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DeSanto, JB, Chadwell CD, Sandwell DT.  2019.  Kinematic post-processing of ship navigation data using precise point positioning. Journal of Navigation. 72:795-804.   10.1017/s0373463318000887   AbstractWebsite

Seafloor geodetic studies such as Global Positioning System (GPS)-Acoustic experiments often require the measurement platform on the sea surface to be positioned accurately to within a few centimetres. In this paper, we test the utility of Precise Point Positioning (PPP) for this application with two experiments. The first fixed platform experiment is a comparison between three independent processing software packages: Positioning and Navigation Data Analyst (PANDA), Global Navigation Satellite System-Inferred Positioning System and Orbit Analysis Simulation Software (GIPSY-OASIS), and the Canadian Spatial Reference System (CSRS)) and a more accurate solution based on conventional differential processing of a remote GPS station in the Aleutian Islands. The second moving platform experiment is a comparison among the three PPP software packages using 40 hours of ship navigation data collected during the Roger Revelle RR1605 cruise 170 nautical miles southwest of Palau in May 2016. We found the PPP solutions were repeatable to 5 center dot 49 cm in the horizontal components and 12 center dot 4 cm in the vertical component. This demonstrates not only that PPP is a useful tool for positioning marine platforms in remote locations, but also that modern ship navigation instruments such as the Kongsberg Seapath 330 + are suitable for seafloor geodetic application.

DeSanto, JB, Sandwell DT, Chadwell CD.  2016.  Seafloor geodesy from repeated sidescan sonar surveys. Journal of Geophysical Research-Solid Earth. 121:4800-4813.   10.1002/2016jb013025   AbstractWebsite

Accurate seafloor geodetic methods are critical to the study of marine natural hazards such as megathrust earthquakes, landslides, and volcanoes. We propose digital image correlation of repeated shipboard sidescan sonar surveys as a measurement of seafloor deformation. We test this method using multibeam surveys collected in two locales: 2500m deep lightly sedimented seafloor on the flank of a spreading ridge and 4300m deep heavily sedimented seafloor far from any plate boundary. Correlation of these surveys are able to recover synthetic displacements in the across-track (range) direction accurate to within 1m and in the along-track (azimuth) direction accurate to within 1-10m. We attribute these accuracies to the inherent resolution of sidescan data being better in the range dimension than the azimuth dimension. These measurements are primarily limited by the accuracy of the ship navigation. Dual-frequency GPS units are accurate to approximate to 10cm, but single-frequency GPS units drift on the order of 1m/h and are insufficient for geodetic application.

Muller, RD, Qin XD, Sandwell DT, Dutkiewicz A, Williams SE, Flament N, Maus S, Seton M.  2016.  The GPlates Portal: Cloud-based interactive 3D visualization of global geophysical and geological data in a web browser. Plos One. 11   10.1371/journal.pone.0150883   AbstractWebsite

The pace of scientific discovery is being transformed by the availability of 'big data' and open access, open source software tools. These innovations open up new avenues for how scientists communicate and share data and ideas with each other and with the general public. Here, we describe our efforts to bring to life our studies of the Earth system, both at present day and through deep geological time. The GPlates Portal ( is a gateway to a series of virtual globes based on the Cesium Javascript library. The portal allows fast interactive visualization of global geophysical and geological data sets, draped over digital terrain models. The globes use WebGL for hardware-accelerated graphics and are cross-platform and cross-browser compatible with complete camera control. The globes include a visualization of a high-resolution global digital elevation model and the vertical gradient of the global gravity field, highlighting small-scale seafloor fabric such as abyssal hills, fracture zones and seamounts in unprecedented detail. The portal also features globes portraying seafloor geology and a global data set of marine magnetic anomaly identifications. The portal is specifically designed to visualize models of the Earth through geological time. These space-time globes include tectonic reconstructions of the Earth's gravity and magnetic fields, and several models of long-wavelength surface dynamic topography through time, including the interactive plotting of vertical motion histories at selected locations. The globes put the on-the-fly visualization of massive data sets at the fingertips of end-users to stimulate teaching and learning and novel avenues of inquiry.

