Cephalopods from a borehole in the type Wenlock area     

Charles Hepworth Holland 《Proceedings of the Geologists' Association. Geologists' Association》2002,113(3):207-215

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The effect of bathymetric filtering on nearshore process model results     

Nathaniel G. Plant  Kacey L. Edwards  James M. Kaihatu  Jayaram Veeramony  Larry Hsu  K. Todd Holland 《Coastal Engineering》2009

Nearshore wave and flow model results are shown to exhibit a strong sensitivity to the resolution of the input bathymetry. In this analysis, bathymetric resolution was varied by applying smoothing filters to high-resolution survey data to produce a number of bathymetric grid surfaces. We demonstrate that the sensitivity of model-predicted wave height and flow to variations in bathymetric resolution had different characteristics. Wave height predictions were most sensitive to resolution of cross-shore variability associated with the structure of nearshore sandbars. Flow predictions were most sensitive to the resolution of intermediate scale alongshore variability associated with the prominent sandbar rhythmicity. Flow sensitivity increased in cases where a sandbar was closer to shore and shallower. Perhaps the most surprising implication of these results is that the interpolation and smoothing of bathymetric data could be optimized differently for the wave and flow models. We show that errors between observed and modeled flow and wave heights are well predicted by comparing model simulation results using progressively filtered bathymetry to results from the highest resolution simulation. The damage done by over smoothing or inadequate sampling can therefore be estimated using model simulations. We conclude that the ability to quantify prediction errors will be useful for supporting future data assimilation efforts that require this information.  相似文献   

Zonal versus meridional velocity variance in satellite observations and realistic and idealized ocean circulation models     

Robert B. Scott  Brian K. Arbic  Christina L. Holland  Ayon Sen  Bo Qiu 《Ocean Modelling》2008,23(3-4):102-112

Global, high-quality, satellite-based observation of oceanic currents over the past 13 years has revealed ubiquitous quasi-horizontal eddies in the mesoscale (tens to hundreds of kilometers), confirming the view of a highly turbulent ocean suggested by observational programs in the 1970s. Idealized quasigeostrophic turbulence models suggest mesoscale turbulent flow can vary between isotropic, and highly anisotropic zonal jets. Here we compare the zonal and meridional velocity variance from satellite altimetry. We find that, for an unexplained reason and despite the chaotic nature of turbulence, the surface flow is organized into mesoscale patches where either zonal or meridional velocity variance dominates. The patches persist over 13 years, much longer than the turbulent timescale of a few months. Implications include potentially highly anisotropic redistribution of tracers by the mesoscale flow. Zonally averaged velocity variances reveal a slight preference for meridional over zonal velocity variance. Realistic primitive equation models succeed in reproducing both the patchy structure in local preference for either zonal or meridional velocity variance, and the zonally averaged preference for meridional variance. Idealized models of fully developed, quasigeostrophic turbulence fail in both regards.  相似文献   

The Transit New Zealand: Year 13 Geography Competition     

Peter Holland 《New Zealand geographer》2007,63(1):69-69

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An Overview of CCD Development at Lawrence Berkeley National Laboratory     

Steve Holland 《Experimental Astronomy》2002,14(2):83-89

Fully depleted, back-illuminated charge-coupled devices fabricated at Lawrence Berkeley National Laboratory on high-resistivity silicon are described. Device operation and technology are discussed, as well as the results on telescopes and future plans. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

In-flight Performance of the Advanced Camera for Surveys CCDs     

Mark Clampin  Marco Sirianni  George F. Hartig  Holland C. Ford  Garth D. Illingworth  Bill Burmester  William Koldewynd  Andre R. Martel  Adam Riess  Ronald J. Schrein  Pamela C. Sullivan 《Experimental Astronomy》2002,14(2):107-115

The Advanced Camera for Surveys (ACS), installed in the Hubble Space telescope in March 2002, will significantly extend HST's deep, survey imaging capabilities. ACS has met, or exceeded, all of its key performance specifications. In this paper we briefly review the in-flight performance of the instrument's CCD detectors and preview early ACS science observations. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Practical use of video imagery in nearshore oceanographic fieldstudies     

Holland  K.T. Holman  R.A. Lippmann  T.C. Stanley  J. Plant  N. 《Oceanic Engineering, IEEE Journal of》1997,22(1):81-92

An approach was developed for using video imagery to quantify, in terms of both spatial and temporal dimensions, a number of naturally occurring (nearshore) physical processes. The complete method is presented, including the derivation of the geometrical relationships relating image and ground coordinates, principles to be considered when working with video imagery and the two-step strategy for calibration of the camera model. The techniques are founded on the principles of photogrammetry, account for difficulties inherent in the use of video signals, and have been adapted to allow for flexibility of use in field studies. Examples from field experiments indicate that this approach is both accurate and applicable under the conditions typically experienced when sampling in coastal regions. Several applications of the camera model are discussed, including the measurement of nearshore fluid processes, sand bar length scales, foreshore topography, and drifter motions. Although we have applied this method to the measurement of nearshore processes and morphologic features, these same techniques are transferable to studies in other geophysical settings  相似文献   

