarine coastal topography within cross-environmental surveys. Elevation measurements were collected over the survey area using the EAARL system, and the resulting data were then processed using the Airborne Lidar Processing System (ALPS), a custom-built processing system developed in a NASA-USGS collaboration. ALPS supports the exploration and processing of Lidar data in an interactive or batch mode. Modules for presurvey flight line definition, flight path plotting, Lidar raster and waveform investigation, and digital camera image playback have been developed. Processing algorithms have been developed to extract the range to the first and last significant return within each waveform. ALPS is used routinely to create maps that represent submerged or first surface topography. Specialized filtering algorithms have been implemented to determine the 'bare earth' under vegetation from a point cloud of last return elevations.

Nayegandhi, Amar; Brock, John C.; Wright, C. Wayne; Segura, Martha; Yates, Xan

2008-01-01

242

EAARL Coastal Topography - Fire Island National Seashore 2007  

USGS Publications Warehouse

These remotely sensed, geographically referenced elevation measurements of Lidar-derived first surface (FS) and bare earth (BE) topography were produced as a collaborative effort between the U.S. Geological Survey (USGS), Florida Integrated Science Center (FISC), St. Petersburg, FL; the National Park Service (NPS), Northeast Coastal and Barrier Network, Kingston, RI; and the National Aeronautics and Space Administration (NASA), Wallops Flight Facility, VA. This project provides highly detailed and accurate datasets of Fire Island National Seashore in New York, acquired on April 29-30 and May 15-16, 2007. The datasets are made available for use as a management tool to research scientists and natural resource managers. An innovative airborne Lidar instrument originally developed at the NASA Wallops Flight Facility, and known as the Experimental Advanced Airborne Research Lidar (EAARL) was used during data acquisition. The EAARL system is a raster-scanning, waveform-resolving, green-wavelength (532-nanometer) Lidar designed to map near-shore bathymetry, topography, and vegetation structure simultaneously. The EAARL sensor suite includes the raster-scanning, water-penetrating full-waveform adaptive Lidar, a down-looking red-green-blue (RGB) digital camera, a high-resolution multi-spectral color infrared (CIR) camera, two precision dual-frequency kinematic carrier-phase GPS receivers and an integrated miniature digital inertial measurement unit, which provide for submeter georeferencing of each laser sample. The nominal EAARL platform is a twin-engine Cessna 310 aircraft, but the instrument may be deployed on a range of light aircraft. A single pilot, a Lidar operator, and a data analyst constitute the crew for most survey operations. This sensor has the potential to make significant contributions in measuring sub-aerial and submarine coastal topography within cross-environmental surveys. Elevation measurements were collected over the survey area using the EAARL system, and the resulting data were then processed using the Airborne Lidar Processing System (ALPS), a custom-built processing system developed in a NASA-USGS collaboration. ALPS supports the exploration and processing of Lidar data in an interactive or batch mode. Modules for pre-survey flight line definition, flight path plotting, Lidar raster and waveform investigation, and digital camera image playback have been developed. Processing algorithms have been developed to extract the range to the first and last significant return within each waveform. ALPS is routinely used to create maps that represent submerged or first surface topography. Specialized filtering algorithms have been implemented to determine the 'bare earth' under vegetation from a point cloud of last return elevations.

Nayegandhi, Amar; Brock, John C.; Wright, C. Wayne; Stevens, Sara; Yates, Xan; Bonisteel, Jamie M.

2008-01-01

243

EAARL Submerged Topography - U.S. Virgin Islands 2003  

USGS Publications Warehouse

These remotely sensed, geographically referenced elevation measurements of Lidar-derived submerged topography were produced as a collaborative effort between the U.S. Geological Survey (USGS), Florida Integrated Science Center (FISC), St. Petersburg, FL; the National Park Service (NPS), South Florida-Caribbean Network, Miami, FL; and the National Aeronautics and Space Administration (NASA), Wallops Flight Facility, VA. This project provides highly detailed and accurate bathymetric datasets of a portion of the U.S. Virgin Islands, acquired on April 21, 23, and 30, May 2, and June 14 and 17, 2003. The datasets are made available for use as a management tool to research scientists and natural resource managers. An innovative airborne Lidar instrument originally developed at the NASA Wallops Flight Facility, and known as the Experimental Advanced Airborne Research Lidar (EAARL), was used during data acquisition. The EAARL system is a raster-scanning, waveform-resolving, green-wavelength (532-nanometer) Lidar designed to map near-shore bathymetry, topography, and vegetation structure simultaneously. The EAARL sensor suite includes the raster-scanning, water-penetrating full-waveform adaptive Lidar, a down-looking red-green-blue (RGB) digital camera, a high-resolution multi-spectral color infrared (CIR) camera, two precision dual-frequency kinematic carrier-phase GPS receivers, and an integrated miniature digital inertial measurement unit, which provide for submeter georeferencing of each laser sample. The nominal EAARL platform is a twin-engine Cessna 310 aircraft, but the instrument may be deployed on a range of light aircraft. A single pilot, a Lidar operator, and a data analyst constitute the crew for most survey operations. This sensor has the potential to make significant contributions in measuring sub-aerial and submarine coastal topography within cross-environmental surveys. Elevation measurements were collected over the survey area using the EAARL system, and the resulting data were then processed using the Airborne Lidar Processing System (ALPS), a custom-built processing system developed in a NASA-USGS collaboration. ALPS supports the exploration and processing of Lidar data in an interactive or batch mode. Modules for presurvey flight line definition, flight path plotting, Lidar raster and waveform investigation, and digital camera image playback have been developed. Processing algorithms have been developed to extract the range to the first and last significant return within each waveform. ALPS is used routinely to create maps that represent submerged or first surface topography. Specialized filtering algorithms have been implemented to determine the 'bare earth' under vegetation from a point cloud of last return elevations.

Nayegandhi, Amar; Brock, John C.; Wright, C. Wayne; Stevens, Sara; Yates, Xan; Bonisteel, Jamie M.

2008-01-01

244

Pre-glacial topography of the European Alps  

NASA Astrophysics Data System (ADS)

We present a reconstruction of the Alpine topography prior to Quaternary glaciation, based on the assumption that the pre-glacial topography of the Alps was a fluvial landscape in equilibrium with tectonic and isostatic rock uplift. Amongst the models that have been proposed, the stream-power law has been profitably used for modeling the dynamics of fluvial bedrock channel incision: dz-= U - KAmSn dt (1) where dz/dt (m a-1) is the time rate of change of channel elevation, U(m a-1) is rock-uplift rate, A(m) is upstream drainage area, S is local channel gradient, K is a dimensionless coefficient of erosion and m and n are positive constants related to basin hydrology and erosion process. Under steady-state conditions (dz/dt = 0), equation (1) can be solved to yield an expression for equilibrium channel gradient: 1 ( U-)n - (m) S = K A n (2) where the ratios U/K and m/n are generally referred to as the steepness and concavity index, respectively. Particular focus is put on the spatial variability of the steepness index over the Alpine mountain belt. Assuming a constant concavity index, the pre-glacial topography of the Alps is obtained through an inversion technique that resolves local slopes (as described in eq. 2) by minimizing the misfit between the elevations of the actual and modeled channel heads. Comparing the present-day and reconstructed pre-glacial topography, we infer patterns and magnitudes of exhumation and rock uplift produced by Quaternary glaciation in the Alps. We find a correspondence between rock type and pre-glacial channel steepness which may indicate that rock erodibility has a significant importance in determining the pre-glacial fluvial network elevation. Our results also provide insight into patterns of glacial erosion and associated isostatic adjustment, and provide estimates of the increase of valley-scale topographic relief and decrease of mean elevation that glaciation seems to have produced in the Alps.

Sternai, P.; Herman, F.; Champagnac, J.-D.; Fox, M.; Salcher, B.; Willett, S. D.

2012-04-01

245

The regulation of integrin-mediated osteoblast focal adhesion and focal adhesion kinase expression by nanoscale topography.  

PubMed

An important consideration in developing physical biomimetic cell-stimulating cues is that the in vivo extracellular milieu includes nanoscale topographic interfaces. We investigated nanoscale topography regulation of cell functions using human fetal osteoblastic (hFOB) cell culture on poly(l-lactic acid) and polystyrene (50/50 w/w) demixed nanoscale pit textures (14, 29, and 45nm deep pits). Secondary ion mass spectroscopy revealed that these nanotopographic surfaces had similar surface chemistries to that of pure PLLA because of PLLA component surface segregation during spin casting. We observed that 14 and 29nm deep pit surfaces increased hFOB cell attachment, spreading, selective integrin subunit expression (e.g., alphav relative to alpha5, beta1, or beta3), focal adhesive paxillin protein synthesis and paxillin colocalization with cytoskeletal actin stress fibers, and focal adhesion kinase (FAK) and phosphorylated FAK (pY397) expression to a greater degree than did 45nm deep pits or flat PLLA surfaces. Considering the important role of integrin-mediated focal adhesion and intracellular signaling in anchorage-dependent cell function, our results suggest a mechanism by which nanostructured physical signals regulate cell function. Modulation of integrin-mediated focal adhesion and related cell signaling by altering nanoscale substrate topography will have powerful applications in biomaterials science and tissue engineering. PMID:17218005

Lim, Jung Yul; Dreiss, Andrea D; Zhou, Zhiyi; Hansen, Joshua C; Siedlecki, Christopher A; Hengstebeck, Robert W; Cheng, Juan; Winograd, Nicholas; Donahue, Henry J

2007-04-01

246

Dependence of the Fracture of PowerTrench MOSFET Device on Its Topography in Cu Bonding Process  

Microsoft Academic Search

Dependence of the fracture-resistance of a PowerTrench MOSFET device on its topography in Cu bonding process was investigated. Two different topographies, namely dimple and round, have been tested. A significantly higher cratering rate has been clearly observed on dimple topography. The dimple topography exhibited a cratering rate of 371 k ppm levels compared to 0 ppm in round topographies. Three-dimensional

Manmohan Daggubati; Q. Wang; Y. V. Sokolov; Yong Liu; Lu-Chang Qin

2009-01-01

247

Modeling of fluidized ejecta emplacement over digital topography on Venus  

NASA Astrophysics Data System (ADS)

The FLOW computer model of McEwen and Malin (1989) modified for application to the study of Venus fluidized ejecta blankets (FEBs) demonstrates that relatively low viscosities, yield strengths, and initial velocities are required to duplicate the observed flow paths of the outflow materials. The model calculates the velocities and simulated flow paths of gravity flows over Magellan topography. The model is formulated to determine flow movements from initial conditions, gravitational acceleration, and resistance to motion as described by Coulomb, viscous, and turbulent resistance forces. Successful duplication of observed FEB flow paths has been achieved for the FEB craters Addams, Isabella, and Cochran. When used as a simple energy-line model, the model requires low coefficients of friction to extend FEBs to near their observed termini in the synthetic aperture radar (SAR) imagery, although the resulting straight flow lines do not follow the observed flow paths well. For Bingham flow, the model requires low values of viscosity and yield strength which are more similar to pyroclastic or debris flows than basaltic lavas. Flows of 100-m depth require 1 to 2 orders of magnitude higher values of both viscosity and yield strength than 10-m-deep flows. The complicated nature of the flow lines for the low velocity model suggests that FEBs were probably emplaced under variably laminar and turbulent flow conditions, where underlying topography influenced both the direction and energy of flow materials.

Johnson, Jeffrey R.; Gaddis, Lisa

248

Tropical Pacific response to continental ice sheet topography  

NASA Astrophysics Data System (ADS)

The last glacial maximum was marked by maximum land ice extent and lowest greenhouse gases concentration during the last ice age. We explore the impact of glacial continental ice sheet topography on the large-scale tropical ocean-atmosphere climate, in particular the tropical Pacific, in an intermediate complexity coupled model. Increasing the thickness of continental ice sheets causes a southward displaced Pacific Intertropical Convergence Zone (ITCZ) and a strengthening (weakening) of northern (southern) hemisphere winter Hadley cell. The equatorial zonal sea surface temperature gradient weakened with an increased continental ice sheets thickness, the reduction being caused by cooling in the western equatorial Pacific and warming in the eastern equatorial Pacific. The evolution of the tropical climate with changing ice thickness has distinct quasi-linear and nonlinear parts. While the linear part is a direct response to the ice topographic changes, the nonlinear part was a result of the tropical thermocline adjustment. Our analysis of a fully-coupled transient deglacial simulation strongly indicates the dominant role of ice sheet topography in determining the deglacial evolution of the simulated Pacific climate. The thickness of continental ice sheet, separate from ice albedo effect, has significant impact on the tropical ocean-atmosphere climate in particular with the meridional displacement in the Pacific ITCZ. The altered circulation states seen in the model may aid understanding of the relationship between tropical and high-latitude climate records in glacial-interglacial cycles.

Lee, Shih-Yu; Chiang, John C. H.; Chang, Ping

2014-05-01

249

Multiview hyperspectral topography of tissue structural and functional characteristics  

NASA Astrophysics Data System (ADS)

Accurate and in vivo characterization of structural, functional, and molecular characteristics of biological tissue will facilitate quantitative diagnosis, therapeutic guidance, and outcome assessment in many clinical applications, such as wound healing, cancer surgery, and organ transplantation. However, many clinical imaging systems have limitations and fail to provide noninvasive, real time, and quantitative assessment of biological tissue in an operation room. To overcome these limitations, we developed and tested a multiview hyperspectral imaging system. The multiview hyperspectral imaging system integrated the multiview and the hyperspectral imaging techniques in a single portable unit. Four plane mirrors are cohered together as a multiview reflective mirror set with a rectangular cross section. The multiview reflective mirror set was placed between a hyperspectral camera and the measured biological tissue. For a single image acquisition task, a hyperspectral data cube with five views was obtained. The five-view hyperspectral image consisted of a main objective image and four reflective images. Three-dimensional topography of the scene was achieved by correlating the matching pixels between the objective image and the reflective images. Three-dimensional mapping of tissue oxygenation was achieved using a hyperspectral oxygenation algorithm. The multiview hyperspectral imaging technique is currently under quantitative validation in a wound model, a tissue-simulating blood phantom, and an in vivo biological tissue model. The preliminary results have demonstrated the technical feasibility of using multiview hyperspectral imaging for three-dimensional topography of tissue functional properties.

Zhang, Shiwu; Liu, Peng; Huang, Jiwei; Xu, Ronald

2012-12-01

250

Influence of atmospheric structure and topography on infrasonic wave propagation  

NASA Astrophysics Data System (ADS)

The effects of topography and atmospheric structures on infrasonic wave propagation from a volcanic source were investigated using observations and numerical modeling. This paper presents the first long-term observational data set showing spatiotemporal variations in patterns of infrasound propagation at distances of up to 60 km from a persistently active infrasound source (Sakurajima Volcano, Japan). The data show that the amplitudes of infrasonic waves received at distant stations relative to those received at a reference station close to the source can vary up to an order of magnitude over short time intervals and short distances and that they do not follow the theoretical geometric decay expected for homogeneous media. Moreover, waveforms also change significantly in both time and space. Numerical simulations were performed using a two-dimensional finite difference time domain (2-D FDTD) method. Effects of atmospheric structure and topography are included in a vertical section parallel to the wave propagation direction. The simulation successfully reproduced the variations of amplitudes and waveforms. Results are interpreted in terms of wave refraction due to sound and wind speed gradients and wave diffraction at topographic barriers. Our numerical results indicate that both atmospheric and topographic propagation effects are nonnegligible. To evaluate the propagation effects and determine source processes in spatially and temporally varying infrasound data, atmospheric data with a time resolution higher than is currently available are required. If the data are available, the present results suggest that the propagation effects could be evaluated using 2-D FDTD modeling at realistic calculation times.

Lacanna, G.; Ichihara, M.; Iwakuni, M.; Takeo, M.; Iguchi, M.; Ripepe, M.

2014-04-01

251

Photoswitchable hydrogel surface topographies by polymerisation-induced diffusion.  

PubMed

Herein, we describe the preparation of patterned photoresponsive hydrogels by using a facile method. This polymer-network hydrogel coating consists of N-isopropylacrylamide (NIPAAM), cross-linking agent tripropylene glycol diacrylate (TPGDA), and a new photochromic spiropyran monoacrylate. In a pre-study, a linear NIPAAM copolymer (without TPGDA) that contained the spiropyran dye was synthesised, which showed relatively fast photoswitching behaviour. Subsequently, the photopolymerisation of a similar monomer mixture that included TPGDA afforded freestanding hydrogel polymer networks. The light-induced isomerisation of protonated merocyanine into neutral spiropyran under slightly acidic conditions resulted in macroscopic changes in the hydrophilicity of the entire polymer film, that is, shrinkage of the hydrogel. The degree of shrinkage could be controlled by changing the chemical composition of the acrylate mixture. After these pre-studies, a hydrogel film with spatially modulated cross-link density was fabricated through polymerisation-induced diffusion, by using a patterned photomask. The resulting smooth patterned hydrogel coating swelled in slightly acidic media and the swelling was higher in the regions with lower cross-linking densities, thus yielding a corrugated surface. Upon exposure to visible light, the surface topography flattened again, thus showing that a hydrogel coating could be created, the topography of which could be controlled by light irradiation. PMID:23821576

Stumpel, Jelle E; Liu, Danqing; Broer, Dirk J; Schenning, Albertus P H J

2013-08-12

252

Topography of Striate-Extrastriate Connections in Neonatally Enucleated Rats  

PubMed Central

It is known that retinal input is necessary for the normal development of striate cortex and its corticocortical connections, but there is little information on the role that retinal input plays in the development of retinotopically organized connections between V1 and surrounding visual areas. In nearly all lateral extrastriate areas, the anatomical and physiological representation of the nasotemporal axis of the visual field mirrors the representation of this axis in V1. To determine whether the mediolateral topography of striate-extrastriate projections is preserved in neonatally enucleated rats, we analyzed the patterns of projections resulting from tracer injections placed at different sites along the mediolateral axis of V1. We found that the correlation between the distance from injection sites to the lateral border of V1 and the distance of the labeling patterns in area 18a was strong in controls and much weaker in enucleates. Data from pairs of injections in the same animal revealed that the separation of area 18a projection fields for a given separation of injection sites was more variable in enucleated than in control rats. Our analysis of single and double tracer injections suggests that neonatal bilateral enucleation weakens, but not completely abolishes, the mediolateral topography in area 18a.

Laing, Robyn J.; Lasiene, Jurate; Olavarria, Jaime F.

2013-01-01

253

Bistatic SAR coherence over non-planar topographies  

NASA Astrophysics Data System (ADS)

Monostatic Synthetic Aperture Radar (SAR) Coherent Change Detection (CCD) has been found to be of great utility in detecting changes that occur on the ground. Detectable changes of interest include vehicle tracks and water flow. The CCD procedure involves performing repeat pass radar collections, to form a coherence product, where ground disturbances can induce detectable incoherence. However there is usually a difference in the radar collection geometry which can lead to incoherent energy noise entering the CCD, which reduces the detectability of tracks. When sensing flat terrain, the incoherence due to collection geometry difference can be removed through a conventional Fourier image support trimming process. However, it has been found that when the terrain contains non-flat topography, the optimal trimming process is substantially more involved, so much so that a new per-pixel SAR back-projection imaging algorithm has been developed. This algorithm trims off incoherent energy on a per-pixel basis according to the local topography. In order to validate the bistatic SAR generalization to the monostatic per-pixel formalism and algorithm, bistatic change detection measurements were conducted with the GB-SAR system, and these are reported here.

Andre, Daniel B.; Morrison, Keith

2012-05-01

254

Three Dimensional Surface Topography Using LCD Pattern Transfer Method  

NASA Astrophysics Data System (ADS)

Laser lithography on curved surfaces has recently been researched due to its applicability in production processes for devices that combine integrated optical, mechanical, magnetic, and/or electronic technologies. Several laser lithography methods have been reported for pattern transfer to convex and cylindrical surfaces, but there is not a general methodology for arbitrary 3D surface lithography. This project implements an optical method for laser lithography on arbitrary 3D surfaces. An illumination pattern generated by a transparent LCD is projected through an optical microscope on top of a 3D surface and recorded by a camera. The focus quality and the distortion of the observed image depend on the local topography of the sample. The effect of the local sample topography on the projected pattern is theoretically investigated using Zemax ray-tracing software. Analysis are made for amplitude and phase modulation LCDs with different resolutions and compared with preliminary experimental results. The authors acknowledge financial support from NSF through an MRI-grant (grant: 0923506).

Gatabi, Javad R.; Geerts, Wilhelmus; Aaron, Bryant; Tamir, Dan; Pandey, R. K.

2012-03-01

255

Feasibility of skin surface elastography by tracking skin surface topography  

NASA Astrophysics Data System (ADS)

Recent advances have led to a multitude of image modalities being used for visualization of tissue stiffness. High-resolution images of tissue stiffness are desirable, as they have the potential to provide useful diagnostic information. A noncontact optical imaging method has the attractions of low cost, simplicity, and utility when skin contact is undesirable. However, previous optical techniques have required the application of paint or ink to the surface of the skin and so have required contact. Therefore, the present study assessed the feasibility of tracking skin surface topography to produce elastograms. The study showed, by analyzing a variety of silicone skin surface replicas from various body sites of subjects of different ages, that skin surface elastography by tracking surface topography would be feasible. The study further showed that the quality of the strain images can be optimized by measuring skin line pattern frequency. Skin samples with high skin line frequency will achieve best spatial resolution, in the order of 1 mm, comparable to contact techniques reported previously. A mechanically inhomogeneous silicone replica was then imaged, illustrating the technique's ability to detect strain contrast. Finally, the feasibility of implementing the technique in vivo was illustrated using a single pigmented skin lesion.

Coutts, Louise V.; Miller, Naomi R.; Harland, Christopher C.; Bamber, Jeffrey C.

2013-12-01

256

Fractal mapping of digitized images - Application to the topography of Arizona and comparisons with synthetic images  

NASA Technical Reports Server (NTRS)

The concept of fractal mapping is introduced and applied to digitized topography of Arizona. It is shown that the fractal statistics satisfy the topography of the state to a good approximation. The fractal dimensions and roughness amplitudes from subregions are used to construct maps of these quantities. It is found that the fractal dimension of actual two-dimensional topography is not affected by the adding unity to the fractal dimension of one-dimensional topographic tracks. In addition, consideration is given to the production of fractal maps from synthetically derived topography.

Huang, J.; Turcotte, D. L.

1989-01-01

257

Internal structure of Io and the global distribution of its topography  

NASA Astrophysics Data System (ADS)

A global topography is presently calculated for two multilayer Io models in which dissipation occurs in a viscous asthenosphere and a solid mantle: (1) a 'thermal swell' model, in which topography and heat flow are positively correlated, and (2) a 'differentiated lithosphere' model, in which topography and heat flow are negatively correlated. Both the polar topography and the hypsometric distribution of elevations in the differentiated lithosphere model are better matched with observations than the thermal swell model. The shift of the equatorial basin-swell pattern indicates a recent zonal rotation of about 25 deg for Io's lithosphere.

Ross, M. N.; Schubert, G.; Spohn, T.; Gaskell, R. W.

1990-06-01

258

Optic disc topography of normal tension glaucoma patients in Malaysia.  