Xu, X, Tong X, Sandwell DT, Milliner CWD, Dolan JF, Hollingsworth J, Leprince S, Ayoub F.  2016.  Refining the shallow slip deficit. Geophysical Journal International. 204:1867-1886.   10.1093/gji/ggv563   Abstract

Geodetic slip inversions for three major (Mw > 7) strike-slip earthquakes (1992 Landers, 1999 Hector Mine and 2010 El Mayor–Cucapah) show a 15–60 per cent reduction in slip near the surface (depth < 2 km) relative to the slip at deeper depths (4–6 km). This significant difference between surface coseismic slip and slip at depth has been termed the shallow slip deficit (SSD). The large magnitude of this deficit has been an enigma since it cannot be explained by shallow creep during the interseismic period or by triggered slip from nearby earthquakes. One potential explanation for the SSD is that the previous geodetic inversions lack data coverage close to surface rupture such that the shallow portions of the slip models are poorly resolved and generally underestimated. In this study, we improve the static coseismic slip inversion for these three earthquakes, especially at shallow depths, by: (1) including data capturing the near-fault deformation from optical imagery and SAR azimuth offsets; (2) refining the interferometric synthetic aperture radar processing with non-boxcar phase filtering, model-dependent range corrections, more complete phase unwrapping by SNAPHU (Statistical Non-linear Approach for Phase Unwrapping) assuming a maximum discontinuity and an on-fault correlation mask; (3) using more detailed, geologically constrained fault geometries and (4) incorporating additional campaign global positioning system (GPS) data. The refined slip models result in much smaller SSDs of 3–19 per cent. We suspect that the remaining minor SSD for these earthquakes likely reflects a combination of our elastic model's inability to fully account for near-surface deformation, which will render our estimates of shallow slip minima, and potentially small amounts of interseismic fault creep or triggered slip, which could ‘make up’ a small percentages of the coseismic SSD during the interseismic period. Our results indicate that it is imperative that slip inversions include accurate measurements of near-fault surface deformation to reliably constrain spatial patterns of slip during major strike-slip earthquakes.

Becker, JJ, Sandwell DT, Smith WHF, Braud J, Binder B, Depner J, Fabre D, Factor J, Ingalls S, Kim SH, Ladner R, Marks K, Nelson S, Pharaoh A, Trimmer R, Von Rosenberg J, Wallace G, Weatherall P.  2009.  Global Bathymetry and Elevation Data at 30 Arc Seconds Resolution: SRTM30_PLUS. Marine Geodesy. 32:355-371.   10.1080/01490410903297766   AbstractWebsite

A new 30-arc second resolution global topography/bathymetry grid (SRTM30_PLUS) has been developed from a wide variety of data sources. Land and ice topography comes from the SRTM30 and ICESat topography, respectively. Ocean bathymetry is based on a new satellite-gravity model where the gravity-to-topography ratio is calibrated using 298 million edited soundings. The main contribution of this study is the compilation and editing of the raw soundings, which come from NOAA, individual scientists, SIO, NGA, JAMSTEC, IFREMER, GEBCO, and NAVOCEANO. The gridded bathymetry is available for ftp download in the same format as the 33 tiles of SRTM30 topography. There are 33 matching tiles of source identification number to convey the provenance of every grid cell. The raw sounding data, converted to a simple common format, are also available for ftp download.

Maia, M, Ackermand D, Dehghani GA, Gente P, Hekinian R, Naar D, O'Connor J, Perrot K, Morgan JP, Ramillien G, Revillon S, Sabetian A, Sandwell D, Stoffers P.  2000.  The Pacific-Antarctic Ridge-Foundation hotspot interaction: a case study of a ridge approaching a hotspot. Marine Geology. 167:61-84.   10.1016/s0025-3227(00)00023-2   AbstractWebsite

The Foundation hotspot-Pacific-Antarctic Ridge (PAI) system is the best documented case of a fast spreading ridge approaching a hotspot and interacting with it. The morphology, crustal structure inferred from gravity anomalies and the chemical composition of the lavas of the axial area of the PAR show evidence of the influence of the hotspot, that is presently located roughly 35 km west of the spreading ridge axis. Along-axis variation in the Mantle Bouguer anomaly is about 28 mGal, corresponding to a crustal thickening of 1.5 km where the hotspot is nearer to the PAR. Anomalous ridge elevation is 650 m and the along-axis width of the chemical anomaly is 200 km. A comparison of these axial parameters with those derived for other ridge-hotspot systems, suggests that the amount of plume material reaching the ridge axis is smaller for the Foundation-PAR system. This implies a weaker connection between the plume and the ridge. Cumulative effects of a fast spreading rate and of a fast ridge-hotspot relative motion can be responsible for this weak plume-ridge flow. The how from the hotspot may be less efficiently channelled towards the ridge axis when a fast ridge is rapidly moving towards a hotspot. (C) 2000 Elsevier Science B.V. All rights reserved.

