Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1991. / Vita. Abstract. Includes bibliographical references (leaves 62-64). Also available via the Internet.

No description available.

No description available.

Climate exerts a fundamental control on ecosystem function, species diversity and distribution. Topographic variability may influence surface climate, through processes operating at a landscape- scale. To quantify and model such influences, the topography of a 72 km(^2) area of complex terrain, (including the Moor House National Nature Reserve in northern England) was analysed at 50 m resolution. A suite of topographic variables was created, including distance relative to the Pennine ridge (dist), and elevation difference between each grid cell and the lowest grid cell within a specified neighbourhood {drain). Automatic weather stations (AWS) were deployed in a series of networks to test hypothetical relationships between landscape and climate. Daily maximum air temperature, daily mean soil temperature and daily potential evapotranspiration can be modelled spatially using a daily lapse rate calculated from the difference between daily observations made at two base stations. On days with a south easterly wind direction, daily mean temperature is estimated as a function of lapse rate and dist; the spatial behaviour of temperature is consistent with a föhn mechanism. Daily minimum temperature is modelled using lapse rate and drain on days with a lapse rate of minimum temperature shallower than -2.03 x 10 C m(^-1), incorporating the effects of katabatic air flow. Daily solar radiation surfaces are estimated by a GIS routine that models interactions between slope and solar geometry and accounts for daily variations in cloudiness and daylight duration. The daily climate surfaces were tested using data measured at a range of AWS locations during different times of year. The accuracy of the daily surfaces is not seasonally-dependent. The spatial climate data are particularly well suited to landscape-scale ecology because the methods account for prevailing topoclimatic constraints and because separate climate surfaces are generated for each day, capturing the high frequency variability characteristic of upland regions.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 112-114). Also available via the Internet.

This dissertation details work aimed at better understanding topographic effects in earthquake ground motions. The experiment, conducted in Central-Eastern Utah, used frequent and predictable seismicity produced by underground longwall coal mining as a source of low-intensity ground motions. Locally-dense arrays of seismometers deployed over various topographic features were used to passively monitor seismic energy produced by mining-induced implosions and/or stress redistribution in the subsurface. The research consisted of two separate studies: an initial feasibility experiment (Phase I) followed by a larger-scale main study (Phase II). Over 50 distinct, small-magnitude (M[subscript 'L'] < 1.6) seismic events were identified in each phase. These events were analyzed for topographic effects in the time domain using the Peak Ground Velocity (PGV), and in the frequency domain using the Standard Spectral Ratio (SSR) method, the Median Reference Method (MRM), and the Horizontal-to-Vertical Spectral Ratio (HVSR) method. The polarities of the horizontal ground motions were also visualized using directional analyses. The various analysis methods were compared to assess their ability to estimate amplification factors and determine the topographic frequencies of interest for each feature instrumented. The MRM was found to provide the most consistent, and presumably accurate, estimates of the amplification factor and frequency range for topographic effects. Results from this study clearly indicated that topographic amplification of ground motions does in fact occur. These amplifications were very frequency dependent, and the frequency range was correctly estimated in many, but not all, cases using simplified, analytical methods based on the geotechnical and geometrical properties of the topography. Amplifications in this study were found to generally range from 2 to 3 times a reference/baseline site condition, with some complex 3D features experiencing amplifications as high as 10. Maximum amplifications occurred near the crest of topographic features with slope angles greater than approximately 15 degrees, and the amplifications were generally oriented in the direction of steepest topographic relief, with some dependency on wave propagation direction. / text