PubMed

There are limited data in the literature on the optic disc topography in normal tension glaucoma (NTG) patients in Asian countries, especially in Southeast Asia. This study is aimed at comparing optic disc topography in NTG patients and a control group in Malaysia, and we discuss the literature on NTG studies in other Asian populations. A comparative cross-sectional study was conducted in two hospitals with glaucoma services in Malaysia from November 2010 to February 2012. A total of 109 eyes of 109 Malay patients were included in this study: 32 NTG patients and 77 subjects in the control group. All participants underwent a thorough ocular examination, including visual acuity, subjective refraction, anterior segment and fundus examinations, Humphrey visual field 24-2, intraocular pressure measurement, gonioscopy examination and fundus photography. Optic disc topography was assessed using the Heidelberg Retinal Tomograph III by an identified masked investigator in each hospital. NTG patients had a notably larger disc area (2.65 (0.41) vs 2.19 (0.43) mm(2), respectively), larger cupping (1.54 (0.43) vs 0.63 (0.40) mm(2), respectively), smaller retinal rim areas (1.12 (0.41) vs 1.56 (0.33) mm(2), respectively), higher cup volume (0.47 (0.28) vs 0.11 (0.19) mm(3), respectively), reduced rim volume (0.23 (0.13) vs 0.41 (0.16) mm(3), respectively), higher cup to disc area ratio (0.58 (0.14) vs 0.27 (0.15), respectively), higher linear cup to disc ratio (0.76 (0.09) vs 0.49 (0.17) mm(2), respectively), higher mean cup depth (0.37 (0.09) vs 0.22 (0.09) mm, respectively), higher maximum cup depth (0.77 (0.16) vs 0.59 (0.20) mm, respectively), higher mean of cup shape measure (-0.04 (0.06) vs -0.16 (0.07), respectively), and thinner mean retinal nerve fibre layer thickness (0.15 (0.15) vs 0.24 (0.07) mm, respectively) compared to the control group (p<0.05). In conclusion, most of the optic disc parameters were significantly different in NTG patients compared to healthy individuals in Malaysia. Our findings are comparable to those reported in NTG studies in other Asian countries. PMID:24145263

Adlina, Abdul Rahim; Shatriah, Ismail; Liza Sharmini, Ahmad Tajudin; Ahmad, Mt Saad

2013-08-01

259

Eye shape and retinal topography in owls (Aves: Strigiformes).  

PubMed

The eyes of vertebrates show adaptations to the visual environments in which they evolve. For example, eye shape is associated with activity pattern, while retinal topography is related to the symmetry or 'openness' of the habitat of a species. Although these relationships are well documented in many vertebrates including birds, the extent to which they hold true for species within the same avian order is not well understood. Owls (Strigiformes) represent an ideal group for the study of interspecific variation in the avian visual system because they are one of very few avian orders to contain species that vary in both activity pattern and habitat preference. Here, we examined interspecific variation in eye shape and retinal topography in nine species of owl. Eye shape (the ratio of corneal diameter to eye axial length) differed among species, with nocturnal species having relatively larger corneal diameters than diurnal species. All the owl species have an area of high retinal ganglion cell (RGC) density in the temporal retina and a visual streak of increased cell density extending across the central retina from temporal to nasal. However, the organization and degree of elongation of the visual streak varied considerably among species and this variation was quantified using H:V ratios. Species that live in open habitats and/or that are more diurnally active have well-defined, elongated visual streaks and high H:V ratios (3.88-2.33). In contrast, most nocturnal and/or forest-dwelling owls have a poorly defined visual streak, a more radially symmetrical arrangement of RGCs and lower H:V ratios (1.77-1.27). The results of a hierarchical cluster analysis indicate that the apparent interspecific variation is associated with activity pattern and habitat as opposed to the phylogenetic relationships among species. In seven species, the presence of a fovea was confirmed and it is suggested that all strigid owls may possess a fovea, whereas the tytonid barn owl (Tyto alba) does not. A size-frequency analysis of cell soma area indicates that a number of different RGC classes are represented in owls, including a population of large RGCs (cell soma area >150 µm(2)) that resemble the giant RGCs reported in other vertebrates. In conclusion, eye shape and retinal topography in owls vary among species and this variation is associated with different activity patterns and habitat preferences, thereby supporting similar observations in other vertebrates. PMID:22722085

Lisney, Thomas J; Iwaniuk, Andrew N; Bandet, Mischa V; Wylie, Douglas R

2012-01-01

260

EAARL Coastal Topography - Northern Gulf of Mexico, 2007: First Surface  

USGS Publications Warehouse

These remotely sensed, geographically referenced elevation measurements of Lidar-derived first surface (FS) elevation data were produced as a collaborative effort between the U.S. Geological Survey (USGS), Florida Integrated Science Center (FISC), St. Petersburg, FL; the National Park Service (NPS), Gulf Coast Network, Lafayette, LA; and the National Aeronautics and Space Administration (NASA), Wallops Flight Facility, VA. The project provides highly detailed and accurate datasets of select barrier islands and peninsular regions of Louisiana, Mississippi, Alabama, and Florida, acquired June 27-30, 2007. The datasets are made available for use as a management tool to research scientists and natural resource managers. An innovative airborne Lidar instrument originally developed at the NASA Wallops Flight Facility, and known as the Experimental Advanced Airborne Research Lidar (EAARL), was used during data acquisition. The EAARL system is a raster-scanning, waveform-resolving, green-wavelength (532-nanometer) Lidar designed to map near-shore bathymetry, topography, and vegetation structure simultaneously. The EAARL sensor suite includes the raster-scanning, water-penetrating full-waveform adaptive Lidar, a down-looking red-green-blue (RGB) digital camera, a high-resolution multi-spectral color infrared (CIR) camera, two precision dual-frequency kinematic carrier-phase GPS receivers, and an integrated miniature digital inertial measurement unit which provide for submeter georeferencing of each laser sample. The nominal EAARL platform is a twin-engine Cessna 310 aircraft, but the instrument may be deployed on a range of light aircraft. A single pilot, a Lidar operator, and a data analyst constitute the crew for most survey operations. This sensor has the potential to make significant contributions in measuring sub-aerial and submarine coastal topography within cross-environmental surveys. Elevation measurements were collected over the survey area using the EAARL system, and the resulting data were then processed using the Airborne Lidar Processing System (ALPS), a custom-built processing system developed in a NASA-USGS collaboration. ALPS supports the exploration and processing of Lidar data in an interactive or batch mode. Modules for presurvey flight line definition, flight path plotting, Lidar raster and waveform investigation, and digital camera image playback have been developed. Processing algorithms have been developed to extract the range to the first and last significant return within each waveform. ALPS is used routinely to create maps that represent submerged or sub-aerial topography. Specialized filtering algorithms have been implemented to determine the 'bare earth' under vegetation from a point cloud of last return elevations.

Smith, Kathryn E. L.; Nayegandhi, Amar; Wright, C. Wayne; Bonisteel, Jamie M.; Brock, John C.

2009-01-01

261

EAARL coastal topography--Alligator Point, Louisiana, 2010  

USGS Publications Warehouse

This project provides highly detailed and accurate datasets of a portion of Alligator Point, Louisiana, acquired on March 5 and 6, 2010. The datasets are made available for use as a management tool to research scientists and natural-resource managers. An innovative airborne lidar instrument originally developed at the National Aeronautics and Space Administration (NASA) Wallops Flight Facility, and known as the Experimental Advanced Airborne Research Lidar (EAARL), was used during data acquisition. The EAARL system is a raster-scanning, waveform-resolving, green-wavelength (532-nanometer) lidar designed to map near-shore bathymetry, topography, and vegetation structure simultaneously. The EAARL sensor suite includes the raster-scanning, water-penetrating full-waveform adaptive lidar, a down-looking red-green-blue (RGB) digital camera, a high-resolution multispectral color-infrared (CIR) camera, two precision dual-frequency kinematic carrier-phase GPS receivers, and an integrated miniature digital inertial measurement unit, which provide for sub-meter georeferencing of each laser sample. The nominal EAARL platform is a twin-engine aircraft, but the instrument was deployed on a Pilatus PC-6. A single pilot, a lidar operator, and a data analyst constitute the crew for most survey operations. This sensor has the potential to make significant contributions in measuring sub-aerial and submarine coastal topography within cross-environmental surveys. Elevation measurements were collected over the survey area using the EAARL system, and the resulting data were then processed using the Airborne Lidar Processing System (ALPS), a custom-built processing system developed in a NASA-USGS collaboration. ALPS supports the exploration and processing of lidar data in an interactive or batch mode. Modules for presurvey flight-line definition, flight-path plotting, lidar raster and waveform investigation, and digital camera image playback have been developed. Processing algorithms have been developed to extract the range to the first and last significant return within each waveform. ALPS is used routinely to create maps that represent submerged or sub-aerial topography. Specialized filtering algorithms have been implemented to determine the "bare earth" under vegetation from a point cloud of last return elevations.

Nayegandhi, Amar; Bonisteel-Cormier, J. M.; Wright, C. W.; Brock, J. C.; Nagle, D. B.; Vivekanandan, Saisudha; Fredericks, Xan; Barras, J. A.

2012-01-01

262

Antarctic hypsometry and the source of East Antarctica's anomalous topography  

NASA Astrophysics Data System (ADS)

The re-examined hypsometry of Antarctica based on BEDMAP2 data reveals deglaciated modal elevations of ~-450 m and ~650 m for West and East Antarctica, respectively. Although the East Antarctic modal elevation is 300 m lower than the original measurement, it still renders the plateau topographically anomalous by ~400-600 m with respect to the existing global continental modal elevation estimates of 87 m and 250 m. Superimposed on the plateau are the Gamburtsev Subglacial Mountains, the Dronning Maud Land Mountains and the Vostok Highlands with modal elevations ~400 m in excess of the East Antarctic mode. To ascertain whether East Antarctica's anomalous topography can be attributed to Airy-type crustal compensation, a continental-scale crustal thickness model is derived from the inversion of GOCO03S satellite gravity data constrained by seismic crustal thickness measurements. The average crustal thickness of East Antarctica is ~40 km (for West Antarctica ~24 km), a value typical of Archean shields. While crustal thickening to >50 km locally beneath the Gamburtsev Subglacial Mountains and Dronning Maud Land can account for their differential modal elevation above the plateau, the evidently typical Archean crust elsewhere across East Antarctica offers no suggestion of crustal-level continental-scale support for the broader plateau. The plateau of southern Africa offers a tectonic analogue: Like East Antarctica, the lithosphere is largely Archean and cratonic, the crust is of typical shield thickness, there is no obvious Cenozoic tectonism and the upper mantle does not appear to be unduly perturbed. The relative accessibility of the African continent, meanwhile, has led to conclusive imaging of large-scale perturbations in the lower mantle beneath the southern African plateau pointing to dynamic, rather that isostatic, support of the associated long wavelength topography. While several global seismic tomography models infer somewhat anomalously slow lower mantle structure beneath Antarctica, the resolution presently offered by such models in this region is poor. That said, the apparent absence of crustal-level continental-scale support for the East Antarctic plateau coupled with the fact that the underlying upper mantle does not appear unduly anomalous suggest, by analogy with southern Africa, lower mantle generated epeirogeny as a likely explanation for the anomalous topography. The incorporation of data from the Antarctic seismic deployments of recent years in the next generation of global tomography models should resolve the issue.

O'Donnell, J.; Nyblade, A.

2013-12-01

263

Continuum Statistics of the Bed Topography in a Sandy River  

NASA Astrophysics Data System (ADS)

Temporal and spatial variabilities in the bed geometry of sandy rivers contain information about processes of sediment transport that has not been fully appreciated. This is primarily due to a disparity between the dynamic nature of the sediment-fluid interface and the relatively static methods of surveying bed elevation, e.g. single profiles or point measurements. High resolution topographic data is paramount to understanding the dynamic behavior of sandy beds. We present and analyze a data set collected on a 2cm x 2cm grid at 1 minute intervals and with a vertical precision of ~1mm. This was accomplished by using Lambert-Beer's Law for attenuation of light to transform low-altitude aerial photographs into digital elevation models. Forty successive models were generated for a 20 m by 30 m section of channel bottom of the N. Loup River, Nebraska. To calculate the average, whole bed translation rate, or celerity, cross-correlations between a reference bed topography and its proceeding configurations were determined. Time differences between models were related to the shift lengths that produced correlation maxima for each model pair. The result is a celerity of ~3.8cm/s with a correlation coefficient of 0.992. Bed topography also deforms while it translates, and this can be seen as a secular decrease of correlation maxima. The form of this decrease in correlation is exponential, and from it an interface half-life is defined. In this case, the bed had become extensively reorganized within ~40 minutes, the time necessary to translate the bed one wavelength of the dominant roughness element. Although the bed is continuously deforming, its roughness is statistically stationary. Essentially, a mean roughness is maintained as the bed creates new realizations of itself. The dynamic nature of the whole bed and similarly transient behavior of individual elements suggests the utility of a holistic approach to studying the feedback between bed topography, fluid flow, and sediment transport. Furthermore, it raises questions about the usefulness of detailed analysis of flow and transport over individual forms.

McElroy, B.; Jerolmack, D.; Mohrig, D.

2005-12-01

264

Novel double path shearing interferometer in corneal topography measurements  

NASA Astrophysics Data System (ADS)

The paper presents an approach for measurements of corneal topography by use of a patent pending double path shearing interferometer (DPSI). Laser light reflected from the surface of the cornea is divided and directed to the inputs of two interferometers. The interferometers use lateral shearing of wavefronts in two orthogonal directions. A tilt of one of the mirrors in each interferometric setup perpendicularly to the lateral shear introduces parallel carrier frequency fringes at the output of each interferometer. There is orthogonal linear polarization of the laser light used in two DPSI. Two images of fringe patters are recorded by a high resolution digital camera. The obtained fringe patterns are used for phase difference reconstruction. The phase of the wavefront was reconstructed by use of algorithms for a large grid based on discrete integration. The in vivo method can also be used for tear film stability measurement, artificial tears and contact lens tests.

Licznerski, Tomasz J.; Jaronski, Jaroslaw; Kosz, Dariusz

2005-09-01

265

High-precision Ice Surface Topography Mapping Using Radar Interferometry  

NASA Astrophysics Data System (ADS)

In May 2009 a new radar technique for mapping ice surface topography was demonstrated in a Greenland campaign as part of the NASA International Polar Year activities. This was achieved with the airborne Glacier and Ice Surface Topography Interferometer (GLISTIN-A): a 35.6 GHz single-pass interferometer. Although the technique of using radar interferometry for mapping terrain has been demonstrated before, this is the first such application at millimeter-wave frequencies. Instrument performance indicates swath widths over the ice between 5-7km, with height precisions ranging from 30cm-3m at a posting of 3m x 3m. However, for this application the electromagnetic wave will penetrate an unknown amount into the snow cover thus producing an effective bias that must be calibrated. To evaluate this, GLISTIN-A flew a coordinated collection with the NASA Wallops Airborne Topographic Mapper (ATM) on a transect from Greenland’s Summit to its West coast. Two field calibration sites were established at Colorado Institute for Research in Environmental Science’s Swiss Camp and the National Science Foundation’s Summit station. Additional collections entailed flying a mosaic over Jakobshavn glacier which was repeated after 6 days to reveal surface dynamics. Through detailed calibration and inter-sensor comparisons we were able to observe penetration biases and compare them with theoretical expectations. We also demonstrated GLISTIN-A’s capability to measure the topography of large glacier systems in a seamless fashion and accurately measuring volume changes with a high level of spatial detail. In particular, repeating the airborne campaigns to observe elevation changes over time will allow very accurate volume change measurements. Not only is this very important for mass balance studies to have a precise mass-loss estimate, but the spatial pattern can reveal ice dynamics effects and surface mass balance effects. In this manner a high resolution, high-precision topographic mapping capability is an ideal complement to the ICESat, ICESat II and Cryosat altimeters. Interpolating between the high-accuracy elevation profiles from altimeters such as the ATM or ICESat II with the high-resolution GLISTIN-A swath will enable detailed ice-surface topography maps and extended spatial coverage. The result is the potential for higher fidelity mass-balance estimates and improved observational coverage. Upgrades are currently underway to improve the performance and portability of GLISTIN-A such that, onboard a long-range aircraft this radar can map Greenland’s significant glaciers in a few days. The upgraded GLISTIN-A will be compatible with GlobalHawk installation making, Antarctica basin and coastal mapping feasible. GLISTIN will make more topographic products available to glaciologists, initially through dedicated airborne campaigns or ultimately, perhaps, as a satellite mission.

Moller, D.; Hensley, S.; Michel, T.; Rignot, E. J.; Simard, M.; Krabill, W. B.; Sonntag, J. G.

2010-12-01

266

Geologic structure of shallow maria. [topography of lunar maria  

NASA Technical Reports Server (NTRS)

Isopach maps and structural contour maps of the eastern mare basins (30 deg N to 30 deg S; 0 deg to 100 deg E), constructed from measurements of partially buried craters, are presented and discussed. The data, which are sufficiently scattered to yield gross thickness variations, are restricted to shallow maria with less than 1500-2000 m of mare basalts. The average thickness of basalt in the irregular maria is between 200 and 400 m. Correlations between surface topography, basalt thickness, and basin floor structure are apparent in most of the basins that were studied. The mare surface is commonly depressed in regions of thick mare basalts; mare ridges are typically located in regions of pronounced thickness changes; and arcuate mare rilles are confined to thin mare basalts. Most surface structures are attributed to shallow stresses developed within the mare basalts during consolidation and volume reduction.

Dehon, R. A.; Waskom, J. A.

1975-01-01

267

Forecasting hurricane impact on coastal topography: Hurricane Ike  

USGS Publications Warehouse

Extreme storms can have a profound impact on coastal topography and thus on ecosystems and human-built structures within coastal regions. For instance, landfalls of several recent major hurricanes have caused significant changes to the U.S. coastline, particularly along the Gulf of Mexico. Some of these hurricanes (e.g., Ivan in 2004, Katrina and Rita in 2005, and Gustav and Ike in 2008) led to shoreline position changes of about 100 meters. Sand dunes, which protect the coast from waves and surge, eroded, losing several meters of elevation in the course of a single storm. Observations during these events raise the question of how storm-related changes affect the future vulnerability of a coast.

Plant, Nathaniel G.; Stockdon, Hilary F.; Sallenger, Asbury H., Jr.; Turco, Michael J.; East, Jeffery W.; Taylor, Arthur A.; Shaffer, Wilson A.

2010-01-01

268

New Orleans Topography, Radar Image with Colored Height  

NASA Technical Reports Server (NTRS)

[figure removed for brevity, see original site] Click on the image for the animation

About the animation: This simulated view of the potential effects of storm surge flooding on Lake Pontchartrain and the New Orleans area was generated with data from the Shuttle Radar Topography Mission. Although it is protected by levees and sea walls against storm surges of 18 to 20 feet, much of the city is below sea level, and flooding due to storm surges caused by major hurricanes is a concern. The animation shows regions that, if unprotected, would be inundated with water. The animation depicts flooding in one-meter increments.

About the image: The city of New Orleans, situated on the southern shore of Lake Pontchartrain, is shown in this radar image from the Shuttle Radar Topography Mission (SRTM). In this image bright areas show regions of high radar reflectivity, such as from urban areas, and elevations have been coded in color using height data also from the SRTM mission. Dark green colors indicate low elevations, rising through yellow and tan, to white at the highest elevations.

New Orleans is near the center of this scene, between the lake and the Mississippi River. The line spanning the lake is the Lake Pontchartrain Causeway, the world's longest overwater highway bridge. Major portions of the city of New Orleans are actually below sea level, and although it is protected by levees and sea walls that are designed to protect against storm surges of 18 to 20 feet, flooding during storm surges associated with major hurricanes is a significant concern.

Data used in this image were acquired by the Shuttle Radar Topography Mission aboard the Space Shuttle Endeavour, launched on Feb. 11, 2000. SRTM used the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. SRTM was designed to collect 3-D measurements of the Earth's surface. To collect the 3-D data, engineers added a 60-meter (approximately 200-foot) mast, installed additional C-band and X-band antennas, and improved tracking and navigation devices. The mission is a cooperative project between NASA, the National Geospatial-Intelligence Agency (NGA) of the U.S. Department of Defense and the German and Italian space agencies. It is managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif., for NASA's Science Mission Directorate, Washington, D.C.

Location: 30.2 degrees North latitude, 90.1 degrees East longitude Orientation: North toward the top, Mercator projection Size: 80.3 by 68.0 kilometers (49.9 by 42.3 miles) Image Data: Radar image and colored Shuttle Radar Topography Mission elevation model Date Acquired: February 2000

2005-01-01

269

The evolution of polymer surface topography in annealing  

NASA Astrophysics Data System (ADS)

Ultrasmooth polymer films are of great importance in a large body of technical application. Photoresist technology plays a very important role in MEMS, and usually is to use optical coatings to transfer the smooth surface. In order to form different value of roughness is bright and clean surface or sacrifice layer microstructure, surface topography and its effect on the microstructure is crucial. Photoresist thin film EPG533 having different thicknesses of 270nm, 500nm, and 1 ?m were deposited onto well-cleaned n-type silicon substrates by spin coating and annealed in the range from 100°C to 200°C.The effects of thermal annealing and thickness variation on the crystalline quality and surface morphology of the films were investigated by white light interferometry measurements. It was found that the film quality and morphology depend on the annealing temperature. The root-mean-square roughness and waviness on the surface change, as a result of increasing film thickness.

Ma, Pengfei; Liu, Weiguo; Liu, Huan

2013-12-01

270

Topography estimation with interferometric synthetic aperture radar using fringe detection  

NASA Technical Reports Server (NTRS)

Methods are presented for using Synthetic Aperture Radar (SAR) interferometry data to estimate surface topography. An expression is given to relate the elevation of a ground point to the phase difference of SAR images received from two spatially separated antennas. An iterative algorithm which solves for the position and elevation of each point in the image simultaneously is developed. One of the critical issues that determines the accuracy of the terrain mapping is the phase unwrapping. An approach to the problem by fringe line detection is proposed. The algorithms are tested with two Seasat SAR images of terrain near Yellowstone National Park. The resultant elevation map is compared with a USGS terrain elevation model. The error of the SAR elevation with respect to the digital terrain map is about 8.2 percent of the total terrain variation.

Lin, Qian; Vesecky, John F.; Zebker, Howard A.

1991-01-01

271

Topography of inland deltas: Observations, modeling, and experiments  

NASA Astrophysics Data System (ADS)

The topography of inland deltas is influenced by the water-sediment balance in distributary channels and local evaporation and seepage rates. In this letter a reduced complexity model is applied to simulate inland delta formation, and results are compared with the Okavango Delta, Botswana and with a laboratory experiment. We show that water loss in inland deltas produces fundamentally different dynamics of water and sediment transport than coastal deltas, especially deposition associated with expansion-contraction dynamics at the channel head. These dynamics lead to a systematic decrease in the mean topographic slope of the inland delta with distance from the apex following a power law with exponent ? = -0.69 ± 0.02 where the data for both simulation and experiment can be collapsed onto a single curve. In coastal deltas, on the contrary, the slope increases toward the end of the deposition zone.

Seybold, H. J.; Molnar, P.; Akca, D.; Doumi, M.; Cavalcanti Tavares, M.; Shinbrot, T.; Andrade, J. S.; Kinzelbach, W.; Herrmann, H. J.