Sandwell, DT, Winterer EL, Mammerickx J, Duncan RA, Lynch MA, Levitt DA, Johnson CL.  1995.  Evidence for Diffuse Extension of the Pacific Plate from Pukapuka Ridges and Cross-Grain Gravity Lineations. Journal of Geophysical Research-Solid Earth. 100:15087-15099.   10.1029/95jb00156   AbstractWebsite

Satellite altimeter measurements of marine gravity reveal 100 to 200-km wavelength lineations over a wide area of the Pacific plate oriented roughly in the direction of absolute plate motion. At least three mechanisms have been proposed for their origin: small-scale convective rolls aligned in the direction of absolute plate motion by shear in the asthenosphere; diffuse N-S extension of the lithosphere resulting in lineated zones of extension (boudins); and minihotspots that move slowly with respect to major hotspots and produce intermittent volcanism. Recently, several chains of linear volcanic ridges have been found to be associated with the gravity lineations. Following ridgelike gravity signatures apparent in high-resolution Geosat gravity measurements, we surveyed a series of volcanic ridges that extend northwest from the East Pacific Rise flank for 2600 km onto 40 Ma seafloor. Our survey data, as well as radiometric dates on samples we collected from the ridges, provide tight constraints on their origin: (1) Individual ridge segments and sets of ridges are highly elongate in the direction of present absolute plate motion. (2) The ridges formed along a band 50 to 70-km-wide in the trough of one of the more prominent gravity lineations. (3) Radiometric dates of the largest ridges show no hotspot age progression. Moreover, the directions predicted for minihotspot traces older than 24 Ma do not match observed directions of either the gravity lineations or the ridges. Based on this last observation, we reject the minihotspot model. The occurrence of the ridges in the trough of the gravity lineation is incompatible with the small-scale convection model which would predict increased volcanism above the convective upwelling. We favor the diffuse extension model because it is consistent with the occurrence of ridges in the trough above the more highly extended lithosphere. However, the multibeam data show no evidence for widespread normal faulting of the crust as predicted by the model. Perhaps the fault scarps are buried under more than 30 m of sediments and/or covered by the elongated ridges. Finally, we note that if ridge-push force is much smaller than trench-pull force, then near the ridge axis the direction of maximum tensile stress must be perpendicular to the direction of absolute plate motion.

Sandwell, DT, Lawver LA, Dalziel IWD, Smith WHF, Wiederspahn M.  1992.  ANTARCTICA Gravity Anomaly and Infrared Satellite Image, USGS MAP 1-2284. : U.S. Geol. Survey Abstract
Detrick, RS, Von Herzen RP, Parsons B, Sandwell D, Dougherty M.  1986.  Heat-Flow Observations on the Bermuda Rise and Thermal Models of Midplate Swells. Journal of Geophysical Research-Solid Earth and Planets. 91:3701-3723.   10.1029/JB091iB03p03701   AbstractWebsite

The Bermuda Rise is a broad topographic swell which is apparent in both residual depth and geoid anomaly maps of the western North Atlantic. The magnitudes of the depth and geoid anomalies associated with the Bermuda Rise are similar to the anomalies associated with other swells surrounding recent volcanic islands (e.g., Hawaii), suggesting that despite the lack of recent volcanism on Bermuda, the rise has a similar origin to other midplate swells. Results are reported from 171 new heat flow measurements at seven carefully selected sites on the Bermuda Rise and the surrounding seafloor. Off the Bermuda Rise the basement depths are generally shallower and the heat flow higher than either the plate or boundary layer models predict, with the measured heat flow apparently reaching a uniform value of about 50 mW m−2 on 120 m.y. old crust. On the Bermuda Rise the heat flow is significantly higher (57.4±2.6 mW m−2) than off the swell (49.5±1.7 mW m−2). The magnitude of the anomalous heat flux (8–10 mW m−2) is comparable to that previously found along the older portion of the Hawaiian Swell near Midway. The existence of higher heat flow on both the Hawaiian Swell and Bermuda Rise indicates that these features fundamentally have a thermal origin. The differences in the shape, uplift, and subsidence histories of the Hawaiian Swell and Bermuda Rise can be quantitatively explained by the different absolute velocities of the Pacific and North American plates moving across a distributed heat source in the underlying mantle. Two-dimensional numerical convection models indicate that the observed depth, geoid, and heat flow anomalies are consistent with simple convection models in which the lower part of the thermally defined plate acts as the upper thermal boundary layer of the convection.

