Error Estimation of Bathymetric Grid Models Derived from Historic and Contemporary Data Sets

The past century has seen remarkable advances in technologies associated with positioning and the measurement of depth. Lead lines have given way to single beam echo sounders, which in turn are being replaced by multibeam sonars and other means of remotely and rapidly collecting dense bathymetric datasets. Sextants were replaced by radio navigation, then transit satellite, GPS and now differential GPS. With each new advance comes tremendous improvement in the accuracy and resolution of the data we collect. Given these changes and given the vastness of the ocean areas we must map, the charts we produce are mainly compilations of multiple data sets collected over many years and representing a range of technologies. Yet despite our knowledge that the accuracy of the various technologies differs, our compilations have traditionally treated each sounding with equal weight. We address these issues in the context of generating regularly spaced grids containing bathymetric values. Gridded products are required for a number of earth sciences studies and for generating the grid we are often forced to use a complex interpolation scheme due to the sparseness and irregularity of the input data points. Consequently, we are faced with the difficult task of assessing the confidence that we can assign to the final grid product, a task that is not usually addressed in most bathymetric compilations. Traditionally the hydrographic community has considered each sounding equally accurate and there has been no error evaluation of the bathymetric end product. This has important implications for use of the gridded bathymetry, especially when it is used for generating further scientific interpretations. In this paper we approach the problem of assessing the confidence of the final bathymetry gridded product via a direct-simulation Monte Carlo method. We start with a small subset of data from the International Bathymetric Chart of the Arctic Ocean (IBCAO) grid model [Jakobsson et al., 2000]. This grid is compiled from a mixture of data sources ranging from single beam soundings with available metadata, to spot soundings with no available metadata, to digitized contours; the test dataset shows examples of all of these types. From this database, we assign a priori error variances based on available meta-data, and when this is not available, based on a worst-case scenario in an essentially heuristic manner. We then generate a number of synthetic datasets by randomly perturbing the base data using normally distributed random variates, scaled according to the predicted error model. These datasets are next re-gridded using the same methodology as the original product, generating a set of plausible grid models of the regional bathymetry that we can use for standard deviation estimates. Finally, we repeat the entire random estimation process and analyze each run’s standard deviation grids in order to examine sampling bias and standard error in the predictions. The final products of the estimation are a collection of standard deviation grids, which we combine with the source data density in order to create a grid that contains information about the bathymetric model’s reliability

Seafloor mapping in the Arctic: support for a potential U.S. extended continental shelf

For the United States, the greatest opportunity for an extended continental shelf under UNCLOS is in the ice-covered regions of the Arctic north of Alaska. Since 2003, CCOM/JHC has been using the icebreaker Healy equipped with a multibeam echosounder, chirp subbottom profiler, and dredges, to map and sample the region of Chukchi Borderland and Alpha-Mendeleev Ridge complex. These data have led to the discovery of several new features, have radically changed our view of the bathymetry and geologic history of the area, and may have important ramifications for the determination of the limits of a U.S. extended continental shelf under Article 76

On the Use of Historical Bathymetric Data to Determine Changes in Bathymetry: An Analysis of Errors and Application to Great Bay Estuary, NH

The depth measurements that are incorporated into bathymetric charts have associated errors with magnitudes depending on the survey circumstances and applied techniques. For this reason, combining and comparing depth measurements collected over many years with different techniques and standards is a difficult task which must be done with great caution. In this study we have developed an approach for comparing historical bathymetric surveys. Our methodology uses Monte Carlo modelling to account for the random error components inherited in the data due to positioning and depth measurement uncertainties

Hatteras Transverse Canyon, Hatteras Outer Ridge and environs of the U.S. Atlantic margin: A view from multibeam bathymetry and backscatter

Previously unknown features in Hatteras Transverse Canyon and environs were recently mapped during multibeam surveys of almost the entire eastern U.S. Atlantic continental margin. The newly identified features include (1) extensive landslide scarps on the walls of Hatteras Transverse and Hatteras Canyons, (2) an area of multiple landslide deposits that block lower Hatteras Transverse Canyon, (3) a large depositional feature down-canyon from the landslide deposits that rises 100 m above the uppermost Hatteras Fan and has buried the transition from the mouth of Hatteras Transverse Canyon to uppermost Hatteras Fan, (4) a zone of cyclic steps on upper Hatteras Fan that suggests super critical turbidity currents performed a series of hydraulic jumps and formed large upstream-migrating bedforms, (5) several knickpoints in the channel thalwegs of both Hatteras Transverse Canyon and Hatteras Canyon, one 40 m high, that suggest both canyon channels are out of equilibrium and are in the process of readjusting, either to the channel blockage by the extensive landslide deposits or by a readjustments to increased sedimentation during the last eustatic lowstand, (6) a large area of outcrop on the lower margin between Pamlico and Hatteras Canyons that previously was interpreted as an area of slumps, blocky slide debris and mud waves, (7) headward erosion in the head region of Hatteras Transverse Canyonwhere it has intercepted the lowest reaches of Albemarle Canyon channel as well as headward erosion in a small side channel that has eroded into Hatteras Outer Ridge and (8) sections of bedforms on Hatteras Outer Ridge that are partially buried by sediment from Washington–Norfolk Canyon channel as well as by sediment transported from Hatteras Abyssal Plain. The newly discovered features add a new level of detail to understand the recent processes that have profoundly affected Hatteras Transverse Canyon, Hatteras Canyon and, to a lesser degree, Hatteras Outer Ridge