2010-04-01

272

Characterization of Mo/Si multilayer growth on stepped topographies  

SciTech Connect

Mo/Si multilayer mirrors with nanoscale bilayer thicknesses have been deposited on stepped substrate topographies, using various deposition angles. The multilayer morphology at the stepedge region was studied by cross section transmission electron microscopy. A transition from a continuous- to columnar layer morphology is observed near the step-edge, as a function of the local angle of incidence of the deposition flux. Taking into account the corresponding kinetics and anisotropy in layer growth, a continuum model has been developed to give a detailed description of the height profiles of the individual continuous layers. Complementary optical characterization of the multilayer system using a microscope operating in the extreme ultraviolet wavelength range, revealed that the influence of the step-edge on the planar multilayer structure is restricted to a region within 300 nm from the step-edge.

Boogaard, A. J. R. vcan den; Louis, E.; Zoethout, E.; Goldberg, K. A.; Bijkerk, F.

2011-08-31

273

Lutetia global shape and topography reconstructed with photoclinometry by deformation  

NASA Astrophysics Data System (ADS)

3D reconstruction of asteroids and cometary nuclei allows us to model their physical, geomorphological and geological properties. We applied a new reconstruction method by photoclinometry based on the minimization of the chi-square difference between observed and synthetic images by deformation of a 3D triangular mesh to a set of images of asteroid (21) Lutetia acquired by the OSIRIS cameras aboard ESA's ROSETTA spacecraft in July 2010. This allowed us to retrieve an improved global shape of the asteroid as well as the local topography of its main features: the large Massalia crater, the North pole crater complex and several other topographic features of interest. A comparison of this model with those obtained with other techniques will be presented.

Capanna, C.; Jorda, L.; Gesquière, G.; Lamy, P.; Kaasalainen, M.

2012-09-01

274

Precision measurement on comprehensive topography of the deep hole surface  

NASA Astrophysics Data System (ADS)

Based on the computer aided test technique, a precision method for measuring the comprehensive topography of the deep hole surface is developed. The measuring principle and data processing method are described in detail. A new built-up function has good linearity and good continuity, therefore it is easy to be subdivided by computer and the error can be corrected conveniently. In order to get a high quality fringe signal, we apply a new correction technique which based on the least square method to correct the A/D values in real-time. Some new methods are firstly employed to predict measuring errors and find the best measuring plan. A serial of experiments are made to verify the method"s availability and reliability by using some especial devices and software. Based on the laser holographic diffraction grating, a new experimental instrument is developed to measure the needle valve seat"s cone of a diesel engine.

Wang, Zhongyu; Fang, Ming

2004-08-01

275

Simultaneous topography and recognition imaging on endothelial cells.  

PubMed

Determining the landscape of specific binding sites on biological samples with high spatial accuracy (in the order of several nanometres) is an important task in many fields of biological science. During the past five years, dynamic recognition imaging (e.g. simultaneous topography and recognition (TREC) imaging) has proven to be a powerful technique in biophysical research. This technique becomes an indispensable tool for high-resolution receptor mapping as it has been successfully demonstrated on different biomolecular model systems. In these studies, the topographical imaging of receptor molecules is combined with molecular recognition by their cognate ligands bound to the atomic force microscope (AFM) tip via a flexible and distensible tether. In this review, we describe the principles of TREC imaging and provide a flavour of its recent application on endothelial cells. PMID:21812052

Chtcheglova, L A; Hinterdorfer, P

2011-01-01

276

The evolution of Tharsis: Implications of gravity, topography, and tectonics  

NASA Technical Reports Server (NTRS)

Dominating the Western Hemisphere of Mars, the Tharsis rise is an elongate area centered on Syria Planum that ascends as much as 8 to 10 km above the datum. It is intensely fractured by long, narrow grabens that extend radially hundreds of kilometers beyond the rise and is ringed by mostly concentric wrinkle ridges that formed over 2,000 km from the center of the rise. Its size, involving a full hemisphere of Mars, gives it a central role in the thermo-tectonic evolution of the planet and has stimulated a number of studies attempting to determine the sequence of events responsible for this feature. The constraints that gravity and topography data place on the current structure of Tharsis, along with insights into its development derived from comparisons of detailed regional mapping of faulting with theoretical deformation models are reviewed. Finally, a self-consistent model for the structure of Tharsis is proposed.

Banerdt, W. B.; Golombek, M. P.

1990-01-01

277

Leaf cuticle topography retrieved by using fringe projection  

NASA Astrophysics Data System (ADS)

The combination (often referred to as phase-stepping profilometry, PSP) of the fringe projection technique and the phase-stepping method allowed us to retrieve topographic maps of cuticles isolated from the abaxial surface of leaves; these were in turn sampled from an apple tree ( Malus domestica) of the variety Golden Delicious. The topographic maps enabled us to assess the natural features on the illuminated surface and also to detect the whole-field spatial variations in the thickness of the cuticle. Most of our attention was paid to retrieve the highly-resolved elevation information from the cuticle surface, which included the trace (in the order of tens of micrometers) left by ribs and veins. We expect that the PSP application for retrieving the cuticle topography will facilitate further studies on the dispersion and coverage of state-of-the-art agrochemical compounds meant to improve the defending properties of the cuticle. Methodological details are provided below.

Martínez, Amalia; Rayas, J. A.; Cordero, Raúl R.; Balieiro, Daniela; Labbe, Fernando

2012-02-01

278

Topography-guided custom ablation treatment for treatment of keratoconus.  

PubMed

Keratoconus is a progressive ectatic disorder of the cornea which often presents with fluctuating refraction and high irregular astigmatism. Correcting the vision of these patients is often a challenge because glasses are unable to correct the irregular astigmatism and regular contact lenses may not fit them very well. Topography-guided custom ablation treatment (T-CAT) is a procedure of limited ablation of the cornea using excimer laser with the aim of regularizing the cornea, improving the quality of vision and possibly contact lens fit. The aim of the procedure is not to give a complete refractive correction. It has been tried with a lot of success by various groups of refractive surgeons around the world but a meticulous and methodical planning of the procedure is essential to ensure optimum results. In this paper, we attempt to elucidate the planning for a T-CAT procedure for various types of cones and asphericities. PMID:23925335

Shetty, Rohit; D'Souza, Sharon; Srivastava, Samaresh; Ashwini, R

2013-08-01

279

Mass and local topography measurements of Itokawa by Hayabusa.  

PubMed

The ranging instrument aboard the Hayabusa spacecraft measured the surface topography of asteroid 25143 Itokawa and its mass. A typical rough area is similar in roughness to debris located on the interior wall of a large crater on asteroid 433 Eros, which suggests a surface structure on Itokawa similar to crater ejecta on Eros. The mass of Itokawa was estimated as (3.58 +/- 0.18) x 10(10) kilograms, implying a bulk density of (1.95 +/- 0.14) grams per cubic centimeter for a volume of (1.84 +/- 0.09) x 10(7) cubic meters and a bulk porosity of approximately 40%, which is similar to that of angular sands, when assuming an LL (low iron chondritic) meteorite composition. Combined with surface observations, these data indicate that Itokawa is the first subkilometer-sized small asteroid showing a rubble-pile body rather than a solid monolithic asteroid. PMID:16741111

Abe, Shinsuke; Mukai, Tadashi; Hirata, Naru; Barnouin-Jha, Olivier S; Cheng, Andrew F; Demura, Hirohide; Gaskell, Robert W; Hashimoto, Tatsuaki; Hiraoka, Kensuke; Honda, Takayuki; Kubota, Takashi; Matsuoka, Masatoshi; Mizuno, Takahide; Nakamura, Ryosuke; Scheeres, Daniel J; Yoshikawa, Makoto

2006-06-01

280

Topography and geomorphology of the Huygens landing site on Titan  

USGS Publications Warehouse

The Descent Imager/Spectral Radiometer (DISR) aboard the Huygens Probe took several hundred visible-light images with its three cameras on approach to the surface of Titan. Several sets of stereo image pairs were collected during the descent. The digital terrain models constructed from those images show rugged topography, in places approaching the angle of repose, adjacent to flatter darker plains. Brighter regions north of the landing site display two styles of drainage patterns: (1) bright highlands with rough topography and deeply incised branching dendritic drainage networks (up to fourth order) with dark-floored valleys that are suggestive of erosion by methane rainfall and (2) short, stubby low-order drainages that follow linear fault patterns forming canyon-like features suggestive of methane spring-sapping. The topographic data show that the bright highland terrains are extremely rugged; slopes of order of 30?? appear common. These systems drain into adjacent relatively flat, dark lowland terrains. A stereo model for part of the dark plains region to the east of the landing site suggests surface scour across this plain flowing from west to east leaving ???100-m-high bright ridges. Tectonic patterns are evident in (1) controlling the rectilinear, low-order, stubby drainages and (2) the "coastline" at the highland-lowland boundary with numerous straight and angular margins. In addition to flow from the highlands drainages, the lowland area shows evidence for more prolific flow parallel to the highland-lowland boundary leaving bright outliers resembling terrestrial sandbars. This implies major west to east floods across the plains where the probe landed with flow parallel to the highland-lowland boundary; the primary source of these flows is evidently not the dendritic channels in the bright highlands to the north. ?? 2007 Elsevier Ltd. All rights reserved.

Soderblom, L. A.; Tomasko, M. G.; Archinal, B. A.; Becker, T. L.; Bushroe, M. W.; Cook, D. A.; Doose, L. R.; Galuszka, D. M.; Hare, T. M.; Howington-Kraus, E.; Karkoschka, E.; Kirk, R. L.; Lunine, J. I.; McFarlane, E. A.; Redding, B. L.; Rizk, B.; Rosiek, M. R.; See, C.; Smith, P. H.

2007-01-01

281

Thermally tailored gradient topography surface on elastomeric thin films.  

PubMed

We report a simple method for creating a nanopatterned surface with continuous variation in feature height on an elastomeric thin film. The technique is based on imprinting the surface of a film of thermo-curable elastomer (Sylgard 184), which has continuous variation in cross-linking density introduced by means of differential heating. This results in variation of viscoelasticity across the length of the surface and the film exhibits differential partial relaxation after imprinting with a flexible stamp and subjecting it to an externally applied stress for a transient duration. An intrinsic perfect negative replica of the stamp pattern is initially created over the entire film surface as long as the external force remains active. After the external force is withdrawn, there is partial relaxation of the applied stresses, which is manifested as reduction in amplitude of the imprinted features. Due to the spatial viscoelasticity gradient, the extent of stress relaxation induced feature height reduction varies across the length of the film (L), resulting in a surface with a gradient topography with progressively varying feature heights (hF). The steepness of the gradient can be controlled by varying the temperature gradient as well as the duration of precuring of the film prior to imprinting. The method has also been utilized for fabricating wettability gradient surfaces using a high aspect ratio biomimetic stamp. The use of a flexible stamp allows the technique to be extended for creating a gradient topography on nonplanar surfaces as well. We also show that the gradient surfaces with regular structures can be used in combinatorial studies related to pattern directed dewetting. PMID:24697617

Roy, Sudeshna; Bhandaru, Nandini; Das, Ritopa; Harikrishnan, G; Mukherjee, Rabibrata

2014-05-14

282

Density constraints of lunar upper crust from gravity and topography  

NASA Astrophysics Data System (ADS)

Remote sensing and in situ measurements have shown that there are large lateral and vertical variations in the composition of the lunar crust. These crustal density diversities can be investigated using newly obtained global gravity and topography data. We applied a localized spectral admittance technique to various crustal regions by windowing the free-air gravity and surface topography with the band-limited localization windows of Wieczorek and Simons (2005, 2007). These admittances were interpreted using a geophysical model that includes both surface and subsurface loads that are supported by an elastic lithosphere. By varying the crustal density, elastic thickness and loading ratio in certain ranges, the best fitting bulk densities for a number of homogeneous regions were constrained to vary laterally from 2590 kg m-3 to 3010 kg m-3, with a mean value of 2700 kg m-3. Assuming the composition of the upper crust is uniform, the porosity of the upper crust could be determined if the pore-free surface density is known. Based on the known compositions of lunar rocks and estimated mineralogical norms, we found that the pore-free densities of lunar rocks were highly correlated with FeO and TiO2 abundance. The rock density can vary from 2884 to 3038 kg m-3 in estimated regions by using the iron and titanium abundances from Lunar Prospector gamma-ray spectrometer. We calculated the porosity of each region and found a mean value of ~7.4±3.4%, with permissible values from 0 to 14%. Furthermore, we took into account the vertical variation of crust density, and developed a novel technique that the density profile of the crust could be inverted using higher resolution gravity models. Since all these analyses are challenging using the recent Kaguya gravity models, higher resolution gravity data expected from NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission would place tight constrains on both the lateral and vertical density variations of the lunar crust.

Huang, Q.; Wieczorek, M. A.; Ping, J.

2011-12-01

283

Lunar South Pole Topography Derived from Clementine Imagery  

NASA Astrophysics Data System (ADS)

During the Clementine Mission both oblique and vertical multispectral images were collected. The oblique and vertical images from a single spectral band collected during the same orbit form a stereo pair that can be used to derive the topography. These stereo pairs are being used to derive the topography of an area (90 deg S to 650S latitude) surrounding the lunar south pole. Work on the lunar north pole topography will start after completion of the south pole topography. This report provides an update on the initial results for the lunar south pole topography. In 1994, the Clementine spacecraft acquired digital images of the Moon at visible and near-infrared wavelengths. Onboard there were four camera systems and a laser altimeter. During the first pass, periapsis was at 30S and the highest resolution images were obtained in the southern hemisphere. Over the northern polar area, a series of oblique and vertical images were obtained with the ultraviolet-visible (UV-VIS) camera on each orbit. During the second pass, periapsis was at 30N and the image acquisition strategy was reversed. The UV-VIS camera image size was 384 x 288 pixels with five spectral bands and one broad band. The 750-nm-band stereo pairs are the primary image source for this study. The ground sample distances (GSD) for oblique images range from 300 to 400m. The GSD for the vertical images, acquired at the end of an orbit, are slightly larger and range from 325 to 450 m. Using the formula for stereo-height accuracy, an estimate of height accuracy is 180m. This formula is IFOVMAX)/(K*B/H with IFOVMAX defined as Maximum Instantaneous Field of View; B/H is the base-to-height ratio and K is an estimate of pixel measurement accuracy on the imagery. The Clementine laser altimeter (LIDAR) data were used previously to produce a global topographic model of the Moon . The model has a vertical accuracy of about 100 m and a spatial resolution of 2.5 deg. Altimetry data were collected between 79S and 810N. These data were filtered and then interpolated to fill in the polar regions where the altimeter did not collect data. A global topography model was then derived based on spherical harmonic expansion. Image mosaic. A global image mosaic of the Moon was produced from the 750-nm. Clementine data . The mosaic includes high-resolution, oblique, and vertical images. Match points were picked to tie the imagery together, and the camera pointing angles were adjusted to align the imagery. This adjustment used a spherical surface, and the elevation of all points was held to a constant value, 1737.4 km. This produced a seamless image mosaic with latitude and longitude information but no information on the elevation. The imagery and support information were downloaded to our digital photogrammetric workstation from the Integrated Software for Imagers and Spectrometers (ISIS) system. The support data included the camera location and pointing angles. Match points used to, produce the image mosaic were also downloaded. The camera angles were adjusted to account for the elevation of the match points. This was accomplished with the Multi Sensor Triangulation (MST) software from LH Systems SOCET Set software package. The revised camera angles allowed for the derivation of a digital elevation model (DEM) from the stereo pairs. The match-point latitude and longitude from the global image mosaic are accurate and used for an initial estimate of the horizontal position. The elevations of the match points were estimated from the altimetry data. The camera angles used in the altimetry processing and in the creation of the image mosaic were adjusted independently. Hence, the horizontal position of the altimetry data and the image mosaic are not aligned correctly. Clementine was designed so the altimeter shared the optical system of the HIRES camera system. The HIRES and UV-VIS camera systems were aligned so the HIRES image was centered in the UV-VIS image. We therefore made an adjustment so that the altimetry points would fall near the centerline of the UV-VIS imagery. A DEM was created from

Rosiek, M. R.; Kirk, R.; Howington-Kraus, A.

1999-01-01

284

A Topographic Analysis of the Colorado River Drainage: Insights into Interaction Between Topography and Incision History  

Microsoft Academic Search

Topography is a fundamental geophysical observable that reflects the geodynamic, geologic, and climatic history of a region. A number of recent studies have explored ways to extract tectonic information from topography and several provocative interpretations have been made about the topographic fabric in the Western U.S., including: 1) The topographic spectral power decreases systematically as the tectonic age of the

D. D. Coblentz; K. Karlstrom

2003-01-01

285

PRK in patients with a keratoconic topography picture. The concept of a physiological 'displaced apex syndrome'  

Microsoft Academic Search

AIMS\\/BACKGROUND: Keratoconus is generally held to be an absolute contraindication for photorefractive keratectomy (PRK). Corneas with inferior steepening on corneal topography are widely thought to have subclinical keratoconus. We were not convinced that this is always the case, as there seems to be a group of patients with a stable inferior steepening pattern on topography who show no other characteristics

S J Doyle; E Hynes; S Naroo; S Shah

1996-01-01

286

Representation of Topography by Shaved Cells in a Height Coordinate Ocean Model  

Microsoft Academic Search

Height coordinate ocean models commonly represent topography as a ''staircase'' of discontinuous steps that are fitted to the model grid. Here the ramifications of an alternative approach are studied in which ''shaved cells'' are used to represent irregular topography. The problem is formulated using the finite-volume method and care is taken to ensure that the discrete forms have appropriate conservation

Alistair Adcroft; Chris Hill; John Marshall

1997-01-01

287

Spatially resolved surface topography retrieved from far-field intensity scattering measurements.  

PubMed

A far-field setup based on the fast and simultaneous recording of 1 million intensity angle-resolved-light-scattering patterns allows both to reconstruct surface topography and to cancel local defects in this topography. A spectral analysis is performed on measured data and allows to extract roughness and slopes mapping of a surface taking into account the spectral bandpass. PMID:24514231

Zerrad, Myriam; Lequime, Michel; Amra, Claude

2014-02-01

288

Dynamic ocean topography for the northeast Pacific and its continental margins  

Microsoft Academic Search

Estimates of dynamic ocean (or sea surface) topography based on satellite altimetry and gravity observations generally become degraded as they approach land. In this study, dynamic ocean topography for the northeast Pacific Ocean is computed independently of satellite observations using a high resolution model and seasonal climatologies of temperature, salinity, and wind stress. Comparisons with estimates based on satellite gravity

M. G. G. Foreman; W. R. Crawford; J. Y. Cherniawsky; J. Galbraith

2008-01-01

289

Generation of internal waves by tidal flow over three-dimensional topography  

NASA Astrophysics Data System (ADS)

An understanding of the internal wave field generated by oscillatory tidal flow over three-dimensional topography is important for ocean models. Recent numerical work has compared the internal wave fields generated by 2D and 3D topography and found that 3D topography can be more than an order of magnitude less efficient at converting the M2 barotropic tide into internal waves. While the previous studies focus on the energy conversion rate, we perform experiments and simulations to examine the generation regions and flow fields in detail. In particular, we present results from numerical simulations of oscillatory flow past supercritical, 3-dimensional topography (a half-sphere on a flat plane). These results are compared to experiments performed on similar topography. In contrast to the 2D case, where all flow is forced to go over the topography, the 3D case has the added complexity that the oscillating flow can either go over or around the topography. We characterize the boundary layer near the topography, and show how regions containing large vertical motion lead to the observed angular dependence of the wave field. [1]P. Holloway, M. Merrifield, J. Geophys. Res. 104, 25,937 (1999) [2]J. R. Munroe, K. G. Lamb, J. Geophys. Res. 110, C02001 (2005)

King, Benjamin; Zhang, Hepeng; Swinney, Harry L.

2008-11-01

290

The surface topography of a magnetic fluid: a quantitative comparison between experiment and numerical simulation  

Microsoft Academic Search

The normal field instability in magnetic liquids is investigated experimentally by means of a radioscopic technique which allows a precise measurement of the surface topography. The dependence of the topography on the magnetic field is compared to results obtained by numerical simulations via the finite-element method. Quantitative agreement has been found for the critical field of the instability, the scaling

Christian Gollwitzer; Gunar Matthies; Reinhard Richter; Ingo Rehberg; Lutz Tobiska

2007-01-01

291

Combined microscale mechanical topography and chemical patterns on polymer cell culture substrates  

Microsoft Academic Search

This paper presents a technique to independently form mechanical topography and surface chemical patterns on polymer cell substrates, and studies the response of osteoblast cells to these surface patterns. The patterns were formed in two separate steps: hot embossing imprint lithography formed the mechanical topography and microcontact printing created the chemical pattern. The resulting substrate had surface features consisting of

Joseph L. Charest; Marcus T. Eliason; Andrés J. García; William P. King

2006-01-01

292

Radii, shapes, and topography of the satellites of Uranus from limb coordinates  

Microsoft Academic Search

Limb coordinates are used to find the radii, shapes, and local topography of the five large satellites of Uranus. Umbriel, Titania, and Oberon are best fit by spheres. Miranda and Ariel are ellipsoids whose equatorial bulges are consistent with published mean densities. Limb topography on Miranda shows substantial deformation of both old cratered terrain and the younger coronae and complex

P. C. Thomas

1988-01-01

293

The role of erosion by fish in shaping topography around Hudson submarine canyon.  

USGS Publications Warehouse

The close match of areas of rough topography and high tilefish populations, the active burrowing of the sea floor, and the clustered distribution of the burrows suggest that the hummocky topography in this area may be the result of continuous erosion by tilefish and associated crustaceans during the Holocene. -from Authors

Twichell, D. C.; Grimes, C. B.; Jones, R. S.; Able, K. W.

1985-01-01

294

Relationship between Oil Palm Yield and Soil Fertility as Affected by Topography in an Indonesian Plantation  

Microsoft Academic Search

Typically, Indonesian oil palm plantations rest on rolling topography. There is limited information on how topography affects soil fertility and oil palm yields. A study was conducted to evaluate these relationships in a commercial oil palm plantation located in South Sumatra, Indonesia. Two sites with differing past management history and fertility regimes were each partitioned into three topographic positions. At

S. K. Balasundram; P. C. Robert; D. J. Mulla; D. L. Allan

2006-01-01

295

Inversion of Gravity and Topography for Mantle and Crustal Structure on Mars.  

National Technical Information Service (NTIS)

Analysis of the gravity and topography of Mars presently provides our primary quantitative constraints on the internal structure of Mars. We present an inversion of the long-wavelength (harmonic degree less than or equal to 10) gravity and topography of M...

W. S. Kiefer B. G. Bills R. S. Nerem

1996-01-01

296

Surface topography of cylindrical gear wheels after smoothing in abrasive mass, honing and shot peening  

NASA Astrophysics Data System (ADS)

The present paper presents the analysis of surface topography of gear teeth as the result of final machining processes. Teeth of multiple cylindrical gears shaped by grinding were smoothed in abrasive mass, honed or shot peened. The measurement of gears were made using coordinate measuring machine and 3D surface topography stylus instrument. The following deviations were studied; pitch deviation, total pitches deviations, variation of teeth thickness and deviation of gear radial run-out. Changes in teeth surface topography during machining process were determined. 3D surface topography parameters, surface directionality as well as areal autocorrelation and power spectral density functions were taken into consideration. As the results of the analysis, the best surface topography with regard to gear operational properties was recommended.