Sandwell, DT, Milbert DG, Douglas BC.  1986.  Global Nondynamic Orbit Improvement for Altimetric Satellites. Journal of Geophysical Research-Solid Earth and Planets. 91:9447-9451.   10.1029/JB091iB09p09447   AbstractWebsite

The largest source of error in satellite altimetry is in the radial position of the satellite. Radial orbit errors of more than a few decimeters prohibit basin-scale studies of sea surface height variability. We explore nondynamic techniques for reducing this error. Sea surface height differences at intersections of satellite altimeter profiles (crossover data) provide a strong constraint on radial orbit error but do not uniquely define it. The portion of orbit error that is a function of latitude and longitude only produces no crossover differences and therefore cannot be recovered with crossover data. Using mathematics (inclination functions) originally developed for satellite dynamics, we determine the entire class of orbit error functions not recoverable with crossover data. These functions are mappings of surface spherical harmonics into the orbit plane. For example, the l = 1, m = 0 surface harmonic maps into sinusoidal orbit error with a frequency of once per orbit. Nonzonal harmonics map into linear combinations of three or more frequencies that are linked by the inclination functions. Between frequencies of 0 and 2.2 cycles per orbit there are nine orbit error components that cannot be recovered using crossover data. These components are uniquely defined, however, by nine globally distributed radial tracking points. Fewer tracking points are sufficient if a smoothness criteria is applied to the orbit correction curve. Our findings suggest that radial orbit error can be significantly reduced by including a few globally distributed radar reflectors (or transponders) in the tracking network.

Cheney, RE, Douglas BC, McAdoo DC, Sandwell DT.  1986.  Geodetic and oceanographic applications of satellite altimetry. Space geodesy and geodynamics. ( Anderson A, Cazenave A, Eds.)., London, United Kingdom (GBR): Academic Press, London AbstractWebsite
Cheney, RE, Douglas BC, Sandwell DT, Marsh JG, Martin TV.  1984.  Applications of Satellite Altimetry to Oceanography and Geophysics. Marine Geophysical Researches. 7:17-32.   10.1007/bf00305408   AbstractWebsite

Satellite-borne altimeters have had a profound impact on geodesy, geophysics, and physical oceanography. To first order approximation, profiles of sea surface height are equivalent to the geoid and are highly correlated with seafloor topography for wavelengths less than 1000 km. Using all available Geos-3 and Seasat altimeter data, mean sea surfaces and geoid gradient maps have been computed for the Bering Sea and the South Pacific. When enhanced using hill-shading techniques, these images reveal in graphic detail the surface expression of seamounts, ridges, trenches, and fracture zones. Such maps are invaluable in oceanic regions where bathymetric data are sparse. Superimposed on the static geoid topography is dynamic topography due to ocean circulation. Temporal variability of dynamic height due to oceanic eddies can be determined from time series of repeated altimeter profiles. Maps of sea height variability and eddy kinetic energy derived from Geos-3 and Seasat altimetry in some cases represent improvements over those derived from standard oceanographic observations. Measurement of absolute dynamic height imposes stringent requirements on geoid and orbit accuracies, although existing models and data have been used to derive surprisingly realistic global circulation solutions. Further improvement will only be made when advances are made in geoid modeling and precision orbit determination. In contrast, it appears that use of altimeter data to correct satellite orbits will enable observation of basin-scale sea level variations of the type associated with climatic phenomena.

Douglas, BC, Agreen RW, Sandwell DT.  1984.  Observing Global Ocean Circulation with Seasat Altimeter Data. Marine Geodesy. 8:67-83. AbstractWebsite