Coupled scattering and reflection measurements in shallow water     

Holland  C.W. 《Oceanic Engineering, IEEE Journal of》2002,27(3):454-470

The characteristics of shallow-water reverberation are often controlled by scattering from the seabed. While scattering mechanisms are understood in general, the state-of-the-art falls far short of predicting the correct angular and frequency dependence of scattering in a given region. A series of acoustic and supporting geoacoustic measurements were conducted over a large area in the Straits of Sicily in order to study seabed scattering in a complex littoral environment. The hypothesis was that exploiting direct path reflection coefficient measurements, in conjunction with the scattering measurements, could help illuminate the underlying scattering mechanisms. The sediment at the seabed interface was found to be a fine silty clay with nearly uniform properties across the area. Notwithstanding this spatial homogeneity, 1-6-kHz reflection and scattering measurements showed significant spatial variability. The coupled reflection-scattering approach resolved this apparent discrepancy, revealing that the reflection and scattering processes are largely controlled by the sediment properties below, rather than at, the water sediment interface. Measurements at 3600 Hz show that site-to-site variability is in part controlled by the thickness of the silty-clay layer. Layers up to 10 m below the water sediment interface contribute to the scattering at 3600 Hz.  相似文献   

Petrology and geochemistry of the archean rocks of the malton gneiss complex,British Columbia     

V.E. Chamberlain  R.St.J. Lambert  J.G. Holland 《Precambrian Research》1980,11(1):1-9

Hornblendic and felsic groups of Archean age and each of broadly similar geochemical composition across the Malton Gneiss Complex southeast of Valemount, Bristish Columbia, show detailed mineralogical and chemical variations from one geographical district to another. The complex appears to be composed of meta-igneous rocks which were originally developed as petrologically discrete units on a roughly 10-km scale, but which all belonged to one similar petrographic province. Overall they are characterized by rather high immobile trace and alkali element abundances. Their nearest geochemical equivalent appear to be found in the grey gneiss complexes of the North Atlantic Craton rather than in the granite-greenstone complexes of the Canadian Shield, but no other Archean complex possesses their overall characteristics. Some similarities in A-F-M and Q-Ab-Or content of these gneisses and those of the Laramie Range, Wyoming, are noted.  相似文献   

Transient sea-ice polynya forced by oceanic flow variability     

David M. Holland   《Progress in Oceanography》2000,48(4)

In the Weddell Sea during the winters of 1974–1976 a significant opening in the sea-ice cover occurred in the vicinity of a large bathymetric feature — the Maud Rise seamount. The event is commonly referred to as the Weddell Polynya. Aside from such a large-scale, relatively persistent polynya in the Weddell Sea, transient, small-scale polynya can also appear in the sea-ice cover at various times throughout the winter and at various locations with respect to the Maud Rise. The underlying causes for the occurrence of such transient polynya have not been unambiguously identified. We hypothesize that variations in the mean ocean currents are one major contributor to such variability in the sea-ice cover. Analysis of the sea-ice equations with certain idealized patterns of ocean currents serving as forcing is shown to lead to Ekman transports of sea ice favorable to the initiation of transient polynya. Aside from the actual spatial pattern of the idealized ocean currents, many other factors need also be taken into account when looking at such transient polynya. Two other such factors discussed are variations in the sea-ice thickness field and the treatment of the sea-ice rheology. Simulations of a sea-ice model coupled to a dynamical ocean model show that the interaction of (dynamical) oceanic currents with large-scale topographic features, such as the Maud Rise, does lead to the formation of transient polynya, again through Ekman transport effects. This occurs because the seamount has a dynamic impact on the three-dimensional oceanic flow field all the way up through the water column, and hence on the near surface ocean currents that are in physical contact with the sea ice. Further simulations of a sea-ice model coupled to a dynamic ocean model and forced with atmospheric buoyancy fluxes show that transient polynya can be enhanced when atmospheric cooling provides a positive feedback mechanism allowing preferential open-ocean convection to occur. The convection, which takes hold at sites where transient polynya have been initiated by sea-ice–ocean stress interaction, has an enhancing effect arising from the convective access to warmer, deeper waters. To investigate all of these effects in a hierarchical manner we use a primitive equation coupled sea-ice–ocean numerical model configured in a periodic channel domain with specified atmospheric conditions. We show that oceanic flow variability can account for temporal variability in small-scale, transient polynya and thus point to a plausible mechanism for the initiation of large-scale, sustained polynya such as the Weddell Polynya event of the mid 1970s.  相似文献