Michalski, J.; Pawlus, P.; ?elasko, W.

2011-08-01

297

An inversion of geoid and topography for mantle and crustal structure on Mars  

NASA Technical Reports Server (NTRS)

Mars has the largest amplitude geoid anomalies and surface topography known on the terrestrial planets. A number of prior studies have analyzed Martian gravity anomalies and topography in terms of isostasy and flexure of the crust and lithosphere. Other studies have emphasized the role of mantle convection in producing gravity anomalies and topography in some regions of Mars. Geoid and topography observations for simultaneous estimates of density anomalies in the crust and mantle of Mars are inverted. In performing this study, a recent degree 50 spherical harmonic expansion of the Martian gravity field (GMM-l) and a corresponding resolution expansion of the USGS Mars topography model are used. However, our analysis is restricted to harmonic degrees up to L equals 25, which are better determined than the higher harmonics. This provides a half-wavelength horizontal resolution of 425 km.

Kiefer, Walter; Bills, Bruce; Frey, Herb; Nerem, Steve; Roark, Jim; Zuber, Maria

1993-01-01

298

Anomalous Accretionary Margin Topography Formed By Repeated Earthquakes  

NASA Astrophysics Data System (ADS)

It has long been recognized that accretionary margins of major subduction zones undergo substantial deformation. However even with the large amounts of shortening accommodated within the margin, for most subduction zones, there is an extended submarine portion to the accretionary, highly-deformed upper-plate between the trench and the coast. This is a vexing situation since this submarine section typically overlies the actual locked or coupled patch of the plate interface. The result of this is added difficulty in directly observing processes related to the plate interface coupling - such processes as micro-seismicity and the actual patterns of plate coupling. There are a few locations globally in which there are sub-aerially exposed terranes that lie closer to the trench and overlie the inferred coupled or seismogenic portion of the plate interface. Such regions have taken on significance in subduction zone studies as they provide locations to observe the plate interface coupling effects in the near-field. In particular the Pacific coast of Costa Rica provides such a location, and there has been substantial geologic, geophysical, and geodetic research exploiting the positions of these near-trench peninsulas (Nicoya, Osa, and Burica). These sites provide near-field access to plate-interface processes, but whether they represent typical subduction zone behavior remains an open question as the deformational processes or inherited structures that have produced this anomalous topography are not well constrained. Simply put, if the existence of these sub-aerial, near-trench terranes is a result of anomalous behavior on the plate interface (as has been suggested), then their utility in providing high-fidelity near-field insight into the plate interface properties and processes is substantially reduced. Here we propose a new mechanism that could be responsible for the formation of both the Nicoya and Osa Peninsulas in the past, and is currently producing a third peninsula - the Burica Peninsula at the intersection of the Panama fracture zone and the margin. Specifically we propose that the anomalous topography along the Pacific coast of Costa Rica has been produced by repeated, great subduction earthquakes that have ruptured across the boundary separating the Cocos and Nazca plates - the subducted continuation of the Panama fracture zone. The pattern of upper-plate shortening generated by such a process (documented in the 2007 Mw 8.1 Solomon Islands earthquake, which produced co-seismic localized uplift above the subducted transform plate boundary) convolved with the migration history of the Panama triple junction (PTJ) is proposed as the mechanism to produce substantial along-margin, long-lived accretionary margin topography. Specifically we argue that repeated great subduction earthquakes that rupture across fundamental plate boundary structures can produce substantial, long-lived upper plate deformation above the inter-seismically coupled plate interface.

Furlong, Kevin P.

2014-05-01

299

Reconstructing past plate motions with abyssal hill topography  

NASA Astrophysics Data System (ADS)

The seafloor spreading history of oceanic plates is primarily reconstructed by using a combination of dated seafloor magnetic anomalies and fracture zone trends to locate Euler poles and determine rotation rates. In some regions, these conventional measures of determining spreading history do not exist and alternative methods are required. Abyssal hills are elongate, topographic highs that are created at and form parallel to the ridge axis of spreading centers. Once formed, the abyssal hills are transported onto the ridge flank and provide a record of ridge axis orientation. We propose using the orientation of abyssal hill topography to supplement existing plate motion reconstruction methods and to serve as a stand-alone method for regions where conventional methods will not apply. Our new method uses high-resolution bathymetry grids created with multibeam data with grid-node spacing of 100-200 m, determined by regional water depths. The bathymetric grids are detrended to remove depth-age relationships and spatially filtered to remove anomalous regions where seafloor age is unknown. The detrended grids are then clipped to remove anomalously deep (e.g., fracture zones) or anomalously shallow topography (e.g., seamounts). Abyssal hill orientations are determined by calculating the modal frequencies of slope azimuth for pre-defined sub-regions (e.g., 50 km x 50 km) of these modified grids. The Euler Pole is then found by an iterative least-squares method from a grid of potential Euler Poles; first a coarse grid and then a fine grid are utilized to avoid local minima. At each potential Euler Pole, the sum of the differences between predicted and observed abyssal hill trends is squared and the minimum value identifies the location of the best-fit Euler Pole. Our method was applied to the well-mapped Cocos-Pacific plate boundary along the northern East Pacific Rise for the past 3 Ma and the poorly constrained Mid-Cretaceous seafloor (84 - 120 Ma) in the southwest Pacific Ocean. The results for the northern East Pacific Rise are very encouraging and our calculated Euler Poles are within 4 degrees of the NUVEL 1a and 2 degrees of the MORVEL global relative motion models. We also applied our method to the EMAG2 magnetic anomaly intensity grids with similar encouraging results; 17 degrees NUVEL 1a & 11 degrees MORVEL. The results for the southwest Pacific are still preliminary, but the method effectively identifies regions with similar abyssal hill trends and may be useful for more detailed tectonic reconstructions of the enigmatic region.

Dahn, M. R.; Pockalny, R. A.; King, C.

2013-12-01

300

Augmented Lagrangian for shallow viscoplastic flow with topography  

NASA Astrophysics Data System (ADS)

In this paper we have developed a robust numerical algorithm for the visco-plastic Saint-Venant model with topography. For the time discretization an implicit (backward) Euler scheme was used. To solve the resulting nonlinear equations, a four steps iterative algorithm was proposed. To handle the non-differentiability of the plastic terms an iterative decomposition-coordination formulation coupled with the augmented Lagrangian method was adopted. The proposed algorithm is consistent, i.e. if the convergence is achieved then the iterative solution satisfies the nonlinear system at each time iteration. The equations for the velocity field are discretized using the finite element method, while a discontinuous Galerkin method, with an upwind choice of the flux, is adopted for solving the hyperbolic equations that describe the evolution of the thickness. The algorithm permits to solve alternatively, at each iteration, the equations for the velocity field and for the thickness. The iterative decomposition coordination formulation coupled with the augmented Lagrangian method works very well and no instabilities are present. The proposed algorithm has a very good convergence rate, with the exception of large Reynolds numbers (Re?1000), not involved in the applications concerned by the shallow viscoplastic model. The discontinuous Galerkin technique assure the mass conservation of the shallow system. The model has the exact C-property for a plane bottom and an asymptotic C-property for a general topography. Some boundary value problems were selected to analyze the robustness of the numerical algorithm and the predictive capabilities of the mechanical model. The comparison with an exact rigid flow solution illustrates the accuracy of the numerical scheme in handling the non-differentiability of the plastic terms. The influence of the mesh and of the time step are investigated for the flow of a Bingham fluid in a talweg. The role of the material cohesion in stopping a viscoplastic avalanche on a talweg with barrier was analyzed. Finally, the capacities of the model to describe the flow of a Bingham fluid on a valley from the broken wall of a reservoir situated upstream were investigated.

Ionescu, Ioan R.

2013-06-01

301

Topography of Titan from Cassini RADAR Stereo Data  

NASA Astrophysics Data System (ADS)

The RADAR instrument onboard the NASA/ESA Cassini spacecraft uses 2.17 cm microwaves to see through the hazy atmosphere of Saturn's giant satellite Titan, forming a synthetic aperture image strip up to 5000 km long with 300-1400 m resolution during a single flyby. To date, 14 such image strips have been acquired, covering a total of 22% of the surface and revealing a strikingly diverse surface shaped by many of the same processes as Earth. Since late 2006, each new image has overlapped previous coverage, providing a stereoscopic view of 5% of Titan's surface. These image overlaps can be analyzed to provide information about Titan's topography at a resolution of a few km horizontally and one hundred to several hundred meters vertically, yielding more detail than any other available source except radarclinometry (shape from shading). Stereo analysis is made challenging by speckle noise and by the link between viewing geometry and illumination: image pairs with the greatest stereo convergence angle would give the most precise height measurements but differ most in illumination and are hardest to compare. We have therefore applied a combination of both manual feature measurements and automated image matching to produce both spot estimates of local relief and digital topographic models (DTMs) of areas where the image quality is suitable. Work to improve the efficiency and geometric rigor of these methods is ongoing at both USGS and JPL. Results to date reveal relief of 1 to1.5 km between the large hydrocarbon seas of the north polar region and surrounding mountains, and 300 to 600 m in caldera-like features containing smaller lakes. These stereo heights agree closely with collocated "SARTopo" elevation estimates obtained by comparison of the overlap between neighboring beams in a single image (Stiles, et al., this conference). The relief near the lakes and seas provides an indirect constraint on the probable depth of those bodies, and hence of Titan's reserves of liquid hydrocarbons (Mitchell et al., this conference). Topography of the extensive longitudinal dunes at low latitudes, and of the presumptive topographic obstacles that divert the dunes, is more subtle and has been difficult to quantify with stereo.

Kirk, R. L.; Howington-Kraus, E.; Stiles, B. W.; Hensley, S.; Mitchell, K. L.; Cassini RADAR Team

2007-12-01

302

Signatures of Asymmetric Topography: From Measurements to Mechanisms  

NASA Astrophysics Data System (ADS)

Some landscapes exhibit the intriguing topographic characteristic that slopes facing a certain direction are systematically steeper than slopes facing other directions, even when there is no bias introduced by bedrock structure. Two fundamentally different mechanisms have been proposed to explain microclimate-induced asymmetry in regions with semi-arid to Mediterranean climates. One hypothesis is that asymmetric aggradation of sediments in a valley bottom forces a river flowing through the valley to migrate away from the side of the valley that experiences faster aggradation, leading to undercutting of the opposite bank and steepening of the adjacent hillslope. The other hypothesis is that differences in the efficiency of erosion processes between pole-facing and equator-facing slopes directly cause topographic asymmetry. Both hypotheses rely on the presence of different microclimates on opposing slopes. Thus, identifying the specific mechanism or mechanisms controlling the topographic asymmetry will be a large step toward understanding the interaction between climate and topography. To accomplish this goal, it is critical to identify measurable characteristics of asymmetric topography - including, but not limited to, the asymmetry in slopes - that may be unique signatures of specific erosional mechanisms. We have developed methods to measure asymmetry in hillslope gradient, valley spacing, and low-order valley depth (first or second order) on opposing slopes. We analyzed fourteen contiguous drainage basins ranging in size from 1.6 km2 to 16.1 km2 at Gabilan Mesa, CA. Strong topographic asymmetry and a simple underlying lithology consisting of moderately consolidated sedimentary rocks have made Gabilan Mesa a popular site for studying the cause of topographic asymmetry, yet no consensus exists on the mechanism or mechanisms causing the asymmetry. We found that the north-facing hillslopes are over 20% steeper than south-facing hillslopes and that low-order valleys on south-facing hillslopes are generally more deeply incised than low-order valleys on north-facing hillslopes. In addition to making the asymmetry measurements, we test whether topographic asymmetry exhibits dependence on distance from the channel head of the main valley bounded by the asymmetric slopes-a relationship that has been predicted to arise if lateral stream undercutting is the primary cause of valley asymmetry. Preliminary numerical modeling results suggest that particular combinations of asymmetries in these measured quantities may be diagnostic of different hypothesized mechanisms for generating the asymmetry. Thus, our measurements should provide a basis for more definitive tests of these conflicting hypotheses.

Richardson, P. W.; Perron, T.; Miller, S. R.

2011-12-01

303

Modelling formation of complex topography by the seagrass Posidonia oceanica  

NASA Astrophysics Data System (ADS)

Posidonia oceanica is a slow growing seagrass species that extends via growing rhizomes that grow only centimetres both horizontally and vertically each year. Posidonia oceanica forms topographically complex biogenic reefs of dead rhizome and sediments that are up to 4 m in height that are called "matte". This study investigates the role of slow horizontal and vertical growth of rhizomes in the formation of topographic complexity in P. oceanica matte using agent-based modelling. The simulated infilling of landscapes by P. oceanica was run over 600 iterations (years) for 10 random starts of 150 agents each. Initial infilling rates were very slow and P. oceanica had limited cover after a century of growth. Growth accelerated after 100 years but plateaued after 400 years such that after 600 years only two-thirds of the landscape was occupied by P. oceanica. The pattern of spread of agents was initially random in direction but after larger patches were formed spread was radial from these patches. The seagrass landscape was initially highly fragmented with many small separate patches made up of a few agents each, with a Landscape Division index close to 1. Between 300 and 600 years Landscape Division declined sharply to 0.42, indicating patches had coalesced into larger more continuous meadows forming a less fragmented landscape. Perimeter to area ratio of seagrass patches declined exponentially from >1 to approximately 0.2 over 600 years of simulation. The matte developed from growth of patches and its greatest height occurred in more continuously occupied cells of the grid. The topography of the reef that occupied two-thirds of the landscape after six centuries of growth could be described as a pattern of channels between reef plateaus elevated 1-2 m above channels. These results demonstrate that development in P. oceanica meadows of three-dimensional structure, in the formation of biogenic reefs, can be explained by, and is an emergent property of, slow horizontal and vertical rhizome growth rates combined with the time it takes for the accumulation of rhizomes in any region of the landscape. As such, the model provides a parsimonious explanation for the development of complex matte topography.

Kendrick, Gary A.; Marbà, Núria; Duarte, Carlos M.

2005-12-01

304

Quantifying Characteristic Length Scales and Patterns in Topography  

NASA Astrophysics Data System (ADS)

The geometry of mountain topography depends on climate, tectonic, and biologic processes that operate on different temporal and spatial scales. Quantitative measures of landscape geometry are of interest for a) identifying potential correlations with the different types of processes, and b) for comparing observed topography with calibrated landscape evolution models of different regions. Over the years, several of these geomorphic metrics have been developed and used. Most of these metrics are regional values, i.e. they are calculated over an area of specific extent. Usually a region's typical horizontal length scale, like the average ridge-to-valley-distance, is used for this. However, this value is often chosen arbitrarily from a visual assessment of the landscape. In this study we aim to develop a quantitative measure of landscape properties that identifies dominant trends in drainage spacing and orientation. This is done by taking into account variations in topographic relief on different wavelenghts. More specifically, we use an autocorrelation function that is evaluated for different directions, thereby identifying prevalent orientation of features. The area of interest is then subdivided into parts of the thus obtained size and the process repeated, so that higher order structures are revealed. The results not only provides a size for the area over which other geomorphic metrics can be calculated such as the mean slope or the hypsometric integral, but may also be used as an additional measure for the form of the landscape itself. The method is applied to three regions along the South American Pacific coastal areas between latitudes of 26°S and 40°S. The study areas have distinctly different climate and vegetation conditions, showing the effect of different landscape forms on the values obtained. Results indicate a systematic variation between the three investigated regions. In the northern drier part of the coast results indicate large variations in the obtained correlation lengths depending on orientation and distinct higher order features. This is in stark contrast to the southern most region where little variation in correlation length and only weak secondary structures can be seen.

Schmiddunser, Matthias; Ehlers, Todd A.

2014-05-01

305

Hysteresis in transient landscape topography recorded by hillslopes.  

NASA Astrophysics Data System (ADS)

On hillslopes considered to be at steady-state, hillslope morphology reflects the rate of denudation and the processes transporting sediment. Roering et al. [2007] expanded the commonly implemented non-linear sediment transport law to predict steady-state hillslope morphology as a function of erosion rate in a non-dimensional framework. This framework allows dimensionless erosion rate and relief to be predicted on the basis of topographic parameters readily predicted from high resolution digital elevation models (LiDAR). Here we extract hilltop curvature (Laplacian), hillslope gradients and hillslope lengths throughout a landscape with a well constrained uplift field in order to search for deviation in hillslope morphology when the steady-state assumption is violated. The Dragon's Back Pressure Ridge, immediately adjacent to the San Andreas Fault (SAF), is a series of south-west trending valleys, approximately perpendicular to SAF, generated as dextral fault motion carries the Pacific plate of a 'knuckle' of uplift which is pinned to the North American plate [Hilley and Arrowsmith, 2008]. As such the topography has been generated by passing through the zone of uplift and subsequently relaxing as it comes out the other side. This facilitates a space-for-time substitution and allows extraction of a time series of hillslope evolution in response to active uplift and erosion and subsequent landscape relaxation during tectonic quiescence over a period of 130 ka. We find that the morphological response of hillslopes to increased surface uplift is markedly different from the response to cessation of uplift. During increased uplift, hillslopes steepen, and hilltops get sharper. This morphological response is near instantaneous, implying that the response time scale for hillslopes to increased valley incision is extremely rapid. Subsequent drainage reorganisation occurs as uplift continues so that hillslopes tend to get longer with time spent in the uplift zone; possibly due to increased landslide frequency escalating the efficiency of hillslope sediment transport relative to valley erosion. During relaxation hilltop curvature and hillslope gradient decline gradually over 50 ka, implying that response time is much longer when a hillslope is responding to a reduction in surface uplift. Non-dimensional analysis reveals that hillslope morphology is markedly different for similar erosion rates depending on whether the landscape is being rejuvenated or relaxing. Hence our ability to interpret rates of tectonic processes based on topography alone may require a priori interpretation of the history tectonic conditions.

Hurst, M. D.; Mudd, S. M.; Attal, M.

2012-04-01

306

Role of mantle flow at the North Fiji Basin: Insights from anomalous topography  

NASA Astrophysics Data System (ADS)

The North Fiji Basin is a complex back-arc system situated between the opposite-verging Tonga and New Hebrides subduction zones. On the basis of two independent calculations, we find that the back-arc region is anomalously high with topography residuals reaching up to 2000 m above what should be isostatically supported. Our study aims to test whether a hot buoyant upwelling is required beneath the North Fiji Basin to support the observed high elevation. The mantle thermal structure beneath the North Fiji Basin is inferred from the global tomographic model S20RTS, where seismic velocity anomalies are converted to density/temperature anomalies. This thermal structure is input into a three-dimensional mantle convection code, CitcomS, and the flow-induced surface topography is calculated and compared with the observed anomalous topography. In a series of experiments, we eliminate various portions of the mantle structure to consider what type of mantle flow can support the anomalous topography. The experiments suggest that the observed topography in the North Fiji Basin is consistent with the support of hot buoyant upper mantle upwelling, and specifically rising material in the depth range from 70 to 120 km is the most critical component. A relatively thin/weak lithosphere is required to produce the high-amplitude and short-wavelength topography residuals, and the presence of discrete breaks in the plate produces further localization of flow-induced topography.

Zhang, Nan; Pysklywec, Russell N.

2006-12-01

307

Substrate Topography Determines Neuronal Polarization and Growth In Vitro  

PubMed Central

The establishment of neuronal connectivity depends on the correct initial polarization of the young neurons. In vivo, developing neurons sense a multitude of inputs and a great number of molecules are described that affect their outgrowth. In vitro, many studies have shown the possibility to influence neuronal morphology and growth by biophysical, i.e. topographic, signaling. In this work we have taken this approach one step further and investigated the impact of substrate topography in the very early differentiation stages of developing neurons, i.e. when the cell is still at the round stage and when the first neurite is forming. For this purpose we fabricated micron sized pillar structures with highly reproducible feature sizes, and analyzed neurons on the interface of flat and topographic surfaces. We found that topographic signaling was able to attract the polarization markers of mouse embryonic neurons -N-cadherin, Golgi-centrosome complex and the first bud were oriented towards topographic stimuli. Consecutively, the axon was also preferentially extending along the pillars. These events seemed to occur regardless of pillar dimensions in the range we examined. However, we found differences in neurite length that depended on pillar dimensions. This study is one of the first to describe in detail the very early response of hippocampal neurons to topographic stimuli.

Micholt, Liesbeth; Gartner, Annette; Prodanov, Dimiter; Braeken, Dries; Dotti, Carlos G.; Bartic, Carmen

2013-01-01

308

Wide-angle cornea-sclera (OCULAR) topography  

NASA Astrophysics Data System (ADS)

Most corneal topographers are slope-based instruments, measuring corneal slope based on light reflected by the cornea acting as a mirror. This mirror method limits corneal coverage to about 9 mm diameter. Both refractive surgery and contact lens fitting actually require a larger coverage than is obtainable using slope-based instruments. Height-based instruments should be able to measure a cornea/sclera area that is twice the size (four times the area) of slope-based topographers with an accuracy of a few microns. We have been testing a prototype of a new model height-based topographer manufactured by Euclid Systems. We find that single shots can produce a corneal coverage of up to 16 mm vertical and 20 mm horizontal. The heights and slopes in the corneal region have good replicability. Although the scleral region is noisier, it is the only topographer available able to measure scleral topography that is critically important to contact lens fitting. There are a number of improvements to the Euclid software and hardware that would enable it to fill an important niche in eye care and eye research.

Klein, Stanley A.; Corzine, John; Corbin, Jacob A.; Wechsler, Sheldon; Carney, Thom

2002-06-01

309

Regional Topography Variation of Earth's Inner Core Boundary  

NASA Astrophysics Data System (ADS)

The Earth's inner core grows from the freezing of the liquid outer core. The growth of the inner core provides driving forces for the thermocompositional convection in the outer core and the geodynamo through the release of latent heat and light elements. The information of the inner core boundary is thus the key to the understanding of the growth of the inner core and driving forces in outer core convection. In recent years, seismic data have revealed localized temporal and spatial changes of the inner core surface. In this study, we have performed a systematic search of events occurring from 2004 to 2013 at the distance range from 0 degree to 90 degree around Hi-net stations in Japan. We collect all the available PKiKP-PcP data and measure the PKiKP-PcP differential time residuals. The differential time residuals exhibit large variations across the seismic array. We report the characteristics of topography variation of the inner core surface in the region inferred from the seismic data.

Tian, D.; Wen, L.

2013-12-01

310

Data acquisition time constraints in elevation mapping corneal topography  

NASA Astrophysics Data System (ADS)

Elevation mapping corneal topography instruments provide an array of x, y, z data points describing the corneal surface. An advantage of elevation mapping instruments is their ability to calculate the 3D data array strictly from the instrument's geometry and calibration data; no assumptions about the corneal surface itself are needed. However, uncompensated eye movements can affect accuracy. Longitudinal eye movements occur along the z axis, due to pulmonary and cardiac pulsations. Eye rotations due to saccades and drifts are normal occurrences, as are translational body movements. An analysis of eye and body movements at the cornea's surface indicates a nearly linear relationship between data acquisition times of less than 33 msec, and the possible change in elevation at a point referenced to an instrument axis. The proportionality constant is expected to vary by a factor of about six over the range of clinical patients, since eye and body movements are exaggerated in juvenile patients, geriatric patients, and patients with poor vision. The analysis estimates an elevation change due to rotation and longitudinal translation of the eye of up to +/- 285 micrometers in 33 msec within the clinical population. This analysis indicates that when a topographer's acquisition time is greater than 100 microsecond(s) ec (during which an apparent elevation change of up to 1.0 micrometers may occur) testing on static objects may not provide a realistic measure of an instrument's clinical performance.