Critical Source Areas (CSAs) of phosphorus (P) are areas within a watershed that have a high propensity to export P to surface waters. CSAs contain two factors: source and transport factors. Source factors include soil P status and fertilizer and manure inputs, while transport factors include hydrologic and erosion processes that mobilize P. The aim of this study was to: 1) identify CSAs of P in an agricultural watershed and the stormflow dynamics controlling P export and 2) to delineate CSAs of P at the agricultural field scale using georeferenced soil test P (STP) and a digital elevation model (DEM) in a geographic information system (GIS). Soil test P (STP) along with dissolved reactive P (DRP), particulate P (PP), and total P (TP) in soil water, groundwater, and surface runoff were monitored in three small (< 8 ha) agricultural watersheds located in Decatur, Illinois, each situated within a separate experimental field. Further, volumetric water content (VWC) was continuously monitored on topographic positions, e.g. foot slopes, hill slopes, and shoulder slopes, to determine topographic position influence on soil moisture distribution. Repeated measures mixed models analysis showed that foot slopes (32.2%) had significantly higher VWC than hill slope (29.6%) and shoulder slopes (30.9%) during the growing season, while foot slopes (38.9%) and hill slopes (38.9%) had significantly higher VWC than shoulder slopes (34.9%) during the dormant season. Persistent shallow groundwater tables were implicated to control spatial and temporal VWC moisture distribution. Both foot slopes and hill slopes were implicated as transport areas. Repeated measures mixed models analysis also showed that foot slopes (73 kg ha&minus1) had significantly higher STP than hill slopes (28.9 kg ha&minus1) and shoulder slopes (33.8 kg ha&minus1) most likely due to the erosion and deposition of sediment from upper slopes to lower slopes. Foot slopes were consequently classified as source areas. A surface runoff event revealed near stream saturation and flushing of soil moisture from upper slopes to lower slopes, indicating that the watersheds are variable source area driven. The peak of PP on the rising limb of the hydrograph was attributed to near stream sediment mobility while the peak of DRP on the falling limb was attributed to flushing of upper slope soil moisture via subsurface flow. GIS delineation of CSAs at the agricultural field scale was conducted to pinpoint precise locations within a field to implement precision P management. The topographic position index (TPI) along with a modified version of the slope classification model &mdash both of which were created by Weiss (2001) and automated by Jenness (2006) &mdash were used to delineate foot slopes, hill slopes, shoulder slopes, and flat areas within a 91.2 ha agricultural field from a DEM. Transport factors were, again, identified as foot slopes and hill slopes. Further, georeferenced STP data collected in spring 2010, fall 2010, and fall 2011 were averaged and interpolated using ordinary kriging to generate a single surface that represented three year spatial soil P status within the agricultural field. Source factors were identified as areas in the field that were excessive in soil P for corn-soybean production. A CSA model was created that identified areas where both source factors and transport factors overlapped. CSAs of P occurred on 2.3 ha of the agricultural field and occurred near grass waterways and roadside drainage ditches. A one way analysis of variance (ANOVA) along with a Tukey mean separation procedure of soil P on the four topographic positions was used to characterize soil P spatial dependencies on landscape attributes associated with topographic position. Foot slopes (79.5 kg ha&minus1) and flat areas (92.9 kg ha&minus1) had significantly greater soil P than hill slopes (59.8 kg ha&minus1) and shoulder slopes (49.8 kg ha&minus1) due to depositional and sink attributes. Depositional attributes exhibit concave curvature, e.g. foot slopes. This curvature effectively reduces the velocity of surface runoff so that sediment bound P suspended in surface runoff can be deposited on the soil surface. Sink areas accrue P inputs but do not lose P to erosion via surface runoff. These areas exhibit linear, non-sloping planes, e.g. flat areas, that are not conducive to surface runoff. Although topographic position explains the spatial dependencies of source and transport factors, the CSA model was able to pinpoint where CSAs of P spatially occur within the agricultural field which can allow for precision P management.

No description available.

No description available.

Over the past several decades, experimental studies of the organisation of spatial frequency (SF) preference in mammalian visual cortex (V1) have reported a wide variety of conflicting results. A consensus now appears to be emerging that in the superficial layers SF is mapped continuously across the cortical surface. However, other evidence suggests that SF may differ systematically with cortical depth, at least in layer 4, where the magnocellular (M) and parvocellular (P) pathway afferents terminate in different sublaminae. It is not yet clear whether the topographic organisation for SF observed in the superficial layers is maintained throughout the input layers as well, or whether there is a switch from a laminar to a topographic organisation along the vertical dimension in V1. I present results from two alternative self-organising computational models of V1 that receive natural image inputs through multiple SF channels in the LGN, differing in whether they develop laminar or topographic organisation in layer 4. Both models lead to topographic organisation for orientation (OR) and SF preference in upper layers, consistent with current experimental evidence. The results suggest that in either case separate sub-populations of neurons are required to obtain a wide range of SF preference from Hebbian learning of natural images. These models show that a laminar organisation for SF preference can coexist with a topographic, columnar organisation for orientation, and that the columnar organisation for orientation is dependent upon inter-laminar feedback. These results help clarify and explain the wide range of SF results reported in previous studies.