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We describe recent mechanical andeelectronic modifications to the Cambridge Ocean Bottom Hydrophone system, enabling it to record in addition three geophone channels from a deployed, disposable geophone package. Examples of data from seismic refraction experiments show good correspondence between records of ground motion detected by the hydrophone and the vertical geophone. Seismic signals are undistorted by noise from instrument related sources. Clear examples of P to S conversions just below the receiver are observed. Improved recording conditions are achieved by deploying the geophones in a small pressure vessel as far away as possible from the main instrument package. 相似文献
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Diagnosing snow accumulation errors in a rain‐snow transitional environment with snow board observations 下载免费PDF全文
Diagnosing the source of errors in snow models requires intensive observations, a flexible model framework to test competing hypotheses, and a methodology to systematically test the dominant snow processes. We present a novel process‐based approach to diagnose model errors through an example that focuses on snow accumulation processes (precipitation partitioning, new snow density, and snow compaction). Twelve years of meteorological and snow board measurements were used to identify the main source of model error on each snow accumulation day. Results show that modeled values of new snow density were outside observational uncertainties in 52% of days available for evaluation, while precipitation partitioning and compaction were in error 45% and 16% of the time, respectively. Precipitation partitioning errors mattered more for total winter accumulation during the anomalously warm winter of 2014–2015, when a higher fraction of precipitation fell within the temperature range where partition methods had the largest error. These results demonstrate how isolating individual model processes can identify the primary source(s) of model error, which helps prioritize future research. 相似文献
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Lance A. Waller Li Zhu Carol A. Gotway Dennis M. Gorman Paul J. Gruenewald 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(5):573-588
Past studies consistently indicate measurable local associations between alcohol distribution and the incidence of violence.
These results, coupled with measurements of spatial correlation, reveal the importance of spatial analysis in the study of
the interaction of alcohol and violence. While studies increasingly incorporate spatial correlation among model residuals
to improve precision and reduce bias, to date, most analyses assume associations that are constant and independent of location,
an assumption coming under increasing scrutiny in the quantitative geography literature. In this paper, we review and contrast
two approaches for the estimation of and inference for spatially heterogeneous effects (i.e., associative factors whose impacts on the outcome of interest vary throughout geographic space). Specifically,
we provide an in-depth comparison of “geographically weighted regression” models (allowing covariate effects to vary in space
but only allowing relatively ad hoc inference) with “variable coefficient” models (allowing varying effects via spatial random
fields and providing model-based estimation and inference, but requiring more advanced computational techniques). We compare
the approaches with respect to underlying conceptual structures, computational implementation, and inferential output. We
apply both approaches to violent crime, illegal drug arrest, and alcohol distribution data from Houston, Texas and compare
results in light of the differing methodological structures of the two approaches. 相似文献
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R.I. Waller A.J. Russell T.A.G.P. van Dijk & Ó. Knudsen 《Geografiska Annaler: Series A, Physical Geography》2001,83(1-2):29-38
During the initial stages of the November 1996 jökulhlaup at Skeiðarárjökull, Iceland, floodwaters burst onto the glacier surface via a series of fractures. This supraglacial drainage led to the formation of a number of distinct ice surface depressions, one of which is investigated in detail. The morphology and structural characteristics of this feature are described, as well as the sedimentology of an associated assemblage of debris-filled fractures. This work suggests that debris-charged subglacial floodwaters travelled up to the glacier surface, where supraglacial flow occurred initially via an extensive network of fractures, orientated parallel to the glacier margin. Supraglacial discharge became progressively more focused into a series of discrete outlets, leading to the mechanical erosion of a number of depressions on the glacier surface. The associated transfer of subglacially derived floodwaters to high levels within the glacier resulted in the rapid entrainment of large volumes of sediment which may influence the patterns, processes and products of ice-marginal sedimentation in the future. 相似文献
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Lower Pleistocene sediments recovered in boreholes from the Aberdeen Ground Formation in the central North Sea indicate that the unit was deposited in a delta front to prodelta/shallow, open shelf marine setting. Possible estuarine and clastic nearshore marine deposits have been identified on the western margin of the basin. The delta front sediments consist of interbedded, structureless to laminated sands and muds with organic debris, ferruginous nodules and common soft sediment deformation structures. Sporadic rippled and graded beds, basal scours to beds and starved ripples suggest periodic wave–current reworking. Prodelta/shelf marine sediments are predominantly argillaceous with only occasional thin sand beds and rare phosphatic bands. One exceptionally thick sand body or submarine channel-fill although this remains uncertain. The estuarine/clastic nearshore marine sediments include coarse channel-lag deposits and rippled and laminated subtidal sands. A rich microfossil assemblage recovered from the prodelta/shelf marine sequence indicates that deposition occurred under fluctuating climatic conditions. 相似文献