Baron, William S.; Baron, Sandra F.

1997-05-01

311

HESS Opinions "Topography driven conceptual modelling (FLEX-Topo)"  

NASA Astrophysics Data System (ADS)

Heterogeneity and complexity of hydrological processes offer substantial challenges to the hydrological modeller. Some hydrologists try to tackle this problem by introducing more and more detail in their models, or by setting-up more and more complicated models starting from basic principles at the smallest possible level. As we know, this reductionist approach leads to ever higher levels of equifinality and predictive uncertainty. On the other hand, simple, lumped and parsimonious models may be too simple to be realistic or representative of the dominant hydrological processes. In this commentary, a new model approach is proposed that tries to find the middle way between complex distributed and simple lumped modelling approaches. Here we try to find the right level of simplification while avoiding over-simplification. Paraphrasing Einstein, the maxim is: make a model as simple as possible, but not simpler than that. The approach presented is process based, but not physically based in the traditional sense. Instead, it is based on a conceptual representation of the dominant physical processes in certain key elements of the landscape. The essence of the approach is that the model structure is made dependent on a limited number of landscape classes in which the topography is the main driver, but which can include geological, geomorphological or land-use classification. These classes are then represented by lumped conceptual models that act in parallel. The advantage of this approach over a fully distributed conceptualisation is that it retains maximum simplicity while taking into account observable landscape characteristics.

Savenije, H. H. G.

2010-07-01

312

HESS Opinions "Topography driven conceptual modelling (FLEX-Topo)"  

NASA Astrophysics Data System (ADS)

Heterogeneity and complexity of hydrological processes offer substantial challenges to the hydrological modeller. Some hydrologists try to tackle this problem by introducing more and more detail in their models, or by setting-up more and more complicated models starting from basic principles at the smallest possible level. As we know, this reductionist approach leads to ever higher levels of equifinality and predictive uncertainty. On the other hand, simple, lumped and parsimonious models may be too simple to be realistic or representative of the dominant hydrological processes. In this commentary, a new approach is proposed that tries to find the middle way between complex distributed and simple lumped modelling approaches. Here we try to find the right level of simplification while avoiding over-simplification. Paraphrasing Einstein, the maxim is: make a model as simple as possible, but not simpler than that. The approach presented is process based, but not physically based in the traditional sense. Instead, it is based on a conceptual representation of the dominant physical processes in certain key elements of the landscape. The essence of the approach is that the model structure is made dependent on a limited number of landscape classes in which the topography is the main driver, but which can include geological, geomorphological or land-use classification. These classes are then represented by lumped conceptual models that act in parallel. The advantage of this approach over a fully distributed conceptualisation is that it retains maximum simplicity while taking into account observable landscape characteristics.

Savenije, H. H. G.

2010-12-01

313

Global Resurfacing on Venus: Implications on Plume Motion and Topography  

NASA Astrophysics Data System (ADS)

ABSTRACT A global resurfacing event is supposed to have taken place on Venus (1; 2). Today, however,Venus is a one-plate planet, i.e. the complete surface is covered by one immobile plate. Such a behaviour is also observed in numerical mantle convection models with variable viscosity. Moresi and Solomatov (3) presented a 2D study of mantle convection with a strong temperature dependence and an additional stress dependence of the viscosity. While the strong temperature dependence causes a cold, rigid and immobile surface atop the convective cycle in the planet's mantle, the additional stress dependence leads to deformation zones in the so-called stagnant lid. By using a 3D study Trompert and Hansen (4) also showed that in this way pieces of the surface are mobilised and take part in the convective cycle. The amount of surface subducted and the temporal evolution of the system depend on the strength of the stress dependence. With increasing stress dependence the surface is more strongly weakened (5) and subduction events occur more rapidly (6). Thus we find that for a low stress dependence sporadic subduction events of the complete surface interrupt otherwise stagnant lid convection. The effect of the subduction of cold, rigid material on both the plume motion and the surface topography is investigated.

Stein, C.; Hansen, U.

2008-09-01

314

The role of bedrock topography on subsurface storm flow  

USGS Publications Warehouse

We conducted a detailed study of subsurface flow and water table response coupled with digital terrain analysis (DTA) of surface and subsurface features at the hillslope scale in Panola Mountain Research Watershed (PMRW), Georgia. Subsurface storm flow contributions of macropore and matrix flow in different sections along an artificial trench face were highly variable in terms of timing, peak flow, recession characteristics, and total flow volume. The trench flow characteristics showed linkages with the spatial tensiometer response defining water table development upslope. DTA of the ground surface did not capture the observed spatial patterns of trench flow or tensiometric response. However, bedrock surface topographic indices significantly improved the estimation of spatial variation of flow at the trench. Point-scale tensiometric data were also more highly correlated with the bedrock surface-based indices. These relationships were further assessed for temporal changes throughout a rainstorm. Linkages between the bedrock indices and the trench flow and spatial water table responses improved during the wetter periods of the rainstorm, when the hillslope became more hydrologically connected. Our results clearly demonstrate that in developing a conceptual framework for understanding the mechanisms of runoff generation, local bedrock topography may be highly significant at the hillslope scale in some catchments where the bedrock surface acts as a relatively impermeable boundary.

Freer, J.; McDonnell, J. J.; Beven, K. J.; Peters, N. E.; Burns, D. A.; Hooper, R. P.; Aulenbach, B.; Kendall, C.

2002-01-01

315

Contact Line Pinning by Microfabricated Patterns: Effects of Microscale Topography  

PubMed Central

We study how the microscale topography of a solid surface affects the apparent advancing and receding angles at the contact line of a liquid drop pinned to this surface. Photolithographic methods are used to produce continuous circular polymer rings of varying cross-sectional size and shape on hydrophilic silicon wafer surfaces. Drops of water and glycerol are dispensed into the areas bounded by these rings, and critical apparent advancing and receding angles are measured and correlated with the parameters that characterize the ring cross-section. For much of the examined parameter space, the apparent critical angles are independent of ring height and width and are determined primarily by the slope of the ring's sidewalls, consistent with a model due to Gibbs. For ring heights below a few micrometers, the critical angles decrease below the values predicted by the sidewall slopes alone. These results provide data for calculation of hysteresis on naturally rough surfaces, and demonstrate a simple method for controlling and enhancing contact line pinning on solid surfaces.

Kalinin, Yevgeniy V.; Berejnov, Viatcheslav; Thorne, Robert E.

2010-01-01

316

Wind-Related Topography in Phoenix's Region of Mars (Animation)  

NASA Technical Reports Server (NTRS)

[figure removed for brevity, see original site] Click on image for animation

This movie shifts from a global zoom indicating the Phoenix landing area on Mars to a topographical map indicating relative elevations in the landing region. The elevations could affect wind patterns at the site.

In particular, Phoenix is in a broad, shallow valley. The edge of the valley, about 150 meters (500 feet) above the floor, may provide enough of a slope to the east of Phoenix to explain winds coming from the east during nights at the site. Cooler, denser air could be sinking down the slope and toward the lander.

Atmospheric scientists on the Phoenix team are analyzing wind patterns to distiguish effects of nearby topography from larger-scale movement of the atmosphere in the polar region.

The elevation information for this topographical mapping comes from the Mars Orbiter Laser Altimeter on NASA's Mars Global Surveyor orbiter. The blue-coded area is the valley floor. Orange and yellow indicate relatively higher elevations.

The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver. JPL managed the Mars Global Surveyor mission for the NASA Science Mission Directorate.

2008-01-01

317

Numerical investigation of Rayleigh-wave propagation on topography surface  

NASA Astrophysics Data System (ADS)

Rayleigh waves propagate along the free surface and vanish exponentially in the vertical direction, which suggests that they are strongly influenced by free-surface topography. Since they have strong energy, Rayleigh waves are the most damaging wave during earthquake, and have strong noise in petroleum exploration. Because of their strong energy and the dispersive characteristic in a vertically inhomogeneous earth, however, they are widely utilized in environmental and engineering geophysics. To study how Rayleigh-wave behaves with topographic free surface, we proposed a finite difference scheme incorporating the acoustic/elastic interface approach into a 'stair-case' mesh for modeling surface-wave propagation. The effectiveness and accuracy were demonstrated by modeling results of a two-dimensional homogeneous half-space model with a slope free surface. The characteristics of Rayleigh-wave propagation strongly affected by topographic free surface are demonstrated by numerical examples of three simple topographic models. The most important revealed by modeling results is that, the dispersion characteristics are determined by the thicknesses of the underground layers in the direction perpendicular to the slope free surface. The middle of receiver-spread assumption was further verified, which provides a guideline to applying surface-wave methods to near-surface problems.

Wang, Limin; Luo, Yinhe; Xu, Yixian

2012-11-01

318

A novel digital x-ray topography system  

NASA Astrophysics Data System (ADS)

X-ray topography (XRT) is recognized as being a powerful tool for directly imaging defects in single crystals, semiconductor wafers and epitaxially grown layers. The timely identification of defects can lead to increased yields and significant cost savings in wafer processing. The primary limitation to its general usage within the semiconductor community has been the difficulty in system use and difficulty in integration into an in-line analytical tool. We have developed a novel, high-speed digital XRT method that can be implemented on a standard high-resolution x-ray diffraction (HRXRD) system equipped with a wafer translation stage and a microfocus tube (or a small aperture in front of a standard point source). It is also appropriate for an in-line fab tool with robot loading and automated operation. In this paper, we discuss the theory and present examples from work undertaken on a variety of materials, including: silicon, compound semiconductors and ionic crystals. Reflection and transmission methods are illustrated. Data were collected on a HRXRD system with a microfocus source and a CCD detector, and an innovative software integration and processing algorithm. Algorithms for full automation of the alignment, exposure and data collection processes have been worked out. It is estimated that the dedicated XRT tool now in prototype form will be capable of scanning a full 300 mm wafer in reflection in under two hours at 50 ?m resolution and one hour at 15 ?m resolution.

Bowen, D. K.; Wormington, M.; Feichtinger, P.

2003-05-01

319

Extraction of Martian valley networks from digital topography  

NASA Technical Reports Server (NTRS)

We have developed a novel method for delineating valley networks on Mars. The valleys are inferred from digital topography by an autonomous computer algorithm as drainage networks, instead of being manually mapped from images. Individual drainage basins are precisely defined and reconstructed to restore flow continuity disrupted by craters. Drainage networks are extracted from their underlying basins using the contributing area threshold method. We demonstrate that such drainage networks coincide with mapped valley networks verifying that valley networks are indeed drainage systems. Our procedure is capable of delineating and analyzing valley networks with unparalleled speed and consistency. We have applied this method to 28 Noachian locations on Mars exhibiting prominent valley networks. All extracted networks have a planar morphology similar to that of terrestrial river networks. They are characterized by a drainage density of approx.0.1/km, low in comparison to the drainage density of terrestrial river networks. Slopes of "streams" in Martian valley networks decrease downstream at a slower rate than slopes of streams in terrestrial river networks. This analysis, based on a sizable data set of valley networks, reveals that although valley networks have some features pointing to their origin by precipitation-fed runoff erosion, their quantitative characteristics suggest that precipitation intensity and/or longevity of past pluvial climate were inadequate to develop mature drainage basins on Mars.

Stepinski, T. F.; Collier, M. L.

2004-01-01

320

Topography of Vesta from Dawn FC stereo images  

NASA Astrophysics Data System (ADS)

The Dawn mission has completed its Survey and High Altitude Mapping Orbit (HAMO) phases at Vesta and is currently in its Low Altitude Mapping Orbit (LAMO) [1]. From the Survey orbit (altitude ~2,700 km) the Dawn Framing Camera (FC) [2] acquired 1,179 clear filter images with a mean image resolution of 256 m/pixel whereas from the HAMO orbit (~700 km altitude) there are 2,674 clear filter images with a mean resolution of 63 m/pixel. In both mapping phases the surface was imaged several times under similar illumination conditions (Sun elevation and azimuth), but different viewing conditions (by tilting the spacecraft). This allows to analyze the images stereoscopically and to construct stereo topographic maps. The topography is particularly important, because it is essential for derivation of physical properties of Vesta, precise ortho-image registration, mosaicking, and map generation of monochrome/color FC images and VIR images, quantitative geomorphologic analysis, and precise photometric analysis (from detailed local surface inclination).

Preusker, F.; Scholten, F.; Matz, K.-D.; Roatsch, T.; Jaumann, R.; Raymond, C. A.; Russell, C. T.

2012-09-01

321

Discriminant analysis of functional optical topography for schizophrenia diagnosis  

NASA Astrophysics Data System (ADS)

Abnormal prefrontal function plays a central role in the cognition deficits of schizophrenic patients; however, the character of the relationship between discriminant analysis and prefrontal activation remains undetermined. Recently, evidence of low prefrontal cortex (PFC) activation in individuals with schizophrenia has also been found during verbal fluency tests (VFT) and other cognitive tests with several neuroimaging methods. The purpose of this study is to assess the hemodynamic changes of the PFC and discriminant analysis between schizophrenia patients and healthy controls during VFT task by utilizing functional optical topography. A total of 99 subjects including 53 schizophrenic patients and 46 age- and gender-matched healthy controls were studied. The results showed that the healthy group had larger activation in the right and left PFC than in the middle PFC. Besides, the schizophrenic group showed weaker task performance and lower activation in the whole PFC than the healthy group. The result of the discriminant analysis showed a significant difference with P value <0.001 in six channels (CH 23, 29, 31, 40, 42, 52) between the schizophrenic and healthy groups. Finally, 68.69% and 71.72% of subjects are correctly classified as being schizophrenic or healthy with all 52 channels and six significantly different channels, respectively. Our findings suggest that the left PFC can be a feature region for discriminant analysis of schizophrenic diagnosis.

Chuang, Ching-Cheng; Nakagome, Kazuyuki; Pu, Shenghong; Lan, Tsuo-Hung; Lee, Chia-Yen; Sun, Chia-Wei

2014-01-01

322

Single cell electric impedance topography: Mapping membrane capacitance  

PubMed Central

Single-cell electric impedance topography (sceTopo), a technique introduced here, maps the spatial distribution of capacitance (i.e. displacement current) associated with the membranes of isolated, living cells. Cells were positioned in the center of a circular recording chamber surrounded by eight electrodes. Electrodes were evenly distributed on the periphery of the recording chamber. Electric impedance measured between adjacent electrode pairs (10 kHz–5 MHz) was used to construct topographical maps of the spatial distribution of membrane capacitance. Xenopus Oocytes were used as a model cell to develop sceTopo because these cells consist of two visually distinguishable hemispheres, each with distinct membrane composition and structure. Results showed significant differences in the imaginary component of the impedance between the two oocyte hemispheres. In addition, the same circumferential array was used to map the size of the extracellular electrical shunt path around the cell, providing a means to estimate the location and shape of the cell in the recording chamber.

Dharia, Sameera; Ayliffe, Harold E.

2010-01-01

323

Surface topography effects in protein adsorption on nanostructured carbon allotropes.  

PubMed

We report a molecular dynamics (MD) simulation study of protein adsorption on the surface of nanosized carbon allotropes, namely single-walled carbon nanotubes (SWNT) considering both the convex outer surface and the concave inner surface, together with a graphene sheet for comparison. These systems are chosen to investigate the effect of the surface curvature on protein adsorption at the same surface chemistry, given by sp(2) carbon atoms in all cases. The simulations show that proteins do favorably interact with these hydrophobic surfaces, as previously found on graphite which has the same chemical nature. However, the main finding of the present study is that the adsorption strength does depend on the surface topography: in particular, it is slightly weaker on the outer convex surfaces of SWNT and is conversely enhanced on the inner concave SWNT surface, being therefore intermediate for flat graphene. We additionally find that oligopeptides may enter the cavity of common SWNT, provided their size is small enough and the tube diameter is large enough for both entropic and energetic reasons. Therefore, we suggest that proteins can effectively be used to solubilize in water single-walled (and by analogy also multiwalled) carbon nanotubes through adsorption on the outer surface, as indeed experimentally found, and to functionalize them after insertion of oligopeptides within the cavity of nanotubes of appropriate size. PMID:23517008

Raffaini, Giuseppina; Ganazzoli, Fabio

2013-04-16

324

Crater Topography on Titan: Implications for Landscape Evolution  

NASA Technical Reports Server (NTRS)

We present a comprehensive review of available crater topography measurements for Saturn's moon Titan. In general, the depths of Titan's craters are within the range of depths observed for similarly sized fresh craters on Ganymede, but several hundreds of meters shallower than Ganymede's average depth vs. diameter trend. Depth-to-diameter ratios are between 0.0012 +/- 0.0003 (for the largest crater studied, Menrva, D approximately 425 km) and 0.017 +/- 0.004 (for the smallest crater studied, Ksa, D approximately 39 km). When we evaluate the Anderson-Darling goodness-of-fit parameter, we find that there is less than a 10% probability that Titan's craters have a current depth distribution that is consistent with the depth distribution of fresh craters on Ganymede. There is, however, a much higher probability that the relative depths are uniformly distributed between 0 (fresh) and 1 (completely infilled). This distribution is consistent with an infilling process that is relatively constant with time, such as aeolian deposition. Assuming that Ganymede represents a close 'airless' analogue to Titan, the difference in depths represents the first quantitative measure of the amount of modification that has shaped Titan's surface, the only body in the outer Solar System with extensive surface-atmosphere exchange.

Neish, Catherine D.; Kirk, R.L.; Lorenz, R. D.; Bray, V. J.; Schenk, P.; Stiles, B. W.; Turtle, E.; Mitchell, K.; Hayes, A.

2013-01-01

325

[Quantitative evaluation of corneal irregular astigmatism using computed corneal topography].  

PubMed

A new method was developed to quantify corneal irregular astigmatism using computed corneal topography. Refractive powers on a mire ring projected on a toric plane (regular cornea) can be approximated to follow a sine curve. The discrepancy between the approximated sine curve and actual refractive powers was calculated and employed as a parameter of corneal irregular astigmatism. Artificial precision models of a sphere and a toric plane showed similar parameters and the least amount of irregular astigmatism (0.02-0.05D). Consecutive measurements on normal human corneas displayed a reproducible irregular astigmatism range of 0.10-0.25D. Irregular astigatism of the eyes with pterygium was significantly greater than that of normal human controls even from early stages of the disease. Surgery for removal of the pterygium normalized the amount of regular astigmatism regardless of the size of the pterygium, but irregular astigmatism of the eyes with large pterygium (the apex reaching within the central 2 mm cornea) remained at a significantly higher than normal level. It was concluded that the current method enables a quantitative analysis of corneal irregular astigmatism, independent by the amount of regular antigmatism. PMID:7732920

Tomidokoro, A; Oshika, T

1995-03-01

326

Hydrodynamic modeling for river delta salt marshes using lidar topography  

NASA Astrophysics Data System (ADS)

Topographic data from lidar and multi-beam sonar create new challenges for hydrodynamic models of estuaries, tidelands, and river deltas. We now can readily obtain detailed elevation data on 1 m scales and finer, but solving hydrodynamics with model grid cells at these small scales remains computationally prohibitive (primarily because of the small time step required for small grid cells). Practical estuarine models for the next decade or so will likely have grid scales in the range of 5 to 15 m. So how should we handle known subgrid-scale features? Simply throwing out known data does not seem like a good idea, but there is no consensus on how best to incorporate knowledge of subgrid topography into either hydrodynamic or turbulence models. This presentation discusses both the theoretical foundations for modeling subgrid-scale features and the challenges in applying these ideas in the salt marshes of a river delta. The subgrid problem highlights some important areas for field and laboratory research to provide calibration parameters for new models that upscale the effects of known subgrid features.

Hodges, Ben R.

2014-05-01

327

Topography of the retinal ganglion cell layer of Xenopus.  

PubMed Central

Cell distribution in the retinal ganglion cell layer of Xenopus laevis was studied by electron microscopy and the retinal wholemount method. Unlike the familiar stratification of the retina, the ganglion cell perikarya and their axons were localised in the same layer, but strictly segregated in alternate rows converging in a radial pattern on the optic disc. Rows of perikarya (retinal cords) were two to ten cells wide and clearly defined for a little more than half the distance between the optic disc and the ora serrata. Detailed analysis of 25% of the retinal surface showed higher cell density (about 3500 cells/mm2) in the centrodorsal region than in the periphery (about 2000 cells/mm2). The higher density regions represent a weak visual streak having no nasotemporal asymmetry. After staining with cresyl violet, the majority of cells appeared to be small (10 micron diameter) with very little Nissl substance. The cytoplasm was scant; this was confirmed by electron microscopy. The difference between the total cell count (68470 +/- 7360) and the total axon count in the optic nerve (Wilson, 1971) suggests a population of 15% non-ganglionic cells (glia and amacrine cells) in the retinal ganglion cell layer. Retinal ganglion cell topography in Xenopus may have relevance to studies on retinal growth and retinotopy. The functional significance of the weak visual streak in Xenopus is consistent with a limited need for visual acuity. Images Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5

Graydon, M L; Giorgi, P P

1984-01-01

328

Shielded piezoresistive cantilever probes for nanoscale topography and electrical imaging  

NASA Astrophysics Data System (ADS)

This paper presents the design and fabrication of piezoresistive cantilever probes for microwave impedance microscopy (MIM) to enable simultaneous topographic and electrical imaging. Plasma enhanced chemical vapor deposited Si3N4 cantilevers with a shielded center conductor line and nanoscale conductive tip apex are batch fabricated on silicon-on-insulator wafers. Doped silicon piezoresistors are integrated at the root of the cantilevers to sense their deformation. The piezoresistive sensitivity is 2 nm for a bandwidth of 10 kHz, enabling topographical imaging with reasonable speed. The aluminum center conductor has a low resistance (less than 5 ?) and small capacitance (?1.7 pF) to ground; these parameters are critical for high sensitivity MIM imaging. High quality piezoresistive topography and MIM images are simultaneously obtained with the fabricated probes at ambient and cryogenic temperatures. These new piezoresistive probes remarkably broaden the horizon of MIM for scientific applications by operating with an integrated feedback mechanism at low temperature and for photosensitive samples.