Investigating the prevalence and causes of prescribing errors in general practice : the PRACtICe Study

Report prepared by the University of Nottingham, University of Reading and University of Hertfordshir

Patellofemoral Pain Syndrome Alters Neuromuscular Control and Kinetics during Stair Ambulation

The aim of the study was to investigate differences in frontal plane knee kinetics, onset timing and dura-tion of the gluteus medius (GMed), adductor longus (AL), and vastus medialis oblique (VMO) during stair ambulation between those with and without patellofemoral pain syndrome (PFPS). Twenty PFPS patients and twenty healthy participants completed stair ambulation while surface electromyography (EMG), video, and ground reaction forces were collected. PFPS patients had a higher peak internal knee abduction moment during stair ascent, and a higher internal knee abduction impulse for both ascent and descent. During stair ascent, PFPS patients displayed earlier onset of the AL and later onset of GMed, compared to the healthy individuals. Also, PFPS patients had longer activation duration of the AL and shorter activation durations of the VMO and GMed during stair ascent. During stair descent, PFPS patients displayed delayed GMed onset and shorter activation duration of GMed and VMO. The results of the study suggest that altered neuromuscular control of the medial thigh musculature may be an important contributor to PFPS

Delayed Response to Radiofrequency Ablation of Accessory Connections

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72240/1/j.1540-8159.1993.tb01019.x.pd

Electronic Chart of the Future: The Hampton Roads Project

ECDIS is evolving from a two-dimensional static display of chart-related data to a decision support system capable of providing real-time or forecast information. While there may not be consensus on how this will occur, it is clear that to do this, ENC data and the shipboard display environment must incorporate both depth and time in an intuitively understandable way. Currently, we have the ability to conduct high-density hydrographic surveys capable of producing ENCs with decimeter contour intervals or depth areas. Yet, our existing systems and specifications do not provide for a full utilization of this capability. Ideally, a mariner should be able to benefit from detailed hydrographic data, coupled with both forecast and real-time water levels, and presented in a variety of perspectives. With this information mariners will be able to plan and carry out transits with the benefit of precisely determined and easily perceived underkeel, overhead, and lateral clearances. This paper describes a Hampton Roads Demonstration Project to investigate the challenges and opportunities of developing the “Electronic Chart of the Future.” In particular, a three-phase demonstration project is being planned: 1. Compile test datasets from existing and new hydrographic surveys using advanced data processing and compilation procedures developed at the University of New Hampshire’s Center for Coastal and Ocean Mapping/Joint Hydrographic Center (CCOM/JHC); 2. Investigate innovative approaches being developed at the CCOM/JHC to produce an interactive time- and tide-aware navigation display, and to evaluate such a display on commercial and/or government vessels; 3. Integrate real-time/forecast water depth information and port information services transmitted via an AIS communications broadcast

Rapid Oscillations in Cataclysmic Variables. XVI. DW Cancri

We report photometry and spectroscopy of the novalike variable DW Cancri. The spectra show the usual broad H and He emission lines, with an excitation and continuum slope characteristic of a moderately high accretion rate. A radial-velocity search yields strong detections at two periods, 86.1015(3) min and 38.58377(6) min. We interpret these as respectively the orbital period P_orb of the binary, and the spin period P_spin of a magnetic white dwarf. The light curve also shows the spin period, plus an additional strong signal at 69.9133(10) min, which coincides with the difference frequency 1/P_spin-1/P_orb. These periods are stable over the 1 year baseline of measurement. This triply-periodic structure mimics the behavior of several well-credentialed members of the "DQ Herculis" (intermediate polar) class of cataclysmic variables. DQ Her membership is also suggested by the mysteriously strong sideband signal (at nu_spin-nu_orb), attesting to a strong pulsed flux at X-ray/EUV/UV wavelengths. DW Cnc is a new member of this class, and would be an excellent target for extended observation at these wavelengths.Comment: PDF, 28 pages, 6 tables, 9 figures; accepted, in press, to appear June 2004, PASP; more info at http://cba.phys.columbia.edu