Yang, Yongliang; Ma, Eric Yue; Cui, Yong-Tao; Haemmerli, Alexandre; Lai, Keji; Kundhikanjana, Worasom; Harjee, Nahid; Pruitt, Beth L.; Kelly, Michael; Shen, Zhi-Xun

2014-04-01

329

Automated object-based classification of topography from SRTM data  

PubMed Central

We introduce an object-based method to automatically classify topography from SRTM data. The new method relies on the concept of decomposing land-surface complexity into more homogeneous domains. An elevation layer is automatically segmented and classified at three scale levels that represent domains of complexity by using self-adaptive, data-driven techniques. For each domain, scales in the data are detected with the help of local variance and segmentation is performed at these appropriate scales. Objects resulting from segmentation are partitioned into sub-domains based on thresholds given by the mean values of elevation and standard deviation of elevation respectively. Results resemble reasonably patterns of existing global and regional classifications, displaying a level of detail close to manually drawn maps. Statistical evaluation indicates that most of classes satisfy the regionalization requirements of maximizing internal homogeneity while minimizing external homogeneity. Most objects have boundaries matching natural discontinuities at regional level. The method is simple and fully automated. The input data consist of only one layer, which does not need any pre-processing. Both segmentation and classification rely on only two parameters: elevation and standard deviation of elevation. The methodology is implemented as a customized process for the eCognition® software, available as online download. The results are embedded in a web application with functionalities of visualization and download.

Dragut, Lucian; Eisank, Clemens

2012-01-01

330

Crater topography on Titan: implications for landscape evolution  

USGS Publications Warehouse

We present a comprehensive review of available crater topography measurements for Saturn’s moon Titan. In general, the depths of Titan’s craters are within the range of depths observed for similarly sized fresh craters on Ganymede, but several hundreds of meters shallower than Ganymede’s average depth vs. diameter trend. Depth-to-diameter ratios are between 0.0012 ± 0.0003 (for the largest crater studied, Menrva, D ~ 425 km) and 0.017 ± 0.004 (for the smallest crater studied, Ksa, D ~ 39 km). When we evaluate the Anderson–Darling goodness-of-fit parameter, we find that there is less than a 10% probability that Titan’s craters have a current depth distribution that is consistent with the depth distribution of fresh craters on Ganymede. There is, however, a much higher probability that the relative depths are uniformly distributed between 0 (fresh) and 1 (completely infilled). This distribution is consistent with an infilling process that is relatively constant with time, such as aeolian deposition. Assuming that Ganymede represents a close ‘airless’ analogue to Titan, the difference in depths represents the first quantitative measure of the amount of modification that has shaped Titan’s surface, the only body in the outer Solar System with extensive surface–atmosphere exchange.

Neish, C. D.; Kirk, R. L.; Lorenz, R. D.; Bray, V. J.; Schenk, P.; Stiles, B. W.; Turtle, E.; Mitchell, K.; Hayes, A.

2013-01-01

331

Crustal structure of Mars from gravity and topography  

NASA Technical Reports Server (NTRS)

Mars Orbiter Laser Altimeter (MOLA) topography and gravity models from 5 years of Mars Global Surveyor (MGS) spacecraft tracking provide a window into the structure of the Martian crust and upper mantle. We apply a finite-amplitude terrain correction assuming uniform crustal density and additional corrections for the anomalous densities of the polar caps, the major volcanos, and the hydrostatic flattening of the core. A nonlinear inversion for Moho relief yields a crustal thickness model that obeys a plausible power law and resolves features as small as 300 km wavelength. On the basis of petrological and geophysical constraints, we invoke a mantle density contrast of 600 kg m-3; with this assumption, the Isidis and Hellas gravity anomalies constrain the global mean crustal thickness to be >45 km. The crust is characterized by a degree 1 structure that is several times larger than any higher degree harmonic component, representing the geophysical manifestation of the planet's hemispheric dichotomy. It corresponds to a distinction between modal crustal thicknesses of 32 km and 58 km in the northern and southern hemispheres, respectively. The Tharsis rise and Hellas annulus represent the strongest components in the degree 2 crustal thickness structure. A uniform highland crustal thickness suggests a single mechanism for its formation, with subsequent modification by the Hellas impact, erosion, and the volcanic construction of Tharsis. The largest surviving lowland impact, Utopia, post-dated formation of the crustal dichotomy. Its crustal structure is preserved, making it unlikely that the northern crust was subsequently thinned by internal processes.

Neumann, G. A.; Zuber, M. T.; Wieczorek, M. A.; McGovern, P. J.; Lemoine, F. G.; Smith, D. E.

2004-01-01

332

Nicotine metabolite ratio predicts smoking topography and carcinogen biomarker level  

PubMed Central

Background Variability in smoking behavior is partly attributable to heritable individual differences in nicotine clearance rates. This can be assessed as the ratio of the metabolites cotinine (COT) and 3'-hydroxycotinine (3HC) (referred to as the nicotine metabolism ratio, NMR). We hypothesized that faster NMR would be associated with greater cigarette puff volume and higher levels of total NNAL, a carcinogen biomarker. Methods Current smokers (n=109) smoked one of their preferred brand cigarettes through a smoking topography device and provided specimens for NMR and total NNAL assays. Results Faster nicotine metabolizers (third and fourth quartiles versus first quartile) based on the NMR exhibited significantly greater total puff volume and total NNAL; the total puff volume by daily cigarette consumption interaction was a significant predictor of total NNAL level. Conclusion A heritable biomarker of nicotine clearance predicts total cigarette puff volume and total NNAL. Impact If validated, the NMR could contribute to smoking risk assessment in epidemiological studies and potentially in clinical practice.

Strasser, Andrew A.; Benowitz, Neal L.; Pinto, Angela G.; Tang, Kathy Z.; Hecht, Stephen S.; Carmella, Steve G.; Tyndale, Rachel F.; Lerman, Caryn E.

2010-01-01

333

STS-99 Shuttle Radar Topography Mission Stability and Control  

NASA Technical Reports Server (NTRS)

The Shuttle Radar Topography Mission (SRTM) flew aboard Space Shuttle Endeavor February 2000 and used interferometry to map 80% of the Earth's landmass. SRTM employed a 200-foot deployable mast structure to extend a second antenna away from the main antenna located in the Shuttle payload bay. Mapping requirements demanded precision pointing and orbital trajectories from the Shuttle on-orbit Flight Control System (PCS). Mast structural dynamics interaction with the FCS impacted stability and performance of the autopilot for attitude maneuvers and pointing during mapping operations. A damper system added to ensure that mast tip motion remained with in the limits of the outboard antenna tracking system while mapping also helped to mitigate structural dynamic interaction with the FCS autopilot. Late changes made to the payload damper system, which actually failed on-orbit, required a redesign and verification of the FCS autopilot filtering schemes necessary to ensure rotational control stability. In-flight measurements using three sensors were used to validate models and gauge the accuracy and robustness of the pre-mission notch filter design.

Hamelin, Jennifer L.; Jackson, Mark C.; Kirchwey, Christopher B.; Pileggi, Roberto A.

2001-01-01

334

Display of Magellan SAR and Topography Data in Google Earth  

NASA Astrophysics Data System (ADS)

Much of our understanding of the geodynamics and geology of Venus has been derived from radar imagery and topography from the Magellan mission (NASA 1989-1994). These data were archived at the Planetary Data System (PDS) and are easily and freely available. Unfortunately, the Magellan Venus data are far less accessible than those of the Earth, Mars, and the Moon. Data for these bodies are available via the Google Earth geobrowser, allowing anyone to easily explore the latest imagery and surface information. In an effort to promote public interest in Venus, we have created content for Google Earth that displays three types of information from the Magellan-era. First the FMAP compilation of the Magellan SAR imagery has been assembled into a global overlay image for rapid panning and zooming. Second, the reprocessed altimetry data [Ford and Pettingell, 1992; Rappaport et al. 1999] have been carefully edited and merged with a global spherical harmonic analysis [Wieczorek, 2007] to form a 10-km resolution global DEM of the planet. Finally the IAU feature names along with the content from ``The Face of Venus'' [Roth and Wall, 1995] have been assembled as an overlay to provide basic naming and geology information. A draft version of this material is available by adding this Network Link in Google Earth: http://byss.arc.nasa.gov/ge-venus/venus.kml. We welcome comments and suggestions on how to best represent Venus data for the public

Beyer, R. A.; Mehnert, E.; Sandwell, D. T.; Kolb, E.; Austin Foulkes, J.; Schwehr, K.; Johnson, C. L.

2012-12-01

335

Residual topography in the north-central Mediterranean: A product of underlying mantle flow?  

NASA Astrophysics Data System (ADS)

The north-central Mediterranean demonstrates an interesting history of horizontal and vertical tectonics, for which the responsible dynamical mechanisms are not well understood. Here we investigate the potential role of interpreted mantle flow in generating anomalous present-day elevation in the region. We inferred underlying mantle structure from regional seismic tomography. A tomography section cutting approximately perpendicular through the northern Apennines was translated into the temperature domain and the temperature anomalies were then superimposed into a 2D thermo-mechanical numerical model. The 2D thermo-mechanical model was then used to predict lithosphere-upper mantle deformation. Residual topography (i.e., non-isostatic topography) for the Mediterranean region was calculated from the global CRUST2.0 database and from independent estimates of crustal structure. The observed residual topography was then compared with the surface dynamic topography signal predicted by the computed mantle flow. A spatial correlation was found between the dynamic effects of underlying mantle structure and 1) the observed negative residual topography signal over the Adriatic Sea, 2) a positive residual topography signal in the Alpi Apuane region of Italy, and 3) a slight negative residual topography signal in the Liguro-Provencal basin. We also tested the response of the surface topography to various configurations of the surface plates, including variably strong lithosphere and the presence of a weak mantle wedge and weak zones in the crust. While it was found that the properties of the overlying plate heavily influence the degree of correlation, the results demonstrate that underlying mantle structure has the potential to play a significant role in supporting the observed residual topography anomalies along the investigated profile.

Shaw, M.; Pysklywec, R. N.

2005-12-01

336

Measurement of fine dynamic changes of corneal topography by use of interferometry  

NASA Astrophysics Data System (ADS)

Paper presents results of in vivo measurements of dynamic variations of the corneal topography by use of the Twyman Green interferometer. Sequence of interferograms were recorded by the CCD camera and stored in the computer memory. Then the fringe tracking method was used separately to each interferogram giving the phase surface of the wave reflected from the cornea in the numerical form. Results from neighboring interferograms were subtracted giving new sequence of changes of the corneal topography within 40 ms. Obtained results show the complex space distribution of the corneal topography variations.

Kasprzak, Henryk T.; Jaronski, Jaroslaw W.

2002-06-01

337

Resurfacing events on Venus: Implications on plume dynamics and surface topography  

NASA Astrophysics Data System (ADS)

Global resurfacing events explain the relatively young and uniformly aged surface of Venus. In numerical models featuring these events a variety of plume classes occur ranging from strong, stable to smaller, wind-driven upwellings. We investigate this plume dynamics in a 3D Cartesian geometry paying special attention to the surface topography. While the stable upwellings of the stagnant-lid phase correlate with an elevation of the surface, the wind-driven upwellings of the resurfacing phase do not necessarily correlate with a positive topography signal. We rather observe that a thick plate can dominate the topography above upwellings.

Stein, C.; Fahl, A.; Hansen, U.

2010-01-01

338

New rules for the old game of porous micro- and nanoparticle synthesis.  

PubMed

The field of research focused on the synthesis of micro- and nanoparticles has not yet conclusively addressed the challenges presented by the hierarchical control of surface topography. An established approach to hierarchical multicomposite nanostructured particles is based on template-directed synthesis, while spectacular advances have been reached in nanoparticle fabrication based on a variety of physicochemical processes. These results exemplify an additive route to hierarchical control, where multiple layers are stacked onto each other or where discretely identifiable particles are assembled into a larger spherical conglomerate. We present here a new strategy for the synthesis of micro- and nanoparticles, which we refer to as "textured isomorphic synthesis", that uses only the toolbox of inorganic chemistry coupled to the physics of cavitation, viscous fingering, and bubble nucleation. The results illustrate a topological route to hierarchical control of particle topography where dimples or holes are deterministically introduced on a planar substrate later transformed into isomorphic hollow spherical micro- and nanostructures. PMID:18166064

Dell'Acqua-Bellavitis, Ludovico M; Siegel, Richard W

2008-02-01

339

Modeling Floods in Athabasca Valles, Mars, Using CTX Stereo Topography  

NASA Astrophysics Data System (ADS)

Among the most remarkable landforms on Mars are the outflow channels, which suggest the occurrence of catastrophic water floods in the past. Athabasca Valles has long been thought to be the youngest of these channels [1-2], although it has recently become clear that the young crater age applies to a coating lava flow [3]. Simulations with a 2.5-dimensional flood model have provided insight into the details of flood dynamics but have also demonstrated that the Digital Elevation Model (DEM) from the Mars Orbiter Laser Altimeter (MOLA) Mission Experiment Gridded Data Records includes significant artifacts at this latitude at the scales relevant for flood modeling [4]. In order to obtain improved topography, we processed stereo images from the Context Camera (CTX) of the Mars Reconnaissance Orbiter (MRO) using methods developed for producing topographic models of the Moon with images from the Lunar Reconnaissance Orbiter Camera, a derivative of the CTX camera. Some work on flood modeling with CTX stereo has been published by [5], but we will present several advances, including corrections to the published CTX optical distortion model and improved methods to combine the stereo and MOLA data. The limitations of current methods are the accuracy of control to MOLA and the level of error introduced when the MRO spacecraft is not in a high-stability mode during stereo imaging, leading to jitter impacting the derived topography. Construction of a mosaic of multiple stereo pairs, controlled to MOLA, allows us to consider flow through the cluster of streamlined islands in the upper part of the channel [6], including what is suggested to be the best example of flood-formed subaqueous dunes on Mars [7]. We will present results from running a flood model [4, 8] through the high-resolution (100 m/post) DEM covering the streamlined islands and subaqueous dunes, using results from a lower-resolution model as a guide to the inflow. By considering a range of flow levels below estimated peak flow, we can examine the flow behavior at the site of the apparent subaqueous dunes and, in particular, assess whether the flow in this area is uniquely conducive to the formation of such bedforms [e.g., 9]. [1] Berman D. C. and Hartmann W. K. (2002) Icarus 159, 1-17. [2] Burr D. M. et al. (2002) Icarus 159, 53-73. [3] Jaeger W. L. et al. (2010) Icarus 205, 230-243. [4] Keszthelyi L. P. et al. (2007) GRL 34, L21206. [5] McIntyre et al. (2012) JGR 117, E03009. [6] Burr D. (2005) Geomorphology 69, 242-252. [7] Burr D. M. et al. (2004) Icarus 171, 68-83. [8] Denlinger R. P. and O'Connell D. R. H. (2008) J. Hyd. Eng. 134, 1590-1602. [9] Kleinhans M. G. (2005) JGR 110, E12003.

Dundas, C. M.; Keszthelyi, L. P.; Denlinger, R. P.; Thomas, O. H.; Galuszka, D.; Hare, T. M.; Kirk, R. L.; Howington-Kraus, E.; Rosiek, M.

2012-12-01

340

Neotectonics and intraplate continental topography of the northern Alpine Foreland  

NASA Astrophysics Data System (ADS)

Research on neotectonics and related seismicity has hitherto been mostly focused on active plate boundaries that are characterized by generally high levels of earthquake activity. Current seismic hazard estimates for intraplate domains are mainly based on probabilistic analyses of historical and instrumental earthquake catalogues. The accuracy of such hazard estimates is limited by the fact that available catalogues are restricted to a few hundred years, which, on geological time scales, is insignificant and not suitable for the assessment of tectonic processes controlling the observed earthquake activity. More reliable hazard prediction requires access to high quality data sets covering a geologically significant time span in order to obtain a better understanding of processes controlling on-going intraplate deformation. The Alpine Orogen and the intraplate sedimentary basins and rifts in its northern foreland are associated with a much higher level of neotectonic activity than hitherto assumed. Seismicity and stress indicator data, combined with geodetic and geomorphologic observations, demonstrate that deformation of the Northern Alpine foreland is still on-going and will continue in the future. This has major implications for the assessment of natural hazards and the environmental degradation potential of this densely populated area. We examine relationships between deeper lithospheric processes, neotectonics and surface processes in the northern Alpine Foreland, and their implications for tectonically induced topography. For the Environmental Tectonics Project (ENTEC), the Upper and Lower Rhine Graben (URG and LRG) and the Vienna Basin (VB) were selected as natural laboratories. The Vienna Basin developed during the middle Miocene as a sinistral pull-apart structure on top of the East Alpine nappe stack, whereas the Upper and Lower Rhine grabens are typical intracontinental rifts. The Upper Rhine Graben opened during its Late Eocene and Oligocene initial rifting phase by nearly orthogonal crustal extension, whereas its Neogene evolution was controlled by oblique extension. Seismic tomography suggests that during extension the mantle-lithosphere was partially decoupled from the upper crust at the level of the lower crust. However, whole lithospheric folding controlled the mid-Miocene to Pliocene uplift of the Vosges-Black Forest Arch, whereas thermal thinning of the mantle-lithosphere above a mantle plume contributed substantially to the past and present uplift of the Rhenish Massif. By contrast, oblique crustal extension, controlling the late Oligocene initial subsidence stage of the Lower Rhine Graben, gave way to orthogonal extension at the transition to the Neogene. The ENTEC Project integrated geological, geophysical, geomorphologic, geodetic and seismological data and developed dynamic models to quantify the societal impact of neotectonics in areas hosting major urban and industrial activity concentrations. The response of Europe's intraplate lithosphere to Late Neogene compressional stresses depends largely on its thermo-mechanical structure, which, in turn, controls vertical motions, topography evolution and related surface processes.

Cloetingh, S.; Cornu, T.; Ziegler, P. A.; Beekman, F.; Environmental Tectonics (Entec) Working Group

341

Oligocene Provenance, Drainage Morphology, and Topography of the Nevadaplano  

NASA Astrophysics Data System (ADS)

Debate surrounds the origin, uplift, and evolution of the northern Sierra Nevada and western Basin and Range. Many consider the Late Cretaceous to early Cenozoic Sierra to have formed the western edge of a high elevation plateau that covered much of what is now Nevada. The topography, extent, and drainage of this plateau remain uncertain. We integrate local paleovalley morphology and alluvial conglomerate stratigraphy with regional assessments of sediment and volcanic provenance and paleo-elevations across the proposed ancestral "Nevadaplano" to gain a better understanding of the early Cenozoic geomorphic evolution of the region, and to assess the possible tectonic and climatic drivers for that evolution. A sequence of Oligocene rhyolitic ignimbrites is preserved from eastern Nevada to the western foothills of the modern Sierra, commonly overlying a basal alluvial/fluvial coarse sand- to cobble-size conglomerate. The stratigraphy and provenance of these units, based on clast composition, detrital zircon and 40Ar/39Ar geochronology, and TREE geochemistry, demonstrates the presence of an active westward-draining fluvial system in the late Eocene to early Oligocene. Although dominated by Mesozoic batholith sources, detrital zircon populations from fluvial deposits in the northern Sierra contain 2-20% zircon grains with U-Pb ages from 42.7 to 33.0 Ma, which were likely sourced from Eocene volcanic rocks in northern Nevada, and 5-30% Precambrian zircon grains, reflecting derivation from basement metamorphic belts of the Sierra, as well as possible contributions from Nevada. Hydrated volcanic glass from overlying ignimbrites was used as a proxy for ?D of Oligocene meteoric water, which reflects the effect of ancient topography on precipitation. ?D decreases gradually from west to east across what is now northern Nevada, although at a significantly lower gradient than Oligocene ?D across the Sierra. ?D of volcanic glass across Nevada decreases from values ranging from -139% ± 3% to -146% ± 3% at locations that are now ~180 km east of the Great Valley, to values ranging from -153% ± 3% to -167% ± 3% at locations ~470 km to the east (near Carlin). This 7-28 ± 3% decrease in Oligocene ?D occurs over less distance than a similar magnitude isotopic change in modern meteoric waters or in 2-5.5 Ma old hydrated volcanic glass, but this decrease does not necessitate orographic fractionation. These data show a significant reduction in the rate of increase of paleo-elevation with distance, in comparison with the region to the west (now the Sierra Nevada), and may reflect a gradual increase in mean elevation or partly closed hydrologic system behavior. Evidence of an active west-flowing fluvial system, providing a conduit for Late Eocene sediment and Oligocene ignimbrites, extending from what is now north-central Nevada to eastern California, supports a gradual increase in elevation from west to east as shown by the paleoaltimetry data. The region that is now northern Nevada was likely a gradually sloping high-elevation (~3-4 km) plateau in the Oligocene.

Cassel, E. J.; Henry, C. D.; Graham, S. A.; Chamberlain, C. P.; Grove, M.

2011-12-01

342

Reproducibility of Newly Developed Spinal Topography Measurements for Scoliosis  

PubMed Central

Objective: In an effort to limit exposure to ionizing radiation and fully characterize three dimensional changes in the spine of patients with scoliosis reliable non-invasive methods of spinal back contour analysis (Milwaukee Topographic Scanner) (MTS) have been developed. Study Design: The current study compares spinal topography measurements among different subject positions and evaluates the reproducibility of the system for both inter-rater and intra-rater reliability. Methods: A dummy cast (plastic cast) of one patient with adolescent idiopathic scoliosis was created in order to test the reliability of the MTS. The dummy cast was positioned and rotated in 3D while scanned by two investigators using the MTS. A total of twelve parameters including Q-angle (an analog to X-ray’s Cobb angle) were extracted. Results: All measurements of intra-rater and inter-rater reliability were excellent (Intraclass Correlation Coefficients ranging from 0.89 to 0.99) with the exception of Pelvic Tilt (intra-rater ICC is 0.61) and lordosis angle (inter-rater ICC is 0.82). No significant variability among investigators was observed for all tested metrics. No significant variability due to position was observed for the majority of back contour measurements but there were significant changes in the T1-S1 angle, T1-S1 deviation, T1-NC angle, T1-NC deviation, and Back Height metric (p< 0.05). Conclusions: The MTS is a reliable method of raster stereography in the measurement of the back contour, which will help monitor the progression of children with idiopathic scoliosis and reduce the use of X-rays.

Rankine, Leah; Liu, Xue C; Tassone, Channing; Lyon, Roger; Tarima, Sergey; Thometz, John

2012-01-01

343

Mantle flow and dynamic topography associated with slab window opening  

NASA Astrophysics Data System (ADS)

A slab window is defined as an 'hole' in the subducting lithosphere. In the classical view, slab windows develop where a spreading ridge intersects a subduction zone. The main consequences of this phenomenon are the modifications of the physical, chemical and thermal conditions in the backarc mantle that in turn affect the tectonic and magmatic evolution of the overriding plate. In this work, we perform dynamically self-consistent mantle-scale laboratory models, to evaluate how the opening of a window in the subducting panel influences the geometry and the kinematics of the slab, the mantle circulation pattern and, finally, the overriding plate dynamic topography. The adopted setup consists in a two-layer linearly viscous system simulating the roll-back of a fixed subducting plate (simulated using silicone putty) into the upper mantle (simulated using glucose syrup). Our experimental setting is also characterized by a constant-width rectangular window located at the center of a laterally confined slab, modeling the case of the interaction of a trench-parallel spreading ridge with a wide subduction zone. We find that the geometry and the kinematics of the slab are only minorly affected by the opening of a slab window. On the contrary, slab induced mantle circulation, quantified using Feature Tracking image analysis technique, is strongly modified and produces a peculiar non-isostatic topographic signal on the overriding plate. Assuming that our modeling results can be representative of the natural behavior of subduction zones, we compare them to the Patagonian subduction zone finding that anomalous backarc volcanism that developed since middle Miocene could result from the lateral flowage of subslab mantle, and that part of the Patagonian uplift could be dynamically supported.

Guillaume, Benjamin; Moroni, Monica; Funiciello, Francesca; Martinod, Joseph; Faccenna, Claudio

2010-05-01

344

High Resolution Topography for Thermal Modeling on Vesta  

NASA Astrophysics Data System (ADS)

For more than a year, NASA's Dawn mission has been providing fascinating data on Vesta. Surface temperatures and thermal parameters are being derived using measurements by the Visual and Infrared Spectrometer (VIR) (Capria et al., 2012). However, the spatial distribution of temperatures is complex due to significant albedo variations over short distance scales and extensive cratering that generates shadows and complex surface features over small spatial scales. This results in VIR pixels that have sub-pixel variations in the temperature that are difficult to deconvolve. Here we report the benefits of using high-resolution topographic modeling when interpreting the thermal component of the VIR observations. Stereo-photoclinometry has been used for years to derive accurate shape models of planetary surfaces. It uses high-resolution images to determine both the surface reflectance and the incidence and emission angles for every pixel of every image. Using this data, we construct both the local surface topography (known as maplets) as well as reflectance values for the Cornelia crater on Vesta (-9.7 Lat, 225 Lon), a fresh crater that has sharp relief and significant variations in albedo. Using this terrain model, we construct high-resolution, time-resolved insolation maps accounting for Bond albedo, incidence angle and shadowing effects of near-by features. From these maps, we calculate the temperature of the surface and subsurface using a 1-D thermal conduction model. This time-resolved model allows us to calculate the temperature at 3 times the spatial resolution for all regions of Cornelia crater at the time when VIR collected its observations. By combining the thermal flux for all the high-resolution points within a single VIR pixel element, we generate a thermal spectrum that accurately models the VIR data because they reflect slope inflections that are generated by sub-pixel temperature variations.

Palmer, Eric; Sykes, M. V.; Gaskell, R. W.; Li, J.

2012-10-01

345

PROSTATE CANCER TOPOGRAPHY AND PATTERNS OF LYMPH NODE METASTASIS  

PubMed Central

Pelvic lymph node (LN) metastasis is a well-recognized route of prostate cancer spread. However, the relationship between topography and pathologic features of primary prostatic cancers and patterns of pelvic LN metastasis has not been well studied. We reviewed original slides of radical prostatectomies and pelvic LN dissections from 125 patients with LN metastasis and recorded total # of LN excised / laterality of positive LN, as well as localization, staging parameters, lymphovascular invasion and tumor volume of primary tumors. LN Quantity and Distribution 14.6 (mean) and 13 (median) LN were resected. 76 (61%), 33 (26%) and 16 (13%) cases had 1, 2 and > 2 positive LN, while 58, 44 and 20 cases had LN metastasis on the right (R), left (L), and bilaterally. Pathologic Features 86% (108/125) and 37% (46/125) demonstrated extraprostatic extension and seminal vesicle invasion, while 64% showed lymphovascular invasion. Mean and median total tumor volume was 6.39 and 3.92 cc, with ? 50% and ? 90% Gleason patterns 4/5 in 105 (84%) and 73 (58%) cases, respectively. Correlation with Dominant Tumor Location Dominant lesions on RP: 50 R lobe, 44 L lobe, 31 bilateral. 15/50 (30%) R lobe and 18/44 (41%) L lobe dominant tumors had LN metastasis on the contralateral side. Only 4% (5/125) of cases were associated with anterior dominant tumors. 30–40% of LN metastases occur contralateral to the dominant tumor. LN metastasis is overwhelmingly associated with high grade, high stage and large volume disease. LN positivity is rarely associated with anterior dominant tumors.

Tokuda, Yuji; Carlino, Lauren J.; Gopalan, Anuradha; Tickoo, Satish K.; Kaag, Matthew G.; Guillonneau, Bertrand; Eastham, James A.; Scher, Howard I.; Scardino, Peter T.; Reuter, Victor E.; Fine, Samson W.

2012-01-01

346

Corneal topography measurement by means of radial shearing interference: Part II - experiment results  

NASA Astrophysics Data System (ADS)

The method of the measurement of the corneal topography was worked out. This measurement system uses an interferometer based on radial shearing. This paper presents the preliminary results of the experiments. The results are compared with other methods.

Garncarz, Beata E.; Kowalik, Waldemar W.; Kasprzak, Henryk T.

347

Corneal thickness measurements: scanning-slit corneal topography and noncontact specular microscopy versus ultrasonic pachymetry  

Microsoft Academic Search

PurposeTo compare central corneal thickness measurements taken with 3 pachymetry systems: Orbscan scanning-slit corneal topography\\/pachymetry, Topcon SP2000P noncontact specular microscopy, and Tomey ultrasonic pachymetry.

Shigenobu Suzuki; Tetsuro Oshika; Kotaro Oki; Isao Sakabe; Aiko Iwase; Shiro Amano; Makoto Araie

2003-01-01

348

Corneal topography measurement of the eye by means of radial shearing interferometer  

NASA Astrophysics Data System (ADS)

The method of the measurement of the corneal topography was worked out. This measurement system uses an interferometer based on radial shearing. This paper presents the preliminary results of the experiments. The results are compared with other methods.

Kowalik, Waldemar; Garncarz, Beata E.; Kasprzak, Henryk T.

2001-03-01

349

Large Volcanic Edifices and Rises on Venus: The Benefits of Improved Topography and Gravity Data  

NASA Astrophysics Data System (ADS)

Venus is a volcanological laboratory, replete with edifices and rises that offer potentially deep insights into its evolution. However, this potential can only be realized with improved topography and gravity data, requiring a new orbital mission.

McGovern, P. J.

2014-05-01

350

New criterion about the topography of W-CMP wafer's alignment mark  

NASA Astrophysics Data System (ADS)

Alignment error that originates in the actual wafer process is one of the factors to deteriorate total overlay accuracy. This error has been called wafer induced shift (WIS). WIS occurs through a change of alignment marks topography under the actual wafer processing. To quantify mark asymmetry WIS, we study the mark asymmetry on tungsten chemical mechanical polishing (CMP) wafers by using an atomic force microscope and define new criterion in this paper. The mark topography of CMP process wafers are measured by AFM and quantified using the new criterion. The asymmetry of the mark topography can be quantified by measuring the profiles of an alignment mark across the wafers. It has been proven, that the rotation error is caused by the asymmetry of the mark topography and the asymmetry is not related to the line width of the mark.

Ina, Hideki; Matsumoto, Takahiro; Sentoku, Koichi; Matsuyama, Katsuhiro; Katagiri, Kazuhiko

2003-05-01

351

Exact three-dimensional spectral solution to surface-groundwater interactions with arbitrary surface topography  

USGS Publications Warehouse

It has been long known that land surface topography governs both groundwater flow patterns at the regional-to-continental scale and on smaller scales such as in the hyporheic zone of streams. Here we show that the surface topography can be separated in a Fourier-series spectrum that provides an exact solution of the underlying three-dimensional groundwater flows. The new spectral solution offers a practical tool for fast calculation of subsurface flows in different hydrological applications and provides a theoretical platform for advancing conceptual understanding of the effect of landscape topography on subsurface flows. We also show how the spectrum of surface topography influences the residence time distribution for subsurface flows. The study indicates that the subsurface head variation decays exponentially with depth faster than it would with equivalent two-dimensional features, resulting in a shallower flow interaction. Copyright 2006 by the American Geophysical Union.

Worman, A.; Packman, A. I.; Marklund, L.; Harvey, J. W.; Stone, S. H.

2006-01-01

352

The Utilization of Side Looking Airborne Radar (SLAR) in the Analysis of Karst Topography.  

National Technical Information Service (NTIS)

Characteristics of mechanical and synthetic radar systems are reviewed. Signature elements of karst topography such as a vertical drainage pattern, knobs, and sinkholes are identified for Side Looking Airborne Radar (SLAR) imagery. SLAR imagery of the Ken...

C. L. Smith A. P. Tribble

1977-01-01

353

Constraints on Gusev Basin Infill from the Mars Orbiter Laser Altimeter (MOLA) Topography  

NASA Technical Reports Server (NTRS)

MOLA topography provides volume estimates for Gusev crater based on higher resolution. Revisiting work previously done by Grin and Cabrol (1997), we find a substantial increase in original sedimentation estimates. Additional information is contained in the original extended abstract.

Carter, B. L.; Frey, H.; Sakimoto, S. E. H.; Roark, J.

2001-01-01

354

Ultrastructure of Epicorneal Topography and Morphogenesis in Insects with Aspects on Phylogenesis and Function.  

National Technical Information Service (NTIS)

The review is based upon the studies described in the following articles: Ontogenesis of corneal surface ultrastructure in nocturnal Lepidoptera; Comparative ultrastructure of corneal surface topography in insects with aspects on phylogenesis and function...

G. Gemne

1970-01-01

355

Investigating Karst topography and its connection to SE Minnesota sinkholes and cave formations.  

NSDL National Science Digital Library

This activity is a field investigation where students will be able to observe sinkholes located in the southeastern Minnesota area and a cave system in Forestville State Park which will assist them in defining Karst topography.

Anne Feist Nrheg Public School New Richland, Mn

356

Corneal topography in asymptomatic family members of a patient with pellucid marginal degeneration  

Microsoft Academic Search

PURPOSE: To report corneal topographic patterns in asymptomatic family members of a patient with pellucid marginal degeneration.METHODS: Computer-assisted corneal topography was used to study the corneas of five family members of a patient with pellucid marginal degeneration.RESULTS: In all five asymptomatic family members, corneal biomicroscopy was normal. Corneal topography, however, showed various abnormalities in different members of this family, particularly

Ruth M Santo; Samir J Bechara; Newton Kara-José

1999-01-01

357

Emmetropisation, axial length, and corneal topography in teenagers with Down’s syndrome  

Microsoft Academic Search

AIMTo study the refractive status and corneal topography in Down’s syndrome.METHODA matched cohort subgroup of 50 individuals with Down’s syndrome in the Manchester area aged 15–22 years was studied by refraction, corneal topography, A-scan biometry, slit lamp examination, and orthoptic examination.RESULTS(1) A linear relation was found between axial length and spherical equivalent refraction. There was no statistical relation between keratometry

Stephen J Doyle; John Bullock; Cath Gray; Alison Spencer; Cliff Cunningham

1998-01-01

358

The spectra of the topography of the earth, Venus, and Mars  

NASA Astrophysics Data System (ADS)

A spherical harmonic analysis is conducted for the topographies of the terrestrial planets using extant data sets to the highest possible degree and order, with a view to establishing the decay of such spectra over a larger range of frequencies and ascertain the limit of validity of the data sets employed. The shape of power spectra is confirmed for the cases of the earth and for Venus; Mars topography is still uncertain in many regions.

Balmino, G.

1993-06-01

359

Calculation of lunar Bouguer gravity anomaly using Chang'E-1 topography data: Interpretation for mascons  

Microsoft Academic Search

Bouguer gravity anomaly (BGA) reveals density structures of planets. Using the new lunar topography data measured by Chang'E-1 Laser Altimeter, we have calculated the Bouguer gravity anomaly (BGA) of the Moon based on gravity field model LP165P. Two different terrain correction (i.e., Bouguer correction) methods are compared. One is using spheric harmonic coefficients of topography model (CLTM-s01) to directly derive

Q. Liang; C. Chen; J. Du; B. Chen

2009-01-01

360

Push in South of the Hellas Basin Showing Topography from MOLA: New Color Map  

NSDL National Science Digital Library

Zoom into the region of Mars just south of the Hellas Basin showing topography data from MOLA. This animation uses a color table designed to highlight the topography at the south pole. White colors indicate elevations in excess of 3012 meters, red shows elevations between 2500 and 3012 meters, yellow shows elevations from 2450 to 2500 meters, dark cyan shows elevations from 2150 to 2450 meters, dark violet shows elevations from 320 to 2150 meters.

Biddlecome, Tom; Smith, David

1999-11-22

361

The influence of eroding topography on steady-state isotherms. Application to fission track analysis  

Microsoft Academic Search

The influence of surface topography on the form of steady-state isotherms during erosion-driven denudation is investigated. This is of particular interest to the interpretation of low-temperature geochronological data, for example fission track data, because this rests generally on the untested assumption that isotherms are not perturbed by topography and, therefore, that the data can be interpreted with one-dimensional models. In

Kurt Stuewe; Lee White; Rod Brown

1994-01-01

362

Mapping of statistical characteristics of topography on Mars with MOLA data  

NASA Astrophysics Data System (ADS)

Mars Orbiter Laser Altimeter (MOLA) produced a huge set of precise measurements of Mars surface elevation with uniform 0.3 km spacing along tracks. We use this data set to study statistical characteristics of the martian topography at the scale from hundreds meters to tens of kilometers. Here we give a summary of our published and new results on mapping of statistical characteristics of topography for the purposes of geomorphology and understanding of surface formation and alteration processes. The interquartile widths of the differential-slope- or curvature-frequency distributions are used as measures of the surface roughness at a series of scales. The Hurst exponent quantifies the scale dependence of roughness. The normalized median curvature characterizes the prevalence of concave or convex topography. The normalized median differential slope being a measure of the asymmetry of the slope-frequency distribution, characterizes the north - south slope asymmetry. All maps clearly show the latitudinal trend. High-latitude areas (from the polar deposits edges to 60 deg latitude) are characterized by lower subkilometer-scale roughness, higher Hurst exponent and stronger prevalence of concave topography than the equatorial zone (within 30 deg). The transitional zones (from 30 to 60 deg) are characterized by transitional values of roughness and Hurst exponent, by prevalence of convex topography, and by noticeable slope asymmetry: the equator-facing slopes are steeper. The roughness and Hurst exponent also shows obvious correlation with geological units. The maps shows also some anomalous regions related to distribution of specific surficial deposits. For example, convex topography prevails for giant polygons; eastern part of Daedalia Planum has anomalous prevalence of concave topography and strong slope asymmetry; south-eastern part of Arabia Terra has slope asymmetry and prevalence of convex topography; the hematite deposit has an anomalous signature in all maps.

Kreslavsky, M. A.; Head, J. W.

2003-04-01

363

Integrated approach to estimate the ocean's time variable dynamic topography including its covariance matrix  

NASA Astrophysics Data System (ADS)

The ocean's mean dynamic topography as the difference between the sea surface and the geoid reflects many characteristics of the general ocean circulation. Consequently, it provides valuable information for evaluating or tuning ocean circulation models. However, the determination of the mean dynamic topography from satellite based gravity field and altimetric observations is not straightforward. For the integration of the dynamic topography into ocean circulation models not only the dynamic topography itself but also its inverse covariance matrix on the ocean model grid is required. We developed a rigorous combination method where both instrumental errors and omission errors are accounted for, including the determination of optimal relative weights between the observation groups. The altimetric mean sea surface is expressed as a sum of geoid heights represented in terms of spherical harmonics and the mean dynamic topography parameterized by a finite element method which can be directly related to the particular ocean model grid. The different observation groups are combined in terms of normal equations. This allows the direct determination of the normal equations of the mean dynamic topography which contain the appropriate weights for model-data misfits in least-squares ocean model inversions. The developed integrated approach can be extended by modeling the time variable component of the dynamic topography to provide estimates not only at a mean state but also at arbitrary points in time including a rigorously computed covariance matrix. The focus of this study is on the North Atlantic Ocean. We will present the conceptual design and dynamic topography estimates based on time variable data from several satellite altimeter missions in combination with GOCE and GRACE gravity field models.

Becker, Silvia; Brockmann, Jan Martin; Schuh, Wolf-Dieter

2014-05-01

364

Vibration modes analysis by X-ray topography in quartz and langasite resonators  

Microsoft Academic Search

This paper presents the results of the vibration modes measurements by X-ray topography in SC-cut quartz and Y-cut unpolished langasite resonators. A comparison of these results with X-ray diffraction topography images on AT-cut quartz resonators and Y-cut polished langasite resonators pointed out the behavior of mass-loading effect with plate orientation angle and with the surface state of the piezoelectric substrate.

J. Mateescu; B. Capelle; J. Detaint; G. Johnson; L. Dumitrache; C. Bran

2004-01-01

365

Where asylum-seekers wait: feminist counter-topographies of sites between states  

Microsoft Academic Search

This article examines topographies and counter-topographies of power operating transnationally across a range of sites inhabited by asylum-seekers en route between nation-states. In locations such as tunnels, detention centers and islands, journeys across time and space are truncated in myriad ways. For asylum-seekers, temporality is often conceptualized as waiting, limbo or suspension. These temporal zones map onto corresponding spatial ambiguities

Alison Mountz

2011-01-01

366

Evaluation of surface topography of metal-bonded diamond wheel utilizing three-dimensional profilometry  

Microsoft Academic Search

A three-dimensional profilometry has been developed for the purpose of evaluating grinding wheel surface topography.By applying this method to the measurement of topography of a metal-bonded diamond wheel dressed by an abrasive stick method, the effect of dressing conditions on the generation mechanism of diamond cutting points has been investigated.The results obtained are as follows. (1) The tips of the

J. Tamaki; T. Kitagawa

1995-01-01

367

Spatial patterns in the evolution of Cenozoic dynamic topography and its influence on the Antarctic continent  

NASA Astrophysics Data System (ADS)

Our knowledge of dynamic topography in Antarctica remains in an infancy stage compared to other continents. We assess the space-time variability in dynamic topography in Antarctica by analysing grids of global dynamic topography in the Cenozoic (and late Cretaceous) based on the tomographic model S40RTS. Our model reveals that the Gamburtsev Province and Dronning Maud Land, two of the major nucleation sites for the East Antarctic Ice Sheet (EAIS) were ~500 m higher 60 Ma ago. The increased elevation may have facilitated ephemeral ice cap development in the early Cenozoic. Between ca 25 and 50 Ma the northern Wilkes Subglacial Basin was ca 200 m higher than today and a major increase in regional elevation (>600 m) occurred over the last 20-15 Ma over the northern and southern Victoria Land in the Transantarctic Mountains (TAM). The most prominent signal is observed over the Ross Sea Rift (RSR) where predicted Neogene dynamic topography exceeds 1,000 m. The flow of warm mantle from the West Antarctic Rift System (WARS)may have driven these dynamic topography effects over the TAM and RSR. However, we found that these effects are comparatively less significant over the Marie Byrd Land Dome and the interior of the WARS. If these contrasting dynamic topography effects are included, then the predicted elevations of the Ross Sea Embayment ca 20 Ma ago are more similar to the interior of the WARS, with significant implications for the early development of the West Antarctic Ice Sheet.

Anderson, Lester; Ferraccioli, Fausto; Eagles, Graeme; Steinberger, Bernhard; Ritsema, Jeroen

2013-04-01

368

Modelling low-frequency volcanic earthquakes in a viscoelastic medium with topography  

NASA Astrophysics Data System (ADS)

Magma properties are fundamental to explain the volcanic eruption style as well as the generation and propagation of seismic waves. This study focusses on rheological magma properties and their impact on low-frequency volcanic earthquakes. We investigate the effects of anelasticity and topography on the amplitudes and spectra of synthetic low-frequency earthquakes. Using a 2D finite difference scheme, we model the propagation of seismic energy initiated in a fluid-filled conduit embedded in a 2D homogeneous viscoelastic medium with topography. Topography is introduced by using a mapping procedure that stretches the computational rectangular grid into a grid which follows the topography. We model intrinsic attenuation by linear viscoelastic theory and we show that volcanic media can be approximated by a standard linear solid for seismic frequencies (i.e., above 2 Hz). Results demonstrate that attenuation modifies both amplitude and dispersive characteristics of low-frequency earthquakes. Low-frequency events are dispersive by nature; however, if attenuation is introduced, their dispersion characteristics will be altered. The topography modifies the amplitudes, depending on the position of seismographs at the surface. This study shows that we need to take into account attenuation and topography to interpret correctly observed low-frequency volcanic earthquakes. It also suggests that the rheological properties of magmas may be constrained by the analysis of low-frequency seismograms.

Jousset, P.; Neuberg, J.

2003-04-01

369

Physiology, pharmacology, and topography of cholinergic neocortical oscillations in vitro.  

PubMed

Rat neocortical brain slices generated rhythmic extracellular field [microelectroencephalogram (micro-EEG)] oscillations at theta frequencies (3-12 Hz) when exposed to pharmacological conditions that mimicked endogenous ascending cholinergic and GABAergic inputs. Use of the specific receptor agonist and antagonist carbachol and bicuculline revealed that simultaneous muscarinic receptor activation and gamma-aminobutyric acid-A (GABA(A))-mediated disinhibition were necessary to elicit neocortical oscillations. Rhythmic activity was independent of GABA(B) receptor activation, but required intact glutamatergic transmission, evidenced by blockade or disruption of oscillations by 6-cyano-7-nitroquinoxaline-2,3-dione and (+/-)-2-amino-5-phosphonovaleric acid, respectively. Multisite mapping studies showed that oscillations were localized to areas 29d and 18b (Oc2MM) and parts of areas 18a and 17. Peak oscillation amplitudes occurred in layer 2/3, and phase reversals were observed in layers 1 and 5. Current source density analysis revealed large-amplitude current sinks and sources in layers 2/3 and 5, respectively. An initial shift in peak inward current density from layer 1 to layer 2/3 indicated that two processes underlie an initial depolarization followed by oscillatory activity. Laminar transections localized oscillation-generating circuitry to superficial cortical layers and sharp-spike-generating circuitry to deep cortical layers. Whole cell recordings identified three distinct cell types based on response properties during rhythmic micro-EEG activity: oscillation-ON (theta-ON) and -OFF (theta-OFF) neurons, and transiently depolarizing glial cells. Theta-ON neurons displayed membrane potential oscillations that increased in amplitude with hyperpolarization (from -30 to -90 mV). This, taken together with a glutamate antagonist-induced depression of rhythmic micro-EEG activity, indicated that cholinergically driven neocortical oscillations require excitatory synaptic transmission. We conclude that under the appropriate pharmacological conditions, neocortical brain slices were capable of producing localized theta frequency oscillations. Experiments examining oscillation physiology, pharmacology, and topography demonstrated that neocortical brain slice oscillations share many similarities with the in vivo and in vitro theta EEG activity recorded in other brain regions. PMID:9163368

Lukatch, H S; MacIver, M B

1997-05-01

370

Gravity, topography, and magnetic field of Mercury from MESSENGER  

NASA Astrophysics Data System (ADS)

On 18 March 2011, the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft was inserted into a ˜12-hour, near-polar orbit around Mercury, with an initial periapsis altitude of 200 km, initial periapse latitude of 60°N, and apoapsis at ˜15,200 km altitude in the southern hemisphere. This orbit has permitted the mapping of regional gravitational structure in the northern hemisphere, and laser altimetry from the MESSENGER spacecraft has yielded a geodetically controlled elevation model for the same hemisphere. The shape of a planet combined with gravity provides fundamental information regarding its internal structure and geologic and thermal evolution. Elevations in the northern hemisphere exhibit a unimodal distribution with a dynamic range of 9.63 km, less than that of the Moon (19.9 km), but consistent with Mercury's higher surface gravitational acceleration. After one Earth-year in orbit, refined models of gravity and topography have revealed several large positive gravity anomalies that coincide with major impact basins. These candidate mascons have anomalies that exceed 100 mGal and indicate substantial crustal thinning and superisostatic uplift of underlying mantle. An additional uncompensated 1000-km-diameter gravity and topographic high at 68°N, 33° E lies within Mercury's northern volcanic plains. Mercury's northern hemisphere crust is generally thicker at low latitudes than in the polar region. The low-degree gravity field, combined with planetary spin parameters, yields the moment of inertia C/MR^2 = 0.353 ± 0.017, where M=3.30 × 10 ^{23} kg and R=2440 km are Mercury's mass and radius, and a ratio of the moment of inertia of Mercury's solid outer shell to that of the planet of C_m/C = 0.452 ± 0.035. One proposed model for Mercury's radial density distribution consistent with these results includes silicate crust and mantle layers overlying a dense solid (possibly Fe-S) layer, a liquid Fe-rich outer core of radius 2030 ± 37 km, and an assumed solid inner core. Magnetic field measurements indicate a northward offset of Mercury's axial magnetic dipole from the geographic equator by 479 ± 3 km and provide evidence for a regional-scale magnetic field approximately collocated with the northern volcanic plains of possible crustal origin. These results from MESSENGER indicate a complex and asymmetric evolution of internal structure and dynamics in this end-member inner planet.

Neumann, Gregory

2012-07-01

371

CMP Fill Synthesis: A Survey of Recent Studies  

Microsoft Academic Search

We survey recent research and practice in the area of chemical-mechanical polishing (CMP) fill synthesis, in terms of both problem formulations and solution approaches. We review the CMP as the planarization technique of choice for multilevel very large-scale integration metallization processes. Post-CMP wafer topography varies according to pattern density. We review density-analysis methods and density-control objectives that are used in

Andrew B. Kahng; Kambiz Samadi

2008-01-01

372

Geoid Anomalies and Dynamic Topography from Time Dependent, Spherical Axisymmetric Mantle Convection  

NASA Technical Reports Server (NTRS)

Geoid anomalies and dynamic topography are two important diagnostics of mantle convection. We present geoid and topography results for several time-dependent convection models in spherical axisymmetric geometry for Rayleigh numbers between 10(exp 6) and 10(exp 7) with depth-dependent viscosity and mixtures of bottom and internal heating. The models are strongly chaotic, with boundary layer instabilities erupting out of both thermal boundary layers. In some instances, instabilities from one boundary layer influence the development of instabilities in the other boundary layer. Such coupling between events at the top and bottom of the mantle has been suggested to play a role in a mid-Cretaceous episode of enhanced volcanism in the Pacific. These boundary layer instabilities produce large temporal variations in the geoid anomalies and dynamic nd to the topography associated with the convection. The amplitudes of these fluctuations depend on the detailed model parameter,.% it of this but fluctuations of 30-50% relative to the time-averaged geoid and topography are common. The convective planform is strongly sensitive to the specific initial conditions. Convection cells with larger aspect ratio tend to have larger fractional fluctuations in their geoid and topography amplitudes, because boundary layer instabilities have more time to develop in long cells. In some instances, we observe low-amplitude topographic highs adjacent to the topographic lows produced by cold downwellings. We discuss applications of these results to several situations, including the temporal variability of m basis. hotspots such as Hawaii, the topography of subduction zone outer rises, and the topography of coronae on Venus.

Kiefer, Walter S.; Kellogg, Louise H.

1998-01-01

373

A consistent data set of Antarctic ice sheet topography, cavity geometry, and global bathymetry  

NASA Astrophysics Data System (ADS)

Sub-ice shelf circulation and freezing/melting rates in ocean general circulation models depend critically on an accurate and consistent representation of cavity geometry. Existing global or pan-Antarctic topography data sets have turned out to contain various inconsistencies and inaccuracies. The goal of this work is to compile independent regional surveys and maps into a global data set. We use the S-2004 global 1-min bathymetry as the backbone and add an improved version of the BEDMAP topography (ALBMAP bedrock topography) for an area that roughly coincides with the Antarctic continental shelf. The position of the merging line is individually chosen in different sectors in order to capture the best of both data sets. High-resolution gridded data for ice shelf topography and cavity geometry of the Amery, Fimbul, Filchner-Ronne, Larsen C and George VI Ice Shelves, and for Pine Island Glacier are carefully merged into the ambient ice and ocean topographies. Multibeam survey data for bathymetry in the former Larsen B cavity and the southeastern Bellingshausen Sea have been obtained from the data centers of Alfred Wegener Institute (AWI), British Antarctic Survey (BAS) and Lamont-Doherty Earth Observatory (LDEO), gridded, and blended into the existing bathymetry map. The resulting global 1-min Refined Topography data set (RTopo-1) contains self-consistent maps for upper and lower ice surface heights, bedrock topography, and surface type (open ocean, grounded ice, floating ice, bare land surface). The data set is available in NetCDF format from the PANGAEA database at doi:10.1594/pangaea.741917.

Timmermann, R.; Le Brocq, A.; Deen, T.; Domack, E.; Dutrieux, P.; Galton-Fenzi, B.; Hellmer, H.; Humbert, A.; Jansen, D.; Jenkins, A.; Lambrecht, A.; Makinson, K.; Niederjasper, F.; Nitsche, F.; Nøst, O. A.; Smedsrud, L. H.; Smith, W. H. F.

2010-12-01

374

SWOT, The Surface Water and Ocean Topography Satellite Mission (Invited)  

NASA Astrophysics Data System (ADS)

Surface fresh water is essential for life, yet we have surprisingly poor knowledge of its variability in space and time. Similarly, ocean circulation fundamentally drives global climate variability, yet the ocean current and eddy field that affects ocean circulation and heat transport at the sub-mesoscale resolution and particularly near coastal and estuary regions, is poorly known. About 50% of the vertical exchange of water properties (nutrients, dissovled CO2, heat, etc) in the upper ocean is taking place at the sub-mesoscale. Measurements from the Surface Water and Ocean Topography satellite mission (SWOT) will make strides in understanding these processes and improving global ocean models for studying climate change. SWOT is a swath-based interferometric-altimeter designed to acquire elevations of ocean and terrestrial water surfaces at unprecedented spatial and temporal resolutions. The mission will provide measurements of storage changes in lakes, reservoirs, and wetlands as well as estimates of discharge in rivers. These measurements are important for global water and energy budgets, constraining hydrodynamic models of floods, carbon evasion through wetlands, and water management, especially in developing nations. Perhaps most importantly, SWOT measurements will provide a fundamental understanding of the spatial and temporal variations in global surface waters, which for many countries are the primary source of water. An on-going effort, the “virtual mission” (VM) is designed to help constrain the required height and slope accuracies, the spatial sampling (both pixels and orbital coverage), and the trade-offs in various temporal revisits. Example results include the following: (1) Ensemble Kalman filtering of VM simulations recover water depth and discharge, reducing the discharge RMSE from 23.2% to 10.0% over an 84-day simulation period, relative to a simulation without assimilation. (2) Ensemble-based data assimilation of SWOT like measurements yields bathymetric slope and depth to within 3.0 microradians and 50 cm, respectively. (3) SWOT measurements of storage changes in lakes larger than 1 km2 will have relative errors generally less than 5% whereas errors for one-hectare size lakes will be about 20%. (4) SWOT estimates of discharge compared to a one-year model-based “truth” data set suggest that instantaneous discharge estimates will have a median relative RMSE of 10.9% and that 86% of all instantaneous errors will be less than 25%. (5) Based on a global distribution of gauge-based discharge and candidate SWOT orbits with varying spatial and temporal sampling, SWOT errors in instantaneous discharge will be less than 25% for rivers wider than 50 m, whereas errors in monthly discharge will be less than 20% for rivers with drainage areas larger than 7000 km2. (6) We estimate that currently available satellite nadir altimetry data cannot monitor more than 15% of the global lake volume variation, whereas from 50% to more than 65% of the global lake volume variation will be observed by SWOT.

Alsdorf, D.; Andreadis, K.; Bates, P. D.; Biancamaria, S.; Clark, E.; Durand, M. T.; Fu, L.; Lee, H.; Lettenmaier, D. P.; Mognard, N. M.; Moller, D.; Morrow, R. A.; Rodriguez, E.; Shum, C.

2009-12-01

375

Numerical studies on the structure of Venusian mantle convection constrained by the geoid and topography  

NASA Astrophysics Data System (ADS)

Venus is a planet very similar to the Earth in terms of size, density and composition. However, different from the Earth which has active plate tectonics, Venus is a one-plate planet covered by a thick immobile lithosphere. Observations show that there may be nine hotspots on Venus and they may be still active. The topography and geoid of Venus have relatively long wavelength character with the degree 3 terms are the highest. Analysis about the geoid and topography of Venus shows that their correlation is high and the admittance ratio at lower degrees is large, suggesting a mainly dynamic origin for the topography and geoid at lower degrees. Using these results above as the main constraints, we systematically investigated the influence of phase transitions on the structure of Venusian mantle convection in 3D spherical shell. Both mantle phase transitions from olivine to spinel and from spinel to perovskite are included in our model. We employed an extended Boussinesq approximation, an infinite Prandtl number assumption and strongly temperature- and pressure-dependent viscosity in our model. Calculations are performed with the finite element code CitcomS. Numerical simulations show that convective structure is affected significantly by phase changes. The amplitude of the Clapeyron slops of phase changes and Rayleigh number control the dominant convective wavelength. When no phase changes are included in the model, a representative convective structure shows dominant short-wavelengths with numerous of plumes, typical of stagnant-lid convection. The geoid and the surface topography are highly correlated with large admittance at lower degrees and the powers of the topography and geoid spectra are significantly reduced at long-wavelengths compared with the observed. Phase changes could promote long-wavelength convective structures as previous findings. When other parameters are kept the same, increasing the Clapeyron slops of the phase changes will increase the powers of the topography and geoid spectra at the lower degrees and decrease the number of plumes. The increase of Rayleigh number will also increase the powers of the topography and geoid spectra at the lower degrees, but it will decrease the powers of the topography and geoid spectra at the relatively higher degrees. All these cases have Venus like large admittance ratio at lower degrees and high correlation for the topography and geoid. The model parameters that most satisfy Venus' observations are with a Rayleigh number of 2×10^8 and Clapeyron slops of +-3.5 MPa/K, which generally satisfy the number of plumes, the geoid amplitude spectra, and the admittance and correlation of Venus. The lithosphere is about 256 Km and the lower mantle viscosity is about 2×10^21 Pa.s.

Yang, A.; Huang, J.; Zhong, S.

2012-12-01

376

Numerical modeling and analysis of the effect of Greek complex topography on tornado genesis  

NASA Astrophysics Data System (ADS)

Tornadoes have been reported in Greece over the last decades in specific sub-geographical areas and have been associated with strong synoptic forcing. It is well known that meteorological conditions over Greece are affected at various scales by the significant variability of topography, the Ionian Sea at the west and the Aegean Sea at the east. However, there is still uncertainty regarding topography's importance on tornadic generation and development. The aim of this study is to investigate the role of topography in significant tornado genesis events that were triggered under strong synoptic scale forcing over Greece. Three tornado events that occurred over the last years in Thiva (Boeotia, 17 November 2007), Vrastema (Chalkidiki, 12 February 2010) and Vlychos (Lefkada, 20 September 2011) have been selected for numerical experiments. These events were associated with synoptic scale forcing, while their intensity was T4-T5 (Torro scale) and caused significant damage. The simulations were performed using the non-hydrostatic Weather Research and Forecasting model (WRF), initialized with ECMWF gridded analyses, with telescoping nested grids that allow the representation of atmospheric circulations ranging from the synoptic scale down to the meso scale. In the experiments the topography of the inner grid was modified by: (a) 0% (actual topography) and (b) -100% (without topography). The aim was to determine whether the occurrence of tornadoes - mainly identified by various severe weather instability indices - could be indicated by modifying topography. The main utilized instability variables concerned the Bulk Richardson number shear (BRN), the energy helicity index (EHI), the storm-relative environmental helicity (SRH) and the maximum convective available potential energy (MCAPE, for parcel with maximum theta-e). Additional a verification of model was conducted for every sensitivity experiment accompanied with analysis absolute vorticity budget. Numerical simulations revealed that the complex topography was denoted as an important factor during 17 November 2007 and 12 February 2010 events, based on EHI and BRN analyses. Topography around 20 September 2011 event was characterized as the least factor based on EHI, SRH, BRN analyses.

Matsangouras, I. T.; Pytharoulis, I.; Nastos, P. T.

2014-02-01

377

How to approximate viscoelastic dynamic topographies of stagnant lid planetary bodies?  

NASA Astrophysics Data System (ADS)

Planetary mantles are viscoelastic media. However, since numerical models of thermal convection in a viscoelastic spherical shell are still very challenging, most of the studies concerning dynamic topography of planetary surfaces generated by mantle convection use one of the following simplified rheological set-up: i) IVF (instantaneous viscous flow), ii) viscous body with a free surface, or iii) hybrid methods combining viscous deformation and elastic filtering of the topography. Justifications for the use of such approximations instead of a fully viscoelastic rheology have been made on the basis of simple tests with step-like viscosity structures, with small to moderate viscosity contrasts. However, because the rheology of planetary materials is thermally activated, the radial stratification of viscosity is more likely to be a continuous function of depth, and global viscosity contrasts might be very large. In our study, we systematically compare viscoelastic dynamic topography induced by an internal load to topographies generated by the three different simplified approaches listed above using a realistic viscosity profile for a stagnant lid associated to the lithosphere of a one plate planete. To this purpose, we compute response functions of surface topography and geoid using three different semi-spectral models that all include self-gravitation: a) a linear Maxwell body with a pseudo free upper surface, b) a viscous body with a pseudo free upper surface, and c) a viscous body with a free-slip condition at the surface. Results obtained with this last model (IVF) can then be filtered using the elastic thin shell approximation: the effective elastic thickness then corresponds to the elastic thickness that is needed to fit the viscoelastic topography with an elastic filtering of the IVF topography. We show that the effective elastic thickness varies strongly with the degree of the load, with the depth of the load, and with the duration of the loading. These results naturally depend on the ratio between the mantle and the lithospheric thicknesses. We show that, in the case of Mars, it is not possible to approximate viscoelastic topographies generated by a stable plume using the elastic filtering of viscous dynamic topographies.

Dumoulin, Caroline; ?adek, Ond?ej; Choblet, Gaël

2013-04-01

378

Local topography of Mars and its relationship to surface weathering processes  

NASA Technical Reports Server (NTRS)

There is a growing body of evidence in favor of the importance of aqueous sedimentary processes on Mars. It is important to understand the role that surface weathering processes have played in the development of the present morphology of the Martian surface. Such an understanding is important not only for its relevance to the study of volatile sources and sinks on Mars through time, but also for its relevance to Martian geologic and tectonic history. Starting in the fall of this year, the Mars Observer Laser Altimeter will begin sending back to Earth data on the topography of Mars that is of a higher quality than most of the topography data available for the Earth. This data will be invaluable, not only for understanding global and large-scale regional processes and landforms on Mars, but also for the study of local and smaller-scale regional processes and landforms. Digital topography is an important part of geologic and geomorphic studies, useful in distinguishing between different lithologies and between different types of weathering. Digital topography data may be used to study a wide variety of local and regional-scale landforms, including valleys, sand dunes, lava flows, landslides, and slopes. Topography data are also essential to the analysis of spectral response patterns, especially in areas of high topographic relief. Geomorphic classification can be significantly improved by the addition of topographic information.

Schaefer, M. W.

1993-01-01

379

Bottom Topography Correction by Assimilation of Tsunami Simulation Model and Tide Gauge Data With Particle Filter  

NASA Astrophysics Data System (ADS)

We demonstrate the results of applying the sequential data assimilation (SDA) to a tsunami simulation model. A shallow water equations model and tide gauge data are employed in DA. Most of our concerns in DA are paid to validate information on depths of sea bottom. The reason is that bottom topography data sets are erroneous and depths affect propagation speed of tsunamis, which results in inaccurate tsunami forecasts. Because the depths are included in the simulation model as boundary condition, we can modify the depths by putting them into state vector. Specifically, we allow for an error term in the bottom topography and its statistical inference is carried out through DA. The filtering method used in SDA is the particle filter (PF) due to the computational and statistical reasons. The PF is also an ensemble based assimilation procedure, and then it has a similar algorithmic structure with the ensemble Kalman filter (EnKF). However, there exist some different characteristics between them. In this study, we conducted three types of numerical experiment and analysis: twin experiment of bottom topography correction, bottom topography estimation based on real tide gauge data of Okushiri tsunami in 1993. The result of twin experiment shows the effectiveness of our DA. The result of DA to real data suggests that almost all part of Yamato Rises is shallower than the average of available data sets (four data sets at hand). We also discuss the differences among raw data, bottom topography data sets and obtained depths by DA.

Nakamura, K.; Hirose, N.; Higuchi, T.

2007-05-01

380

Topography and coating of platinum improve the electrochemical properties and neuronal guidance.  

PubMed

To improve neuronal-electrode interfaces, we analyzed the influence of surface topographies combined with coating on the electrochemistry of platinum and neuronal differentiation of PC-12 cells. Surface structuring on nanoscale was realized by femtosecond laser ablation. Additional coating with laminin (LA), collagen type I (COL) or poly-d-lysine (PDL) did not change the produced topography. We further demonstrated that impedance could be improved in all cases. The pre-requisites of differentiation - viability and attachment - were fulfilled on the topography. Cell attachment of non-differentiated and differentiated cells and their formation of focal adhesion complexes were even enhanced compared to unstructured platinum. However, without the nerve growth factor (NGF) no cellular outgrowth and differentiation were possible. The topography enabled cell elongation and reduced the amount of rounded cells, but less effective than coating. Differentiation was either comparable or increased on the structures when compared with unstructured coatings. For instance, microtubule associated protein (MAP2) was detected most on the topography alone. But a combination of surface structuring and coating had the strongest impact on differentiation: the usage of COL provoked best cell elongation and beta III tubulin expression, PDL best synaptophysin. LA-coating had no noteworthy effect. These findings point out that innovative electronic devices like cochlear implants include two aspects: (a) nanotopography to improve the transmission of electrical signals and neuronal attachment; and (b) an additional coating to stimulate neuronal differentiation. PMID:23327880

Schlie-Wolter, Sabrina; Deiwick, Andrea; Fadeeva, Elena; Paasche, Gerrit; Lenarz, Thomas; Chichkov, Boris N

2013-02-01

381

Flow of evaporating, gravity-driven thin liquid films over topography  

NASA Astrophysics Data System (ADS)

The effect of topography on the free surface and solvent concentration profiles of an evaporating thin film of liquid flowing down an inclined plane is considered. The liquid is assumed to be composed of a resin dissolved in a volatile solvent with the associated solvent concentration equation derived on the basis of the well-mixed approximation. The dynamics of the film is formulated as a lubrication approximation and the effect of a composition-dependent viscosity is included in the model. The resulting time-dependent, nonlinear, coupled set of governing equations is solved using a full approximation storage multigrid method. The approach is first validated against a closed-form analytical solution for the case of a gravity-driven, evaporating thin film flowing down a flat substrate. Analysis of the results for a range of topography shapes reveal that although a full-width, spanwise topography such as a step-up or a step-down does not affect the composition of the film, the same is no longer true for the case of localized topography, such as a peak or a trough, for which clear nonuniformities of the solvent concentration profile can be observed in the wake of the topography.

Gaskell, P. H.; Jimack, P. K.; Sellier, M.; Thompson, H. M.

2006-01-01

382

Impacts of Topography and Land Cover Changes on Regional Climate Over the Eastern Mediterranean  

NASA Astrophysics Data System (ADS)

The influence of the topography (mountain ranges, lowlands etc) on Mediterranean climate leads to different climatic types. There are extensive south to north range of mountains (Italian and Balkan Peninsula), as well as smaller mountainous regions with east - west orientation that separate the warm southern region from the cooler north regions. In addition, the wide indentation of Mediterranean coasts (Aegean, Adriatic etc), provide additional moisture sources. During winter season, heavy precipitation assists vegetation growth of Mediterranean forests and woodlands, whereas during summer, absence of precipitation and severe heat waves result to arid and semiarid vegetation. For that reason, it was quite interesting to track the changes that may occur in the climate of the Mediterranean region due to changes in topography and land use. The main objective of the study is the assessment of the impacts of topography and land cover changes on regional climate over the eastern Mediterranean. The examined regional climate model is RegCM4.3. Its spatial resolution is 25x25km and for the future projections the model is using the A1B SRES emission scenario. For the purposes of this study, different simulations were performed with changes in topography and land cover for the time period 1981-2000. The different simulated data were compared in order to examine the modifications that occur from the topography and land cover changes in extreme events and atmospheric circulation in the domain of study.

Velikou, Kondylia; Anagnostopoulou, Christina; Tolika, Konstantia

2014-05-01

383

Venus - Comparison of gravity and topography in the vicinity of Beta Regio  

NASA Technical Reports Server (NTRS)

The Doppler tracking data obtained from the Pioneer Venus Orbiter when it passed near Beta Regio yielded a peak vertical anomaly of 150 mGal when analyzed by our two stage procedure. A comparison of maps of the gravity and topography at comparable resolution shows a striking correlation. A scatter plot shows that the observed gravity anomaly is approximately 0.4 of that expected from uncompensated topography of half the mean density of Venus. However, the spectral admittance shows that the gravity anomalies can not be explained either by Airy compensation at fixed depth or by a model comprising an elastic plate atop an inviscid fluid. The gravity and topography variations may signify deep compensation or dynamic support for Beta Regio and more shallow compensation for other features.

Reasenberg, R. D.; Goldberg, Z. M.; Shapiro, I. I.

1982-01-01

384

Wind Energy Forecasting Utilizing High Resolution Topography in the WRF Model  

NASA Astrophysics Data System (ADS)

Local topography has considerable effects on the dynamics of low-level winds. Many wind farms take advantage of the local landscape when deciding where to place their turbines. In this study we attempt to better model these unique local features by representing them more accurately. The current default WRF topography has a maximum resolution of 30 arc seconds which at mid-latitudes is roughly 1 kilometer whereas the USGS database currently covers 95% of the United States at 30 meter resolution. In this study the 1/3 arc second national elevation database (NED13) is interfaced with the WRF model using a tool developed specifically to make this process simple and the effects of modeling with the updated topography are investigated.

Beechler, B. E.; Zupanski, D.

2012-12-01

385

Geoid and topography for infinite Prandtl number convection in a spherical shell  

NASA Technical Reports Server (NTRS)

Geoid anomalies and surface and lower-boundary topographies are calculated for numerically generated thermal convection for an infinite Prandtl number, Boussinesq, axisymmetric spherical fluid shell with constant gravity and viscosity, for heating both entirely from below and entirely from within. Convection solutions are obtained for Rayleigh numbers Ra up to 20 times the critical Ra in heating from below and 27 times critical for heating from within. Geoid parallels surface undulations, and boundary deformation generally increases with increasing cell wavelength. Dimensionless geoid and topography in heating from below are about 5 times greater than in heating from within. Values for heating from within correlate more closely with geophysical data than values from heating from below, suggesting a predominance of internal heating in the mantle. The study emphasizes that dynamically induced topography and geoid are sensitive to the mode of heating in the earth's mantle.

Bercovici, D.; Schubert, G.; Zebib, A.

1988-01-01

386